Apple Inc.
Wireless Power Systems With Foreign Object Detection

Abstract:

A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device. The wireless power transmitting device determines whether an external object is present. The external object may be a foreign object such as a coin or paperclip or may be a wireless power receiving device. External objects are detected using quality-factor measurements. Wireless communications are used to discriminate between foreign objects and wireless power receiving devices. Quality factor measurements may be compensated for aging and temperature effects using temperature measurements and compensation factors based on frequency and measured resistance.