Coil structures for alignment and inductive wireless power transfer

1. A coil structure for wireless power transfer comprising:

a ferrite core; and

at least two coils wound around the ferrite core, the at least two coils located symmetrically about a geometric center of the ferrite core,

the at least two coils wound in such a way that when a first current flows in a first spatial direction in one of the at least two coils a second current flows in a second spatial direction in the other one of the at least two coils, the second spatial direction being opposite to the first spatial direction.

2. The coil structure of claim 1 , wherein the at least two coils are coupled together in series and the first current and the second current have equal magnitudes.

3. The coil structure of claim 1 , wherein the first current is induced by magnetic flux passing through the ferrite core and one of the at least two coils and the second current is induced by magnetic flux passing through the ferrite core and the other one of the at least two coils.

4. The coil structure of claim 1 , wherein the ferrite core has a shape of one of a parallelepiped, a circular cylinder, and an elliptic cylinder.

5. The coil structure of claim 1 , where the ferrite core comprises a plurality of arms arranged symmetrically around the geometric center of the ferrite core.

6. The coil structure of claim 1 , wherein the ferrite core has a shape of a disc and comprises at least two sections around which the at least two coils are wound.

7. A coil structure for wireless power transfer comprising:

a ferrite core having a plurality of arms and a geometric center; and

a coil wound around each of the plurality of arms of the ferrite core, the plurality of coils spaced symmetrically about the geometric center of the ferrite core,

wherein each of the plurality of coils is wound in such a way that when a first current flows in a first spatial direction in one of the plurality of coils a second current flows in a second spatial direction in another one of the plurality of coils, where the second spatial direction is opposite to the first spatial direction.

8. The coil structure of claim 7 , wherein the plurality of coils are coupled together in series and the first current has the same magnitude as the second current.

9. The coil structure of claim 7 , wherein the ferrite core has a shape of one of a parallelepiped, a circular cylinder, and an elliptic cylinder.

10. The coil structure of claim 7 , where the ferrite core comprises a plurality of arms arranged symmetrically around the geometric center of the ferrite core.

11. A coil structure for wireless power transfer comprising:

a ferrite core;

at least two coils wound around the ferrite core, the at least two coils arranged symmetrically about a geometric center of the ferrite core and coupled together in series,

the at least two coils wound in such a way that when a first current flows in a first spatial direction in one of the at least two coils a second current flows in a second spatial direction in the other one of the at least two coils, the second spatial direction being opposite to the first spatial direction; and

a third coil wound around the ferrite core.

12. The coil structure of claim 11 , wherein windings of the third coil at least partially overlap with windings of each of the at least two coils.

13. The coil structure of claim 11 , wherein the third coil is coupled in series with the at least two coils.

14. The coil structure of claim 11 , wherein the ferrite core has a shape of one of a parallelepiped, a circular cylinder, and an elliptic cylinder.

15. The coil structure of claim 11 , where the ferrite core comprises a plurality of arms arranged symmetrically around the geometric center of the ferrite core.