Foreign object detection in wireless energy transfer systems
A wireless energy transfer system includes a foreign object debris detection system. The system includes at least one wireless energy transfer source configured to generate an oscillating magnetic field. The foreign object debris may be detected by at least one field gradiometer positioned in the oscillating magnetic field. The voltage of the at least one field gradiometer may be measured using readout circuitry and a feedback loop based on the readings from the gradiometers may be used to control the parameters of the wireless energy source.
1. A wireless energy transfer system with foreign object debris detection, the system comprising:
at least one wireless energy transfer source configured to generate an oscillating magnetic field;
at least one magnetic field sensor comprising at least two loops of conductive wire through which the oscillating magnetic field passes, wherein a first current induced in a first loop of the magnetic field sensor flows substantially in an opposite direction to a second current flowing in a second loop of the magnetic field sensor;
at least one readout circuit configured to measure an electrical parameter of the at least one magnetic field sensor to determine a presence of a metallic foreign object.
2. The system of claim 1 , wherein the at least one readout circuit is configured to measure the electrical parameter of the first loop and the second loop in sequence.
3. The system of claim 1 , wherein the at least one readout circuit is configured to multiplex measurement of the electrical parameter for the first loop and the second loop.
4. The system of claim 1 , wherein the at least one magnetic field sensor comprises an array of loops, wherein the first and second currents flow through an equal number of loops.
5. The system of claim 4 , wherein the at least one readout circuit comprises an analog-to-digital converter coupled to at least two loops of the array with the first current flow direction.
6. The system of claim 1 , wherein each loop has a substantially square shape.
7. The system of claim 1 , wherein each loop has a substantially rectangular shape.
8. The system of claim 1 , wherein each loop is printed on a circuit board.
9. The system of claim 1 , wherein the at least one magnetic field sensor comprises multiple layers of offset and overlapping loops.
10. The system of claim 1 , further comprising control circuitry configured to interrupt the oscillating magnetic field based on a value of the electrical parameter measured by the at least one readout circuit.
11. The system of claim 1 , wherein the at least one magnetic field sensor is configured to verify that a metallic foreign object has not moved onto or over the at least one wireless energy transfer source during generation of the oscillating magnetic field.
12. The system of claim 1 , wherein the at least one magnetic field sensor is configured to verify that a metallic foreign object has not moved onto or over the at least one wireless energy transfer source prior to generation of the oscillating magnetic field.
13. The system of claim 1 , wherein the at least one readout circuit is configured to measure a first voltage in the first loop and a second voltage in the second loop, and to determine the presence of the metallic foreign object based on a difference between the first voltage and the second voltage.