Multiphysics circuit of a magnetostrictive energy harvesting device

Kinetic energy harvesting devices based on magnetostrictive materials are composed of several parts, for dealing with multiphysics, including mechanical, magnetic, and electric quantities. An effective method to simulate the effects of different working conditions is important to fully exploit such devices. The aim of this paper is to present an equivalent circuit that can be identified with standard measurements on the device and simulated with a standard circuit simulator, such as Spice. The circuit is a nonlinear three-port circuit, related to the mechanical, magnetic, and electrical parts of the device. Unlike many of the published papers on the subject, the magneto-mechanical modeling is quite realistic and exploits nonlinear functions and the full coupling among the involved physical quantities of the employed magnetostrictive material. The nonlinear equivalent circuit is preliminarily validated on a concept device with permanent magnets biasing on a Stress Annealed Galfenol rod. Experimental data with different resistive loads and magnetic biasing are considered and compared with simulation outputs, in terms of the RMS voltage and harvested power.