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ELI:C07RTC~ PROPERTIES OF OTTERW. A. YagerBell Telephone Laboratories, Murray Hi1 l, N. I.T. Introduction The Subject of the Electrical Properties of Matter is sogeneral and broad in scope that one reviewing it is immediatelyfaced smith the problem of ,.~'ha~c material to include and karat tore ject. This sorting-out process is to some extent inf luenced bythe T,ersonal equation and refit ects the reviewer' ~ own interest.In Arriving this section of the Digest ~ an at~Gem~t has been madeto mace the emphasis an the physical aspects of dielectric be_. . .havior Bind on the relation between dielectric behavior and structure.The various aspects of microwave technology are also Stressed inview of the nearness of this flied and the growing interest in di-electric investigations at micro rare frequencies a- The volume of literature on dielectrics and relatedsub jects for 1946 was ~ arge. Research and development in thisfield was stimulated and actively pursued during the ~.~ andmany laboratories and industrial concerns are continuing theirir~ves&Gigations on a peace_tirne basis. A considerable amount ofclassified material accumulated during the war was published in1946 but much still remains in as yet unpublished reports. Several dielectric symposia were her ~ last year. TheLondon branches of the Royal Institute of, Chemistry and theInstitute of Physics held a Joint meeting aid the Royal Instituteon March 20th at which 'Ghe fields of physical theory, chemicalre~arati on and industrial application of dielectrics severe broadlysurreys The Fawaday Society sponsored a symposium on dielec-trice at the Wills Physical Institute at Bristol, April 24-26th.General surreys and many original papers on the present stateand immediate trends of ~hysical-chemica' and physical researchin dielectrics severe presented at this meeting. A very good re-sume of these two meetings entliled Dielectrics in Theory andApplication appeared in Nature. New Dielectric and InsulatingMaterials in Radio Engineering was the topic for discussion ata meeting of the Patio Section of the Institute of ElectricalEngineers (London) on May 2Ist. A retriever of this discussion onnear developments in Plastic and ceramic dielectrics appeared inEngineering and also in Engineer .Three dielectric symposia revere held in this country.Five Scrapers , Plastic Compositions for Dielectric Application,High Dielectric Constant Ceramics, Paper Capacitors Containing~ ~ _
ChIorinated Tm~regnants, Dielectric Constants of Dimethgl Silo-~ane Poly!ners, Id Polystyrene Plastics as High Frequency Di-elect~ice, 'were presented at the April Meeting of the AmericanChemical Society at Atlantic Giber. This program was rangedin cooperation High the Committee of Chemistry of the Conferenceon Electrical Insulation, National Research Council. The newlyorganized Electric Insulation Division of the Electrochemical130cielg~ sponsored a symposium on New Plastic Insulators at theBoth General Meeting of the Society at Toronto, October 16_19that which the following papers were presented: Thermoset~cing VinylPolymers (90~9), Molding Material preforms at Radio Frequencies(90-13), The Dielectric Properties of Phenolic Resins and MoldedCompositions (90~3), Introduction to Silicon Che~nistr~r (90-18),Silicones as Electrical Insulating Materials (90_16), Propertiesof PolYtetrafluorethyler~e of Interest to the Electrical Industry(90-15), Polyethylene (~36 ), The Q-Me~Ger f or DielectricMeasure~nenta on Polyethylene arid Other Plastice at Frequenciesup to 50 me/sec. (90-~), and Styrene Copolymer Solvent ReactingVarnishes - Foaterite {90_24~. The Preprint number is given inarentheois. These papers will be published in the forthcomingTransactions of the Electrochemical Society. The conference on Electrical Insulation, NationalResearch Council has resumed its activities by ho1 cling a meetingat Baltimore, November 7-9th. The papers user e divided into twogroups: one dealing ·.'rith Progress in Fundamental Research andthe Development of blear Materials, the Decor High MeasurementTechnique and Application of Dielectrics. The first group in-cluded: a survey Aver on Dielectric Constant and ~e followedby papers on Selects ve Absorption of Microwaves by Polar Stators,d Dielectric Absorntion of Solutions of Electrolytes in Solventsof Lo`' Dielectric Constant; a survey pacer on FerroelectricDielectrics followed by Darers on Development of Titanta Di.electrics, and Barium Titana~.te and Barium Strontium Titanate asNon-Linear Dielectrics; a survey paper on Plastics with paperson Solvent Reactive Astonishes, Silicones, and Teflon; and, asurvey paper on Conductivity and Breakdown with papers onElectro~Che~nical Breakdowns of Boo id Insulation, and Conductionand Bre~Xdo,~ in High Vacuum. The second group consisted of 19pacers as follows: Dielectric Constant and Lo98 Measurementsfrom ~ cycle to Shiv cycles; two papers on Dielectric Measurementsat Microwave Frequencies; Modification of the Resonant CavityMethod for Dielectric Measurements at a Fixed Frequency; aResonant Cavity Method for Dielectric Measurements at 300 mc/sec.;Dielectric Heating- The Measurement of Loas Under Rising Tem-perature; Electrical Identity Test for Plasticizers of the TypeUsed in Polyvinyl Chloride Plastics; New Instrumentation andUni_direction Direct_Current Measurement; The Significance ofCurrent_Time Curves in Determining Dielectric Properties; In--aulation Resi=tar~ce Measurements smith Particular Reference toCharging Currerit Errors; Use of the Scale Model Method in De-termining O,rerheat~ng of Cables; Corona Starting VoltageMeasurements' a survey Hater on Developments in Microwave Cables;a survey Baser on Technic ques and Problems in the Production andDevelopment of Condensers; Effect of Asphalt as a contamination- 2 -
in Oil and in Impregnated Paper; The Use of a Redid D.C. Lifequest in the Evaluation of Capacitor Paper; Vitreous CeramicCompositions; Ceramic Sheet Condensers; and Righ AltitudeFlashover and Corona Correction on Ceramic Bushings. Abstractsof these Daters will appear in a forthcoming report of theConf erence .~ ' ~A few parers have appeared dealing with liquids, ionized.gases, crystals and metals. The influence of the concentration and mobility of ionson dielectric los s of ~ nsulating oils has been investigated byRang . Re concludes that provided there is no dipole loss, therelatiorlship between dielectric loas, W. and viscosity, I, of aninsulating oil may be exceeded as log W = A-B log, enrich pointsout that the mobility of ions is an important factor in the di-elec1;ric loss of an inking oil. Thermal agitation, whichcauses further dissociation of the oil, increases the dielectric1 oss by increasing the number cuff ions present. The addition ofdeteriorated oil rabidly increases the dielectric loss thusshoaling that this ~ oss is a function of the concentration orcontent of free ions in the oil. An increase in the concentrationof ions in en oil may result in a critical decrease in dielectricToss it the viscosity is increased to the point where the mobilityof the ions is decreased relatively more than -the ion concentrationis increased. Finally, it is concluded that if non-~ol ar oils ofthe same degree of 'electrical purity' are used for low frequencyapplications where the floss of the liquid is unimportant, the of]of higher viscosity is ,3refera~b~e from the standpoint of poorerhi electric los ~ . Gonick6a has obtained data for the osmotic behavior,conductance, bend relative viscosity of solutions of hexanolamineca~r~ylate and diiso~ro~y~amine crate and has determined theconcentration of free cations in the former Re concludes thathexanolamine carry ate associe.tes fire t ~Q neutral ion pairsf°~°~b by secondary association to col~oid. In a later cater,Gonick conceders the relation between Stokers law and the imiting conductance of organic ions. Equations are proposedfor expressing the limiting ionic cor.ductances of organic ionsin terms of CHUB groups cr their equiva:1 ents for monobasic anddibasic ~.li~hatic carboxylic acids, ali~hatic primary, secondaryand tertiary am.ines end ali~hatic divines. Hydration throughhydrogen bonding increases the ionic conductances as a resultof the reduction of the van der Cal' s radius of the group in-~ro~ red . The effective ' spherical volumes ' as Cal cul ated byStokers low severe founcr to agree Cal osely with the volumes cal-culated from. independent date., and are 'Ghought to be a~croxi-mutely the same as their true ~rolurnes. With other series thesevalues differ from the true volumes. The limiting cor~ductancesof severer alkyd cerboxylate ions vrere calculated .! ma- methodcorps proposed for determining the en,3rox.ima~ce CH2 eoui~ralents of- 3 -
substituted methyl enes anci ethyl enes . The electrical conductances of aqueous solutions ofr~ote~sium meta~eriodate and potassium r~errhenate were measuredby Jones7 over the concentration range 0.0004 m to approximates~.~uration. The lin~i~cing conauctences were determined by threetr~ecendent ~r.ethod.s with sP~tis~actory agreement. The limitingcond~'lcta~.ces of the anions were determined by use of the reco-^dedrevue for the K ton e.ncl the ~.e~sured values for the salts fromthis in~resti~P.tion. The values acc elated for ~0 are 127.90 forthe metP.r)eriodete and 128.20 for the ~errhenate with an accuracybetided to be ~ 0~07 conductance unite. The fol~o:~ng valuesf or the 2nobilitles ,~rere obtained: metaneriodate ion - 54.380~07 ond ~errhena~re ion - 54~68 ~ .07. P!alstion and '-oerr8 have investigated the electricalconductivity of hexed _ and dodecyl _ arnn~onium chlorides in purecoaler, pure ethanol and in various concentration of aqueouse~ch?.nol. The ads it' on of ethanol to aqueous solu~Gi one of he~:yl-em-.oniur~ chloride ].o~Ters the conductivity at all concentrationsinvestigated. The conductivitles of concentrated soluti one ofdodecylam~onium chloride are increased by the addition of smallamounts of alcohol. The addition of alcohol to more dilutesolutions of this salt 1P accompanied by an irregular decreasein the conductivities. The difference in behavior of these twosalts is ascribed to micel le formation in solutions of dodecyl-ammonium ch1 oride. Mlcelle Coronation is completely inhibitedby the addition of large amounts of alcohol. The behavior ofthese salts in the solvents used is discussed in the light, ofthe present micel le theory. The formation of ionized water films on dielectricsunder-condition of high humidity was studied by Field e Wher.a dielectric is placed in a saturated atmosphere, art ionizedfilm of fretter forms on the surface whose conductance at the er]of one minute is Thin a factor of 10 of its equilibrium valuewhich is usually Chained in an hour. This ea,uilibrium con-ductance ranges from loo micromhos for. ordinary glass and quartzto er,~roximately zero for silicone resins, silicone _ treatedg1 ~ n and hydrocarbon pries. Time _ rely curves areshown for Polystyrene, Polyethylene, quartz, mica and asbestosfilled ohenolics, polyamide, s'reati~Ge and mica. Ce7lllloseacetate butyrete ~neint~-ins ~ high resisti~ri~cy even after at'_sorbing a~ rater. The ~e~axatior~ frequency for dielectricColors zatior~ shears to be in the audits e range . Chau~hur~; ~ studied the effect of the change in theconcentration of Acne near the electrode surface upon the corl-ductivities or mobs ~ ~ ties of lone in strorl~ electrolytes anddeduced an equation for the conductivity of electrolytes. Itis shown the t Onnager' s equation is a limiting equation for lowconcentrations of electrolytes, lower voltages and high frequenciesThe variation of the c~nducti~rity Keith varying voltage and con-centretions and ureter dirferen~c conditions is discussed.- 4 _
Fox} investiga~Ged the effect of ultrasonic waves onthe conductivity of Bait solutions. Adiabatic compression raisesthe conductivity of an aqueous sal1; solution because of directpressure influences and of increase in temperature e An ultrasonicA.wave, therefore, modifies periodically the conductivity of themedium. If a filament of current passes normal to the wave promr~agation, the Brave train produces under proper conditions analternating potential Rich can be picked up. A convenient re-ceiver can be constructed which indicates absolute intensity andcan be used for the investigation of ultrasonic fields in waterprovided the frequency is not above ~ .5 me e Ogg has reported a new effect in metal_am~nonia solu_lions which is a~eribed to the Physical interaction of electronswith liquid dielectric media. Re found that extremely diluteliquid asnmonta solutions of metallic solid show a marked in-crease in electrical! conductivity upon irradiation ~.~rith visiblelight. This effect was observed in the temperature range _35 to-7500. and the phenomenon is discussed ore the basis of quantum_mechanical considerations. The absorption spectrum and magneticsusceptibilities of meter ammonia solutions are in at least quali-tati~re agreement with theory. In a second paner, Ogg)3 outlinesbriefly the theoretical considerations which preceded the e~eri-mental discoveries relating to the properties of metal ammoniasolutions. Weissm.an has observed the de~x~ase in resistanceenrich occurs when a solution of sodium in ~i.quld ammonia, in aconcentration range which yields two liquid phases, is rapidlyfrozen as reported by C}gg. Rapid freezing of solutions of methyl_amine to which several per cent of ammonia has been added seasfound to produce similar changes in resistances When a 0.05Nsolution of potassium in JO to ~ methylamine ammonia was rapidlychilled. frown 260 ° to 90° E. and then 'heal edit at 1 70°E, theresistance propped from a Prague of 700 ohms at the highest Hem_-Erasure to a steady value of OR ohm in the solid state. The changes in the electrical conduc~Givities arid vis-cosities smith temperature of the negatively charged colloidalsolutions of ferric venede.te' mo~ydate, tunstate, borate, ar_senate and phosphate have been investigated by Mushran andPrakeshS. The temperatures of zero conductance of the vari oursolutions have been obtained by extrapolating the conductanceversus temperature curves to zero conductance. Values lyingbetween -16° and -2~3~5°Co were found. The temperature coeffi-ciente of conductivity of the various solutions have been ce.~-cul ated and it is observed I the values are a] 'rays ~ es ~ chart2< of the conductences at 35°C. The temperatures or infiniteviscosity for these solu~Gions were ~ike~.rise obtained by extra_Orion of the inverse viscosity versus temperature curves.These temperatures lie between _17° and _28°~. It is concludedthat the temperatures of zero conc~,uctance of the various solutions. ~are nearly the same as those of infinite Viscosity.I:x~eriments on the Hill effect by Kelabukho~rl6 show- 5 _
that ~ crystals saturated stitch iodine possess an electronicconductance. A mechanism of such a conductance is suggestedTuna is used to explain previously observed results for KIcrystals in a strong electric field. The electrical conductivityof. twenty singe e crystals of SiC have been measured by BuschA sensitive null method using a Alfferential gal manometer loranused to test Ohm's law. For currents between 10-5 and a~nroz:l-m~te 1 ampere per sq. cm. t the law was found to hold withinexperimental error. No volume rectifying effect was observed.A vacuum tube voltmeter was used. to measure the temperaturedependence of the cond~ucti~rity between 80 and 1400°E. Both theconduc~Givi~cy and the temperature variation are re~roclucible forthe same crystal but wlae hart ations were observed be~c~'een dif-ferent crystals At room temperature, the conductivity variesbetween 5 x 10-13 e.nd 5 reciprocal ohms/c!n. At high t.emcerature,the conductivity goes through a maximum. At sufficiently lowtemperatures, t,`'o temperature regions were found in ditch logconductivity is a linear function of the reciprocal temperature,the Diodes of the lines in the two regions being different. Thetheory of disordered crystal ~ is applied go the semi_conductorproblem . Morton)8 demonstrated that cat culation of the ioniza-~cion current in a gaseous discharge by means of the classicalTownsend equati on is likely to lead to large errors when thefield distribution is non_uniform. A differential-differenceequation for the electron current as a function of the electronenergy aria distance from the cathode is derived an, the ioniza-tion current is calculated for ~ restricted range of pressureand applied frontage. The results vrere found to agree withneesurea current Are thin the range There the assumed functionsapply. The conduction and dlsoersi~n of l onlzed gases at highfrequencies were studied by Margenau 9. Re derived a distal_button 1~w for the energy of electrons in a high frequencyelectromagnetic fl eld by kinetic theory methods. By means ofthis la1'`7, the currents density and the complex conductivity arecalculated as functions of electron den.si!X treasure and fre_quency of the field. The real Cart of the conductivity has amaximum for gas pressures or frequencies such that the mean freepath of an electron is approximately equal to the bellow of thefield. From the complex conductivity the dielectric constantof the medium, its index of refraction and its extinction co_efficient are deducecl. The results are applicable in micro-~ra~re res earche ~ and in ionospher e ~rob] ems . Although perhaps a little far afield from dielectrics,the electrical resistance of metals at high frequency is never-theleas an important consideration in the design of high frequencytest equipment. The electrical resistance of iron wires =d ermalloy strips ~,rere measured by Smith20 and his collaboratorsire the frequency range from l.5 to 6 me. Empirical equations
