Gaussian Beam Scattering by a Spheroidal Particle with an Embedded Conducting Sphere

A method is provided for calculating the scattering of Gaussian beam incident obliquely on a spheroidal particle with a conducting spherical inclusion within the framework of the generalized Lorenz-Mie theory (GLMT). By virtue of a transformation between the spheroidal and spherical vector wave functions, a theoretical procedure is developed to deal with the boundary conditions. Numerical results of the normalized differential scattering cross section are presented, and the scattering characteristics are discussed concisely.     

离轴球形粒子对高斯波束的散射

本文根据广义米氏理论，将入射高斯波束用矢量球谐函数展开，研究离轴球形粒子的电磁（光）散射。获得波束因子／ｇ表达式和它的局域近似结果，以及散射系数ａｎ和ｂｎ的计算公式。讨论了波束宽度和粒子离轴位置对散射系数、消光系数、散射强度角分布，以及对粒子的内场和表面场分布的影响     

Scattering by a Conducting Infinite Cylinder Illuminated with a Shaped Beam

An analytic solution to the shaped beam scattering by a conducting infinite cylindrical particle is constructed within the framework of the generalized Lorenz-Mie theory (GLMT). The expansion coefficients of the scattered electromagnetic fields are derived by using the boundary conditions. As an example, for a tightly focused Gaussian beam propagating perpendicular to the cylinder axis, the scattering characteristics that obviously demonstrate the three-dimensional nature, as with the case of a dielectric infinite cylinder, are described in detail, and numerical results of the normalized differential scattering cross section are evaluated.     

Scattering of a Gaussian Beam by Stepped Index Luneberg Lens

The scattering and focusing characteristics of a Gaussian beam with phase distribution is studied by a stepped index Luneberg lens. A model experiment was performed using a six-layer spherical lens. Two kinds of beams, that is, broad and narrow beam are examined for the incident Gaussian beam. We find that focusing effect of a narrow beam is wholly lower than that of a broad beam. The focal point is also shifted toward outer of sphere because of phase lag for the beam source. The spot size equals almost the wavelength for the various beam parameters.     

介质基片上导带TM散射的矩量法计算

用矩量法、预条件共轭梯度法和快速傅立叶变换相结合的混合技术来快速计算介质基片上导体带的TM散射。在这个问题的矩量法计算中,构造阻抗矩阵要耗费大量的CPU时间。这里着重考虑了缩短阻抗矩阵填充时间的方法,提出了按周期分段积分法来处理所涉及的高振荡性Sommerfeld积分．使阻抗矩阵的填充时间大大缩短。     

Plane Wave and Gaussian Beam Scattering by Long Dielectric Cylinders: 2.5D Simulations versus Measurements

For the development of millimeter wave imaging systems, it is important to be able to simulate some representative scattering configurations. Typically, Gaussian beams are used in active imaging systems. Since these beams only illuminate a spatially limited region, many objects can be treated as infinitely long 2D (in)homogenous cylinders. However, the incident Gaussian beams have a 3D character. Therefore, a dedicated 2.5D scattering simulator was developed. In this paper, simulation results obtained with this simulator are compared to measurements obtained from a bi-static microwave set-up and from a W-band millimeter wave set-up. Comparison of simulations and measurements proves that the 2.5D algorithm is a good simulation tool to study scattering of long inhomogeneous cylinders, illuminated by 3D plane waves or 3D Gaussian beams under different elevation angles.     

多层球对高斯波束的散射

本文根据广义米氏理论，将入射高斯波束用矢量球谐函数展开，研究多层介质球的电磁（光）散射，提出波束因子ｇｎ的改进算法以及散射系数ａｎ和ｂｎ的迭代公式和算法，并进行了数值计算与讨论。     

Scattering of Cluster Spheres Located on Axis by a Gaussian Beam in Millimeter Waves

Multi-spheres scattering has been fully discussed, but almost all kinds of these researches are in plane wave. The special case of an incident shaped beam is introduced in this paper. While some numerical results for cluster spheres illuminated on the axis of a shaped beam in millimeter waves are presented. Finally, results of numerical computations illuminated by a shape beam in different beam waist radius are compared with those for a plane wave illumination.     

