Abstract: A method may comprise determining a coupling factor between a coil of a transmitter and a coil of a relay based on a joint resonance frequency between the coil of the transmitter and the coil of the relay. The determining may occur when the coil of the relay and the coil of the transmitter are separated by a medium. The transmitter may inductively transmit power for wirelessly charging a device located near the relay. An operating frequency range, having a minimal operating frequency and a maximal operating frequency, may be determined based on the coupling factor. Power may be inductively transmitted in accordance with the minimal operating frequency and the maximal operating frequency.