Magnetic Resonance Wireless Power Transfer Over 10 m With Multiple Coils Immersed in Seawater

An autonomous underwater vehicle (AUV) is used for exploring marine resources and monitoring infrastructure facilities. Because an AUV is powered by batteries, it needs to be lifted out of the water to have them replaced or recharged. Thus, wirelessly feeding power to an AUV under the sea would improve the efficiency of marine activities. However, it is difficult to wirelessly power an object under the sea because seawater has high conductivity. We examine the electromagnetic field in lossy materials such as a conductor, a coil cover, and seawater. We design a wireless magnetic resonance-based power transfer system with multiple coils using bandpass filter (BPF) theory. The coil structure is sealed so that water cannot enter it. We perform experiments on this system completely immersed in seawater and measure the coil coupling coefficient, efficiency, and wattage. The results confirm wireless power transfer exceeding a distance of 10 m in an undersea setting. We verify the transmission efficiency by changing the receiving-coil position on the central axis of the transfer coils. Furthermore, we confirm a dependence on transfer on the order of 1 to 100 W.