Rectifying loose coils: Wireless power transfer in loosely coupled inductive links with lateral and angular misalignment

This article presents novel analytic solutions to the problem of predicting the power transfer efficiency between lateral and angularly misaligned solenoidal coils. Inductive coupling is extensively used as a method of wireless powering and offers significant advantages over wired powering schemes. However, coil misalignment is an inherent problem that can significantly impair the power transfer efficiency of such systems. This article describes a novel analytical derivation for the near field power transfer efficiency of loosely coupled inductive links under lateral and angular coil misalignment. The analytical power transfer expressions given show good agreement with experimental data. The advantage of this approach lies in the fact that the effect on the link efficiency of variation of a specific parameter in the model can quickly be identified. This model can predict the response of the system under misalignment conditions, with different coil geometries, and operating frequencies without the need for repeated and costly simulation runs. This allows a designer to create a model of a WPT system with a mathematical package such as Mathcad to explore “what if?” situations. The approach taken in this article can be extended to other coil geometries such a circular flat spirals and square flat spirals to obtain modified versions of (13) and (17), [18], [19].