obtained are compared With ex' sting theoretical equations derivedon the assumption of constant permeability. Pip~ard2) determinedthe skin resistance, R. of suora-conducting tin and mercury at afrequency of 1200 me. relative to Rn for the normal metal Justabove the transition point. A plot of R/Rn is given for both metalsin the temperature range 2.0 _ 4.2°~. This ratio is less than0.01 for mercury all 3. 7°K . , and for tin at 2.6OR ~ and ri ses steeplyto ~ . O at the transition temperatures ~ Partington22 has prepared electrets by allowing differenttypes of dielectric materials to got ~ dify in a field of a~proxi-m~tely 10,000 v/cm. bet~.~reen into parallel metal electrodes, thevo] tage being maintained f or about 2 hours. Measurements of boththe anode and cathode surface charges were taken from time to timeusing a Lindemann electrometer. Typical charge-time curves forelectrets prepared from4G~ro different grades of prime yellow car-n?~be. wax, from rosin, and from a mixture of rosin~and carnaubawax are shown and d! acumen.IT B. Dielectric Constant and Dielectric Lose A number of papers appeared last year dealing with dinen echoic logs mechanisms and the dielectric ~?ro~erties of Sari ousgases, liqulde and solids. Many of these fall into the categoriescovered by other sections of the Digest and hence are omitted here.Some of there, hoverer, particularly those dealing ~.~rith the di-en ectric behavior of the ~citanates, represent important contri-b~ions to the uncleretanding of the correlation between dielectricproperties and structure. In such cases, it was considered worth_.'Chile to risk duplication and retried the more important conclusionstroth the emphasis ple.ced on the ch~rsical and st~c~cura~ aspects of the investigation. Gros s and Denard have shown by curves, that ~ permanent charge may be of carnaub& wax by charging it at an e] cooling to R 1 offer temperature. _ ~v ~is reco~rerer1 which cou15 be stored at the Coverer temperature, theremainder being 'frozen in'. By mear~s of a graphical analysis of-the d~gche.rge course lt curves using the method of Cole and Cole,Field shows the t the temperature coefficient of all three Earl7,ati on ~era.meterS ~ - change in dielectric constant, relaxati on tineand storage coeds ici ent are all ~o~iti~re. This beha~rio~ is inc ~n~crast to corresponding negative values for morn! dipol e pol ari _7.~' one. Similar experiments with capacity ~ made of oil-fir ledBarer, glass, steatite, and mica liked shower ~ positive temoe~ature coefficient of dielectric constant and a 'frozen in'charge ',hen the color is cooled. Field concludes that itseems reasonable to expect similar behavior for ocher material sin 'which the in~ertaciP1 type polarization is important. means or current-timesavored in a capacitor Badeevated temperature and thenOn discharge. only that chargevitro ev and Jurevich24 have modified Debye's dispersionfr3rmu1?.s to take into account the inertia of rote-~Gion- vibrational_ 7 _
notion of dipole canticles. As a consequence, the electrical con-dUCtlYity yes through ~ maximum which increasing frequency in-stead of approaching a limiting value as required by the formulaewhen the effect of inertia is neglected. Snoek and Pre 5 describethe atter_effect (relaxation) phenomena enrich are the cause of thed' en ectric losee.s in dielectrics and of at leapt pert of the 1GSSeSin ferromagnetic substances. The close analogy and the connectionbeeper el ectrice.1 and megne~sic aft~er-ef~ect <end the ~her~omena ofe? fistic a.fter_effect ore pointed out. Hector and ,toernley26 here measured the dl electric con-~12nt 04 eight gases using a heterodyrle beat frequency method.Special Precautions were taken to improve those minor defects inthe equipment that are bel'e~r~ci to have contributed to the dif-ferent values obtained by other observers. The At electric constants of the methanol_~.rat~ systemfrom 5 ~ o 55 °C ~ ,~rere measured by Albrig;h t 2- nd Gos tiny Hi th anA.~. bridge circuit to an estimated accuracy of one part in 1000or better, based upon the assumption that the dielectric constantof strafer at 55aC. in 73.48. The authors report that their valuesdiffer consid.era.bly from those of Akerl~f. The red ation betweenthe d' electric constant and the electrostriction of solutions ofelectrotype es was investigated theoretically by Davt',an28. Thevariation of dielectric constant was found to be proportional Gothe electrostriction. The value of the electrostatic saturationden upon the square of the effective electric field of theions and also upon the external field. The dielectric constantof diluted solutions appears to be proportional to the concert_'ration. The proportionality coefficient characterizes the amountof el ectrostriction. Cooper29 describes a series of measurements on solutionsof sodium chn oride in distilled Beater over frequency ranges O.g5_13end 6gO_4320 me. The results are discussed in terms of the Debye-Falkenhagen theory of el ectro~ytes and the available data on theabsorption band exhibited by strafer in the region of l°1°°° me. Acorn~nris on is made 'pith the published results on the electricalproperties of seawater for frequencies up to 10 me. and deductionsare made e~s to its probable behavior at Mercy high frequencies.The electrical conductivity loran measured in the freouer?cy range0e 95 t;0 13 Tic e while the dielectric constant and attenuate on co_efficient flare measured at frequencies between 690_4320 me. Themeasuring techniques are described. Schallamach30 published ~ paper on the dielectric re-laxe.tion and viscosity of a number of long-chain Bipolar liquids.Mee.surernente were made in the frequency range 95 kc. to 268 me.and in the temperature range between about -190° and +50°C. Enrelaxation time (<r) and In viscosity (~) are plotted es functionsof reciprocal abeol ate temperature Tt loran found that the acti-vation energies of fir and ~ for these long-chain liquids are notgeneral ly equal except at low temperatures ~ ~ n contrast to the
behavior of liquids of low molecular Freight. The relation between~ and ~ depends on the nature of the Bipolar group. In mixtures ofgeranio! and medicinal naraffin,.t is little changed over that forSure gerantol despite a nine fold increase in ~ at _27°C. In mi';-tures of geraniol in n-he~tane, it was observed that ~ and ~ de_grease but there arrears to be no correlation in the activation.energies deri~red from the data. In these mixtures, ~ is not asdecisive a factor for ~ as would be expected from Debye8s theory.One conclusior~ is that the mechanism of viscous flow of these longchain alcohols changes with rise in temperature.'2 ~ Osiers has applied the Onsager_Kirkwood theory of di-electric polarization of polar liquids to solutions of Solarmolecules . A correlati on parameter, Ashore value differing fromunity is a measure of the hindering effect of a molecule on itsneighbors, is calculated for Solutions of polar molec ales in non-nolar solvents. This parameter is a direct measure of the extentand nature of molecular association. Al ~ of the systems examinedshower the same general behavior: parallel association of dipolesin solutions of large concentrations of the polar components andantinarallel association at some lower concentration. At extreme-ly dilute solutions, the dipoles become free of each other. Low-ering the temperature enhances both parallel and antiparal~elassociations, the latter arrangement becomes more Pronounced atlower concentrations. Low concentrations of ~Tari¢~us polar mole-cures in crater generally alter the dielectric constant of thecrater in a predictable manner. However, dioxane lowers the di-electric constant of crater much more than predicted by theory,indicating strong interaction with water. The variation of the dielectric constant of the nl-ohaseof p 9 ~'~azoxyaniso] by magnetic fields has been investigated byMaier32. The change in dielectric constant in longitudinal (I-)and transverse (T) magnetic fields up to 5000 gauss wee determinedand it was found that the ratio T/L is not -~/2 as predicted butrather -~/10. By means of X-raya, it is demonstrated that phi adifference is due to orientation in the field free state which inturn is largely due to convection currents. A horizontal tem_Erasure gradient of O.Io/cm. produces almost complete rotation.This result invalidates existing data on the dielectri c constantas evidence for or against- the Disarm theory. The basic aesump:tionof the a warm theory that the normal state of a cl-~hase is com_repletely random is not yet Proven. Several comprehensive Caners have been riven ~ eel ingwith the dielectric ~ror~ertieg of solic dielectrics. One of theseis the contribution of Severs 3 whose gaper on the RelationBetween the Po,¢-er Factor an] the Temnera~Gure Coeffici ent of theDielectric Constant of Sol ice. Die, ectrics consists of five cartsGevers has measured tan ~ and Ac (temperature coefficient ofcapacity) or At (temperature coefficient of dielectric constant)for a number of solid dielectrics over a aside range of tem~eraturand frequency . Thes e me&suremen~Gs hare shown that in generaldie' ectri can having a large T.C. (tem~era~Gure coefficient) also_ 9 _e
have a large ~ra3..ue of tan ~ whereas dielectrics having a smallT.C ~ al so hare a small value of tan ~ . A remarkable fact isthat the ratio of An to the value of tan ~ at a given temperaturecroci frequency is nearly the same for most Delia dielectrics. At20°C. and over a elide range of frequencies, the fold owing re_Cation was found to hold: And Ac - 0.06 tan ~ . Gevers pointsout that it is impossible to explain this behavior on the basisof existing theories . In Part ~ of thi ~ report a summary isgiven of several well knows. theories concerning the causes ofthe dielectric loa ses and A£ of ionic crystals . Arguments aregiven to show that these theories are not able to explain theabove relation and must, therefore, be replaced by a new one.part T] given a critical Luminary of avail able data in the liter-ature on tan ~ and Ac or A£ restricted to solid clielectrice andradi o frequencies. As far as doe sible , the causes of the di-electric losses are inclicated. From this summary, Severs con-cludes that the data found in the literature is not affrays re_liable and is insufficient to check adequately the Proposedrelation bet~reer~ AC and tango Revere, therefore, found itnecessary to repeat all measurements as a function of temperatureand frequency. Part ITI explains Severs' never theory about dielectric losses and the temperature coeffici ent from 'which theproposed relation above follows in a natural prays The negativeT.C. of some dielectrics (i.e., TiO2 and polystyrene) is ex_claimed from the fact that these solids either have a high di-electric constant or a high temperature coefficient of thermalexpansion. Another conclusion from Ge~rerst theory which isconfirmed by experiment is the existence of a similarity Grin_ci~le. Finally in Part TIT some remark' are given concerningthe dielectric Properties of mixtures of dielectrics. The methodof measuring tan it and A£ of dielectrics and the apparatus usedfor these measurements are described ~ n Part TV. Sources of errorand the corrections to be applied are indicat,ea. With the ap-naratua described, the Ac of condensers up to 1000 muff. can bemeasured at a great number of frequencies in the range from100 kc. up to 40 me. and at temperatures ranging from 90° to450°R. The results of ten S and As measurements as a functionof ~ em~era~re and frequency are given in Part; V. For some. -materlals the results are treated in detail. The effect ofadmixtures of a small amount of a foreign substance on the di-e'ectric losses is described. It is shown that al ~ the reach FIGSof the experiments are in accordance with the new theory. Es-Specially the result that the ratio of Ac to ten S has a definitevalue (~..bout 0~06) for many dielectrics is of particular im-nor~Gance. Tt is pointed out that the nature of the dielectricloss mechanism cannot be deduced from the measurements of tanSand As only; kno'viedge of the chemical composition and thestructure of the substance under consideration is inflisnensib~ e .Quartz, mica, various glasses, porcelain, mycalex, marble,ebonite, wood, celluloid, Philite, Pertinex and ~Tovotext areamong the materials studied.A reader by StAger34 and his associates deals with_ 10
organic insulating materials in electrical engineering. ThisHer is primarily concerned 'rith the die1 ectric properties oflarnina1;ed structures . The Jie1 ectric ~ronerti es of d.ipolewsolids is discussed by Fr~hlich35. Ball a36 found that the di_electric constant of cotton fibers dried at IGO°C. is about 6and 3 in the longitudinal and transverse di Sections respectively.Measurements were also made as a functi on of moisture contentin both direct) ons un to about 105 of the dry weigh1; at 100°CO..The experimental procedure and test equipment are described. Ashort table of the 60 cycle poorer factor at various temperaturesfrom 20° to 100°c. and of the dielectric cores Ant of variousmaterials alas Published in the Electric li~orId~ ~ ~ Schallamach38 reported dielectric dispersion in crys-ta1line aii~o~ro~yl ketone. Data are given for the dielectricconstant of this material at lol2 mcO an] 20.4 tic. and for thedielectric loss factor at 1.12, 4.4 and 20.4 mc. over the tem_erasure range _150 to +20°Co When Roaching the M.P. (-72~5to -75.5°C.) from higher temperatures, both ea and £~' increase,the rise of £~' indicating incipient anomal ous dispersion. Theiallid sunerc cola generally to about -80°C O an] then crystal_lization is accompanied by ~ sharp drop in c' to a value enrichis still appreciably higher then the optical Braille arid is Be_Dependent on frequency. Anomalous dispersion is observed in thecrystalline state as evidenced by loss factor maxima. It istentatively suggested that branching of the molecu] e causes acrystal lattice somewhat looser than that of straight ketonesand thus reduces the in~Gra-molecular forces sufficiently toallow restricted molecular rotation. Mason39 has nerd the elastic, ~piezoelectric andd' electric constants of NR4H2PO*(ADP) and KH2PO`(KDP) crystalsthrough temperature ranges dn;~m to the curia temperatures. Thedies ectric properties of KDP agree Well Irish the theory pre-sented by Sl&ter based on the interaction of the hydrogen bondsPerish the PO4 ions. ADP undergoes a transition at _125°C. at*which the crystal fractures. This transition is probably notconnected enrich the H2PO~, hydrogen bond system which controlsthe dielectric and piezoelectric properties for these lie onsmooth curares Rich do not change clone as the transition isencroached. It is suggested that two separate mnd independenthydrogen bond systems awe involved in ADP. The transition axedspecific heat anomaly appear to be connected witch hydrogenb ond ~ be Aloe e n the ~ and i: he ~ of the PO. i on s Forte r e as the di_e' ectric and ~ie%oelectric properties are control 7 ed by the}I2PO4 hydrogen bonds. Mason O has also investigated the elastic ~ niezo-electric and die: ectric properties of sodium chlorate arid sodiumbromide otter ~ wide temperature range. At high tem~era~Gures,the dielectric end ~iezoelectric constants increase and in-dice.te the presence of a trans~ormati on point; which occurs at~ temperature slightly higher then the melting point. A large_ 11 -
dipole piezoelectric conste.n'G (ratio of lattice distortion todipole ~olexiza~icn) results for these crystals but the elect~o-mechanical coupling factor is small because the dipole polari-za~ion is small compared to the electronic and ionic polarizationsand little of the applied energy goes into orienting the dipoles.Tile tem~e~a~Gu-~e variation of the diet ectric constant can be ex-ressed by the empirical vacation:= 4.7 + 3~0 _ 67 50 for NaClO3 320_0 ~ 320-0 ~ 2and ~ = 4.87 ~ ~, for NaBrO3where 4 is the temperature in °C. The constant term which isindependent of temperature is ascribed to electronic and ionicpolarization while the temperature variable term is attributedto changes in orientations of dipoles or the displacement ofloosely bound ions such as exist in glass.4' The paper by Navias and Green ~ on the Dielectric Pro-pPrties of Glasses at IJltra_High Frequencies an] their Relationto Composition will no doubt be reviewed in sorrel detail in thesection on ceramic insulation. However ~ in view of the courtration between die] ectric properties and structure inherent inthis paper, it is likewise included in this section. The di-electric constant and dielectric loss of 104 glasses of a widerange of compositions were measured at wave_lengths of 10 and 3by the resonant cavity method. By correlating the power factordata with glass compositions, there is proposed a qualitativeexplanation of the mechanisms producing energy absorption anddiel ectric losses in the microwave range. These mechanisms areDetermined by the nature of the bonds Joining the atoms and ionsin the randomly orientated atomic networks. The rigid and con-tinuolle networks of SiC a and B O3 glasses are relatively trans-parent to cm. wavelengths energy absorption and diel ect riclosses are low. Addition of network_ modifying oxides yieldsglasses of greater energy absorption owing to the oxcillationof the interstitial ions thus produced. Increasing the contentof any one of these ions results ire higher losses while the co-e:s<:iatence of a variety of these ions generally results in lowerlosses. Alkali ions glare rise to high losses which increasewith ion concentration. Glasses containing a combination ofalkalies show lower losses than the equivalent compositions withonly one alkali. Bivalent ions do not contribute as much tolosses as alkalies but high power factors are shown by glassesEdith high 3~0 or Pb: contents. Dissimilar interstitial ionsinteract in ultra high frequency fields and thus reduce energyabsorption. The losses of high PbO glasses are talus reduced byalkalies and, on the other hand, the presence of RO lowers thelosses of glasses containing RHO. Dielectric losses are in-creased by p:LsO3 in much the same manner as by other networkmodifiers._~
The unique dielectric behavior of the alkaline earthtita.nites wee discovered Just prior to the Alar. Preliminaryexperiments indicated may commercial a~licationsO Consequent~y9the investigation of this group of dielectrics loran greasily in-tensified during the war and Bras placed in the category ofc]~.sified material. Noes that restrictions have been lifted,the resul~Gs of these in~reetigations are being Published. Se~rera.lSeders appeared already in 1945 and at least six different irl-vestigations reported the results of their work during 1946.Among those contributing capers last year are P~G{eSSOr VOHHi~pel42 and his associates, de Brittevil~e43, WI44, Ginaburg45Jackson and Peddish46, ana Coursey and Brand470 These researchesare being continued by numerous theorists and ex~eri~.er~orseHere again the ,eriter of this section is trespassing on groundrightfully belonging to the section on ceramic insulation. Conssequen~cly,~, only brief reference will be given to the ~rariotasbakers dealing Pith Chin sub ject Pith one exception. JUG is feltthat the splendid postula~Gion of Professor von Elipnel and his. .a~socia~ces concerning the correlation between dielectric be_havior and structure deserves special consideration in thissection. Wul has published a number of mpers dealing withvarious aspects of the dielectric behavior of the titar~tes.. .Ginsburg ~liscusses the die, ect-~ic properties of ferroelectriccrystals and barium titanate. Jackson and Reddish report theresults of their investigations on high permittivity crystallineaggregates. Coursey and Brand discuss their measurements onBaTi03, Ce.-TiO3, BrTiO3, and mixtures of BaTiO3 High SrTiO30 Theyf ound that the temperature at which the peak dielectric c onstentoccurs in such mixtures decreases ~ inearly from 1 250C. forBeTiO3 to . 6C>oC. for l:l mixture. deBritte~ril7e has made anoscillogra~h study of the dielectric properties of 13aTiO30Professor Ron Ridge] and his associates give a very com~rehen-si~re treatment of the whole sub fleck inc1 udi ng a general surveyof the fi eld and their own original contributions. I4c seemsgo be general! y agreed among the various investigators thatBaTiO3 end the 3a_Br titivate solid solutions constitute ~ newc las ~ of f erroe Technic mat eri ale O von Hin~elts namer gives particular consideration tothe correlation between dielectric behavior and structure ofthe titanates. Tt is pointed out that the alkaline earth titan-ates may be classified into Agree groups * The flirts, representedby MgTiO3 alone, choirs the properties of a norme1 tonic crystal _)01' 6 ', TOW 1088 9 and a positive temnere~re coefficient of di-electric constant. The fig++ and Tim+ ions are about equal inradius; c onsequent~ y ~ the Or ions share three oxygen ions asequal Anew, in equivalent ~sition.s Rheas producing a hexa-gone~ structure of predominantly ionic bond character. Thefunde-mental atomic arrangemer~G in the other two groups can berepresented by the ~eudo-cubic 't~ero~rskite structured EachPi ion is surrounded by six oxygens forming an octahedral~ ]!3
