WIRELESS POWER TRANSFER

A power transmitter (101) wirelessly providing power to a power receiver (105) comprises a driver (301) generating a drive signal for an output resonance circuit (103, 303) to generate an electromagnetic signal. A level determiner (315) determines a maximum electromagnetic signal level for the power transfer in response to a loading parameter representing a measured loading of a transmitter coil (103) in comparison to a reference loading. The reference loading is determined as a function of a position parameter, and the power receiver (105) transmits data indicative of the relationship between the position parameter and the reference loading for that specific power receiver (105). An adapter (321) adapts the function used to determine the reference loading based on the data received from the power receiver. An improved power transfer operation can be achieved by adapting the maximum power to the specific conditions.