Wireless power transfer pad with multiple windings and magnetic pathway between windings

1. A wireless power transfer (“WPT”) pad apparatus comprising:

a ferrite structure; and

four windings adjacent to the ferrite structure,

wherein for adjacent windings of the four windings, the ferrite structure comprises a magnetic pathway, and

wherein a ferrite pathway between adjacent windings of the four windings comprises a thickness and a width to provide a low impedance, unsaturated magnetic pathway for an electromagnetic field generated by the adjacent windings, wherein a horizontal surface of the ferrite structure is adjacent to each of the four windings, each of the four windings wound in a horizontal pattern that is planar to the horizontal surface, wherein the four windings are arranged in a two-by-two square pattern in a north-south-north-south polarity arrangement,

and wherein the ferrite structure comprises an opening in a center section, wherein the center section is located at a center of the two-by-two square pattern and the center section is external to each of the four windings.

2. The WPT pad apparatus of claim 1 , further comprising a vertical shield external to the ferrite structure positioned to shunt an electromagnetic field radiating in a direction horizontal with the horizontal surface of the ferrite structure.

3. The WPT pad apparatus of claim 2 , wherein the vertical shield comprises a metallic structure oriented transverse to the horizontal surface of the ferrite structure.

4. The WPT pad apparatus of claim 2 , wherein the vertical shield comprises a width, the width measured in a direction transverse to the horizontal surface of the ferrite structure, wherein the width comprises at least a thickness of an edge of the ferrite structure and a thickness of the winding.

5. The WPT pad apparatus of claim 2 , wherein the vertical shield comprises an opening at each corner of the ferrite structure.

6. The WPT pad apparatus of claim 1 , wherein the horizontal surface comprises a first horizontal surface and further comprising a horizontal shield positioned on a second horizontal surface of the ferrite structure, the second horizontal surface distal to the first horizontal surface and planar with the first horizontal surface.

7. The WPT pad apparatus of claim 6 , wherein the horizontal shield comprises metallic plate and the horizontal shield reduces a strength of an electromagnetic field generated by the four windings and radiating through the horizontal shield to below a specified limit.

8. The WPT pad apparatus of claim 6 , wherein the ferrite structure is thermally coupled to the horizontal shield, wherein heat generated in each of the four windings and in the ferrite structure is transmitted to the horizontal shield.

9. The WPT pad apparatus of claim 6 , further comprising a vertical shield external to the ferrite structure, the vertical shield coupled to the horizontal shield and extending in a direction transverse to the horizontal shield in a direction of the ferrite structure and the four windings.

10. The WPT pad apparatus of claim 1 , wherein each of the four windings comprises a spiral pattern starting at an edge of a winding center section and expanding away from the center section, the center section comprising an area without conductors at a center of a winding.

11. The WPT pad apparatus of claim 10 , wherein each winding of the four windings comprises two or more winding sections wound in parallel, and each winding section is connected to a capacitor located at the center section of the winding.

12. The WPT pad apparatus of claim 10 , wherein the center section of each winding comprises a ferrite chimney coupled to a horizontal surface of the ferrite structure and extending in a direction transverse to the horizontal surface at least a thickness of the winding associated with the center section.

13. The WPT pad apparatus of claim 1 , wherein each of the four windings comprises a conductor, each conductor comprises multiple strands, the strands electrically isolated from each other, the conductor comprising a wide side and a narrow side, wherein the wide side of the conductor is oriented transverse to the horizontal surface.

14. The WPT pad apparatus of claim 13 , wherein the conductor is a litz wire.

15. A wireless power transfer (“WPT”) pad apparatus comprising:

a ferrite structure; and

four windings adjacent to the ferrite structure, wherein the four windings are arranged in a two-by-two square pattern in a north-south-north-south polarity arrangement,

wherein for adjacent windings of the four windings, the ferrite structure comprises a magnetic pathway,

wherein a ferrite pathway between adjacent windings of the four windings comprises a thickness and a width to provide a low impedance, unsaturated magnetic pathway for an electromagnetic field generated by the adjacent windings, and

wherein the ferrite structure comprises an opening in a center section, wherein the center section is located at a center of the two-by-two square pattern and the center section is external to each of the four windings.

16. The WPT pad apparatus of claim 15 , wherein a horizontal surface of the ferrite structure is adjacent to each of the four windings, each of the four windings wound in a horizontal pattern that is planar to the horizontal surface,

wherein the WPT pad apparatus further comprising one or more of:

a vertical shield external to the ferrite structure positioned to shunt an electromagnetic field radiating in a direction horizontal with the horizontal surface of the ferrite structure; and

a ferrite chimney coupled to the horizontal surface of the ferrite structure in the center section of each winding and extending in a direction transverse to the horizontal surface at least a thickness of the winding associated with the center section.

17. A wireless power transfer (“WPT”) system comprising:

a first stage comprising one or more of a resonant converter and an alternating current (“AC”) to direct current (“DC”) converter, the first stage configured to wirelessly transmit power to a second stage on a vehicle;

a WPT pad apparatus that receives power from the first stage and transmits power wirelessly to a secondary pad of the second stage, the WPT pad apparatus comprising:

a ferrite structure; and

four windings adjacent to the ferrite structure,

wherein for adjacent windings of the four windings, the ferrite structure comprises a magnetic pathway,

wherein a ferrite pathway between adjacent windings of the four windings comprises a thickness and a width to provide a low impedance, unsaturated magnetic pathway for an electromagnetic field generated by the adjacent windings, wherein a horizontal surface of the ferrite structure is adjacent to each of the four windings, each of the four windings wound in a horizontal pattern that is planar to the horizontal surface, wherein the four windings are arranged in a two-by-two square pattern in a north-south-north-south polarity arrangement,

and wherein the ferrite structure comprises an opening in a center section, wherein the center section is located at a center of the two-by-two square pattern and the center section is external to each of the four windings.