An examination of Galfenol mechanical–magnetic coupling coefficients

Abstract

Magnetostrictive materials are distinguished by an inherent coupling between theirmechanical and magnetic processes which is manifested as a direct (actuator) and aninverse (sensor) effect. The piezomagnetic equations for modeling these attributes can bederived from the thermodynamic potentials, with the usual assumptions regardingadiabatic conditions (negligible heat exchange) and isothermal conditions. The termsd andd* are often used to represent the actuator and sensor coupling coefficients that relate strainto field, and stress to magnetic induction respectively, with equivalence of these two termsfor any given operating point imposed to satisfy energy conservation. In this paper, wepresent experimental results which suggest that the operating regimes in which differencesin these terms have been observed also exhibit atypical trends in their closed-loop energytransduction cycles. The paper presents results from experimental studies in whichclosed-loop cyclic loading of Galfenol samples was conducted, with measurement ofmagnetostriction and magnetization as a function of magnetic field and compressivestress. The work done on/by the sample is calculated based on the measurementsand the anomalous trends on work done on/by the samples will be discussed.