Patent ID: 11936208
Assignee: KONINKLIJKE PHILIPS N.V.
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H | IPC H

Claim 19:
20. A power transmitter comprising:
a transmitter coil;
a driver circuit,
wherein the driver circuit is arranged to generate a drive signal for the transmitter coil,
wherein the driver circuit is arranged to generate the drive signal for the transmitter coil so as to generate a power transfer signal during at least one power transfer time interval of a repeating time frame,
wherein the driver coil is arranged to generate the drive signal for the transmitter coil so as to generate an electromagnetic test signal during at least one foreign object detection time interval of the repeating time frame;

a first plurality of balanced detection coils coupled in series,
wherein the first plurality of balanced detection coils comprises a first detection coil and a second detection coil,
wherein the first detection coil and the second detection coil are arranged such that a first signal induced in the first detection coil by an electromagnetic field generated by the transmitter coil is compensated by a second signal induced in the second detection coil by the electromagnetic field generated by the transmitter coil;

a foreign object detector circuit coupled to the first plurality of balanced detection coils,
wherein the foreign object detector circuit is arranged to perform foreign object detection during the foreign object detection time interval,
wherein the foreign object detector circuit is arranged to detect a foreign object in response to a property of a signal meeting a foreign object detection criterion,
wherein the signal is from the first plurality of balanced detection coils,

wherein the drive signal has a first frequency during the foreign object detection time interval and a second frequency during power transfer time interval,
wherein the first frequency is at least 50% higher than the second frequency.