Search Results (929)

Dual-beam circularly polarized antenna arrays are widely demanded in high-capacity wireless and satellite communication systems. However, conventional designs typically suffer from complex feeding networks, large profile, and high insertion loss, which limit their integration level and efficiency. To address these issues, this paper proposes a low-loss, highly integrated dual-beam circularly polarized antenna array based on a substrate-integrated waveguide equivalent ENZ feeding network. A new physical phenomenon is revealed that the tangential electric field in the slots exhibits an equal-amplitude and anti-phase distribution due to the combined effect of the uniform field distribution in the ENZ medium and the boundary conditions of the slotted perfect electric conductor. Using this inherent mechanism, the antenna achieves symmetric dual-beam radiation at approximately ±27° in the E-plane. A polarization conversion meta surface layer is loaded to convert linear polarization into circular polarization. A prototype is fabricated and measured. At 8.3 GHz, the measured peak gain is 9.1 dBi, the minimum axial ratio is better than 1.5 dB, and the radiation efficiency is higher than 85%. The proposed array features simple structure, low loss, and high integration. Compared with conventional feeding structures, it eliminates the need for additional phase shifters or power dividers, effectively reducing insertion loss and structural complexity. It exhibits good application potential in compact base stations and satellite communication terminals. Full article

Flat-top beams with uniform intensity distribution and well-defined profiles have broad application prospects. However, current design methods can only achieve circular or square beam shaping. Recently, a method enabling the generation of polygonal flat-top beams has been proposed, yet its energy utilization rate is limited at the 70% level only. To solve this issue, we propose a hybrid iterative algorithm for the purpose of generating polygonal flat-top beams with high diffraction efficiency while maintaining excellent uniformity. The hybrid algorithm combines the advantages of the mixed-region amplitude freedom (MRAF) algorithm and the overcompensation (OC) algorithm. The MRAF is firstly employed to achieve high diffraction efficiency. Subsequently, the OC algorithm is adopted to optimize uniformity. In addition, a more convenient convolution-based method is used to construct the descending edge of the target flat-top beam. A series of polygonal flat-top beams, such as triangular, square, pentagonal, and hexagonal, are obtained, and comparisons with the original methods are also carried out by means of simulations and experiments. Our experimental data demonstrate that an average diffraction efficiency above 97% is achieved. Full article

In this study, the influence of thermal loading in a supersonic flight environment on the mechanical stiffness of elastic structures and the corresponding aeroelastic stability limits is investigated analytically. Recognizing that elevated temperatures inherently alter constituent elastic properties, a temperature-dependent continuous elasticity framework is incorporated directly into the governing differential operators of the structural domain. The macro-mechanical behavior of representative panel- and wing-type elements is modeled utilizing the Euler–Bernoulli beam formulation, while high-speed supersonic aerodynamic effects are represented through linearized first-order piston theory. The continuous spatial displacement fields are discretized by means of a modal expansion, and the coupled aeroelastic system is subsequently transformed into a finite set of dynamic state-space equations using the Ritz–Galerkin truncation method. The numerical and analytical outputs demonstrate that aerothermal softening not only induces continuous erosion in the material stiffness but also directly modulates the aeroelastic pole trajectories, thereby prematurely contracting the safe supersonic flight envelope. The primary novelty of the proposed framework lies in the derivation of explicit analytical expressions that directly map temperature-dependent stiffness variations onto supersonic aeroelastic instability boundaries. Because this approach is formulated in a generalized analytical form, it can be applied across diverse material systems, geometric profiles, and thermal conditions with reduced computational overhead compared to full fluid–structure interaction solvers, thereby providing a theoretical basis for preliminary stability assessment of supersonic aerospace configurations operating under high-temperature conditions. Full article

