Reconfigurable intelligent surfaces (RISs) are an emerging transmission technology for application to wireless communications. RISs can be realized in different ways, which include (i) large arrays ...of inexpensive antennas that are usually spaced half of the wavelength apart; and (ii) metamaterial-based planar or conformal large surfaces whose scattering elements have sizes and inter-distances much smaller than the wavelength. Compared with other transmission technologies, e.g., phased arrays, multi-antenna transmitters, and relays, RISs require the largest number of scattering elements, but each of them needs to be backed by the fewest and least costly components. Also, no power amplifiers are usually needed. For these reasons, RISs constitute a promising software-defined architecture that can be realized at reduced cost, size, weight, and power (C-SWaP design), and are regarded as an enabling technology for realizing the emerging concept of smart radio environments (SREs). In this paper, we (i) introduce the emerging research field of RIS-empowered SREs; (ii) overview the most suitable applications of RISs in wireless networks; (iii) present an electromagnetic-based communication-theoretic framework for analyzing and optimizing metamaterial-based RISs; (iv) provide a comprehensive overview of the current state of research; and (v) discuss the most important research issues to tackle. Owing to the interdisciplinary essence of RIS-empowered SREs, finally, we put forth the need of reconciling and reuniting C. E. Shannon's mathematical theory of communication with G. Green's and J. C. Maxwell's mathematical theories of electromagnetism for appropriately modeling, analyzing, optimizing, and deploying future wireless networks empowered by RISs.
Most organic polymeric materials have high flammability, for which the large amounts of smoke, toxic gases, heat, and melt drips produced during their burning cause immeasurable damages to human life ...and property every year. Despite some desirable results having been achieved by conventional flame‐retardant methods, their application is encountering more and more difficulties with the ever‐increasing high flame‐retardant requirements such as high flame‐retardant efficiency, great persistence, low release of heat, smoke, and toxic gases, and more importantly not deteriorating or even enhancing the overall properties of polymers. Under such condition, some advanced flame‐retardant methods have been developed in the past years based on “all‐in‐one” intumescence, nanotechnology, in situ reinforcement, intrinsic char formation, plasma treatment, biomimetic coatings, etc., which have provided potential solutions to the dilemma of conventional flame‐retardant methods. This review briefly outlines the development, application, and problems of conventional flame‐retardant methods, including bulk‐additive, bulk‐copolymerization, and surface treatment, and focuses on the raise, development, and potential application of advanced flame‐retardant methods. The future development of flame‐retardant methods is further discussed.
Flame‐retardant methods for polymeric materials are reviewed with particular focus on advanced flame‐retardant methods developed in recent years. Both the advantages and drawbacks of these methods are discussed, and prospects for the future development of flame‐retardant methods are presented. It is hoped that this review will guide the development of flame‐retardant polymeric materials.
Axial piston pumps have three important friction pairs (valve plate–cylinder, swashplate–slipper, and cylinder–piston interfaces), which are crucial to the performance and service life of the pumps. ...The friction pairs of the piston pumps are facing challenges due to the demands for high-performance piston pumps with high speeds, large flow rates, and higher pressures. This article provides an overview of studies on the wear mechanisms of the three friction pairs and a summary of current research seeking solutions for the friction pairs, including structural improvement, material selection, and surface treatment. Existing issues in the development of high-performance axial piston pumps are also discussed. This review article is delivered with an attempt to provide a reference for designing high-performance.
•Summarized the method to improve the friction performance of axial piston pumps.•Analyzed the wear mechanism of three key friction pairs of axial piston pumps.•Discussed the structural, material and surface modifications of the interface.•Proposed the challenges of developing high performance piston pumps.
To reduce the surface defects of additive manufacturing forming parts and improve surface quality such as surface roughness and corrosion resistance, a two-step surface treatment technology, namely, ...pre -polishing combined with micro-arc oxidation (MAO), is employed to treat bulk samples constructed by selective laser melting (SLM) and selective electron beam melting (SEBM), respectively. Effects of surface morphology and coating thickness on surface roughness and corrosion resistance are systematically studied. Results show that the two-step surface treatment weakens the step effect of the original sample surface distinctively. Meanwhile, the MAO coating can improve the corrosion resistance of the original sample significantly. The corrosion current density Icorr of SLM specimen- is reduced from 6.212 × 10−5 A/cm2 to 2.493 × 10−7 A/cm2 (t = 15 min), and the Icorr of SEBM specimen- is reduced from 8.013 × 10−6 A/cm2 to 2.562 × 10−6 A/cm2 (t = 15 min).
