To address challenges such as small target sizes, blurred target features, and difficulty in distinguishing between targets and backgrounds in small object detection, we propose a method based on Multi-Scale Image Degradation combined with the Contrastive Learning model. By leveraging contrastive learning techniques, our approach aims to enhance the discriminative features necessary for accurately distinguishing objects from backgrounds. To specifically target small objects, we subject target samples to various multi-scale image degradation modes before inputting them into the contrastive learning model. Augmentation techniques are then applied to these degraded samples to facilitate effective contrastive feature learning. Consequently, the model is better equipped to uncover the differences between small targets and backgrounds, thereby improving small object detection performance. Furthermore, considering that spatial domain features are sensitive to local changes in the image, while frequency domain features are sensitive to global structural changes, our approach applies the contrastive learning model in both spatial and frequency domains, aiming to acquire more robust features for small object detection. Extensive experiments conducted on the MS COCO dataset and the VisDrone2019 dataset validate the effectiveness of our proposed method in significantly enhancing small object detection accuracy.

Yttria stabilized zirconia (YSZ) presents a promising option for infrared camouflage applications due to its lower emissivity within the 3-5 mu m waveband. Nevertheless, its emissivity increases within the 8-14 mu m waveband, which is attributed to lattice vibration-induced absorption characteristics, combined with an extended Christiansen wavelength (K-point). In this study, we regulate YSZ's infrared radiation performance in the 8-14 mu m band by combining a material with lower infrared emissivity in the 8-14 mu m band and lower lattice resonance frequencies such as titanium dioxide (TiO2) based on lattice vibration theory and classical electromagnetic theory. The results showed that as the TiO2 content increases, the emissivity of the composite ceramic block remains relatively stable in the 3-5 mu m band. Notably, With a TiO2 content of 80 %, the emissivity within the 8-14 mu m band decreases from 0.55 to 0.48 and within the 5-8 mu m band increases from 0.33 to 0.41, the K-point of ceramics shifted from 12.8 mu m to 11.8 mu m. It provides an effective approach for modulating the infrared emissivity and K-point of YSZ.

Ice accumulation poses considerable challenges in transportation, notably in the domain of general aviation. The present study combines the strengths and limitations of conventional aircraft deicing techniques with the emerging trend toward all-electric aircraft. This study aims to utilize laser-induced graphene (LIG) technology to create a multifunctional surface, seamlessly integrating hydrophobic properties with efficient electrical heating to mitigate surface icing effectively. We investigated the utilization of a 10.6 μm CO2 laser for direct writing on polyimide (PI), a widely used insulating encapsulation material. From the thermomechanical perspective, our initial analysis using COMSOL Multiphysics software (V5.6) revealed that when the laser power P exceeds 5 W, the PI substrate experiences ablative damage. The experimental results show that when P ≤ 5 W, an increase in power has a positive impact on the quality, surface porosity, roughness reduction, line-spacing reduction, and water contact-angle enhancement of the graphene. Conversely, when P > 5 W, higher power negatively affects both the substrate and the graphene structure by inducing excessive ablation. However, it influences the graphene line height positively and is consistent with overall experimental–simulation congruence. Furthermore, the incorporation of high-quality graphene resulted in a surface that exhibited higher contact angles (CA > 120°), lower energy consumption, and higher heating efficiency compared to the use of traditional electrically heated materials for anti-icing applications. The potential applications of this one-step fabrication method extend across various industries, particularly aviation, marine engineering, and other ice-prone domains. Moreover, the method has extensive prospects for addressing pivotal challenges associated with ice formation and serves as an innovative and efficient anti-icing technology.

