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5t7 MT`~C,~.4~. P..tT~.~OMF.MA In LTclJlr:~ AND cOI.7D.~ Sh.eperd Roberts General. Electric Research Laboratory Schenectad;~r ~ -1 ~ Y O Papers on +,he subject of m~crowa~re dielectric measurements and their interpret~ati.on ,.~hi.ch were pub2..ished or received in this country in 1947 are re- v3-e~ed belong It is ink,erest~ng to note the large number of foreign contributions Axe this field. Tire creed in The design of measuring instruments reveals definite advances in their precision and ~rersatiJit.~,r. The results of micro,.~ave dielectric measurements have substantially aided our understanding of dielectric phenomena' especially those involving polar molecules. on the practical side high-pc,wer magnetrons have been developed along with tec~nr~iques-for using microwaves in dielectr~ c hearings iJeas';~rin~ Equic~ren^_ard~Tec~hnioues The princir~alL types of rr~eas~.ring equipment inclu3.e re-erltrant cavity resonators' ~vaveguide-rnode ca-`Tit~T resonators - and coat a] lines or waveguides with standing~ve Indicators or other means for measuring reflection and absorption. A theorem: discussion or' t'ne rei:at,ive merits of the resonance methods of measure~nert versus standing leave ~r.ethods by Jackson concludecZ that, other things being eq~.al9 the resonance '`-r~etiods ale r,~os' convenient then dealing with 1QW-1OSS materials, While for lossy materials, or for those pith Values of dielec.tr.id constant, the sta~ding-~ave method has unquestionable advantages. The use of a aveguide-mode resc~n.at.or with three die3~.e¢ trio regions for ineas~lug dielectric constant and loss ~as;ana]:rzed in a theoretical Paperboy Knorre -. Prec- sion resow: cavities of the re-entrant t,~,~e, suitable for fneasure- ments in the fit eq'. ency :~anrre 1()0 to 1000 3.Ec. Here described o-`,r Forks 30 These included cne of fixed length arid one of variable length By application of the s;:sce?~ance ~rar;~.o~ method one coii].d cleter~r&~.ne dielectric constant and loss of solids quickly and accurately. -A fined resonant ca~.Titv o~l~milar design but for a frequency range 400 to GOC tic. bar descr bed by Reynolds . . . . . .. . . Resonant cy~.indr~,ca' cavities em~.oy~..ng the s~.~.et~ica]. transverse electric mode ~i7~.re~descri.be'd.'c~r'B].eaney9 Loubser and Penrose''~.' By filling these cavities with a 1'ot;,-~oss nonpolar li,qu~,.d and''~r~ovin~ the e~d'p].~:ger so as to Treasure the dis~ance'''~>et,;.eei;'' s'~.cce,ss~.ve pGintis of 'resonance'~'one could determine the dielectric cons't~:lt, wh~.~.e',t,he loss Was derived from the Q of 'the l-qu~'d-fil7ed resonator. An accuracy- of 00'03% wa.,~ opined by this method i,.n measuring the Hi-' electric constants o: six non-~clar Ji.qu'.ds at freque.nc~.es of 9.~.'+ and 2,2.2 Talcs' - t`4easuIements at d',.ffeYent temperatures Inane it possib].e to evaluate te;n.perat~:lre coefficients ~, A ~
58 A resonant cylindrical cavity containing a concentric cylindrical bottle and em~loy~.ng the syr~met,ric transverse magnetic mode ~-r~as used 'oy Dunsmuir and Po~les for measuring the dielectric properties of several nonpolar ~iq,'.ids in the frequency range 600-~3200 ~,Jc. The dielectric properties of fifteen low-loss solids were irivestige.ted at a frequency 25 ·~Mc. by Penrose O A flat circular disc of dielectric was inserted at one end of a cylindrical cavity resonator operating in the s~vmmetrj.cal transverse electric mode. Dielectric constant was determined from -the ~educt~.on in resonant length of the resonator, While loss was derived from,th,e red~..ction in its Q. A precision coax~.al-line,instrument with,a'.stan~ing-~ave detector was described by Jelatisl°. In this instrument the standing-wave pattern Was a measure of the terminating i.mpedance, which consisted of a'short section of line filled with the dielectric sample and closed at one end. The dielectric properties of the sample Were deduced from the impedance of this s=~,p~e-fi~led line. A single instru- ment was used at frequencies of 1, 3 and 9 .