Maximum Available Efficiency of Undersea Capacitive Coupling in a Wireless Power Transfer System

This paper studies the maximum available efficiency of a capacitive power transfer (CPT) system submerged in seawater. The maximum efficiency for a dissipative CPT system is derived using the network theory, namely the conjugate-image method. Submerging CPT system in seawater gives a coupling capacitance in the nF range, which is higher than that in an air-gapped CPT system with similar dimensions. The experimental results demonstrate that the capacitive coupling decrease by 6.3% when the distance increase from 100 mm to 300 mm. The results also show that the efficiency decreases by about 17.5% when the frequency increases from 300 kHz to 1 MHz. These results imply that submerging the CPT system in seawater does not need to operate at a high-frequency range, as in air-gapped CPT counterparts. Thus, a loosely coupled underwater CPT system is a promising solution for wireless charging applications.