Abstract
We have developed a micro-electro-mechanical systems (MEMS) electrostatic vibratory power generator with over 100 W of (root-mean-square) output electric power under 0.03 G (G: the acceleration of gravity) accelerations. The device is made of a silicon-on-insulator (SOI) wafer and is fabricated by silicon micromachining technology. An electret built-in potential is given to the device by electrothermal polarization in silicon oxide using potassium ions. The force factor, which is defined by a proportional coefficient of the output current with respect to the vibration velocity, is 2.34 × 10 C/m; this large value allows the developed vibration power generator to have a very high power efficiency of 80.7%. We have also demonstrated a charging experiment by using an environmental acceleration waveform with an average amplitude of about 0.03 G taken at a viaduct of a highway, and we obtained 4.8 mJ of electric energy stored in a 44 F capacitor in 90 min.
Highlights
An increasing number of studies have been performed on micro-electro-mechanical systems (MEMS) vibration power generators to realize autonomous electric power sources for sensor network systems
Energy harvesters are categorized into three types depending on the operational principles, that is, electromagnetic transduction (EM) [1,2], electrostatic transduction (ES) [1,3], or piezoelectric transduction (PZ) [1,4]
Wei et al have reported a 25% energy conversion efficiency by using PZ devices made of piezoelectric lead zirconate titanate (PZT) film, and they showed the effects on device parameters for cantilever vibration
Summary
An increasing number of studies have been performed on micro-electro-mechanical systems (MEMS) vibration power generators to realize autonomous electric power sources for sensor network systems. A 6 μW output was reported on an ES power generator with a 0.65 g proof mass [10], while Despesse et al have shown 1.76 mW on a 104 g mass in an ES harvester [11]. Wei et al have reported a 25% energy conversion efficiency by using PZ devices made of piezoelectric lead zirconate titanate (PZT) film, and they showed the effects on device parameters for cantilever vibration. A RMS value we measured at a viaduct for a highway was about 0.03 GRMS, and we need to develop a vibration power generator that enables us to charge sufficient electric energy to operate a sensor network device from such a small vibration source. Using the developed power generator, we conducted a charging experiment under an acceleration waveform observed on a viaduct and established an electric energy of 4.8 mJ stored in a 44 μF capacitor in 90 min
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