Search Results (291)

This study examines the flexural behavior of slender ultra-high-performance fiber-reinforced concrete (UHPC) beams with cross-sections intended for scalable precast production. The members are prestressed only, with no passive reinforcement. An experimental program on eighteen beams combined three cross-sectional typologies (rectangular as a reference, I-shaped, and H-shaped), three UHPC mixes with fiber contents of 130, 160, and hybrid 130 + 60 kg/m³, and two prestressing layouts (bottom-only and symmetric top-and-bottom). Prestress was indirectly controlled by evaluating effective tendon stress, with time-dependent prestress losses quantified using vibrating-wire strain gauges. Four-point bending tests provided material characterization and structural response, enabling assessment of stiffness and ultimate capacity. The results highlight the coupled influence of cross-section, fiber dosage, and prestress configuration on global response. Post-cracking residual strength in UHPC promoted stable multiple cracking, while prestressing governed deflection control. Residual equivalent flexural tensile stresses above 35 MPa at deflections over 50 mm, span/70, were achieved in I- and H-shaped sections, exceeding those of rectangular sections. Overall, the study substantiates the feasibility of lightweight, durable, prestressed UHPC members that deliver significant self-weight reductions without compromising reliability. Full article

Rectangular waveguides, serving as a standardized versatile platform for manipulating terahertz radiation within controlled environments, have been extensively employed across a broad range of terahertz systems. However, conventional fabrication methods encounter significant challenges in realizing such submillimeter-scale structures within a monolithic integration, particularly when subwavelength features or intricate geometries are incorporated for advanced functionalities. In this work, we propose a fabrication route integrating stereolithography 3D printing and electroless plating, and demonstrate its broad applicability, intrinsic benefits and limitations through the realization of various high-performance D-band terahertz rectangular waveguides and antennas. The resulting rectangular waveguides achieve an insertion loss below 0.3 dB and a return loss above 15 dB across the D-band, while remaining stable across extreme temperatures (−50 °C to 150 °C) and offering a weight reduction of over 60%. A monolithically fabricated smooth-walled conical horn antenna exhibits beam-shaping characteristics that closely align with theoretical expectations. Attempts on corrugated horn antennas in conventional design reveal degraded performance, primarily arising from the inherent staircase effect associated with 3D printing. A novel design featuring obliquely oriented corrugations is developed, effectively mitigating uncontrolled deformation in periodic subwavelength features. Compared with the classical corrugated design (θ = 90°), the proposed obliquely oriented corrugations (θ = 30°) improve the agreement between experimental and theoretical radiation patterns, reducing the gain deviation from 1.45 dB to less than 0.5 Db—a quantitative improvement of over 60% in pattern fidelity. We believe that this fabrication route together with the process-adaptive design paradigm establishes a robust technical foundation for realizing high-performance, lightweight, and design-flexible terahertz waveguide components and holds significant promise for advancing the development of next-generation integrated terahertz systems. Full article

Freeform Fresnel lenses combine the powerful beam-shaping capability of freeform optics with the lightweight and compact characteristics of conventional Fresnel structures, leading to their increasing adoption across diverse applications. This paper proposes and experimentally validates a method for generating rectangular dark hollow beams using a freeform Fresnel lens. The lens is divided into multiple fan-shaped sectors centered on the optical axis, with each sector generating a defocused spot at a distinct spatial location. Based on geometrical optics, a freeform Fresnel lens with a 25 mm aperture is designed to produce a square hollow beam with a side length of 10 mm. A lens with a division angle of 5° was fabricated using ultra-precision diamond turning. The angular form error was measured to be below 0.1°, and the surface roughness was found to be below 10 nm. An optical testing system was established to characterize the generated beam profile. The experimental results successfully demonstrate the formation of the desired rectangular dark hollow beam. The measured results agree well with the simulations, confirming the feasibility and practical potential of the proposed method. Full article