金属介质混合目标散射分析的快速偶极子法

基于等效偶极矩法,该文利用快速偶极子法用于快速计算金属介质混合目标的电磁散射。通过分组技术和简单的泰勒级数展开,将远场组之间的矩阵向量积自然地转化为聚集-转移-发散的形式,实现了矩阵向量积的快速计算。另一方面,由于远场组之间的互阻抗元素不用存储,大大降低了内存消耗。在仿真分析中,为了进一步快速计算近场组中的互阻抗元素,还采用了等效偶极矩法。数值结果表明该方法具有较高的计算效率和令人满意的数值精度。     

Rainbow Scattering by an Inhomogeneous Cylinder with an Off-Axis Gaussian Beam Incidence at Normal

The problem of an off-axis Gaussian beam incident perpendicular on an infinitely long multi-layered cylinder is investigated. The efficient and accurate recursive algorithm for computing the scattering field is discussed. The stability of the numerical scheme allows us to extend the feasible range of computations, both in size parameter and in number of layers for a given size. Particular attention is paid to rainbow scattering of homogeneous and inhomogeneous fibers.     

Influence of Gaussian Beam on Terahertz Radar Cross Section of a Conducting Sphere

In RCS estimation, usually a plane wave is assumed; while in real measurements at terahertz frequencies, generally a Gaussian beam or a similar beam source is adopted. In this paper, the RCS of a conducting sphere is discussed under the condition that the incident wave is a Gaussian beam. In the estimation, the influence of 2.52 THz collimated laser beam on RCS is discussed and the RCS changing with scattering angle and some other factors is obtained; at the same time, the comparisons between different incident beams, plane wave and Gaussian beam, are also given. The estimation results show that choosing a beam width of 40 mm is appropriate when the sphere radius is 10 mm and the distance between the sphere and the beam source is 1 m.     

Gaussian Beam Summation Representation of a Two-Dimensional Gaussian Beam Diffraction by a Half Plane

A Gaussian beam summation (GBS) representation for half plane diffraction of an incident two dimensional Gaussian beam (GB) that hits arbitrarily close to the edge is presented. The scattered field is expanded into an angular spectrum of GBs that emerge from the edge. We derive asymptotic expressions for the diffracted beams amplitudes, that are valid uniformly as a function of the distance of the incident beam from the edge and of the scattering beams angles. In the limiting cases when the incident GB hits far from the edge, these expressions reduce uniformly to a geometrical optics model plus a weak edge diffractions due to the off-axis beam field that hits the edge. Applications to GBS modeling of indoor propagation are discussed.     

混合场积分方程结合MLFMA分析导体介质复合目标电磁散射问题

针对组合目标电磁散射问题,采用一类新的混合场积分方程进行分析.通过合理选择比例系数组合表面电场和磁场积分方程,构造出具有良好收敛性的阻抗矩阵.MLFMA的迭代求解采用广义最小残差方法(GMRES),结合预条件技术进一步减少迭代次数,加速计算并提高处理电大尺寸导体介质复合目标的能力.研究了几类典型目标电磁散射特性并比较了计算效率,数值算例验证了该方法的准确性和高效性.     

Calculations of Infrared Laser Beam Scattering from Rough Dielectric Objects

The coherent and incoherent scattering cross sections of Infrared Laser Gaussian beam scattering from arbitrarily shaped convex dielectric objects with rough surfaces are investigated by using plane wave spectrum method and physical optics approximation. In the paper, the infrared laser scattering cross sections of rough sphere are calculated at 10.6 μm , and the influence of the beam size, permittivity, and polarization as well as roughness parameters is analyzed numerically. When the beam size is much larger than the size of object, the results in the paper can reduce to those of an incident plane wave. On the other hand, for the case of roughness statistical parameter close to zero, only the forward scattering has a parent difference compared with the result of gaussian beam scattering from smooth sphere.     