grou~lng ss in TiO2 Whereas the alkaline earth ions placed atthe corners of the cube are surrounded by twelve oxygen ions.It is shown that all titanates containing Riot octahedra may beexpected to exhibit high dielectric constants resulting fromthe transition between hetero~olar arid homopolar bonds as theTi ion is dis?~?~ced Judith respect to its oxygen surroundings.In addition, a trend from Ca to Ba may be er~ticinated becauseWith increasing size of these spacer ions, the octahedra willbe systematically distorted X-ray data shover that the structurecuff CaTiO3 persists up to at least 550°~. so that there is rtotransition and cor~seauently only the high ~olarizability of therutile type may be expected without dielectric anomalies. Thesituation for BrTiO, is similar.The case of Patios is considerably more complicated. ts dielectric constant of abmt 355 at -121 °C . and corres~ond-ing values at about +~00°C. indicate that a high polarizationof the usual Futile type exists; superimposed on it are someother effects in the intermediate temperature range. The ~ argeneek in £ ~ iS connected with a transition in lattice structurefrom ~Getragonal to cubic . The fold ocarina tentative picture forthe behavior of BaTiO3 is proposed: The pseudo_cubic form con-sists really of hero modifications characterized by a Permanentmoment, oriented in opposite directio ns . The two equivalentenergy states of the twinned modifications coalesce at thetransitior~ temperature into a simple state corresponding tothe nonpolar cubic structure. The diel ectric constant peakwould represent ~ situation in 'which the applied field maybeing about transitions bets een the hero states with oppositeelectric moments, whereas at low temperatures the energy barrierseparating the states becomes too high anile at higher t em_Erasures the Hero states merges As the transition between theeq'`~i~ralent states becomes impossible at lower temperatures, ~. . .decrease in £ ~ t0 the val.ae elected from the normal rutiletype notarization is antici~atede Although no structuralchange is observed, the region of the lower maxima in £' andit eventual drop is accompanied by substantial 1 attice changes .This region of strong contraction of. the lattice may well co-in c i de tori th th e r egi on '-die r e the f i e l ~ can n o ~ o nger o~rerc omethe barrier between the 'win modifications. 'the complex natureOf the i' and tan ~ choracteristic.s for BaTiO3 shows thug thes itue.ti on is very i evolved.IT C e Di~ol e Moments and Structure~ _ Dixon e moment measurements have in many instances beena. useful cool for determining the Ire of molecules es_ecin11.y cord th regard to the disposition of cola' groups. The theory of poled dielectrics is considered by Bauer48in torso goners, Part I dealing with the theory of the crystallinefield in solids and liquids and Part IT, high the comparisonbetween theory and ex~e~iment~1 xesu11~. Expressions are derived- 14 _
for the resultant dipole moment (ft) and the effect of the crys-tel~ine field on the molar polarization of orientation of thedipoles in solids and liquids. These expressions are ade~r'!ed tothe Sari our field sharers thug depend on the charge distributionin the molecules. In general, satisfactory agreement wets ob_tained between these formulae and ex',erimental results for av~.ri ety of subetenc e ~ such as lo e, water, alumna, hat ide s of hydr o-gen end. salts of ammonia. Tt is found that the properties of thecrystalline field in li quids ~ are analogous to those of solids ~tthe ~elaxati on times are much shorter of the order of 10-~0 to10-~i see e due to the brief lifetime of as sociation of a molecul ewith the immedia.te neighbors. Another treatment of the theory ofdipole interaction ire crystele is given by Luttinger and Tiaza49.The results of their analysis were found to be in good agreementPith the experiments of He as and Wiersma on CsTi alum. B5ttcher50 has shown mathematically that even for aniso_tropic dipole molecules the mean nolarizability is practicallyequal to (~l+~2+<X5)/3 adhere the at e are the polm~iza.biJities irethe three principle directions provided tne electric field ishomogeneous and there is no saturation. In a second paper,B51tcher describes a method for calculating the polerizabilityof the particles of a substance from the index. of refraction endthe density of dilute solutions of that substance. The stasis_t;ca~ treatment for determining the variation of the heat ofadsorption of Molar molecules is extended by Millers) to showhow the varia4ci on of the dipole moment Erich the fracti on of thesurface covered can be Ogden into account. The equations havebeen used to determine the variation of the heat of adsorptionof t~3 on a non-conducting surface. Hanney and Smyth have Published a series of four rawerdiscussing the results of their dipole mount investigations.The first r)pner52 is on the dinoJe moment of hydrogen [luoricleah.. the ionic character of bonds. The moment ads measured inthe error state and. is numerically identical with the el ectro_negativity difference be~G~'reen the ~ aunt F calculated from energydacha. ~ ~ is concluded they; the X-F bond has 43)~; ionic character.A new tal?1e of ionic bonci character ~ given. The second na~er53deal ~ '`~i Ah further inure ~ hi get ions of pole. rity in hyc ro ce rbons?:os~esaing con jug~cecl systems. They found that i;he measuredmoments of severed additional compounds are c insistent 'ritl~^ themod ecus or st~rUct:ures required by the theory of hy~ercon.jugationand resonance discussed in ~ Previous ~a.r~er and thus lendesunr~ort to this the ory e Dinole moment and resonance in viny' sulfide and sixunsaturated.. chlorohydrocarbons is the subject of the third r~aner54.ERG lops found the t the double bonds remote from the Cl in Ache oro_1,2_butadlene and ally chloride cause only small. lo.,erings of theZircon e mo~;ents but the addend effect of the methyl group in methe lL_ly! chlorite gives ~ propylene _ like dipole moment in the h,y~ro-carbon chain and increases the ~ offering of the dipole moment
below t.het of the corresponding satu-~.ted molecule. The threechlorocrocylene molecules here dipole moments the t conform closelygo the r~a,~irements of Their k.nol~rn geome~riGe] configurations,the dinol e moments associated smith component ~arts, end theeffects of resonance. In these molecules, as in many others, theeffects of resonance lend thern.~e1'res to vector addition alongwith the group moments whi ch they effect, alto Hugh there may beUnusual influence of resonance effects with consequent alterationin moment. The dipole moment of vinyl s~.Ifiae gives evidence ofowering by resonance like that in vinyl chat oride. In the fourth ~a~er55, handy and Srnyth discuss thedivot e moments and structures of ketene and of several molarnotes containing con.Jugated systems. The 7c,~`r~ of keteneis consistent with the recut ~Gs of electron diffraction and ~ n-dica.tes some ansiogy between its structure and that of CO. Theoxygen has much less negative charge then the ordinary cerbony~oxygen. The dipole moments of the four mol ecules ,`!~th conjugatedsystems give e~ricence cuff resonating structures and consequent o~ari4cie~. ene~ogous to those previously observed in their ]~.bore-t cry . Rogers and Young56 reported on the electric moment ofn butyllithium and the nature of the Li_C bond. Taking themolar Doe erization of n-butyIlithium in benzene at infinitedilution e-s 40, and estimating a Prague of l.0 for the atomicfraction of Li, the authors ce`Icul?.te a ~ - 0.97D for the dipolemoment of n-buty, ~ ithium, thus indicating; that the Li_C bondmust have consid.er~.ble comer ent character since ion pairs wouldrecult in very much higher ~re.]ues of the molar dot arization.From the electronega~civity difference, 1.5 units, between C andLi, one would ~red' ct about 45< ionic character for the Li-Cbond and a bond moment of about l.5D. The observed bond moment~ s le37D assuming the C-R bond moment to be 0.4D and taking Lias the flus end calf +,he dipole. Lithium alkyl s may thus be re-g~sraea as covalent compounds, the rather large amount of ioniccharacter of the Li_C bond being about equal in magnitude tothe ~c of the C_F bond.atorni c Sauer and Mead57 hare determined the dielectric con-stants at 20oC. ana 60 cycles/sec. for a series of linear holy_me~chyl~olysiloxanes: (CF333Si ~Si(CH3 )2] qC~3 in which q has thevalues 1, 2, 3, 4 and 5, and for a series of cyclic polymethylcolysiloxanes: g(CE3 )aSiO]q in which q has the values 4, 5, 6,7 and 8. The dipole moments of these compounds were computedusing Onsager' ~ eaua~Gion. The moments of the linear compoundsDeere founc' to agree satisfe.ctorily smith the simple empiricalrelation: ~ = 0.70 by. For the cyclic compounds, the momentsof the larger rings appear to approach the values predicted bythe ~ equation. The Si_O_Si bond angel e Ares calcul ated from theof hexernethyl disiloxane (0.74D) and appears to be 160 ~ 15°The dipole moment of ~ -nitrobutane ~ n benzene solution- 16
at 25°C. hes been measured by Miller and Angel58. The value ob_tained is 71 = 3.40 + 0.01D. A review of previously reportedmeasurements on the higher nitro~=affins suggests that 3.4D isa correct figure for the solution Prague of the nitro-group momentin these compounds. According to Gent59, the molecular electricmoments for nonmesomeric molecu] es is divided into the vector sumsof the group moments and of the induced moments. In model 1, theinduced ~ is calculated separately for every atom in the molecule.Equations relating molecular~, group moments and induced momentsgive `~(CH2_0) = 2.05D and ,*~-C) = _0.46D. In model 2, i'G is aB-sumed that the bonding electron pair between two atoms is concen-trated et the point of contact of spheres of the appropriate co-ve.lent radii. For this model, p(CHz-O) = 1.83D end ~(H-C) = -0.41Dthe ~re..lues for '`(CH~)~:O and ~(CH;~)3:0 lie between the twocalculated rally: ~(CH2)4:0 id close to that for model 2;theme O Me) is remold from the ca-1cule-~ce values. Ste~oanenko and Agranat60 have determined the dipolemoments of pal~nitic acid and triT)almi~rin in benzene, cyclohexaneand dioxane soluti one . Ster~anenko and Noviko~ra.6) hare measuredthe Selectric constants and absorption coefficients of stearic,oleic ~d linoleic acids and of tristearin and triolein at a serape_1 ength of 3.44 meters and at temperatures frown ~60 to 100°C .Various proposed formulae severe tried for red ating the results tothe dipole moments of the same compounds measured in solution,but all failed, presumably because of molect~ar association. Data are liven by Sninrad62 for the dielectric constant,molar polarization, molar refraction and dipole moment of chlorbenzene, monochIorocyc] onronane, and I, 2-dichiorocyclo~ropane asmeasured in benzene solution with a Schering-bridge. The momentof I,2-dichloroc`Yc~opropane indicates that this molecule must herethe dt _configu~ation. mbe angle of the C-C! bond ,'!ith the ringplane appears to be 48° which would make the exterior angle ofcycle onronane 96°. Rogers and Robertson give data for the di-electric constant, density and co]arization in benzene at 25°C.,and for the molar refraction, polarization and dipole moment ofa number of cyclo~ro7?ane derivatives. The moments of cycle_rocy~chlo~ide and I, 1_clichloroc,ycl opropane in benzene solutionare about 0.30 Begs thmn the corresponding cyclopenty~ coonhounds.This behavior is in4Ger~-eted as indicating a small contribution. ..from ionic resonance structures analogous to the principal tonicres onance st~llcture.s in vinyl chl office and chl orobenzene. Themo~..en.-s of the cyclor~enty! halides and cyand de are close to thoseo~ the corresponding secondary aliphe.tic compounds.II D. Plgh Voltage Phenomena The Parsons Memorial Lecture delivered by Da~ris64 beforeAh e I n s ti Put e of El e c t r i c al anti n e er s ~ Loncl. o n ) rTo~rember, 1945,gave an account of the methods for producing and mea.suring highTo rer e..c . ~ d.c., and surge vo]tage.s. Two problems towards thesolution of which high voltage research has made a contribution_ 17 -
e.re considered. The first is concerned '^rith the insulation ofhigh Rotate t-ar3~mi`ssion lines and the disposition of such in-su~ Cation so as to insure that ine~rite.ble breakdowns are confinedGO the more readily renewed carts of the system. The secondproblem is a Alar time an~1ice.tion concerned with the prot.ec4cionof teal loons Band crepe from hazards due to lightning. A rather long summery dealing Faith the influence ofirrn.diati,on on the measurement of impulse Frontages with anheregets is given by Meek65. Posin66 has investigated the loweringOf electrical breekdo',rn field strength at microspore frequenciesdue to an exterr~1 ly earlier m~gne~cic field. The followingeffects liege obeer~red in connect; ton with 3 cm. microwa~re brea.'x_corn studies conducted on eir gaps in Rave guides: 1. An encroach. of ~ ~ermcQ-nent magnet to a gad which ison the verge of create sparking can make the gap scarkover. 2. A reigned of pole_fe.ce cross section smaller than theHatch of 'rove guide over which it is passed may lower the break_~ In field strength by 204~ or more depending on certain con-ditions such as the strength of the magnetic fiel ~ and height ofthe breakdown gap. Be then a magnet is street along on the outside of theve~tically_narrowed t.~a~reguide, the gar, may spark at a fieldstrength lo-,~rer try as much as a factor of 2 or more than when themagnet is a-been-. 4. No sparking effect can be reliably reported when thenagnetic field is applied at right angles to the micro areelectric Vector, either along the direction of propagation orcrosswise to it. 5. Wher1 broad face permanent magnets are used, the poisedeffect and the s'`reen effect are very much diminished. tlarious possible explanations of these phenomena arec ons idered but none ~ eems at the moment to be adequate . In ~ letter to the editor, Thonemann67 reports theresults of his experiments Perish high-freauency discharge as anion source. Diel ectric recovery by an a.c. arc in air blast isdi s cue s e d by Br of . The permanent r~hysicochemical changes resu: tiny fromd.lech~rges in hydrogen were investigated by tTikuradse and Berger69f or rare of ~ , 11 n s e ed of ~ a, Of f in of l ~ olelc ac id and ~ t earl cacid in a special a.p~aratus ~ The increase in ~ ' and in dielectric .. ..~ol~ization :~s found to be proportional to the increase in vis.~comity _ Molar substances showing the greater change. The dipolemoment of oleic acid eras observed to change from 0.7~ to 1.08Diffier ~ hours treatment._ 18 -
Various high trot tage investigations on miscellaneoussolids have been reported. Seeger70 has given a discussion ofelectric breakdown in solids. Adamant has studied certainfactors influencing the dielectric strength of paper such asgas Are. cure, moisture content, temperature, sheet density andsheet th$c~ese. The method and apparatus used in the expert_meets are de scribed and the results are discussed. Rutol.o and Graves72 present data for the breakcrownstre ~gth of 17 samplers of straight-cut varnished cambrics andlo samples of bias_cut varnished combine The samples in-cluded 4 thicknesses of by ack varnished cambric cloth, bothbias ma strai~ht_cut, representing 5 manufacturers and severalse.m~?len of yellow varnished cambric. The effects of humidity,electrodes and breakdown media were studied. Thee electrodeassemblies were used: (~) 1/4~ ala. circular, (2) 2' dia. cir-cular, e.nd (3) l/4~ ~ 4' rectangular. The test equipment andprocedure are described. Dielectric strength after moistureconditioning (96¢ R.SI.) in general Auras found to be about 75%Coverer than the dry Prague (clo~c R... This-difference variedwith thickness, ~nois~cure .sho:~,ing 1 ess effect on the thickersamples. hen considering 12 mid black materials only, it wasnoted that the bias-cut shorted a greater moisture effect thanthe straight_cut. Considerable difference in the effect ofhum' city alas found for samples from various manufacturers.Using the 2' ciroul ar electrodes as a reference base, ap~roxi_mately 590 higher dielectric strengths and about 27jo highervalues there obtained smith the l/~' x 4't rec~Gan~lar and 1/~'dia. circular electrodes respectively. These variations there.more accentuated on the bias_cut than on the strai£ht-cutme.&Gerials. Dielectric breakdown in air ached to be abo':t 9,<lower than that in oil . In genes, the average dielectricbreakdown strength of oias_cut cloths was about 25% lower thanAche ~ f or ~ tori ~ht-cut Gnat Erich .n . Aueten and Pelzer have measured the dielectricstrength of paraffins end some high polymers for comparisontheories of electronic breaks and also on account of thebearing on industrial applications of dielectrics. Attempts tomeasure the dielectric strength of paraffins severe unsuccessful,except for material oriented by pressing, because of the poormechanical properties of such substances. Satiefactor~r testswere made on noly~hene, which gave a Prague of ably 6.5 x 10volts/cm. frown room temperature to -190°C. and on polyvinylchloride-acetate, the dielectric strength of which increasedfrom about 6.5 x 10 volte/cm. at room tem~era~Gu~e to 12 a lo6room. at -190°C. The nolythene eras crystalline end theresults correspond to those for inorganic crys~ca.~line me4Gerialsand with the theory for such crystal ~ . The conol yawner was amok_Shout, its behavior being similar to the t of varnishes and maybe explained by Fr~hlich's snort recent development of the theoryfor amorphous substances.The effect of tem~era~Gu~e upon the ore entation of
