Foreign object detection using heat sensitive material and inductive sensing
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.
1. A wireless power transfer pad comprising:
a wireless power transmitter configured to generate an alternating magnetic field for wirelessly transferring power to a wireless power receiver;
a foreign object detection circuit including sense elements, the foreign object detection circuit configured to detect a presence of a foreign object in a space between the wireless power transfer pad and the wireless power receiver;
an enclosure comprising a cover shell positioned over the wireless power transmitter and the foreign object detection circuit, the cover shell comprising:
a first portion made of a first material; and
a second portion made of a second material, wherein the second portion faces the wireless power receiver when wirelessly transferring power, and wherein the second material has a heat resistance that is higher than a heat resistance of the first material, the heat resistance of the second material being sufficient to protect electrical components of the wireless power transfer pad from potential damage due to heat that is generated by the alternating magnetic field in a foreign object that is undetectable by the foreign object detection circuit.
2. The wireless power transfer pad of claim 1 , further comprising a metallic back plate.
3. The wireless power transfer pad of claim 1 , wherein the higher heat resistance of the second material includes one or more of a higher melting temperature, a higher heat conductivity, higher flame retardence, and a higher autoignition temperature.
4. The wireless power transfer pad of claim 1 , wherein the second material comprises at least one of a nylon resin, a perfluoroelastomer, a polymerized siloxane, a reinforced plastic, glass reinforcement, a carbon-fiber reinforcement, a structural composite, or a ceramic matrix composite.
5. The wireless power transfer pad of claim 1 , wherein the second portion of the cover shell comprises a portion of a surface of the cover shell.
6. The wireless power transfer pad of claim 1 , wherein the second portion of the cover shell is embedded in the cover shell.
7. The wireless power transfer pad of claim 1 , wherein the second portion of the cover shell comprises one or more tiles.
8. The wireless power transfer pad of claim 1 , wherein the second portion further comprises a thermal insulation layer.
9. The wireless power transfer pad of claim 1 , wherein the sense elements include one or more sense coils configured to inductively sense the foreign object.
10. The wireless power transfer pad of claim 1 , wherein the sense elements include an electrode grid structure configured to capacitively sense the foreign object.
11. The wireless power transfer pad of claim 1 , wherein the second portion of the cover shell includes a heat sensitive material configured to change a characteristic as a function of a temperature and to sense the foreign object when inductively heated by the alternating magnetic field.
12. The wireless power transfer pad of claim 11 , wherein the characteristic is one or more of an electrical characteristic including at least one of a resistance, impedance, capacitance, or inductance.
13. The wireless power transfer pad of claim 11 , wherein the characteristic is one or more of a non-electrical characteristic including at least one of a refractive index, a wave propagation velocity, or a mass density.
14. The wireless power transfer pad of claim 1 , wherein a cost of the first material is lower than a cost of the second material.