Small-Signal Modeling and Optimal Operating Condition of Magnetostrictive Energy Harvester

Magnetostrictive energy harvesting has drawn attention in recent years for its high energy conversion efficiency and environmental durability. Magnetostrictive harvesters are mainly composed of giant magnetostrictive material, a magnetic circuit, and an electric circuit, which involves complex mechanical-electromagnetic coupled problems. Therefore, in many studies, the analysis of such device was implemented by finite element method. However, numerical calculation generally requires a great deal of time and does not provide adequate physical understanding of the effect of the design parameters on the harvester characteristics.

In many previous studies, magnetostrictive harvesters have been operated under a small-signal vibration imposed over a constant prestress and magnetic bias. In such operating conditions, linearized small-signal models can be used to derive important analytical expressions for the harvester characteristics and their dependency on the design parameters. This paper presents the linearized modeling of a magnetostrictive energy harvester using linearized constitutive equations. The energy loss due to eddy currents is also considered for high-frequency application. The influence of parameter variation on the output power is investigated from the algebraically obtained output power, and the existence of an optimal value in resistance and capacitance of the electric circuit is discussed. These optimal design parameters are also presented in form of an algebraic solution. The obtained output power is finally proven to fit with experimental results when an appropriate permeability and magnetostrictive constant are given.