用于热真空环境下整星微波无线测试的低PIM吸波热沉研制

随着通信卫星技术的发展,收发共用已成为通信卫星有效载荷常用的设计方法,在这种情况下,无源互调(passive intermodulation,PIM)问题就显得尤为突出。为了完成整星及转发器分系统在热真空环境下的PIM指标测试,利用碳化硅吸波材料研制了一种低PIM吸波热沉,并利用该吸波热沉建立了指标小于150 dBm的低PIM测试环境,同时兼具热流模拟功能和微波功率耐受能力。在热真空环境下圆满完成了国内首次有整星参与的微波载荷无线PIM测试试验。     

SiC MOSFET短路特性

为确保碳化硅(SiC)功率器件在过载、短路等工况下能安全可靠地工作,必须充分认识SiC器件的短路机理。首先对SiC MOSFET硬开关短路故障下短路电流原理进行了分析,在此基础上对不同电路参数对SiC MOSFET短路特性的影响进行了对比分析,揭示了短路特性的关键影响因素,并对Si与SiC MOSFET短路能力和器件恶化机理进行了对比分析,从而为设计SiC MOSFET短路保护电路提供一定的指导。     

Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide

The metabolic consequence of suboptimal (400 μmol mol⁻¹ or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO₂] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO₂]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO₂] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO₂] and physiological age. In general, plants grown under high [CO₂] exhibited a metabolite profile characteristic of older plants under ambient CO₂. Elevated [CO₂] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO₂] to a much greater extent at 10,000 ppm CO₂ than at 1500 ppm CO₂. The percentage increase of starch content resulting from CO₂ enrichment declined as plants develope. In contrast, elevated [CO₂] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO₂] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO₂] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO₂-grown plants, both elevated CO₂ levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO₂] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO₂ on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO₂ levels.     

高速冲液脉冲放电制备纳米硅球

通过Ansys对单脉冲放电过程进行温度分布仿真时发现,当脉宽很小时,汽化体积所占比例很高,即材料利用率较高,但是产率较低;而加大脉宽时,产率较高,但是汽化比例较低。为综合两者的优势,利用大脉宽加工,使放电通道移动。仿真结果表明,相对于放电通道静止,其在材料利用率和产率上都有了大幅度提高。当在加工中引入高速冲液时,实验表明其能促使放电通道发生漂移,收集产物后称量、计算,其产率达到了1g/h。     

石英陶瓷与碳纤维增强复合材料间胶接增强的优化工艺

为提高硅橡胶胶黏剂胶接石英陶瓷和碳纤维增强复合材料的强度和耐温性能,研究了胶接面湿热状态、打磨程度、胶层厚度、操作等待时间等工艺参数对胶接强度的影响。在试片正常烘干、打磨的情况下,当胶层厚度为0.4 mm、操作等待时间小于0.5 h时,胶接效果最优,其压缩剪切强度达到了3.06 MPa。探索了底涂剂处理对胶接强度和耐温性能的影响。在温度不高于100℃时,底涂剂A的效果较好。经底涂剂A处理后,胶接试片常温下的强度提高了13.7%,达到3.48 MPa;100℃时的强度提升率达到37.7%。在更高温度下,底涂剂B的效果更为显著。经底涂剂B处理后,胶接试片常温下的强度提升了10.1%,达到3.37 MPa;300℃时的强度提升了44.0%,达到1.57 MPa;200℃时的强度提升率最高,为49.0%。测试结果为高温条件下石英陶瓷胶接结构的胶接工艺优化及其应用提供了参考。     

基于激光旋切法的陶瓷材料盲孔加工方法研究

介绍了激光打孔的基本原理,对激光能量、离焦量、轨迹在激光旋切法加工盲孔过程中对孔形和表面质量的影响进行了分析和试验验证,并给出了一般规律.依据试验结果确定了合理工艺参数,采用旋切法在碳纤维增强碳化硅陶瓷基复合材料（Cf/SiC）上打出了孔径为1 mm,孔深为1.1 mm,锥度小于15°的盲孔.     

一种新型的硅微机械陀螺数字读出系统

为了简化系统设计,进一步改善陀螺的控制性能,提出了一种新型的微机械陀螺数字读出系统方案.该方案采用EPLL和AGC技术实现陀螺驱动模态的相位与幅度闭环控制,采用EPLL技术实现检测模态的信号解调.不仅降低了对陀螺品质因数的要求,而且省去了低通滤波器的设计.通过仿真实验不仅验证了该方案的可行性,还研究了EPLL参数对陀螺数字读出系统性能的影响.该方案对今后微机械陀螺系统的实现与性能的进一步提高有一定的指导作用,同时也为今后陀螺系统的误差补偿以及自标定、自校准奠定了基础.     

电极面型对横向激励高气压CO2激光器放电的影响

计算并讨论了均匀场电极中电极板安装结构、电极板厚度对实际电场分布影响。计算表明在基本参数类似的条件下,近罗可夫斯基电极表面电场强度具有17%的非均匀性,但在垂直放电方向的对称面上却有更好的均匀性。对放电区辉光的时间积分照片和像增强型CCD相机记录的瞬态照片进行了分析,结果表明:电极表面的电场强度分布,仅对放电的初始发展具有影响,而放电区中央的电场分布以及预电离强度,对最终放电区的均匀性具有决定性的影响。     

用有机硅树脂YR3370连接RBSiC陶瓷

 以一种聚硅氧烷类有机硅树脂YR3370(GE Toshiba Silicones)为连接剂，连接了反应烧结SiC(RBSiC)陶瓷。连接件在1 100~1 300℃的99.99%N₂气流中进行热处理。用三点弯曲强度实验测定连接件的强度，用场发射扫描电镜、X射线衍射和热重测试分析显微结构和化学反应。在连接温度为1 200 ℃时，连接件的三点弯曲强度达到最大值197 MPa。连接层是由有机硅树脂YR3370裂解生成的无定形Si_xO_yC_z陶瓷，其结构连续均匀致密，厚度在2~5 μm之间。连接机理是通过无定形Si_xO_yC_z陶瓷的无机粘接作用在RBSiC陶瓷基体和连接层之间形成连续的化学键。     

四氧化二氮与卫星贮箱材料的长期相容性研究

本文进行了N_2O_4与N_2O_4+1%NO两种介质与TC_4钛合金、304L不锈钢及二者焊件的长期相容性研究.实验中一方面对试件和介质进行了较为全面细致的检测与分析,得出了一级相容性数据,另一方面对浸泡后试件进行了XPS深度剖析,初步阐明了TC_4与304L的抗蚀机理.