RESUMO
The powerful capability of reconfigurable intelligent surfaces (RISs) in tailoring electromagnetic waves and fields has put them under the spotlight in wireless communications. However, the current designs are criticized due to their poor frequency selectivity, which hinders their applications in real-world scenarios where the spectrum is becoming increasingly congested. Here we propose a filtering RIS to feature sharp frequency-selecting and 2-bit phase-shifting properties. It permits the signals in a narrow bandwidth to transmit but rejects the out-of-band ones; meanwhile, the phase of the transmitted signals can be digitally controlled, enabling flexible manipulations of signal propagations. A prototype is designed, fabricated, and measured, and its high quality factor and phase-shifting characteristics are validated by scattering parameters and beam-steering phenomena. Further, we conduct a wireless communication experiment to illustrate the intriguing functions of the RIS. The filtering behavior enables the RIS to perform wireless signal manipulations with anti-interference ability, thus showing big potential to advance the development of next-generation wireless communications.
RESUMO
Hand gesture plays an important role in many circumstances, which is one of the most common interactive methods in daily life, especially for disabled people. Human-machine interaction is another popular research topic to realize direct and efficient control, making machines intelligent and maneuverable. Here, a special human-machine interaction system is proposed and namedas computer-vision (CV) based gesture-metasurface interaction (GMI) system, which can be used for both direct beam manipulations and real-time wireless communications. The GMI system first needs to select its working mode according to the gesture command to determine whether to perform beam manipulations or wireless communications, and then validate the permission for further operation by recognizing unlocking gesture to ensure security. Both beam manipulation and wireless communication functions are validated experimentally, which show that the GMI system can not only realize real-time switching and remote control of different beams through gesture command, but also communicate with a remote computer in real time by translating the gesture language to text message. The proposed non-contact GMI system has the advantages of good interactivity, high flexibility, and multiple functions, which can find potential applications in community security, gesture-command smart home, barrier-free communications, and so on.
RESUMO
Surface plasmon polaritons (SPPs) are interactions between incident electromagnetic waves and free electrons on the metal-dielectric interface in the optical regime. To mimic SPPs in the microwave frequency, spoof SPPs (SSPPs) on ultrathin and flexible corrugated metallic strips were proposed and designed, which also inherit the advantages of lightweight, conformal, low profile, and easy integration with the traditional microwave circuits. In this paper, we review the recent development of SSPPs, including the basic concept, design principle, and applications along with the development from unwieldy waveguides to ultrathin transmission lines. The design schemes from passive and active devices to SSPP systems are presented respectively. For the passive SSPP devices, the related applications including filters, splitters, combiners, couplers, topological SSPPs, and radiations introduced. For the active SSPP devices, from the perspectives of transmission and radiation, we present a series of active SSPP devices with diversity and flexibility, including filtering, amplification, attenuation, nonlinearity, and leaky-wave radiations. Finally, several microwave systems based on SSPPs are reported, showing their unique advantages. The future directions and potential applications of the ultra-thin SSPP structures in the microwave and millimeter-wave regions are discussed.