A Novel Equivalent Parameter Extraction Method of Cross-Frequency Metasurface for WPT System

The application of metasurface in wireless power transfer (WPT) systems has attracted great attention due to its excellent properties. However, most studies focus on single-frequency transmission of energy (generally MHz-band frequency), while the operating frequency of most WPT systems is the kHz band. In this letter, a cross-frequency (both kHz and MHz bands) metasurface cell for the WPT system is designed, and an equivalent permeability extraction method is proposed for the first time. Firstly, a double-layer nested structure with two different helical coils is utilized to enable the metasurface cell to obtain two different resonant frequencies. Secondly, the equivalent circuit of this metasurface cell is established, and a detailed theoretical analysis of equivalent relative permeability is derived for cross-frequency metasurface unit cells. Finally, the precise prototype of a unit cell is designed. The experimental results agree well with the theoretical ones. This work paves the way for a dual-frequency band WPT system based on metasurface. Particularly, it provides a good preparation for the application of cross-frequency metasurface to realize simultaneous wireless power and data transfer in WPT system.