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 miniaturized implantable antenna with bandwidth enhancement is proposed for cardiac pacemaker application in MICS band (402-405 MHz) and ISM band (433-434.8 MHz, 902-928 MHz) in this paper. By introducing split resonant rings, the proposed antenna has achieved ultra-wideband characteristics, which can cover from 272 MHz to 1504 MHz, and the relative bandwidth is 138.7%. Additionally, a new wireless power transfer (WPT) system is designed by integrating with a miniaturized metasurface to enhance the WPT efficiency and extend the lifetime of the implantable device. The transmission coefficient S21 of the WPT system loaded with metasurface is 11 dB higher than the initial system at the resonance point. Furthermore, biosafety is taken into consideration for practical applications. The experiments in the equivalent body environment are performed to demonstrate the reliability of the proposed antenna. The measured and simulated results are in good agreement, which shows that the proposed antenna is appropriate to be applied in wireless body area network communication and power transfer systems simultaneously.

A new wide-angle and polarization-insensitive metasurface (MS) instead of traditional antenna is built as the primary ambient energy harvester in this paper. The MS is a two-dimensional energy harvesting array that is composed of subwavelength electrical small ring resonator that is working at 2.5 GHz (LTE/WiFi). In the case of different polarization and incidence angles, we demonstrate the metasurface can achieve high harvesting efficiency of 90%. The fabricated prototype of 9 × 9 MS energy harvesting array is measured, and the experimental results validate that the proposed MS has a good performance more than 80% of energy harvesting efficiency for arbitrary polarization and wide-angle incident waves. The good agreement of the simulation with the experiment results verifies the practicability and effectiveness of the proposed MS structure, which will provide a new source of supply in wireless sensor networks (WSN).

Aiming at the critical problem of wireless power transfer (WPT) for the current growing number of wireless devices, the multitarget WPT system based on metasurface-holography multifocal beams and the design methods is investigated and analyzed in this article. As the propagator in near-field synthesis, a new field calculation formula is derived based on the Friis formula between the metasurface unit (MU) and the field point, which breaks the limitation of paraxial approximation and makes metasurface holography applicable in a wide-angle, long-distance, and nonplane space. Besides the phase response of MUs, the amplitude response is also introduced, which achieves the simultaneous amplitude–phase optimization of the metasurface to improve transmission efficiency. A metasurface with holography multifocal beams is first designed and engaged in forming a planar multitarget WPT system, which has been proven to radiate the designed multifocal beam and transfer power to each focal spot uniformly and efficiently after simulated, fabricated, and measured. To verify that the proposed method can achieve a near-field synthesis of multifocal beams in nonplane space over a wide angular range, a metasurface with 23-focus beam distribution on a spherical surface with an elevation angle from $-$ 60 $^{\circ}$ to 60 $^{\circ}$ , omnidirectional azimuth, and 66.67 $\uplambda $ radius is designed and simulated, which shows that the simulated radiation field distribution is in good agreement with the initial preset target field. This work demonstrates a feasible high-efficiency and long-distance WPT strategy for multiple targets in wide-angle and spatial scenarios.

Breathing is an important health metric for tracking diseases, and non-contact respiration detection under multitarget scenarios has attracted wide attention in recent years. However, conventional solutions are difficult to achieve breathing separation when people sit closely or sleep together sharing the same bed, otherwise complex hardware system is required. In this context, this article proposes MetaBreath: a multitarget and high-resolution respiration detection method based on space-time-coding (STC) digital metasurface. To design MetaBreath, we fully explore the harmonics generated by STC digital metasurface, and these harmonics are equivalent to the multiple virtual sensor nodes evenly distributed in different directions, making the observations more comprehensive. Then we model respiration detection as the problem of blind source separation (BSS) when people are close to each other, and solve it by the technique of independent component analysis (ICA). Experiments show that MetaBreath enables respiration detection and separation whether people sit apart or close together, which is reflected in the recovered waveform keeping consistent with ground truth. Besides, for the first time, we realize up to four-person detection in this single-input single-output (SISO) system, which is outperforming the state-of-the-art methods. With both low complexity and high practicality, MetaBreath is expected to apply to sleeping monitoring, life detection, and baby care.

We present a wideband 1-bit reconfigurable electromagnetic surface (REMS) for monopulse radar applications at X-band. The proposed REMS element integrates a 1-bit reflection-type phase shifter controlled by a PIN diode. By altering the working states of the PIN diode, well-defined beam scanning is obtained. Furthermore, selecting different feeding states can realize the sum (Σ) and difference (Δ) patterns. The key design issues, including element modeling, coding design, and feed optimization, are studied to obtain good Σ and Δ beam performance. Experimental results show that REMS achieves a high gain of 23.3 dBi, a low sidelobe level of -15 dB, and a low null depth of -30 dB. The wide-angle monopulse beam-scanning up to ±60° is obtained. The gain bandwidth of -3 dB ranges from 9.35 to 11.75 GHz, with a relative bandwidth of 22.75%. Thus, the proposed multi-feed REMS brings new freedom for the Σ and Δ beam scanning, which provides wide application prospects for the monopulse radar system.