Search Results (481)

Maritime search and rescue is an important component of emergency response frameworks and primarily relies on Unmanned Aerial Vehicles (UAVs) for maritime object detection. However, maritime accidents frequently occur in low-visibility environments, such as foggy or low-light conditions, which lead to low contrast, blurred object boundaries, and degraded texture representations. Most existing maritime object detection algorithms are developed for natural light scenes, and their performance deteriorates markedly when deployed directly in low-visibility environments, primarily due to reduced image quality that hinders feature extraction and semantic information aggregation. Although several studies incorporate image enhancement techniques prior to detection to improve image quality, these approaches often introduce significant additional computational overhead, limiting their practical deployment on UAV platforms. To tackle these challenges, this paper proposes a lightweight model built upon a recent YOLO framework, termed Multi-Scale Adaptive YOLO (MSA-YOLO), for maritime detection using UAVs in low-visibility environments. The proposed model systematically optimizes the backbone, neck, and detection head networks. Specifically, an improved StarNet backbone is designed by integrating Efficient Channel Attention (ECA) mechanisms and multi-scale convolutional kernels, which strengthen feature extraction capability while maintaining low computational overhead. In the neck network, a high-frequency enhanced residual block branch is inserted into the C3k2 module to capture richer detailed information, while depthwise separable convolution is utilized to further reduce computational cost. Moreover, a non-parametric attention module is incorporated into the detection head to adaptively optimize features in the classification and regression branches. Finally, a joint loss function that combines bounding box regression, classification, and distribution focal losses is utilized to improve detection accuracy and training stability. Experimental results on the constructed AFO, Zhoushan Island, and Shandong Province datasets demonstrate that, relative to YOLOv11-s, MSA-YOLO reduces model parameters and FLOPs by 52.07% and 41.36%, respectively, while achieving improvements of 1.11% and 1.33% in mAP@0.5:0.95 and mAP@0.5. These results indicate that the proposed method effectively balances computational efficiency and detection accuracy, rendering it suitable for practical maritime search and rescue applications in low-visibility environments. Full article

One of the bottlenecks in realizing all-optical computing is the lack of on-chip all-optical logic devices that combine compactness, low loss, and high robustness. Valley photonic crystals (VPCs) have become an important solution for realizing such devices, relying on the excellent transmission characteristics of topological valley states. However, existing structures still face issues such as limited design flexibility. In this paper, a high-performance topological all-optical logic device based on VPCs consisting of circular ring dielectric columns is designed and demonstrated. By introducing the inner radius as an independent design parameter, we construct a new type of VPC and systematically investigate its influence on the photonic band gap. Based on this, we design a beam splitter with high operational bandwidth and low insertion loss (<0.5 dB) and then realize fundamental OR and XOR logic gates, achieving extinction ratios of 18.9 dB for the OR gate and up to 44 dB for the XOR gate at an operating frequency of 193.5 THz. The platform also supports the NOT gate and, through cascading, can implement more logic functions such as the AND gate. Full article

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

A compact, low-profile dual-band feed network operating at 37–40 GHz (Ka-band) and 70–86 GHz (E-band) is presented for millimeter-wave backhaul applications. The proposed network integrates a quad-ridged orthomode transducer (OMT) and four ridge-waveguide diplexers into a three-layer all-metal stacked architecture, eliminating the cascaded inter-stage flanges of conventional feed chains and yielding a monolithic-like assembly that is mechanically robust and CNC-friendly for mass production. Stepped-impedance matching stubs in the OMT junction provide broadband matching across the widely separated bands, while compact ridge-waveguide T-junction diplexers, comprising stepped-impedance low-pass filters and rectangular high-pass paths, perform the spectral separation. Back-to-back measurements of the fabricated prototype demonstrate an insertion loss below 0.6 dB across both bands. The measured VSWR at the four output ports remains below 1.5 across both bands, and the port-to-port isolation exceeds 32 dB at the Ka-band and 45 dB at the E-band. The proposed network thus offers a highly integrated, low-loss solution for next-generation dual-band mmWave links. Full article