The exceptional performance of graphene has driven the advancement of its preparation techniques and applications. Laser-induced graphene (LIG), as a novel graphene preparation technique, has been applied in various fields. Graphene periodic structures created by the LIG technique exhibit superhydrophobic characteristics and can be used for deicing and anti-icing applications, which are significantly influenced by the laser parameters. The laser surface treatment process was simulated by a finite element software analysis (COMSOL Multiphysics) to optimize the scanning parameter range, and the linear array surface structure was subsequently fabricated by the LIG technique. The generation of graphene was confirmed by Raman spectroscopy and energy-dispersive X-ray spectroscopy. The periodic linear array structure was observed by scanning electron microscopy (SEM) and confocal laser imaging (CLSM). In addition, CLSM testings, contact angle measurements, and delayed icing experiments were systematically performed to investigate the effect of scanning speed on surface hydrophobicity. The results show that high-quality and uniform graphene can be achieved using the laser scanning speed of 125 mm/s. The periodic linear array structures can obviously increase the contact angle and suppress delayed icing. Furthermore, these structures have the enhanced ability of the electric heating deicing, which can reach 100 °C and 240 °C within 15 s and within 60 s under the DC voltage power supply ranging from 3 to 7 V, respectively. These results indicate that the LIG technique can be developed to provide an efficient, economical, and convenient approach for preparing graphene and that the hydrophobic surface array structure based on LIG has considerable potential for deicing and anti-icing applications.

The presence of various defects in carbon fiber-reinforced composites (CFRP) can be highly detrimental to the safety of aircrafts during their operation. Therefore, it is crucial to employ an accurate and efficient nondestructive technology to detect such defects and ensure safe operation of aircrafts. In this study, we used COMSOL Multiphysics simulation software and terahertz time-domain spectroscopy (THz-TDS) to investigate the THz spectral characteristics of manually preset microcracks in CFRP. Results showed a linear relation between the THz spectral characteristics of the microcracks, including the reflectance, time-spectral amplitude, power spectral density, absorption, and absorption coefficient, with their geometric parameters such as the length, width, and position. This relation can help predict the geometric information of the microcracks through THz-TDS, facilitating a quantitative detection of microcracks in CFRP and providing a reference for practical applications in this detection.

Yttrium stabilized zirconia (YSZ) possesses notable thermal stability and high conductivity, rendering it indispensable in the realm of infrared stealth. While YSZ demonstrates relatively low emissivity within the 3-5 mu m wavelength range, the escalating application temperatures of aircraft demand a further reduction in the infrared emissivity within this specific band, as per Wien displacement law. This study employs first principles calculations to establish that the strategic doping of YSZ with Mg atoms effectively diminishes the absorption coefficient and enhances the material's conductivity. Based on these computational results, YSZ samples doped with varying concentrations of MgO were prepared via high-temperature solid-state reactions. Subsequently, the effects of different MgO doping levels on the microstructure, crystal structure, and infrared emissivity of YSZ were thoroughly examined. The findings indicate that as the MgO content increases, the porosity and grain size of the YSZ ceramic gradually escalate. Concurrently, the lattice constant and crystal plane spacing of YSZ experience reductions. Notably, when the doping quantity reaches 5mol%, the infrared emissivity of YSZ diminishes to its minimum level owing to the combined influences of microstructure, optical properties, and conductivity. Specifically, the emissivity within the 2-14 mu m wavelength range decreases from 0.336 to 0.296.

There has been a significant shift in research focus in recent years toward laser-induced graphene (LIG), which is a high-performance material with immense potential for use in energy storage, ultrahydrophobic water applications, and electronic devices. In particular, LIG has demonstrated considerable potential in the field of high-precision human motion posture capture using flexible sensing materials. In this study, we investigated the surface morphology evolution and performance of LIG formed by varying the laser energy accumulation times. Further, to capture human motion posture, we evaluated the performance of highly accurate flexible wearable sensors based on LIG. The experimental results showed that the sensors prepared using LIG exhibited exceptional flexibility and mechanical performance when the laser energy accumulation was optimized three times. They exhibited remarkable attributes, such as high sensitivity (~41.4), a low detection limit (0.05%), a rapid time response (response time of ~150 ms; relaxation time of ~100 ms), and excellent response stability even after 2000 s at a strain of 1.0% or 8.0%. These findings unequivocally show that flexible wearable sensors based on LIG have significant potential for capturing human motion posture, wrist pulse rates, and eye blinking patterns. Moreover, the sensors can capture various physiological signals for pilots to provide real-time capturing.

