Coil design for improved power transfer efficiency in inductive links

The coupling coefficient of two magnetically coupled coils can be considerably enhanced, if the turns of the coils are not concentrated at the coils circumferences, but distributed across the radii of the coils. However, such a distribution of turns results in a reduction of the unloaded quality factors of the coils. If the coupled coils are used within an inductive link system for transcutaneous power transfer, enhancement of the coupling coefficient improves the efficiency of power transfer, while the reduction of unloaded quality factors caused by the suggested pattern of coil distribution reduces efficiency. In spite of this loss of efficiency, it is possible to design coils allowing a net gain in the efficiency of power transfer.