光子晶体太赫兹双波长滤波器的设计

这里提出一种新型的光子晶体太赫兹（THz）双波长滤波器,应用平面波法（PWM）分析其带隙结构,应用时域有限差分法（FDTD）研究THz波在该滤波器中的传输特性。结果表明,采用复式正方晶格结构的太赫兹滤波器,可以通过一个点缺陷实现两个波长的选择,通过选择合适半径的点缺陷,并在点缺陷处填充非线性介质砷化镓（GaAs）和增大某些介质柱的半径,可使该滤波器实现高耦合效率的单信道双频率选频滤波功能。     

智能温控系统设计

智能温控系统是当下发展较为迅速的一个方向,在各类货物的室内存储中,各类货物对于温度、湿度、光照等环境因素都有着各自不同的要求.因此对于温控系统而言,室内环境的检测,控制极为重要.本系统以STM32F103ZET作为核心控制器,小型直流电机等基本外部设备.并且使用轻量级嵌入式操作系统FREERTOS进行任务调度.该操作系...     

基于改进YOLOv5的复杂背景红外弱小目标检测算法

针对传统算法依赖于对红外目标与环境背景的精确分离和信息提取,难以满足复杂背景和噪声等干扰因素下的检测需求。论文提出一种基于改进YOLOv5（You Only Look Once）的复杂背景红外弱小目标检测算法。该算法在YOLOv5基础上,添加注意力机制提高算法的特征提取能力和检测效率,同时改进原YOLOv5目标检测网络的损失函数和预测框的筛选方式提高算法对红外弱小目标检测的准确率。实验选取了来自不同复杂背景的7组红外弱小目标数据集,将这些图像数据集进行标注并训练,得到红外弱小目标检测模型,然后从模型训练结果和目标检测结果的角度评估算法和模型的正确性。实验结果表明:改进的YOLOv5算法训练出来的模型,检测准确性和检测速度对比实验列出的几种目标检测算法均有明显的提升,平均精度均值（mean Average Precision,mAP）可达99.6%以上,在不同复杂背景下均可有效检测出红外弱小目标,且漏警率、虚警率低。     

Hydrothermal synthesis of SnO2 nanocorals,nanofragments and nanograss and their formaldehyde gas-sensing properties

Morphology plays an important role in the properties of nanomaterials. We successfully synthesized three new SnO₂ morphologies, nanocorals, nanofragments and nanograss, via a simple hydrothermal method with surfactant additives. The final products were characterized by field-emission scanning electron microscopy and X-ray diffraction. We found that the surfactants played a critical role in the synthesis of different SnO₂ nanostructures. In particular, when poly(ethylene glycol) was added as a surfactant, a unique grass-like structure was obtained. The mechanism of formation for this novel structure is discussed. The gas-sensing performance of all the products was investigated. The results show that the nanograss morphology had a superior gas response to formaldehyde than the other morphologies.     

Donor–acceptor copolymers incorporating polybenzo[1,2-b:4,5-b′]dithiophene and tetrazine for high open circuit voltage polymer solar cells

Two new low band gap conjugated polymers containing a benzo[1,2-b:4,5-b′]dithiophene donor unit and a tetrazine acceptor unit were synthesized by Stille cross-coupling polymerization. The structural and thermal properties of copolymers were characterized using nuclear magnetic resonance, gel permeation chromatography and thermogravimetric analysis. The results show that the donor–acceptor copolymers thus developed have good thermal stability with decomposition temperature of 294 °C and 305 °C. Cyclic voltammetric study revealed that the copolymers possess a deep-lying highest occupied molecular orbital energy level, which is desired for high open circuit voltage polymer solar cells (PSCs) and is also favorable for stable device operation in air. Bulk-heterojunction PSCs based on blend of low band gap copolymers: [6,6]-phenyl-C71-butyric acid methyl ester on indium tin oxide/glass substrates were fabricated. This work yielded a promising power conversion efficiency of >5.0%, with a high open circuit voltage of ～1.0 V, measured under air mass 1.5 global irradiation of 100 mW/cm².     

