Tuneable resonance frequency vibrational energy harvester with electret-embedded variable capacitor

An electret-based electrostatic energy harvester featuring tuneable resonance frequency, small size, light weight, and high output power was designed and its performance predicted by the finite element method and verified by experiment. The device consists of a resilient fluorinated polyethylene propylene (FEP) electret film that is metallised on one side with a small seismic mass attached to its centre and an arc-shaped counter electrode. In principle, such an energy harvester is mechanically a mass-spring system and electrically a self-bias voltage variable capacitor and converts vibrational energy into electrical energy by electromechanical coupling. For an energy harvester sample with dimensions of 30 × 10 × 9 mm for which the last dimension denotes the initial depth of the centre of the harvester, the resonance frequency can be tuned from 17 to 70 Hz by stretching the length of the FEP film loaded with a given seismic mass of 0.06 g. For a seismic mass of 0.1 g, the harvester generated a power up to 797 μW to a matching resistor at its resonance frequency of 17 Hz at an acceleration of 1×g, where g is the gravity of the earth. Such energy harvesters are promising candidates for use in self-powered electronic devices and wireless sensor network nodes.