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Engineered electromagnetic surfaces enable enhancing the strength of a signal in the desired direction(s) using anomalous reflection/transmission. However, to boost the gain of the conventional surfaces, the common solution is to increase its aperture size where this method limits the gain performance for limited space in scenarios for large-distance communication. This paper proposes a gain-controlled beam-steering polarization-engineered transmissive surface to tackle this challenge. To implement such a functionality, a transmissive unit cell properly integrated with transistors and phase shifters is introduced with the ability of simultaneous manipulation of phase, amplitude (reduction and amplification), and polarization. Then, a supercell including the array of unit cells with desired linear phase gradient is designed and analyzed using Floquet approach to tilt the transmitted beam. Finally, to verify the proposed idea, a surface including $12\times 12$ unit cells is designed, fabricated and verified. It is demonstrated that a maximum gain of 25 dB compared to air aperture and 11 dB compared to the passive one are achieved by assuming a constant size at 5 GHz. Based on this gain improvement, the active surface’s aperture efficiency is 12.58 times greater than that of the passive surface. Moreover, the surface gain can be reconfigured by the amplification level of the transistors, providing efficient dynamic way for changing the gain instead of the static resizing of aperture.

Massive multiple-input multiple-output (mMIMO), assisted by reconfigurable intelligent surface (RIS), can ensure reliable and energy-efficient data transmission. However, the receiver design for large-scale networks based on traditional mathematical approaches requires complex statistics. Therefore, in this paper, machine learning (ML) approaches are investigated to design receivers for the RIS-assisted multi-user MIMO (muMIMO) systems to avoid complicated channel information requirements. Extreme learning machine (ELM) is an effective ML tool for MIMO receiver design because it simplifies the learning process. However, the learning performance of the ELM can get affected by the random choice of its hidden layer size. To address this issues, this paper proposes an incremental ELM (I-ELM) based receiver for the RIS-mu-MIMO system. The proposed receiver computes the weights between the hidden and the output layer based on the automated incremental addition of hidden neurons and provided conditions. The suggested receiver is contrasted with the multilayer perceptron (MLP), conventional ELM, and minimum mean square error (MMSE) receivers. The simulation results show that the throughput performance of the proposed receiver is satisfactory.

This article presents a model through which the reflection coefficient amplitude as well as phase of reflective intelligent surfaces can be estimated accurately. The reconfigurability of the surface was achieved by incorporating the varactor diodes into the surface of the cell unit. The manipulation of the phase of the reflection coefficient can be achieved by making adjustments to the biasing state of the varactors. The model, which makes use of a physics-based methodology and is based on a transmission-line circuit description of the Reconfigurable Intelligent surfaces (RIS) unit cells, considers every pertinent electrical and geometrical characteristics of the proposed surface. With the method proposed in this paper, fast and accurate RIS-based communication lines can be created. The recommended accuracy of the proposed method was confirmed through the use of a CST microwave studio full-wave simulations. [ABSTRACT FROM AUTHOR]

Terahertz (THz) band will play an important role in enabling sixth generation (6G) envisioned applications. Compared with lower frequency signals, THz waves are severely attenuated by the atmosphere temperature, pressure, and humidity. Thus, designing a THz communication system must take into account how to circumvent or diminish those issues to achieve a sufficient quality of service. Different solutions are being analyzed: intelligent communication environments, ubiquitous artificial intelligence, extensive network automation, and dynamic spectrum access, among others. This survey focuses on the benefits of integrating intelligent surfaces (ISs) and THz communication systems by providing an overview of IS in wireless communications with the scanning of the recent developments, a description of the architecture, and an explanation of the operation. The survey also covers THz channel models, differentiating them based on deterministic and statistical channel modeling. The IS-aided THz channels are elucidated at the end of the survey. Finally, discussions and research directions are given to help enrich the IS field of research and guide the reader through open issues.

