Electromagnetic human motion generator with magnetic spring and ferrofluid

An inertial electromagnetic generator realised with magnetic spring and ferrofluid to scavenge energy from low-frequency human motion is presented. The magnetic spring is formed by magnetic attraction force between the fixed and the moving permanent magnet (PM). The kerosene-based ferrofluid is used on the moving PM and suspends the moving PM due to the fluid-magnetic pressure to reduce the mechanical friction as a fluid lubricant. The resonance frequency of the generator 3.5 Hz is experimentally validated with the sinusoidal excitation. The generator can generate an open-circuit voltage of ~10 V and 0.26 mW average power at a load resistance of 465 Ω on resonance condition with the acceleration of 0.55778 m/s², and the corresponding power density of the generator is 40.35 μW/cm². The generator can be fastened to the belt on the backside of waist to harvest human vibration for walking and low running, and the power lever of the generator can reach 1.4-3.4 mW, which is a considerable power for low-power electronic devices.