Multi-Layered Frequency Selective Surfaces for Magnetic Field Shielding in Megahertz Wireless Power Transfer Systems

As the research paradigm of wireless power transfer (WPT) shifts towards the megahertz (MHz) range, the pronounced hysteresis and eddy current losses within ferromagnetic materials at these frequencies renders existing magnetic shielding techniques neither efficient nor effective. To address this challenging issue, we propose a novel multi-layered frequency selective surface (FSS) magnetic field shielding structure suitable for MHz WPT applications. This design method incorporates multiple FSS layers, each precisely tuned to the fundamental or harmonics of the inverter. By blocking these frequencies, the structure can effectively shield the magnetic fields emitted by wireless power resonators. As an example, a triple-layered FSS (TFSS) is designed and analyzed by conducting full-wave simulation and equivalent circuit model calculation, which operates at the fundamental frequency of 6.78 MHz and two harmonic frequencies. Based on finite element simulation and experimental measurements, the proposed TFSS shield is verified in a 6.78 MHz WPT system. As a result, the TFSS shield strongly suppresses magnetic field leakage (attenuation of about 13.4 dB) with only slight impact on the transfer efficiency of the WPT system (reduction about 1.11% and 2.2% for the WPT system with transmission distances of 1 cm and 10 cm, respectively).

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