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Helmholtz线圈与共轴三线圈磁场均匀性分析.docx

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Helmholtz线圈与共轴三线圈磁场均匀性分析 Introduction Helmholtzcoilsandcoaxialthree-coilsystemsarewidelyusedinexperimentalphysicsandengineering.Thesemagneticfieldgenerationsystemshaveakeyroleinvariousapplicationssuchasmagneticresonanceimaging,particleaccelerators,magneticseparation,andmagneticlevitation.Theuniformityandcontrollabilityofthegeneratedmagneticfieldsareofessentialimportanceinsuchapplications.ThisessayaimstoanalyzeandcomparethemagneticfielduniformityofHelmholtzcoilsandcoaxialthree-coilsystems. HelmholtzCoils Helmholtzcoilsarecomposedoftwoidenticalcircularcoilsplacedparallelandseparatedbyadistanceequaltotheradiusofeachcoil.Thearrangementresultsinauniformmagneticfieldataspecificpoint,whichisconfinedtotheoverlappingareabetweenthecoils.ThemagneticfieldgeneratedbyasinglecoilcanbemathematicallyexpressedusingtheBiot-Savartlaw.ApairofHelmholtzcoilsisconsideredwhentwocoilsareplacedparalleltoeachother,andthedistancebetweenthemisequaltotheradiusofeachcoil.Thisarrangementresultsinamagneticfieldwithahighdegreeofuniformitywithinthecoils'overlaparea. ThemagneticfieldgeneratedbyaHelmholtzcoilsystemdependsonvariousparameterssuchasthenumberofturnsinthecoil,theradiusofthecoils,andthedistancebetweenthecoils.Ingeneral,theuniformityofthegeneratedmagneticfielddecreasesasthedistancefromthecenterofthecoilsincreases.Theuniformityofthemagneticfieldincreasesastheradiusofthecoilsincreases.Thegenerationofauniformmagneticfieldisacompromisebetweentheseparameters. CoaxialThree-CoilSystems Coaxialthree-coilsystemsconsistofthreecoilsplacedconcentricallyaroundacentralaxis.ThecoaxialarrangementprovidesalargeruniformityregioncomparedtoHelmholtzcoils.Thecentralcoilisusedasashieldtominimizetheinterferencefromtheexternalmagneticfieldsources.Thetwooutercoilsareconnectedinseries,andthecurrentflowsthroughtheminthesamedirection.Thecentralcoilisconnectedintheoppositedirection,andthecurrentflowsthroughitintheoppositedirectiontotheoutercoils. Themagneticfieldgeneratedbyacoaxialthree-coilsystemcanbemathematicallyexpres