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Wireless power transfer (WPT) is a promising charging method without physical contact for the electronic products energy supply. However, low transfer efficiency, short transmission distance, as well as the electromagnetic (EM) leakage are commonly main bottlenecks of the WPT technology in the practical applications. The electromagnetic metamaterials (EMMMs) used in WPT system have opened up a brand-new approach for better transfer properties and EM shielding. This paper is intended to provide an overview of the current studies and breakthroughs of the WPT system based on EMMMs. First, we demonstrate the fundamentals of the WPT based on the magnetic resonant coupling. Then, various key considerations of the EMMMs, such as working mechanisms, fabrications have been taken into accounted in detail. Moreover, the applications of EMMM in WPT systems are elaborated. Finally, the technical challenges in connection with working frequency and design miniaturization are investigated in this paper. This novel interdisciplinary technology shows important meanings on the extensive application of energy transmission in the future.

In a wireless power transfer (WPT) system, the power transfer efficiency (PTE) decreases sharply with the increase in transfer distance. Metamaterials (MMs) have shown great potential to enhance PTE in mid-range WPT systems. In this paper, we propose two MM slabs of a 3 × 3 array to enhance the magnetic coupling. The MM unit cell was designed by using square spiral patterns on a thin printed circuit board (PCB). Moreover, the asymmetric four-coil WPT system was designed and built based on the practical application scenario of wireless charging for unmanned devices. The simulation and experimental results show that two MM slabs can enhance power transmission capability better than one MM slab. By optimizing the position and spacing of two MM slabs, the PTE was significantly improved at a mid-range distance. The measured PTEs of a system with two MM slabs can reach 72.05%, 64.33% and 49.63% at transfer distances of 80, 100 and 120 cm. When the transfer distance is 100 cm, the PTE of a system with MMs is 33.83% higher than that without MMs. Furthermore, the receiving and load coils were integrated, and the effect of coil offset on PTE was studied.

Wireless power transfer (WPT) technology offers a potential solution for the energy-supply problem. In this paper, we propose a novel magnetic coupling mechanism for omnidirectional and multiplepickup energy transfer based on the magnetic dipole coils. Firstly, a cubic transmitter structure capable of generating three-dimension (3D) homogeneous magnetic field is fabricated to weaken directional sensitivity of receiving coil. Furthermore, the direction of current flowing through each dipole coil is also studied in detail. Numerical and simulated analysis is implemented to verify the omnidirectionality of the transmitter. Secondly, the equivalent circuit model for WPT systems with ferrite is analyzed. In addition, optimal loads, power distribution and transfer efficiency for multiple receivers are discussed and used to achieve the proper system design. Finally, experimental prototype is set up to validate the transmission performance of the proposed WPT system. The results have showed that genuine 3D high degree of freedom (DoF) can be achieved. Meantime, above 60% efficiency at least 30 W of total output power can be obtained for WPT systems with eight pick-ups. We believe the proposed system will give a new guideline for future low power electronic applications, such as monitoring sensors, miniature robots and household devices.

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