Patent ID: 7863861

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 the surface to receive power when the system is in use; a primary unit having a field generating means, distributed in two dimensions across a generating area at or substantially parallel to said power transfer surface, for generating an electromagnetic field over a power transfer area of said surface within which area the secondary device can couple flux effectively when in its said working disposition and which area is not substantially smaller than said generating area; and a secondary device separable from the primary unit and including at least one electrical conductor with which the electromagnetic field generated by the field generating means couples with and induces a current to flow in the conductor when the secondary device is in said working disposition; wherein the field generating means is configured such that, when a predetermined current is supplied thereto and the primary unit is effectively in electromagnetic isolation, field lines of the electromagnetic field generated by the field generating means are distributed in two dimensions over said power transfer area and, when considering the angles subtended by the field lines to a measurement plane that is parallel to the power transfer surface and is at the same distance therefrom as the secondary device when that device is in its said working disposition, an average of said angles over any quarter length part of said power transfer area, measured parallel to the direction of the field lines, is 45Â° or less.