~4c. and, With different sample holders, it could be adapted either for liquids or'so1.ids at high or low ten~peratures. Precision construction facilitated accurate measurement of high-loss or low-loss materials with di.ssipat~on factors even as low as 10 4. An improved rectangular "w~aveguide instrument using standing ~ayes-for measurements in the vicinity of.lO Tic. leas described by Dakin and tories . A simplified method of calculating' dielectric constant and loss was presented. Values Were quoted for the dielectric Properties of some common pl~st~c-and ceramic materia~s,,at frequencies 3 C. and 10 Medico Inve,sti~ations of Polar Liquids ~ _ . .! ~ . ~ ., _ _ __ The most common polar liquid, namely ,.'ater9''has'receaved attention in several papers. Heavy Hater and ionic solutions have also been measured' as Bell as a variety of polar liquids In the undiluted state. Perhaps the greatest activity has been concerned With.. the measurement of dilute solutions G.{ polar compounds in non-polar solvents. Ryan2i has measured dielectric,constant and loss of ordinary Hater and of heavy water at a frequency 9.4 Arc. in a temperature range 15 to 65°Co ~'avegui.de standing-wave techniques were used. The difference in dielectric properties v'a.s correlated With the difference in moment of inertion of the two molecules. Co))ie9 Ritson and Hatsted3s2Q in too papers reported measurements of the dielectric constant and loss (or inc3.ex of refraction and absorption) of v.'ater9 heavy water and ionic solutions at frequencies 3, 10 and 24 Id. in a range of temperature extending above and below ambient. Wave guide and. resonator techniques were used With equivalent results. The experimental data are interpreted v~it,h modification of Debye's theory. liquids were measured in a coaxial line by Abadiel at freo~.lencies 1.76, 2.839 5 and 10 chic. Results Were quoted for Aver benzene, acetone' nitrobenzene and normal props alcohol.
59 PLeasurements of die'ec-tr:~c constant and loss in a frequency range up to 25 tic. ' reported by Jackson and Poshest, allowed a ctixect determination of the rel.axat~on tines of five polar compounds in dilute benzene solutions. In each case ~ sine rel.a~:ation tine was found in conformity With Debye7s tl~eor,.r. On the other hand measurements of a dilute solution of benzo,!:henone in liquid paraffin shorted a spectrum of relaxation times, however the dipole Monet was the same as that; found in the benzene solution. Measuremer~ts of d.ie2.ectri.c absorption at ~ frequency of about JO T~Ic. in dilute solutivrts of polar co.rn~?ounds in two-con~conex~t mixtures of non-polar solvers Here reported by Italy, I~all.iday5 Johnson and lF;alker7. The viscosity of the solution IS controlled by varying the proportions of the two solvents, one Being a very vi. scous liquid ~ Whi~fe:1 amuck Tho:;~pson 22 measured loss tangents of Pollens and solutions of tern polar compc,unBs in benzene at frequencies 9.2 arid 23.6 Alice From. these data relaxation times and dipole moments were calcu:~;ed. Similar results rere obtained for solutions of four polar compounds in cyc~o-7.lexane an] paraffin in varying con- centrations. The relaxatior~ time airs. ~riscosit~r of toluene were measured versus temperature and There found to be incompatible with Debye's s~mp].e equation. Data for viscosity and dielectric relaxation of a variety of compounds and solutions over a range of temperature Were analyzed by treating these phenomena as rate processes. Acti~r=tion energies were calc,.