介质涂敷导电凸曲面上磁振子辐射场一致性几何绕射理论

本文研究了介质涂敷导电凸曲面上磁振子辐射与绕射一致性高频渐近理论。文中在典型曲面辐射场一致性高频近似解基础上发展了介质涂敷导电凸曲面上磁振子辐射与绕射的一致性几何绕射理论,导出了涂敷导电凸曲面上磁流源高频电磁辐射场的一致性几何绕射理论公式。在这个公式中,辐射与绕射场用四个广义Ｆｏｃｋ型函数表示,深光区这些函数退化为几何光学场,暗区场则表示为不同模式爬行波的叠加。     

Research into Influence of Gaussian Beam on Terahertz Radar Cross Section of a Conducting Cylinder

In RCS measurement, usually the incident beam is a Gaussian beam or a similar beam source; however, in the theoretical RCS estimation, usually a plane wave is assumed as the incident beam for sake of simplicity. In this paper, the RCS of an infinite perfect conducting cylinder is estimated. In the estimation, the influence of a 2.52 THz laser beam on RCS is studied and the RCS in dependence with scattering angle and some other factors is obtained after the change of RCS equation; meanwhile, comparisons of RCS when the incident beam is a plane wave and a Gaussian beam respectively, are also given. The estimation results show, when the cylinder radius is 10 mm, choosing a beam width of 40 mm can keep the relative error less than 0.48 dB.     

椭圆高斯波束中小粒子的一阶散射特性

研究电磁波束的小粒子散射特性在环境监测等领域有着广泛的应用。将电磁波束做级数展开,给出了各项对应电磁波的物理意义及粒子内电场的解析式。以椭圆高斯波束为例,对粒子内电场以及后项与前项电磁波束中粒子内电场的大小的比值随照射距离、频率的变化做了仿真。研究了椭圆高斯波束中小粒子的散射特性,通过仿真分析了波束腰宽和频率对散射特性的影响,验证了算法的有效性。研究表明,波束腰宽可以改善粒子的识别性能,粒子对高阶项的散射场远小于对次阶项的散射场,瑞利粒子内场表达式中坐标的幂次与外场波束表达式中坐标的幂次相同。所提方法简单,为研究电磁波束的粒子散射特性探索了新的途径。     

导电平面上槽与缝的散射

在雷达散射截面（ＲＣＳ）和电磁脉冲（ＥＭＰ）研究中，我们常常需要考虑目标上各个部分结合处存在的槽或缝的散射。在现代，随着ＲＣＳ减缩技术的发展，这些槽和缝对目标双站散射行为的影响已经日益突出。对此，通过等效原理导出相应问题的全波公式，研究了具有不同几何形状和不同材料填充的槽或缝对目标散射图形的影响     

Diffraction of a Gaussian Beam by a Periodic Screen

Based on the plane wave analysis and the superposition of the plane waves, the diffraction of a Gaussian beam by a periodic screen with a dielectric plate is analyzed. The reflection power coefficient for different parameters of the beam and the screen is given. When the beam waist size is increased the results reaches that of the plane wave. It has been found that the power reflection coefficient is not sensitive to the beam waist size, however, it is sensitive to the period of the grating and polarization angle.     

Scattering of a Gaussian beam by a dielectric rectangular cylinder

For purpose of finding the dielectric constant, a new expression of the beam scattering is obtained by using the boundary element method (BEM) with extended boundary conditions. Comparison between with and without the resonant condition was made for the total scattered power. To find the accuracy, convergence property of the total scattered power versus divided number has been examined. To check the boundary conditions at the corner of the scatter, the electric field difference between inner and outer side has also been calculated and confirmed. The total electric field distributions in space are illustrated for the plane and beam wave. Microwave experiments was also performed