Reconfigurable intelligent surface (RIS) has been introduced as a promising emerging paradigm to design a smart radio environment for improving wireless capacity. It has the potential to reshape wave propagation via its tunable and low-cost reflecting elements. Therefore, it is regarded as a propitious solution that provides alternative paths for the propagation of high-frequency signals, which are vulnerable to blockages and suffer from penetration losses. Because of those features, RIS has been considered to be integrated into the wireless vehicular network (WVN), which is characterized by high mobility and high quality of service (QoS) requirements. Hence, similar to relaying systems, a vehicle needs to select the best available RIS that maximizes the signal-to-noise ratio (SNR) at the receiver. Inspired by that, in this paper, we introduce the partial RIS selection for enhancing capacity and reducing error rate. We derive closed-form expressions for the ergodic capacity, symbol error probability (SEP), and energy efficiency for a partial RIS selection design. Besides, we compare its performances to the partial relaying design while considering: decode-and-forward (DF) and amplify-and-forward fixed gain (AF). Moreover, we consider a wireless attack scenario, where an eavesdropper intends to overhear the transmitted signal at the receiver’s end. Then, we compare partial RIS to partial relay selection from this security perspective, where we derive closed-form expressions for the average secrecy capacity. Furthermore, we compare the partial RIS selection to a single RIS architecture scenario from the literature, where our solution outperforms the related existing work. [ABSTRACT FROM AUTHOR]

Since the radio frequency identification (RFID) technology was put forward,it has been widely used in the transportation,logistics,industry and business due to its convenience and high efficiency.As a carrier for storing recognizable data,the RFID tags play a crucial role in the Internet of things (IoT).More and more functions and modules are embedded in the RFID tags and developed into smart tags in different application fields.Recently,wireless batteryless smart tags have arisen and grown rapidly with the development of the IoT and various emerging backscatter technologies.Wireless batteryless smart tags use the passive backscatter technology to harvest the energy and transmit information through radio frequency signals.Starting from the RFID technology,the history of the RFID and smart tags was introduced briefly,the differences between traditional smart tags and emerging wireless smart tags were compared,the advantages of wireless batteryless smart tags were concluded,several specific applications of it in different fields were listed,and the open challenges were analyzed.

Reversible switching from a highly rough surface to another entirely smooth surface under external stimuli is crucial for intelligent materials applied in the fields of anti-fogging, self-cleaning, oil-water separation and biotechnology. In this work, a thermal-responsive liquid crystal elastomer (LCE) surface covered with oriented micropillars is prepared via a facile two-step crosslinking method coupled with an extrusion molding program. The reversible change of topological structures of the LCE surface along with temperature is investigated by metallographic microscope, atomic force microscopy and optical contact angle measuring system. At room temperature, the LCE sample is filled with plenty of micropillars with an average length of 8.76 µm, resulting in a super-hydrophobic surface with a water contact angle (WCA) of 135°. When the temperature is increased to above the clearing point, all the micropillars disappear, the LCE surface becomes entirely flat and presents a hydrophilic state with a WCA of 64°. The roughness-related wetting property of this microstructured LCE surface possesses good recyclability in several heating/cooling cycles. This work realizes a truly reversible transformation from a highly rough surface to an entirely smooth surface, and might promote the potential applications of this dynamic-responsive LCE surface in smart sensors and biomimetic control devices. [ABSTRACT FROM AUTHOR]

Bacterial biofilm contamination has caused significant damage to the medical and food industries, and there is an urgent need to develop new antimicrobial coatings to address this problem. In this study, temperature-sensitive coatings with bacteria-killing and bacteria-releasing functions were prepared based on silicone rubber (SR) surfaces by ultraviolet (UV) polymerization and UV photocatalysis. Firstly, N-isopropylacrylamide (NIPAAm) was formed into poly(N-isopropylacrylamide) (PNIPAAm) by UV polymerization and grafted onto the SR surface. Then, Ag+ was rapidly reduced to silver nanoparticles (AgNPs) by tannic acid (TA) under UV catalysis to form TA@Ag complexes, depositing onto the SR surface. The modified SR surface has an extremely strong and persistent bactericidal effect, greatly inhibiting the formation of bacterial biofilm. Moreover, the smart surface can effectively release bacteria and resist bacterial adhesion through temperature changes. Moreover, the modified SR surface did not exhibit cytotoxicity against mouse epithelioid fibroblasts (L929). Taken together, the smart SR surface has antibacterial ability and good biocompatibility, which is a promising medical material. • The smart antifouling surface of SR-PNIPAAm/TA@Ag has both bacteria-killing and bacteria-releasing functions. • The SR-PNIPAAm/TA@Ag coatings can be recycled and has sustained and strong antibacterial ability. • The intelligent antibacterial surface has broad-spectrum antibacterial properties and good biocompatibility. [ABSTRACT FROM AUTHOR]