Typhoons and extreme rainfall significantly exacerbate engineering risks during deep excavation construction. Based on an asymmetric deep excavation project in Hainan under the influence of Super Typhoon Yagi, this study analyzes the evolution of Soil Mixing Wall (SMW) pile deformation and prestressed anchor cable axial forces through field monitoring. PLAXIS 3D 2023.2.0.1059 finite element software is employed to investigate the deformation response of the supporting structure under the coupled effects of excavation and extreme rainfall, revealing the optimal design for embedment depth under such adverse conditions. The results indicate that the presence of existing buildings leads to asymmetric deformation and pronounced corner effects. The synergistic action between the capping beam and the waler transforms the pile displacement profile from a cantilever mode to a bow-shaped distribution. Parametric analysis determines the optimal embedment depth to be 10.6 m and the critical safety embedment depth to be 7.6 m. Under a 400 mm/d typhoon rainfall condition, the maximum horizontal displacement of the supporting structure increases by 1.6–2.0 mm compared to non-rainfall conditions. With a 3.5 m water head, increasing the embedment depth from 6.1 m to 10.6 m reduces the maximum horizontal displacements on the east, south, and west sides by 98%, 42%, and 10%, respectively. This study provides a theoretical basis and practical reference for embedment depth optimization in typhoon-prone regions. Full article

There is a substantial demand for lightweight, low-profile, and conformal antenna integration on the wing platforms of unmanned aerial vehicles (UAVs). This paper presents an S-band (2–4 GHz) flexible conformal metasurface array antenna based on a highly conductive graphene-assembled film (GAF). The main contributions of this work are twofold. First, flexible and highly conductive GAF is used as the conductor together with a flexible polyimide (PI) dielectric substrate to form a GAF-based wing-conformal antenna configuration with a low-profile, lightweight, and easily conformal performance. Second, a GAF conformal antenna element is developed by combining a dipole antenna with a directive and reflective frequency selective surface (FSS), achieving effective control of the beam and stable directional radiation at 2.4 GHz. Full-wave simulations using CST Studio Suite show that the directive FSS narrows the feed beam, whereas the reflective FSS redirects and narrows the H-plane radiation. The simulated results show that the integrated wing-conformal antenna operates over 2.19–2.65 GHz and achieves a gain of 4.65 dBi at 2.4 GHz. The measurement results indicate that the GAF conformal antenna and 1 × 4 GAF conformal array antenna shows measured reflection coefficients below $-10$ dB at 2.4 GHz and effective adjacent-element isolation. In addition, simulated results indicate that the GAF array antenna can perform beam scanning within the ±40° range, verifying the beam-control capability of this structure for UAV forward communication. Overall, this work highlights the feasibility of using GAF as a conductive material for both a high-efficiency radiator and an FSS beamforming structure, offering a practical material and design approach for lightweight, low-profile, and wing-conformal airborne array antennas. Full article

Current terahertz (THz) metasurfaces are often constrained by fixed operational states, lacking the flexibility to switch dynamically between transmission and reflection modes. To address this limitation, we propose a tunable coded metasurface based on the photo-adjustable conductivity of silicon, enabling seamless mode switching and versatile wavefront manipulation. By leveraging the photo-induced dielectric-to-metallic transition, the device functions as a high-efficiency transmission-type polarization converter under zero pump fluence, transforming incident X-polarized waves into Y-polarized waves across a broad frequency range of 0.85–1.5 THz, with a polarization conversion ratio (PCR) exceeding 99%. Upon excitation by 800 nm near-infrared laser pulses, the metasurface transitions to reflection mode, where it simultaneously achieves linear polarization conversion and generates dual-channel orbital angular momentum (OAM) beams through a phase-coding strategy integrated with Fourier convolution. Furthermore, by employing the Gerchberg–Saxton (GS) algorithm to optimize the phase profile, holographic reconstruction is realized in the far field. This design integrates diverse manipulation capabilities into a single, dynamically controllable platform, offering a promising technological approach for THz information processing and integrated photonic systems. Full article

Electron beam powder bed fusion (E-PBF) requires reliable in situ process monitoring, and electron emission signals offer a promising avenue for this purpose. Most prior studies have relied on dedicated beam scans performed before or after melting, leaving open the question of whether the signal acquired during the melt itself can directly indicate geometric and topographical features of the fabricated part. In this work, the in-operando electron emission signal was recorded during spot-melting of a Ti-6Al-4V spur gear and evaluated for its ability to reconstruct geometric features and surface topography, with optical microscopy and profilometry serving as ground truth. A melt-pool dilation correction was applied to compensate for the geometric expansion of individual melt spots. After correction, the in-operando reconstruction reached agreement deviation values below 2.2% across the tooth tips, tooth bases, and chord widths, which are comparable to or better than those obtained from post-melt ELO imaging. Comparison with profilometer height profiles confirmed strong correlation with surface topography (Pearson 0.67–0.87 across all four profiles, p < 0.05 for all), indicating that the signal captures meaningful surface-topography variation in addition to geometric boundaries. The results demonstrate that the in-operando electron emission signal shows strong potential for in situ geometric and topographical assessment of complex parts in E-PBF, supporting its future integration into closed-loop process monitoring. Full article

