粗糙介质面对高斯波束的散射

该文研究了当入射场为光波束时粗糙介质面的散射问题。利用波束的平面波谱展开方法及基尔霍夫近似理论导出了散射场和非相干截面计算公式,并对后向非相干截面进行了数值计算,最后对其结果进行了分析讨论。     

精糙介质面对高斯波束的散射

该文研究了当入射场为光波束时粗糙介质面的散射问题,利用波束的平面波谱展开方法及基尔霍夫近似理论导出了散射场和非相干截面计算公式,并对后向非相干截面进行了数值计算,最后对其结果进行了分析讨论。     

有源随机球粒媒质的非弹性多散射

依据有源分子的等效偶极子模型,本文首先用并矢格林函数方法给出了含有有源分子的单球粒的非弹性散射分析。然后,以建立的随机球状颗粒媒质的弹性多散射理论为基础,导出了含有有源分子的随机球粒媒质的非弹性多散射理论,给出了非弹性多散射场在整个空间的矢量球波函数展开,展开系数可由一组耦合线性方程解得。     

用激光散射法测量纤维的截面形状

本文详细分析了一端固定和两端固定纤维的弯曲振动频谱,以及截面为椭圆形、圆形和任意形状时的偏心率,并导出了一系列计算公式;介绍了用激光散射法测量纤维截面形状的原理图,并给出了试验结果.     

粗糙金属和介质目标的太赫兹散射特性分析

太赫兹频段金属和介质粗糙目标的散射特性是研究太赫兹雷达目标特性的重要基础。当目标表面的主曲率半径远远大于入射波长,且粗糙表面高度起伏与斜率起伏远小于入射波长时,根据稳定相位法和标量近似法,可获得粗糙金属和介质目标的相干散射截面和非相干散射截面。基于稳定相位法,任意目标的相干散射截面可退化为粗糙导体、光滑介质和粗糙介质目标的相干散射。该文分析了电大尺寸光滑金属铝和介质白漆球的散射截面,与Mie理论计算的介质球的散射特性吻合,散射截面误差小于0.1 dBm2。采用朗伯定理,验证了粗糙介质球的太赫兹非相干散射精确解,当目标表面剖分精度越高,非相干散射的计算精度越高。该文数值计算了粗糙介质球的太赫兹相干和非相干散射特性,分析了表面粗糙度和表面材料对散射特性的影响,为电大尺寸空间目标太赫兹散射特性分析提供了理论基础。      

空间碎片地基雷达探测综述

微动特征是空间碎片目标特性研究与识别的重要特征量。为提升非相干散射雷达在空间碎片微动特征提取中的应用,设计了一种基于雷达的目标微动特征提取方法,包括距离徙动修正、目标平动速度和加速度余项修正、时频分布计算、逆Radon变换等,并利用曲靖非相干散射雷达实测回波数据进行分析验证。结果表明,利用非相干散射雷达实测回波可有效提取空间碎片自旋或翻滚半径、周期、频率以及姿态角等特征参数,进而初步判断其形状,仿真和实测数据分析结果与预期情况基本相符。本文工作验证了电离层非相干散射雷达用于空间碎片微动特征提取的可行性,为空间碎片监测与目标特性研究识别提供了新技术手段。

     

任意形状矩形波导耦合窗的矩量法分析

本文针对任意形状矩阵形波导耦合窗进行了矩量法分析，给出了它们的散射参量和等效电路参量计算方法。在分析中，未对窗孔的几何形状加任何限制，所得计算公式及计算机软件适宜于分析矩形波导内各类感性耦合窗，容性耦合窗，谐振窗以及其他开有任意形状窗孔的波导膜片，用本文理论方法分析计算了若干波导耦合窗实例，获得了满意的结果。     

任意形状粗糙物体的激光后向散射

本文研究具有粗糙表面凸形物体的光频后向散射。由几何光学基尔霍夫近似,获得相干后向散射截面和非相干后向散射截面理论计算公式。以粗糙球和粗糙椭球为例分析了物体几何参数,介电常数和粗糙表面统计参数对红外激光后向散射截面的影响。     