We present a family of compact, programmable wavelength demultiplexers enabled by an etchless silicon nitride platform integrated with the low-loss phase-change material Sb₂Se₃. Using topology optimization (LumOpt) with a p-norm (p = 2) figure-of-merit defined over a 10 nm bandwidth, we design several devices within a common 24 × 24 μm² design region: single-wavelength routers (1530, 1550, 1570, 1590 nm), two-channel (1550/1570 nm), three-channel (1530/1550/1570 nm), and four-channel (1530–1590 nm) coarse wavelength-division demultiplexers, all sharing the same input/output waveguide configuration. Simulation results show that all devices achieve low insertion loss at target wavelengths (peak transmission better than −1.21 dB across all channels), high average transmission over the respective 10 nm bands (typically within 0.1 dB of the peak), and suppressed crosstalk (worst case below −11.52 dB). Leveraging the reversible amorphous-to-crystalline phase transition of Sb₂Se₃ via laser pulses, all devices support post-fabrication reconfiguration, overcoming the static functionality of conventional etched photonic circuits. This work establishes a scalable, software-defined platform that combines inverse design and phase-change materials for high-density, reconfigurable wavelength-routing photonic integrated circuits. Full article

This article presents the results of a numerical CFD study of heat exchanger channels with passive heat transfer enhancement methods. Two types of channel geometry were analyzed with different flow turbulization methods. In case I, internal micro-fins were applied to the tube wall, which disturbed the flow directly in the boundary layer; the investigated relative fin heights ranged from 0.01 h/D to 0.08 h/D, and the dimensionless longitudinal spacing varied from 0.92 L/D to 3.27 L/D. In case II, an insert with repeating drop-shaped elements was used, causing fluid turbulization in the tube core; the relative droplet diameter ranged from 0.38 d/D to 0.73 d/D, with the same longitudinal spacing as for the fins. The influence of the geometry and longitudinal spacing of the disturbance elements on the thermal–flow characteristics of such channels, namely, the friction factor, Nusselt number, and thermal efficiency evaluated using the PEC, was investigated over a Reynolds number range of 5000 to 400,000. The results show that the insert produces a larger increase in the Nusselt number, whereas the micro-finned tube generally achieves higher PEC values due to lower hydraulic losses. The results clearly indicate that, in most cases, the PEC is higher for the finned tube, particularly at low Reynolds numbers not exceeding 50,000. In turn, for the insert, the longitudinal distance between the elements, L, has a significant influence on the PEC; as L increases, the PEC also increase, reaching its maximum value for the largest L. Full article

Transformerless inverters are increasingly becoming essential in renewable energy generation, particularly for grid-connected photovoltaic (PV) and other sustainable and alternative energy resources. The transformerless designs offer higher efficiency, compact size, and reduced cost compared to traditional inverters with bulky transformers. These inverters minimize energy losses and enable direct connection to the grid by removing the low-frequency transformer. This paper investigates a highly reliable single-phase common-ground inverter for solar panels and other alternative energy generation. The proposed PV inverter has the benefits of existing non-isolated common-ground PV inverters, including direct connection of an input source’s negative terminal to the AC neutral terminal, eliminating leakage ground currents. The inverter is an enhancement of the dual-buck inverter, incorporating one additional diode and a flying capacitor. The dual-buck structure with the inductor inserted between the inverter phase leg prevents short-circuiting. This increases the reliability of the entire power electronics system. Moreover, using external diodes to freewheel the current, the configuration has no reverse recovery issues, allowing power MOSFETs to be employed with safe commutation at higher DC-link voltage and achieve higher efficiency. Summarily, this design prevents short-circuit issues, enhancing reliability and efficiency, and relaxing pulse-width-modulation dead times. The derivation of the PV inverter is carefully analyzed. A 700 W prototype of power converter hardware has been built. The comparative study validates the operational performance, and the grid-connected experiment confirms its theoretical analysis. Experimental results of the hardware prototype are discussed to prove the feasibility and effectiveness of the proposed PV inverter. Full article

This paper proposes a novel low-pass frequency selective surface (FSS) with high-frequency rejection. Through theoretical derivation of the equivalent circuit model (ECM), an additional transmission pole can be generated below the transmission zeros by cascading two band-stop FSSs incorporated with an air spacer, therefore enhancing the low-pass performance. Based on the above findings, a compact and simple FSS is designed, which consists of two dual band-stop FSS with an air spacer. The staggered distribution of the four transmission zeros substantially broadens the stopband. The full-wave simulation result shows that the proposed FSS has an ultra-wide out-of-band rejection with transmission coefficient under −10 dB from 4.42 GHz to 27 GHz (143%), while maintaining a relatively good low-pass characteristic under 4.42 GHz with a maximum insertion loss of 1.36 dB. The full-wave simulation result matches closely with the ECM result. Full article

