PiezoMEMS Nonlinear Low Acceleration Energy Harvester with an Embedded Permanent Magnet.

Increasing the power density and bandwidth are two major challenges associated with microelectromechanical systems (MEMS)-based vibration energy harvesting devices. Devices implementing magnetic forces have been used to create nonlinear vibration structures and have demonstrated limited success at widening the bandwidth. However, monolithic integration of a magnetic proof mass and optimizing the magnet configuration have been challenging tasks to date. This paper investigates three different magnetic configurations and their effects on bandwidth and power generation using attractive and repulsive magnetic forces. A piezoMEMS device was developed to harvest vibration energy, while monolithically integrating a thick embedded permanent magnet (NdFeB) film. The results demonstrated that repulsive forces increased the bandwidth for in-plane and out-of-plane magnetic configurations from <1 to >7 Hz bandwidths. In addition, by using attractive forces between the magnets, the power density increased while decreasing the bandwidth. Combining these forces into a single device resulted in increased power and increased bandwidth. The devices created in this paper focused on low acceleration values (<0.1 g) and low-frequency applications.