System and method for reducing leakage flux in wireless electric vehicle charging systems

1. An apparatus for collecting leakage magnetic flux of a wireless field in a wireless power transfer system, comprising:

a wireless power receiver configured to couple to a wireless field generated by a wireless power transmitter, wherein a portion of the wireless field comprises the leakage magnetic flux; and

a leakage collector comprising a ferromagnetic material having a predetermined geometry and composition and configured to absorb or redirect at least a portion of the leakage magnetic flux away from an outer edge of an electric vehicle, wherein the leakage collector is positioned at a first distance from the wireless power receiver within the wireless field and wherein a width of the leakage collector varies from a first width to a second width, and wherein the first width is narrower than the second width.

2. The apparatus of claim 1 , wherein the leakage collector is disposed on a bottom portion of the electric vehicle at approximately an outer edge of the electric vehicle, and wherein the leakage collector at least partially surrounds the wireless power receiver in a substantially horizontal plane.

3. The apparatus of claim 1 , further comprising a magnetic vehicle shield disposed on a bottom portion of the electric vehicle, wherein the wireless power receiver and the leakage collector are positioned below the magnetic vehicle shield.

4. The apparatus of claim 1 , wherein the leakage collector is disposed on a bottom portion of the electric vehicle and completely surrounds the wireless power receiver.

5. The apparatus of claim 1 , wherein the leakage collector has a perimeter greater than a perimeter of the wireless power receiver, and wherein the leakage collector has a relative magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

6. The apparatus of claim 5 , wherein the relative magnetic permeability is greater than μ r =10.

7. The apparatus of claim 1 , wherein the leakage collector is shaped in one of a square, a rectangle, a circle, a triangle, a polygon, or a semicircle, and wherein a perimeter of the leakage collector extends away from a bottom of the electric vehicle below the wireless power receiver.

8. The apparatus of claim 1 , wherein the ferromagnetic material has a magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

9. The apparatus of claim 8 , wherein the ferromagnetic material comprises one of a soft magnetic composite, a nanocrystalline magnetic material, or a plastic bonded ferrite powder.

10. The apparatus of claim 1 , wherein the leakage collector has a cross section configured to influence the leakage field, the cross section having dimensions that extend orthogonally away from the bottom of the vehicle.

11. The apparatus of claim 1 , wherein the first distance is equal to at least one half of a distance between the wireless power receiver and the outer edge of the electric vehicle.

12. A method for collecting leakage magnetic flux of a wireless field in a wireless power transfer system, comprising:

coupling, via a wireless power receiver, to the wireless field generated by a wireless power transmitter, wherein a portion of the wireless field comprises the leakage magnetic flux; and

absorbing or redirecting at least a portion of the leakage magnetic flux away from an outer edge of an electric vehicle via a leakage collector, the leakage collector comprising a ferromagnetic material having a predetermined geometry and composition and positioned at a first distance from a wireless power receiver within the wireless field, wherein a width of the leakage collector varies from a first width to a second width, and wherein the first width is narrower than the second width.

13. The method of claim 12 , further comprising substantially removing the leakage flux from the wireless power field using the leakage collector.

14. The method of claim 12 , wherein the leakage collector is disposed on a bottom portion of the electric vehicle at approximately an outer edge of the electric vehicle, and wherein the leakage collector at least partially surrounds the wireless power receiver in a substantially horizontal plane.

15. The method of claim 12 , wherein a magnetic vehicle shield is disposed on a bottom portion of the electric vehicle, wherein the wireless power receiver and the leakage collector are positioned below the magnetic vehicle shield.

16. The method of claim 12 , wherein the leakage collector is disposed on a bottom portion of the electric vehicle and completely surrounds the wireless power receiver.

17. The method of claim 12 , wherein the leakage collector has a perimeter greater than a perimeter of the wireless power receiver, and wherein the leakage collector has a relative magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

18. The method of claim 17 , wherein the relative magnetic permeability is greater than μ r =10.

19. The method of claim 12 , wherein the leakage collector is shaped in one of a square, a rectangle, a circle, a triangle, a polygon, or a semicircle, and wherein a perimeter of the leakage collector extends away from a bottom of the electric vehicle below the wireless power receiver.

20. The method of claim 12 , wherein the ferromagnetic material has a magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

21. The method of claim 20 , wherein the ferromagnetic material comprises one of a soft magnetic composite, a nanocrystalline magnetic material, and a plastic bonded ferrite powder.

22. An apparatus for collecting leakage magnetic flux of a wireless field in a wireless power transfer system, comprising:

means for coupling to a wireless field generated by a wireless power transmitter, wherein a portion of the wireless field comprises the leakage magnetic flux; and

means for absorbing or redirecting at least a portion of the leakage magnetic flux away from an outer edge of an electric vehicle, the pair of absorbing means having a predetermined geometry and composition, wherein a width of the absorbing means varies from a first width to a second width, and wherein the first width is narrower than the second width.

23. The apparatus of claim 22 , wherein the coupling means comprises a wireless power receiver, and wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux comprises a leakage collector comprising a ferromagnetic material and positioned at a first distance from the wireless power receiver within the wireless field.

24. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux is disposed on a bottom portion of the electric vehicle at approximately an outer edge of the electric vehicle, and wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux at least partially surrounds the coupling means in a substantially horizontal plane.

25. The apparatus of claim 22 , further comprising a magnetic vehicle shield disposed on a bottom portion of the electric vehicle, wherein the coupling means and the means for absorbing or redirecting at least a portion of the leakage magnetic flux are positioned below the magnetic vehicle shield.

26. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux is disposed on a bottom portion of the electric vehicle and completely surrounds the coupling means.

27. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux has a perimeter greater than a perimeter of the coupling means, and wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux has a relative magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

28. The apparatus of claim 27 , wherein the relative magnetic permeability is greater than μ r =10.

29. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux is shaped in one of a square, a rectangle, a circle, a triangle, a polygon, or a semicircle, and wherein a perimeter of the means for absorbing or redirecting at least a portion of the leakage magnetic flux extends away from a bottom of the electric vehicle below the coupling means.

30. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux has a magnetic permeability value sufficient to absorb or redirect the leakage magnetic flux.

31. The apparatus of claim 1 , wherein the leakage collector has opposite ends equal to the first width and a center equal to the second width.

32. The apparatus of claim 1 , wherein the leakage collector has opposite ends equal to the first width and a center equal to the second width.

33. The apparatus of claim 1 , further comprising another leakage collector having a width that varies from the first width to the second width and wherein the leakage collector and the other leakage collector are disposed along opposite sides of the wireless power receiver.

34. The method of claim 12 , wherein the leakage collector has opposite ends equal to the first width and a center equal to the second width.

35. The method of claim 12 , wherein the leakage collector has opposite ends equal to the second width and a center equal to the first width.

36. The method of claim 12 , further comprising another leakage collector having a width that varies from the first width to the second width and wherein the leakage collector and the other leakage collector are disposed along opposite sides of the wireless power receiver.

37. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux has opposite ends equal to the first width and a center equal to the second width.

38. The apparatus of claim 22 , wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux has opposite ends equal to the second width and a center equal to the first width.

39. The apparatus of claim 22 , further comprising another means for absorbing or redirecting at least a portion of the leakage magnetic flux having a width that varies from the first width to the second width and wherein the means for absorbing or redirecting at least a portion of the leakage magnetic flux and the other means for absorbing or redirecting at least a portion of the leakage magnetic flux are disposed along opposite sides of the means for coupling to a wireless field.