DETECTION OF FOREIGN OBJECT AND FRIENDLY METAL

A power transmitter may send a digital ping to a receiver. The power transmitter may transfer power to the receiver. The power transmitter may receive a report from the receiver which may comprise a received power value. The power transmitter may determine a transmitted power parameter value, which may be based on a threshold value subtracted from a transmitter power and based on transmitter losses subtracted from the transmitter power. The power transmitter may determine that the received power value is less than the determined transmitted power parameter value and may send an analog ping to the receiver in response to a determination that the received power value is less than the determined transmitted power parameter value. The power transmitter may measure a decay pattern of the analog ping. The power transmitter may determine that the receiver comprises a friendly foreign object. The power transmitter may update the threshold value.