大截面SOI脊型波导单模条件的研究

利用有限差分方法（FDM）对大横截面SOI（Silicon-on-insulator）脊型光波导的本征模进行了计算分析, 从而确定了SOI脊型波导的单模条件, 即归一化外脊高和归一化脊宽的关系. 通过比较, 进一步明确了归一化外脊高大于0.5时现有的单模条件解析公式中常数项的取值为0.3. 同时, 还对归一化外脊高小于0.5时的单模条件也做了计算和讨论.     

基于Optiwave的脊形SiGe OI光波导结构设计

利用有效折射率的数值解法,计算出了SiGe OI脊形光波导的有效折射率.通过对SiGe OI光波导结构参量的理论分析和计算,得到了SiGe OI脊形光波导传输单模光波时内外脊高H,h及脊宽W的尺寸.通过Optiwave软件对SiGe OI脊形光波导进行建模仿真,验证了理论分析和计算的正确性.     

前缘突脊倾斜气膜冷却效果的实验

为了研究前缘突脊结构对气膜冷却的影响规律,设计了3种不同堵塞比的突脊模型,研究了气膜冷却效率随吹风比、堵塞比的变化规律.研究结果表明,与典型的圆柱型气膜孔相比,前缘突脊的存在大大提高了气膜冷却效率;前缘突脊在大吹风比下的作用更加明显;研究范围内存在最佳堵塞比.     

光子晶体平面波导与脊波导高效耦合技术的研究

利用一维变周期谐振腔阵列和非线性缓变边界，可以实现光波从脊波导到光子晶体平面波导 （PCW）的高效耦合.基于平面波展开法（PWE）和时域有限差分法（FDTD），深入分析和讨 论了普通脊波导、2D-PCW结构和本征模以及工作模式、缓变边界形状等对耦合效率的影响， 从而得出光波从脊波导到2D-PCW、再返回脊波导的统一图景.指出考虑模式转换和采用缓变 边界条件可以极大提高PCW与脊波导间的耦合效率.对PC-PW边界采用线性和非线性缓变结构 进行了仿真，讨论了边界缓变程度对耦合效率的影响.结果表明，采用模式耦合和PC-PW余弦 缓变边界时的耦合效率在较宽的带宽内超过了95%. 关键词： 光子晶体波导 脊波导 PWE FDTD 耦合边界     

直角棱镜棱脊倾斜对方位瞄准的影响

火箭制导系统中惯性器件的方位敏感轴方向通常是借助于直角棱镜来确定的,因而直角棱镜的棱脊倾斜对方位瞄准精度有影响.本文推导了直角棱镜的棱脊倾斜造成的反射光矢量的精确表达式,并在此基础上讨论了棱脊倾斜对线阵CCD测角的影响.     

基于脊波变换的渐变镜头转场检测算法

分析了脊波变换在处理含“线奇异”信号上的优势.提出用脊波变换后的各高频系数和作为图像的特征量.渐变镜头脊波变换的实现分两步：首先,对图像帧进行一定方向参量的Radon变换;其次,对Radon变换得到各数组进行Haar小波二级分解,采用分解后的高频系数和描述图像.在检测窗内,计算连续帧间脊波变换系数和之间的欧式距离判别渐变转场的边界.     

聚合物脊形光波导的变分有效折射率法分析

聚合物脊形光波导是聚合物集成光电子器件的重要构成单元.利用有效折射率法计算聚合物脊形光波导的横向折射率分布及有效折射率,将各区域中的光场分布近似用分段函数表达.基于导模满足的标量波动方程,利用变分法确定变分参量,以求得准确的横向光场分布.对聚合物脊形多模光波导基模和高阶模的色散特性与横向场分布进行分析,研究了波导结构参数对色散特性的影响,计算出TM基模和高阶模的光场分布,得出了聚合物脊形光波导的单模传输条件.研究表明,该方法计算量小、精度高,对聚合物光电子器件中脊形光波导的理论分析与设计优化提供了简单高效的方法.     

