Design of a Low-Frequency Magnetic Metasurface for Extremely Focused and Long Range Wireless Power Transfer Applications

An efficient methodology to design low-frequency metasurfaces for resonant inductive WPT applications able to extremely focus the magnetic field distribution at large distances from the source is presented. The proposed approach consists of two phases. First, the optimal distribution of currents on the metasurface realizing the desired magnetic field hotspot is analytically defined. In this phase, the metasurface is considered to be composed of a planar distribution of ideal loops. Subsequently, from the ideal loops, the corresponding real-scenario copper spiral unit-cells are designed. In particular, attention must be directed to consider the effect of losses that can deviate the behavior from the ideal case. Thus, the number of turns of the copper unit-cell which allows it to be treated as an almost imaginary self-impedance, neglecting the losses, is determined. To verify the methodology, we conceived a numerical test-case by designing a 5×5 metasurface with overall size of 20 cm ×20 cm, opportunely excited by an actively fed driving coil placed 50 mm below it. The obtained results at 4 MHz proved that a 40 mm diameter magnetic field beam was created between the plane of the metasurface and a point set 10 cm above the driver. Notably, the extreme focusing properties are achieved with any means of guiding structure and the volume around the system consists exclusively of air.