Acoustic energy harvesting via magnetic shape memory alloys

This study investigates acoustic energy harvesting via magnetic shape memory alloys (MSMA). The acoustic pressure impacts the neck of a Helmholtz resonator (HR) with a flexible face made of an elastic membrane. The design of the proposed energy harvester let radial force in the membrane be tunable. An MSMA is clamped to the membrane, and a proof mass is attached to the other end. The enhanced sound pressure vibrates the membrane and, therefore, excites the base of the MSMA specimen made of Ni–Mn–Ga to apply strain to it. Inserting strain onto the MSMA leads to variant reorientation and change of magnetization vectors, resulting in a change in flux passing through the pick-up coil. Therefore, based on Faraday's law of induction, the voltage will be generated in the coil surrounding the MSMA element. On the other hand, an electrical circuit with a resistor and a capacitor is added to the energy harvester to obtain electrical resonance. After obtaining the governing equations of motion, the modeling approach is verified based on the experimental results reported in the literature. The equations are solved numerically to study the effect of different factors on the power generated by the proposed energy harvester. According to the obtained numerical results, changing the geometric parameters and the proof mass, one can obtain power from the MSMA-based acoustic energy harvester as comparable as that from the piezoelectric one. (paper)