Ka波段曲折双脊波导行波管的研究

提出了一种曲折双脊波导慢波结构,理论分析了慢波结构的高频特性,并在此基础上设计了工作在Ka波段的曲折双脊波导行波管.利用三维粒子模拟软件MAGIC 3D建立了曲折双脊波导行波管模型,并对行波管中的注-波互作用进行了模拟分析.在相同工作条件下,分析比较了曲折双脊波导行波管和曲折波导行波管的各种性能参量,从中发现：在行波管增益峰值相近的情况下,曲折双脊波导行波管具有更好的带宽性能,其3 dB增益带宽为22％;同时具有更高的电子效率,其峰值接近9％. 关键词： 曲折双脊波导 高频特性 注-波互作用 带宽     

Ka波段曲折双脊波导行波管的研究

提出了一种曲折双脊波导慢波结构,理论分析了慢波结构的高频特性,并在此基础上设计了工作在Ka波段的曲折双脊波导行波管.利用三维粒子模拟软件MAGIC 3D建立了曲折双脊波导行波管模型,并对行波管中的注-波互作用进行了模拟分析.在相同工作条件下,分析比较了曲折双脊波导行波管和曲折波导行波管的各种性能参量,从中发现：在行波管增益峰值相近的情况下,曲折双脊波导行波管具有更好的带宽性能,其3 dB增益带宽为22％;同时具有更高的电子效率,其峰值接近9％.     

脊加载曲折波导行波管注波互作用的线性理论研究

提出了一类新型毫米波大功率微波器件——脊加载曲折波导行波管,推导出了引入电子注后的"热"色散方程.通过数值求解此方程,研究了加脊尺寸和电子注参数对小信号增益影响.计算结果表明:通过适当的尺寸设计和工作参数的选择,此结构在Kα波段具有18.51%的3 dB增益带宽和1.15 dB/周期的增益;相比于常规曲折波导结构,脊加载结构在保证一定带宽的情况下,具有更高的增益和电子效率;为了进一步提高增益,可以适当增加脊宽度和高度,也可在一定范围内增加电子注电流. 关键词： 毫米波 曲折波导 脊加载 小信号增益     

Analysis of Elliptical Thin Ridged Waveguide

Elliptical waveguides and ridged waveguides have found broad applications in many microwave structures. The elliptical waveguide with double infinite thin ridges has been formulated using the mode-matching method. Exact closed-form expressions for eigenvalue problem of all TE and TM modes are presented. Numerical results suggest that the elliptical ridged waveguides have larger bandwidth than that of circular ones. Supported in part by the National Natural Science Foundation of China under Grant 60532010, and in part by the Scientific Research Foundation for the Returned Overseas Chinese Scholars under Grant 04LXJ01.     

加脊TEM喇叭初步研究

针对恒阻抗TEM喇叭的上下面板电流分布不对称,采用小反射理论和阻抗渐变思想并通过设计脊结构对恒阻抗TEM喇叭进行了改进,研制了加脊TEM喇叭。仿真及实验研究结果表明:对于脉冲宽度约为1 ns的高斯脉冲,通过加脊在一定程度上改善了恒阻抗TEM喇叭上下面板电流分布的不对称性和E面辐射电场的不对称性;相对于相同口径的恒阻抗TEM喇叭,加脊TEM喇叭作为辐射天线和反射面脉冲天线馈源时系统的主轴远场辐射因子均有提高。     

Investigation of the Dielectric-Loaded, Ridged Helical Groove Slow-Wave System for the Millimeter Wave TWT

A dielectric-loaded, ridged helical groove slow-wave structure for the millimeter wave traveling wave tube is presented in this paper. The effects of the groove depth, ridge dimensions and the dielectric permitivety on the wave propagating properties and the interaction impedance are investigated in detail. From the analysis, it is indicated that for broader band amplification in a helical groove travelling wave tube, a ridged helical structure with shallow groove and loaded by dielectric with proper relative permitivety may be applied.     

