Abstract Kirigami technique, a method to reconfigure structures via mechanical approaches, has received much attention in material science, due to its versatile and unconventional structural transformations. The counterparts in the electromagnetic metamaterial field has recently allowed for the tunable control of electromagnetic responses. However, they are limited to global tuning of absorption, chirality, etc., leaving much potential of controlling spatially varying distribution and therefore the optical wavefront unexploited. Here, the authors propose a class of kirigami‐based reconfigurable gradient metasurfaces through which the electromagnetic wavefront can be tuned over continuous‐state ranges by changing the meta‐structures from folded (compact) to unfolded (large surface) configurations. As the proof‐of‐concept, meta‐devices including switchable anomalous refractor and reconfigurable metalens are demonstrated both in simulations and experiments. Moreover, a new paradigm to mitigate chromatic dispersion is also realized by the kirigami‐based reconfigurable metalens, which is able to keep the focal length unchanged over a continuous frequency band by setting metalens with various folding states. Their approach provides a new alternative for designing reconfigurable gradient metasurface with additional mechanical properties and may have potential applications in advanced devices such as reconfigurable optical components and imaging system.
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.
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.
Abstract Reconfigurable metasurfaces have emerged as a versatile platform for reshaping the wireless environment into a desirable form at low cost. Despite the rapid growth, most of the existing metasurfaces only support reflection operation or transmission operation, only providing service coverage of backward or forward half‐space when they are used for wireless communications. Here, an intelligent programmable omni‐metasurface integrating reflection mode, transmission mode, and duplex mode of simultaneous reflection and transmission modes in the same polarization and frequency channel is proposed, capable of providing ubiquitous full‐space service coverage for multiuser wireless communication applications. As exemplary demonstrations, a series of dynamic functionalities have been realized, including twin‐beam scanning in reflection mode, twin‐beam scanning in transmission mode, and identical/distinct dynamic beams for both forward and backward half‐spaces in duplex mode, which are customized for signal reflection, transmission, and simultaneous symmetric/asymmetric reflection and transmission in wireless communication scenarios. The proposed tunable omni‐metasurface provides a new method for full‐space wave manipulation, which may offer untapped potentials for real‐time, fast, and sophisticated wave control in applications such as miniaturized systems, integrated photonics, and intelligent communications.
In this paper, we propose a low-scattering antenna that can realize a wide reconfigurable frequency band by adjusting the external biasing voltages of the loaded varactor diode. A checkerboard polarization conversion metasurface (PCM) is placed on the upper layer of the structure to scatter the detected waves. Simulated results show that the -10 dB operation frequency can be dynamically tuned from 3.8 to 5.26 GHz, and good radiation performance can be attained with a peak gain of 5.5 dBi. Furthermore, the backward monostatic radar cross section (RCS) is significantly suppressed in the range of 2–12 GHz for the two orthogonal polarizations. With the merits of reconfigurability, low profile, and low backscattering, the proposed antenna may be a promising candidate for applications in communication and stealth platforms.
Abstract Achieving simultaneous amplitude and phase control is crucial in various spin‐selective optical applications, particularly for chiral mirrors that exhibit distinct responses when illuminated by orthogonal circularly polarized waves. However, conventional chiral metasurface approaches for amplitude manipulation can only be implemented by adjusting absorption, which limits the bandwidth due to the dispersion nature of the meta‐structure and cannot ensure that the chiral mirror output only one circular polarization component with independent amplitude and phase manipulation at multi‐polarization incidence. Here, an interference‐mechanism‐assisted methodology is proposed for broadband chiral meta‐mirrors with independent control over amplitude and phase. Such controls are achieved by simply setting the rotation angle of each meta‐atom in the integrated quad‐atom structure. The rotation angle of each meta‐atom and the difference between adjacent meta‐atoms rotation angles provide flexible degrees of freedom for controlling phase and amplitude, respectively. Notably, this mechanism stemming from the Pancharatnam‐Berry phase allows for wideband operation due to its dispersion‐free nature of phase control. As proof‐of‐principle demonstrations, numerically verify a series of amplitude‐tailorable phase‐gradient meta‐mirrors and experimentally demonstrate a broadband chiral Airy beam generator. This method offers a straightforward solution for spin‐selective amplitude/phase manipulation which may have the potential to advance the engineering application of chiral metasurfaces.
Janus metasurfaces, a category of two-faced two-dimensional (2D) materials, are emerging as a promising platform for designing multifunctional metasurfaces by exploring the intrinsic propagation direction (k-direction) of electromagnetic waves. Their out-of-plane asymmetry is utilized for achieving distinct functions selectively excited by choosing the propagation directions, providing an effective strategy to meet the growing demand for the integration of more functionalities into a single optoelectronic device. Here, we propose the concept of direction-duplex Janus metasurface for full-space wave control yielding drastically different transmission and reflection wavefronts for the same polarized incidence with opposite k-directions. A series of Janus metasurface devices that enable asymmetric full-space wave manipulations, such as integrated metalens, beam generators, and fully direction-duplex meta-holography, are experimentally demonstrated. We envision the Janus metasurface platform proposed here to open new possibilities toward a broader exploration of creating sophisticated multifunctional meta-devices ranging from microwaves to optical systems.
A strategy for designing a dual-circularly polarized (DCP) transmit-reflect-array (TRA) based on a mosaic metasurface is proposed. The mosaic metasurface with a thin panel thickness of 0.14 $\lambda_{0}$ is created by mixing two types of full-space meta-atoms using a genetic algorithm-based optimization method, which provides four degrees of freedom of beamforming to independently manipulate the transmitted and reflected DCP beams. The measured bandwidth of the prototype is better than 30.7% for the transmitarray and 47.5% for the reflectarray, with both gain variation and axial ratio below 3 dB.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)