Wideband low-scattering metasurface with an in-band reconfigurable transparent window

Active metasurfaces with dynamically reconfigurable functionalities are highly demanded in various practical applications.Here,we propose a wideband low-scattering metasurface that can realize an in-band reconfigurable transparent window by altering the operation states of the PIN diodes loaded on the structures.The metasurface is composed of a band-pass frequency selective surface(FSS)sandwiched between two polarization conversion metasurfaces(PCMs).PIN diodes are integrated into the FSS to switch the transparent window,while a checkerboard configuration is applied in PCMs for the diffusive-reflective function.A sample with 20×20 elements is designed,fabricated,and experimentally verified.Both simulated and measured results show that the in-band functions can be dynamically switched between beam-splitting scattering and high transmission by controlling the biasing states of the diodes,while low backscattering can be attained outside the passband.Furthermore,the resonant structures of FSS also play the role of feeding lines,thus significantly eliminating extra interference compared with conventional feeding networks.We envision that the proposed metasurface may provide new possibilities for the development of an intelligent stealth platform and its antenna applications.

Reconfigurable Intelligent Surfaces: Design, Implementation, and Practical Demonstration

Metasurfaces,ultrathin two-dimensional version of metamaterials,have attracted tremendous attention due to their exotic capabilities to freely manipulate electromagnetic waves.By incorporating various tunable materials or elements into metasurface designs,reconfigurable metasurfaces and related metadevices with functionalities controlled by external stimuli can be realized,opening a new avenue to achieving dynamic manipulation of electromagnetic waves.Recently,based on the tunable metasurface concept,reconfigurable intelligent surfaces(RISs)have received significant attention and have been regarded as a promising emerging technology for future wireless communication due to their potential to enhance the capacity and coverage of wireless networks by smartly reconfiguring the wireless propagation environment.Here,in this article,we first focus on technical issues of RIS system implementation by reviewing the existing research contributions,paying special attention to designs in the microwave regime.Then,we showcase our recent attempts to practically demonstrate RIS systems in real-world applications,including deploying reflective RIS systems in indoor scenarios to enhance the wireless network coverage and utilizing intelligent omni-metasurfaces to improve both indoor and through-wall wireless communication quality.Finally,we give our own perspectives on possible future directions and existing challenges for RISs toward a truly commercial intelligent technology platform.

Anisotropic tribology and electrification properties of slidingmode triboelectric nanogenerator with groove textures

Sliding-mode triboelectric nanogenerator(S-TENG)is based on the coupling of triboelectrification and electrostatic induction,converting electrical energy from sliding motion.Introducing micro-textures into the sliding surface,and adjusting the angle between the texture and sliding direction(direction angle)may achieve performance anisotropy,which provides novel ideas for optimizing the tribology and electrification performance of S-TENG.To guide the performance optimization based on the anisotropy,in this paper,groove micro-textures were fabricated on the surface of S-TENG,and anisotropic tribology and electrification performance were obtained through changing the direction angle.Based on the surface analysis and after-cleaning tests,the mechanism of the anisotropy was explained.It is shown that the anisotropy of friction coefficient can be attributed to the changes of texture edge induced resistance and groove captured wear debris,while the voltage anisotropy is due to the variations of debris accumulated on the sliding interface and the resulting charge neutralization.Among the selected 0°–90°direction angles,S-TENG at angle of 90°exhibits relatively small stable friction coefficient and high open-circuit voltage,and thus it is recommended for the performance optimization.The open-circuit voltage is not directly associated with the friction coefficient,but closely related to the wear debris accumulated on the sliding interface.This study presents a simple and convenient method to optimize the performance of S-TENG,and help understand the correlation between its tribology and electrical performance.