Multibeam backscatter data are important for marine resource exploration and benthic habitat mapping. However, accurate estimation of absorption loss without concurrent CTD measurements can be challenging. This paper proposes an inversion method that combines a global Argo salinity model with sound speed profiles (SSPs). The method enables absorption loss correction using only SSP data, offering a potential engineering alternative that reduces the need for dedicated CTD casts and may support real-time processing. Salinity is interpolated from the Argo grid, temperature is inverted via empirical formula for sound speed, and the absorption coefficient is computed using the Francois–Garrison model. The method is evaluated using two open-access multibeam datasets from the NCEI: one from the Blake Plateau (depth 1050–1250 m, 26.5 kHz) and another from Johnston Atoll (depth 2000–5000 m, 28 kHz). Compared to concurrent CTD profiles, the maximum deviations observed are 0.3 ppt for salinity, 0.1 °C for temperature, and 0.06 dB/km for absorption coefficient. The difference in absorption loss between the inversion and the CTD-based reference is within 0.1 dB. A precomputed lookup table indexed by incidence angle and one-way travel time is constructed for rapid estimation. In a test of 5196 swaths (432 beams per swath), the total interpolation time is 0.726 s. These results suggest that the proposed method provides a practical solution for absorption loss correction when CTD data are unavailable. Full article

This work presents a refined theoretical and numerical framework for shaping the axial intensity of finite-energy Bessel–Gaussian beams through programmable nonlinear phase modulation. Starting from the scalar Fresnel diffraction integral, we reformulate the propagation of a Gaussian-apodized axicon beam using a dimensionally consistent stationary-phase method. This analysis directly relates the radial phase gradient to the saddle-point trajectory, phase curvature, and on-axis intensity distribution. A Gaussian phase modulation (GPM) serves as a reference design to achieve a flattop axial profile while preserving the characteristic transverse Bessel ring structure. This work is validated against beam propagation simulations and previously reported spatial light modulator (SLM) experiments, confirming its accuracy within the paraxial regime. A parametric study then clarifies the scaling of wavelength, beam waist, axicon angle, and refractive index for extended focusing. Beyond standard GPM, several alternative nonlinear phase functions are systematically compared. High-performing profiles must replicate not only the amplitude scale but, more importantly, the radial phase-gradient structure of the Gaussian reference, which governs energy redistribution from annular regions to the axis. The results identify smooth, localized nonlinear functions as promising candidates for stable flattop Bessel beam generation. The proposed framework offers a flexible optical design for applications such as through-glass via (TGV) micromachining and light-sheet illumination, while prospective high-intensity laser plasma uses remain beyond the present linear model. Full article

To address the erosion-induced failure of large-caliber gun barrels under extreme thermochemical coupling, this study systematically investigates the microstructural evolution of multi-layered gradient regions along the radial direction of 32CrNi3MoV steel under extreme thermochemical cycling. Leveraging SEM, EBSD, TKD, and double-beam aberration-corrected TEM, combined with JMatPro thermodynamic simulations, the phase transitions, crystallographic characteristics, and substructural evolution spanning from the bore surface to the matrix are elucidated. The results demonstrate that a three-layer gradient structure forms along the radial direction. The topmost layer is a chemically stabilized metastable austenite diffusion layer with a thickness of 1.5–4.0 μm. which is attributed to the suppression of martensitic transformation due to C/N interstitial diffusion lowering the MS temperature. The observed high-density dislocation tangles and stacking faults within this austenite diffusion layer result from thermal mismatch stresses during rapid thermal cycling. The subsurface region is a martensitic transformation layer with a thickness of 70–97 μm, exhibiting a substructural gradient from nanostructured high-density twinned martensite to refined lath martensite. Thermodynamic analysis indicates that rapid heating (≈10⁵ °C/s) facilitates significant austenite nucleation and growth during the reverse phase transformation, subsequently forming nanostructured martensitic grains via non-equilibrium transformation during rapid cooling. Adjacent to this is a matrix tempering layer extending approximately 160 μm. Nanoindentation hardness profiling reveals that the peak radial hardness (≈1000 HV) occurs within the fine-grained martensitic zone approximately 40 μm from the surface. In contrast, the tempered layer exhibits reduced hardness (≈400 HV) compared to the original matrix (≈500 HV). This is primarily attributed to transient high-temperature over-tempering effects, which induces carbide coarsening and the loss of solid solution strengthening, alongside the softening of prior austenite grain boundaries. This study clarifies the micro-to-nanoscale evolution of the barrel microstructure, providing critical theoretical insights for understanding erosion mechanisms and improving lifetime predictions. Full article

