Dynamically Self-Reconfigurable Multifunctional All-Passive Metasurface

Broadband High Optical Transparent Intelligent Metasurface for Adaptive Electromagnetic Wave Manipulation

Intelligent metasurfaces have garnered widespread attention owing to their properties of sensing electromagnetic (EM) environments and multifunctional adaptive EM wave manipulation. However, intelligent metasurfaces with broadband high optical transparency have not been studied to date, and most of the previous intelligent metasurfaces lack an integrated design for their actuators and sensors, resulting in lower integration levels. This study proposes a novel intelligent metasurface with adaptive EM wave manipulation ability and high optical transparency from visible to infrared bands. This metasurface consists of a transparent and current-controlled reconfigurable metasurface as an actuator by integrating patterned vanadium dioxide (VO2) into metal-meshed resonant units, transparent broadband microstrip antenna as a sensor, recognition-and-feedback module, and actuator- and sensor-integrated design on the same substrate. The EM-regulating capability of the designed transparent intelligent metasurface is theoretically analyzed using the coupled mode theory, and a prototype metasurface device is fabricated for experimental verification. Simulation and experimental results demonstrate that the metasurface exhibits over 80% normalized transmittance from 380 to 5,000 nm and adaptive EM wave manipulation (reflective strong shielding function with a shielding efficiency of over 24 dB, high transmittance function with a transmission loss of 1.24 dB, and strong absorption function with an absorption of 97%) according to the EM wave power parameters without manual intervention. This study provides an avenue for transparent intelligent metasurfaces with extensive application prospects in areas such as intelligent optical windows, radar enclosures, and communication.

Controlling Radiation Beams by High-Efficiency Metasurfaces with Enhanced Refractive Index Elements

The efficient manipulation of the electromagnetic wavefront using metasurfaces (MSs) has attracted a continuous amount of attention in recent years. MSs with arbitrarily controllable amplitude and phase are highly desirable in many emerging fields. However, in previous research, the resonance effect has mainly been used to accomplish the task. This article presents a nonresonant metamaterial element with stronger capacitive coupling. The broadband sandwich-structured meta-atom achieves an enhanced refractive index ranging from 2.44 to 8.90. By using the enhanced refractive index elements, the proposed transmissive MS has an ultrathin thickness (0.23 free-space wavelength). It consists of a specially designed gradient index MS placed on top of the transmitting antenna. The MS is designed to convert the spherical surface wave into a plane wave with high efficiency. One core layer (CL) gradient index MS and two impedance matching layers (IMLs) have been designed to transform the magnitude and phase of the radiation beam from the transmitting antenna. An efficient transmissive MS has been designed and experimentally evaluated with a maximum measured efficiency of over 85%. The proposed control strategy increases the design flexibility of the MS and shows great potential for broadband applications in the realization of efficient functional devices.

Intelligent metasurface system for automatic tracking of moving targets and wireless communications based on computer vision

The fifth-generation (5G) wireless communication has an urgent need for target tracking. Digital programmable metasurface (DPM) may offer an intelligent and efficient solution owing to its powerful and flexible controls of electromagnetic waves and advantages of lower cost, less complexity and smaller size than the traditional antenna array. Here, we report an intelligent metasurface system to perform target tracking and wireless communications, in which computer vision integrated with a convolutional neural network (CNN) is used to automatically detect the locations of moving targets, and the dual-polarized DPM integrated with a pre-trained artificial neural network (ANN) serves to realize the smart beam tracking and wireless communications. Three groups of experiments are conducted for demonstrating the intelligent system: detection and identification of moving targets, detection of radio-frequency signals, and real-time wireless communications. The proposed method sets the stage for an integrated implementation of target identification, radio environment tracking, and wireless communications. This strategy opens up an avenue for intelligent wireless networks and self-adaptive systems.

Biobased and Programmable Electroadhesive Metasurfaces

Electroadhesion has shown the potential to deliver versatile handling devices because of its simplicity of actuation and rapid response. Current electroadhesion systems have, however, significant difficulties in adapting to external objects with complex shapes. Here, a novel concept of metasurface is proposed by combining the use of natural fibers (flax) and shape memory epoxy polymers in a hygromorphic and thermally actuated composite (HyTemC). The biobased material composite can be used to manipulate adhesive surfaces with high precision and controlled environmental actuation. The HyTemC concept is preprogrammed to store controllable moisture and autonomous desorption when exposed to the operational environment, and can reach predesigned bending curvatures up to 31.9 m^-1 for concave and 29.6 m^-1 for convex shapes. The actuated adhesive surface shapes are generated via the architected metasurface structure, incorporating an electroadhesive component integrated with the programmable biobased materials. This biobased metasurface stimulated by the external environment provides a large taxonomy of shapes─from flat, circular, single/double concave, and wavy, to piecewise, polynomial, trigonometric, and airfoil configurations. The objects handled by the biobased metasurface can be fragile because of the high conformal matching between contacting surfaces and the absence of compressive adhesion. These natural fiber-based and environmentally friendly electroadhesive metasurfaces can significantly improve the design of programmable object handling technologies, and also provide a sustainable route to lower the carbon and emission footprint of smart structures and robotics.

