尾流气泡激光散射的测量

采用收发分置的光学结构实现了尾流气泡对532 nm激光在散射角5°～175°内的散射测量,同时测量了水的激光散射。散射角度的改变是通过发射系统不动而转动接收系统来实现的。解决了散射信号大动态范围的压缩问题,讨论了接收视场内散射体积随散射角的变化。分析了气泡散射的信号特征,并提出了气泡散射信号的功率谱密度处理法。将实验结果与米氏理论结果进行了对比,发现尾流气泡的激光散射强度及其随散射角的变化趋势与米氏理论结果吻合得很好,与水的散射相差近一个数量级。研究结果表明利用激光可以将气泡和水的散射区别开,即利用激光探测尾流气泡的存在具有可行性。     

Scattering from conjugate-matched antennas

The scattering properties of antennas are discussed in terms of the scattering matrix. It is shown that one retains some control over the scattering properties of the antenna after the radiation pattern is specified and the scattering matrix can be used to optimize these scattering properties. The scattering matrix is used to design a simple antenna which absorbs more power than it scatters under conjugate-matched conditions. A loop-dipole configuration is given which corresponds to the scattering matrix.     

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。     

Backscattering from a randomly rough dielectric surface

A backscattering model for scattering from a randomly rough dielectric surface is developed. Both like- and cross-polarized scattering coefficients are obtained. The like-polarized scattering coefficients contain single scattering terms and multiple scattering terms. The single scattering terms are shown to reduce to the first-order solutions derived from the small perturbation method when the roughness parameters satisfy the slightly rough conditions. When surface roughnesses are large but the surface slope is small, only a single scattering term corresponding to the standard Kirchhoff model is significant. If the surface slope is large, the multiple scattering term will also be significant. The cross-polarized backscattering coefficients satisfy reciprocity and contain only multiple scattering terms. The difference between vertical and horizontal scattering coefficients increases with the dielectric constant and is generally smaller than that predicted by the first-order small perturbation model. Good agreements are obtained between this model and measurements from statistically known surfaces     

磷化铟粒子散射强度的计算与分析

根据Mie氏散射理论,给出了粒子散射场强度的计算公式,得到了散射强度与散射角及入射波长的关系以及散射强度与参数X的关系.结果表明,粒子的前向散射占优势;入射波长越小,散射越明显;红外区的散射强度接近零,该结论对磷化铟材料光学特性的研究和应用具有指导意义.     

Scattering from a Layered Medium Connected with Rough Interfaces: Matrx Doubling Method

A theoretical scattering model is developed that computes the scattered and transmitted intensities from an inhomogeneous layered medium above the half-space. A matrix doubling method technique is extended to handle multilayer scattering problems of which each scattering layer of spherical particles has rough boundary interfaces. Incoherent scattering is assumed in the formulation so that the Stokes vector representations are used to calculate the polarimetric multiple scattering effects. The scattering coefficients are computed for a two-layered Rayleigh scattering medium with a rough boundary. The developed scattering model of a radiative transfer approach is useful for scattering computations dealing with a random medium often encountered in active and passive microwave remote-sensing problems.     

基于扩展OTSM图的滑动型散射中心建模方法

雷达目标散射中心建模是雷达目标特性分析与雷达目标识别中的关键步骤,光滑流线型结构在雷达目标上的广泛应用,给传统散射中心建模带来了巨大挑战。该文针对滑动散射中心建模开展研究,首先分别基于曲面边缘散射和曲面散射两种情况,推导了滑动散射中心的位置表达式;其次,提出一种基于扩展1维-高维(2维/3维)散射映射图(One–Two/Three Dimensional Scattering Mapping, OTSM)的滑动散射中心估计方法,通过相邻视角的投影几何关系推导滑动散射中心的位置;然后,综合RANSAC算法获取的固定散射中心,获得目标完备的散射中心模型。利用暗室测量数据对算法进行了验证,结果表明了该文算法的有效性。     

Cd1-xMnxTe/CdTe量子阱中电子-LO声子散射率

基于费米黄金法则,理论计算了Cd1-xMnxTe/CdTe量子阱中第一激发态到基态的电子-LO声子的散射率,讨论了平均散射率随阱宽、温度及Mn组分的变化规律。结果表明：电子-LO声子的散射率随总初态能的增大逐渐减小;散射率和平均散射率随阱宽增大先增加后减小,最大值出现在20 nm阱宽附近,当阱宽大于等于20 nm时散射会发生”中断”;散射率和平均散射率随温度的增加逐渐增大,且温度较低时平均散射率的变化不明显,温度较高时明显增大;量子阱中电子-LO声子的平均散射率随Mn组分的增大逐渐减小。     

