Using shifting layer to shift and expand coils in a wireless power transfer system

In previous work, we have proposed a cone-shaped shifting medium shell that can shift the enclosed region forward to a given position. The shifting shell is a metamaterial device proposed according to transformation optics. It can be applied in a wireless power transfer system by covering the coils to move them closer in magnetic field and enhance the mutual inductance between the coils. However, the shifting shell is kind of bulky to enclose the whole coil. In this paper, we propose another application of the shifting medium - to enclose the cross-section of the coil with the shifting layer. In this way, the coil is not only shifted but also expanded so that the magnetic coupling could be enhanced to a larger extent. Moreover, the shifting layer is more compact than shifting shell.