A Novel Structure for Cantilever-Beam MEMS Power Generator

Abstract

A novel cantilever-beam type MEMS power generator is proposed for the conversion of vibration mechanical energy to electrical energy through piezoelectric effects. In the various MEMS-based micro power generating schemes, piezoelectric conversion usually achieves a higher efficiency than that of electromagnetic or electrostatic schemes. Currently, most cantilever-beam type MEMS power generators are suitable for harvesting energy in relatively high frequency ranges (500 Hz to 14 kHz), but are not effective in harvesting low frequency (<10 Hz) vibration energy, such as energy from human walking or ocean wave, for which MEMS power generators are most desired. In this paper, a new cantilever-beam MEMS power generator is proposed, which can greatly improve the power conversion for low frequency circumstances. The power generator consists of two sets of cantilever beams: 1. A properly designed mm-size cantilever-beam with metal as the proof mass, and having low resonant frequency matching that of the external low frequency excitation sources. This is to be used to effectively couple the external motion. 2. An array of micro thin film piezoelectric (PZT) cantilever-beams, each with metal as proof mass, and having higher resonant frequencies. The external excitation is coupled to the single cantilever beam with kinetic energy. Through impact between the mm-size cantilever beam (low frequency) and the micro cantilever beam array (high frequency), the coupled mechanical energy is transferred to electrical energy through piezoelectric effect. Simulation results show that energy conversion efficiency can be greatly improved by using such a coupled structure as compared to that of only using MEMS cantilever beams with high frequency or a single mm-size beam structure. This may have a wide range of applications in pervasive computing and biomedical engineering.