In this paper, we have designed, fabricated, and characterized a micro-scale electrostatic energy harvester based on microelectromechanical system technology. Sandwich structure with dual electrets was utilized, which can be fully packaged with optimal pressure control to reduce the energy loss from squeeze air damping. With out-of-the-plane gap closing scheme, the energy harvester mainly consists of two variable capacitors, and the overall size of the micro device is about 1.3 cm × 1.8 cm × 0.15 cm. With dual electrets, the output power of the device can be increased to 1.5-2 times higher. With low damping effect at packaging pressure of 5 Pa, the normalized power density can be improved by about 2300 times. The device has been used to provide power supply for a battery-free wireless sensor network, and a temperature signal can be posted to internet every 265 s.
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