Foreign object detection in a wireless power transfer system

A method comprising:

• providing a transmitter coil,
• wherein the transmitter coil is arranged to generate an electromagnetic test field;
• providing two detection coils,
• wherein signals induced in the two detection coils by the electromagnetic test field compensate each other;
• providing a foreign object detector circuit coupled to the two detection coils,
• wherein the two detection coils are arranged to perform foreign object detection,
• wherein the foreign object detector circuit is arranged to detect a foreign object in response to a property of an output signal,
• wherein the output signal is produced by the two detection coils meeting a foreign object detection criterion;
• providing a communication antenna;
• and
• providing a communicator circuit coupled to the communication antenna,
• wherein the communicator circuit is arranged to communicate with a power receiver via the communication antenna;
• wherein the communication antenna comprises at least a first communication coil and a second communication coil,
• wherein the first communication coil and the second communication coil are coupled in parallel with the first communication coil,
• wherein the communication antenna is arranged with a first segment of the first communication coil having a first capacitive coupling to the first detection coil,
• wherein the communication antenna is arranged with a second segment of the second coil having a second capacitive coupling to the second detection coil,
• wherein the first coupling and the second coupling is at least one of a capacitive couplings and inductive couplings,
• wherein the first coupling and the second coupling compensating each other in the output signal.