Abstract: A power transmitter (101) comprises a driver (201) generating a drive signal for an output resonance circuit comprising transmitter coil (103) generating a power transfer signal. A resonance detector (307) determines a coupled resonance frequency for the output resonance circuit during where the coupled resonance frequency is a resonance frequency for the output resonance circuit for the transmitter coil (103) being coupled to a receiver coil (107) which is part of a power transfer input resonance circuit of the power receiver (105). The input resonance circuit has a quality factor of no less than ten. An estimation circuit (309) determines a coupling factor estimate for the coupling between the transmitter coil (103) and the receiver coil (107) in response to a non-coupled resonance frequency of the output resonance circuit and the first effective resonance frequency. An adapter (311) sets an operating parameter in response to the coupling factor estimate.

Abstract: 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 measurement 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. An estimation circuit (205) determines a position/coupling factor estimate for the power receiver (105) in response to signals from the plurality of sets of balanced detection coils (207, 209) during the at least one measurement time interval.

Abstract: 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 foreign object detection criterion requiring that at least one signal from a set of balanced detection coils (207, 209) exceeds a first threshold and not more than a given threshold number of at least two of the signals exceed a second threshold.