Electret-Based Wind Energy Harvester With Ultra-Low Cut-In Velocity

In this report, we propose an electret-based wind energy harvester that enables wind energy extraction efficiently at low wind speeds below $1 \mathrm{~m} / \mathrm{s}$. A $20-\mathrm{cm}-$ diameter windmill equipped with a rotational electret generator without a connecting rod is prototyped. Thanks to the high electromechanical coupling of the electret generator, the mean output power of 1.8 mW has been obtained at $0.7 \mathrm{~m} / \mathrm{s}$, corresponding to the efficiency of 27%. Furthermore, in the outdoor environment, the cut-in velocity is as low as $0.6 \mathrm{~m} / \mathrm{s}$, and the mean output power is 1.5 mW at $1 \mathrm{~m} / \mathrm{s}$. KEYWORDS