Capacitive Wireless Power Transfer Independent of Load Impedance Fluctuation with Transfer Distance

The transfer distance variation of a coupler is a significant issue for capacitive wireless power transfer (WPT). This paper presents a capacitive WPT system independent of load impedance fluctuation with the transfer distance for underwater drones operating in freshwater. A capacitive coupler with opposite feeding is the primary design element. Maximum efficiency and stable power transmission are provided that a phase difference between the feeding point and the coupler electrode edge becomes π/2, and an unloaded Q-factor of surrounded dielectric is large, such as freshwater. Furthermore, the constant-current output inverter suppresses input power to the coupler at a distance where the efficiency drops, automatically reducing electricity waste. Finally, their prototypes are demonstrated at a transfer distance of 20, 50, and 100 mm in tap water.