In accordance with an embodiment, a wireless power transmitter includes a charging surface, a transmitting antenna configured to generate an electromagnetic field extending above the charging surface, a sensing array disposed between the transmitting antenna and the charging surface, and a controller coupled to the sensing array. The sensing array includes a plurality of sensors. Each sensor of the plurality of sensors is configured to generate a respective signal indicative of a strength of the electromagnetic field. The controller is configured to detect a presence of a metallic object, other than a receiving antenna of a power receiver, in the electromagnetic field based on the respective signal generated by one or more sensors of the plurality of sensors.

In accordance with an embodiment, a wireless power transmitter includes a charging surface, a transmitting antenna configured to generate an electromagnetic field extending above the charging surface, a sensing array disposed between the transmitting antenna and the charging surface, and a controller coupled to the sensing array. The sensing array includes a plurality of sensors. Each sensor of the plurality of sensors is configured to generate a respective signal indicative of a strength of the electromagnetic field. The controller is configured to detect a presence of a metallic object, other than a receiving antenna of a power receiver, in the electromagnetic field based on the respective signal generated by one or more sensors of the plurality of sensors.

A system and method to detect the presence of conductive foreign objects for a multi-coil wireless power system is described. A wireless power receiver resonant circuit quality information may be obtained without any costly hardware or termination of power delivery to the power receiver load. The power receiver free-running coil current or voltage may be measured during a very short time window. In this time window, the measurement may be unaffected by transmitter and receiver load due to the transmitter coil disconnection and because the wireless power receiver has sufficient DC-bus capacitance.

A system and method to detect the presence of conductive foreign objects for a multi-coil wireless power system is described. A wireless power receiver resonant circuit quality information may be obtained without any costly hardware or termination of power delivery to the power receiver load. The power receiver free-running coil current or voltage may be measured during a very short time window. In this time window, the measurement may be unaffected by transmitter and receiver load due to the transmitter coil disconnection and because the wireless power receiver has sufficient DC-bus capacitance.

A method for determining the relative position of a metal object in relation to a user device and to a transmitter antenna of an inductive charging support when charging the user device. The method includes measuring the quality factor of the transmitter antenna, measuring the quality factor of the receiver antenna, and comparing the measured quality factor of the transmitter antenna with a predetermined quality factor threshold of the transmitter antenna and comparing the measured quality factor of the receiver antenna with a predetermined quality factor threshold of the receiver antenna so as to deduce therefrom the relative position of the metal object in relation to the user device and to the transmitter antenna or the absence of an interfering metal object.

A method for determining the relative position of a metal object in relation to a user device and to a transmitter antenna of an inductive charging support when charging the user device. The method includes measuring the quality factor of the transmitter antenna, measuring the quality factor of the receiver antenna, and comparing the measured quality factor of the transmitter antenna with a predetermined quality factor threshold of the transmitter antenna and comparing the measured quality factor of the receiver antenna with a predetermined quality factor threshold of the receiver antenna so as to deduce therefrom the relative position of the metal object in relation to the user device and to the transmitter antenna or the absence of an interfering metal object.

A power transmitter (101) comprises a driver (201) generating a drive signal for a transmitter coil to generate a power transfer signal during a power transfer time interval and an electromagnetic test signal during a foreign object detection time interval. A set of balanced detection coils (207, 209) comprise two detection coils arranged such that signals induced in the two detection coils by an electromagnetic field generated by the transmitter coil compensate each other. A foreign object detector (205) is coupled to the detection coils and performs foreign object detection during the foreign object detection time interval. The foreign object detector (205) is arranged to detect a foreign object in response to a property of a signal from the detection coils meeting a foreign object detection criterion. A transformer (1101) has a primary winding and a secondary winding coupled in series with the set of balanced detection coils A compensation circuit (1103) is coupled to the primary winding and arranged to generate a compensation drive signal for the primary winding which offsets a combined voltage of the set of detection coils.

A power transmitter (101) comprises a driver (201) generating a drive signal for a transmitter coil to generate a power transfer signal during a power transfer time interval and an electromagnetic test signal during a foreign object detection time interval. A set of balanced detection coils (207, 209) comprise two detection coils arranged such that signals induced in the two detection coils by an electromagnetic field generated by the transmitter coil compensate each other. A foreign object detector (205) is coupled to the detection coils and performs foreign object detection during the foreign object detection time interval. The foreign object detector (205) is arranged to detect a foreign object in response to a property of a signal from the detection coils meeting a foreign object detection criterion. A transformer (1101) has a primary winding and a secondary winding coupled in series with the set of balanced detection coils A compensation circuit (1103) is coupled to the primary winding and arranged to generate a compensation drive signal for the primary winding which offsets a combined voltage of the set of detection coils.

In certain aspects, an enclosure for a wireless power transfer pad is disclosed. The enclosure includes a cover shell configured to be positioned over a portion of the wireless power transfer pad configured to face a wireless power receiver when wirelessly transferring power, wherein at least a portion of the cover shell is made of a heat resistant material.

In certain aspects, an enclosure for a wireless power transfer pad is disclosed. The enclosure includes a cover shell configured to be positioned over a portion of the wireless power transfer pad configured to face a wireless power receiver when wirelessly transferring power, wherein at least a portion of the cover shell is made of a heat resistant material.