Development of an automatic frequency tracking electret vibration energy harvester

Abstract

Abstract This paper presents the development of a vibration energy harvester where the resonant frequency of the energy harvester automatically tracks the vibration frequency of environments. This device consists of two movable structures: a cantilever structure that displaces in the out-of-plane direction ( z -direction) and a folded beam structure that displaces in both the out-of-plane and in-plane directions ( x -direction). Between the two movable structures, triangular comb-electrodes are designed, and these form a coupled vibrating system connected by electrostatic springs. By applying a charging voltage of a half-wave voltage doubler rectifier circuit between the comb-electrodes of the harvester via a 200 MΩ feedback resister, the resonant frequency can be followed to the environmental vibration frequency automatically. Although the half-width of the developed harvester was only 4 Hz, we successfully achieved tracking over a range of 11 Hz, allowing us to generate a high charging voltage across a wide frequency range.