散射对量子阱隧穿电流的影响

本文从单带双谷模型出发研究了电子在量子阱内遭到散射时电子状态及隧穿几率的变化。弹性散射使用δ散射势来计算,非弹性散射则用虚散射势来描述。前者使隧穿电流峰向高电压端移动,后者减弱了电流峰的谐振强度。分别讨论了位于势阱和势垒层中的散射中心的不同散射作用。隧穿电流的变化趋势同中子辐照实验数据相吻合。     

任意取向非球形群聚粒子极化散射及其数值模拟

利用Ｔ矩阵法，通过严格求解Ｎ个粒子的多次数散射方程，发展了任意大小、空间分布和取向的多个非球形粒子集合性相干散射的数值计算方法。     

INELASTIC MULTIPLE SCATTERING BY ACTIVE RANDOMLY DISTRIBUTED SPHERICAL SCATTERERS

According to the model of equivalent dipoles for active molecules, the analysisof inelastic EM scattering by active molecules embedded in a sphere is given by the method ofdyadic Green's functions at the first, and then based on the theory of elastic multiple scattering byrandomly distributed spherical scatterers, a new theory for analysis of inelastic multiple scatteringby active molecules embedded in randomly distributed spherical scatterers also is developed. Thistheory gives the expansions of the multiple scattering fields in all space region in terms of vectorspherical wave functions in which the expansion coefficients can be solved from a set of coupledlinear equations.     

Ultrasonic Reflectivity Imaging in Three Dimensions: Exact Inverse Scattering Solutions for Plane, Cylindrical, and Spherical Apertures

The problem of reconstructing the reflectivity of a three-dimensional medium with density and compressibility variations is examined. For the special case of continuous-wave (CW) insonification, exact inversion formulas have recently been reported for recovering an unknown scattering parameter from scattering measurements. In this work, exact solutions, or inversion formulas, are obtained for the general case of arbitrary broad-band insonification where the incident wave is assumed to be a spherically diverging broad-bandwidth pulse of arbitrary shape. Solutions are derived under the assumption that the scattering is sufficiently weak for the Born approximation to hold. Exact inversion formulas are obtained for three aperture geometries: a plane, cylindrical, or spherical recording surface enclosing the scattering region. Under most practical conditions, the process of back projection and coherent summation over spherical surfaces in image space, without prior filtering, is shown to provide a close approximation to the exact inversion procedure. Finally, in the case of the spherical geometry, the mathematical equivalence between the three-dimensional inverse Radon transform and the far-field approximation to the exact solution is demonstrated.     

Layer-by-Layer Analysis of the Thickness Distribution of Silicon Dioxide in the Structure SiO<Subscript>2</Subscript>/Si(111) by Inelastic Electron Scattering Cross-Section Spectroscopy

The SiO₂-concentration profile in the structure SiO₂/Si(111) is determined from experimental spectra of the cross section for the inelastic scattering of reflected electrons in the primary electron energy range from 300 to 3000 eV. The spectra are analyzed with the use of a proposed algorithm and developed computer program for simulating the spectra of the cross section for the inelastic scattering of reflected electrons for layered structures with an arbitrary number of layers, arbitrary thickness, and variable concentration of components in each layer. The best agreement between the calculated and experimental spectra is attained by varying the silicon dioxide and silicon concentrations in each layer. The results obtained can be used for profiling film-substrate structures with an arbitrary composition.     

Digital computer solutions of the rigorous equations for scattering problems

A survey of recently developed techniques for solving the rigorous equations that arise in scattering problems is presented. These methods generate a system of linear equations for the unknown current density by enforcing the boundary conditions at discrete points in the scattering body or on its surface. This approach shows promise of leading to a systematic solution for a dielectric or conducting body of arbitrary size and shape. The relative merits of the linear-equation solution and the variational solutions are discussed and numerical results, obtained by these two methods, are presented for straight wires of finite length. The computation effort required with the linear-equation solution can be reduced by expanding the current distribution in a series of modes of the proper type, by making a change of variables for integration, and by employing interpolation formulas. Solutions are readily obtained for a scattering body placed in an incident plane-wave field or in the near-zone of a source. Examples are included for both cases, using a straight wire of finite length as the scattering body. The application of these techniques to scattering by a dielectric body is illustrated with dielectric rods of finite length.     

