Closed-form analysis of Switchless Electrostatic Vibration Energy Harvesters

Batteries drawbacks are represented by the high cost, the limited reliability and the frequent maintenance requirements (recharge or replacement). Energy Harvesting (EH) offers an alternative to batteries replacement or, at least it allows the increase of their lifetime. EH is the conversion of ambient energy, which is present in the environment, into electrical energy. Different energy sources for EH applications have been reported in the literature: light, radio frequency (RF), temperature gradients, solar energy, vibrations. In this paper we will focus on vibration EH. In a Vibration Energy Harvester (VEH) electrical energy is generated by allowing an inertial mass to vibrate with respect to a frame. In this paper a closed-form analysis of the model of a single-degree of freedom Out-of-Plane Switchless Electrostatic Vibration Energy Harvester (SEVEH) will be presented and discussed. We will demonstrate that, under suitable reasonable assumptions, it is possible to study SEVEHs by using models that admit closed form solutions and, at the same time, are enough accurate if the simplifying hypothesis are met. In particular, a circuital model will be developed which describes both the mechanical and the electrical subsystems composing a SEVEH.