FOREIGN OBJECT DETECTION IN A WIRELESS POWER TRANSFER SYSTEM

A wireless power transmitter () comprises a driver () generating a drive signal for a transmitter coil () thereby generating a power transfer signal during power transfer intervals of a repeating time frame comprising at least one power transfer interval and one foreign object detection interval. A test generator () generates a test drive signal for a test coil () thereby generating an electromagnetic test signal during foreign object detection intervals. A foreign object detector () performs a foreign object detection test in response to a measured parameter for the test drive signal during the foreign object detection intervals. An adapter () generates a varying test drive signal for the test coil () during an adaptation interval, and determines a test drive signal parameter value in response to the varying test drive signal. The test generator () sets a signal property of the test drive signal during at least one foreign object detection interval in response to the test drive signal parameter value.