Near-field capacitive wireless power transfer array with external field cancellation

In this paper, a near-field phased-array cancellation technique for a modular and scalable capacitive wireless transfer system is presented. The application is for kW power transfer to static electric vehicles and vehicles in motion. The goal of the distributed array approach is to increase maximum transferable power while decreasing the external electric field produced by the WPT system, accomplished by field focusing through phase control. Full-wave simulations show that high power transfer efficiency with an accompanied 40% reduction in maximum external field can be accomplished with an 8-element array with 180° alternating phase difference between adjacent elements. A comparison is made for allocated bands at 6.78, 13.56 and 27.12 MHz showing improved focusing with increasing frequency. A system prototype at a scaled power level is currently being designed, taking account tradeoffs in circuit element loss and focusing loss.