~1a+ed in each case and Were fourth to be roughly equals or perhaps somewhat liigher for viscous flow. Sma]] negative ent,ropy ckanges in the activation processes Were observers [evils stlowed that tile activation ellerg,, "nd entropy terms associated with dielectric :reiaxat~on and svelter vapor Fusion in solids are capable of ~nter- pretation in terms of the molecular processes involved. Positive entropy changes Were attributed to the occurrence of lattice disordering (ho].e formaticn) ~ negative changes to the requirement of ~ parti.cu]-ar v~bratiortal orientation by the molecule ;~ro'ved in either Recess. The Toss tangent of to~uene arid solutions of ten Collar corr pounds irt ~ b`?~zene here measured by Crip~,``el' and Suther3andi' at frequencies 902 and 24 ~c. C~-ic~llat~ed relaxation +,iIres arid dipole ~o~r~ents showed slight d:~screpancies in con- . prison With the results of TYF!h~..~fen and Thompson. Kapustinl1 used Drude's second method in measuring dielectric properties of liquid mixtures at a frequency 3 Chico Light binary, liquid svet~.s here investi- g<:ted and the resu] ts Were used to calculate dipo4.;= ~r.oments. Microwave DO e].ectric Floating Dielectric lieating techniques have been extended to the microwave range in order to take ;~6v'-~?~ge of the Large losses occu'~;ing in many substances at these fries. Interest ',n this field was stimulated bit two papers by Finn and Mar- C'~1 ~ which described c-~rre`nt te~hnlques for generating and using microwave energy at high power levels. I;`lethods of plain these techniques to industrial heating problems Mere postulated. Nielson ~ described a magnetron delivering five kilowatts continuous output at 1050 I.Ec. and discussed its application for dielectric heating. An equipment for thawing and heating precooked and frozen food emp].oying this magnetron was described by Morse and Revercomb . The unit made vegetables' - potato and meat too hot to eat in seventy seconds.
60 BIBI,IOGRAPH-I 1. P. Akadi.es Trans. FaredaT7 Soc,, 4?~9 143-~*cj (19i~6 supplement,) . . . . . . . 2. B ~ Blearley, .T 0 H o M. Lc,ubser and R ~ P . F enro~se o Proc O ~ h~rs . Soc ~ I;ond 0, r,9 3 85. 199 (11ar. 1947! . . . 3e Ce Ho Col'ie, D. IdO Ritson and JO B. Hast~ed? Tr£~ns. ~raday Soc., _2A, 129-136 (1946 surplelr.ent ) 40 F. J. Cri~well and G~ B. 3. M. Sutl~eriand Tr=ns. Fa:~day So,c. I`2A, 168-169 (1946 su~ 1 ementi T. ~ . Daki n and C ~ N. 7!orks ? Jour. Ap~. PI,ys.29 1S, 7S'i-796 ~Se~t. 1947) 5. 6. 7 R. Dun smuir and ~ . G. Powles' P' il. idag. .~9 '747-756 (Nov. 1946) P. ~. Fal' 9 To G. Hall.ida~r, W. A. Johnson and S. iTalker; TransO Faraday Soc., 42A9 136-143 (192;.6 supplement) 80 W. Jackson5 Trans. Farada,J Soc. 9 I,?A, 91 101 (' 946 s~lpplement) 9. ~. Jackson and ..J. G. Powles, TransO Faraday Soc.9 42A S 101-1 GS ~1946 sup7~.ement) 10. D. G. Jelatis, Ann. Report 19475 Conf. on Elec, Insul. 18-19. iabst;"act of paper r~resented Se~. 269 1947) A. P. ~apustin9 2~ho EkSp. Teox.. Fizo g 17 (no. 1) g 30-4~) (1947 11o 12. T0 P. Kinn and u. ~.rarcu~r~5 ProcO Nat. 33~ectror~ic,= 5onf. (Chicago) <5 470-487 (1946) . .. ].3. G. F. Knorre,Bull. Acad. Sci., ~.RiS.S., ser. phys., lQ' (no. 1) 117-123 (1946) 14. D. 1. 1.evi, TransO Faraday SocO, 42A, 152-155 (1946 sur,l31emerlt~ 1.50 d. Marcum and T. T-;. Kinn, Electronics 20, (no. 3) 82-85 (LvEar. 1947) . · . b o Po l~q. Dllorse and .~. . ~. Re rerco~b 9 L' ectroni.cs 20 (no . lO), 85-39 (Oct. :L°47) i7. R. B. Nelson' Jour. ApnO Ph-,rs. g ]89 356-361 (Apri~ 1947) ]_8. R. P. Penrose, Trans. ~araday Soc., 42A9 108-114 (1946 su~plemert) 19. S. I. Reynolds^ G. L0 Rev.9 50 (no. 9) 34~39 (S~0to 1947) -
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