Magnetic shield
A magnetic shield for shielding adjacent coils of an ICPT system. One or more conductors are configured to distribute induced eddy currents from the surface of the shield to below the surface and thus reduce heating due to eddy currents. The magnetic shield may be employed to transfer power over rotary couplings, such as the shaft of a wind turbine.
1. An ICPT system including a transmitting coil and a receiving coil wherein at least one coil is at least partly shielded by a magnetic shield formed of one or more conductors wherein the shield has a surface which in use is exposed to an incident magnetic field wherein the one or more conductors undulate towards and away from the surface so as to distribute currents induced in portions of the one or more conductors at the surface of the shield to portions of the one or more conductors away from the surface of the shield.
2. An ICPT system as claimed in claim 1 wherein the one or more conductors undulate from a depth within about one skin depth from the surface to greater than one skin depth below the surface.
3. An ICPT system as claimed in claim 1 wherein the one or more conductors are elongate conductors.
4. An ICPT system as claimed in claim 3 wherein the one or more conductors are arranged to distribute the eddy currents along a path length that is long with respect to the size of the shield.
5. An ICPT system as claimed in claim 1 wherein the one or more conductors have an average thickness of about 1 to 3 skin depths in a plane transverse to the surface cross section.
6. An ICPT system as claimed in claim 1 wherein the conductors are arranged in a generally circular path.
7. An ICPT system as claimed in claim 1 wherein the conductors are arranged in a generally spiral path.
8. An ICPT system as claimed in claim 1 wherein the conductors are arranged in a semicircle.
9. An ICPT system as claimed in claim 1 wherein the conductors are arranged in a curved sheet.
10. An ICPT system as claimed in claim 1 wherein the one or more conductors are formed of Litz wire.
11. An ICPT system as claimed in claim 1 wherein the one or more conductors are capacitively loaded.
12. An ICPT system as claimed in claim 1 wherein the one or more conductors are inductively loaded.
13. An ICPT system as claimed in claim 1 wherein the magnetic shield is tuned to screen a magnetic field oscillating at a desired frequency.
14. An ICPT system as claimed in claim 1 in the form of a disc.
15. An ICPT system as claimed in claim 1 , wherein the at least one coil is at least partly shielded from its surrounds.
16. An ICPT system as claimed in claim 15 , wherein the at least one coil is at least partly shielded from surrounding metallic elements.
17. An ICPT systems as claimed in claim 16 , wherein the at least one coil is at least partly shielded from an adjacent coil.
18. A wind turbine including an ICPT system as claimed in claim 1 .