Metasurface-Based Wireless Power Transfer System

Wireless power transfer (WPT) technology, originally proposed by Nikola Tesla, has regained prominence and garnered significant attention in academia and industry in recent years. WPT can generally be categorized into magnetic induction and magnetic coupling resonances (MCRs) for short-distance applications (typically less than 1 m), and microwave or laser radiation for long-distance applications (typically greater than 1 m). However, there remains a crucial challenge in improving the transmission distance and efficiency of WPT systems. Fortunately, metasurfaces (MSs) offer a promising solution to address these issues. This chapter introduces two metasurface-based WPT systems, namely a magnetic coupling resonance WPT system and a microwave radiation WPT system. In the first system, highly sub-wavelength magnetic negative (MNG) metasurfaces and double negative (DNG) metasurfaces are designed and integrated into the WPT system to enhance its efficiency. The tunneling effect of equivalent epsilon-near-zero (ENZ) metamaterials in the MCR-WPT system is uncovered, and a theoretical analysis using the effective medium model is proposed to study the WPT behavior. In the second system, a general synthesis procedure is outlined to design a reflective metasurface that enables high-efficiency WPT through near-field focusing, while accommodating desired multi-feed and multi-focus characteristics. Leveraging metasurface element design and phase synthesis techniques, the planar reflective metasurface controls the transmission of electromagnetic waves from specific sources, enabling the formation of near-field focusing beams towards desired destinations in the near-field region. This achieves wireless power multi-feed synthesis and multi-focus allocation with high efficiency. Two element structures are introduced to form arrays: the tri-dipole structure with single-polarization characteristics and the cross-dipole structure with dual-polarization characteristics. Several metasurface prototypes are designed, fabricated, and experimentally measured for various scenarios. The stability and feasibility of the near-field focusing reflective metasurface for practical WPT applications are demonstrated through analysis and comparison of measured results with simulation data.