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 letter, an active metasurface for vortex beam generation is proposed. This metasurface can transform the incident plane wave into beams carrying orbital angular momentum (OAM) of three different orders. This active metasurface is composed of an array of varactor diodes loaded unit cells. The transmission phase of each metasurface unit cell can be fully controlled by the capacitance of the varactor diodes. Different modes of vortex beams can be separately generated by simply changing the transmission phase distribution on the metasurface aperture. The properties of the proposed active metasurface are demonstrated by simulation and measurement results, which have a good agreement with each other.

In this letter, a frequency-diverse transmission metamaterial aperture (FDTMA) with bunching random beam (BRB) is proposed for coincidence imaging. The FDTMA consists of a random modulation metamaterial lens and a broadband microstrip patch antenna array which is used as a feed source. Firstly, an equivalent medium containing both dielectric layer and metamaterial structure is modeled and analyzed using the electromagnetic theory. The zoom coefficients of the metamaterial elements are analyzed to simplify the design of the broadband aperture. Then the basic metamaterial elements are designed based on the proposed model. Moreover, the FDTMA is designed using the basic metamaterial elements considering the requirements of the coincidence imaging system. Finally, the waved metal plate (WMP) leveraged in the FDTMA with BRB is optimized using the High-Frequency Structure Simulator (HFSS) software. The radiation patterns of the proposed FDTMA with BRB are randomly distributed in a limited angle range in the X band. The proposed equivalent model and FDTMA with BRB are validated through simulations and experiments.

In this paper, metasurfaces with both cross-polarization conversion and vortex beam-generating are proposed. The proposed finite metasurface designs are able to change the polarization of incident electromagnetic (EM) waves to its cross-polarization. In addition, they also can modulate the incidences into beams carrying orbital angular momentum (OAM) with different orders ( $l=+1,l=+2,l=-1$ and $l=-2$ ) by applying corresponding transmission phase distribution schemes on the metasurface aperture. The generated vortex beams are at 5.14 GHz. The transmission loss is lower than 0.5 dB while the co-polarization level is −10 dB compared to the cross-polarization level. The measurement results confirmed the simulation results and verified the properties of the proposed designs.

This letter proposes an ultra-wideband 1-bit suspended reconfigurable intelligent surface (RIS) designed to enhance the signal coverage of wireless communication networks. The RIS unit cell comprises two metal gratings connected via a PIN diode, a dielectric-air-dielectric interlayer, and a metal reflective layer. The RIS achieves a stable reflection phase difference of 180° ± 30° between the ON and OFF states of the PIN diode within the ultra-wideband range of 2.75–6 GHz. This range includes the 3.4 GHz and 4.9 GHz bands for 5G communication, the 5.2 GHz band for indoor wireless communication, and the 5.8 GHz band for Wi-Fi and Bluetooth signals. A prototype, consisting of 20 × 20 unit cells, was fabricated and measured, demonstrating two-dimensional wide-angle beam scanning of ± 60° within the working frequency range. Furthermore, a RIS-assisted wireless communication system was constructed, confirming that deploying RIS can significantly enhance communication quality in targeted areas by transmitting and receiving image information at different frequencies. The proposed RIS holds substantial potential for RIS-assisted wireless communication systems.

Vortex beam, manifesting the characteristic helical phase front and amplitude singularity, carries inherent orbital angular momentum (OAM) and has received intensive research from its generation, detection to various promising applications. To flexibly impart OAM to the electromagnetic (EM) waves and further control the topological charge, propagation, polarization, bandwidth and efficiency of the vortex beams, various approaches have been proposed by the science community. In this review, we briefly introduce the established methods for the generation and manipulation of vortex beams, with the focus on the fast-growing guided-wave metasurface based approach. Guided-wave metasurface contains sub-wavelength guided-wave subsystems that are capable of versatile control of the EM wave and we review some recent advances that enabled multifunctional vortex beam generation and manipulation, with an outlook towards the future development in this field. OAM topological charges switching, polarization control, divergence control, full-space vortex beam generation, broadband vortex beam generation and vortex multibeam are covered in this paper aiming to accommodate the ever-increasing demands from the vortex beam applications.