Considering several sources that cause global position system (GPS) interference in civil aviation and the challenges faced by interference recognition algorithms in terms of efficiency and accuracy, we propose an improved You Only Look Once (YOLO)v7-CHS algorithm (YOLOv7-CHS) and investigate its effectiveness in identifying GPS signals and different types of interference signals. First, continuous wavelet transform (CWT) is introduced as a method for processing and analyzing signals in the time-frequency (TF) domain to effectively obtain their temporal and spectral characteristic information. Second, the ConvNeXt structure is integrated into the YOLOv7 backbone network to create a ConvNeXtBlock (CNeB) module to enhance the classification and recognition accuracy of interference signals. Additionally, an attention mechanism is introduced to further improve model recognition accuracy. To effectively improve the capability of signal feature extraction and mitigate the impact of background noise on TF feature suppression, we have integrated the efficient channel attention (ECA) channel attention module with the convolutional block attention module (CBAM) spatial attention module, thereby proposing a hybrid CBAM and ECA (HCE) attention module. Last, to address issues arising from accidental deletion of detection frames and multipath interference negatively affecting model recognition performance, we have employed the soft nonmaximum suppression (Soft-NMS) algorithm while selecting an optimal loss function through comparative analysis. The comparative evaluation experimental results under different circumstances show that YOLOv7-CHS achieves recognition accuracies of 98.0% and 99.6% for various types of signals, respectively. These values represent an increase of 1.7% and 1%, respectively, compared to YOLOv7. Moreover, in terms of lightweight indicators, YOLOv7-CHS exhibits a significant improvement in performance: the frames per second (FPS) is increased by 75.1, the number of parameters (Params) was reduced by 4.75 M, and giga floating point operations per second (GFLOPs) were reduced by 65.9 G while effectively enhancing recognition capabilities. The proposed YOLOv7-CHS not only improves signal recognition accuracy but also reduces model Params and computational complexity, achieving a lightweight model with promising application prospects in the rapid detection and recognition of GPS interference sources in civil aviation.

The advancement in performance in the domain of flexible wearable strain sensors has become increasingly significant due to extensive research on laser-induced graphene (LIG). An innovative doping modification technique is required owing to the limited progress achieved by adjusting the laser parameters to enhance the LIG’s performance. By pre-treating with AgNO3, we successfully manufactured LIG with a uniform dispersion of silver nanoparticles across its surface. The experimental results for the flexible strain sensor exhibit exceptional characteristics, including low resistance (183.4 Ω), high sensitivity (426.8), a response time of approximately 150 ms, and a relaxation time of about 200 ms. Moreover, this sensor demonstrates excellent stability under various tensile strains and remarkable repeatability during cyclic tests lasting up to 8000 s. Additionally, this technique yields favorable results in finger bending and hand back stretching experiments, holding significant reference value for preserving the inherent characteristics of LIG preparation in a single-step and in situ manner.

Topological materials with well-defined surfaces and edges have become a prominent research topic. As topological insulators, MnBi2Te4 thin films, with their unique surfaces, exhibit exceptional electron transport properties and good applicability in low-noise, high-sensitivity photoelectric detection. This paper reports a straightforward, efficient, and cost-effective thermal evaporation method for preparing quantum MnBi2Te4 thin films, along with an investigation into their photoelectric detection performance. These films can be used to fabricate array devices, with the resulting photodetectors achieving a response current of 97 mA W−1 at room temperature and a response speed of <1 ms. Moreover, they demonstrate stability in the air for >30 d, with the photoelectric performance degrading by <15%. Our research introduces a new application for topological materials in photoelectric detection and establishes a strong foundation for the design and development of high-performance photodetectors in the future.

Due to its exceptional thermal stability and high conductivity, Yttrium stabilized zirconia (YSZ) has become an essential material in the field of infrared camouflage. Although YSZ exhibits relatively low emissivity within the 3-5 mu m wavelength range, the increasing operating temperatures of aircraft necessitate further reduction in infrared emissivity within this specific band, in accordance with the Wien displacement law. This study focuses on the preparation of ceramic samples of YSZ doped with varying concentrations of Yb2O3 through a high-temperature solid-state reaction. It aims to investigate the influence of different doping concentrations on the microstructure, crystal structure, and infrared radiation characteristics of YSZ ceramic blocks. The experimental results demonstrated that the addition of Yb2O3 induces changes in the grain size and phase content of YSZ. Notably, as the amount of Yb2O3 doping increases, the infrared emissivity of YSZ samples in the 3-5 mu m wavelength range exhibits a pattern of initial decrease followed by an increase. Remarkably, at a doping amount of 3 % mol, YSZ ceramics demonstrated the lowest emissivity, with the average emissivity of the 3-5 mu m wavelength range decreasing from 0.41 to 0.38.