Additively Manufactured Multi-Material Ultrathin Metasurfaces for Broadband Circular Polarization Decoupled Beams and Orbital Angular Momentum Generation

Controlling the wavefront and manipulating the polarization of the electromagnetic wave using an ultrathin flat device are highly desirable in many emerging fields. To shape the wavefront between two decoupled orthogonal circular polarization states, that is, the right-hand circular polarization (RCP) and the left-hand circular polarization (LCP), most state-of-the-art metasurfaces (MSs) combine the propagation phase and Pancharatnam-Berry phase into meta-atoms. This article proposes a different strategy to fully decouple the LCP and RCP and control their wavefronts independently. By taking advantage of the conductive and dielectric multi-material-integrated additive manufacturing technique, the proposed transmissive MS has an ultrathin thickness (0.11 free-space wavelength) and controls the LCP and RCP wavefronts independently under linearly polarized incidence illumination. The proposed meta-atom consists of a receiving antenna on the top, a transmitting antenna at the bottom with a strip-line connecting them. The strip-line introduces the same phase shifts for both RCP and LCP waves, while the transmitting antenna with in-plane rotation leads to the opposite phase shifts for RCP and LCP waves. Therefore, the phase delays from the strip-line and the angular rotation of the transmitting antenna provide two degrees of freedom, enabling independent beam shaping of LCP and RCP waves. Two MSs with different functionalities are printed for proof-of-concept, and the performances are experimentally verified.

Four-Dimensional Printed Shape Memory Metasurface to Memorize Absorption and Reflection Functions

Functional metasurfaces help wireless communication to reach beyond current electromagnetic control device limitations. However, current reconfigurable functional metasurfaces require separate systems for function control. In particular, it is difficult to realize millimeter-wavelength regimes due to the increasing number of active elements with the reduction in unit cell size. This paper proposes a four-dimensional printed memory metasurface to memorize absorption and reflection function in millimeter-wavelength regimes. Thus, metasurfaces with electromagnetic absorption and reflection functions can be realized through mechanical shape memory by memorizing electromagnetic properties using four-dimensional printed structures. The desired electromagnetic performance was experimentally demonstrated and deformation time to memorize the initial structure was measured. The results confirmed that the proposed four-dimensional printed metasurface has potential for considerable contribution to multifunctional wireless devices such as smart electromagnetic wave control systems in reconfigurable intelligent surface, stealth, and wireless sensing systems.

Phase-change reconfigurable metasurface for broadband, wide-angle, continuously tunable and switchable cloaking

Being invisible at will has fascinated humanity for centuries and it has become more tangible with the development of metasurfaces, which have demonstrated the extraordinary ability of wavefront manipulation. However, state-of-the-art invisibility cloaks typically work in a deterministic system with a limited bandwidth and small incident angle ranges. Here, by integrating the phase-change material of Ge₂Sb₂Te₅ and the wavefront tailoring functionality of a reflective metasurface, we have achieved a unique carpet cloak that is endowed with broadband invisibility from 6920 to 8220 nm, fully concealing objects over a wide angular span of ±25° and a prominent radar cross-section reduction. Furthermore, the central cloaking wavelength can be continuously tuned with Ge₂Sb₂Te₅ film under different intermediate phases by precisely controlling external stimuli, which will provide a flexible and encouraging way to achieve active features once fabricated. Simulation results also show that the cloaking bandwidth can be significantly extended by triggering Ge₂Sb₂Te₅ from the amorphous to crystalline states. Importantly, the hybrid metasurface can realize switching of "ON" and "OFF" states in terms of cloaking features by converting Ge₂Sb₂Te₅ from the amorphous to the crystalline state. To the best of our knowledge, this is the first metasurface carpet cloak that utilizes the phase-change material of Ge₂Sb₂Te₅ to achieve ultra-broadband, wide-angle, continuously tunable and switchable cloaking with low profiles, light weights, and easy access. This design of a reconfigurable cloak is expected to find potential applications in various areas such as vehicle cloaking, illusions and so on.