Abstract
This study concerns a piezoelectric vibration energy harvester consisting of a bistable nonlinear oscillator with hardening behavior designed to have wideband resonance characteristics. A vibration energy harvester is an energy-harvesting device that is designed to collect mechanical energy from vibrating objects which is ordinarily discarded as heat. A conventional energy harvester is composed of a linear oscillator. In this design, the natural frequency of the oscillator is matched with the dominant frequency of the vibration source and the mechanical Q factor is designed as large as possible in order to maximize the captured power. The large Q factor, however, bounds resonance in a narrow frequency band, therefore, the converted power decreases significantly if the dominant frequency of the source moves out of this band. This trade-off is recognized as one of the most significant issues in resonance-type vibration energy harvesters because the actual vibration sources present in the environment are likely to have fluctuations in their frequency components. In this paper, in order to mitigate the power-bandwidth trade-off, the resonance frequency band of the harvester is extended by introducing a bistable oscillator with mechanical stoppers which is designed to have widely changing stiffness from nearly zero to quite hard. The presented design enables the harvester to generate larger electric power in a wider frequency range, exploiting the given stroke limit. An oscillator design to improve the global stability by eliminating the hysteresis phenomenon is also presented.