To address the problem of insufficient shear bearing capacity of highway reinforced concrete (RC) T-beams, this paper systematically conducts a comparative study on the shear performance of RC T-beams strengthened with UHPC-CFP toughened composite plates of different configurations, and proposes a shear strengthening method using UHPC-CFP toughened composite plates. Comparative tests on different strengthening configurations are carried out. Meanwhile, a finite element numerical model is established to compare with the experimental results, analyze the influences of different strengthening schemes on the shear bearing capacity and mechanical properties of the beams, reveal the shear strengthening mechanism, and put forward a recommended formula for calculating the shear bearing capacity. The results show that after the diagonal cracks appeared in Beam T-0, they propagated rapidly from the support to the loading point. Beam T-1 had more diagonal cracks in the concrete between the UHPC-CFP toughened composite strips, while Beam T-2 had fewer. Fine cracks occurred in the UHPC-CFP toughened composite strips of Beams T-1 and T-2, whereas no cracking was observed in the UHPC composite rectangular plate of Beam T-3. The shear capacity of all strengthened beams was improved, with increases of 27.0%, 40.5%, and 43.2% for Beams T-1, T-2, and T-3, respectively. Beam T-3 exhibited the maximum deflection, and the strengthening configuration of Beam T-2 was determined to be the optimal. The carbon fiber strips embedded in UHPC effectively delayed the propagation of cracks in the UHPC plate and played the role of “reinforcement”. The truss–arch model theory is also applicable to the shear mechanism of concrete T-beams strengthened with UHPC-CFP toughened composite plates. Verification of Beams T-2 and T-3 using the proposed formula for shear design of strengthened beams showed that the average ratio of the calculated shear capacity to the experimental value was 0.87, indicating the reliability of the calculation results. Full article

In this study, the comparative residual performance of fire-exposed reinforced concrete (RC) beams with rectangular and T-shaped cross-sections is investigated. Two concrete beams, one with a T-section and the other with a rectangular section, were tested under the combined effects of fire exposure and structural loading. Data generated in the tests during and following fire exposure is utilized to compare the thermal and structural response of the beams. The results indicate a notable difference in the temperature evolution, mid-span deflection, and the residual capacity of the beams. The T-beam experienced greater deflection and stiffness degradation due to its larger exposed surface area (approximately 17% higher than the rectangular beam) and flange geometry, despite comparable peak rebar temperatures. A simplified approach, based on the maximum concrete and rebar temperatures and corresponding strength reductions, is proposed to evaluate the residual capacity of fire-exposed RC beams. For equal cover depth to reinforcement, peak rebar temperature is unaffected by cross-section shape as long as the web of the T-beam is not slender. T-shaped beams with similar overall depth exhibit greater post-fire strength retention than rectangular beams when the neutral axis lies within the flange. A 20% reduction in the web thickness and a combined reduction of 20% in web and 37% in flange thickness result in a comparable decrease in the flexural capacity to that of the rectangular beams of similar depth, indicating that the flange plays a key role in maintaining post-fire performance. Full article

In nature, organisms have evolved unique structures that feature low weight, high strength, and damage resistance. The Eurasian eagle-owl serves as a representative example, with specialized feather architectures that enable stable flight in intense and turbulent airflow conditions. Herein, driven by classical design layup guidelines, and inspired by the distinctive fiber architecture of the feather shaft cortex, we propose a regionally tailored layup (RTL) design to enable mass-efficient composite beams with high load-bearing capacity and enhanced damage tolerance. The feather shaft reference lay-up rectangular beam (FSRB) adopts the RTL, and a flange overlap is introduced to preserve the integrity and strength of the flange–web interface; it is then manufactured using inner–outer matched molds in conjunction with vacuum bag molding. Three-point bending shows that the FSRB achieves a flexural strength of 180 MPa and a flexural modulus of 12.1 GPa. Relative to conventional axial (ALRB), Cross-ply (CPRB), single-helix (SLRB), and quasi-isotropic (QLRB) lay-up rectangular beams, the FSRB improves strength by 59.5%, 46.6%, 26.8%, and 21.2%, and increases modulus by 81.7%, 34.7%, 25.1%, and 10.8%, respectively. FEA and SEM observations confirm an RTL architecture in the rectangular beams, characterized by differentiated fiber arrangements in the flange and web. Flanges with an axially dominated layup provide high initial flexural strength and stiffness. The web, formed by a crossed-ply/axial hybrid layup, provides transverse support and redirects crack/delamination growth, thereby promoting progressive failure and enhancing energy dissipation. Overall, this RTL design enables concurrent improvements in load-carrying capacity and damage tolerance. This study offers a design perspective for high-performance load-bearing components. Full article

