Electret-based Vibration Energy Harvesters Research Articles

Optimal geometry of a parallelized electret-based vibration energy harvester

Electret-based vibration energy harvesters often contain electrets forming a pattern of periodically repeated strips with period L to increase the output power by parallelization. Given a gap length g between the stationary electrets and the movable electrodes facing them, the natural question is how to choose L to maximize the output power. Our analysis, based on conformal mapping, shows that the optimal ratio L/g is represented by a rapidly convergent series starting with the dominant term π = 3.14, followed by terms amounting to a correction of less than 0.3%. We establish the practical relevance of this finding through an experiment involving a voltage-biased energy harvester.

New DRIE-Patterned Electrets for Vibration Energy Harvesting

This paper is about a new manufacturing process aimed at developing stable SiO2/Si3N4 patterned electrets using a Deep Reactive Ion Etching (DRIE) step for an application in electret-based Vibration Energy Harvesters (e-VEH). This process consists in forming continuous layers of SiO2/Si3N4 electrets in order to limit surface conduction phenomena and is a new way to see the problem of electret patterning. Experimental results prove that patterned electrets charged by a positive corona discharge show excellent stability with high surface charge densities that may reach 5mC/m^2 on 1.1\mu m-thick layers, even with fine patterning and harsh temperature conditions (up to 250{\deg}C). This paves the way to new e-VEH designs and manufacturing processes.