电磁兼容入门(英文版)3.ppt

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1、BackgroundKnowledgeforEMCBasicsofElectromagneticFieldNoiseSignalAnalysisEMIFilterDesignToolsforCircuitSimulationCircuitNetworkTheoryBasicsofElectromagneticField1.ElectricFieldofElectricDipoleAsshowninFig.1,thevectorofanelectricdipoleisgivenbythevoltageatafieldpointPisIfr>>l,thentheelectricfieldatth

2、efieldpointPisgivenbyElectricDipole2.MagneticFieldofMagneticDipoleThevectorofamagneticdipoleisdefinedasThevectormagneticpotentialatafieldpointPisgivenbyThemagneticfieldgeneratedbythemagneticdipoleatthefieldpointPisMagneticDipoleElectricDipoleFieldandMagneticDipoleFieldElectromagneticFieldofDipolesR

3、adiationThepropagationofelectromagneticfieldinspaceiscalledelectromagneticwave.Theelectricandmagneticfieldscanpropagateinspacefarawayfromthesource.Thephenomenaiscalledelectromagneticradiation.Thebehaviorofelectromagneticfielddependsonitsdistancefromthesource.Innear-fieldzone,thefieldisdominatedbyin

4、ductionfield.Theenergycanbetransferredbetweenelectricandmagneticfields,anditcanalsobetransferredbetweensourceandnear-fieldspace.Infar-fieldzone,thefieldisdominatedbyradiationfield.Theenergypropagatesinthespaceandcannotbetransferredbacktothesource.RadiationFieldofDipoles-ElectricDipoleForasmallcurre

5、ntsegment(dl<<λ)ThevectormagneticpotentialisgivenbyFromWherekisthepropagationconstantSmallcurrentsegmentRadiationFieldofDipoles-magneticDipoleAccordingtoreciprocity(互易性),canbetransformedasfollowsSmallcurrentloopInfar-fieldregion,kr>>1(orr>>λ/2π),ForelectricdipoleFormagneticdipoleTherefore,theradiat

6、ionfields(bothelectricdipoleandmagneticdipole)areinverselyproportionaltothefielddistanceInnear-fieldregion,predominantlyinductionfield,kr<<1(orr<<λ/2π)ForelectricdipoleFormagneticdipoleinnear-fieldregion,forelectricdipole,Efieldisdominant.Formagneticdipole,Hfieldisdominant.WaveImpedanceThewaveimped

7、anceisdefinedaswhereETandHTaretransverseelectricandmagneticfields,respectively.Infar-fieldregion,radiationfielddominatesInnear-fieldregion,inductionfielddominatesForelectricdipoleFormagneticdipoleUsuallyhig