electrica ~ breakdown Lathe in the alkali halide cryostats hasbeen investigated by Davis son74. The results obtained suggestthe existence of a path sequence:random - -- ~ (loO) r (1 ll) - -A (~10) Waxy)assumed by the direction of breakdown as the 1 Entice energy ortemperature ~ ncreases. Ster ~at!,erns of 12 non-primitive latticedirections were observed in Li C] and Li F. Mixed and imbuecrystal ~ grown from the melt tena to exhibit high temperaturebash ~&Gterns at low temperatures. By extending the study atroom temperature to crystals possessing difference bonding andsymmetry Properties, general laws governing path orientation areestablished. Tt is shown that the Toshiba e path directions de-~end upon the macroscopic symmetry prevailing and are a~paren~Glynot influenced by the type of lattice bond. The author concludesthat before crsnsid.ering ~ meche.nis~n for breakdown path orientation,one should be temilier moth ret ated electronic phenomena in crys-tals. A revie:~.r of pertinent information Bras presented byProfessor von lithe at the Conference on Dielectrics et Bristolin 1946.von Hillel discusses the problem of breakdown math. .ori~ente!4 on in the frame of his general theory on the breakdowno' solid ale7ectrice. The mechanism which he has evolved isbased on the assumption that the paths mark directions for whichthere is least transfer of energy from excess electrons, Richare accelerated by the applied fielcl., to the lattice. The pathdirections are believed to depend upon the wavelength and henceupon the velocity of excess electrons . The orienting mechanismProposed by him ts electron 'acre interaction with the lattice.that results in sca.Gtering into preferential lice directions. A retried of surface discharge phenomena on bushing in-sulators is given by Wright75. It is nolnted out that a generalsolution for the electrical characteristi cs of bushing insulatorsis not at Present possible because of the complex laws of elec_lyrical breaRc~o,~rn and discharge phenomena of dielectrics and thenathemat;ical diff~icu~ ties of solving the La~lace equation for a3-dirnensiona' electric field having the boundary conditions metwith for practical bushings. Several methods have been proposedto obtain some general principles of design but only that dealingenrich the Caleb] ation of the surface discharge voltage and anark-o~rer voltage based on the laws of the gliding discharge and theconcert of. surface capacitance are dealt Erich in this papersIT E. Microwaves We now come to the subject of micro~'rav~es which are al_ready Playing an important rol e in s~tlOying the carrel ation be-t~?een dielectric Properties and structure. A better under-standing of the fundamental concerts of microwaves and theanalysts and rapid de~re70~ment of microwave components and equi~-ment as ~ result of the last war have overfed up new horizons for_ 20
dielectric exploration. All microwave research and developmentwork during the Terror was classified material and hence was notgenerally availehie. Now the t these restrictions have in manyinstances been removed, the literature is flooded :'rith articlesdealing with the various aspects Or microwave Necrology. In hew of the newness of this field, and the presentand future interest in dielectric investigations at microwavefreauencles, it ',Tas decided to corer the literature rather ex_tens ively in this retried. The ~ ecus ai on of microwaves willaccordingly be divided into three Subgroups: the fires dealingErich the fundamental sconce,;, the second, Keith the analysis ofnQicrowa~re coa'nonenta and the third, with microstate resonance~ no abs orr'1i on Phenomena. . . ,IT Eels Fundamental Concerts of Micro,~avea As previously indicated, the literature on microwavesf or 1946 is i refeed ~rolumir~ous. In order to keep this review areasonable length, it is necessary to limit the number of refer_ences cited and to merely indicate in most instances the natureof the sub Sect matter treated. The artic les range ~ n scope fromvery general articles written for popular consumption to verydetailed mathematical anaigsia of specif ic croble ~ . Hil176 has written a very interesting popular andpictorial articl e showing the smooth conti nudity of the changesthat prewrap ~ as one proceeds up the en ectromagnetic frequency.. ~spectrum from d-c up to cm. waves and higher. Maxtrell's electro_magnetic field theory is shown to be completely adequate to ex_In the whole range of electrical phenomena from a_c to say10 cycles/sec. Generators and detectors of higher frequenciesconsist of atomic arid molecular systems and many of the phenomenarequire the quantum theory for their descri rtion. Power ~daudio_commun'cation frequenciescircuit elements of inductance, capacitance and resistance andworking Erich current and voltage measurements. This procedureessentially eliminates the necessity of considering the electricena magnetic fields in the description of the electrical phenomenainvolved.. This so-called t'1um~ed circuit' treatment can be en_tended gel into the radio-frecuency region if proper precautionsare takenO Unhewn dealing filth the microbe region, ho,.^rever,these methods are of little use. The electric and magneticfields are now of prime importance. Instead of resonant circuitsconsisting of A, C, and R. resonant caviJGies operating inspecific modes or field configurations are encountered. Tra.ns-mission lines become hollow Flies, not parallel 'rtres ortwisted hairs. Their very name _ waveguides _ emphasizes thattheir prime function is to contain and hide the electric andmagnetic fields that constitute these 'guided ~`raves'. Theanant,it]es measured are like~r.'ise different. At loser frequencies,currents, rouge, inductance, ca~aci~Gance, resistance and fre-quency measurements are of prime importance; in micro~.ra~re measure_Detente, Moorer attenuation, wavelength, standing wave ratio andposition are the Quantities ~ought.are adequa~cel.Y treated by defining- 21 _
A ~3P.~er77 by Andrew on microwave optics is concernedweigh the study of micron in free space and the performanceboth micro' cares of the experiments commonly discussed in text_books and 1 at?or~.tory Unequals in physical optics . The essentialunits designed for the study of microwave optics are a trans-mitter for reduction of the radiation and an intensity meterwith~which to explore the field of radiation. The Constructionend operation of these hand-sized units are described. The. .transmitter has a coffer output of a few hundred rrilllwatts andone at a '~.'rel ength of about 1 2.5 cm. Some of the ennui_meets that can be performed Parish this equipment are indicated. Slater78 has written a splendid 71 page review articleor micro are electronics . By microwave el ectronics g Slaterrefers to the study of electromagnetic fields in regions ofthe order of ~ crave ength in dimensions, bounded by reflectingIrk] ~ 8., arid of the int;er~c~Gion of these fields with electrons,ions, or other forms of space charge . It includes the holehigh frequency side of micro~,Ta~re radar; the nature of waveguides alla resonant cavities; and the rapture of electronic tubessuch es klystrons and magnetrons in which transit time is offundamental importance. Tt also includes such devices as cyclo-tron~q' synchrotrons, linear accelerators, and other Reprices forthe acceleration of charged Articles* During the I! therewas a very great development in the knowledge of microwaves.The study of wave guides and resonant cavities, originated be_fore the ever, loran carried to a point of great advancement. Theklystron developed before the war became much better known andhighly perfected. The magnetron oscillator Arty improved to theAunt where it pros a generator of mlcro';rave power of very greatca~a~bilities . All of these developments, particularly as they,~rere carried on at the MIT Radiation Laboratory drill be dis_cussed at length in the series of books to be issued from thatleboretory and published by the ~c~ra~r-Hill Book Company. Otherversions of the same information halve beer, or will be, containedin publications from industrial laboratories in various ~eriodi_calm Even these articles, extensive as they '.~1 be, representbut a small fraction of the great literature Which exists in theform of cle-~sified, or farmer' y classified reports prepared duringthe war. Slater has tried to introduce into this fief ~ a corre-lotion and unity 'which are perhaps ~ acking in most of the otherwork . The sub] ect matter is treated in five chapters: I, thefour-terminal network and the t~ansm.is~ on line; IT, wave guides;TIT g resonance cavities; T1r, anplicatior~s of the theory of re ~Boning cavities and Ire electronics of the reflex klystron andmagnetron. The first chapter deals with (13 the definition ofthe four-term~nal network and the transmission line, (2) theexponential solution for voltage and currents (33 the terminatedline, (4) the impedance of the terminated line, (5 ) bilineartransformations, (6) graphical discussion of bilinear tranceformation, (7) special types of networks and lines, (~) trans-~ormation of residuary and reactance coordinates, (9) the22
continuous transmission line, (10) standing wave ratios, (11)transformers between transmission lines, (12) determination oftransformer constants, (13) a loasless transformer as a shuntor series reactance, (14) Dower flow in netw~or3~e and bans_mission knee, (15) power flow from a lossless line into a ter-mine~l impedance, (16) circuit efficiency and insertion loss of aresistive network and (17) a resume of network theory. ChanterTI deals Erich ~ l) the electromagnetic field in a wave guide 9(2) transverse electric and transverse magnetic modes, (3)standing waves and reflection coefficients, (4) impedance andTourer flow, (5) expansion of the field in normal modes and (6)08SeS in the wave Mae. In Chapter TIT, Slater discusses (~)orthogonal functions for a hollow cavity, (2) Maxwe11ts equationsfor a hollower cavity, (3) free and damped oscillations of a re_sonant cavity, (4) the unloaded Q. (5) the incus impedance of aclarity, (6) currents within the cavity and (7) perturbation ofboundaries. Chanter IV treats (1) the tuning of resonant cavities,~ 2) measurement of the properties of a cavity resonator, (3)Coffer flow through ~ cavity, (4) ~ropertles of ~ nelf_excitedoscillator ~ (5 ~ out nut of an oscillator as a function of load(6) starting of an oscillator and (7) ex:>eri~nental investigationof electronic admittance. The final chapter deals with (l) thereflex klystron, (2) the electronic operation of the reflexklys tron S ~ ~ ~ power and frequency of re f lex klystrons , ~ ~ ~ themagnetron, (5) the resonant circuit of the magnetron, (6) elec_tron motions in the magnetron and (7) opera.ting^r~racteristic~of the magnetron. The relation between nodal Positions and standing waveratio in a composite transn~1ssion system is discussed by Feenberg79Reflection generally occurs at a lossless transition region Join-ing To uniform transmission lines. If the output line feedsinto a matched load (no reflections, a sang '`rave ratio,~o,different from unity exists on the input side of the transitionregion. If the output line is terminated by a ~raria.ble positionshort, a relation exi sts between the nodal Positions on oppositesides of the transttion region. This relation can be used todete~ine 40 thus dispensing with the need for a calibrated de_tecting system to measure this quantity. For the purpose or thispaper, a composite transmission line is defined to be one composedof into uniform ~oss~ess sections (coaxial or cadre guide) Joinedby any sort of lossless adapter. In pe rticu:Lar, the system maybe simply ~ single uniform line containing a Ios sless irregularity(window' supporting bead, gab section, etc.; Size somewherealong the line. Systems of this general type are employecl inmany veri etie s of microwave equipment and me ;~.surement apparatus .Actual systems are not lossTess bare it is gene-~ly true thatpoker losses are kept to a minimum by good design. vilest has gi Wren a rigorous discussion of impedanceconcerts in Claire guides and has appalled them to the analysisOf a plane discontinuity in the form of a Junction between twoguides of arbi trary cross -sections se?:ar~ted by an infinitely- 23 -
thin diaphragm having arbitrary openings. The general equivalentcircuit is represented by ~ ~ network but it is chosen that thereis one important category of problems where this T section reducesto art Intel. transformer flus ~ shunt element which in turn may bereduced to a~ afire shunt element. The formulation of a Or networkis also discussed. The theory is applied to ~ transverse Curare,ca~citative and inductive Ins, arid ca,:acitative and inductivechanges of cross~secti on in a rectangul or where guide, and ap~roxi-mate expressions for their impedances are deduced. A rather ex_tensive treat~.ent of the ca?~.citative window is given in order todemonstrate the Potentiality es of the method. The feasibi lily of dielectric crave guides is discussedin Electronics8~. Solid dielectric wave guides might be used atthe upper limits of the sunerhigh frequency range. Hoverer, someof the transmitted energy is carried outside of the dielectricProve guide unless the guide is made large enough or of ~ materialhaving ~o high ~ died ectric constant that very many modes arenron~gated. If such ~ guide were used 9 there aground be the as yetunsoured problem of coupling in such a manner as to match to thesemany higher Bodes. An Stick e by Travison~~ sets forth the basic conceivesof the transmission of electric and magnetic cadres through aClaire guide. Until ~ fell years ago, serape guides were a type of trans-mission 1 ine having considerable theoretical interest but ~ ittlePractical unit ity. The basic physical ~rinctn~ es governing theiroperation ~`rere dearer owed and published before the war but wide_spread use during the last few years has reduced their seeminglycomplex behavior tc' a set rid engineering principles ~ Prac Vicarcon.sidera~cione in the choice and fabrication of cadre guides aretreated by Morenot33 from the engineering standpoint. The advan-sages of ho] ].o1Y, rectangular guides are described by co~nparisonwith coaxial cable characteristics at su~er-high frequencies.The fo1lo,dng thrice are discussed: choices of conductor, lowattenuatior1 in guides, high ocher capacity, disadvantages oflimited bandwidth, dimensions vet applications, standard sizesin use, Mare guide materials, metal finishes, nlating techniques,losses in related surfaces, velocities in cadre guides, power limi-~ca~Gions and breakdown at high a.:~titudes. A microwave spectrumcovering the range 2100 to 30,000 mc. shoaling the F.C.Ce allo_co.ti ons and the standard wave guide dimensi one suitable for useat various frequencies is i~ ~ ustrated. A condensed review of basic principles and some of thelo artime developed techniques which make the field of ultra_highfrequency fertile ground for many never developments in Peacetimeis given by Seely84. In a second Leper, Seely discusses thefund~m~entn~ che.racterist] Cal of USE transmission lines with alkali_cations in UHF equipment used in radar, television and otherc ommuni c anti on ~ ye tems O~ 24
Glinski85 shoals hoer by the a~plica.tion of the standardtransmission line the ory9 the standing Grave method of measuringimpedance can be extender} to the case of trana~niesion lines with?~ckenuation if the e.~ronriate corrections are introduced. The - er brings together and acmek~at systematizes informationavail able in the existing technical literatil~e. The condition for minimum atf:entuation in Grave guidesis treated by Phillins8 . A short mathematical article by Walkerana `raX87 gives a first order differential equation for the volt_age reflection coed cient of a non-unif orm line and it is shownhow this equation may be used go calculate the resonant Berate_lengths of. tapered lines Attenuation and Q factors in wave guidesare discussed by Clavier§8. Eem439elucidates the nuzzling pheno-menon of decreasing attenuation with increasing frequency whichoccurs in a few isolated instances, by treating the guides con-cerned as limiting cases of a 'aide of snore general share in theinterior of Rich the waves display the normal properties charac-teristic of ret in guides generality. The equations of theelect~c>_magnetic field, cut-off frequencies ~d attentuation des-cr'bing the isolated cases are then, in like manner, deduced aslimiting caSes from Choose appropriate to a guide of General shape.he ~erturba4Gion theory of the normal anodes for an ex. .exponential M-cur~re in non-ster~dard propagation of ~nicrowa~res isexpounded by Pekeria90. Electron ballistics in high frequencyfields is the subject of a 30 cage article by Sa.muel9~. Clarke92presents some novel expires si one for the propagation constant ofa uniform line in enrich the attenuation constant its expressedin te~s of the !nost fundamental entity known, nP-~me~y energy, andthe characteristic impedance is stated in therms of the chasevelocity. A discussion of the present status of the microwaveart nertic,~larly as it applies to radio detection and ranging isriven by Whited. Ford exit Oli~rer94 report the results of theirexperimental investigation of the refl ection and absorption ofradiation of 9 cm. wave_length. Millimeter wave propagation isdiscussed by Lamont and Watson95 and also by Mueller96. Robertsonand K'r~g97 have investigated the effect of rain upon the ~ropa`-ga~Gion of bares in the 1_ and 3-cm. regions. The Doppler effectin ~ waste guide has been examined by Ma1.ov98. Roz ovsky99 hereconsidered the propagation of the electro_me gnetic fief ~ indielectrics with a dielectric afteraction and in conductors Irishmagnetic af~ceraction. Thone~ann ad King)°° have observedthat the inner conductor of ~ coaxial line which is tuned tofrequencies near 1000 mc. and which projects into an arc dis-char~e in mercury orator can be excited by the discharge if a bargarnet is brought near the tube. Kelliher and b~raltonlOl havestudied the Production of mic~o-electromagnetic Graves by .s}'ar kingtechnique ~ .The 7 it;er&+ure on the principles of ope-~tion, construction- 25 _
and application of Sari ~s com~onen~Gs for microwave systems isso extensive that little more than ~ bibliography can be givenin this review. A wave guide system may contain a considerablenumber of 'eve gamine sections and components such as microwaveoscil ~ Store , straight; sections, bends, Egoists, right angle corners,rotating Joints ~ ca~acitati~re or inductive windows, coaxial towave guide affecters, adapters from one size guide to another,Are meters, a resonant cavity, standing wave indicators, direc-tiona~ couplers, 'magic teest', variable and fixed attenuations,dummy loads or terminations, flexible wave guide sections, trans-formers and crystal converters or rectifiers. Since it isger~era.1ly desirable to be able to interchange components theymust be assembled High suitable connectors. Al 1 these com-nonents must be carefully engineered and fabricated to avoidundue ~ oases or undesirable ref] actions . A general discuselon of Caere guide connectors, waveguide bends, wave guide thyme, wave guide corners, tee Jointsin wave guides, matching dis~hragms arid Boats and coaxial lineto wave guide transformers is given by Morenot02. The appli_cation of mic& Norms as elements in ~nicro~rave systems is dis-cussed by Master and 0a associates, and Fiske 04 describesthe use of resonant Rancor for vacuum seals in rectangular Braveguides. The theory and exoerimental behavior of right any] edJunctions in rectangular ware guides is considered by Allansonl05and hire coworkers. La~b)°~ has determined the experimental be-havior of the coaxial line stub. Flexible wave guides are des-cribed by Winchell '07, an] by Anderson and Winchel1~3. Thetonics; included in Hill' ~ O paper are: the stability of mag-netrons, C.W. oscillators, micro~va~re transmission lines, coaxiallines, 'ave guides, impedance measuremen1;s on transmission lines,moving Joints, duplexing, detection of microwaves, crystal mixers,and crystal impedances. A detailed account of the developmentof silicon crystal rectifiers for microwave radar receivers ispresented by Scaff and OhlliO. Hassel and Jenks 1 describe therincinies of electroforming techniques for the fabrication ofhigh precision wave guides and other parts for microwave apparatus. The heart of any micro''ave system is of course the sourceof dower or the oncil lator. Some idea of the intense researchand develoumen~G Whorl: on microwave oscillators carried on duringthe Bran can be obtained by referring to the excellent Sl pagedisserta~Gion on the magnetron as a generator of cm. waves ~ub-fished by Fisk, Rage trum and Hartman and by the wealth ofliterature on this subject. In Part ~ of their paper, Fisk andhis collaborators review the present knowledge and the fundamen-te.~s of the theory of the magnetron oscillator, bringing togetherin one place the results of work done by all the magnetron re_search groups. The topics conquered include: (~) a generaldiscussion of the magnetron oscillator, (2) types of magnetronoscillators, (3) the electronic mechanism, (4) conditions re-lating measureabJe parameters, (5) the r.f. circuit of. the mag-netron oscillator, (6) resonator systems, (7) separation of modefrequencies (~) output circuit and load, (9) equivalent circuittheory arid t1Q) special topics. Part IT traces the research and- 26
