A bending-mode galfenol electric power harvester

Abstract

Iron–gallium alloys (galfenol) are promising transducer materials that combine high magnetostriction, desirable mechanical properties, high permeability, and a wide operational temperature range. In this study, we present results from a proof-of-concept prototype energy harvester that produces an output voltage proportional to the load-induced bending of the galfenol element caused by a base acceleration of the device. The device consists of a polycrystalline galfenol strip bonded to an aluminum cantilever beam, which has an effective length of 35.81 mm. Two brass pieces, each containing a permanent magnet, are used to mass load each end of the beam and to provide a magnetic bias field through the galfenol strip. The voltage induced in an induction coil closely wound around the cantilever beam captures the time rate of change of magnetic flux within the galfenol strip as the beam vibrates. The first bending-mode resonant frequency of the device was 223 Hz. The power generated from the prototype when subjected to a 1g acceleration at 222 Hz was 2.2 mW (root mean square), which corresponded to an efficiency of more than 60% for the electrical power output per unit mechanical power input to the harvester.