•TC4 sample is successively fabricated by SEBM SLM technology.•The effect of MAO time on the roughness of SEBM and SLM samples was investigated.•The effect of MAO time on corrosion resistance of SEBM and SLM samples was investigated.•The different effects of two-step treatments on the roughness and corrosion resistance of SEBM and SLM samples were compared.•MAO coating can improve corrosion resistance of SEBM and SLM samples.
Functional gradient materials are interesting for optimizing the properties of engineering parts. Laser surface treatment makes it possible to obtain a stiffness gradient on titanium parts; such ...graded material is attractive due to the potential for orthopedic implant performance improvement and other applications as well. This work used laser surface treatment without fusion on two aged titanium alloys: Ti8Mo and Ti30Nb1Fe. This processing route aimed to fully dissolve the α-phase precipitates in a surface layer and, consequently, reduce the elastic modulus, producing a stiffness gradient from the surface to the inner material. Firstly, single tracks were obtained for different laser powers, kept constant the other parameters, aiming to determine the optimum condition to avoid surface fusion and produce the thickest-possible modified layer. Then, multi-track overlapping produced a modified continuous layer. The aged titanium alloys were characterized by optical and scanning electron microscopy and X-ray diffraction. The single tracks were characterized by stereoscopic and optical microscopy. Transmission electron microscopy and instrumented indentation completed the characterization of the laser-modified layer. Laser surface treatment produced a less-rigid surface layer in the Ti8Mo alloy due to the obtainment of β and α″ titanium phases with lower elastic modulus. The surface treatment did not change the material's hardness in this case. On the other hand, the precipitation of the ω phase during surface cooling of the Ti-30Nb-1Fe alloy prevented the elastic modulus from decreasing and increased the modified-layer hardness. Hence, the absence of ω phase precipitation is a condition to obtain a less-rigid surface layer by laser surface treatment on aged titanium alloys.
•Laser surface treatment without fusion was applied in aged β‑titanium alloys.•Optimized processing parameters produced the thickest-possible treated layer.•Laser surface treatment yielded a less-rigid surface layer on the aged Ti8Mo alloy.•ω phase precipitation prevented stiffness from decreasing in the Ti30Nb1Fe alloy.•An adequate alloy selection is mandatory to produce a less-rigid surface layer.
•Plasma treatment was used to improve the adhesion property between the recycled CF and polymer matrix.•In order to evaluate the adhesion between plasma treated recycled CF and polymer, micro droplet ...test was conducted.•The interfacial shear strength and the interfacial adhesion of recycled carbon fiber increased.
We studied the effects of plasma surface treatment of recycled carbon fiber on adhesion of the fiber to polymers after various treatment times. Conventional surface treatment methods have been attempted for recycled carbon fiber, but most require very long processing times, which may increase cost. Hence, in this study, plasma processing was performed for 0.5s or less. Surface functionalization was quantified by X-ray photoelectron spectroscopy. O/C increased from approximately 11% to 25%. The micro-droplet test of adhesion properties and the mechanical properties of CFRP were also investigated.
Antibiofouling
Harmful microbes can grow freely on implanted medical devices such as catheters (as shown on the right). In article number 2200254, Amir Sheikhi, Richard B. Kaner, and co‐workers, ...report a new method to apply a robust surface coating containing zwitterions, which creates a water layer that prevents biofilm formation (as shown on the left). This can improve the safety of the medical devices and reduce patient complications. Image credit: Amir Sheikhi/Penn State.
The aim of this study is to increase thermal conductivity of polypropylene (PP) composites filled with hexagonal boron nitride particles. Two types of BN with different types of surface treatment ...were used – pristine and covered with 3-amino-propyl-3-ethoxy-silane (APTES), which was bonded to hydroxyl groups, formed on the h-BN surface by annealing at 1100°C. The presence of covalently bonded silane functional groups on the surface of h-BN particles was proved by Fourier transform infrared spectroscopy (FTIR) method. Surface treatment of h-BN particles allowed to introduce 3-times increased amount of the filler in the composite produced by extrusion casting technique as compared with non-treated h-BN filler. The thermal conductivity of PP composites filled with surface-modified h-BN was effectively enhanced – up to 2 times as compared with the composite filled with pristine h-BN and more than 2.5–4 times as compared with pure PP.
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