遥感、遥测、遥控

TP72 2007011920一种新的微波频率下混合电解质水溶液复等效介电常数的计算方法/杨晓庆,黄卡玛(四川大学电子信息学院)//电子学报.―2006,34(2).―356～360.目前,大部分电解质水溶液的等效介电常数计算模型是针对静止频率下其实部进行的,而对于实部与虚部同时计算方法的报道中,都是通过大量实验测量,利用德拜参数拟合而得到相应结果的,且局限于少数几种溶液,例如盐水和海水等,文中,通过实验得到了不同电解质水溶液的     

高介电常数铁电瓷料的改性

<正> 随着电子工业的发展,对电子元件的小型化提出了更高的要求。国内许多生产企业已在低频高介电常数(ε=20000)瓷料方面作了大量的研究工作,并已实现了工业规模的生产。 目前,低频高介电常数瓷料大多是采用     

单层ITO薄膜在ENZ波段增强非线性光学效应的研究

在玻璃基底上镀35 nm厚的ITO薄膜,通过椭偏仪测量ITO薄膜的线性介电常数.由于ITO具有高掺杂浓度,因此其介电常数可以用Drude模型来进行量化计算,得到其介电常数近零(ENZ)波长约为λ=1 100 nm.借助双温模型计算电子温度和晶格温度随时间的变化,根据电子温度的升高计算等离子体频率的变化,将其带入Drude模型中,可以得到一个新的介电常数,最后可以通过计算折射率的变化,从而求出非线性折射率n2.计算结果表明,在ENZ波长入射时,可以得到最大非线性折射率n2=4.66×10-15 m2/W.因此,实验中选取的材料可在低功率光照下得到显著的折射率变化,可望应用于全光存储、全光开关等纳米光子器件的设计.     

准气密空腔型外壳的封装技术

基于非陶瓷、金属等材料的空腔型封装是近年来兴起的一种非气密或准气密封装技术。这种封装技术采用环氧树脂或液晶聚合物等塑料材料制作空腔型外壳,相对于陶瓷、金属等无机材料而言,基于塑料材质的空腔型外壳具有重量轻、介电常数低等优势,目前已经在射频电子、便携式产品中得到了应用。介绍了3种类型的空腔型外壳及相应的盖板密封技术,并对空腔型外壳的准气密封装技术在国内的应用进行了展望。     

CdS电子结构及光电特性的第一性原理研究

研究了各向极化对CdS电子结构及光电特性的影响。采用基于密度泛函理论(DFT)的第一性原理超软赝势方法对CdS基态的电子结构和光电特性进行系统地计算,计算得到CdS是带隙宽带为1.943eV的直接带隙半导体材料。价带主要由S 3p态电子贡献,Cd 4p和Cd 4d态电子贡献较少;导带主要由Cd 4d5s和S 3p态电子决定,S 3s态电子贡献较少。在a、b、c三个方向的极化下研究CdS光学特性的各向异性,沿a方向和b方向极化的各个光学参量都完全相同,静态介电常数为7.234,但沿c方向的静态介电常数为6.273。其它光学参量的各向异性变化与介电函数相同,表明CdS晶体光学性质存在各向异性。计算结果为CdS光电特性的研究提供理论依据。     

高压烧结的BaTiO3陶瓷的介电性能

用两种高压法烧结得到致密的细晶BaTiO3陶瓷。由压力辅助烧结得到的陶瓷晶粒没有过分长大,晶粒尺寸保持在纳米尺度内;用高压成型常压烧结法得到的陶瓷晶粒明显长大。当BaTiO3陶瓷的晶粒尺寸从400 nm减小到50 nm时,相应的介电常数从3 000减小到1 900。介电常数的减小可由晶粒尺寸的减小而导致四方度的降低和非铁电低介电常数的晶界层解释。且铁电-顺电转变由一个尖锐峰变成一个宽的区域,宽的转变区域表现出扩散相变的特征。     

激光束在强电离的等离子体中的自聚焦

研究了强电离的等离子体的介电常数在存在强高斯激光束时的非线性。非线性的出现是由于电子的加热和再分布;从场获得的电子能量的损失被假设为由于热传导引起的。即使非线性介电常数在饱和区并不下降,此自感应的非线性引起了光束的自聚焦和振荡的波导传播。预示了在10¹⁰瓦激光器的典型情况下,在0.6厘米的长度内,轴向强度将增加25倍。     

