共查询到19条相似文献,搜索用时 125 毫秒
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给出了一种结合射线追踪和蒙特卡罗方法计算含核粒子光散射的方法,内核粒子可以为稀疏分布也可为浓密分布.粒子外边界的反射和折射由射线追踪方法计算,而粒子内部的多次散射过程由蒙特卡罗方法模拟;当内核粒子为浓密随机分布时,其单次散射特性由基于静态结构因子(static structure factor)的浓密介质光散射理论计算.最后讨论了含核椭球粒子模型的单次散射特性.
关键词:
射线追踪技术
蒙特卡洛方法
光散射
椭球粒子 相似文献
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针对自然界的非球形粒子问题,对典型非球形粒子的偏振传输特性进行研究,采用T矩阵算法研究椭球、圆柱和切比雪夫粒子的偏振传输特性,及其与球形粒子偏振传输特性的差异。研究结果表明:对于横纵轴之比中等的椭球粒子,当散射角小于60°时,不同形状椭球粒子的偏振度(DOP)差异较小,可用Mie散射方法进行粒子偏振特性的近似计算;当散射角大于60°时,DOP随横纵轴之比的变化较大,且球形与椭球粒子的DOP差异随着横纵轴之比的增加而增大;对于直径与高度之比中等的圆柱体粒子,DOP的变化相比于椭球粒子更加平稳,但后向散射与侧向散射区域仍不能采用Mie散射进行近似计算;形状比例极端的椭球粒子和圆柱体粒子的偏振曲线均类似于钟形,且在散射角约为90°时DOP达到最大值;切比雪夫粒子的形变参数和级次都对粒子前向散射偏振特性的影响较小,但对后向散射偏振特性的影响较大,且灵敏度随级次的增加而减小。本研究结果可为非球形粒子偏振传输特性的研究及球形粒子近似提供理论指导。 相似文献
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非球形粒子的散射特性分析 总被引:1,自引:0,他引:1
本文首先利用T矩阵方法计算了复折射率吸收指数和折射指数变化时的椭球粒子和Chebyshev粒子在不同等效尺度参数下的光散射特性,并与等效的球形粒子的光散射结果进行了比较;然后分析以上两种类型非球形粒子散射特性之间的关系.结果表明:椭球粒子和Chebyshev粒子的散射特性与等效球形粒子的散射特性存在着差别,粒子的形状越偏离球形,这种差别就越大;复折射率折射指数的变化对非球形散射效率因子的影响要比吸收指数的影响更大一些;当等效尺度参数相同时,椭球粒子与等效球形粒子的散射效率因子的差别要远远大于Chebyshev粒子与等效球形粒子散射效率因子之间的差别. 相似文献
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由于重力和向上气流的作用,高速摄影显示较大的雨滴在降落过程中表现为一底部扁平、顶部圆滑的非球形对称体,已有的模型中BC模型(由Beard和Chuang提出)被认为能准确描述雨滴的形状。本文利用沿降落方向旋转对称的扁椭球体和均匀球体模拟降落中的雨滴,扁椭球体的短轴(旋转轴)与BC模型的相等,长轴通过与BC模型截面积等效法确定;利用T矩阵方法研究了水平取向的旋转扁椭球体和BC雨滴模型的散射特性,利用Mie理论计算了均匀球的散射特性,比较了半径分别为2 mm和3 mm大小的三种雨滴模型对94 GHz电磁波斜入射时的单次散射相矩阵,以及对频率为30 GHz~100 GHz电磁波的单次散射反照率,最后讨论了半径为0.5 mm~3.5 mm雨滴对35 GHz和94 GHz的后向散射函数。计算结果表明,利用均匀球模拟雨滴将带来较大误差,而利用截面积等效的旋转扁椭球体模型可以较好地模拟雨滴的散射特性。 相似文献
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《光学学报》2010,(5)
计算沙尘暴对电磁波的衰减特性,以及利用卫星反射率遥感反演沙尘暴的光学厚度时,通常假设沙尘粒子为球形,但实验室和现场测量结果都表明,自然界中的沙尘粒子为非球形,因此利用球形粒子模型模拟沙尘暴对激光的散射和衰减特性将带来较大误差。利用具有一定尺寸分布、形状分布、随机取向的椭球粒子模型模拟自然界中的沙尘粒子,利用T矩阵方法计算了其单次散射特性,并与球形粒子模型进行了比较,结果表明,混合椭球粒子的相函数随角度分布是平滑的、无特征的、且在侧散射方向上是平坦的,这和自然界中的沙尘粒子散射特性非常类似。最后利用累加法计算了沙尘暴对激光的多次散射特性,结果表明,利用任何一种单一形状的粒子模拟沙尘粒子的散射特性都会带来较大的误差。 相似文献
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聚集速率是评估胶体体系特性及稳定性的关键参数, 静态光散射和动态光散射则是测量聚集速率的两个重要方法. 然而, 用静态光散射和动态光散射测量聚集速率时, 需要知道有关单粒子和双粒子聚集体光散射特性的数据. 为此, 通常需要把动、静两种方法结合, 才能消去这个数据. 以前各种近似理论曾用来解决这个问题, 但因粒子尺寸和形状的限制, 结果并不理想. 而T矩阵方法可以不受粒子大小和形状的限制计算其光散射特性. 本工作用T矩阵方法直接计算静态光散射和动态光散射所必须的粒子散射特性, 并将该法得到的聚集速率与动静态光散射结合法得到的聚集速率进行了比较, 两者结果很接近. 本工作为简化静态光散射和动态光散射测量聚集速率, 扩展其应用范围开辟了新途径.