Multiple scattering and depolarization by a randomly rough Kirchhoff surface

A matrix approach has been developed to compute bistatic scattering coefficients which include shadowing and multiple scattering effects for a randomly rough Kirchhoff surface. The method permits the computation of these coefficients in terms of the existing single-scatter bistatic scattering coefficients. Thus the effects of multiple scattering are readily recognized from the expressions obtained. The bistatic scattering coefficients are shown to satisfy energy conservation to at least two significant figures. It is observed that while polarized backscattering is dominated by the single-scattering process, the depolarized backscattering is due to multiple scattering. Unlike depolarization by slightly rough surfaces or volume scattering, the angular behavior of the depolarized backscattering is similar to that of the polarized backscattering. The transitional behavior of the relative dominance between single and multiple scattering for the polarized and depolarized scattering coefficient as a function of the azimuth angle is illustrated.     

基于Mie散射理论的磷化镓粒子散射特性

基于Mie散射理论,对磷化镓微球粒子从紫外光区到红外光区的光散射特性进行了数值计算与理论分析,得到了散射强度与散射角、粒子尺寸参数、偏振度与散射角以及光学截面与粒子尺寸参数的关系。结果表明,入射波长越长,粒子半径越小,散射越弱;并且在红外波段光散射很弱,在散射角90°方向上能观测到线偏振光,这为磷化镓材料的制备与应用提供了理论参考。     

激光信号大气散射探测分析

有些应用场合需要利用大气气溶胶对激光的散射来探测激光。在都市郊区大气模型条件下,利用米氏散射理论,对1.06μm激光在低空大气中传输时散射辐照度的分布进行了理论分析和数值计算。得到激光大气散射辐照度随离轴距离的增大近似按反比规律缓慢下降、能见度仅影响散射强度的大小而不影响散射强度的分布等特征。这些特征在激光散射实验中得到了初步的验证,可为激光信号的散射探测提供理论依据和参考。     

Extraction of Virtual Scattering Centers of Vehicles by Ray-Tracing Simulations

Radar images of complex targets can be understood as a superposition of the reflected signals from a high number of scattering centers. To model complex targets for radar simulations, the plurality of scattering centers should be reduced to few significant scattering centers in order to minimize computational effort. The scope of this work is to present a technique to generate a significantly simplified RCS model of the vehicle with a limited number of virtual scattering centers, each with its own scattering characteristic, and how to group these scattering centers in a cluster database. The work is based on ray-tracing simulations of complex vehicle models. The ray-tracing simulations have been validated by measurements. The scattering centers may not be physically existing strong scattering centers, but virtual scattering centers representing a certain scattering behavior. In this paper, a technique for extracting such virtual scattering centers from a complex 3D-vehicle-model is presented. It is based on ray-tracing simulations of such models. As an example, the design model of a Ford Focus is used.      

舰船远程尾流气泡群的前向光散射特性研究

利用Mie理论计算了舰船尾流气泡群的归一化体散射函数和散射能量分布函数,分析了尾流气泡群的前向光散射特性。计算和分析结果表明,气泡群的前向散射光强度远大于后向散射,前向散射能量占总散射能量的90%以上;散射能量分布函数在小于1°的前向小角度散射角范围内迅速增加到40%以上,然后随散射角的增加缓慢增加;气泡表面附着的有机膜会显著地增强气泡群的后向散射,但对前向散射的影响不大。     

A polarimetric model for the recovery of the high-frequency scattering centers from bistatic-monostatic scattering matrix data

The objective of this investigation is to develop multistatic electromagnetic identification/discrimination algorithms using the complete polarimetric scattering data. At high frequencies the electromagnetic scattering from a complex object is modeled by certain scattering centers. The high-frequency (physical optics) bistatic and monostatic scattering matrix properties of a flat plate model of such a scattering center are developed in detail. For the complex target representations, the single scattering center results can be extended to two and three scattering center models. It is suggested that the knowledge of the locations and the local geometries of these scattering centers can be useful in developing identification and pattern recognition algorithms.     