This paper proposes a novel shielded quad-axis differential through-silicon via (SQDTSV) structure. Initially, the parasitic parameters are extracted, and the applicability of the equivalent circuit model and analytical formulas is verified through a combined approach of HFSS simulations and MATLAB computations, leading to the establishment of an accurate equivalent circuit model. Subsequently, based on the single-variable principle, a systematic investigation is conducted to analyze the influence of multidimensional physical parameters—such as via height, signal conductor radius, and dielectric isolation thickness—on the transmission characteristics. An optimization model is then constructed via parameter sensitivity analysis. Simulation results demonstrate that, within the 0–100 GHz frequency band, the optimized SQDTSV structure has significantly improved performance across the entire frequency range. The differential-mode return loss has increased by more than 6.98 dB in the 50–100 GHz high-frequency band after optimization. In terms of transmission efficiency, the insertion loss in the low-frequency range (0–10 GHz) has decreased by more than 27%, and in the high-frequency range (10–100 GHz), it has decreased by over 11%, thereby significantly improving overall transmission performance. Full article

The systematic influence of signal electrode width on electro-optic bandwidth and insertion loss in L-type traveling-wave lithium niobate modulators has not yet been comprehensively quantified, limiting the parametric engineering design of this device configuration. This study presents a full-band systematic simulation sweep of signal electrode width and three auxiliary geometric parameters in an L-type traveling-wave lithium niobate Mach–Zehnder modulator, combined with optical mode simulation to establish joint microwave–optical optimization constraints. The study reveals the coupled modulating effect of signal electrode width on characteristic impedance, velocity mismatch, and transmission loss; it elucidates the competition mechanism underlying non-monotonic high-frequency loss behavior; and it identifies the complete impedance-neutral characteristic of the electrode–waveguide contact width as an independent loss-tuning degree of freedom decoupled from the impedance constraint. Full-system validation confirms that the final design simultaneously satisfies broadband impedance matching, low insertion loss, and high electro-optic bandwidth. The results are distilled into four quantitative design rules that provide simulation-driven guidance directly applicable to the engineering design of L-type thin-film lithium niobate modulators, advancing the systematic establishment of a parametric design methodology for this device configuration. Full article

Reconfigurable radio frequency (RF) attenuators are critical passive components for 5G-Advanced and emerging 6G wireless systems. Conventional tunable attenuators rely on solid-state switches combined with fixed resistor networks, which suffer from unavoidable static power consumption and severe parasitic degradation at high frequencies. Here, we systematically demonstrate HfO₂-based non-volatile memristors as RF switches with tunable ON-state resistance (R_ON), enabling a switching-attenuation-integrated multistate attenuator. The fabricated Au/HfO₂/Ag devices exhibit stable bipolar resistive switching with an ON/OFF ratio exceeding 10⁹, reliable retention of 10⁵ s, and programmable R_ON continuously tuned from 5.8 Ω to 197.5 Ω. On-wafer RF characterizations from 10 MHz to 43.5 GHz reveal low insertion loss (−0.53 dB), high isolation (−26.8 dB), and clear scaling laws governing the effects of device geometry and R_ON on RF performance. Leveraging these unique characteristics, we propose a symmetric π-type programmable all-memristor attenuator architecture with a cascaded 2-unit configuration. The design achieves 12 discrete attenuation levels from 2 dB to 24 dB, a return loss better than 10 dB across the full band, and zero static power consumption without additional passive components or bias networks. This work establishes the fundamental material-device-RF performance relationship in HfO₂-based RF switches and provides a compact, low-power, and highly integrable solution for next-generation reconfigurable RF front-ends. Full article