声表面波气体传感器研究进展

从机理模型构建、物理功能结构优化两方面出发对覆盖聚合物敏感膜的高性能声表面波(SAW)气体传感器技术进行了研究和探讨.实验研制了一种以具有高频率稳定性的声表面波延迟线型振荡器为传感元,结合六氟异丙醇基聚硅氧烷敏感膜的SAW传感器,开展了针对DMMP的检测实验,检测下限与检测灵敏度分别达到了0.04 mg/m3和485 Hz/mg/m3.     

Frequency-Domain Channel Estimation for SC-FDE in UWB Communications

Recently, single-carrier block transmission with frequency-domain equalization (SC-FDE) has been shown to be a promising candidate for ultra-wideband (UWB) communications. In this paper, we address the channel estimation problem for SC-FDE transmission over UWB channels. A mean-square error (MSE) lower bound for the frequency-domain linear minimum mean-squared error (LMMSE) channel estimator is derived, and the optimal pilot sequence that achieves this lower bound is obtained. Further simplification leads to a frequency-domain channel estimator with reduced computational complexity. The performance of the simplified estimator for SC-FDE over UWB channels is evaluated and compared with that with perfect channel state information. The effects of nonoptimal and optimal pilot symbols are also investigated. Our results show that the proposed frequency-domain channel estimator performs well over UWB channels with only small performance degradation, compared with that with perfect channel estimation     

InxGa1-xN合金薄膜In的表面分凝现象

用MOCVD方法在α-Al2O3(0001)衬底上外延生长了InxGa1-xN合金薄膜.测量结果显示:所制备的InxGa1-xN样品中In的组分随外延生长温度而改变,生长温度由620℃升高到740℃,In的组分由0.72降低到0.27.这是由于衬底温度越高,In进入InxGa1-xN薄膜而成键的效率越低.样品的X射线衍射谱和X射线光电子能谱均显示:在生长温度为620℃和690℃时所生长的InxGa1-xN样品中均存在明显的In的表面分凝现象;而生长温度升至740℃时所得到的InxGa1-xN样品中,In的表面分凝现象得到了有效抑制.保持生长温度不变而将反应气体的Ⅴ/Ⅲ比从14000增加到38000,In的表面分凝现象也明显减弱.由此可以认为,较高的生长温度使得In原子的表面迁移能力增强,In原子从InxGa1-xN表面解吸附的几率增大,而较高的Ⅴ/Ⅲ比则能增加N与In成键几率,从而有利于抑制In的表面分凝.     

A Family of Far‐Infrared‐Transmitting Glasses in the Ga–Ge–Te System for Space Applications

Conditions of formation of bulk tellurium chalcogenide glasses, containing 70–80 at % Te associated to Ga and Ge are described. The characteristic temperatures are measured: the glass‐transition temperature, T_g, is situated in the range 140–185 °C and the difference T_x – T_g, where T_x is the onset crystallization temperature, is in the range 76–113 °C. Moreover, the optical transmission window is exceptional, ranging from 1.99 μm in the bandgap up to 28 μm in the phonon region. Developed within the framework of requirements for the Darwin mission (a search for and study of extrasolar planets), feasibility of infrared optical fibers formed from these glasses is studied. Drawing experiments are conducted with the glass Ga₂‐Ge₃Te₁₅, which possesses the maximum T_x – T_g, and a first optical fiber is presented.     

Thermal resistance investigations on new leadframe-based LED packages and boards

In Solid State Lighting, thermal management is a key issue. Within the CSSL consortium, we have developed an advanced leadframe based LED package to reduce the thermal resistance of the component. Numerical simulations have been implemented using Ansys® software and thermal measurements have been carried out using the forward voltage method to derive the thermal resistance. The T3ster® transient thermal analysis has been used to determine the different thermal resistance contributions in the package and in the board, showing good correlation between experimental and simulation results. As a result, low thermal resistances of 5.5 K/W have been obtained on our advanced leadframe based LED package and have been compared with the standard configuration of multiple Rebel LEDs on FR4 board.