This study used finite element simulation and theoretical analysis to predict the crack distribution patterns that may occur during the shrinkage cracking process of rectangular timber beams. Based on the predictions, experimental specimens with six typical crack distribution patterns (I–VI) were designed. Subsequently, a four-point bending test method was employed to conduct large-sample size fracture tests on a total of 1200 small-sized Pinus sylvestris var. mongolica specimens, quantifying the effects of the crack depth, location, and distribution patterns on the specimens’ load-bearing capacity. The results indicate that when multiple cracks exist in a timber beam, their collective effect is not a simple superposition of individual cracks but a spatial distribution coupling effect. Both the depth and location of the cracks play crucial roles in their interaction. This study introduces three coefficients for evaluating the influence of cracks on timber beams, namely the load-bearing capacity coefficient (R), the decline ratio of load-bearing capacity (D), and the comprehensive crack-influence coefficient (β), which can effectively quantitatively evaluate crack damage effects. The framework established in this study, which links shrinkage crack characteristics with the load-bearing capacity of timber beams, along with the experimental data provided, can serve as a reference for the safety evaluation and scientific maintenance of historical timber components and modern timber structures with shrinkage cracks. Full article

Background/Objective: Resin-based composite (RBC) gained wide popularity in dentistry due to its excellent biocompatibility, superior aesthetics, and good bonding to enamel and dentine. However, they have several shortcomings, including mechanical insufficiency and shrinkage tendency. Many researchers have utilized nanoparticles (NPs) as a reinforcing filler for RBCs. This article focused on assessing the impact of three different nanoparticles, ZrO₂, TiO_2, and SiO_2, with concentrations of 3 wt% and 7 wt%, on the elastic modulus (E) and fracture toughness (K_IC) of one commercial light-activated dental resin composite. Methods: 140 rectangular specimens were constructed according to ISO 4049 with dimensions (25 × 2 × 5 ± 0.03 mm) and (25 × 2 × 2 ± 0.03 mm) for fracture toughness and elastic modulus, respectively. Specimens were categorized into four main groups based on nanofiller types. Control: plain without filler (CC) and three modified ones with ZrO₂ (ZC), TiO₂ (TC), and SiO₂ (SC). Furthermore, modified groups were divided into two subgroups according to nanofiller concentration, 3 and 7 wt% (ZC3, ZC7, TC3, TC7, SC3, and SC7), n = 10. Mechanical testing for fracture toughness was completed using a single-edge notched beam, while a three-point bending test was used for elastic modulus. Analysis of data was based on two-way ANOVA and Bonferroni post hoc (α = 0.05). Results: ZrO₂ provided the most substantial improvement in both E and K_IC, with the optimal performance observed at 3 wt% for stiffness and 7 wt% for toughness. TiO₂ groups also enhanced these properties at both concentrations; however, the gains were less pronounced compared to ZrO₂. SiO₂ improved mechanical performance at 3 wt%, but a higher loading of 7 wt% resulted in reduced values. Conclusions: Resin-based composite modified with 3 wt% of NPs tends to possess higher fracture toughness and modulus of elasticity. Fracture toughness enhancement was concentration-dependent with ZrO₂ NPs, where the best result was obtained with 7 wt%. Nanoparticle-reinforced composite, particularly ZrO₂, may be suitable for prosthodontic applications. Full article

