ASTM_D_4935_-_10.pdf

Designation:D493510Standard Test Method forMeasuring the Electromagnetic Shielding Effectiveness ofPlanar Materials1This standard is issued under the fixed designation D4935;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method provides a procedure for measuring theelectromagnetic(EM)shielding effectiveness(SE)of a planarmaterial for a plane,far-field EM wave.From the measureddata,near-field SE values may be calculated for magnetic(H)sources for electrically thin specimens.2,3Electric(E)field SEvalues may also be calculated from this same far-field data,buttheir validity and applicability have not been established.1.2 The measurement method is valid over a frequencyrange of 30 MHz to 1.5 GHz.These limits are not exact,but arebased on decreasing displacement current as a result ofdecreased capacitive coupling at lower frequencies and onovermoding(excitation of modes other than the transverseelectromagnetic mode(TEM)at higher frequencies for thesize of specimen holder described in this test method.Anynumber of discrete frequencies may be selected within thisrange.For electrically thin,isotropic materials with frequencyindependent electrical properties of conductivity,permittivity,and permeability,measurements may be needed at only a fewfrequencies as the far-field SE values will be independent offrequency.If the material is not electrically thin or if any of theparameters vary with frequency,measurements should be madeat many frequencies within the band of interest.1.3 This test method is not applicable to cables or connec-tors.1.4 UnitsThe values stated in SI units are to be regardedas standard.No other units of measurement are included in thisstandard.1.5 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.Referenced Documents2.1 ASTM Standards:4D1711 Terminology Relating to Electrical Insulation3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1711.3.2 Definitions of Terms Specific to This Standard:3.2.1 dynamic range(DR),ndifference between the maxi-mum and minimum signals measurable by the system.3.2.1.1 DiscussionMeasurement of materials with goodSE require extra care to avoid contamination of extremely lowpower or voltage values by unwanted signals from leakagepaths.3.2.2 electrically thin,adjthickness of the specimen ismuch smaller(1100)than the electrical wavelength within thespecimen.3.2.3 far field,nthat region where vectors E and H areorthogonal to each other and both are normal to the direction ofpropagation of energy.3.2.4 near field,nthat region where E and H are notrelated by simple rules.3.2.4.1 DiscussionThe transition region between nearfield and far field is not abrupt but is located at the distanceclose to/2 from a dipole source,where is the free-spacewave length of the frequency of the source.This concept ofregions is further blurred by reradiating as a result of scatteringby reflecting materials or objects that may be distant from thesource.The interior of metallic structures often contains amixture of near-field regions.3.2.5 shielding effectiveness(SE),nratio of power re-ceived with and without a material present for the sameincident power.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved May 1,2010.Published June 2010.Originallyapproved in 1989.Last previous edition approved in 1999 as D 493599.DOI:10.1520/D493510.2Wilson,P.F.,and Ma,M.T.,“A Study of Techniques for Measuring theElectromagnetic Shielding Effectiveness of Materials,”NBS Technical Note 1095,May 1986.3Adams,J.W.,and Vanzura,E.J.,“Shielding Effectiveness Measurements ofPlastics,”NBSIR 85-3035,January 1986.4For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.2.5.1 DiscussionSE is usually expressed in decibels(dB)by the following equation:SE5 10logP1P2dB!(1)where:P1=received power with the material present,andP2=received power without the material present.If the receiver readout is in units of voltage,use thefollowing equation:SE5 20logV1V2dB!(2)where:V1and V2=respective voltage levels with and without amaterial present.According to these eq