Micro electret-based power generator for ambient vibrational energy harvesting

Energy harvesting systems refer to devices that capture and transform unused ambient energy into the electrical energy. Unlike traditional large-scale renewable energy harvesting systems such as solar panels and wind turbines, these harvesting devices mostly target on powering small low-power electronic devices. Such harvesters may pave the primary step forward to actualizing of self-autonomous devices and performing of intelligent monitoring activities. A typical vibration-based MEMS energy harvester normally makes use of piezoelectric, electromagnetic or electrostatic transduction mechanism. Among these, electrostatic energy harvesters have the advantages in micro-scale applications as they are more compatible with the silicon CMOS processes while offering greater flexibilities in the design of mechanical and electrical features separately. This chapter begins with a brief introduction of three energy conversion schemes with special emphasis placed on micro electret-based electrostatic energy conversion mechanisms. Recent advances in MEMS-based electret vibrational energy harvesters (e-VEHs) have been described and reviewed, including operating principles, electret materials and charging methods, structural design and efficiency enhancement approaches.