The limiting effect of electromechanical coupling in self-biased electrostatic Vibration Energy Harvester

This paper reports on the drastic impact of the electromechanical coupling on the operating mode of a MEMS electrostatic Vibration Energy Harvester (e-VEH). A similar behavioral pattern was observed for two different conditioning circuits, which biased the e-VEH: one based on a classical charge pump circuit and one based on the Bennet doubler. The result of this study mitigates the commonplace opinion about the need of maximization of the bias voltage of electromechanical transducer for optimization of the converted power. When the circuits operated in self-biasing mode, in which the reservoir capacitor voltage increases exponentially for weak voltages, a slow down and saturation were consequently observed at average and high voltages. It is due to several phenomena, among which the nonlinear dynamics of the system, increase of the electromechanical damping with bias voltage, and basically by the fundamental limitation of the power that can be extracted from external vibrations.