Relay effect on wireless power transfer using resonant coupling

The relay effect in resonantly coupled wireless power transfer systems is investigated in this paper. An explicit solution is derived with respect to the efficiency of power transfer. We found that the optimal position of the relay resonator is dependent on the system load, rather than in the midpoint between the source and device resonators. In order to verify this theoretical result, some parameters of a wireless power transfer system are measured experimentally. Our result is consistent with that from our derivation.