Glass fiber–reinforced polymer (GFRP) reinforcement provides an effective alternative to conventional steel in concrete structures due to its corrosion resistance. Nevertheless, the lower elastic modulus of GFRP necessitates careful consideration of serviceability behavior in GFRP-reinforced concrete members. This study presents a numerical sectional analysis model for predicting the flexural response and ultimate capacity of hybrid reinforced concrete beams incorporating embedded GFRP profiles in combination with either mild steel or GFRP reinforcement bars under monotonic static loading. The proposed model employs realistic nonlinear stress–strain relationships for concrete and steel, together with secant moduli of elasticity evaluated at different loading stages. Particular emphasis is placed on detailed stress distribution in flexural sections, including the contribution of tension stiffening in the post-cracking regime. The formulation integrates nonlinear constitutive material behavior with theoretical sectional equilibrium to evaluate the effective flexural secant stiffness. For practical serviceability assessment and to reduce dependence on complex analytical procedures, strain vectors and stiffness matrix components are derived using elasticity coefficients that reflect modulus degradation obtained from numerical analysis. The accuracy of the model is verified through comparison with experimental results, including ultimate flexural capacity and moment–deflection responses. Many crucial parameters were studied, such as the longitudinal reinforcement ratio, type of reinforcement, concrete compressive strength, position of the I-GFRP profile, and rotation of the I-GFRP profile. The results of this study demonstrated that both the longitudinal reinforcement ratio and the rotation of the I-GFRP profile have a significant influence on the ultimate load capacity and deflection behavior. The close agreement between numerical predictions and experimental observations demonstrates the reliability and applicability of the proposed model for structural engineering analysis and design. Full article

The controllable fabrication of tapered three-dimensional (3D) microstructures by ion-beam processing remains challenging, especially when both profile fidelity and geometric controllability are required. Tapered conical microstructures are of interest because they are relevant to a variety of applications, including micro-optical elements, functional textured surfaces, biomimetic interfaces, and field-enhancing emitter-related structures, where taper angle, aspect ratio, and structural uniformity strongly influence the resulting performance. In this work, a longitudinal layer-wise strategy is proposed for tapered micro-cone fabrication by ion-beam etching. The core idea is to discretize a continuous cone profile along the vertical direction into a sequence of annular layers whose dimensions are determined by the local geometry of the target three-dimensional structure. After this geometric discretization step, each individual layer is executed using a conventional multi-pass strategy, thereby combining longitudinal profile construction with stabilized local material removal. A dedicated pattern-design software, EBWriter, was developed to automatically generate annular patterns and process files from user-defined geometric parameters. Experimental validation was carried out on single-crystal silicon substrates using a dual-beam microscope platform operated at 30 kV. The results show that increasing the longitudinal layer number effectively weakens the staircase effect and improves the continuity of the reconstructed cone profile. For positive micro-cones fabricated using annular patterns with a nominal outer processing diameter of 3 μm, the increasing-inner-radius strategy enables preservation of the cone apex and reconstruction of tapered morphologies with improved fidelity. Under the present processing conditions, an empirical correspondence between the target geometric ratio and the recommended layer number was further summarized: layer numbers of approximately 50, 100, and 300 support cone structures with base-diameter-to-height ratios close to 1:2, 1:3, and 1:4, respectively. In addition, a 3 × 3 positive micro-cone array was successfully fabricated, with a total processing time of about 80 s. The measured cone base diameter and height were 0.886 ± 0.005 μm and 2.354 ± 0.023 μm, respectively, with dimensional variations controlled within ±2%. These results demonstrate that the proposed method provides a feasible layer-wise ion-beam fabrication route for tapered microstructures and offers a useful process basis for future studies on micro-optical surfaces, functional textured interfaces, and emitter-related microstructures. Full article

