| CPC H02J 50/12 (2016.02) | 20 Claims |

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1. A power transmitter comprising:
an output resonance circuit, wherein the output resonance circuit comprises at least one transmitter coil and at least one capacitor;
a driver circuit, wherein the driver circuit is arranged to generate a drive signal for the output resonance circuit so as to generate a power transfer signal;
a resonance detector circuit,
wherein the resonance detector circuit is arranged to measure a first coupled resonance frequency for the output resonance circuit during a resonance measurement time interval,
wherein the first coupled resonance frequency is for a coupling between the output resonance circuit and a power transfer input resonance circuit of a power receiver,
wherein the power transfer input resonance circuit has a quality factor of no less than ten during the resonance measurement time interval;
an estimation circuit, wherein the estimation circuit is arranged to determine a coupling factor for a coupling between the at least one transmitter coil and at least one receiver coil in response to a non-coupled resonance frequency of the output resonance circuit and the first coupled resonance frequency; and
an adapter circuit, wherein the adaptor circuit is arranged to set an operating parameter in response to the coupling factor.
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