Multi-layer tubular conductor for high Q-factor wireless power transfer system resonators

In this paper we investigate multi-layer tubular conductor for multi-MHz Wireless Power Transfer (WPT) systems high-Q (quality factor) resonators. The conductor layers thickness and current sharing between them are optimized at 13.56 MHz, showing significant reduction in conductor AC resistance (R_AC). Capacitive ballast is used as a practical method for current sharing between layers and operation of coil near resonance. A two-layer conductor is designed, fabricated and characterized showing 18.1% reduction in R_AC at 27.93 MHz using capacitive ballast.