Wireless charging optimization

A wireless charging method and apparatus comprises transmitting a wireless charging signal using an antenna 118, determining or measuring the power being transferred from the antenna 118 to a coupled device 104, and adjusting an impedance of the antenna to increase the power being transferred. The wireless charging device 102 may be an RFID or NFC reader, and the receiving device 104 may be an RFID chip, a mobile phone, or other device. Load current on the transmission coil 118 may be determined, or the signal voltage, or the phase difference between the current and the voltage. The system seeks to maximise charging efficiency whatever the relative position or orientation of the transmitter 102 and receiver 104. Impedance adjustment may include altering resistance or reactance, and may include adjusting the load on a power amplifier 106 connected to the antenna 118.