时域物理光学法计算目标的微波短脉冲散射

目标的短脉冲散射问题本质上是其宽带散射特性,从时域上获取短脉冲散射问题更为直接。时域物理光学方法具有计算速度快、物理近似意义清晰明确等特点,可直接计算电大尺寸目标的微波短脉冲散射的时域波形。介绍了时域物理光学的理论公式,通过三角型网格剖分建立目标模型,引入Radon 变换计算目标的“冲击响应”,利用卷积计算获得目标的微波短脉冲散射时域波形。通过仿真算例进行验证,计算双导体球模型散射回波验证了该方法的可行性;计算大飞机的微波短脉冲散射波形展示了该方法处理电大尺寸问题的能力。用该方法计算的目标短脉冲散射回波波形可直接作为信号处理研究的输入。     

低频太赫兹准目标雷达散射截面的实验研究

以研究太赫兹雷达散射截面的特性为目的,选用所搭建低频太赫兹雷达测试系统,并借助于标准目标法开展了有关太赫兹雷达粗糙铝盘散射截面的实验研究工作.实验结果表明:在小角度散射中太赫兹雷达散射截面随散射角的增大变化比较明显,在散射角超过5后太赫兹雷达散射截面随散射角的变化趋向缓慢,但当散射角超过12后探测信号的强度已衰减到无法测量,在太赫兹雷达散射截面的测试中没有出现微波雷达散射截面的大小随散射角的变化而剧烈振荡的现象;将测试结果与同尺寸微波、激光雷达散射截面的结果进行了对比,得到结论:在0附近太赫兹雷达散射截面的数值比同尺寸微波雷达散射截面的数值要小两个数量级,但比同尺寸激光雷达散射截面的数值要高一个数量级.     

A survey of the physical optics inverse scattering identity

The physical optics approximation is applied to the acoustic and electromagnetic direct scattering integral representation, yielding an inverse scattering identity which relates the characteristic function of a scatterer to the three-dimensional spatial Fourier transform of the augmented far-field scattering amplitude. This identity requires full scattering information for all frequencies and aspect angles. An integral equation for incomplete scattering information for this identity is developed. This integral equation is for the unknown characteristic function of the scatterer in terms of the known incomplete scattering information. The kernel of this integral equation is the three-dimensional spatial Fourier transform of the known characteristic function of the scattering information aperture. A regularized analytic closed-form solution to this integral equation is obtained. Synthesized numerico-experimental results verifying this solution are presented. The details of some special cases, consisting of a priori knowledge about the scatterer or the scattering information aperture, are presented.     

喇曼散射的数值仿真及其应用探索

为了研究喇曼散射的全过程及其规律,首先,采用数值仿真的方法,基于对喇曼散射耦合微分方程的量纲重新匹配,演示喇曼散射光谱产生及其演化的过程,给出自发喇曼散射向受激喇曼散射过渡的结果。结果表明:阈值的意义突出,阈值前后的喇曼散射光谱截然不同;抽运光强大于阈值以后,喇曼散射光谱呈现出三个典型规律,即抽运光强和散射光强峰值出现的光纤长度呈反向关系;抽运光强越大,散射光强峰值和抽运光强的比值越大;散射光谱在同级内和不同级间都存在能量红移。然后,在已有研究的基础上,总结喇曼散射的各种实际应用,特别是应用于光纤喇曼放大器的研制。对于喇曼散射的理论和应用研究以及相应的实验工作有一定的参考价值。     

海洋悬浮粒子的光学后向散射率特性研究

后向散射率不仅是机载激光雷达探测海水后向散射信号的重要参量,也是海洋悬浮粒子重要的光学特性,根据米氏散射理论及其散射相函数计算公式,推导出了海洋悬浮粒子后向散射率的计算公式.通过对海水中的藻类粒子和悬浮泥沙颗粒散射相函数的分析,获取这两类主要海洋悬浮粒子各自的后向散射率,并进一步分析了后向散射率与粒子半径和波长的关系.仿真计算结果表明,当探测波长一定时,藻类粒子的后向散射率随粒子半径的增大而增大,而悬浮泥沙颗粒的后向散射率随粒子半径的增大而减小;当粒子半径一定时,藻类粒子和悬浮泥沙颗粒的后向散射率均随探测波长的增大而增大.