Foreign object detecting device, wireless power transmitting apparatus, and wireless power transfer system

1. A foreign object detecting device, comprising:

a first coil that includes a first wound wire having first and second terminals;

a second coil that includes a second wound wire having third and fourth terminals and is disposed adjacent to the first coil;

a third coil that includes a third wound wire having fifth and sixth terminals and is disposed adjacent to the second coil, the second coil being disposed between the first coil and the third coil, a winding direction of the third wound wire from the fifth terminal to the sixth terminal being the same as a winding direction of the first wound wire from the first terminal to the second terminal; and

a foreign object detecting circuit operative to

output a first detecting signal having a first predetermined waveform to the first terminal of the first coil, and output second detecting signal having a second predetermined waveform to the fifth terminal of the third coil, to cause a combined magnetic field extending over the first and third coils, a polarity of the second predetermined waveform being an inverted polarity of the first predetermined waveform;

measure an amount of change of an impedance value with respect to one of the first and third coils corresponding to a change in the combined magnetic field, which is caused by presence of the foreign object; and

determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value,

wherein a potential of each of the second, fourth, and sixth terminals is at the same as a reference potential of the foreign object detecting circuit.

2. The foreign object detecting device according to claim 1 ,

wherein each of the first, third, and fifth terminals is one of an outer terminal disposed on an outer side of a corresponding one of the first, second, and third coils, and an inner terminal disposed on an inner side of a corresponding one of the first, second, and third coils; and

each of the second, fourth, and sixth terminals is the other one of the outer terminal and the inner terminal of a corresponding one of the first, second, and third coils.

3. The foreign object detecting device according to claim 1 ,

wherein a winding direction of the second wound wire of the second coil from the third terminal to the fourth terminal is the same as the winding direction of the first wound wire of the first coil from the first terminal to the second terminal.

4. The foreign object detecting device according to claim 1 ,

wherein the foreign object detecting circuit measures the amount of change of the impedance value of the first and third coils connected with each other with respect to the change in the combined magnetic field in the case of the presence of the foreign object, and determines that the foreign object is present above the second coil if the amount of the change exceeds the predetermined value.

5. The foreign object detecting device according to claim 1 ,

wherein each of the first, second, and third coils is disposed in a direction perpendicular to an axis of a corresponding one of the first, second, and third coils.

6. The foreign object detecting device according to claim 1 ,

wherein the first and second detecting signals are alternating current signals or pulse signals.

7. The foreign object detecting device according to claim 1 ,

wherein the foreign object detecting circuit simultaneously outputs the first and second detecting signals to the first and third coils, respectively.

8. The foreign object detecting device according to claim 1 , further comprising:

four or more coils including the first, second, and third coils and one or more coils having the same structure as a structure of the first and third coils; and

at least one switch that electrically connects the first and third coils among the four or more coils to the foreign object detecting circuit,

wherein, before outputting the first and second detecting signals, the foreign object detecting circuit selects the first and third coils among the four or more coils by using the at least one switch, as two coils disposed adjacent to both sides of one coil.

9. A wireless power transmitting apparatus, comprising:

the foreign object detecting device according to claim 1 ;

a power transmitting coil; and

a power transmitting circuit that transmits high-frequency power to the power transmitting coil.

10. The wireless power transmitting apparatus according to claim 9 , further comprising:

a housing within which the power transmitting coil is disposed,

wherein an outer periphery of each of the first and third coils is smaller than an outer periphery of the power transmitting coil, and

the first and third coils are disposed between a main surface of the housing and the power transmitting coil.

11. The wireless power transmitting apparatus according to claim 9 ,

wherein the power transmitting coil and at least one of the first and third coils are the same component.

12. The wireless power transmitting apparatus according to claim 9 ,

wherein power of the first detecting signal and power of the second detecting signal are lower than the high-frequency power.

13. The wireless power transmitting apparatus according to claim 9 , further comprising:

a control circuit that causes the power transmitting circuit to transmit the high-frequency power after it is determined by the foreign object detecting circuit that there is no foreign object within a magnetic field formed by the first and third coils.

14. The wireless power transmitting apparatus according to claim 9 ,

wherein the second coil and the power transmitting coil are the same component.

15. A wireless power transfer system, comprising:

the wireless power transmitting apparatus according to claim 9 ; and

a wireless power receiving apparatus.

16. A foreign object detecting device, comprising:

a first coil that includes a first wound wire having first and second terminals;

a second coil that includes a second wound wire having third and fourth terminals and is disposed adjacent to the first coil;

a third coil that includes a third wound wire having fifth and sixth terminals and is disposed adjacent to the second coil, the second coil being disposed between the first coil and the third coil, a winding direction of the third wound wire from the fifth terminal to the sixth terminal being the same as a winding direction of the first wound wire from the first terminal to the second terminal;

a foreign object detecting circuit that outputs a first detecting signal having a first predetermined waveform; and

a phase shifter that converts the first detecting signal into a second detecting signal having a second predetermined waveform, and outputs the second detecting signal to the fifth terminal of the third coil, a polarity of the second predetermined waveform being an inverted polarity of the first predetermined waveform,

wherein the foreign object detecting circuit is operative to

output the first detecting signal to the first terminal of the first coil and to the phase shifter to cause a combined magnetic field extending over the first and third coils,

measure an amount of change of a combined impedance value of the first and third coils with respect to a change in the combined magnetic field in a case of the presence of the foreign object, and

determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value, and

wherein a potential of each of the second, fourth, and sixth terminals is at the same as a reference potential of the foreign object detecting circuit.

17. The foreign object detecting device according to claim 16 ,

wherein each of the first, third, and fifth terminals is one of an outer terminal disposed on an outer side of a corresponding one of the first, second, and third coils and an inner terminal disposed on an inner side of a corresponding one of the first, second, and third coils; and

each of the second, fourth, and sixth terminals is an other one of the outer terminal and the inner terminal of a corresponding one of the first, second, and third coils.

18. The foreign object detecting device according to claim 16 ,

wherein a winding direction of the second wound wire of the second coil from the third terminal to the fourth terminal is the same as the winding direction of the first wound wire of the first coil from the first terminal to the second terminal.

19. The foreign object detecting device according to claim 16 ,

wherein each of the first, second, and third coils is disposed in a direction perpendicular to an axis of a corresponding one of the first, second, and third coils.

20. A foreign object detecting device, comprising:

a first coil on which a wire is wound;

a second coil on which a wire is wound and that is disposed adjacent to the first coil;

a third coil on which a wire is wound and that is disposed adjacent to the second coil, the second coil being disposed between the first coil and the third coil; and

a foreign object detecting circuit operative to

output a first detecting signal having a first predetermined waveform to the first coil, and output a second detecting signal having a second predetermined waveform to the third coil, that causes one of a current based on the first detecting signal flowing through the first coil and a current based on the second detecting signal flowing through the third coil to flow clockwise, and causes an other one of the current based on the first detecting signal and the current based on the second detecting signal to flow counterclockwise to cause a combined magnetic field extending over the first and third coils;

measure an amount of change of a complex impedance value of the first and third coils with respect to a change in the combined magnetic field in the case of the presence of the foreign object; and

determine that the foreign object above the second coil is present if the amount of change exceeds a predetermined value.