Ferrofluid liquid spring for vibration energy harvesting

This paper reports ferrofluid liquid spring used to suspend a magnet array for harvesting vibration energy. A new idea of ferrofluid-based suspension is used for a low resonant frequency for a microfabricated vibration-energy harvester as well as high reliability. The ferrofluid liquid spring has reduced the resonant frequency of a microfabricated electromagnetic energy harvester to around 340 Hz, at which 36 nW is delivered into a matched load of 2.3 Ω from 7 g acceleration.