Intrabody cage augmentation has emerged as a minimally invasive technique for anterior column reconstruction in Kümmell disease and osteoporotic burst fractures. These osteoporotic conditions lead to progressive vertebral collapse, kyphosis, and instability. While cement augmentation provides rapid pain relief, it often fails to reliably restore sagittal balance or ensure biological integration in advanced stages of collapse. Although conventional anterior corpectomy with long-segment posterior fusion can achieve satisfactory deformity correction, these procedures are associated with substantial surgical morbidity. In contrast, screw fixation alone often fails to withstand anterior loading, resulting in loss of correction or hardware failure. By adapting standard interbody devices for off-label intravertebral use, this technique utilizes the intravertebral cleft as a natural cavity to restore vertebral height and sagittal alignment while preserving adjacent intervertebral discs and reducing stress on posterior instrumentation. The surgical technique involves transpedicular access, meticulous curettage of necrotic tissue, and insertion of a cage packed with osteoinductive material. This approach minimizes surgical trauma and operative time compared with conventional corpectomy procedures. Reported outcomes from retrospective series suggest promising pain relief, maintenance of correction, and low complication rates. Collectively, current evidence suggests that intrabody cage augmentation may serve as a potential, less invasive surgical option, acting as an intermediate approach between cement augmentation and corpectomy. However, as the existing evidence remains preliminary, high-quality prospective comparative studies are required to establish definitive indications and long-term efficacy. Full article

This paper presents the design and simulation of a dual-redundant broadband low-noise amplifier (LNA) module for inter-satellite communication links operating in the V-band (59–71 GHz). The growing demand for high-capacity space communication systems requires highly reliable, low-noise front-end architectures capable of maintaining performance over long mission lifetimes. To address these needs, a selectable dual-input receiver architecture is proposed, integrating a waveguide dual-probe, redundant switching, and a two-stage LNA within a single Gallium Arsenide (GaAs) MMIC. The design methodology accounts for the non-ideal behavior of the redundant branch and its impact on noise figure and insertion loss. The front-end is implemented using a 70 nm GaAs mHEMT technology optimized for millimeter-wave low-noise applications. Simulations show an insertion gain higher than 15 dB across the operational band, with gain ripple below 1.3 dB peak-to-peak. The simulated system noise figure is approximately 3.0 dB, closely matching the target specification. The results demonstrate that the proposed architecture provides improved reliability through redundancy while maintaining competitive noise and gain performance for future V-band inter-satellite links. Full article

To address the demand for low-cost, low-loss, and environmentally friendly optical power dividers in short-range visible light communication (VLC) systems, a low-loss 1 × 2 Y-branch optical splitter based on the integration of a planar optical waveguide (POW) and plastic optical fiber (POF) is proposed and experimentally demonstrated. The device employs a large-core step-index POF with a core diameter of 1 mm, enabling efficient coupling of multimode optical signals. The design and structural optimization of the 1 × 2 POF splitter are simulated by the beam propagation method (BPM). We fabricated the device through a low-cost manual assembly process, followed by packaging and experimental characterization. Measurements at 650 nm on ten samples show a minimum insertion loss of 3.4 dB and a lowest excess loss of 0.8 dB. The splitting ratio ranges from 49.6%:50.4% to 37%:63%, with a minimum uniformity of 0.06, indicating stable power distribution performance. These results confirm that a simple, low-cost fabrication approach can achieve practical optical performance, offering a feasible route toward scalable polymer-based photonic integration. Full article

This paper presents a compact, single-layer substrate-integrated waveguide (SIW) bandpass filter for 5.8 GHz WiMAX applications. The filter achieves an improved performance trade-off through a novel hybrid design strategy that combines central vertical perturbation vias with symmetrically etched complementary split-ring resonators (CSRRs). This configuration implements a hybrid magnetic–electric perturbation within a single cavity, enabling simultaneous control of electric and magnetic field confinement. The proposed topology achieves an optimized balance among unloaded quality factor Q_u, insertion loss, selectivity, and structural simplicity. Through targeted intra-cavity field manipulation, the filter attains a Q_u of 239.7, a narrow fractional bandwidth of 3.08% (5.75–5.93 GHz), and a low insertion loss of 1.12 dB. It also delivers enhanced selectivity compared to conventional single-cavity designs and performs competitively with multi-resonator architectures. An equivalent circuit model accurately captures the via–CSRR interaction and agrees closely with full-wave electromagnetic simulations. Experimental results confirm excellent return loss and robust performance across the entire WiMAX band (5.725–5.850 GHz). Thus, the proposed filter offers a practical, high-performance, and manufacturable solution for selective RF front-end applications. Full article