METHOD FOR DETECTING FOREIGN MATERIAL, AND APPARATUS AND SYSTEM THEREFOR

A power transmission method for a wireless power transmitter, the power transmission method including transmitting sequentially a plurality of sensing signals to a wireless power receiver through transmission coils to sense a presence of the wireless power receiver; identifying transmission coils that receives a signal strength indictor transmitted from the wireless power receiver in response to the plurality of sensing signals; selecting, as a power transmission coil, a transmission coil that receives a signal strength indicator having the largest amount or the largest value among the transmission coils, receiving, from a wireless power receiver, a foreign object detection (FOD) status packet including information on a reference quality factor or a reference peak frequency; determining whether a foreign object is present in a charging area of the wireless power transmitter based on the FOD status packet; and generating a foreign object detection indicator indicating whether the foreign object is present in the charging area of the wireless power transmitter based on a result of the determination and transmitting the generated foreign object detection indicator to the wireless power receiver.