The drilling and cutting of carbon fiber-reinforced epoxy resin matrix composite (CFRP) structural parts is a prerequisite for one-off moulding and assembly connections. However, the thermal ablation effect observed during nanosecond laser hole-making of CFRP results in significant accuracy errors and thermal damage defects in the quality of the holes obtained from the process. To enhance the quality of laser-drilling CFRP holes, a spiral drilling path was employed in this work. The influence of diverse drilling methodologies, encompassing the trajectory of the laser beam, the spacing between scans, and the direction of the suction system's pumping, on the quality of the holes was examined. The impact of these techniques on the precision and integrity of the holes was assessed in terms of their dimensions, the quality factor, the width of the heat-affected zone (HAZ), and the prevalence of microscopic defects. The results demonstrated that when the drilling strategy involves moving the laser beam from the outside to the inside (Scheme I), a scanning spacing of 20 mu m, and backward pumping, the optimal micro-hole accuracy and surface morphology, as well as minimal thermal damage defects can be achieved. This study provides a reference for further optimization of the nanosecond laser drilling process.

This work presents a two-step non-destructive method for cleaning the surface paint of CFRP. The method combines ablation and vibration, using a pulsed laser with a wavelength of 1064 nm. The effects of laser power, beam and path overlap rate on the removal of paints are investigated. The analysis focuses on the cleaning and the damage threshold of the paints and fibers. Additionally, the study analyzed the thermal accumulation effect and fiber damage resulting from various laser parameters. The cleaned samples were analyzed for micro- morphology, elemental composition, surface roughness, three-dimensional morphology, and contact angle to demonstrate the modulation of derivatization phenomena of CFRP surface paints under different cleaning states using this method. This points to the reliability and feasibility of the relevant treatment parameters and provides a reference for the subsequent research on the practical application of laser cleaning.

The effect of fibre laser surface treatment with different energy densities on the surface microstructure and bonding performance of a carbon fibre reinforced polymer (CFRP) composite was investigated. Results indicate that the effect of laser surface treatment on the CFRP with a defocusing amount of 4 mm is the optimal. With increasing energy density the resinremoval degree of the CFRP structure surface increases gradually, the surface free energy of CFRP greatly increases and the contact angle of CFRP decreases. At the same time, the high energy density will lead to the fibre being easily damaged. A combined mechanism of laser treatment on CFRP is discussed.

柔性可穿戴传感器因柔软轻便、延展性强且可用于健康管理、环境监测、食品检测、储能器件等领域而备受关注,基于激光诱导石墨烯的柔性可穿戴传感器克服了传统可穿戴设备的不足,其制备过程具有单步原位制备、绿色环保、低成本等优势,符合新型便携式/可穿戴电子产品向着智能化、微型化、高集成度、柔性化方向发展的趋势,具有良好的发展前景.本文首先阐述了石墨烯的传统制备工艺与激光诱导石墨烯的优缺点;然后分析了碳前体、激光器类型、激光参数、掺杂改性等影响因素对激光诱导石墨烯的结构和性能的影响;接着介绍了激光诱导石墨烯在柔性应变传感器、柔性生理传感器、柔性化学传感器等方面的应用研究;最后,对其应用前景进行了展望.

