In this paper, a wideband 1-bit 12×12 reconfigurable beam-scanning reflectarray is designed, fabricated, and measured. The 1-bit reconfigurable element is realized by soldering PIN diode into a slotted metallic square patch. To enhance the bandwidth of 1-bit reconfigurable reflectarray, we choose the central frequency at 5.0 GHz whose phase shift is 200° where the maximum phase shift occurs. Phase difference within 180°± 20° is realized from 4.7 GHz to 5.3 GHz. Utilizing this wideband element, the 12 × 12 reconfigurable reflectarray antenna is fabricated and measured. A control board which can display phase shift distributions in real-time is designed to regulate all PIN diodes independently. Experimental results show that beam-scanning within ±50° can be achieved both in xoz- and yoz-plane at 5.0 GHz. Also, the measured results present that -1dB gain bandwidth is 8.4% from 4.85 GHz to 5.275 GHz.

This paper presents a new design of near-field focused metasurface for high-efficiency wireless power transfer with multi-focus characteristics. A general synthesis procedure is outlined to design metasurfaces with desired multiple foci in the near-field zone. The unit cell of printed tri-dipole is used to realize the focused metasurface which has a large range of phase shift and is adapted to near-field focusing applications. Different feeding and focusing designs of the printed tri-dipole metasurfaces are proposed and analyzed. Two kinds of metasurfaces with 20-20 elements are designed, fabricated and measured at 5.8 GHz. One is the single-feed and single-focus case, and the other is single-feed and two-focus case. Two-dimensional planar near-field scanning technique is implemented to measure the E-field focusing characteristics. Full-wave simulations and experiments demonstrate that the proposed focusing metasurfaces have a high wireless power transfer efficiency of 70%. The relative bandwidth with 50% power focusing efficiency is about 16%. The measured results are in good agreement with the theoretical designs and simulated results, which verify the feasibility and correctness of the proposed approach in this paper.

A comprehensive review of metamaterials and metasurfaces for wireless power transfer (WPT) and wireless energy harvesting (WEH) is presented in this article. According to the features of the electromagnetic field from the source to the receiver, WPT is divided into nonradiative near-field technology and radiative (near and far-field) technologies. Many different and important designs are reviewed and compared. It is shown that metamaterials and metasurfaces can significantly improve the power transfer efficiency and operational distance for WPT systems. They can also improve the energy conversion efficiency of wireless energy harvesters by making the reception less sensitive to incident wave angle and polarization. A rectenna is a critical element for both WPT and WEH. It is shown that metamaterial-based rectennas can achieve a higher RF to dc conversion efficiency. Furthermore, metamaterials can also be used as either parasitic elements or loading components to improve WEH performance in terms of circuit size, beamwidth, and conversion efficiency. Future development directions and opportunities of metamaterials and metasurfaces for WPT and WEH are also proposed in this article.

Wireless power transfer (WPT) is a key technique for many existing and emerging applications in biomedical devices. This paper presents a novel implantable magnetic coupling resonate WPT system by integrating with metasurface for biological applications. The receiver element is implanted under the skin surface 3 mm and has the dual-band property for transferring power and data telemetry simultaneously. A conformal strongly coupled magnetic resonator coil is used as the transmitting coil to construct the wireless power link. In addition, we integrate the proposed WPT system with negative permeability (MNG) metasurface over the human skin surface as a miniaturized wearable device to improve the WPT efficiency. The property of the MNG and its effect on the WPT efficiency are analyzed. Considering the special implantable environment, various misalignment tolerances between the metasurface and the receiver are discussed to evaluate the coupling response of the proposed WPT system. Finally, the efficient WPT system integrating with MNG has been verified by the experimental measurements, and the measured result shows that 15.7 dB coupling enhancement can be obtained by integrating with the MNG metasurface.

A dual-band and polarization-angle-independent rectifying metasurface (MS) with a miniaturized dimension and a wide incident angle range are presented in this article. The proposed structure consists of a single layer of periodic cell arrays with integrated diodes, a dc feed, and a load. A novel method of incorporating surface-mount components (e.g., diodes) into the texture is developed to simplify the structure. The matching network between MS and the nonlinear rectifier can be eliminated directly due to the multimode resonance and adjustable high-impedance characteristics of the MS. Moreover, the proposed MS can maintain high conversion efficiency by using different diodes without changing the overall topology. In addition, the proposed design can effectively capture incoming waves with arbitrary polarizations and a wide incident angle range of 60°. The 4 × 4 MS array is fabricated and measured. Experimental results show that the proposed structure can achieve maximum efficiency of 58% at 2.4 GHz and 50% at 5.8 GHz with an input power of 0 dBm under different polarizations and incident angles. Importantly, it is also shown that the rectifying MS can maintain high efficiency over a wide power range from -3 to 10 dBm. The proposed design concept is very suitable for the adaptive wireless power supply of portable devices.

An adaptively smart wireless power transfer (WPT) system is proposed by using a 2-bit programmable metasurface (PMS), in which an indoor dynamic charging application scenario is described and near-field focused (NFF) technique is adopted to transmit wireless powers. Theoretical analyses of NFF PMS are presented to illustrate its WPT capabilities. To implement dynamic WPTs, digital phase-shift quantization of PMS element is investigated, indicating that 2-bit quantization scheme is a preferred solution. As experimental demonstrations, a 2-bit 12 × 12 PMS operating at 5.8 GHz is designed, fabricated, and tested. High-power focal spots that can be regulated to focus at different near-field positions are measured in an anechoic chamber. We conduct multiple WPT experiments by using the 2-bit PMS as the transmitter and a 4 × 4 microstrip array antenna as the receiver. Experimental results show that the proposed 2-bit PMS can continuously transmit the wireless powers to the receiver even though the target is moving, and the WPT efficiency is maintained over 9.1%, which has about 16.3 dB improvement at the end of the trajectory compared to the fixed NFF beam. This work is one of the first attempts to thoroughly examine the possibility of the dynamic WPTs using PMS, offering a brand-new manner for the adaptively smart WPT systems.