用于液体违禁品检测的电容传感器设计

提出了利用液体介电常数的电子测量,实现一种快速、无辐射、非接触、低成本的液体违禁品探测的新方法。在研究了液体介电常数测量的理论,并结合具体应用场合的基础上,提出了基于平面板电容器原理的平面板电容传感器和改进型的梳妆电容传感器电极,从理论的角度上对电极的参数进行了探讨。通过实验证明了改进型的梳状电极能够在不开瓶取样的情况下,有效鉴别出在厚度为4mm以下的非金属容器中浓度50%以上的酒精和水,可以用于非接触式液体违禁品快速检测。     

水热条件下钛酸钡在海泡石上生长习性的SEM研究

电子陶瓷用钛酸盐是电子工业的重要原料。其中钛酸钡又是电子陶瓷中最重要的一种 ,是具有压电性和极高介电常数的电子功能材料[1] 。但钛酸钡具有立方相、四方相两种不同的晶型 ,只有后者才具有压电性和较高的介电常数。随着研究的深入 ,在水热条件下可直接得到四方相钛酸钡[2 ] 。但一般在温度较低时 ,水热法得到立方相钛酸钡 ,随着温度的提高和原料中钡 钛摩尔比的增加 ,生成四方相钛酸钡的可能性增加[3 ] 。但产物的原始粒径通常为10 0ｎｍ左右 ,难以满足压电陶瓷的需要。本研究采用在水热体系中加入海泡石的办法 ,在较低的温度下 ,得到…     

1维3元非磁化等离子体光子晶体禁带特性研究

为了研究1维3元非磁化等离子体光子晶体的禁带特性,采用传输矩阵法仿真计算了电磁波在1维3元非磁化等离子体光子晶体的传播规律,用计算得到的电磁波透射系数讨论了周期常数、介电常数、介质层厚度和等离子体参量对其禁带特性的影响。结果表明,改变介电常数、介质层厚度和等离子体频率可以实现对带隙的调制,增加周期数和等离子体频率不能实现对禁带的拓展。这一结果为设计1维3元非磁化等离子体光子晶体器件提供了理论参考。     

任意横截面形状非均匀介质波导传输特性的分析

用阶梯近似与边缘元和模匹配相结合的方法分析了一大类任意横截面形状非均匀介质波导的传输特性，将非均匀部分用一系列级联的台阶近似，各台阶用微波多模网络等效，用边缘元方法求得各本地波导的本征值问题后，用模匹配法算 出各微波网络的散射参数，最后通过级联的微波网络求得融洽上非均匀结构的传输特性，由于边缘元方法的通用性，此法可对各种不同横截面形状的非均匀介质波导进行分析。     

Bistatic scattering by arbitrarily shaped objects with rough surface at optical and infrared frequencies

The scattering cross sections for arbitrarily shaped dielectric objects with rough surface are determined for optical and infrared frequencies using the Kirchhoff approximation. The formula of the coherent scattering cross section is derived, and numerical method of incoherent scattering cross section is given. As a specific example, the infrared laser scattering cross sections of rough spheres are calculated at 1.06 μm.     

Plane wave scattering by a corrugated conducting cylinder atoblique incidence

The problem of scattering from a corrugated conducting cylinder due to an obliquely incident plane wave is solved by a boundary-value method. The region between the corrugations is considered as a medium with tensor permeability and tensor permittivity, which is a valid assumption when the corrugation constant is much less than the free-space wavelength. By loading this region with a dielectric material, one of the components of the scattered electric field in the far-field region can be altered significantly with no change in the other component. These components, in turn, determine the bistatic scattering cross sections, and the dielectric loading of the corrugated region appears to have no effect on the cross section due to the polarized component, while showing significant changes in the cross section due to the depolarized component     

激光场中电子被氩原子散射的微分截面研究

应用第二玻恩近似理论，在电子入射方向平行于激光场的极化方向这种特殊的散射模式下，利用光学势模型对激光场中电子一氩原子散射进行了研究。利用静电屏蔽势，分别应用低频近似和第二玻恩近似公式对激光场中电子一氩原子散射进行了计算。和实验相比较，第二玻恩近似方法给出了较好的结果；应用这个较好的理论，利用光学势模型进行了计算，得到了更好的结论。     

Low-frequency scattering by rectangular cylinders

An integral equation formulation is used to investigate potential problems associated with low-frequency scattering by both dielectric and perfectly conducting cylinders of rectangular cross section. Induced dipoles and scattering cross sections are obtained for 1) waves withbar{E}orbar{H}parallel to the axis, and 2) directions of propagation perpendicular and parallel to the broad side of the rectangle.     