development work done at the Bel1 Telephone Laboratories on themagnetron oscillator during the war ye are; fifteen differenttypes or tami, les cuff magnetrons were developed. Work has beendone throughout the range at wave-lengths from *5 cm. to ~ cm. allaon magnetrons capable of developing over one megawatt peak r . f.power. This program has included Ok on such {eatl;~res as 'tuning,coaxial and wave guide outputs, several types of resonator systemsand stra~nlug schemes, and on the lncor~oration of the magneticcircuit into the magnetron structure in so-called 'packaged'tynea.. . 8later's78 review already referred to likewise containsan excellent discuselon of magnetism. papers on the cavity mag-netror~ were published by Flanders , by Randallll4, and byJohnson~l5 Coltmanll6 discusses resonant cavity magnetrons,and Le.tha~nil7 and his associates give an introduction to multi_resonator magnetrons The Magnetron and Klystron is the sub feetof a Barer by Wall' '8, and the Mult~reflection Tube _ ~ NewOsclllator for very Short <raves 1e the title of a paper byCoeterieril9 . The factors which affect the frequency limitation ofreflex oscillators are discussed by Lafferty]2C' in a paper en_titled Kl1limeter wave Reflex Oscillator. General design con-aiaeratione are given for the construction of oscillators of theshortest possible wave_lengtha; the highest frequency obtainedbeing 72,000 me. Lafferty expresses doubt that oscillations ofwavelengths appreciably shorter than 4 mm. can be obtained by thevelocity ~nodula~Gion reflex principle 7'rith the present type ofcathode and electron gun. The power output obtained from severaltubes constructed with wave guide outputs ranged from 0.2 milli-watts (A - 4Ol5 mm.) to 12.7 milllwatt~ (> = 5.S c.. Thispoller output is regarded as ample for die~ec;~;ric measureinent andabsorption studies on gases. By making one side of the resonantcavity flexible, it should be ~oe~ible to construct tubes whichmay be continuously tuned over a 10 to 15% wave_]ength range. Fores and Braudel2l have analyzed the moti on of electronsin an inhomogeneous electric and a homogeneous magnetic field andhave demonetrated the possibility of periodic motion of electronscorresponding to harmonic vibrations. Tt is suggested to usesuch movements of electrons for the generation of sunerfrequenciee. Two circuits for use to con~Grol~the frequency of a micro-'~rave Qsc,1lator by an external. high Q cavity are described byPounding in a na,ner entitled. Electronic Frequency Stabilizationof Micro'ave Oscillators ~ One of the circuits us es a microwaveeculva~ent of the frequency discriminator in conjunction Keith ad.c. amr'1ifier. The other uses the cavity in a special circuitthat ~ro~rides an intermediate frequency signal that is ~ m.eaeureof the difference bet''een the frequencies of the osci.] Rancor andthe cavity. The resulting stability of the occult atore is suchthat audible beat freauencles clan be produced between two _ it, ~
once Restore at 10,000 me. A technique by which the frequency_stebi]~.at' on systems described could be used to investigate,with high res olution, the structure of microwave abs orationsr~ec~Gra is discussed. Some of the other Capers dealing 'with high frequencyouch Galore are:High moorer tubes for V_~_F operation _ Salisbury:23The reenatron _ Saliabury)24Development of pulse triodes and circuit to give onemegawatt at 60G me. - Law and others 5Wide tuning range microwave oscillator tubeClark and Samuell26Cavity oscil lator circuits - Gurewitsch)27Osci~ ~ ators and amplifiers at ~ OGO me . using light-house tubes and cavity resonators in the UHF regionRandy 4~3 . A description of a pride band microwave amplifier tubeis given in an article in Electronicsl28 and also in an articleby Kom~fnerl29 ~ Design or space considerations frequently make it difficulture incorporate a vacuum transformer into Brave guide- outputmagnetrons. Malter and Molll30 indicate hose the use of quartztransformere may simplify the constructional problems. In testsat 1.25 cm., substantially identical results were obtained intubes with quartz transformers as with those incorporatingvecuum_filled transformers. A cavity res onator or resonant cavity such as employedat microstate frealuencies is a special f orm of linear circuit Richhas Pronounced advantages at extreme! y high frequencies beingsuperior to other f orms of microt`~ve tuned circus ts . It is thefrequency determini ng element in oscillators, amplifiers anddetector circuits and often is employed for frequency checkingin a manner similar to the lower frequency use of, absorption,~avemetera. At cm. ~rave-lengths, the cavity resonator is theOnly practical form of tuned circuit. A general discussion ofvarious types of cavity resonators, of resonant frequency andmodes, of coupling methods and of tuned cavities is published inAerovox33~. Numerous theoretical investigations c'{ various typesof resonant cavities have been made. Mo~zi32 has undertaken thecalculati on of the electromagnetic fields, frequency and circuit- 28
parameters of high_frequency resonator charities. A mathematicalanaigsis in which the resonant frequency of the nosed-in type ofcavity is studied as a function of the cavity dimensions ts Siren:by Mayerl33, while Ludil34 is concerned with the natural fre-quencies of the E-type of a cylindrical capacitive cavity. Lindernand deVriesl35 consider the problem of flat cavities as electricalresonators and Micolasl36 presents a mathematical analysis dealingwith the characteristic oscillations of solia conductors andel ectromagnetic cavities. Rezoned Cavities is the subject of aopener by ~iacolettol37 and Tunable Microwave Cavity Resonators tathe title of ~uarrera's138 paper. A very comprehensive article dealing with high Q resonantcavities for microwave testing has been published by Wil-eon,-39 andhis collaborators. Formulas and charts are given which aid thedesign of right circular cylindrical cavity resonators operatingin the TEoln mode Rich yields the highest Q for ~ given volume.:~he apnlicati on of these to the design of an echo box radar teatset is shown and Practical considerations arising in the con-struction of a tunable cavity are discussed. Another comprehen_sive article dealing filth the met'~'ods and devices for testingmicrowave radars in the r.f. range from about -SOO mc. to 25,000 me.and at associated video frequencies ~s been published by Green,Fisher and Fergusoni40. Tt is pointed out that in general thecede instruments and techniques are applicable also for othermicrostate testing. A mathematical treatment of the coupling of cavityresonators through small orifices is given by Brodekil4l. Harrtesl42has studied the ef.-=ect of size and placement of apertures and slotsin '<alla of resonators upon loading, internal field distortion andefficiency of energy transfer from cavity to 1 oad. Ex?erimen~Garesults indicate the effect of o~eni~y; size for wanted and un-wanted radiation. A good wavemeter is an important requisite for mostn'.icro:~'re measurements. Various types of we're meters coveringvari cue Anti one of the frequency spectrum are described in theJi~Gerature. A cut scussion of Awes ~d applications of microwavefrequency meters is given by Jones343. A wave meter for the fre_fluency range 155 to 255 mc. is described bar Banner)440 A yes_cri~tion of a circular and of a rectangular type resonant cavitywavemeter for frequency measurements in the microwave region isgiven by McQuayl45, Rile Peakel46 deals faith cylindrical-ca~rity,~a~remeter design. Essenl47 gives a descri~cion of four simplyconstructed cavity resonat;or wa~remeters covering the frecuei,cyranges lO,f)00~4~000 me., 5,600_2,000 me., 2700-1000 mce and000_200 mc. The use of transmission lines as transformers is c on-side red by Bardi49 and by Quailed L50. QuariesI51 1ike~ise dealsIrish tranemisei on knee as resonant circuits. Crosby aridPenny~act~er352 have mule a theoretical study c.f radio_frequency-29 ~
re ~ i store as uniform trenemi ~ si on line ~ . The increasing use of decimeter and centimeter ware_lengths has necessitated some changes in techniques for measuringcowers The application of the bolometer method to the measurementof small r.f. Coverers is described by Hickinl55. In this method,the Tower is dissipated in a resistance having a large temperaturecoefficient which forts one arm of a Wheatstone bridge. By directcurrent Bower sub~Gution the indicator may be calibrated and theone measurement of resistance bill give the power in the load.Some Beta ils are given of indicators and circuits to deal withroosters from a feT* microwatt to a few watts at frequenci es up to10,000 mc. The limitations of the method and possible sourcesof error are considered. Earlyl54 has described a wide_banddirect_re2.ding wattmeter for wave guide. It uses a directionalcoupler and one or more thermocouples to monitor the poster trans-mitted by a cadre guide or a coaxial transmission line. It wasused in connection with a 1000 '.~t magnetron transmitter whichhe.d a tuning range of 8 to 12 ems. and the calibration was sub_stantially constant over this range. According to Beggsl55, aseries of concentric line load lames have be en developed to meetthe demand f or Bother indicati ng and measurement lamps that Hi llovercome the limitations of ordinary lamT>s at microwave frequencies.The lame sizes made to dP-te have an upper frequency limit of 1000to 3000 mc. at which reliable measurements may be quickly andeasily made. At higher frequencies, they are useful for in-d~ catting relative or maximum levels when making circuit adjust_Pent ~ . The standing 'save detector or indicator is a snort Mensa_Agile instrument for development and measurement 'cork. Measurementsof complex impedance and standing wave rati o of transmission lineloads, of attenuation and characteristic impedance of the lines,and of net Dower flow at any point in the system are but a fever ofits applications. The theory for determining the power law ofdetec4Gors, complex impedance, reflection coefficients of cableconnectors, micro~^~ave_cable attenuation, and net power floor isPresented by Feikerl56. He likewise dlecueees the structuralfeatures of the standing Have indicator for both coaxial and waveguide systems. The effect of Probe Penetration upon the standingGrave Pattern has been investigated by Altarl57 and his associates.They show that distorted patterns observed in standing wave de-tectors vrith deeT'er Probe penetrations are attributable to r-e_Elections from the probe wire, and that the probe, over a Priderange of penetrations, acts as a slmnle shunt admittance acrossthe transmission line. The mathe~natlcal treatment developed givesa satisfactory account of observed probe patterns and enablesexact readings to be obtained even from badly distorted patterns.Applying their results, the sensitl~rity of standing wave measure_mental at low_nower levels may be improved without loss of accuracyby using much deeper probe penetrations. A dl~ectlonal coupler is a very useful microwave devicewElch has a number of applications such as, for example, monitoring_ 30
the Dower in a trar~emission line, tapping off sonae of the energyin a~ transmission line and conversely injecting energy fromanother ~ ource into a transmission line, and the measurement ofsmall or moderate standing wave ratios. The frequency range overwhich moat types of directional couplers will operate is ratherlimited. This is especial ly true of Brave guide couplers sincethe impedance of the guide changes smith frequency. Earlyl513 hasdescribed a new type of coupler which employs a. small loop thatresponds to both the electric and magnetic fields. When usedin conjunction with a special section of ridged wave guide, itis possible to obtain excellent directional characteristics overa 2 to ~ frequency range.TI E3. Microwave Resonance and Aberration Phenomena. The development of radio_frequency sources and techniquesin the con. ~rave-length range has made possible the observation ofresonance phenomena of considerable interest in molecular structure.Numerous pioneers, who there fortunate enough to have access tomicro~.ra~re test equipment, are already e=loring this never field ofmicrostate s~3ectroacopy. Microwave resonance phenomena fall inIntro categories, tho se associated ,^.~ith electric moments, and thoseassociated with magnetic moments. Although this reviewer is con-cerned primarily Irish dielectri c phenomena, the arriver is takingthe liberty of including a brief discussion of magnetic resonancephenomena because of its physical and structural imD1ications. During the war, an unaers~Ganding of microwave resonanceand ebso~tion in gaseous media wee of vital importance sincethese processes effect radar tranamieelon in the atmosphere atcertain wave_lengtha. Consequently, the adsorption of cm. wavesin atmospheric gases has received considerable attenti on. Thereare now two known contributions to this absor~tionl59,16~0; oxygen,which has a bard of abeo=tion lines in the region of 0.5 cm.sunerimoo.sed An a weak continuum extending up TO long wave_length;and water vapor, Rich has a weak absorption line at apnro}dmatel5rl.3 cm. and a number of stronger lines below 0.2 cm., the tells ofwhich contribute to the absorption in the cm. ~rave-1ength region.Both of these adsorptions there Predicted theoretically by VanV1eck in lo42 and their absorption coefficients there calou1atedsubject to experimental determinations of the line widths due tocollision broadenix~gI6l, 162 and some uncertainty in the ~ onionof the crater valor resonance. lIainer, King and Crossl63 havece~cu'.ated the exact values of the energies and transition ~ro-babiJities of Her valor and. have determined the position andintensity of the absorption in the micro,.~a~re region. The microbe absorption by Boater valor has been deter_mi ned experimentally by various in~restlgators. Becker endAutlerI64 have measured the water valor absorption line resultingfrown the rotational transition Q~_6_5. Microwave radiation erasfed into an air_fi] led cubical copper cavity ~ ft. on an edge.Strings of thermocouples earth alternate ,Junc~cions coated Edith' 1 osey' mater) a,1 were placed at random in the cavity. The enf_ 31 -
of these ~chermocounles is ~roporticha1 to the Q of the cavityarid its. contents. With the total Pressure inside the cavityat 1 atm., the na.rtia1 Pressure of Rater vapor was varied from~ to 55 mm. of mercury. A measure clef the change in emf wishh~miclity yields a Prague for the losses in the strafer van or ~ro-~rided the 0, of the cavity is known. This Q may be determinedfrom additional measurements taken '^rith an aperture opened inthe side of the cavity. The ,^!ave-:Length range between 0.7 cm.and ~ .7 cm. has been explored Their results indicate an ate_sorption peak at 1.54 cm. and a. broadening of the absorption~ ine as the crater vapor density is increased. It is pointedout that the cross section for a HOBO - E2O collision angst benearly 5 tins that for a R;~0 _ air collision to account forthe observed change in band width Keith Orator density. The peakattenuation eras found to be 0~025 db/ki~ome~cer for ~ gram ofwater Orator ner cubic meter.. Eyhl, Dicke and Beringerl65 have determined the atmos-r~heric absorption of Beater vapor indirectly by measuring thethermal radiation from the atmosphere using the microstate radio_meter of Dicke)66. With the addit ion of the humidity and tem-~erature obtained from ~netearalogical soundings, it is possibleto determine the absorption of the entire etmos~here, and tosenara4Ge the c ontribution due to Plater vapor. Measurements weremade at 'ave-1engthe of 1.00 cm., 1.25 cm., and 1.50 cm. Fromthe observed values of the atmospheric attenuation due to Graterrazor at tines e vrave-lengths, it Ala ~ deduced that the abs orb online centered at ~ = 1.34 cm. has a width of 0.~l cm.~~. Thereresults are reported to be in fair agreement Irish those of otherobservers. The observed line '..~dth and position are in agree_rent with Tan VIeck' ~ theory, bug the absolute absorption ob_served is greater than predicted. Townes and Mer~ittl67 have likewise detected the watervapor line reported in the above papers and have measured it forPollee water at Dressurf?s near 0.l mm. Hg. AN this pressure, theline is a few megacycles Deride and the resonance frequency can bemeasured thigh great accuracy. The agreement between these lowpressure measurements and the da4Ga of Becker and Autler appearsto be 'ithin the combined e~erimenta~ errors in all cases. Theagreement in the redone nce frequency f or the Beater vapor line atlog and high pressures is Curtis ingly good. Townes and Merri tthave also found one of the several EDO lines predicted near ~ cm.,~ave_lengt~hs by Weiner, Ring and Crosel63. Beringer368 has reported the results of absorptionmea.~uremen4Gs in the 0.5 cm. weve_length range for oxygen allaox,ygen_nitrogen mixture as a function of pressure. The measuredvalues were found to be in agreement ith the theory of Van VIeckboth Irish regards to the absolute value of the adoration (whichis as great as 67 db/km, at the band center for pure oxygen ata tore of ~ axiom.) and the aenendence on pressure.. . Hershtergeri69 and his associates have investigated theabsorption spectra of a variety of gases at rnicro:'ra~re frequencies._ 32 -
