Method for detecting foreign object and apparatus for same

A wireless power transmission method of a wireless power transmitter, the wireless power transmission method comprising:

• performing a foreign object detection procedure based on a quality factor value before power transmission;
• and
• performing a foreign object detection procedure based on path loss during the power transmission,
• wherein the foreign object detection procedure based on the quality factor value comprises:
• storing a measured quality factor value of a resonant circuit;
• receiving a foreign object detection status packet comprising a reference quality factor value;
• determining a quality factor threshold value based on the reference quality factor value;
• and
• comparing the measured quality factor value with the quality factor threshold value to determine whether the foreign object is present,
• wherein the foreign object detection procedure based on the path loss comprises:
• calculating the path loss based on a transmit power strength and a receive power strength;
• and
• comparing the calculated path loss with a path loss threshold value to determine whether a foreign object is present, and
• wherein the path loss threshold value is dynamically determined.