Methods for detecting mated coils

A power transfer system comprising:

• an inductive power receiver comprising a receive coil;
• an inductive power mat comprising:
• a housing defining a surface configured to receive the inductive power receiver;
• a transmit coil positioned below the surface;
• a sensor positioned below the surface and configured to detect alignment of the inductive power receiver relative to the surface, the sensor comprising a permanent magnet and a strain sensor mechanically coupled to the permanent magnet;
• and
• a processor coupled to the transmit coil and the sensor;
• and
• a power supply in communication with the processor and operable in a sustained power transmit mode, an intermittent power transmit mode, and an inactive mode;
• wherein
• the inactive mode is associated with a first output of the sensor that corresponds to absence of the receiver;
• the intermittent power transmit mode is associated with a second output of the sensor that corresponds to possible presence of the receiver;
• and
• the sustained power transmit mode is associated with a third output of the sensor that corresponds to a detected alignment between the transmit coil and the receive coil.

A method of activating transmit circuitry within a transmitter of an inductive power transfer system, the method comprising:

• receiving a signal from a strain sensor coupled to a permanent magnet, the signal corresponding to a condition that the permanent magnet is attracted to an object;
• determining whether the object is associated with a receiver device of the inductive power transfer system;
• verifying that the receiver device is ready to receive power;
• activating the transmit circuitry;
• and
• activating a sustained power transmission mode of the transmit circuitry.