Optimization of an electret-based energy harvester

Thanks to miniaturization, it is now possible to imagine self-powered systems that use vibrations to produce their own electrical energy. Many energy harvesting systems already exist. Some of them are based on the use of electrets: electrically charged dielectrics that can retain charge for years. This paper presents an optimization of an existing system and proves that electret-based electrostatic energy scavengers can be excellent solutions to power microsystems even with low-level ambient vibrations. Thereby, it is possible to harvest up to 200 mu W with vibrations of acceleration lower than 1g (typically 50 mu m(pp) at 50 Hz) using thin SiO2 electrets with an active surface of 1 cm(2) and a mobile mass of 1 g. This paper optimizes such a system (geometric, electrostatic and mechanical parameters), using FEM (finite element method) software (Comsol Multiphysics) and Matlab to compute the parameters, and proves the importance of such an optimization to build efficient systems. Finally, it is shown that the use of electrets with high surface potential is not always the best way to maximize output power.