Patent ID: 7714537

Claim:
A system for transferring power without requiring direct electrical conductive contacts, the system comprising: a power transfer surface shaped and arranged such that a secondary device can be placed in a working disposition on or in proximity to a power transfer area of the surface to receive power when the system is in use; a primary unit having a field generating means for generating an electromagnetic field distributed over the power transfer area; and a secondary device separable from the primary unit and having an inductive coupling circuit which is arranged to couple with the electromagnetic field generated by the primary unit when the secondary device is in its said working disposition, said coupling circuit being adapted to couple primarily with field lines of the field that are generally parallel to the power transfer surface; wherein the field generating means comprises a spiral coil arranged generally parallel to the power transfer surface at or beneath the power transfer area; and when the secondary device is in its said working disposition the inductive coupling circuit extends over a plurality of radially-spaced portions of the spiral coil, the part of the power transfer area over which the inductive coupling means extends being sufficiently small, relative to the coil, that within said part said coil portions extend generally in parallel with one another in one general direction.