Inelastic hot-electron Bloch scattering from quantum-confined systems

The phenomena of electric field-assisted inelastic Bloch-electron scattering from an atomically confined bound-state electron is reported. A novel formalism for treating Bloch electron dynamics and quantum transport in electric fields of arbitrary strength and time dependence is utilized. The two-electron inelastic scattering rate obtained herein shows an electric field-dependent broadening; as a novel addition, the calculated scattering rate includes an explicit dependence on band structure, predicting a strong influence from band non-parabolicity and anisotropy.     

Physics of Carrier Backscattering in One- and Two-Dimensional Nanotransistors

The physics of carrier backscattering in 1-D and 2-D transistors is examined analytically and by numerical simulation. An analytical formula for the backscattering coefficient is derived for elastic scattering in a 1-D channel. This formula shows that the critical length for backscattering is somewhat longer than the $kT$ length, and it depends on the shape of the channel potential profile. For inelastic scattering, Monte Carlo (MC) simulations show that the critical length is related to the phonon energy. The MC simulations also show that although the scattering physics in 1-D and 2-D transistors is very different, the overall backscattering characteristics are surprisingly similar. For an elastic process, this similarity is due to the compensating effects of the scattering rate and the fraction of scattered carriers, which contribute to the backscattering coefficient. For an inelastic process, the critical length is determined from the phonon energy for both 1-D and 2-D channels.      

Simulations of Kikuchi patterns due to thermal diffuse scattering on MgO crystals

Inelastic scattering of fast transmission electrons from a perfect crystal is investigated using the Bloch wave theory. A comprehensive expression for the scattering of electrons is given, which includes both elastic and inelastic multiple scatterings. This expression is an extended form of Fujimoto's expression for elastic scattering (J. Phys. Soc. Japan 14:1558 (1959)). For the approximation of single inelastic scattering, the expression becomes equivalent to the formula of Rez et al. (Phil. Mag. 35: 81 (1977)). When thermal diffuse scattering (TDS) is considered using the Einstein model or the scattering factor for TDS given by Hall and Hirsch (Proc. R. Soc. A 286: 158 (1965)), Rossouw and Bursill's expression (Acta Cryst. A 41: 320 (1985)) is derived. This expression has been used in computer simulations of TDS intensity distribution (Kikuchi pattern). It is shown that the simulations for magnesium oxide (MgO) using 357 beams agree quite well with the experimental ones.     

CFIE MM solution for TE and TM incidence on a 2-D conducting bodywith dielectric filled cavity

The problem of determining the scattering cross section of an arbitrarily shaped two-dimensional conducting body with an arbitrarily shaped dielectric filled cavity is considered. The problem is solved using a method-of-moments solution for the combined field integral equations. The particular form of the method of moments solution used here uses a minimum number of expansion coefficients. Results are given for transverse electric and transverse magnetic incident waves     

Effective permittivity of dielectric mixtures

General mixing formulas are derived for discrete scatterers immersed in a host medium. The inclusion particles are assumed to be ellipsoidal. The electric field inside the scatterers is determined by quasi-static analysis, assuming the diameter of the inclusion particles to be much smaller than one wavelength. The results are applicable to general multiphase mixtures, and the scattering ellipsoids of the different phases can have different sizes and arbitrary ellipticity distribution and axis orientation, i.e. the mixture may be isotropic or anisotropic. The resulting mixing formula is nonlinear and is suitable for iterative solutions. The formula contains a quantity called the apparent permittivity, and with different choices of this quantity, the result leads to the generalized Lorentz-Lorenz formula, the generalized Polder-van Santen formula, and the generalized coherent potential-quasicrystalline approximation formula. The results are applied to calculating the complex effective permittivity of dry and wet snow, and sea ice