Numerical modeling of generalized millimeter-wave transmission media with finite element and transmission line matrix methods

In this paper, a general finite element method as well as a graded-mesh TLM procedure for determining the dispersion characteristics, field distribution, pseudo-impedance and losses of generalized millimeter-wave transmission media are described. These methods cover arbitrary cross-sections and account for realistic features (finite metallization thickness, substrate mounting grooves etc.) that are often neglected in theoretical analysis. Dispersion characteristics and characteristic impedances obtained for dielectrically loaded ridged wave-guides compare well with the available data. Conductor and dielectric losses are also computed for these structures. A modified finline structure called ridged finline is also analysed. The main advantages of this structure are its large monomode bandwidth and reduced dispersion. The cutoff frequencies of bilateral finlines in circular waveguides are also computed.     

Reflection of Waves from a Ridged Surface and the Zeno Effect

Reflection of waves from a ridged surface is interpreted as the spatial Zeno effect. This interpretation leads to a simple estimate for the coefficient of reflection. This estimate shows good agreement with experimental data of scattering of cold atoms from ridged surfaces.     

A ceramics-free waveguide for ITER ion cyclotron wave system

A ceramics-free waveguide for the high-power International Thermonuclear Experimental Reactor ion cyclotron (ITER IC) system (15-80 MHz), which is a TEM waveguide supported mechanically by T-shaped ridged waveguides, is proposed. The transmission-line theory shows that this waveguide has power handling capability of more than 3 MW, where an optimized antenna impedance is used for the ITER plasma parameters. The transmission line model used for the analysis is verified by the experiments on a one-tenth scale model     

Low-loss polymeric optical waveguides with large cores fabricated by hot embossing

A simple low-cost method of fabricating polymeric optical waveguides with large core sizes for plastic optical fibers is presented. The waveguides are fabricated by hot embossing with an ultraviolet-cured epoxy resin stamper. The stamper is fabricated by replication of a rectangular groove mold that is made from silicone rubber replicated from a ridged original silicon master. The master is fabricated by anisotropic etching of (110) single-crystal silicon. Optical waveguides with large core sizes of 100-500 microm have been fabricated, and a low propagation loss of 0.19 dB/cm at 650 nm was achieved.     

Input Impedance Characteristics of a T-Shaped Ridged Waveguide

This paper presents input impedance characteristics of a T-shaped ridged waveguide calculated by a magnetic wall model. They are also confirmed experimentally.     

Compositional evolution of lava plains in the Syria-Thaumasia Block,Mars

Tharsis is the most prominent volcanic province on Mars,yet the compositions of lava flows and how composition relates to the development of Tharsis are poorly known.Most of Tharsis is covered with air-fall dust,which inhibits spectroscopic determination of lava mineralogy.The Syria-Thaumasia Block(STB)is a complex tectono-volcanic province closely related to the Tharsis bulge.The lava plains of STB have different emplacement ages,which provide an opportunity to examine whether magma composition changed with the evolution of Tharsis.In this study,we assessed the lava plains using Thermal Emission Spectrometer(TES)data.Using derived physical properties,we targeted dust-free regions from four different-aged geological units’surfaces and determined the mineralogical composition by modeling the average TES surface spectrum from each of the four surfaces.All units have similar mineralogy but the younger two units have elevated abundance of high-SiO2phases.The spatial distribution of wrinkle ridges indicates lava plains of unit HNr(older ridged plains material)and Hr(younger ridged plains material)were emplaced before the rise of Tharsis,whereas Hsl(flows of lower member)and Hsu(upper member)were emplaced after Tharsis uplift was initiated.We show that the magma composition differed in the lava plains of STB after the uplift of Tharsis.This study further characterizes early martian magma composition and evolution.