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 mu W power into 80-Omega 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 mu W at 3.56 m/s.