Wireless Charging of a Metal-Body Device

Conventional tightly coupled inductive charging has been popular in the mobile device market for years. However, tightly coupled solutions have been unable to efficiently charge a metal encased device due to substantial heat generation. In this paper, we demonstrate that loosely coupled inductive charging technology is a viable solution to charge a metal encased device. Ample power can be delivered through the metal case with negligible case heating. Our prototype is built by machining a lump of aluminum which is attached to a commercial smart phone. Resonator coupling efficiency is measured to be 90% with a certified AirFuel Alliance transmitter. Measured power to a load is 8.2 W, which is suitable for mobile devices.