METHOD FOR DETECTING FOREIGN MATERIAL, AND DEVICE AND SYSTEM THEREFOR

A method of transmitting power by a wireless power transmitter, the method including sequentially transmitting a sensing signal a plurality of times to a wireless power receiver through a plurality of transmission coils to sense the presence of the wireless power receiver; identifying transmission coils that receive a signal strength indictor transmitted by the wireless power receiver in response to the plurality of sensing signals; and selecting, as a power transmission coil, the transmission coil that has received the signal strength indicator having the largest amount or the largest value among the transmission coils that have received the signal strength indicator, receiving a plurality of packets including a foreign object detection (FOD) status packet from the wireless power receiver; determining whether a foreign object is present in a charging area of the wireless power transmitter on the basis of the FOD status packet; and transmitting, to the wireless power receiver, a response signal indicating whether the foreign object is present in the charging area of the wireless power transmitter on the basis of a result of the determination, wherein the response signal is determined using a measured peak frequency of a power signal transmitted by the wireless power transmitter and a reference peak frequency included in the FOD status packet received from the wireless power receiver.