Non-Resonant Electromagnetic Broad-Band Vibration-Energy Harvester Based on Self-Assembled Ferrofluid Liquid Bearing

This paper reports a non-resonant, broadband electromagnetic vibration-energy harvester based on self-assembled ferrofluid liquid bearing. Magnet array is suspended by the liquid bearing over a microfabricated multi-layer coil plate such that the energy harvester does not rely on any mechanical resonance, and can harvest vibration energy over a broad frequency range. An analytical model of the non-resonant energy harvester with liquid bearing is developed to predict the frequency responses under various external accelerations. Experimental results show that the electromagnetic energy harvester occupying 1.1 cm 3 and weighing 2.5 gram generates an induced electromotive force of V rms = 61 to 93.7 mV (delivering 11.6-27.5 μW power into 80-Ω load) from 2-g acceleration at 2-4 Hz. When the energy harvester is placed on the back of a human walking at various speeds, the power output is increased as the walking speed is increased from 0.44 m/s (walking) to 3.56 m/s (running), and reaches 18.1 μW at 3.56 m/s.