Electret based micro energy harvesting device with both broad bandwidth and high power density from optimal air damping

This paper presents an electret based vibration energy harvester, which has excellent performance with both broad bandwidth and high normalized power density (NPD). Wafer-level MEMS fabrication process is proposed with detailed study on the packaging pressure and air damping effect. With an overall volume of about 0.187 cm³, the harvester can generate a maximum power of 4.95 μW with bandwidth of 12 Hz and NPD of 3 mWcm^-3g^-2 at 3 Pa. The broad bandwidth of the device makes it possible to harvest the energy from random vibrations, and makes it feasible to pile up multi-device stacks for better power output. The all-round performance of the device shows promising applications for the wireless sensor networks technology.