A coil arrangement and matching network is
introduced that is resonant in both 6.78-MHz and 100-kHz bands,
allowing the same power conversion circuitry to operate in either
mode. The multi-mode PRU converts 5 W of ac power to a regulated
5-V output with an efficiency of up to 83% in Rezence mode
and up to 86% in Qi mode. A wireless charging power transfer unit
(PTU) using the Rezence specification charges three such PRUs at a
power level of 5 W each with a power transfer efficiency of 66%. An
in-band communications protocol provides enhanced capabilities
to the Rezence system. Multiple layers of encoding ensure reliable
delivery of messages under difficult channel conditions. Another
PTU design allows the same receiver to charge through a table of
30-mm thickness while maintaining the in-band communications
link. We show that a wide variety of multimode devices are possible,
enabling widespread adoption of wireless power even in the
absence of a single unified standard