《磁性材料的特性》PPT课件

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1、CHAPTER16MAGNETICPROPERTIESOFMATERIALS16.1EffectonMagneticFieldbyMaterials16.2Magnetization16.3VectorHandItsCircuitalTheorem16.4MagneticShielding16.1EffectonMagneticFieldbyMaterialsTheinteractionbetweenmagneticfieldsandmaterialscanbeobservedexperimentally.Themostsimplemethodistousealong

2、straightwithvacuumorairinsidefirst(Fig.16.1(a))andmeasurethemagneticfieldinitwhencurrentIisflowinginthecoils.Nextfillthesolenoidwithsomematerialandthenmeasureagainthemagneticfieldinitwhenthesamecurrentisledinthecoils(Fig.16.1(a)).LetB0andBbethemagneticfieldmeasuredinthetwocasesrespectiv

3、ely.Experimentalresultsshowthatthetwodifferfromeachotherandcanrelatedasiscalledtherelativepermeabilityofthematterdifferentfordifferentmaterial.Somematerialshaveconstantofvaluesslightlysmallerthanunit.Suchmaterialiscalleddiamagneticmaterial.Somematerialshaveconstantofvalueslightlylargert

4、hanunit.Suchmaterialiscalledparamagneticmaterial.Theeffectsofthesetwokindsofmaterialsonthemagneticfieldareverysmallandthenalwaysneglectedinordinarytechnique.TheofthethirdkindofmagneticmaterialisalwaysmuchlargerthanoneandalsousuallychangeswiththemagnitudeofB0.Suchmagneticmediaiscalledfer

5、romagneticmaterialwhichinteractwithmagneticfieldstronglyandhencearealwaysusedinelectricalandelectronicengineering.16.2MagnetizationInanatom,theelectronsorbitaroundthenucleusandhavealsospin.Thenucleusalsohasspin.Thesemotionallfromequivalentcircularelectriccurrents.Asawholethesemotionsofc

6、hargesinamoleculemaybeconsideredasconstituteasinglemicroscopiccircularcurrentcalledmolecularcurrentiwithmolecularmagneticmomentm.Example16.1Alongstraightsolenoidofnturnperunitlengthisfilledinsidewithuniformmaterialofrelativepermeability.Findthesurfaceboundcurrentdensityonthesurfaceofthe

7、materialinthesolenoid.Insidethesolenoidthemagnitudeofmagneticfieldproducedbythefreecurrentalone(asthereisvacuuminthesolenoid)is,whennIisthefreecurrentperunitlengthofthesolenoidandthedirectionisparalleltotheaxisofthesolenoid.Onthesurfaceofthematerialthereisproducedboundcurrentsd