Coupling factor of planar power coils used in contactless power transfer

Contactless power transfer is a major concern due to its many applications in the modern technique. Different topologies for transmission in near field (magnetic or electric) are presented in literature, with emphasis on the process efficiency, especially when such systems are used for medium or high powers, like those needed for charging the storage batteries from electric/hybrid cars. One of the key elements of the system that provides the contactless magnetic inductive coupling between the power source and user, herein after referred to as inductive coupler, is analyzed in this paper. For reasons of space, this is usually an air-core transformer, with planar, movable windings, for easy adaptation to the conditions of using it. In order to indentify rapidly its parameters, the automatic determination of the transfer function by a vector network analyzer (VNA), apparatus currently used in laboratories, is utilized in this paper. No previous measurement is required.