基于串/并联电路超宽带小型化功分网络技术

提出了一种串联式功分器结构设计,将其与并联式功分器相结合,可以实现小型超宽带1:4功分网络.文章给出了两种实现小型超宽带功分网络的拓扑图,并设计了2～10GHz范围的超宽带小型功分器,加工、测试结果,计算与实验结果吻合很好.     

超宽带印制矩形单极天线设计

针对超宽带通信应用,研究影响印制单极天线阻抗带宽的主要因素,设计基于微带馈电的小型化印制矩形单极天线。按照等效性原理,采用黄金分割比设计矩形振子体;通过接地面上端引入渐变梯形或凹形结构,同时调整馈入端接地面间隙,可实现印制矩形单极天线的超宽带特性。对具有渐变梯形或凹形接地面结构的微带馈电矩形印制单极天线结构进行优化,仿真结果表明,前者的阻抗带宽为2.96～17.94GHz,后者的阻抗带宽为2.9～13.3GHz,而两者的辐射方向基本保持不变。实测结果与仿真结果基本一致,达到了超宽带通信应用的要求。     

新型弯折偶极子RFID天线的小型化分析与设计

标签天线是RFID系统的关键部件,UHF频段RFID系统多采用偶极子天线及其变型型式,由于受RFID卡尺寸的限制,天线的小型化成为制约RFID技术发展的瓶颈之一.文章创新性地设计了一种最大理论读取距离为5.6m的新型弯折线偶极子RFID标签天线,尺寸仅为22.5mm×30.5mm×1.6mm,小于目前已出现的标签天线,其方向性及带宽性能良好,阻抗调节臂的引入使得天线与标签芯片的匹配变得更加方便.采用无通孔和短路结构的单层印刷电路板加工天线,其测试结果与仿真结果具有良好的一致性.     

Vorteile von Open-Source-Ansätzen bei der Etablierung einer automatisierten wirkungsbezogenen Analytik

The determination of toxic compounds in wastewater is perfomed using thin layer chromatography. For automation of effect-directed analytics, an existing technical solution was adapted as an open-source hardware approach in combination with additive manufacturing. The system is flexibly applicable to specific issues of automated determination of environmentally relevant compounds and makes a valuable contribution to the digitalization and automation of high-performance thin-layer chromatography systems.     

State of the Art on Micromilling of Materials,a Review

The trend towards miniaturization has increased dramatically over the last decade, especially within the fields concerned with bioengineering, microelectronics, and aerospace. Micromilling is among the principal manufacturing processes which have allowed the development of components possessing micrometric dimensions, being used to the manufacture of both forming tools and the final product. The aim of this work is to present the principal aspects related to this technology, with emphasis on the work material requirements, tool materials and geometry, cutting forces and temperature, quality of the finished product, process modelling and monitoring and machine tool requirements. It can be noticed that size effect possesses a relevant role with regard to the selection of both work material (grain size) and tooling (edge radius). Low forces and temperature are recorded during micromilling, however, the specific cutting force may reach high values because of the ploughing effect observed as the uncut chip thickness is reduced. Finally, burr formation is the principal concern with regard to the quality of the finished part.     

微型逆布雷顿循环透平制冷机及其发展

介绍了在空间制冷中具有良好发展前景的微型逆布雷顿循环透平制冷机。这种制冷机采用微型高速透平机械提供压缩和膨胀、动压气体轴承支撑 ,并采用低压比下具有高效率的紧凑式换热器 ,最后对其发展概况进行了阐述     

三维地震目标处理在天然气勘探中的应用

目的：在刘庄地区寻找有利的天然气勘探目标，开展三维地震资料目标处理。方法：运用道编辑、宽带滤波、多次叠加、叠后反褶积等多种新技术、新方法提高资料品质。结果：基本解决了地层对比、小断层识别、断层组合及油气分布等诸多难题。结论：三维地震目标处理能有效地改善新老油气田地震资料的品质，可以为地质研究人员提供更多有效的地质信息，为寻找有利圈闭提供资料保证。     

爆炸平面开关的设计及研究

为了进一步减小爆炸箔起爆器系统体积,并降低生产成本,设计并制备了一种爆炸平面开关,并对该爆炸平面开关的电极间隙和放电特性进行研究.结果表明:随着间隙电极的间隙距离减小,其开关的作用时间缩短;对于同一起爆电压的爆炸平面开关,随着放电电极间隙的增大,其冲击片雷管的爆发电流呈下降趋势.     

星载行波管高效率、高可靠阴极热子组件研究

阴极热子组件是星载行波管的核心部件,其性能的好坏直接影响到整管的性能和寿命。由于星载行波管工作环境特殊,要求在保证阴极正常工作的前提下,尽可能地降低阴极热子组件的加热功率以提高阴极热子组件可靠性、延长阴极热子组件寿命,同时阴极热子组件必须具有良好的抗振性能。本文利用ANSYS有限元软件对某星载脉冲行波管栅控电子枪阴极热子组件进行了热学和结构动力学性能分析和研究,通过优化阴极热子组件支撑结构和尺寸,降低了它的加热功率,并进行了热学实验验证;同时为了保证其力学可靠性,分析了阴极热子组件在随机振动条件下的力学性能。研究结果表明,新阴极热子组件结构加热功率由10.50 W降低至8.21 W,轴向尺寸缩短了45.4%,满足某星载行波管小型化的需求,结构同时符合抗机械振动性能的要求。     

Improvement of water management in polymer electrolyte membrane fuel cell thanks to cathode cracks

The role of cathodic structure on water management was investigated for planar micro-air-breathing polymer electrolyte membrane fuel cells (PEMFCs). The electrical results demonstrate the possibility to decrease, with the same structure, both cell drying and cell flooding according to the environmental and operation conditions. Thanks to a simultaneous study of internal resistance and scanning electronic microscope (SEM) images, we demonstrate the advantageous influence of the presence of crack in cathodic catalytic layer on water management. On the one hand, the gold layer used as cathodic current collector is in contact with the electrolyte in the cracked zones which allows water maintenance within the electrolyte. It allows to decrease the cell drying and thus strongly increase the electrical performances. For cells operated in a 10% relative humidity atmosphere at 30 °C and at a potential of 0.5 V, the current density increases from 28 mA cm⁻² to 188 mA cm⁻² (+570%) for the cell with a cathodic cracked network. On the other hand, the reduction in oxygen barrier diffusion due to the cathodic cracks allows to improve oxygen diffusion. In flooding state, the current densities were higher for a cell with a cracked network. For cells operating in a 70% relative humidity atmosphere at 30 °C and at a potential of 0.2 V, a current density increase from 394 mA cm⁻² to 456 mA cm⁻² (16%) was noted for the cell with a cathodic cracked network. Microscopic observations allowed us to visualize water droplets growth mechanism in cathodic cracks. It was observed that the water comes out of the crack sides and partially saturates the cracks before emerging on cathodic collector. These results demonstrate that cathode structuration is a key parameter that plays a major role in the water management of PEMFCs.