The absorption coefficients and dielectric constants of 16 gaseshere been mea`~u~ed ~t two wave-lengths, lo- 1.2,4 cm.. and ~ = 3.18cm. The gases are H2S, COS, (CH3 )~0, C;~H.O, C2HsOl, SO2, N}I3,Six halogenated methanes and three amines. It its claimed thatabsorption coefficients as small as o.2.x10~4 cm.~] can be detectedand ~ arger coefficients can be measured with an accuracy of ~ 5~.The measured dielectric conetan~Gs at these wa~re_1engthe are es_Gentian By equal to the static values. A quantitative interpre_tation of the absorption coefficients in terms of the known structureand sr~ec~cra of the individual molecules is given. The theory in-dicates that all non-~lanar molecules which cossese a permanentdinol e moment should shear a~r~reciab~ e absorption in the microwa~reregion. The energy absorbed by the gas from the microwaves re-a~nee~re as heat and sound. Experiments demonstrating these thermaland acoustic effects attending the absorption of microstates bygames ore described. Amrnoni a gas ha ~ be en known fair ~ ome ~ i me ~ ~ exhibi ~ astrong ab,ror~tion bend in the region of 1.25 cm. ~.re..,re_le~;ths whichis associated. 'rith the inversion of the ammonium molecule relativeto the alone of the hydrogen ascots. At re~ati~re~y high Treasures,a single broad absorption band is observed. Recen4Gly, a numberof ex.ce1.] ent determinations have been made at reduced pressure ofthe fine structure of this inter on band. Ex~eri rents were r,er-rormed independently by Bleaney and Penrosel?O9 by Townes1-71 andby Gocd772 and are a? 1 in substantial agreement. BY eaney aridPenrose measured the absorption over the pressure range 600_0.2ma. Eg. and resolved the anionic spectrum into at least 20 obeer_va.bJe lines at low pressure. The line breadth was found to bero~ort, onal to pressure and indicates an effective diameter for.. . .collision_broadening of the ammonia mod ecule 3_5 times largerthan the usual ~re'.lues. This behavior is attributed go the largeexternal field of the molecule. Townes has also resolved the in-version lines near 1 .25 cm. , their widths being decreased at ~ owpressures to 200 kc. Line shapes, intensities and frequencieswere measured and correlated Bath theory. Ca~cula~Ged intensitiesand the Lorentz-tyr~e broadening theory fit the experimental re_suits if the frequency of collision is 15 times greater than thatmeasured by vi sco~ity methods. S~1 ingoing due to rotati on is infair agreement with a -recalculation of theoretical values. Hadleyand Denni~on 7-73 have likewise recalculated the splittings in anattempt ~c ~ obtain better agreement between the ory and observations.Tonnes has observed a ~a~Guration effect with increase of powerabsorbed per molecule and has offered an interpretation of thisbehavior. Good has observed 30 lines of the fine structure ofammonia in the region of ~ .25 cm. He measured their intensitiesand frequencies for two different temperatures and deduced anempirical expression for the line frequencies in tenures of theirrotational quantum numbers. At pressures of 5~10~ mme Hgo andbelow, the lines are very well recolored and at ~re~.Qures of lo-2moo fig. and below, e. definite hy~erfine structure appears. Goodhas also observed the Stark effect on applying a. d.c. field tothe absorbing gem.- 33 -
The hy~erfine structure of the ammonia spectrum wasexplained slmultaneQusly by Coles and Goodl74, and by Daileyl75and associates. Cores and Good.have resolved a hyperfine struc-ture ~ n most of the rotational lines of New H3 and lnte~ret thestructure as a splitting of the ratatior~al energy levels by acoupling between the angular momentum of the molecule as a wholeand the spin of the nitrogen nucleus. This Interaction appears Goresult from an electric quadrunole moment of the N74 nucleus.tI)5lI sho',rs no trace of hyperflne structure since N15 has a spinof i72. In order to test the quadruple hypothesis as an Lana_tion for the hy~erfine structure of N14ES, Dailey an] his asso_clates have carried out e. quantum mechanical treatment of the~ nteraction arid the results ~Are-~e compared with accurate measure_. .meets of the hy~erti ne structure . Excellent agreement 'as ob.tained. It Alas concluded the t the hypothesis that the hyperfinestructure of ^tT~4R is caused by a quadrupole interaction isstrongly au~orted by several types of observations. Codes and GoOdi74 have observed Stark Ed Zeeman effectsin the microwave sneci~r4um of NHa in the 1.25 cm. regi on using}~3 containing both ~ and N15 isotopes. A magnetic field of6600 oersteds applied perpendicular to the high frequency f ieJ dsplits a rotational line into a doublet with ~ separation ofarrow - rely 2.0x10-4 cm.~1 independent of J and R: within ex_experimental error. A magnetic field parallel to the high frequencyfield produced no observable effect. The type of structural information Chant can be obtal nedby micro are a~ectroscopy is demonstrated by the investigations ofDakin, Good and Co'.eal76 and clef Townes, Holden end Merrittl77,Dakin and his co17aboratore have resolved the absorption line due.to the transition from the ~ - 1 to the ~ = 2 molecular rotationallevel in the OCS molecule. This line appears at 24,300 me; andwas resolved at pres sures leas than 10- En. Hg. At greaterpressures, the pressure broadening of the line was so great thatthe line was hardly ob.ser~rable by their oscilloscope method. Themoment of inertia of OCS calculated from the above frequency if,1.379x10-38 g cat , which agrees well with the Prague 1.3RxlO-~g cant , calculated using the interatomic distances observed bycross and Brock'.ray. A linear molecule of this sort should show Stork effect and solltting Proportional to the square of theelectric field strength and the square of the dipole moment. Ashen~ d. c. electric field eras applied ~Go the OCS gas in the Grave guidewith the d.c. fiel] parallel to the direction of the Polarizedelectric vector of the t-ravelling micro~ra.ves, the rotational lineSplit into two lirtes; one snored to a Coffer frequency, the otherto a higher frequency than that of the unperturbed transitionlines The equation relating the frequency of the two lines tothe moment of inertia, the a. c . field strength and the dipolemoment is given. The dipole moment was calculated and found tobe 0.72D comparers with the brogue of 0.65D -reported by Zahn andAil es from dielectric constant data.- 34 _
In the experiments of Tourney, Holden and Merritt, therotational spectra of several line an Molecules were found in theregion near i cm. wave-length at pressures of the order of ~ fewtenths of ~ mm. Hg. of the absorbing gas e In some cases, a num-ber of weaker ~ ines were ford to accompany the main rotationalline. The measured frequencies and intensities of lines in therotational spectra of Br ON, ClON arid OCS are tabulated. TheC1CN likes at 23,885 and 23,389 mc. appear to be caused by C135CHand C] tCN molecules respectively which are in the ground vibra_tional atate and undergo a ~Gr=sition from J-l to J=2. Similarly,the BrCN lines ~ 24,712.5 And 24,570 me. are a~GIributed to themolecules of Br YCN and Bra ON respectively in the ground vibra-tional state which make a transition from J=2 to J=5. The singleOCS line is caused by the rotational transition J=1 to J=2. Themoments of Iberia are computed. Using the isotople frequencyshift in CICN, the internuclear distance C-N is cat culated tobe 1.15 I. The isotonic shift in BrCN is also consistent withthi ~ Prague. The internuclear bond distances Br-C and Cl-C werealso calculated. All three distances were found to be in goodagreement with electron diffraction measurements. These datacan be used to distinguish between alfferent possible structuresf or these mol ecules . The data are consistent with the structuresCl Cat and Br-C-N but not Perish the structures Cl-N-C and Br-~-Cwhich have sometimes been proposed. In the firing paragraph of th' ~ section, it was statedthat microwave resonance phenomena fall into Into categories,those associe.ted smith electric moments and those associated withmagnetic women; The microstate resonance and absorption pheno-mena discussed so far Perish the exception of that pertaining tooxygen once their origin to the existence of a permanent electricmoment. The microwave absorption by oxygen gas on the other handis due to its magnetic moment. The remainder of thia action Trilldeal Perish magnetic resonance Phenomena. The permeability of ferromagnetic materials at fre_quenches between 105 and 10 0 cycle a per sec. wee investigatedby Allanson'78 . Methods of measuring the permeability of ferro_magnetic materials in high frequency fields are described andthe resul ts obtained by various investigators are correlated anddiscussed. It appears that hysteresis effects cease between 10and 107 cycles per sec. and that the ~ermeabi, ity decreases withincrease of. frequency until 1 t reaches unity it, the region of10 cycles/sec. Various explanatory hypothesis are discus Bedand it iB cone] uded that the most Probably explanation is thatthe phenomena are due to eddy currents Erich delay magnetizationroceases. These eddy currents are caused by the extensions orrotations o' the magnetic domains and act so as to slow down andfinally prevent these changes. The theoretical data evaluatedon the basis of this hypothesis are reported to be in good agree-~nent smith experimental observations. Eittel}79 has proposed a theory for the dispersion ofmagnetic Derineati~ity in ferromagnetic materials at microTralrefrequencies. The transition in the Prague of the initial_ 35
permeability of iron and nickel frown the d.c. value ~ ~ 100,go the infra red, TV = 1, is known to occur princinaily in themicrowave region. An explanation of the experimental facts isproposed by c onsidering the equation of motion of a domain boundary~ n an applied magnetic field for frequencies such that the skindeath of the magnetic field is smaller than the thickness of adomain. An analytical solution of Maxwell' g equation is found forthe r~agnetiza~Gion of a layer one domain thick. The definition ofthe permeability at high frequencies is considered carefully andit is shown that the natural definition leads to c complex valuesfor the permeability. In experiments, two different types ofare found. The relationship of the complex ,~ toters determined-from resistive losses in a circuit elements and toils, determined:from reactive changes, is developed. The status of Becker stheory of eddy current damping is considered and several suggestionsare made for further experiments. The electromagnetic properties of ferroso_ferric oxideend ganuna-ferric oxide have been investigated by Birksl80. Theoxides in nodder form were mixed in various proportions with aloll :08B, non-magnetic binder~p~affin wax). From measurementson nicer es up to 5040 concentrati on at three wave_lengths, italas found that the complex ,~ varies with ~ (volume Proportion ofoxide) in accordance with the theoretical Clauslus-Mossotti re7~.~on:- _ vail~+2- ~Fa+2whereby is the complex ~t of the oxide extrapolated to 100< con-centratlon. The derived magr~etic ~ropertles of the two oxlde8are liated and the real and imaginary components of Ma forr-Fe~O3 are plotted together with ROttlgls data on the solid oxidefor ~rave_lengths from 39 to 174 cm. Both oxides show ma.gne ticdisperse on accompanied by a loge ma~netlc abortion. Forr7-FeaO, maximum absorption occurs at a ~^ve-length in the neighbor-hood of ~ a cm. The mechanism of nuclear induction has been investigatedindependently by Purcell and 0a co-workers and by Block and 0aassociates. PurcelliS] and his co-workers in a letter to theeditor of Physical Prier report observat;ione of the transitionsbetween energy ~ evels corresponding to different orientations ofProton spin in a conatar~t magnetic field by measuring the absorp_tlon of r.' energy in solid paraffin. Experimentally, a resonantcavity witn a resonance frequency of ap~ro:~lmately 29.8 me. wasPlaced in a strong magnetic field, the inductive part of thecruelty being frilled with paraffin. On verging the static magneticfield, a very share resonance absorption was abeerved at a fieldof 7100 oersteds giving ~ value of 2.75 nuclear ma~netons for themagnetic moment of the Proton which is in good agreement with theaccented value . The relaxation time was found to be les ~ than 1minute thus bet ng several hundred times smaller that would bededuced from the type of ~i n-la~ctice coupling sugges'G by Waller.Torrey, Purcell and Pound 2 Presented parers on The Theory of_ 36
Magnetic Resonance Abduction by Nuclear Moments in Solids andMeasurement of Magnetic Resonance Absorption by Nuclear Momentsin Solids at the Cambridge meeting of the Physical Society. Morerecently Purcell:83 and his associates observed nuclear resonanceabsorption in hydrogen gas at room temperature and at pressuresranging from 10 to 30 atme. The - resonance eras found to occur atthe frequency and magnetic field strength corresponding to the 'g'value for the proton but the process involves both protons in theortho_hydrogen molecule only. A single extremely sharp resonanceline was observed, the width of which remained constant at 0.25gauss over the whole ~,ree~ure range. The intensity of the linewas found to be directly proportional to the gee pressure. Thenature of the relaxation mechanism is discussed. Purce11184 andhis associates have also investigated the resonance absorption bynuclear magnetic moments in a single crystal of Cafe. The magneticdi~ole_dipole interaction between nuclei arranged on a cubic [atticin the presence of a strong external magnetic field, lIo, dependsmarkedly on the direction of lIo, with respect to the lattice aces.If the width of the r.f . absorption line at ~ = ~Ho/Th arisesmainly from this interaction, the width and ale b the peak intensityof the resonance absorption observed in a suitable single crystalshould vary as the crystal is rotated in the field, lIo' Such aneffect was found in ~ single crystal of fluorite, Cafe, in whichthe magnetic nuclei occupy a simple cubic lattice. As pointed out previnusIy, Blockl85 and 0a co-workershave carried on an independent investigation of nuclear inductionusing a Someday different experimental procedure. The magneticmoments of nuclei in normal matter uroduce-nuclear naramagneticpolarization upon estab~ ~ shment of equilibrium in a constantmagnetic field. An r.f. magnetic field applied at right angles~ ~ the constant field causes ~ forced precession of the totalpolarization around the constant field wi th decreasing amplitudeas the Larmor frequency approaches adiabatically the frequency ofthe r.f. magnetic field. Thus there results a component of thenuclear nole.rization at right angles to both the constant andr.f. magnetic fielde. Block has shown that under normal laboratoryc onditions, this component can induce obser~rab, e voltages which canbe detected in a cod] vrith axis perpendicular to the two fields.Block gives a discussion of nuclear induction considering firstthe external fields only and then those modifications which ori-ginate from internal fields and finite relaxation times. Bloc3:and his associates heave carried out experiments in which thesignals from Protons contained in a variety of substances severeobserved. The results show the role Played by the relaxationtime, which was found to vary between about 10- sece. and manyseconds ~ The phenomenon of naramagnetlc resonance has been in-vestigeted by Frenkel, by Za~roisky and by deVri jer, Volger and(sorter. Frenkell86 has extended Rabits theory of magneticresonance to the case of the existence of friction; forces andapplied it to the calculation of magnetic lo9 see in a solid_ 37 -
diamagnetic material for the case of a high_frequency magneticfield Perpendicular to ~ strong constant magnetic field. Thedependence of these los see on the intensity of the constant fieldor the frequency of the r.f. field is in agreement with the ex~eri~mental results of Za~roisky. Frenkel Choirs in cor~clusion that thetotal broadening of the resonance line must contain a term ~ro-nortiona~ to the square of the ratio of the rift field strengthto constarlt field strength. The diamagnetic absorption of energyby OUC18 SPIRO, CUSO4.58;10, OrCIB, and MnCO3 WEE investigated byZavoiskyi87 in a constant magnetic field Perpendicular to an r.f.magnetic field having a frequency of 1~51xI0 eycles/sec. Theresults of these measurements are discussed from the standpointof Frenkel' ~ theory of snin-magnetic resonance. dettriJer, Volgerand Gorter]87a have measured the reef. paramagne tic absorption ofgedolintum sulfate oct~drate al 77o and 90°K. in order to obtainan indener~der~t determinati on of the specific heat of the spinsystem -ma of the lattice relaxation constants. The value ofthe win relaxation constant obtained is in good agreement withBrc~er'~ thearetica1~ Prague of 2~5 :~: 10~ 0 sec. A new magnetic resonance in ferroma~gnetl~ materials atmicrowave frequencies was discovered by Grifflths 88. Grifflths'e:gneriT~nta are analogous to the nuclear lnductior~ experimentsexcel the t the phenomenon is dus ~Q the absorption of Or..energy by Recessing electrode and oc cure in the microwave regionfor static field strengths comparable to those in the nuclearinduction experiments. Griffithe found that the resonance fre_quenches he observed were greater than the calculated Harmonfrequencies for electron spin by fact ore of about ~ to 6. RittellB9has given a theory of this resonance effect which leads to valuesof the resonance frequency in close agreement with the expert_mental determination. He shored that it is important to considerthe dynamic coupling caused by the demagnetiza~Gion field normalto the surface of the teat specimen with the result that theappropriate Labor frequency should be calculated as for a fieldstrength (BH)~/2 rather than -or H. Furthermore, by introducinga damming term, Rittel has derived an expression for the compl enpermeability in the direction of the r8 me- m~etic field fromRich 'Ghe apparent permeability,~L6r, can be calculated. Hughes igO has proposed a new method of measuring theelectric dipole moments and momenta of inertia of diatomic polarmolecules. The moQeculee of a molecular beam are caused to under-go a transition in a steady homogeneous electric field by anoscillating electric field at right angles to the deco component.This experiment is, therefore, closely analogous to the magneticresonance method. Hughes considers the new method ~ advancemer~tover previous Methods in that a single rotational state of themolecule is studied even though it is present to only one pairsin 10,000 as a component of the beam. The dipole moment andmomer^t-of inertia of. cesium tInoride were determined by thismethod. A feature of this method in common with the magneticresonance method is its extraordinary resolution of close energylevels which so far exceeds that of infra_red spectroscopy that_ 38
