Multi-frequency vibration-driven electret generator for wireless sensor applications

We had reported the power output enhancement of an electret harvester and the operation of wireless sensor modules only on electricity from our electret harvester^[1]. Since vibration is random and irregular in actual fields, there is the issue that power output of vibration harvesters can't be obtained outside the range of frequencies designed to resonate the inner mass. As a way to solve, we fabricated four electret harvesters tuned to different resonant frequencies only by assembling different springs and weights, and developed voltage conversion circuits with 73% efficiency from 70V AC to 3.6V DC. We demonstrated to obtain stable DC power output at a broad range of frequencies from 27.6Hz to 30.6Hz by combining the four electret harvesters and voltage conversion circuits