GPS信号在极区中层顶PMSE尘埃层的衰减分析

极区中层夏季回波(PMSE,Polar Mesosphere Summer Echoes)是通过雷达在高纬当地夏季中层顶附近探测到的异常强大雷达回波,发生PMSE现象的区域属于尘埃等离子体范畴,现在已经在1290 MHz处用雷达观测到PMSE现象。GPS系统卫星的L2频率为1227.60 MHz,容易受到PMSE尘埃层的影响。GPS信号穿越极区中层顶时,其中的尘埃等离子体区域必然对信号产生影响。利用分层媒质方法结合ECT-02实验数据研究GPS系统L2载波信号经过尘埃层的吸收系数和信号的衰减程度,证实PMSE尘埃层能影响GPS通信。     

衬底温度对制备出CNT膜的影响

在陶瓷衬底上通过磁控溅射方法镀上金属钛层,用含铁杂质的氧化硅对钛层进行抛光,通过微波等离子体化学气相沉积（MPCVD）法在不同的温度下短时间里制备出CNT膜。利用扫描电子显微镜、拉曼光谱,X射线衍射,分析了薄膜的结构和表面形貌。仔细研究不同温度下制备的CNT膜,得出衬底温度400℃时制备的碳膜是以非晶碳为主,600℃时置备的碳膜是良好的碳纳米管膜,800℃制备的碳纳米管膜的缺陷变得很多,以碳纳米链为主。最后得出了温度对催化活性有很大影响的结论。     

Control of Snow Falling Flow around NACA0015 Blade using a Plasma Electrode with Weather Resistant Design

The plasma actuation (PA) effect on the snow falling flow was investigated using a plasma electrode with weather resistant design and the natural snow wind facility of the Hokkaido University of Science. NACA0015 test blade with chord length c of 300 mm was used. Wind tunnel tests were carried out under the angle of the attack of the blade was fixed at 15 degrees, and the main flow velocity is U=5 m/s. PIV (Particle image velocimetry) measurements were conducted on various PA conditions using natural dry snowflakes as a tracer. When the actuator was driven under the condition of the fundamental frequency of F=50 kHz, and the pulsed modulated frequency f of fc/U=1 and Duty ratio (Ratio of plasma ON time to pulse duration time) =1%, movement of snowflakes was controlled the most effectively tested. It was clarified that the fundamental frequency of PA also affects the control of snow flow. Under snowfall conditions, the weather resistant designed plasma electrode has suffered no damage and operated successfully.     

等离子体柱阵列应用于目标隐身的可行性分析

设想了一种等离子体柱阵列技术,并利用CST电磁仿真软件对等离子体柱阵列覆盖金属平板的情况进行了仿真,分析了等离子体柱阵列在2～8GHz频段内对金属平板的散射衰减,并与金属平板覆盖等离子体层的散射特性进行了对比。结果表明,对于TE波,等离子体柱阵列对金属板的散射衰减与等离子体层对金属板的散射衰减相差不大;对于TM波,柱阵列的散射衰减要大于等离子体层的散射衰减,因此,利用等离子体柱阵列覆盖目标来实现目标隐身是完全可行的。     

电感耦合等离子体质谱法测定土壤中砷的含量

利用电感耦合等离子体质谱法（ICP—MS）测定土壤中砷的含量。样品经过微波消解,在线加入内标校正基体效应,通过修正方程校正质量数干扰。测定砷元素校正曲线的相关系数0．9999,检出限0．01mg／kg,样品分析结果的变异系数为1．6％～2．4％（n=6）,加标回收率在84．0％-96．8％。同时采用国家标准方法氢化物-原子荧光光度法验证了方法的准确度,两种方法结果无显著差异。实验结果表明,该方法具有简单、快速、检出限低等特点,可用于土壤中砷含量的测定和监控。     