The increasing demand for reliable and high-performance electric vehicle (EV) batteries requires precise and defect-free welding of battery components. Conventional Gaussian laser beam welding faces challenges such as keyhole instability, spattering, porosity, and brittle intermetallic compound formation, particularly in dissimilar Al-Cu joints. These issues significantly affect the electromechanical performance and durability of battery connections. Beam shaping technology has emerged as a core method for improving weld quality, process stability, and efficiency in laser welding, making laser beam welding increasingly vital for high-volume production of e-mobility components. This review systematically evaluates recent advancements in laser beam shaping for laser welding, especially static beam configurations, such as core-ring profiles, flat top, elliptical, and shaped beams; emphasis has been placed on how altering the intensity distribution influences the challenges associated with conventional welding and emerges as an effective solution to address these challenges. By tailoring the spatial energy distribution, beam shaping improves control of heat input, stabilizes melt pool dynamics, and enhances microstructural uniformity. Static beam shaping, compatible with cost-effective near-infrared continuous-wave laser systems, is already being adopted in industry, whereas dynamic beam shaping remains at an earlier stage of industrial maturity. This review highlights key welding challenges in EV battery manufacturing, evaluates beam shaping strategies as practical solutions, and identifies future research directions for large-scale industrial implementation. Full article

Bessel beams, one of the four known types of beams that are exact solutions of the Helmholtz equation, are remarkable with their non-diffracting nature. In reality, generated with real (Gaussian) laser beams with finite transverse profiles, Bessel-Gaussian beams (BGBs) are quasi-non-diffracting and remarkably stable against spatial perturbations. Quasi-non-diffracting means that the central peaks of the BGBs typically have divergences of the order of microradians. Here, we present experimental evidence that the truncation of the concentric rings surrounding the central peak of the long-range BGBs has a pronounced and controllable effect on the divergence of their peaks. The method is well suited for microradian divergences and has a minimal effect when the divergence of the BGB approaches one milliradian. The truncation of the rings of the BGBs could be applied, for example, in free-space communications, in locating a receiver station with a more divergent beam, after which the spreading of the central peak in space could be reduced to ensure a more secure data transfer. Full article

Additive manufacturing (AM) has revolutionized industrial production. However, the repair of AM components remains a critical challenge due to their unique microstructural features. While repair approaches for conventionally manufactured alloys are well established, their direct transferability to AM parts remains largely unexplored due to the unique thermal history and anisotropic microstructure of additive components. This study investigates a novel repair and improvement strategy for Powder Bed Fusion–Laser Beam/Metal (PBF-LB/M)-fabricated AlSi10Mg components, combining Electrospark Deposition (ESD) for dimensional restoration with subsequent Ultrasonic Peening Treatment (UPT) for surface enhancement. Microstructure, porosity, surface roughness, hardness profiles, residual stresses, and corrosion behaviour were systematically characterized using SEM, optical microscopy, profilometry, Vickers microhardness testing, XRD, and electrochemical polarization tests. The results show that the ESD process is capable of producing coatings with excellent interfacial adhesion to the substrate, with an initial porosity of 3.6 ± 0.5%. The subsequent UPT induces a significant densification effect on the deposited material, reducing porosity by approximately 50% and increasing surface hardness by up to 48% in the upper region of the coating. Furthermore, XRD analysis reveals that UPT completely reverses the residual stress state from tensile (typical of the ESD process) to compressive in all measured directions, thereby improving the overall structural integrity. Ultimately, the combined ESD + UPT alters the electrochemical response of AlSi10Mg deposits, resulting in a nobler corrosion potential, albeit with a slightly higher corrosion current density. Full article