Theprincipleand1:3internalresonanceofarectangularthinplateinatransversemagneticfieldisinvestigated.Basedonthemagneto-elasticvibrationequationandelectromagneticforceexpressionsofthethinplates,thenonlinearmagneto-elasticvibrationdifferentialequationsofrectangularplatesunderexternalexcitationinatransversemagneticfieldarederived.Forarectangularplatewithonesidefixedandthreeothersidessimplysupported,thetwo-degree-offreedomnonlinearDuffingvibrationdifferen-tialequationsareproposedbythemethodofGalerkin.Themethodofmultiplescalesisadoptedtosolvethemodelequationsandobtainfourfirst-orderordinarydifferentialequationsgoverningmodulationoftheamplitudesandphaseanglesinvolvedviathefirst-orderorthesecond-orderprimary-internalreso-nances.Withanumericalexample,theamplitudefrequencyresponsecurves,timehistoryresponses,phaseportraitsandPoincaremapsofthefirsttwoordervibrationmodesviaprinciple-internalresonancearerespectivelycaptured.Andtheeffectsofexternalexcitationamplitudes,magneticfieldintensitiesandthicknessesonthevibrationofsystemarediscussed.Theresultsshowthattheresponseisdominatedbythelowmodewhenprinciple-internalresonanceoccurs.Theinternalresonanceprovidesamechanismfortransferringenergyfromahighmodetoalowmode.