This study presents a novel beam-scanning ground-penetrating radar (BS-GPR) system based on a wide-angle beam-scanning antenna array, aimed at extending the lateral detection range and improving the imaging fidelity without increasing the size of the transceiver antennas. The BS-GPR comprises a signal transceiver, a wide-angle beam-scanning antenna array for transmission and a bowtie antenna for reception. Unlike conventional commercial ground-penetrating radar (GPR), the transmitting signal of the wide-angle beam-scanning antenna array designed in this study can cover a fan-shaped region of ±90°, enabling the detection of abnormal targets outside the rectangular region directly below it. In field tests on air and sand, the BS-GPR proposed in this study can detect anomalous targets in the 55° and 30° directions, respectively. In brief, this study confirms the effectiveness of the wide-angle beam-scanning antenna array for extending the lateral detection range of GPR. Full article

Remotely operated vehicles (ROVs) equipped with multibeam forward-looking sonar are widely used for underwater object search in environments where visibility is limited. Ensuring complete three-dimensional (3D) scan coverage within a bounded mission duration remains a challenging planning problem due to sonar beam geometry and vehicle motion constraints. This study presents a deterministic, geometry-driven framework for volumetric path planning of ROV-based forward-looking sonar scanning in predefined circular and rectangular underwater volumes. The proposed approach constructs layered planar scan trajectories by explicitly incorporating sonar detection range, horizontal and vertical beamwidths, and scan volume geometry. Mission duration is analytically estimated from path length and vehicle kinematic parameters, enabling systematic comparison among multiple planning strategies. To support qualitative interpretation of scan effectiveness, a distance-based target position certainty metric is introduced and combined with the active sonar equation to estimate likely target locations within the scanned volume. Simulation results under idealized sensing and motion assumptions demonstrate that the corrected zigzag pattern for rectangular scan areas, as well as the corrected zigzag-II and corrected arithmetic spiral-III patterns for circular scan areas, achieve complete volumetric coverage with bounded mission duration and consistent localization performance. The proposed framework provides a transparent analytical baseline for evaluating volumetric scan path planning strategies for forward-looking sonar–equipped ROVs. Full article

This paper presents a new beamforming algorithm for Multi-User Multiple-Input Multiple-Output (MU-MIMO) systems using Multi-Agent Reinforcement Learning (MARL). The proposed approach is shown to significantly enhance the efficiency and performance of future wireless communication systems. The system comprises two base stations, each equipped with a Uniform Rectangular Array (URA) of directional antennas. Each base station has RL algorithms that use beamforming to provide the optimal Signal-to-Interference-Plus-Noise Ratio (SINR) for each user. These algorithms also work with the other base stations to prevent user interference and ensure efficient resource use. Simulation results demonstrate that the potential of the proposed method has the potential for dynamically adapting beam patterns and maintaining high SINR across the network, resulting in more than a 2-fold improvement in throughput and a 5453% improvement in SINR. Full article

This paper presents a thermal management solution for a Ka-band gyrotron traveling wave tube (gyro-TWT) with non-superconducting magnets. At present, the miniaturization and non-superconductivity of gyro-TWT have become a trend, but miniaturization leads to a significant increase in power density and a severe limitation in heat sink volume, which critically limits power capacity. To address this challenge, a joint microwave–thermal management evaluation model is used to investigate the heat transfer process and identify the crucial factors constraining the power capacity. A cylindrical heat sink with narrow rectangular grooves is introduced. Based on this, the cooling efficiency has been enhanced through structural optimization. The beam–wave interaction, electrothermal conversion, and heat conduction processes of the interaction circuit are analyzed. The compact heat sink achieves a 1.2-fold increase in coolant utilization and reduces the overall volume by 27.4%. Meanwhile, this heat sink improves the cooling performance and power capability of the gyro-TWT effectively. At 29 GHz, the gyro-TWT achieves a pulse power of 150 kW. Simulation results show that the maximum temperature is 348 °C at a 45% duty cycle, reduced by 159 °C. The power capacity of the Ka-band gyro-TWT increases by 40.6%. Full article

