Electrostatic/Electret‐Based Harvesters

This chapter discusses electrostatic/electret generator models, different configurations of electrodes, electret materials/charging methods, generator design, and prototyped micro-electro-mechanical-system (MEMS) devices. Electrets have been commercialized for use in microphones and air dust filtering systems. The performance of an electret is often characterized with the surface charge density. However, the charge is not located on the surface but distributed in the depth direction. Electret/electrostatic generators are superior to electromagnetic counterparts for small area and low operation frequency, which is usually true for vibration energy harvesters. The advantages of electrostatic/electret generators include freedom of spring material choice, high output voltage, and applicability to low-profile devices. In addition, as shown by recent prototypes, electrostatic/electret generators give high effectiveness more than 50% even in small volume or at low resonant frequency.