ASTM_A_893_-_A_893M_-_03_2015.pdf

Designation:A893/A893M03(Reapproved 2015)Standard Test Method forComplex Dielectric Constant of Nonmetallic MagneticMaterials at Microwave Frequencies1This standard is issued under the fixed designation A893/A893M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of the com-plex dielectric constant of isotropic ferrites for extremelyhigh-frequency applications.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-conformancewith the standard.Within this standard,SI units are shown inbrackets.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Summary of Test Method2.1 In an isotropic dielectric medium with a steady electricfield,E,the electric displacement,D,is given by the equation:D 5 k0E(1)where:0=permittivity of free space andk=dielectric constant.If the medium is subjected to analternating electric field,the electric displacement is notnecessarily in phase with the field.This fact may beexpressed mathematically by taking k as a complexquantity.If we write k=k jk,the imaginary part,k,determines the dissipation in the medium.2.2 This test method uses a cavity perturbation technique asa means of separating electric from magnetic effects.Quanti-ties that must be measured are the resonance frequency,f,ofthe cavity with and without the sample,the loaded Q of thecavity with and without the specimen,and the cavity andspecimen dimensions.2.3 The specimen is in the form of a rod and is placedparallel to the microwave electric field in a region of substan-tially uniform electric and zero microwave magnetic fields.The perturbation theory requires that the diameter of thesample rod be small compared to one quarter of the wavelengthof the microwave radiation in the specimen.Estimation of thiswavelength requires knowledge of the permittivity,=k0,andpermeability,of the specimen under the conditions ofmeasurement.The wavelength,in the specimen is given bythe equation:5 1/f!1/2(2)For many ferrites,may be taken equal to 0,the perme-ability of empty space,without serious error.The permittivity,is determined by measurement as described below;afterobtaining a value of,it is necessary to ascertain with the aidof Eq 1 that the sample diameter is sufficiently small.2.4 This test method is not suitable for materials with losstangents 0.1,with the loss tangent defined as tan =k k.2.5 The results of the perturbation theory calculation may beexpressed in the form:f/f 52k 2 1!?MivsEoEidv#/2?MivcEo!2dv(3)where:f=f +jf 2Q;Q=loaded Q of the cavity;vs=specimenvolumecontainedwithinthecavity,in.3mm3;vc=cavity volume,in.3mm3;andE=microwave electric field strength.The superscript o refers to fields in the empty cavity and thesuperscript i refers to fields inside the specimen.2.6 A specific cavity suitable for this test method is a TE10nrectangular cavity,2where n is odd.With the rod running1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved April 1,2015.Published April 2015.Originallyapproved in 1963.Last previous edition approved in 2008 as A893/A893M03(2008).DOI:10.1520/A0893_A0893M-03R15.2See,for example,Montgomery,C.G.,Ed.,Technique of MicrowaveMeasurements,McGraw-Hill Book Co.,Inc.,New York,1947,pp.294295;Bronwell and Beam,Theory and Application of Microwaves,McGraw-Hill BookCo.,Inc.,1947,pp.368337.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 completely across the cavity at the center,Eq 2 for f/f can bereduced to the following:f/f 5 22k 21!vs/vc!;1/Q!5 4k vs/vc!(4)f and(1/Q)are,respectively,the difference in the cavityresonant frequency with and without the specimen and thedifference in the reciprocal Q of the cavity with and without thespecimen,and f is the resonant frequency of the empty cavity.2.7 In many cases it is convenient to describe the dissipativeproperties of the medium by alternative notation.An effectiveresistivity at the frequency f =2 may be defined by theequation:5 1/k o(5)3.Significance and Use3.1 This test method can be used to evaluate batch type orcontinuous production of material for use in microwaveapplications.It may be used to determine the loss factors ofmicrowave ferrites or