momenta of inertia may be obtained for heavy molecules whichhave previously been beyond reach. In contrast to solutionmethods in which the variation of dielectric constant is measuredas a function of temperature, this procedure gives the dipolemoment entirely independent of mass interference effects.[I ~ o Practical Applications In the first part of this Digest, the emphasis is placedon the theoretical aspects of the electrical properties of matterand measurement methods for inveatigati ng the se properties . Thereduction of dielectric the ore to practice is of equal, if notgreater, importance. However, an extensive treatment of this sub lect would result in a sizeabl;e addition to art already lengthyreview. Furthermore, other parts of the Digest will undoubtedlydeal with the practical applications of various dielectric ~naterial;~.Consequently, the discussion in the present section will be limitedto Dielectric Heating, Coaxial Cables and Transmission Lines.ITIA ~ Die ~ ectric Heating~ _ The introduction of electronics to industry has broughtabout many outstanding improvements in production and qualitydurtry; the nest few years. Among the more important of theseachievements are those Chose effectiveness depends on the use ofelectronic heat which may be aped fed in two forms, inductionheating and dielectric heating. Only the latter form will bec onaidered in thi ~ reviewer. The development of dielectric heatinghas been rapid in the la8t fe,¢ years and much h' been writtenconcerning the fundamental principles of dielectric heating9 thed e s i ~ of hi gh-fr eque no y he alp ing equipment and the applic at i onof dielectric heating to various processes. The literatureduring 1946 has again been voluminous. Maddock:9] gives - an account of the modern theories ofdielectric behavior so that the mechanisms of dielectric heatingmany be understood. There is also a section on energy and powerred ations and the choice of frequency. The final section isdevoted to the practical aspects including a discusaion of tem_Denature distribution, applications of dielectric heating andmiscellaneous notes. This article cites 21 references. Thebasic factors in dielectric heating are set forth by Winiund ]92in the form of equations, tables and charts; trio graphs for com_outing the poorer required per 100°F. temperature rise for given'heights of materials of various specific heave are presented byBocki93. Oebornl94, Hartahornl95, and Cablel96 have publishedrevere on High Frequency Heating and Tinnerholm)97 has an articleon High Frequency Preheating. Nielson)98 considers the questionas to 'chat frequency to Ale for induction and dielectric heating.An erticl e by Bosomworth:YY discusses the theory of die] ectricheeding, applications in general fields, applications in therubber industry, radio-freauency curing, Ogle Or equipment re-auired, choice of frequency, radiation measurements, screenings_ 3g -
material handling, temperature control , maintenance of equipment,ant testing instruments required. Prob] ems in the design of hlgh-freauency heating ea~uip-ment are considered by Roberda200 and Reifel 20] describes an auto_acetic tuning system developed by the s~cevene_~nol ~ Co. , Inc . , andEnrich comprises taco servomechanisms for varying the coupling be-tween the load circuit and the oscillator tank circuit and fortuning the 1 cad circuit; to resonance as the effective load im-~edance varies. Another coupling method is described byK1 einberger202. Xohier203 deals Ah the- heat sealing of Atlantic filmsinc] uding such items as the danger of overheating, the mechanicaleaui~men~G and electrodes, electrode design, equalization ofpressure, a good weld, valuable design factors, operating freagencies and the necessity for a well filtered power supply.Another arts ale on segl],r~g ceJ Europe acetate with high-frequencywas Smitten by Coiner. Seal ey205 describes the application ofdielectric heat in mold' ng ins-A1a~Gion.are:Other references to literature on dielectric heatingRadio-frequency dehydration of penicillin solutionBro`.'n206 and <ethers.Dielectric heating of granular materials. Aluminumand silicon oxides - Schutz and McMahon207.Electronic he ating in the furniture industryHigh-frequency en ectric heating. Some notes on itsindustrial a~licati ons209.High_frequency heating de~relo~nenta2~0.Dielectric heating equipment su~r)liee heat go curef cam rubber.Dielectric heating dries and cures rubber21 2.- Winalund203.Electronic eouiument to preheat molded material preformable.Electronic rubber preheater - Mittelmann and Bo~o~nworth214.High_frequency heating conference215.Induction and dielectric heating formulas23 6.High_frequency heating in U.~. plastics ~ractlce - Brumleve217Reating and vul canizing rubber and simile; resinswith high-frequency cur-rent - Smithers (3._ 40
Case studies of RF heating. Modern methods of usinghi gh_f requenc y he e.ti ng 219.High-trequency head cures Foamex producte220.Radlo_frequency a.c. current acpl fed to industrialhe'atlngZ21.Dielectric heating dries transformer bushings _ Cole222.Dielectric heating analyzed for textile auplications223.Electronic machines to Join thermoplastic sheetmater) a, ~ 224.Electronic heat. Neweat in electronic heating is aunit that sprays r.f. energy onto the ob ject tobe heatea225.Electronic blowtorch226.Induction and d' electric heating data. Dielectriche ating f ormu~a'; 227 .Industry Cooke wi th electrons _ Stimson228.Dielectric machine to preheat molded plastic fief ormS229Electronic2geating equipment to preheat plastic moldingBeef ores 0AFO f or R ~ F. he ating - Rambo23i ~Induction and die1 ectric heating232R.F. heat ~ aboratory 33.TIlB. Coaxial Cables and Transmission - Lines. . . Coaxial ~ abl es and transmission lines are an importantcomponent of high-frequency and micro are equipment. Considerabledevel opment work Moran carried on during the war especially on thedesign and production of low_loss flexible solid dielectriccoaxial cables. A discussion of developments in solid dielectricr.f. transmission lines, including sections on polyethylene, typesand design of cabs es line efficiency and available cable typesis given by Jraham234. ,1arner235 has written an excellent articleclearing Erich the problems encountered in the manufacture of ult-ra-high-frequency solld-dielectrlc cables. The various types ofsemiflexible solid_dieJectric transmission lines suitable foruse at ~f are discussed and five general types are described.These are (a) coaxial, (b) dual, (c) dual-coaxial, (~) lo'_capacitance and (3) high impedance. Types (a) and (b) aregenera' r~urnose lines Anile type (c ~ is used in direction find' ngequipment, instrmnent-landing systems, etc. ETigh impedance_ 41
cables fi nd use in cathod e_follower and special delay circuits .The manufacture and problems associated Perish extruding Band braidingare considered. The question of penetration of the braid into the-dielectric and ',~.cket a=d the recent steps taken to eliminate thisprobe em are discussed. The contribution of the individual com-~onents of the cab] e to the to~Gal lose is examine and an apparatusde scribed Enrich e nable ~ ~ direc ~ me Deuce ment of bra id re ~ i ~ tanc eto be made at 150 mc. A typical example is given for R=~/u cableshowing c~ ore agreement between the measured total loss of thetires and the lose obtained by a summation of the individual dossesof cry el ectr'c, inner conductor and braid. The effect of varyingthe braid c ons true ti on ~ ~ demons trat ed . Finally, a brie f de ~ crtr'-t i on i s gi ven of the vary ous t e s t s and the e quipm2e at f or t e s t inght transmission l' nest In another later, Warner 3 c insiders thechoice of ¢~ecketing; materials for high-frequency trane~ninsion7 iH=8e According to ECr7'eger and Raabe237, few manufactured productseve flub ject to the elaborate and extensive tests through MuchEGOS yethylene dielectric cabs e is but, in order to insure its uni-'c~m que.lit.y snd performance. Strict end_to_end uniformity isme' ntained throughout the entire manufacturing process. This isaccom~7 ished by prec'sion-extrusion, accurate temperature control ,constant Process inspection and micrometer gauging standards. Adiscussion of oo:~ye~Ghy~ene dielectric cables is also given.Krueger also has a Caper on flexible coaxial cable2~. A brief account of the cables used in radar equipment withspect~.l reference to ~olythene (polyethylene) insulated typesi ~ Presented by Smith 239. The rf characteristics of radar cablesare determined by Resonant lines and nstanding wave' methods.In anion to the rf tests, all cable is subject to d.c. measure-ments to determine conductor and dielectric resistances, the'ester being usually at least 105 megohms/LOO ft. A high voltagetest at 50 cycles/sece is also applied, the frontage chosen beingsuch that the maximum stress in the dielectric ~ B 90 kv. (~eak)/cm~chneon240 testis with the development of a low_loss 300 ohmParallel Are polyethylene transmission line. Loss curves aswell as a Photograph of a production run. sample of line areinc luded. Design data and cheracteristice of high-frequency cablesare dealt with by zimmermann241. Design data for beaded coaxiallines are given by Cox242. A note concerning a coaxial design,gas _ f ~ Iled e le c tri c c able f or hi gh-f r ep uency c irc ui ~ ~ apse ar inIndustrial Equipment Ne~re245. Oraggs and Rant er244 derivemathematically the capacity of tin cable. A cable with an im-r~edar~ce of lOOO ohms ~ ~ described by Kalimann245. Tt resemb, esthe usual flexible concentric cable but its inner conductor issing~e-~ayer coil continuously wound on a flexible core. Alo~'r_los~ coaxial line called CO-X using dielectric filaments be_tween ounces and inner conductors is a new product of the BostonInsulated Wire and Cabs e Company246. The principles used in_ 42 -
calculating the temperature rise in cables for transmitting rfpower ere cons idered by Mildner247. The theoretical attenuati onche.racteristice and power ratings of a number of standard rfcables are get down in graphical form for a wide range of opera_tiny frequencies. The effect of the presence of standing wavesand the effect of end cooling are considered in relation to therating of the cable.:~:= I: ~ A discussion of the characteristics and a~nliceti~ns ofFiberglas to 'ire and cable ~ nalllation is given by Sam~son~48.The basic charecteristic6 of Fiberglas yarn are incorporated inmany commercial! y avai ~ able cables today. Fiberglas insulatedmagnet wire has been produced now for many years and is an es_Ad. . .tablished product in the electrical industry. Fiberglas leadwire, resistors, radio hook-u~ Refire end ignition ce.bl e are alsofamiliar commercial products. To meet the demand of many ~nli-cations where an ins :lator is needed to withstand operatingtem~era~:ures of 1000°F. or more, Fiberglas textiles are especiallyprocessed to make them heat stable up to 2000°F. In the electricalfield, Fibe;rgIes special high temperature tace and sleeving havebeen used experimentally with considerable success airy thesematerials can be furnished in limited quantities. This material,hoverer, is not recommended for applications where severe flexingor Technical abuse is encountered since no imoregnant is used. Increasing interest in the electrical industry in thesuperior properties of Fiberglas-silicone combination materialshas resu1 ted in considerable de~reloc~nent work. Silicone-varni~,h-im~re-gnated FibergIas-covered magnet wire is being produced on ~semi-comn~ercial scale by several manufacturers. Laboratory workis being conducted on cable constructed with a silicone-rubberextrusion over the conductor followed by an outer Fiberg] as braidimpregnated 'pith silicone varnish. Also in the development stageis Rework on the application of Gil icone v~rni shecl Fiberglas Cal othapplied as cable fare '.~ma~. The superior electrical Properties,resistance to high temperature and to moisture and the ~erma.nenceof Fiberglas and silicone combinat;ions warrant further developmentwork and u711mate3,y co~r.mercia~ e.~lice~rions in the wire and cableindustry ,~l be ~ rea~itye various other applications or noten-tia' e.~3 icetions are cited in Sam~non' ~ cater. The manufacture and use of p;1 ass_bonded mica are describedby Re~lo~le249. An article or In.3ection_~1ded G3~-Bonded picaReared in Elec . Meg. 250. An improved glass_bonded ~nice.-(mycelex 410) provides a lo'.~!-1oss insulating material for injectionmolcsi:~g. It; hoe been developed for ~ arge_run production of smallelec~Grica] serfs D~r~:icu~arly in irregular shares. Molding tech-nioues permit irco-r~ors tion of merges inserts of bras =, courter, steel,nones, etc. and result in smooth mold first sh end erect si ontolerances. The electrical characteristics of this material makeit ~ticul~rl y suitable for high-frequency ep~licat;ion~-. There a- 43 _
low_]oss factor ~ ~ .016 at ~ me. ~ is required or for applicationswhere it is e~sentie7 to Iran high voltages without car-oon1-~ation in the ever of arcing. The electrical Properties are:Power factor tory at ~ mc. ~ - 0.0015, £' (1/~c. 3 _ 8~3 volumeresistivity _ 6.0xlOi ohm cm., dielectric strength _ 400 volts/mil,arc resistance, A. Be TeMe ~ 250 see ~ The replication of insulators in contaminated atmospheres~ s considered by Frey25l.IV Elect;r'cel Measurement Methods The methods and equipment for making D. C. and loller fre_cuency measurements are now fairly well established e.nd stanc~ar-d' zed* The conventional t'lum~ed' circuits, however, become in ectical at frequencies much above 100 mc. and. the experimentermust work with transmission lines and resonant charities. He snuck,therefore, become familiar with transmission line theory and thefundamental ~rinci~s of microstates as d.iscus~ed in Section IT E1oSeveral ~ e ~ methods for microwave measurements have been describedin the lit endure for 1946 and several other methods developedd. urtr~g the war have not yet been Published. In this section, theemphasis w'T: be Pieced on n~cro~a~re measurements since they re_Present the most recent developments and are ~erha~e unfamiliewto many 'corking in the field of dielectrics.IV A ~ Re ~ i ~ ti vity ~ nd C onduct ~MeasurementsA review of the Parlous methods used in the measurementof resistance, from the Simon eat form to the more highly accuratelaboratory methods, is given by Litt252. The article discussedseverer methods ~ nc~uding the vo~ tmeter - ammeter method, thesimple ohm meter, the Wheat: Bt0 ne bridge and the Key vin bridge.D.C. insulation resistance and capacitance measurements are alsodescribed by Hutchine253. Dexter254 shores how the resistanceof a sensitive d. c . meter can be determined. Polgreen andTomlin255 decal with the electrical non-destructive testingmaterials and an accounts ofFederal Telephone and Radioarticle ~ubllahed in Electronic Indus~Gries'~. Mohler andSternisha257 point Out that conductivity measurements providea rapid and reliable method for plant control of certain types. . ,of solutions such as cleaner baths, acid or alkali rinse waters,din tee the and etc. The application of resistance measurementsto oil testing ts diacuseea by Pike258 who cites the Forrestinept ation test set as an enable of a suitabl e apparatus f <:xrthi ~ Burros e .ofthe Insu? at ion Laboratory of theCorporation is~gi~ren in a pictorialIV B Impedance Dielectric Constant and Loss MeasurementsA method of making impedance measurement With thec~thoJe_ray oscilloscope is described by Viesere 5 ~ The_ 44 -
measurement of arc. capacitance and induc~G~ce of cables isdealt zenith by Hutchins260 and Rosen261 considers the problem ofend leakage in cable power-factor n~easuremen~Gs. The conductingfib of moisture on the surface of the end insulation causes: anerror in a.c. measurements on cables which cannot be avoided bythe simple provision of a guard Afire. The mains tude of theerror is estimated by considertry; each cable end as a transmit sionline. A means of effectiveig eliminating this end leakage erroris described. Stamford and Quarmby262 consider the characteristicsof or.. cables. They describe a measurement technique for thedeterminati on of the ~ mpedance and propagati on constants ofr.f. cables which is fundamental in principle and requires onlyHe apparatus. The authors point out that this method has nowbeen su~erceded by methods employing more refined techniques, butthey fee] that it is useful for certain applications. The tech_nique is equally applicable to coaxial or t~rin-type cables andthe frequency of 600 me. is a convenient one and -~^ HATo determine thely count ed to anThe input current to the line i8 measured and plotted as afunction of line length e The chase constant is obtained frons thedistance between two succesolve minima of incus current. Then.tten,~ z; to~ We- Ul1~; 111~13UL'=~r1 bs .phase c onstant, a length of cable is magnetical_oscillator at one end and left oven at the other. on cons tent of the cableoutputs of short; and long lengths of line hay' ng equal inputs.The characteristic impedance of the cable is determined usinga simple ve..riation of the arrangement used for the attentua tionmeasurements. A method for measuring the Velocity of propage.tionin cables is proposed by Kramer and Stolte~63 and an instrumentauitab, e for measurements at 100 me . i ~ described.can be found by comparing the Zhilenkov264 has investigated the source of errors inthe measurement of the diet ectric constant and absorption by themethod of the Mernst bridge over a wide range of frequencies.Wang~gard and Hazen265 have used the Q-meter for dielectricmeasurements on polyethylene and other plastics at frequenciesup to 50 me. Ike detail ~ of the method employed and the Are_cautions +?~..en to minimize errors are given. A method of measuring complex: resistances in the rangeof decimeter revel eng~Ghs is described by Knol and Strutt 266.In this method, a. screened Lecher wire System is fed symmetry_Cal 7 y from a voltage source; the unknown resistance and a`~lidable diode indi cator are placed across the wires . Two~ riding shorting links simplify the procedure and permitmeasurements to ye made over a Mae frequency range by cancel-ling the reactance of the source arid directing the reflectedwave to,'e.rds the diode. The refl action coefficient is deter_mined by diode location and yields the real and imaginary Dartsof the unknown imnede.nce. The characteristic impedances ofconcentric, r,aralle] and twin cables '~.^ri~chin different ouncesscreens ore derived and the ~ nf~uence of the diode admittance- 45 _
