FOREIGN OBJECT DETECTION IN A WIRELESS POWER TRANSFER SYSTEM

According to some implementations, a wireless power transmitter and a wireless power receiver of a wireless power system are disclosed. According to one aspect, the wireless power transmitter includes a wireless power transmitter circuit configured to generate a power transfer signal, a driver circuit configured to generate a drive signal for the wireless power transmitter circuit during a power transfer time interval. The wireless power transmitter includes an adapter circuit configured to generate a varying test drive signal during an adaptation time interval by varying at least one of a frequency, voltage, current, duty cycle, signal level, or amplitude of the test drive signal. Wireless power transmitter is configured to perform foreign object detection based on the signal parameter determined by the adapter circuit. According to some implementations, the wireless power receiver is configured to transmit messages which indicate the timing for detection of the signal parameter by the adapter circuit.