To meet the requirements of non-mechanical beam scanning and acquisition in space laser communication, this study proposes a two-dimensional scanning and acquisition method based on a silicon-based optical phased array (OPA). The OPA utilizes thermo-optic phase modulation to achieve horizontal beam pointing, while vertical beam pointing is controlled by wavelength tuning. By combining the OPA with a rectangular spiral scanning strategy, non-mechanical scanning is realized and beam acquisition experiments are carried out. Experimental results demonstrate that for an 8° step signal, the horizontal and vertical rise times are 156.8 μs and 214.76 ms, respectively. A full scan of 440 points covering a ±4° field of view is completed in 8.119 s. Acquisition experiments were conducted assuming a Gaussian-distributed uncertainty region (standard deviation $\sigma =1°$). Out of 106 independent trials, a success rate of 97.17% was achieved with an average acquisition time of 0.41 s. This work experimentally applies a rectangular spiral scanning strategy to an OPA-based acquisition system, addressing a capability that has been largely missing in previous studies. These results verify that the OPA technology has good scanning efficiency and acquisition robustness in space laser communication applications. Full article

Energy harvesting systems face performance limitations, and existing optimizations are not always sufficient; this study addresses these gaps by enhancing piezoelectric energy systems. To improve the performance of piezoelectric energy harvesting systems, an optimization methodology is developed in this study. Since the mechanical strain distribution directly affects energy conversion efficiency, this issue is addressed through optimization of the thickness geometry of a common cantilever-type harvester elastic substrate element via a state-space gradient projection method combined with design sensitivity analysis. The gradient projection method is implemented in MATLAB R2024b software to determine the optimal elastic substrate design, after which the optimized design is simulated in COMSOL 6.3 Multiphysics for strain analysis in a transient study. The optimized cantilever designs are produced by 3D printing using a photopolymer and experimentally validated using piezo sensors and laser measurements for dynamic analysis. Theoretically compared with traditional uniform beams, the optimized cantilever designs maximize strain along the upper layer of the elastic substrate element, leading to a substantial increase in the energy conversion efficiency. This maximization is validated by experimental measurements showing a significant increase in strain in the elastic substrate (approximately 30% at the first eigenfrequency and 70% at the second). The correlation between the experimentally obtained data and the simulation results validates the optimization results. Deviation between the results did not exceed 3% and indicates that cantilever-type energy harvesters with optimized thickness profiles outperform traditional rectangular beams in energy conversion efficiency. Full article

Polarization beam combining (PBC) is an important technology for enhancing laser brightness. The conventional bulk polarization beam combiners are Brewster plates and birefringent polarization prisms. However, in the mid- and long-wave infrared range, the beam combining performance is limited by the transmission and birefringent coefficient of the available materials. In this paper, a polarization beam combiner based on a reflection metasurface was proposed. The phases of incident beams with orthogonal linear polarizations were individually manipulated by the side lengths of the rectangular silicon pillar. A metasurface polarization beam combiner operating band was designed and fabricated. When the two beams at 4.6 μm with orthogonal linear polarizations were incident on the metasurface at angles of −13.3° and 13.3°, respectively, they were reflected in the 0°-direction. The overall beam combining efficiency was 88.9%. When both of the quantum cascade lasers used in the experiments were in the fundamental transverse Gaussian mode, the measured beam quality factors M² of the combined beam were 1.21 and 1.14 along the fast and slow axes, respectively. Both simulation and experimental results demonstrated that the proposed metasurface was an efficient polarization beam combiner with negligible wavefront distortion. It is a promising alternative to traditional bulk optics for the mid- and long-wave infrared. Full article