Fabrication and investigation of a millimeter-scale electromagnetic generator for large-amplitude impact motions

Environment vibrations are an important source of energy, often occurring at very low frequencies, but with large amplitude. The possibility to use the large amplitude of the motions is important to enhance the energy harvester's output power. In this paper, an electromagnetic energy harvester is designed and fabricated to produce electricity from low- frequency high amplitude impact motions using an elastic polyurethane cylinder. This millimeter-scale electromagnetic generator (MS-EMG) includes a movable magnet attached to a free sliding mass, a fixed coil, and a polyurethane holding chamber. Polyurethane is a very stable elastic polymer that provides continuous large-amplitude movement for the magnet and plays an effective role in impact capability. Therefore, the effect of impact excitation and the polyurethane foam was investigated simultaneously. The performance of the device was studied, experimentally, for the environment vibrations in the range of 1 to 10 Hz. The impact motions were applied using a simulator that was fabricated for this work. The fabricated MS-EMG with a volume of 1.07 cm3 and a mass of 8.74 g show the capability of producing a voltage of 44.41 mV and power of 10.48 µW over a 100 Oresistive load, using a 6 Hz frequency impact motion. Finally, an analytical model is used to simulate the device performance which showed a good agreement with the experimental results.