ICP-AES法测定海水中钾、钠、钙、镁、锂、锶、锰

研究了采用等离子体发射光谱法(ICP-AES)测定海水中钾、钠、钙、镁、锂、锶、锰7种元素的方法。此方法标准曲线线性关系好,相对标准偏差3.35%,相对误差5.5%,加标回收率达90%～104.3%,有较高的测定精密度和准确度,干扰小,值得推广应用。     

基于改进WKB的非均匀等离子体中脉冲波形研究

WKB是研究非均匀等离子体中电磁波传播现象时经常采用的一种经典计算方法,但是该方法忽略了电磁波传播过程中前向波和后向波的耦合效应。为了提高计算结果的准确度,可利用差分传输矩阵技术,将WKB解由原来的一阶近似提升至二阶近似,使得计算结果中包含了由于耦合效应引起的衰减部分。通过此改进WKB方法,以对称分布参数等离子体层模型为例,对电磁波信号经等离子体层传播后波形的变化进行了计算和分析。并通过快速傅里叶变换,给出了时域高斯脉冲信号波形的具体算例,计算结果表明通过该种方法能够有效的分析信号波形变化。     

基于等离子体相位特性的谐波抑制方法

本文对等离子体的相位特性进行分析并给出详细的公式推导过程。基于此,提出了一种波导滤波器谐波抑制新方法并进行了新型等离子体滤波器的设计。仿真结果表明,此等离子体滤波器的三次谐波能够抑制在-20dB以下,其峰值相比传统滤波器结构的结果降低了18.5dB,起到了显著的抑制效果,充分证实了方法的有效性。     

Fabrication of highly reflective gratings in 1.5 μm semiconductor lasers using focused ion beam-based etching

This paper reports on fabrication of semiconductor/air gratings in 1.5 μm double-section semiconductor lasers to achieve a high reflectivity in order to compensate low round-trip gain. Fabrication of the gratings with varying thicknesses and with thicknesses down to 160 nm is carried out at the gain section of the double-section diode laser using focused ion beam etching (FIBE) and inductively coupled plasma (ICP) techniques. Theoretical results of reflectivity are given for 1.5 μm AlGaInAs/InP semiconductor lasers by adding wavelength dependence of the refractive index into the calculations. We also compare our reflectivity results with that of a commercial simulation program and show a good agreement between them. Our results demonstrate that the gratings fabricated consist of only six air/semiconductor layer pairs and achieve theoretical reflectivity higher than 99%. Due to a high index contrast of the both layers, n_l = 1, n_h ∼ 3.5, a reflectivity bandwidth of >230 nm is obtained in 1.5 μm semiconductor lasers. Finally, lasing operation from AlGaInAs/InP semiconductor lasers with highly reflective grating section is achieved with a low threshold current of ∼8 mA, which is almost three times lower than devices without semiconductor/air gratings.     

用于功率变换的高击穿增强型AlGaN/GaN HEMTs

首次采用CF4等离子体技术实现可用于功率变换的增强性AlGaN/GaN功率器件。实验结果表明,当AlGaN/GaN器件经功率150W和时间150s等离子体轰击后,器件阈值电压从-4V被调制约为0.5V,表现为增强型。当漂移区LGD从5μm增加到15μm,器件的击穿电压从50V迅速增大到400V,电压增幅达350V。采用长度为3μm源场板结构将器件击穿电压明显地提高,击穿电压增加约为475V,且有着比硅基器件更低的比导通电阻,约为2.9mΩ.cm2。器件模拟结果表明,因源场板在远离栅边缘的漂移区中引入另一个电场强度为1.5MV/cm的电场,从而有效地释放了存在栅边缘的电场,将高达3MV/cm的电场减小至1MV/cm。微波测试结果表明,器件的特征频率fT和最大震荡频率fMAX随Vgs改变,正常工作时两参数均在千兆量级。栅宽为1mm的增强型功率管有较好的交直流和瞬态特性,正向电流约为90mA。故增强型AlGaN/GaN器件适合高压高频大功率变换的应用。