Geometry optimization of sliding inductive links for position-independent wireless power transfer

In this paper we describe a geometry design solution to minimize performance variations of a wireless power transfer system on the move (WPT-Mob). A sequence of switchable couples of coils, connected in series or in parallel, is adopted at the fixed transmitting link side; the geometry of the moving receiver is optimized to keep the coupling factor, and thus the power transfer, constant during the movement. First the analytical formulation of the link coupling factor is derived as a function of its circuit-equivalent parameters computed by full-wave simulation. Then selected geometry parameters of the receiver side are optimized to keep the coupling factor constant while the link is moving. A set of TX-RX arrangements are simultaneously analysed to emulate the sliding movement of the WPT-Mob. The final optimized geometry demonstrates that a constant power transfer on-the-move is enabled, even for variable TX-to-RX link distances. Design and experimental verification are carried out for a geometry suitable for medium power transfer (tens of Watts) at 6.78 MHz, but the method is formulated in such a way that the system can be scaled up and down to accomplish different application needs.