Receivers for Multifrequency Wireless Power Transfer: Design for Minimum Interference

Inductive (or wireless) power transfer is proving to be an effective way to deliver power over short distances in a wide range of applications. Frequently, there is a need to deliver power from a single transmitter to multiple mutually coupled receivers. In this paper, we quantify how the power delivered to each receiver is affected due to the resonant frequency shift resulting from receiver mutual coupling. We show that the effect on power delivered is quite severe, especially in high-quality-factor systems. We develop the mathematical framework and demonstrate experimentally that the problem disappears if each receiver is tuned at one of the frequencies emitted by a single transmitter. We adopt the concept of frequency traps as a method to completely decouple the receivers.