Patent ID: 7525283

Claim:
A primary unit for use in a power transfer system having a power transfer surface shaped and arranged such that a secondary device, separable from the primary unit, can be placed in a working disposition on or in proximity to a power transfer area of the surface to receive power from the primary unit without requiring direct electrical conductive contacts between the primary unit and the secondary device, the primary unit comprising: an AC power source; a field generator electrically coupled to the AC power source, the field generator having a plurality of substantially coplanar conductive elements arranged at or beneath the power transfer surface in a generating area, which elements extend generally in parallel with one another across said generating area, and which generate an electromagnetic field distributed across the power transfer area, wherein the conductive elements have a mutual spacing sufficiently small that the secondary device overlaps two or more of the conductive elements when in its said working disposition, and the respective instantaneous currents which flow simultaneously through all the conductive elements in said generating area have the same general direction.