Microwave scattering model for grass blade structures

The EM scattering solution for a grass blade with complex cross-section geometry is considered. It was previously shown that the scattering solution for such problems, in the form of a polarizability tensor, can be obtained using the low-frequency approximation in conjunction with the method of moments. In addition, that study showed that the relationship between the polarizability tensor of a dielectric cylinder and its dielectric constant can be approximated by a simple algebraic expression. The results of that study are used to show that this algebraic approximation is valid also for cylinders with cross sections the shape of grass blades, providing that proper values are selected for each of three constants appearing in the expression. These constants are dependent on cylinder shape, and if the relationship between the constants and the three parameters describing a grass blade shape can be determined, an algebraic approximation relating polarizability tensor to blade shape, as well as dielectric constant, can be formed. This algebraic approximation can replace the cumbersome method of moments model. The moment method model is therefore used to generate a small but representative set of polarizability tensor data over the range of values commonly observed in nature. A conjugate gradient method is then implemented to correctly determine the three constants of the algebraic approximation for each blade shape. A third-order polynomial fit to the data is then determined for each constant, thus providing a complete analytic replacement to the numerical (moment method) scattering model     

A tetrahedral modeling method for electromagnetic scattering by arbitrarily shaped inhomogeneous dielectric bodies

A method for calculating the electromagnetic scattering from and internal field distribution of arbitrarily shaped, inhomogeneous, dielectric bodies is presented. A volume integral equation is formulated and solved by using the method of moments. Tetrahedral volume elements are used to model a scattering body in which the electrical parameters are assumed constant in each tetrahedron. Special basis functions are defined within the tetrahedral volume elements to insure that the normal electric field satisfies the correct jump condition at interfaces between different dielectric media. An approximate Galerkin testing procedure is used, with special care taken to correctly treat the derivatives in the scalar potential term. Calculated internal field distributions and scattering cross sections of dielectric spheres and rods are compared to and found in agreement with other calculations. The accuracy of the fields calculated by using the tetrahedral cell method is found to be comparable to that of cubical cell methods presently used for modeling arbitrarily shaped bodies, while the modeling flexibility is considerably greater.     

Nonlinear saturation and efficiency enhancement in a Cherenkovlaser using a dielectric grating

With the aid of particle simulation, this paper discusses nonlinear saturation and efficiency enhancement in a single-pass Cherenkov laser using a dielectric grating, taking into account the nonlinear properties of a relativistic electron beam. For the analysis of the problem, a two-dimensional model for the Cherenkov laser is considered which is composed of a planar relativistic electron beam and a parallel plate waveguide, one plate of which is loaded with a dielectric grating. First, the nonlinear characteristics for the growth of the electromagnetic wave are considered for a dielectric grating with constant parameters. The variation of the groove depth or the slot width in a dielectric grating is found to have the same effect on the growth characteristics as the variation of the permittivity of a dielectric sheet with constant thickness. Then, in order to enhance the efficiency in energy transfer from the electron beam to the electromagnetic wave in the Cherenkov laser, one of the grating parameters or the groove depth is adiabatically decreased in accordance with the decrease in the average velocity of the electron beam. The result of numerical simulation shows that sufficient efficiency enhancement in energy transfer is achieved with the use of a dielectric grating with a variable parameter     

Solution of the problem of electromagnetic scattering by a thin dielectric cylinder with the use of the auxiliary source method

The problem of electromagnetic scattering by a thin solid dielectric cylinder is solved in the resonance frequency range by means of the auxiliary source method. The developed computer code is briefly described. The domain of applicability of the method for calculating the scattering characteristics of thin dielectric objects is investigated. The scattering cross sections of cylinders having various lengths and various values of the relative permittivity are numerically calculated.     

Two-dimensional microwave imaging by a numerical inverse scatteringsolution

A numerical approach that aims to detect, by means of interrogating microwaves, the locations and the dielectric permittivities of unknown inhomogeneous dielectric cylindrical objects of arbitrary cross sections that might be present inside a fixed area of interest is proposed. An illumination is assumed with the electric field vector polarized along the cylindrical axis. The two-dimensional Lippman-Schwinger integral equation of electromagnetic scattering is transformed into matrix form by the moment method. The system obtained is solved by using a pseudoinversion algorithm to overcome ill-conditioning problems. The first-order Born approximation is also applied when the dielectric inhomogeneities are weakly scattering. Computer simulations have been performed by means of a numerical program. Results show the capabilities and limitations of the proposed approach