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OCR for page 57
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 ~
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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.
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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.
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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) -
OCR for page 61
sir
2(?.
<1 .
D. M. Ritson, ~. P. Thirsted and C. H. Collies
285-.2c7 baud. 4, ~ 947)
C,om~tes Rends 2~25 ~
A O JET o R:re.n 9 ~H . Report 1947, C one . on Elec . Tnsul. . 17 ~ ~ abstract of
parer Presented Sept. 269 ~.94~)
D. H. Whiffen and P. T. Thomrson5 Trans. Feraclay Soc. ALA, ll4-129
(:1946 su~>piemer~t!
CO N. I'Yorks9 Jour. AppO Phys. 189 6Q5-612. (dilly 1947)
l
l
Representative terms from entire chapter:
dielectric constant
