FOREIGN OBJECT DETECTION IN A WIRELESS POWER TRANSFER SYSTEM

A power transmitter comprises a transmitter coil () generating an electromagnetic field. A set of balanced detection coils (, ) comprises detection coils in series and compensating each other. A foreign object detector () performs foreign object detection, by potentially detect a foreign object in response to a property of an output signal from the set of balanced detection coils (, ) in response to the electromagnetic test meeting a foreign object detection criterion. A communicator () is coupled to a communication antenna () communicates with a power receiver () via this. The communication antenna () comprises a plurality of communication coils (, ) coupled in parallel. A first segment of a first communication coil () has a first coupling to a first detection coil and a second segment of a second coil () has a second coupling to a second detection coil. The couplings are capacitive and/or inductive couplings and the first coupling and the second coupling compensate each other in the output signal.