Long distance high efficient underwater wireless charging system using dielectric-assist antenna

We demonstrated a long-distance high-efficient underwater wireless charging system, which composed of a wireless power transfer antenna and a charging unit. To suppress the seawater conductor loss, which has a high conductivity of ~4 S/m, we analyzed underwater near field EM characteristics and designed dielectric-assist radiative antenna in a magnetic type. It is found that the propagation is dominantly guided by eddy current and low-frequency-operation is suitable from this analysis. The designed antenna size is 24 cm × 24 cm × 1.5 cm. Using this antenna in the sea, high efficiency of 60% through over 10 cm of sea water was achieved. The charging unit composed of a matching circuit, a rectifier, a DC-DC converter and a battery charging circuit. The wireless charging system achieved transmission distance of 5 cm and system efficiency of approximately 50%.