Apple Inc.
Wireless Charging System With Metallic Object Detection

Abstract:

A wireless power transmission system has a wireless power receiving device that is located on a charging surface of a wireless power transmitting device. The receiving device has a wireless power receiving coil and the transmitting device has a wireless power transmitting coil array. Control circuitry in the transmitting device uses inverter circuitry to supply alternating-current signals the coil array, thereby transmitting wireless power signals. Measurement circuitry coupled to the coil array makes impulse response measurements while the control circuitry uses the inverter circuitry to apply impulse signals to each of the coils. The control circuitry analyzes output from the measurement circuitry to detect the presence of a metal foreign object on the charging surface. In response to such a detection, the control circuitry reduces the power of subsequent impulse signals to minimize physical vibration and audible noise generated in the system by the metal foreign object.