module02_fundamental_behavior外文

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1、Module2:FundamentalBehaviorofElectricalSystems2.0IntroductionAllelectricalsystems,atthemostfundamentallevel,obeyMaxwell'sequationsandthepostulatesofelectromagnetics.Undercertaincircumstances,approximationscanbemadethatallowsimplermethodsofanalysis,suchas

2、circuittheory,tobeemployed.However,theproblemsassociatedwithEMCusuallyinvolvedeparturesfromtheseapproximations.Therefore,areviewoffundamentalconceptsisthelogicalstartingpointforaproperunderstandingofelectromagneticcompatibility.2.1Fundamentalquantitiesan

3、delectricaldimensionsspeedoflight,permittivityandpermeabilityinfreespaceThespeedoflightinfreespacehasbeenmeasuredthroughverypreciseexperiments,andextremelyaccuratevaluesareknown(299,792,458m/s).Formostpurposes,however,theapproximationc
3x108m/sissuffici

4、entlyaccurate.IntheInternationalSystemofunits(SIunits),theconstantknownasthepermeabilityoffreespaceisdefinedtobe47H/m.0×10Theconstantpermittivityoffreespaceisthenderivedthroughtherelationship1cµooandisusuallyexpressedinSIunitsas118.854×10129F/m.

5、×100236cµoBoththepermittivityandpermeabilityoffreespacehavebeenrepeatedlyverifiedthroughexperiment.wavelengthinlosslessmediaWavelengthisdefinedasthedistancebetweenadjacentequiphasepointsonawave.Foranelectromagneticwavepropagatinginalosslessmedium,t

6、hisisgivenby2-2vfwherefisfrequency.Infreespacev=c,andinasimplelosslessmediumotherthanfreespace,thevelocityofpropagationisv1µ,whereandµµµ.Hereareandµarer0r0rrknownastherelativepermittivityandrelativepermeabilityofthemedium,respectively.Thesewill

7、bediscussedingreaterdetaillaterinthischapter.Fornowitissufficienttonotethatasthevaluesofpermittivityandpermeabilityincrease,velocityofpropagationdecreases,andthereforewavelengthdecreases(thusthewavelengthataparticularfrequencyisshorterinamaterialthaninfr

8、eespace).Thefreespacewavelengthsassociatedwithwavesofvariousfrequenciesareshownbelow:frequencywavelength60Hz5000km(3107mi)3kHz100,000m30kHz10,000m300kHz1000m3MHz100m30MHz10m300MHz1m3GHz10cm30GHz1cm300GHz0.1cmrelationshipb