磁學(xué)量常用單位換算

磁學(xué)量常用單位換算磁學(xué)■名稱SI符號(hào)和單位CGS符號(hào)和單位單位換算磁通量韋伯（Wb）麥克斯韋（Mx）1Mx=10-8Wb磁感應(yīng)強(qiáng)度B特斯拉（T）B高斯（Gs）1Gs=10-4T磁場(chǎng)強(qiáng)度H安/米(A/m)H奧斯特（Oe）1Oe=103/4兀A/m磁化強(qiáng)度M安/米(A/m)M高斯（Gs）1Gs=103A/m磁極化強(qiáng)度J特斯拉（T）4兀M高斯（Gs）1Gs=10-4T磁能積BH焦/米3（J/m3）BH高?奧（GOe）1MGOe=102/4兀kJ/m3真空磁導(dǎo)率4兀?10-7H/m-1-亠 —L -L _1_注：在園際標(biāo)淮單位制（Si）中B= +J：.J= 在高斯單位制CCGS5中5=磁概念永磁材料：永磁材料被外加磁場(chǎng)磁化后磁性不消失，可對(duì)外部空間提供穩(wěn)定磁場(chǎng)。釹鐵硼永磁體常用的衡量指標(biāo)有以下四種：剩磁（Br）單位為特斯拉（T）和高斯（Gs）lGs=0.0001T將一個(gè)磁體在閉路環(huán)境下被外磁場(chǎng)充磁到技術(shù)飽和后撤消外磁場(chǎng)，此時(shí)磁體表現(xiàn)的磁感應(yīng)強(qiáng)度我們稱之為剩磁。它表示磁體所能提供的最大的磁通值。從退磁曲線上可見(jiàn)，它對(duì)應(yīng)于氣隙為零時(shí)的情況，故在實(shí)際磁路中磁體的磁感應(yīng)強(qiáng)度都小于剩磁。釹鐵硼是現(xiàn)今發(fā)現(xiàn)的Br最高的實(shí)用永磁材料。磁感矯頑力（Hcb）單位是安/米（A/m）和奧斯特（Oe）或1Oe~79.6A/m處于技術(shù)飽和磁化后的磁體在被反向充磁時(shí)，使磁感應(yīng)強(qiáng)度降為零所需反向磁場(chǎng)強(qiáng)度的值稱之為磁感矯頑力（Hcb）。但此時(shí)磁體的磁化強(qiáng)度并不為零，只是所加的反向磁場(chǎng)與磁體的磁化強(qiáng)度作用相互抵消。（對(duì)外磁感應(yīng)強(qiáng)度表現(xiàn)為零）此時(shí)若撤消外磁場(chǎng)，磁體仍具有一定的磁性能。釹鐵硼的矯頑力一般是110000e以上。內(nèi)稟矯頑力（Hcj）單位是安/米（A/m）和奧斯特（Oe）1Oe~79.6A/m使磁體的磁化強(qiáng)度降為零所需施加的反向磁場(chǎng)強(qiáng)度，我們稱之為內(nèi)稟矯頑力。內(nèi)稟矯頑力是衡量磁體抗退磁能力的一個(gè)物理量，如果外加的磁場(chǎng)等于磁體的內(nèi)稟矯頑力，磁體的磁性將會(huì)基本消除。釹鐵硼的Hcj會(huì)隨著溫度的升高而降低所以需要工作在高溫環(huán)境下時(shí)應(yīng)該選擇高Hcj的牌號(hào)。磁能積（BH）單位為焦/米3（J/m3）或高?奧（GOe）1MGOe~7.96kJ/m3退磁曲線上任何一點(diǎn)的B和H的乘積既BH我們稱為磁能積，而B(niǎo)xH的最大值稱之為最大磁能積（BH）max。磁能積是恒量磁體所儲(chǔ)存能量大小的重要參數(shù)之一，（BH）max越大說(shuō)明磁體蘊(yùn)含的磁能量越大。設(shè)計(jì)磁路時(shí)要盡可能使磁體的工作點(diǎn)處在最大磁能積所對(duì)應(yīng)的B和H附近。各向同性磁體：任何方向磁性能都相同的磁體。各向異性磁體：不同方向上磁性能會(huì)有不同；且存在一個(gè)方向，在該方向取向時(shí)所得磁性能最高的磁體。燒結(jié)釹鐵硼永磁體是各向異性磁體。取向方向：各向異性的磁體能獲得最佳磁性能的方向稱為磁體的取向方向。也稱作“取向軸”，“易磁化軸”。磁場(chǎng)強(qiáng)度：指空間某處磁場(chǎng)的大小，用H表示，它的單位是安/米（A/m）。磁化強(qiáng)度：指材料內(nèi)部單位體積的磁矩矢量和，用M表示，單位是安/米（A/m）。磁感應(yīng)強(qiáng)度：磁感應(yīng)強(qiáng)度B的定義是：B=Uo（H+M），其中H和M分別是磁化強(qiáng)度和磁場(chǎng)強(qiáng)度，而氣是真空導(dǎo)磁率。磁感應(yīng)強(qiáng)度又稱為磁通密度，即單位面積內(nèi)的磁通量。單位是特斯拉（T）。磁通：給定面積內(nèi)的總磁感應(yīng)強(qiáng)度。當(dāng)磁感應(yīng)強(qiáng)度B均勻分布于磁體表面A時(shí)，磁通①的一般算式為①=BxA磁通的SI單位是麥克斯韋。相對(duì)磁導(dǎo)率：媒介磁導(dǎo)率相對(duì)于真空磁導(dǎo)率的比值，即賞“//。在CGS單位制中，妒1。另外，空氣的相對(duì)磁導(dǎo)率在實(shí)際使用中往往值取為1，另外銅、鋁和不銹鋼材料的相對(duì)磁導(dǎo)率也近似為1。磁導(dǎo)：磁通①與磁動(dòng)勢(shì)F的比值，類似于電路中的電導(dǎo)。是反映材料導(dǎo)磁能力的一個(gè)物理量。磁導(dǎo)系數(shù)Pc:又為退磁系數(shù)，在退磁曲線上，磁感應(yīng)強(qiáng)度Bd與磁場(chǎng)強(qiáng)度Hd的比率，即Pc=Bd/Hd，磁導(dǎo)系數(shù)可用來(lái)估計(jì)各種條件下的磁通值。對(duì)于孤立磁體Pc只與磁體的尺寸有關(guān)，退磁曲線和Pc線的交點(diǎn)就是磁體的工作點(diǎn)，Pc越大磁體工作點(diǎn)越高，越不容易被退磁。一般情況下對(duì)于一個(gè)孤立磁體取向長(zhǎng)度相對(duì)越大Pc越大。因此Pc是永磁磁路設(shè)計(jì)中的一個(gè)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