Freestanding piezoelectric rings for high efficiency energy harvesting at low frequency

Energy harvesting at low frequency is a challenge for microelectromechanical systems. In this work we present a piezoelectric vibration energy harvester based on freestanding molybdenum (Mo) and aluminum nitride (AlN) ring-microelectromechanical-system (RMEMS) resonators. The freestanding ring layout has high energy efficiency due to the additional torsional modes which are absent in planar cantilevers systems. The realized RMEMS prototypes show very low resonance frequencies without adding proof masses, providing the record high power density of 30.20 mu W mm(-3) at 64 Hz with an acceleration of 2g. The power density refers to the volume of the vibrating RMEMS layout. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3551725]