Abstract
A wide-band vibration energy harvester using a Duffing-type nonlinear oscillator with self-excitation circuit is presented. For the conventional linear vibration energy harvester, the resonance frequency is matched to the source frequency, and the mechanical Q factor is designed as large as possible to maximize the oscillator's amplitude. The large Q factor, however, bounds the resonance in a narrow frequency band, and the performance of the vibration energy harvester can become extremely worse when the frequency of the vibration source fluctuates. As is well known, the resonance frequency band can be expanded by introducing the Duffing-type nonlinear oscillator. However, it is difficult for the nonlinear vibration energy harvester to maintain the regenerated power constant because such nonlinear oscillator can have multiple stable steady-state solutions in the resonance band. We introduce a self-excitation circuit with a variable resistance which has two values with negative (excitation mode) and positive (regeneration mode) switched depending on the response amplitude so as to enable the oscillator entrained by the excitation only in the large amplitude solution. In this paper, the energy flow in the excitation mode is analyzed for some specific cases to reveal how the negative resistance works to push the response back to the large amplitude solution, and the possibility of more power-efficient control algorithm is suggested.
