MEMS Electrostatic Energy Harvesters with Nonlinear Springs

Abstract

Design of nonlinear proof mass suspensions is one among several possible strategies that can be adopted to enlarge the operating frequency range of energy harvesters. Emphasizing continuous mode operation, this chapter gives a brief overview of the working principles of electrostatic energy harvesters. We argue that nonlinear springs are particularly well suited to make nonlinear suspensions for MEMS electrostatic energy harvesters. We then discuss from a theoretical point of view how nonlinear springs will modify the vibration spectrum of the devices and what can be expected from them in terms of performance. Different nonlinear spring designs are presented together with recent experimental results on characterization of micromachined devices. With frequency sweeps or white-noise vibration, nonlinear devices have shown dramatic increases in bandwidth compared to their linear counterparts. Experiments with band-limited noise show that the use of nonlinear springs is a viable method to increase the harvester tolerance towards variations in vibration bandwidth and center frequency.