Wireless power transfer apparatus

A wireless power transfer apparatus for wirelessly transferring electrical power to a power receiving apparatus, the wireless power transfer apparatus comprising:

• a power output circuit configured to output alternating-current power having a predetermined operating frequency;
• at least one power transmission unit configured to transmit the alternating-current power to the power receiving apparatus, the at least one power transmission unit comprising:
• a resonant power transmission circuit that includes a power transmission coil, which has a reactance, and a resonant capacitor;
• and
• at least one characteristic adjuster configured as a closed loop and that comprises:
• a characteristic adjustment coil magnetically coupled to the power transmission coil without being connected in series to the power transmission coil;
• and
• a characteristic adjustment capacitor connected to the characteristic adjustment coil, wherein
• the at least one characteristic adjuster has a frequency characteristic that:
• causes, in a power transfer mode from the at least one power transmission unit to the power receiving apparatus in which the power transmission coil is magnetically coupled to a power receiving coil of the power receiving apparatus, the resonant power transmission circuit to have a resonance frequency that substantially matches the operating frequency, the reactance of the power transmission coil having a reference value in the power transfer mode;
• and
• causes, in a power non-transfer mode from the at least one power transmission unit to the power receiving apparatus in which the power transmission coil is not magnetically coupled to the power receiving coil, the reactance of the power transmission coil to become an adjusted value that is higher than the reference value, and
• the frequency characteristic of the at least one characteristic adjuster changes based on a change between:
• a first state of magnetic coupling between the power transmission coil and the power receiving coil in the power transfer mode;
• and
• a second state of non-magnetic coupling between the power transmission coil and the power receiving coil in the power non-transfer mode.