Method for detecting foreign material, and device and system therefor

A wireless power transmitter for detecting a foreign object disposed in a charging area of the wireless power transmitter, the wireless power transmitter comprising:

• a transmitting unit configured to transmit a power signal having a predetermined strength;
• and
• a controller configured to:
• measure a peak frequency of the power signal,
• receive, from a wireless power receiver, information about a reference peak frequency of the wireless power receiver,
• determine a threshold frequency based on the reference peak frequency, and
• determine whether the foreign object is present in the charging area based on a comparison of the measured peak frequency of the power signal with the determined threshold frequency.

A method for detecting a foreign object disposed in a charging area of a wireless power transmitter, the method comprising:

• transmitting, by a wireless power receiver to the wireless power transmitter, a foreign object detection status packet including information about a reference peak frequency of the wireless power receiver;
• and
• receiving, by the wireless power receiver from the wireless power transmitter, a response indicating the foreign object is present or not present in the charging area,
• wherein the response is determined based on the reference peak frequency of the wireless power receiver.