A micro-oscillation-driven energy harvester based on a flexible bipolar electret membrane with high output power

Abstract

This paper reports the successful assembly of a micro-oscillation-driven energy harvester with bipolar electret membrane and dual air gap. Bipolar electret membrane, which has the electrostatic field with opposite poles on the top and bottom surfaces, is a flexible sandwiched FEP/THV/FEP membrane prepared via hot-pressing method and thermal-corona polarization technology. With a dual air gap oscillation structure, this energy harvester is equivalent to two variable capacitors in series and can produce a symmetrical resonance and induce capacitance variation to drive the charge flow, therefore generating current output. Output characteristic measurement of the energy harvester indicates that the output power presents an exponential dependence on oscillation driving force, and an extrapolated output power of 11.12 mW could be generated when the oscillation driving force is 2 N. Moreover, the output power displays a linear correlation with the electret membrane area. The influence of oscillation frequency on the output power results in a symmetric distribution of output power around 86 Hz when the oscillation driving force is 0.5 N, with the maximum output power of 14.14 μW. It is also concluded that the oscillation frequency for peak output power shifts to a higher level with the increase of average surface potential, whereas it drifts to a lower level with the enlarging electret membrane area. This novel micro-oscillation-driven energy harvester provides an up-to-date idea for electret application in self-powered sensor systems.