In this paper, we provide a detailed account of our efforts in the design, development and prototyping of a novel intelligent surface by adapting initially curved diaphragms. Unlike the shortcomings that characterize current designs of functional surfaces, our adaptive surface design is characterised by simplicity, multifunctionality, adaptability, high flexibility and robustness as well as controlled autonomy. Four aspects of the work are accordingly examined. The first is concerned with the conceptual design of the new functional surface. The second with the development of functional prototypes of intelligent surfaces, showing its characteristics and ease of manufacturing using 3D additive manufacturing. The third with demonstrating the multi-frictional ability of the newly designed surface. Our friction test results show wide range friction control ability from the friction coefficient value 0.3 (same value of material itself) to 3 times higher value 1.1. Finally, we address the challenges that are faced in our new design and the efforts that are currently being adopted to overcome them. [ABSTRACT FROM AUTHOR]

Terahertz (THz) band will play an important role in enabling sixth generation (6G) envisioned applications. Compared with lower frequency signals, THz waves are severely attenuated by the atmosphere temperature, pressure, and humidity. Thus, designing a THz communication system must take into account how to circumvent or diminish those issues to achieve a sufficient quality of service. Different solutions are being analyzed: intelligent communication environments, ubiquitous artificial intelligence, extensive network automation, and dynamic spectrum access, among others. This survey focuses on the benefits of integrating intelligent surfaces (ISs) and THz communication systems by providing an overview of IS in wireless communications with the scanning of the recent developments, a description of the architecture, and an explanation of the operation. The survey also covers THz channel models, differentiating them based on deterministic and statistical channel modeling. The IS-aided THz channels are elucidated at the end of the survey. Finally, discussions and research directions are given to help enrich the IS field of research and guide the reader through open issues.

Heterotopic ossification(HO) is a potential severe complication after many biomaterial implanting surgeries, and the inflammation environment caused by the implanting-associated infections is considered as the main nosogenesis. Herein, an inflammation-responsive drug release system was designed by chemically conjugating indometacin (via ester group) onto hydrogel coating to realize local self-regulated drug release to prevent HO. In our strategy, poly(3-mercaptopropyl)trimethoxysilane-co-acrylic acrylate and polyvinyl alcohol (providing anchoring sites for drug molecules) were firstly synthesized and functionalized with ene-groups, then a hydrogel layer was formed and covalently attached onto thiol-modified substrate via thiol-ene click chemistry, followed by grafting indometacin. A porous structure of the attached hydrogel layer was observed by scanning electron microscopy, and the presence of drug molecules in the hydrogel layer was confirmed by X-ray photoelectron spectroscopy and UV–vis absorption spectra. The drug release could be triggered under the mimicking inflammation environment, and the release rate was responsive to the inflammation degree. In addition, after attaching the hydrogel coating, the substrate showed low cytotoxicity, and high promotion for cell adhesion and proliferation. The excellent hemocompatibility of the hydrogel coating was also demonstrated by prolonged clotting time and suppressed platelet adhesion. This work suggests that the inflammation-responsive indometacin conjugated hydrogel coating has great potential to be used for prophylaxis HO. [ABSTRACT FROM AUTHOR]

We report a Ag-nanoparticle (AgNP)-based substrate-independent bactericidal hydrogel coating with thermoresponsive antibacterial property. To attach the hydrogel coating onto model substrate, we first coated ene-functionalized dopamine on the substrate, and then the hydrogel thin layer was formed on the surface via the UV light initiated surface cross-linking copolymerization of N-isopropylacrylamide (NIPAAm) and sodium acrylate (AANa). Then, Ag ions were adsorbed into the hydrogel layers and reduced to AgNPs by sodium borohydride. The coating showed robust bactericidal ability against Escherichia coli and Staphylococcus aureus toward both contacted bacteria and the bacteria in the surrounding. Upon a reduction of the temperature below the LCST of PNIPAAm, the improved surface hydrophilicity and swollen PNIPAAm could detach the attached dead bacteria. Meanwhile, the long-lasting and regenerable antibacterial properties could be achieved by repeatedly loading AgNPs. By precisely controlling the AgNP loading amounts, the coating showed excellent hemocompatibility and no cytotoxity. Additionally, the coating could be applied to modify cell culture plate, since it could support cell adhesion and proliferation at 37 °C, while detach the cell by changing the temperature below lower critical solution temperature without the treatment of proteases. The study thus presents a promising way to fabricate thermoresponsive and regenerable antibacterial surfaces on diverse materials and devices for biomedical applications.