磁学量常用单位换算

磁学量常用单位换算磁学■名称SI符号和单位CGS符号和单位单位换算磁通量韦伯（Wb）麦克斯韦（Mx）1Mx=10-8Wb磁感应强度B特斯拉（T）B高斯（Gs）1Gs=10-4T磁场强度H安/米(A/m)H奥斯特（Oe）1Oe=103/4兀A/m磁化强度M安/米(A/m)M高斯（Gs）1Gs=103A/m磁极化强度J特斯拉（T）4兀M高斯（Gs）1Gs=10-4T磁能积BH焦/米3（J/m3）BH高•奥（GOe）1MGOe=102/4兀kJ/m3真空磁导率4兀・10-7H/m-1-亠 —L -L _1_注：在園际标淮单位制（Si）中B= +J：.J= 在高斯单位制CCGS5中5=磁概念永磁材料：永磁材料被外加磁场磁化后磁性不消失，可对外部空间提供稳定磁场。钕铁硼永磁体常用的衡量指标有以下四种：剩磁（Br）单位为特斯拉（T）和高斯（Gs）lGs=0.0001T将一个磁体在闭路环境下被外磁场充磁到技术饱和后撤消外磁场，此时磁体表现的磁感应强度我们称之为剩磁。它表示磁体所能提供的最大的磁通值。从退磁曲线上可见，它对应于气隙为零时的情况，故在实际磁路中磁体的磁感应强度都小于剩磁。钕铁硼是现今发现的Br最高的实用永磁材料。磁感矫顽力（Hcb）单位是安/米（A/m）和奥斯特（Oe）或1Oe~79.6A/m处于技术饱和磁化后的磁体在被反向充磁时，使磁感应强度降为零所需反向磁场强度的值称之为磁感矫顽力（Hcb）。但此时磁体的磁化强度并不为零，只是所加的反向磁场与磁体的磁化强度作用相互抵消。（对外磁感应强度表现为零）此时若撤消外磁场，磁体仍具有一定的磁性能。钕铁硼的矫顽力一般是110000e以上。内禀矫顽力（Hcj）单位是安/米（A/m）和奥斯特（Oe）1Oe~79.6A/m使磁体的磁化强度降为零所需施加的反向磁场强度，我们称之为内禀矫顽力。内禀矫顽力是衡量磁体抗退磁能力的一个物理量，如果外加的磁场等于磁体的内禀矫顽力，磁体的磁性将会基本消除。钕铁硼的Hcj会随着温度的升高而降低所以需要工作在高温环境下时应该选择高Hcj的牌号。磁能积（BH）单位为焦/米3（J/m3）或高•奥（GOe）1MGOe~7.96kJ/m3退磁曲线上任何一点的B和H的乘积既BH我们称为磁能积，而BxH的最大值称之为最大磁能积（BH）max。磁能积是恒量磁体所储存能量大小的重要参数之一，（BH）max越大说明磁体蕴含的磁能量越大。设计磁路时要尽可能使磁体的工作点处在最大磁能积所对应的B和H附近。各向同性磁体：任何方向磁性能都相同的磁体。各向异性磁体：不同方向上磁性能会有不同；且存在一个方向，在该方向取向时所得磁性能最高的磁体。烧结钕铁硼永磁体是各向异性磁体。取向方向：各向异性的磁体能获得最佳磁性能的方向称为磁体的取向方向。也称作“取向轴”，“易磁化轴”。磁场强度：指空间某处磁场的大小，用H表示，它的单位是安/米（A/m）。磁化强度：指材料内部单位体积的磁矩矢量和，用M表示，单位是安/米（A/m）。磁感应强度：磁感应强度B的定义是：B=Uo（H+M），其中H和M分别是磁化强度和磁场强度，而气是真空导磁率。磁感应强度又称为磁通密度，即单位面积内的磁通量。单位是特斯拉（T）。磁通：给定面积内的总磁感应强度。当磁感应强度B均匀分布于磁体表面A时，磁通①的一般算式为①=BxA磁通的SI单位是麦克斯韦。相对磁导率：媒介磁导率相对于真空磁导率的比值，即賞“//。在CGS单位制中，妒1。另外，空气的相对磁导率在实际使用中往往值取为1，另外铜、铝和不锈钢材料的相对磁导率也近似为1。磁导：磁通①与磁动势F的比值，类似于电路中的电导。是反映材料导磁能力的一个物理量。磁导系数Pc:又为退磁系数，在退磁曲线上，磁感应强度Bd与磁场强度Hd的比率，即Pc=Bd/Hd，磁导系数可用来估计各种条件下的磁通值。对于孤立磁体Pc只与磁体的尺寸有关，退磁曲线和Pc线的交点就是磁体的工作点，Pc越大磁体工作点越高，越不容易被退磁。一般情况下对于一个孤立磁体取向长度相对越大Pc越大。因此Pc是永磁磁路设计中的一个重要的物理量。GlossaryofMagnetTerminologyAirGap一The""external""distancefromonepoleofthemagnettotheotherthoughanonmagneticmaterial（usuallyair）.Anisotropic一Ananisotropicmaterialhasdifferentpropertiesindifferentdirections.Forexample,woodwhichhasagrainisstrongerinsomeonedirectionthananother.Likewood,neodymiummagnetsarealsoanisotropic.Evenbeforeitismagnetized,aneodymiummagnethasa""preferred"magnetizationdirection.Seeourarticle AllAboutMagnetizationDirectionformoreinfo.Neodymiummagnetsaremadewithapreferredmagnetizationdirectionwhichcannotbechanged.Thesematerialsareeithermanufacturedintheinfluenceofstrongmagneticfieldsorpressedaspecificway,andcanonlybemagnetizedthroughthepreferredaxis.SinteredNeodymium(IronBoron)andSamariumCobaltmagnetsareanisotropic.B/HCurve-Theresultofplottingthevalueofthemagneticfield(H)thatisappliedagainsttheresultantfluxdensity(B)achieved.Thiscurvedescribesthequalitiesofanymagneticmaterial.Agraphicexplanationcanbefoundhere.BHmax(MaximumEnergyProduct)- TheMaximumEnergyProductatthepointontheB/HCurvethathasthemoststrength,expressedinMGOe(MegaGaussOersteds).Whendescribingthegradeofaneodymiummagnet,thisnumberiscommonlyreferredtoasthe"N"number,asinGradeN52magnets.Inthepictureatright,itistheareainsidethebox,underthecurve.Brmax(ResidualInduction)- Alsocalled"ResidualFluxDensity".Themagneticinductionremaininginasaturatedmagneticmaterialafterthemagnetizingfieldhasbeenremoved.ThisisthepointatwhichthehysteresisloopcrossestheBaxisatzeromagnetizingforce,andrepresentsthemaximumfluxoutputfromthegivenmagnetmaterial.Bydefinition,thispointoccursatzeroairgap,andthereforecannotbeseeninpracticaluseofmagnetmaterials.C・G・S・-Abbreviationforthe"Centimeter,Grams,Second"systemofmeasurement.previouslybeenbroughttosaturation.CurieTemperature(Tc)-Thetemperatureatwhichamagnetlosesallofitsmagneticproperties.DemagnetizationCurve-Thesecondquadrantofthehysteresisloop,generallydescribingthebehaviorofmagneticcharacteristicsinactualuse.AlsoknownastheB-HCurve.FindthesecurvesforsomeofourmostpopularmagnetgradesonourBHCurvespage.DemagnetizationForce-Amagnetizingforce,typicallyinthedirectionoppositetotheforceusedtomagnetizeitinthefirstplace.Shock,vibrationandtemperaturecanalsobedemagnetizingforces.Dimensions-Thephysicalsizeofamagnetincludinganyplatingorcoating.DimensionalTolerance-Anallowanee,givenasapermissiblerange,inthenominaldimensionsofafinishedmagnet.Thepurposeofatoleranceistospecifytheallowedleewayforvariationsinmanufacturing.(Magnetic)DipoleMoment(m)-aquantitythatdescribesthetorqueagivenmagnetwillexperienceinanexternalmagneticfield.Somefolks(likephysicists)useamagneticdipolemodeltosimulateormathematicallymodelamagnetorgroupofmagnets.Mathematically,it'seasierthanconsideringthecomplexitiesofweirdmagnetshapes.It'snottheoreticallyperfect.Usingitwon'talwaysmatchmeasuredfieldstrengthsnearaneodymiummagnet.Itworksgreatforasphere,butisn'tcorrectnearothershapeslikediscsorblocks.It'sagreatapproximationwhenyou'remeasuringfarawayfromamagnet,butnotsogoodcloseup,especiallyneartheedgesofamagnet.Calculatethedipolemomentusingtheformulam=dipolemomentinAm2=BrxV/Mo,where:BrisBrmax,theResidualFluxDensity,expressedinTesla.Visthevolumeofthemagnet,expressedincubicmeters.poisthepermeabilityofavacuum,or4nx10-7N/A2.Electromagnet-Amagnetconsistingofasolenoidwithanironcore,whichhasamagneticfieldonlyduringthetimeofcurrentflowthroughthesolenoid.LearnmoreinourElectromagnetsarticle.FerromagneticMaterial-Amaterialthateitherisasourceofmagneticfluxoraconductorofmagneticflux.Mostferromagneticmaterialshavesomecomponentofiron,nickel,orcobalt.Gauss-Unitofmagneticinduction,B.LinesofmagneticfluxpersquarecentimeterintheC.G.S.systemofmeasurement.EquivalenttolinespersquareinchintheEnglishsystem,andweberspersquaremeterorteslaintheS.I.system.10,000gaussequals1tesla.Gaussmeter-Aninstrumentusedtomeasuretheinstantaneousvalueofmagneticinduction,B,usuallymeasuredinGauss(C.G.S.).AlsocalledaDCmagnetometer.Gilbert-Theunitofmagnetomotiveforce,F,intheC.G.S.system.HysteresisLoop- Aplotofmagnetizingforceversusresultantmagnetization(alsocalledaB/Hcurve)ofthematerialasitissuccessivelymagnetizedtosaturation,demagnetized,magnetizedintheoppositedirectionandfinallyremagnetized.Withcontinuedrecycles,thisplotwillbeaclosedloopwhichcompletelydescribesthecharacteristicsofthemagneticmaterial.Thesizeandshapeofthis"loop"isimportantforbothhardandsoftmaterials.Withsoftmaterials,whicharegenerallyusedinalternatingcircuits,theareainsidethis"loop"shouldbeasthinaspossible(itisameasureofenergyloss).Butwithhardmaterialsthe"fatter"theloop,thestrongerthemagnetwillbe.Thefirstquadrantoftheloop(thatis+Xand+Y)iscalledthemagnetizationcurve.Itisofinterestbecauseitshowshowmuchmagnetizingforcemustbeappliedtosaturateamagnet.Thesecondquadrant(-Xand+Y)iscalledtheDemagnetizationCurve.Agraphicexplanationcanbefoundhere.Induction,(B)-Themagneticfluxperunitareaofasectionnormaltothedirectionofflux.MeasuredinGauss,intheC.G.S.systemofunits.IntrinsicCoerciveForce(Hc)-Indicatesamaterials'resistaneetodemagnetization.Itisequaltothedemagnetizingforcewhichreducestheintrinsicinduction,Bi,inthematerialtozeroaftermagnetizingtosaturation;measuredinoersteds.IrreversibleLosses-Partialdemagnetizationofthemagnet,causedbyexposuretohighorlowtemperatures,externalfields,shock,vibration,orotherfactors.Theselossesareonlyrecoverablebyremagnetization.Magnetscanbestabilizedagainstirreversiblelossesbypartialdemagnetizationinducedbytemperaturecyclesorbyexternalmagneticfields.

IsotropicMaterial-Amaterialthatcanbemagnetizedalonganyaxisordirection(amagneticallyunorientedmaterial).TheoppositeofAnisotropicMagnet.Keeper-Asoftironpiecetemporarilyaddedbetweenthepolesofamagneticcircuittoprotectitfromdemagnetizinginfluences.Alsocalledashunt.KeepersaregenerallynotneededforNeodymiumandothermodernmagnets.TheyaremorecommonlyusedwitholderAinicoHorseshoeMagnets.Kilogauss-OneKilogauss=1,000Gauss=Maxwellspersquarecentimeter.Magnet-Amagnetisanobjectmadeofcertainmaterialswhichcreateamagneticfield.Everymagnethasatleastonenorthpoleandonesouthpole.Byconvention,wesaythatthemagneticfieldlinesleavetheNorthendofamagnetandentertheSouthendofamagnet.Thisisanexampleofamagneticdipole("di"meanstwo,thustwopoles).Ifyoutakeabarmagnetandbreakitintotwopieces,eachpiecewillagainhaveaNorthpoleandaSouthpole.Ifyoutakeoneofthosepiecesandbreakitintotwo,eachofthesmallerpieceswillhaveaNorthpoleandaSouthpole.Nomatterhowsmallthepiecesofthemagnetbecome,eachpiecewillhaveaNorthpoleandaSouthpole.IthasnotbeenshowntobepossibletoendupwithasingleNorthpoleorasingleSouthpolewhichisamonopole("mono"meansoneorsingle,thusonepole).SurfaceFieldBy』centerMagneticCircuit-SurfaceFieldBy』centerMagneticField(B)-Whenspecifiedonoursite,thesurfacefieldormagneticfieldreferstothestrengthinGauss.Foraxiallymagnetizeddiscsandcylinders,itisspecifiedonthesurfaceofthemagnet,alongthecenteraxisofmagnetization.Forblocks,itisspecifiedonthesurfaceofthemagnet,alsoalongthecenteraxisofmagnetization.Forrings,youmayseetwovalues.Bycenterspecifiestheverticalcomponentofthemagneticfieldintheairatthecenterofthering.Byringspecifiestheverticalcomponentofthemagneticfieldonthesurfaceofthemagnet,mid-waybetweentheinnerandouterdiameters.Somedepictionsofmagnetfieldscanbefoundhere.MagneticFieldStrength(H)-Magnetizingordemagnetizingforce,isthemeasureofthevectormagneticquantitythatdeterminestheabilityofanelectriccurrent,oramagneticbody,toinduceamagneticfieldatagivenpoint;measuredinOersteds.MagneticFlux-Isacontrivedbutmeasurableconceptthathasevolvedinanattempttodescribethe“flow"ofamagneticfield.Whenthemagneticinduction,B,isuniformlydistributedandisnormaltothearea,A,theflux,0=BA.MagneticFluxDensity-Linesoffluxperunitarea,usuallymeasuredinGauss(C.G.S.).OnelineoffluxpersquarecentimeterisoneMaxwell.MagneticInduction(B)-Themagneticfieldinducedbyafieldstrength,H,atagivenpoint.Itisthevectorsum,ateachpointwithinthesubstanee,ofthemagneticfieldstrengthandtheresultantintrinsicinduction.Magneticinductionisthefluxperunitareanormaltothedirectionofthemagneticpath.MagneticLineofForce-Animaginarylineinamagneticfield,which,ateverypoint,hasthedirectionofthemagneticfluxatthatpoint.MagneticPole-Anareawherethelinesoffluxareconcentrated.MagnetomotiveForce(Formmf)-Themagneticpotentialdifferencebetweenanytwopoints.Analogoustovoltageinelectricalcircuits.Thatwhichtendstoproduceamagneticfield.Commonlyproducedbyacurrentflowingthroughacoilofwire.MeasuredinGilberts(C.G.S.)orAmpereTurns(S.I.).MaterialGrade-Neodymium(NdFeB)magnetsaregradedbythemagneticmaterialfromwhichtheyaremanufactured.Generallyspeaking,thehigherthegradeofmaterial,thestrongerthemagnet.WefindthatthePullForceofamagnetrelatesdirectlytothe"N"number.NeodymiummagnetscurrentlyrangeingradefromN35toN52.ThetheoreticallimitforNeodymiummagnetsisgradeN64,thoughitisn'tcurrentlyfeasibletomanufacturemagnetsthisstrong.ThegradeofmostofourstockmagnetsisN42becausewefeelthatN42providestheoptimalbalaneebetweenstrengthandcost.WealsostockawiderangeofsizesingradeN52forcustomerswhoneedthestrongestpermanentmagnetsavailable.MaximumEnergyProduct(BHmax)-Themagneticfieldstrengthatthepointofmaximumenergyproductofamagneticmaterial.ThefieldstrengthoffullysaturatedmagneticmaterialmeasuredinMegaGaussOersteds,MGOe.MaximumOperatingTemperature(Tmax)-Alsoknownasmaximumservicetemperature,isthetemperatureatwhichthemagnetmaybeexposedtoeontinuouslywithnosignifieantlong-rangeinstabilityorstrueturalchanges.Maxwell-UnitofmagneticfluxintheC.G.S.electromagneticsystem.Onemaxwellisonelineofmagneticflux.MagnetizationCurve-Thefirstquadrantportionofthehysteresisloop(B/H)Curveforamagneticmaterial.MagnetizingForce(H)-Themagnetomotiveforceperunitofmagnetlength,measuredinOersteds(C.G.S.)orampere-turnspermeter(S.I).Maxwell-TheC.G.S.unitfortotalmagneticflux,measuredinfluxlinespersquarecentimeter.MGOe-Mega(million)GaussOersteds.Unitofmeasuretypicallyusedinstatingthemaximumenergyproductforagivenmaterial.SeeMaximumEnergyProduct.NorthPole-Thenorthpoleofamagnetistheoneattractedtothemagneticnorthpoleoftheearth.Thisnorth-seekingpoleisidentifiedbytheletterN.Byacceptedconvention,thelinesoffluxtravelfromthenorthpoletothesouthpole.Oersted(Oe)-TheC.G.S.unitformagnetizingforce.TheEnglishsystemequivalentisAmpereTurnsperInch(1Oerstedequals79.58A/m).TheS.I.unitisAmpereTurnsperMeter.Orientation-Usedtodescribethedirectionofmagnetizationofamaterial.OrientationDirection-Thedirectioninwhichananisotropicmagnetshouldbemagnetizedinordertoachieveoptimummagneticproperties.ParamagneticMaterials-Materialsthatarenotattractedtomagneticfields(wood,plastic,aluminum,etc.).Amaterialhavingapermeabilityslightlygreaterthan1.PermanentMagnet-Amagnetthatretainsitsmagnetismafteritisremovedfromamagneticfield.Apermanentmagnetis"alwayson".Neodymiummagnetsarepermanentmagnets.Permeance(P)-Ameasureofrelativeeasewithwhichfluxpassesthroughagivenmaterialorspace.Itiscalculatedbydividingmagneticfluxbymagnetomotiveforce.Permeaneeisthereciprocalofreluctanee.PermeanceCoefficient(Pc)-Alsocalledtheload-line,B/Hor"operatingslope"ofamagnet,thisisthelineontheDemagnetizationCurvewhereagivenmagnetoperates.Thevaluedependsonboththeshapeofthemagnet,andit'ssurroundingenvironment(somewouldsay,howit'susedinacircuit).Inpracticalterms,it'sanumberthatdefinehowharditisforthefieldlinestogofromthenorthpoletothesouthpoleofamagnet.AtallcylindricalmagnetwillhaveahighPc,whileashort,thindiscwillhavealowPc.OuronlinePullForceCalculatorcancalculatePcforcommonshapes.Itassumesasinglemagnetinfreespace.Othernearbymagnetsorferromagneticmaterialscanchangematters.Permeability(p)-Theratioofthemagneticinductionofamaterialtothemagnetizingforceproducingit(B/H).Themagneticpermeabilityofavacuum(po)is4nx10-7N/Amp2.Pole-Anareawherethelinesofmagneticfluxareconcentrated.Plating/Coating-Mostneodymiummagnetsareplatedorcoatedinordertoprotectthemagnetmaterialfromcorrosion.Neodymiummagnetsaremostlycomposedofneodymium,iron,andboron.Theironinthemagnetwillrustifitisnotsealedfromtheenvironmentbysomesortofplatingorcoating.Mostoftheneodymiummagnetsthatwestockaretripleplatedinnickel-copper-nickel,butsomeareplatedingold,silver,orblacknickel,whileothersarecoatedinepoxy,plasticorrubber.Polarity-Thecharacteristicofaparticularpoleataparticularlocationofapermanentmagnet.DifferentiatestheNorthfromtheSouthPole.PullForce-Theforcerequiredtopullamagnetfreefromaflatsteelplateusingforceperpendiculartothesurface.Thelimitoftheholdingpowerofamagnet.Thepullforcelistedisactualdataacquiredbytestingusingourstate-of-the-artforceteststand.Acomprehensivetableofthepullforceforallofourstockmagnetsisavailablehere:PullForceTable.Wetestfortwodifferentvaluesofpullforceusingtwodifferentsetups.Readmoreaboutthesetwopullforceshere.RareEarth-CommonlyusedtodescribehighenergymagnetmaterialsuchasNdFeB(Neodymium-Iron-Boron)andSmCo(Samarium-Cobalt).RelativePermeability-Theratioofpermeabilityofamediumtothatofavacuum.IntheC.G.S.system,thepermeabilityisequalto1inavacuumbydefinition.Thepermeabilityofairisalsoforallpracticalpurposesequalto1intheC.G.S.system.Reluctance(R)-Ameasureoftherelativeresistanceofamaterialtothepassageofflux.Itiscalculatedbydividingmagnetomotiveforcebymagneticflux.Reluctanceisthereciprocalofpermeance.Remanence,(Bd)-Themagneticinductionthatremainsinamagneticcircuitaftertheremovalofanappliedmagnetizingforce.ResidualFluxDensity(Brmax)-SeeBrmax.ResidualInduction(Brmax)-SeeBrmax.ReturnPath-Conductionelementsinamagneticcircuitwhichprovidealowreluctancepathforthemagneticflux.ReversibleTemperatureCoefficient