Wireless power transfer (WPT) is a technology that enables energy transmission without physical contact, utilizing magnetic and electric fields as soft media. While WPT has numerous applications, the increasing power transfer distance often results in a decrease in transmission efficiency, as well as the urgent need for addressing safety concerns. Metamaterials offer a promising way for improving efficiency and reducing the flux density in WPT systems. This paper provides an overview of the current status and technical challenges of metamaterial-based WPT systems. The basic principles of magnetic coupling resonant wireless power transfer (MCR-WPT) are presented, followed by a detailed description of the metamaterial design theory and its application in WPT. The paper then reviews the metamaterial-based wireless energy transmission system from three perspectives: transmission efficiency, misalignment tolerance, and electromagnetic shielding. Finally, the paper summarizes the development trends and technical challenges of metamaterial-based WPT systems.

Wireless power transfer (WPT) systems have been hamstrung by modest energy efficiencies and electromagnetic safety concerns. Conventional electromagnetic shielding devices can reduce the electromagnetic interference (EMI) to the ambient environment but at the same time deteriorate the transfer performance. In this article, a novel hybrid resonance optimization-based passive shielding magnetic structure and the corresponding circuit are proposed. The shielding structure and topological network have the advantage of minimizing electromagnetic fields (EMFs) around the system while guaranteeing transfer performance (PTE, G_V, P_OUT, phase relation) constant. Moreover, a multiobjective genetic algorithm is utilized to optimize the shielded directional coils (SDCs) parameters in consideration of the transfer efficiency, EMF, and shielding structure volume. Finally, a reasonable prototype of the proposed WPT system is designed, fabricated, and tested. Experimental results show that the maximum leakage EMF level in the evaluated area is reduced by 4.18 dBmV (nearly 39.5 µT). Additionally, the PTE changes by only 1.5%, the G_V changes by just 9.5%, and the phase relationship remains unaffected under the 80 W output power condition. The presented solution merges design approach, compensation network, and optimization plan. It can be further extended to analyze arrays of arbitrary order and shielding in different orientations, providing useful insights for smart homes.

The application of metasurface in wireless power transfer (WPT) system has attracted great attention due to its excellent properties. However, most studies focus on singlefrequency transmission of energy (generally MHz-band frequency), while the operating frequency of most WPT systems is kHz band. In this letter, a cross-frequency (both kHz and MHz bands) metasurface cell for WPT system is designed and 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 detailed theoretical analysis of equivalent relative permeability is derived for cross-frequency metasurface unit cell. Finally, the precise prototype of unit cell is designed. The experimental results agree well with the theoretical ones. This work paves the way to 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

Metasurface provides a promising solution to address the efficiency-distance-safety challenges in magnetic coupling resonant wireless power transfer (MCR-WPT) systems through subwavelength electromagnetic field manipulation. Current research primarily focuses on single-frequency operation or mostly MHz-band applications. It lacks theoretical and simulated studies of kHz band, let alone the cross-frequency band (both kHz and MHz simultaneously). In this article, a cross-frequency metasurface in the MCR-WPT system has been proposed. First, an equivalent circuit model of a cross-frequency metasurface has been derived. Then, EMF analysis of WPT system based on the cross-frequency metasurface has been presented. Particularly, an improved dual-population cooperative evolutionary algorithm has been employed to optimize both cross-frequency mu-negative (CF-MNG) and cross-frequency mu-near-zero (CF-MNZ) metasurfaces. Finally, the cross-frequency metasurface exhibits excellent performance on efficiency improvement and EMF leakage reduction in MCR-WPT system. The system with CF-MNG loading achieved nearly double the transfer efficiency at both 350 kHz and 6.78 MHz frequencies. Additionally, the decline of leakage electromagnetic field (EMF) with CF-MNZ metasurface can reach up to 2.42 and 6.51 dB at two frequencies, respectively. Therefore, this article not only provides significant guidance for low-frequency metasurface design but also offers potential for future applications in simultaneous power and information transfer systems.

Concrete embedded sensors play a very important role in structural health monitoring. However, the time of endurance of sensors remains a performance bottleneck and sensors need to be charged without damaging the structure as well. Wireless power transfer (WPT) technology is a promising approach to solving this problem. However, the electromagnetic characteristics of concrete medium can cause WPT systems to be untuned and can reduce the energy transmission efficiency of the system. In this paper, the induced medium loss and eddy current loss of a WPT system in concrete are calculated using analytical equations and finite element analysis method. The equivalent circuit model of a concrete–air transmedia WPT system is established according to the calculated losses and a composite tuning control technology is proposed based on the above analysis. In addition, the composite tuning control technology combines the advantages of frequency-modulation tuning and dynamic compensation tuning to ensure the overall resonance of the WPT system. The tuning control technology can ensure the whole resonance of the WPT system and make the natural resonant frequencies of primary and secondary sides consistent. The experimental results show that compared with the untuned control technology, the output power and efficiency of the tuned control system increased by 73% and 11.05%, respectively. The proposed tuning control technology provides direction for future charging of concrete-embedded sensors.