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 displacement and velocity of the oscillator so as to enable the oscillator entrained by the excitation only large amplitude solution. In this paper, by the method of phase reduction in the vicinity of limit cycle, phase dynamics focused on a phase difference between the oscillator and external force was introduced. Moreover, by using stable and unstable points of the oscillator introduced from phase dynamics, an analysis of entrainment characteristics to large amplitude from each phase on the limit cycle is shown. As a result, the necessity to switch the load resistance near stable point to cut power used by self-excitation mode is suggested.
