Metasurfaces have shown their great capability to manipulate electromagnetic waves. As a new concept, reconfigurable metasurfaces attract researchers’ attention. There are many kinds of reconfigurable components, devices and materials that can be loaded on metasurfaces. When cooperating with reconfigurable structures, dynamic control of the responses of metasurfaces are realized under external excitations, offering new opportunities to manipulate electromagnetic waves dynamically. This review introduces some common methods to design reconfigurable metasurfaces classified by the techniques they use, such as special materials, semiconductor components and mechanical devices. Specifically, this review provides a comparison among all the methods mentioned and discusses their pros and cons. Finally, based on the unsolved problems in the designs and applications, the challenges and possible developments in the future are discussed.

In this paper, a dual circularly-polarized (CP) multi-beam antenna is proposed for future vehicular radar applications. The antenna is composed of two pillbox reflector beamforming networks (BFNs) and a series-fed microstrip line based dual CP leaky-wave antenna (LWA) array, which has a symmetrical structure and can obtain both left hand circular polarization (LHCP) and right hand circular polarization (RHCP) by switching the exciting current direction of the microstrip line. Besides, a shorted stub is loaded in the LWA to suppress the open-stop band (OSB), and thus achieve the broadside radiation and good impedance matching of the LWA. To realize the dual-polarized radiation characteristic with low-cost passive beam scanning capability, two pillbox BFNs are connected at both sides of the LWA to share the LWA aperture. The two different BFNs can excite different CP radiation patterns. A prototype of the proposed antenna is fabricated in the frequency band 23.5–24.5 GHz, and the measured results approve that the proposed antenna can realize ±36° beam scanning range with −4.0 dB crossover level, and the gain is higher than 17.7 dBi in the operating band. The advantages of the proposed antenna, including low-profile, low-cost, passive beam scanning ability, and dual circular polarization, make it an attractive choice for low-cost millimeter-wave radar applications.

A hybrid implicit explicit-finite-difference time-domain (HIE-FDTD) method is used to simulate a graphene-based absorber. Both the interband conductivity and intraband conductivity of the graphene are incorporated into the HIE-FDTD method directly through an auxiliary difference equation. Because the time step size in the proposed method is not confined by the fine spatial cells in the graphene layer, the simulation time of the proposed method is greatly reduced compared with that of the conventional FDTD method. By using the proposed HIE-FDTD method, a graphene-based absorber is simulated and analyzed. The numerical result shows that the operating frequency of the absorber is tunable through controlling graphene's chemical potential. It also shows that the interband conductivity has an important effect on the performance of the graphene device, especially at the frequency band larger than 10 THz.

A high gain low-frequency bow-tie antenna with artificial magnetic conductor (AMC) and metamaterial lens for ground penetrating radar (GPR) is proposed. First, a bow-tie antenna working in 348–772 MHz frequency band is designed. The substrate is a square with side length of 420 mm. A periodic AMC reflector is designed. The in-phase reflection region of the unit is 481 MHz–1.44 GHz. The results show that the gain of antenna loaded with reflector is increased by 5 dB. A metamaterial lens based on the zero-index metamaterial element is also proposed to improve the gain. The zero refractive index frequency point is 810 MHz, the unit size of the metamaterial is 60 mm, and the lens size is consistent with the antenna substrate size. The gain of the antenna loaded with AMC reflector and the metamaterial lens is increased by 6.5 dB and the front-to-back ratio is 23 dB. The directivity of the antenna is further optimized. The measured results are in good agreement with the simulations.

A method of improving the diversity and capacity of multiple-input-multiple-output (MIMO) systems in nonisotropic multipath environments by loading a scatterer array is proposed. The difference between array diversity and super-resolution imaging is discussed first. The phase differences caused by the “effective space” between adjacent antenna elements are the critical factors of diversity enhancement. The scatterer array, which is made of cross-structure periodically, is placed on top of the antenna array to adjust the phase center of the radiation pattern of each antenna port. By increasing the “equivalent size” of the antenna array, the correlation of part of the adjacent ports in the antenna array is decreased; thus, the array diversity is improved. Through a set of comparative examples, the effectiveness of the scatterer array is clearly demonstrated.

This paper presents a metasurface (MS)-based wideband wearable circularly polarized (CP) antenna to communicate with in-body devices. The antenna consists of a crossed dipole, an MS plane and a CP feeding network. The feed network generates a quasi-90° phase delay between each adjacent arm of the crossed dipole. This produces CP radiation and reduces polarization mismatch between the telemetry antenna and the implantable antenna. The MS consisting of a 5×5 unit cell array functions as a reflector for the crossed dipole to improve forward radiation while maintaining a low profile structure. This is by designing the unit cells with a near-zero phase reflection over the operating band. To enable conformity with on-body usage, the antenna is designed fully using flexible materials. Textile conductive elements are embedded into a PDMS substrate. It is sized at 106×106×5mm3 (1.24λ×1.24λ×0.05λ at 3.5 GHz). Results indicated a -10 dB impedance bandwidth from from 2.25 to 6 GHz (90%). The 3-dB axial ratio bandwidth is from 2.9 to 4.95 GHz (52%), with a maximum on-body gain of - 10.5 dBi. Finally, the specific absorption rate (SAR) assessment of the antenna indicated values far lower than the limits of the FCC.