Study on Micro-energy Harvesting Device Using Iron-Gallium Alloy

Abstract

We propose a micro-energy harvesting device using an iron gallium alloy (Galfenol) that is capable of providing electrical energy through environmental vibrations. Galfenol is a ductile magnetostrictive material with high piezomagnetic constant, good machinability, and a large inverse magnetostrictive effect in which the magnetization can be varied by mechanical stress. The proposed device consists of two columns of Galfenol those ends are connected at the end with iron yokes, coils and a bias magnet. When bending force is applied on the mover with the other end fixed like a cantilever, the magnetization in one column increases because of tensile force due to the inverse magnetostrictive effect, and the other decreases due to compression. The time variation of the magnetization generates voltage on the wound coils. This energy harvesting device is advantageous over other types such as those using piezoelectric material, in size, high robustness, and low electrical impedance. In addition, the two columns structure requires low mechanical force to provide sufficient stress to change the magnetization. We fabricated a prototype using stress-annealed Galfenol with 314 coil turns and in experiments verified a maximum voltage of 0.48 V at forced vibration with a frequency of 333 Hz. The frequency response was also measured to understand the behavior at resonances of the 1st and 2nd bending modes as well as the effect of additional weight.