Power feeding apparatus, power receiving apparatus, power feeding system, and method of controlling power feeding

A power transmitting device comprising:

• circuitry configured to:
• electronically perform a measurement on a resonance circuit to obtain a quality factor of the resonance circuit,
• electronically use a reference value from a power receiving device to obtain a threshold value, and
• electronically use the quality factor and the threshold value to detect an absence of a foreign object in a magnetic field or a presence of the foreign object in the magnetic field.

A power system comprising:

• a power transmitting device that has a resonance circuit, the power transmitting device is configured to obtain a quality factor of the resonance circuit;
• and
• a power receiving device configured to output a reference value, the power transmitting device is configured to use the reference value to obtain a threshold value,
• wherein the power transmitting device is configured to use the quality factor and the threshold value to detect an absence of a foreign object in a magnetic field or a presence of the foreign object in the magnetic field.

A power transmitting method comprising:

• performing a measurement on a resonance circuit to obtain a quality factor of the resonance circuit;
• receiving a reference value from a power receiving device;
• using the reference value to determine a threshold value;
• and
• using the quality factor and the threshold value to detect an absence of a foreign object in a magnetic field or a presence of the foreign object in the magnetic field.