on the accuracy of the me Shod is discussed. Hof:'feegen267 discusses severe: methode for measuring im-~ed~nce ~rticu~arly at decimeter w~,ve-~.eng~hs. At wa,~re_lengthegreater then one meter, it ~ ~ customary to connect the unknowniml3edence in ~re.17 e ~ Perish an 3sciila.10r~y circuit and to determinethe unknown impedance from the retuning and Clamping influence ex_r,erienced by the circuit. For decimeter ~ave_lengths, a Lechersystem is used s~ the oscillatory circus ~ and ~ diodle vo~ tmeteras Nor. Ire a second barer, Hofweegen268 describes anotherme Tahoe for measuring impedance which supplements the previousmethod for decin~e1;er measurement,~. The characteristic featureof this method is the use of a Lecher sys~Gern Which is not tunedto the measure ng frequency. The refl ec~Gion factor can be deter-mined by measuring the ~rolta.ge varieticn along the Lecher system',-hen it is ~ oa`~.ecI by the unknown impedance. From this measure-ment, the ur~kno~m i=nec-ar~ce can be calculated. Numerous investigators are now making dielectricmeasurements at very high and microstate frequencies. Many of theAvers airendy cl ted, particularly in section TI Ed, containdescrtr'1ions cuff test equipment eared Procedures used in the variousmic~o~'ave investigations. Molov269 has considered the a~licatior~of wave guides to the Augury of the electr'ce] properties of matterat ultra_high f-~eouenciee and several other Caters deal Greece_f ically Erich measurement methods and techniques . Horner£70 andhis associates cover resonance methods of dielectric measurementat centimeter wave_'engthe. This paper discusses the theory ande~erimenta1 development of resonator sys~ceme suitable for di-electric constant and cooker factor measurements on solid d1-electric materials at wa.ve-lengths below 50 cm. The refiresuitability of three forms of resonator, namely, a shortsc' vcuited length of coaxial transmission line overacting in the -inci~.l mode ~ and hollow cylindrical cavity - resonators ope_retina in the Echo and Coin modes respectively is discussed. Thetheory governing the resonant behavior of these systems whenwholly end partially filled enrich ~ osay dielectric is developedFind the relations connecting 6' and power factor of the die~ec-tric smith the resonant we~re-length and -factor are derived. MacLean27: describes a microwave dielectric lossmetering technique which is especial ly good for measurementson very lo~r_Ioas dielectrics. The dielectric loas is measuredby determining the Q; of ~ resonator partial 1 y fil led with theWe. Double sample technique is used to eliminate dominant~ ~llriou.s [oases. Metal loss is reduced by confining the fieldmostly to the ambles The deturling process f or determining ~is accomplished by a ledge movement of ~ small rod, the Retuningbeing calculated by the action theorem. ~ The difficul~les filchart ~ e in the m - Inurement of very arne.ll los ~ factors are enumerated.The author Solute out that the method i ~ restricted to the diffic_uric measurement of small loss factors and will not work for largeToes factors. I~c also requires knowledge of the approximate
dielectric constant. The apparatus used in an experimental teston ~olyst,yrene at e. ~rave_length of 10 cm. is described. Eitherthe TE >~, or TEo~2 resonator modes are used. The design of theresona-Gor and the factors determining the size of sample' size ofresonator, and the geometry of the tuning rod are discussed.The J oss factor for the sample of pal ystyrene tested was foundto be 2.7 x 10-4 with a r.m.s. fluctuation of 0.1 x 10-4.Mac Lean believes that even better results can be obtained withbetter equipment. In Ig40, dielectric measurements in the cm. range wereconsidered as difficult and not very accurate. van RiPpel andhis associates, therefore, developed a hollow pipe method wilichovercame these objections end required only a Bleak oscil~ atorend s~na7~l amounts of the dielectric material. The publication0~ their work ma den eye d by Government security rend ationsduring the war. Roberts and von Hi~pel272 have given an accountof the theory and its Practical applications as Quebec ted u~ toMarch 1941 in a Dater Enrich appeared in 1946. Since 3941 themethod and test equipment have been developed to the Point InherePrecision measurements can note be made. In their method, atransmitter radiates wearer of a given frequency into one end of~ closed Cave guide; they are reflected by the metals ic boundaryat the other end. Standing ,^raves ire ~ et up and can be measuredby a probe standing Are detector trave1ling along a slot in theDine Parallel to its axis. The dielectric is inserted in the closedend of the pile opposite the transmitter fi Iling the volume to aheight 59 and the wave pattern above it is measured in air. Thedielectric constant and loss factor are ca.Iculated from the vol_Cage standing scare ratio and the distance xO, of the first nodefrom the surface of the dielectric. The mathematical theory ofthe method is given, the structural details of the apparatusare described and ~ Cone resul 4~s aid ~ wave_len~;th of -6 cm. aregi ven to illustrate its performance ~ Since 1940, more accuratedate. at ~ = 3 cm., ~ = l:) cm., emd at longer ~a~re-lengths havebeen obtained for ~ Deride variety of dielectrics in the Labor&toryfor Insulation P-esearch at MAT. These results are summarizedin two volumes - Tebles clef Dielectric Materials _ prepared uncl er0. S.R.D. Contract Oh~ar_191. The analogy between Lecher lines and wave guides firstsuggested by Schelkunoff (1937) and later developed by Flint andPincherie (1943) hers been used by Wilkins and Bolton273 toderive ~ rare guide method for the me~.~-ement of the ~ronerti es04 dielectrics at very high frequencies. Experimental resultsare given which support the theoretic al c one lusi one obtainedusing the ?.. ogy. Basically the method consists in terminating ine (coaxial or Breve guide) with a merged Ante end measuringthe impedance of the dielectric fill ed guide Enrich the dielectricin contact Parish the end elate and s.1 so been it ~ ~ moved ~ diefence of one quarter we.ve_1 ength along the wide. The input im-~ede~nce of the dielectric fil led guide is determined from themagnitude and Chase of the reflection coefficient by means of° 47 _
s tending wave me~-ementse From these measurements, the nor-m~3 i red character' sty ~ Awe impedance of the diet ectric is ot-1;~.ined from which the at~cenuetion and chase constants end inburrs e' and e, or +~n A ~n be caucus specs.. A discussion of thet~a.namission ' ine theory and the e.~nro~ri~te ecuet'ons is given.Mee.surements at ~ Ire length of 33 cm. using this method arereported for paraffin ),r~9 d~ strene, e.nd ebonite Pond a.re com-n~rec! 'pith measurements by other investigators. Eesentie~1y thegaffe method an] technique seems to have been developed and needindependently by Birkel~O for his measurements on the magnets cdispersion of iron oxides at centimeter weve_lengths, by thebaiter for dielectric measurements at micro~^rave freauer~c'es duringthe firer (unpublished) end by Willis and Crouch274.As indicated in Section IT, Bevel papers dealing ~;n dielectric measurements at microwave frequencies were ~re-sented at the Bat timbre meeting of the Conference on Electrical7~su~ ation. These included a reamer on Dielectric Constant and~s Me~'tlrements from ~ to INTO cycles/sec. by vleatphal; Herohaters on Dielectric Measurements at Microwave Frequencies, oneby Dakin and Works, and the other by Yager; a Hater on Modifi-cetion of the Resonent Cavity Method for Dielectric Measurementsat ~ Fixed Frequency ty Beker5 end a. later on A Resonant CavityMethod for Dielectric Measurements at 300 me. by Muller, Leefand t.~.Ja~rner e Abstracts of there pulpers Bail ~ appear in the forth-coming Annual Report of the Conference on I:lectrica.1 Insulation.V ~ Frecuency Measurements A fear ~e~s dealing specifically filth frequencymen appeared during 1946. A paper by Dexter 275 aimsto give an overall picture of the nets frequency measurementrequirements and to do scribe some of the special e~pr~aratus bei ngusecl. Tt includes ~ non-mathematical di scussion of Butterflycircuits and resonant cavities. A resume of the more conven-timing types of waverneters the t are used to measure u1~Gra-high-f~requencles is given by Endall 276. Inetruments are described+~$t make it possible to messmre freauencles in the Ah. f.and micro rare region up to 3000 mc. Tuned-circult absorptionwa~re~netera covering the frequency range 100 to 800 cm., avariable capacitance any inductance '`ravemeter that is tunablewithin the range 150 to 800 me., a commercial ~r~iabl e ca~aci-tance and inductance wavemeter that is tunable within the range55 to 400 me., a commercial wavemeter using a butterfly tunedcircuit with a. turning range from 240 to 1200 me., a transmission~ ine abeorn~Gi on wavemeter9 a Lecher Brace system, and a commerce alheterodyne frequency meter for measurements UT' to 3000 me. aredescribed, Dickson 77 discusses the determination of very highfrequencies, and Es Ben and ¢ordon_.Smith278 describe ~ reportableenDa~atus for frequency measurements in the range 100_10~000 me.in terms of a standard q,;:artz oscillator. Several papers citedin Section IT E2 also deal With frequency measurements.~ ~8
Measurements An arts cle bye Clayton279 and others surveys the mentholsand techniques used in the O.E.~. Research Laboratories. Magne_irons and velocity_modulated tubes form convenient sources.Frequency measurements involve either heterodyne methods or re_sonant circuits such as the cavity ',ravemeter, the latter beingdescribed in detail. Power may be measured by a bo~ometer or byan artificial good, lawns or strafer. Imnedance, voltage, currentand field strength measurements are discussed. - Gaffney280 ore-sents a brief Summary of some of the more import=' measurementsmethods and discusses the electrical and mechanical considerationsin the design of Tnicrowa~re measurement equipment. Accuraciesobtainable trith the Present state of the art are given.. . Sprouts and Linder281 are concerned with resonant cavitymeasurements, using a cathode-ray oscilic~scope as indicator. Thetraced astern indicates the frequency response of- the cavity..The limitation a and accuracy of the method are discussed. The Qis measured by reading the half-not`~rer points versus frequencydeviation. The shunt resistance is defined as a voltage differencebetween two Points, divided by into times the power dissi~tecl. inthe caviler. Methods of measuring this quantity are described. Other papers dealing with microwave measurements arelisted below:Microstate Measurement _ Banks282HighIt~ht;s of' High Frequency Measuring Techniquefehrlin 283.High-Frequency Mee.surernents - SinClair284.Micro'`,ave Test and Measuring Equipment - Cones 285.,`.ra~reguid e Measurements _ Ashdown286.Scientists Retriever Progress in the measurement andUtilization of UHF Siennas ~ and PropagationCh?~racterts~ic~2~37 ~Meesurement of the Angle of Arri~re~ of vicro:ra~resShern3.es~3238Further Observations of the Angle of Arri~-a] of',icro~re'.ves _ Cre'~ord and Sharps ess269.IV E. Anelysis of_ Cir~n~and Components In order to conserve spice the darers dealing huh thetonics of this section are merely lleted by title belong:_ 49
The Ge.~ ~re.nometer and the Bridge - Mlller290Near Type of Electrostatic Generator - Miller29)Portable High-Voltage Cable Test Unit - Hui~chins292Stabs 1 1 ted De C ~ High-Voltage Supply _ Gurewitschand Noble 293.Trs.r`smit+ing High Currents on Eliding ContactsAntrim 294.Cherac4cerist;ice and Errors of Capacitors Used ForMeasurement Purposes _ Gerton295.ED ectrical Men. suring Ins~;rumen1;s - ockenden andGal ~ 296.Hi~h_Pesistance D.C. Vol~met;er - WaiAelick297..Electrometer Innut Circuits _ Thomas 298.Meter for High-Vol+~ge Measurement - Alfren andEklund299.Inverse Vacuum Tube V£)1 tmeter _ Dike300 eTheoretical Study of the Use of ~ Thermocouple inPrecisign veasurement of A.C. Power - Coffin andMarchal~°~.Test Osci] ~ actor _ Moore302.Frequency Meters as Master Osci1 lators _ Conklin505.Sirn`~le Square_W.eve Generator - Roadley304.bees of Souare-~.aves and How They May be GeneratedI~ebens305 .elide Range Test Oscillator _ A Generator Delivering;Sine _ or Square-Wave Output - Lober306.135 to 500 me . Signal Generator - Won8 OWt C Z andBri er307 .Coaxiel Butterfly Circuits - ~ro8~5o8.Oscillators ena A~n~llfiers at 100 me. Using Llght-house Tubes axld Cavity Resonators in the U.H.F.Region - Rand309.The Resnatron - Can Generate 50 KW Continuous Wareat Any Frequency Between 350 and 650 me. - Sa:Lisbury3~0- 50
Blmnlified Bridge Analysis - Ml1-ler3ll.Production Bridge for Incremental Tests ~ I!Uller3~2.lied Radio ~ Frequency Bridge - Tiffany3~3.A Radio Frequency C3~a4clte~nce and Conductance Bridge Proctor and James .Ne,' Righ Frequency Bridge _ Whaley3~5.Equal Ratio Impedance Bridge - Alexander316.Phase Sensitive Bridge Detector - Hunt,er3~7.A Visual Mull Indicator for Impedance Bridge Measure_meets at Radio-Frequencies - Brine and '.~itehead3~80Bridged- Circuit - Essex319.Note og a Parallel_T Resistance-Ca~P-citance NetworkWolf 20~-Theory and Application of Perallel-T Resistance- ~Can~.citance Frequency Selective Networks _ Stanton32~.Analysis of ~ Resistance-Ca~acitance Paral~el_TNetwork and Applications - HaStinge322.Note on a Reflection_Coefficient Meter - Korman323.Radio-Frequency Spectrum Analyzers - Wi]1isms324Theory of a Microwave Spectroscope _ ~a~25.Bridge for High-Resistance, Righ-Volte~e MeasurementeMiller326.V. Bibliography of Some .~7ew and Improved Commercial InstrumentsFor Electrical Testing . The following bibliography of some net and improvedcommercie! instruments for electrical testing is not a11-inclusiveNO COULD there are many others which have not come to the ,witer'sattention. It is included here primarily to give the reader abird's eyebvie,~r of the nature end extent of deveJo~ment.s in thefield. of commercial electrical teet equipment.Conductivity Cell - Positive Floss Type. IndustrialInstruments' Inc e ~ Elec. Equip., 6, 7, den. (1946)Portable Instrument Checks Electric Insulation Resistance.Associated Research. Ind. Equip. Mews, 14, 2QS ~ct-~194~)- 51 _
Port Able Lumen Checks E1 ectric Insu] ation Resistance .Id en] tndllstri e s ~ Into Equip O .~7et~s, 14 ~ 59 , Beat . ~ l~46Insulation Tester Designed to Test Insulatior~ frown ~ to10,000 megohms at 500 Violas. Radio City Products Co.,Into, Electronics, Ig., 230-2, Beat. (1946)Insulati on Tester _ Volta~e ~lariabJ e to ~ S kv. LymanE1ectronic Oorc.; Elec. E:qui~. 6, 33, A~ri7 (1946)YJond,.action O~ri ~ Cur-fent FIego~meker. ~leston Engg.~To~ces, l, l_2, Aor. (1946)3ri ~ge ~ n strume n~ f or Te ~ ti ng Re g i ~ ~ or ~, C ondens er s, and` nd.uctors. Freed Transformer Co. $ Ind. I:quin. News,~4, 71, May (1946)2e ] 261 Vibro_Test i s ~ Portable ana Entirel y SeltCorttsined Insulat. on Resistance Meter ~esting to~ ~ ~ 000 Meg~hms . E3adi ~ News, Radi Q - Elec tr oni c Dent ._, 20, ]~ly ~ 1946ACom~1 ete Llne of S~here Geps for the AccurateMeasurement of Righ Voltages Used in D.C. or A.C.Testing. Gene Elec. Co. G.E. Rev., 4~3' 74, Nov.(1945)n A.~. Onerated Power Sun~ly for Instruments. Gen.Re di ~ E=er ., 20 , 4_6 , Mar . ~ 1946 ~Me~F DUa] RegUTa~eJ POT~er SU~.Y. PG1~ad Ele-ctronicsCO. InStrUmentS, 19, 364, JUne (1946)Z-Meter for Electrica~ and E:lectroacoustic Mee~surernente.Packard, L.E. ~ Electronic Inds., 5, 42-5, Dec. (1946)Whe?~:stone Bridge e Winsio,? Co.; Elec. Eauip., 6,4, Ar)r. (1946):.~1heatetone 3ridge. Wilson Co.Feb. ~ 1946 ~Elec. WorId, 125, Il4,Mod el 406 Electronic Volt-Ohmmeter Feetures Ex~GremePan~e and a New Bridge Type circuit for Maximum Stability and Accuracy. Cli~ard Instrument Lab.; Instre.1 9, 22S, Arr e ( 1946 )__Mode~ 20~3 ie Desi~ned to Perform More Functions ThanMost Volt-Ohm-Mi~ 4.iamme~Gere. It measures wide rangesof capacity, reelstance, a_c and d-c current andvoltage. Inductarlce ~neasurements are a~ so nossib~ e eHiskok Elec. Instr. Co.; Radio, 30, 44, A~re (Ig46)- 52
No. 3030 d-c volt_emmeter is a ~ortab~ e instrument fromRich 40 interchangeable ranges can be obtained Keithen accuracy of 0.5~ of ful l-ece~1 e deflection. StandardScience Supply Co.; Inetrs., 19, 228, Air. (1946)Sensitive r.f. voltmeter presents the principal Leafeature of greater band width, the high frequency limitbeing extended to beyond 5 me. Ballantine Lebore~cories.Rear. Sci. Instr., 17, 161-2, Apr. (1946)VT Von tmeter With 7' Meter. Precision Apparatus Co.;E] ec. Equip. 6, 32, Feb. (1946)A Vow tmeter Rich Extends the Range of Measurement TenTines - From 50 to 500 me. Alfred W. Psarber La.bora_tories; Radio, 31, 24, ~Jan. (1947)Radio Frequency Voltmeter to Read Die J ectric HeatingPotential . R.C.A.; Mona. Equip. Nests, 14, 30, Dec.(1946)Near Voltohmyst can be employed for high impedancecircuit testing at frequencies un to 250 me. R.C.A.Electronic s, 19, 23S, Dec . ~ 1946 ~Peak_Reac~ing Voltmeter for the U.H.F. Ranges. Gen.Radio Enter., 21, l_S, Oct. (1946)bHigh Frequency Voltmeter. Hewlett_Packard CO.; Electronics,19, 208 Aug. ( 1946 )Ne;' 'Model 424 Volt-Ohm-Milliammeter'l incorporates a 5~1Syndical or ,~.Tith a sensitivity of 2500 ohms per volt and~ Increment of 400 microamperes. Radio City ProcluctsCo.; Instrs. 19, 286-7, May (1946)Electronic Voltmeter Peads 0.001 to 1 Volt in 3 DecadeRanges. Ballantine Laboratories; Ind. Equine Nears,14, 32, June ~ 1946 ~New 'Mooched 29' high-frequency probe is said to representthe firing practical answer to the Problem of measuringrestages in very high-freo,uency circuits. Alfred W.Barber Laboratorl es. Instrs., 19, 277, May (1946)Type 650 Impedance Bridge. Den. Radi 0 Expel., 20,1, Acre (1946)T?andy Pair of Bridges. Lameon, R.,J., Gen. Radio ExPer.,20, 3-7, Feb. ~ 1946 ~Frequer~cy-Insensi4sive Rest store. Corning GIas~ Works .Electronic Inde., 5, 6S, Mar. (1946)- 53 -
Thermocouples for Making Measurements at Q.H.F. FieldElectrical Instrument Co. ; Electronic Inde ., 5, ll2,]~n~ ~946~Thermocour'1e Ammeters for Very High Frequency. WestonEngg. Notea, I, 7_S, Apr. (1946)UHF Signal Generator for General Laboratory Use. Fre-quency Range of 500 to ~ ,350 me. Hew~et+_P7.ckard Co.,Elec ~ World ~ 127 ~ 94, Feb O ~ 1947 ~Aide Range URF Test Oscillator, Gen. Radio Exacter., 2l,4~ ~ ~ ~Tov ~ ~ ~ 946 ~New 'Ty~e SD-835- Fit Reflex Klystron Designed forOperate on at Slave ~ erigth$ Between 6 and 7 cm. Re-seareh Laboratories of Sylvania Electric Products,Ino.; Tsars., :l9' 299 May (1946)Inner precision_Buil~G, High_Leve', R.F', Signal GeneratorCovering the Range from 400 kco t;0 60 me. in SixSheds. Barker and ,'[illiameon. Radio Nears, Radio_Electronic Dect., 6' 26' Feb. (1946)Frequency Meter Covers Range from l.5 to 100 me.;Browning Laboratories, Inc.; Alec. Equip., 6, 25,June ~ 1946 ~7~IF Wa~remeter Designed f or Rapid Measurements of Fre-quency in the Range 240 to 1200 me. Gen. Radio Co*,Elec. Equip., 6, 23, Feb. (1946~; E-lec+,ronics, 19,302 ~ Jan. (1946 ~Wave Guides Designed for EN ectrical Equipment. Amer.Bums Co.; E1ec. ,nrOrId, 1~5, 146, ITS, May (1946)Flexible ~laveguide Trademarked 'lfavef~ex.' Titef~ex,Inc ~ , Radio News, Radio_E1 ectronic Dent. , 6, 28-9,Air. t 1946 )SIot4ced Measuring Line for Measurir~ Impedances atV.~.F.; Ferris Instr. Co.; Elec. Equip., 6, 24, May~ ~ 946 ~Micro~.~.ve Tnstruments. Sherry Gyroscope Co.; Radio,30 44 ~ Febe ( 1 946 ~Lightweight micro are event inch udes an oscillatorand band intensity meter for study of practical lyEl]_7 the Rowena or e] ectro~t~.gnetic redi ations at ultra-high frequency Get. Heart , 49, 50, July (1946)Tern Electra c Silicon arty Germanium Crys-~1 Pectin fierce R., 30, 34., Mar. (1946)
Crystal Converter. Type lN21B silicon crystal 8 can beused as first detectors in high frequency sur~er-heterodyne receivers in the region of 3,000 me.SyIve~ia Elec. Products, Inc.; Electronics, 19,22S, Oct. (1946)Field Indicator. Nell R.F. probe for testing highfrequency po''rer circuits. Radio Frequency Labora_tories, Inc.; E]ect;ronics, 19, 226, Oct. (1946)Near Vacuum Type Bolometer for Une in URF Bridge CircuitMeasuring Equipment. Lynn Engineering Co.; ElectronicInd., 5, ll2, Mar. 1946.Computation AidsAm. A fen' pacers have appeared ashore aim is to simplify andexpedite the ce. Iculation of Sari ous quantities. GlinsM327 showshow high-freauency impedance matching network problems are sirn~li_fled by ~ method based on circle diagrams. The graphical ca.]cu-lation of double stubs is considered by paine528 and a simplifiedmethod of ~l otting a~Gtenuati on curves is described by Biberman329.6~ decibel conversion chart is given by Mie~ke330 and an impedancenomogram, by Wheeler331. Baine352 presents a universal chartf or unbalanc e bri dge5 _ $ ~-
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