Based on the double-periodic characteristics of a sine waveguide, the dispersion equation, interaction impedance, and transmission losses of slow-wave structures are derived. The dispersion equation indicates that the waves propagating in the sine waveguide should belong to two mode types, which can exist independently rather than as “pseudo-modes.” The dispersion equation, interaction impedance, and transmission losses are obtained using a theoretical model. A 220 GHz traveling wave tube (TWT) is used as an illustrative example to verify the validity of the analytical model. The calculated results show that the dispersion curve is in good agreement with that given by the Ansys high-frequency simulation software over the entire frequency range and that the theoretical numerical calculation time is less than 2% of that of the Ansys software package. In addition, the results demonstrate that the interaction impedance of the symmetric φ0 + π mode is much higher than that of the asymmetric φ0 mode. Therefore, the symmetric φ0 + π mode should be used for propagation in sine waveguide traveling-wave tubes. Moreover, when the conductivity is set at 1.6 × 107 S/m, the loss of the sine waveguide is ∼1.15 dB/cm for 220 GHz. The equivalent conductivity of the metal can be used appropriately in the design of the mm-wave and the THz TWT.

A novel slow wave structure (SWS) called semielliptical groove sine waveguide (SGSWG) is proposed for millimeter-wave sheet electron beam traveling-wave tube. The simulation results show that the cold bandwidth of the SGSWG is similar to the sine waveguide structure, the interaction impedance of the SRWG is about 87% higher than sine waveguide at 220GHz under the same structural parameters. Meanwhile, the transmission loss is very small from the calculations of CST.

Flexible electronic devices have received increasing attention due to their potential applications in wearable human motion and healthcare monitoring and thermal management. Nevertheless, flexible electronic devices for more precise health monitoring of human physiological movement under low strain are still a pressing issue to solve. Herein, a wearable flexible strain sensor with a three-dimensional (3D) conductive network is developed for healthcare monitoring and thermal management by embedding silver nanowires (AgNWs) and Ti 3 C 2 T x MXene composite films into a polydimethylsiloxane matrix. The sensor can be utilized for human health monitoring, pulse detection at the wrist, and breathing monitoring of human physiological movement due to its low strain detection capacity (0.05% strain) and high sensitivity (gauge factor up to 9472). The primary detection range of the sensor is 0%–1% of tiny strains. Moreover, the exceptional electric heating and optothermal effect supported by the AgNWs and MXene protects human health in extremely cold environments. The MXene/AgNW strain sensor with high sensitivity under low strain has great potential for more precise health monitoring of human physiological movements and thermal management.

碳纤维复合材料因其具有耐腐蚀、耐高温、比强度高、比模量大及易于成型等独特性能,广泛应用于体育用品、风力发电、航空航天领域.碳纤维复合材料与传统材料相比,减轻了飞机的近30％质量,很大程度上减少了油耗,在提升飞机飞行性能的同时,还能降低其制造与运营养护成本.国产大型飞机C919中复合材料的比例达到了12％,国外大型飞机B787和A350中碳纤维复合材料比例更是达到了50％以上.碳纤维复合材料在服役过程中受到飞行环境的影响会产生不同类型的缺陷,其中裂纹是飞机安全运行潜在隐患的因素之一,裂纹会在飞行恶劣的环境下快速生长并可能引发飞行事故.如何快速地判断裂纹的存在和精确的定位其位置是飞机检测的重要任务之一.

Ice accumulation on the surface of aircraft is a serious threat to flight safety and a fatal factor causing air accidents. However, traditional aircraft deicing methods no longer meet the requirements of safe flight due to changes in aircraft structural materials. In recent years, the application of carbon fiber-reinforced polymer (CFRP) materials in the aviation structure industry has increased. In this study, we demonstrate an economical, easy-to-prepare, and pollution-free approach to deice an aircraft through induction heating. The nickel-coated carbon fiber-reinforced polymer used as the induction heater for aircraft deicing is obtained by electroless nickel plating on the surface of the CFRP. The result shows that it takes just 110 s to achieve a temperature of 205 °C on the nickel-plated CFRP when the input voltage is 30 V, as well as melting the ice layer with a thickness of 30 mm, while the temperature of this material can reach up to 81 °C by electric heating when the input voltage is 1.5 V. Meanwhile, the nickel-plated CFRP exhibits good repeatability during the induction heating. Based on the excellent electrothermal properties, the nickel-plated CFRP polymer shows a prominent deicing ability, which provides a promising strategy for the deicing of aircraft.