关键词:
T矩阵')" href="#">T矩阵
光散射法
聚集速率 相似文献
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基于离散偶极子近似法(DDA),对水雾包裹沙尘颗粒的核壳结构光学特性进行研究,计算了长短轴比例为2∶1的椭球形粒子的核壳结构内、外层厚度及散射角度变化对光散射特性的影响。结果表明,内核大小不变,外层厚度由1.2 μm增大到4.8 μm,核壳双层颗粒散射系数和消光系数由3.4和3.43降低到2.543和2.545,且散射相对强度也明显增大。外层厚度不变,内核厚度由0.6 μm增加到2.4 μm,散射系数和消光系数由3.105和3.111变化为2.76和2.9;可见外层厚度对核壳双层颗粒散射特性的影响更大,这是由于散射光主要与外层物质相互作用引起的。散射相对强度随波长的增加而降低,随核壳结构尺度的增加呈现递增的规律。该结果对大气中气溶胶和水雾共同作用时的散射特性,激光在其中的传输特性等研究有参考价值。 相似文献
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散射相函数是研究电磁波传输特性的重要参数,直接影响电磁波传输方程的简化程度和解的精度。基于电磁散射与辐射传输中的基本理论,对非球形粒子散射相函数的经验公式进行了研究。为了很好的模拟非球形粒子的后向散射峰值,提高辐射传输方程的简化程度和解的精度,提出了一种新的相函数经验公式。分析新的相函数对非球形粒子的适用性,以单个沙尘性气溶胶为例,计算了不同形状粒子的Henyey-Greenstein*相函数和新的相函数随角度的变化,并与T矩阵法的计算结果进行了对比,发现椭球形粒子的长短轴比和有限长圆柱形粒子的径长比大于0.5时,新的相函数在大角度后向散射部分与T矩阵法的吻合程度较高。考虑波长变化,对比了尺寸谱满足对数正态分布的四种气溶胶粒子的Henyey-Greenstein*相函数和新的相函数与T矩阵法的计算结果。研究表明,对于椭球形粒子和有限长圆柱形粒子,在大角度(大于90°)后向散射部分,除了0.694时的椭球形海洋性气溶胶,新的相函数均方根差较小的占100%,证明了新的相函数可以较好的模拟非球形粒子的后向散射特征。新的相函数对准确模拟辐射传输过程具有重要意义。 相似文献
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V. G. Farafonov 《Optics and Spectroscopy》2001,90(5):743-752
A new recursive algorithm for the solution of the problem of scattering of light (of an arbitrarily polarized plane electromagnetic wave) by multilayer confocal spheroidal particles is constructed. This approach preserves the advantages of the two approaches proposed earlier by us for single-layer and two-layer spheroids (special choice of scalar potentials and utilization of the basis of wave spheroidal harmonics) and for homogeneous axially symmetric particles (formulation of the problem in terms of surface integral equations, calculation of the potentials inside the particle from the potentials of the incident radiation, and calculation of the potentials of the scattered radiation from the potentials inside the particle). In the case of multilayer particles, the potential inside each shell is a sum of two terms. The first has the properties of the incident radiation (no singularities inside the volume enclosed by the external boundary of the shell), whereas the second term has the properties of the scattered radiation (satisfies the radiation conditions at infinity). Therefore, as the calculation progresses from one layer to the next (from the core to the outer shell), the dimensionality of the reduced linear matrix equations for the unknown expansion coefficients of the scattered field potentials does not increase with respect to the case of a homogeneous spheroid. The algorithm is particularly simple and lucid (as far as possible for such a complex problem). In the case of spherical multilayer particles, the solution can be found explicitly. 相似文献
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A procedure for analytical averaging of the attenuation and scattering cross sections for systems of chaotically oriented axially symmetric particles was developed for the first time within the framework of the modified T-matrix method and the method of separation of variables for spheroids. These approaches essentially complement each other: one is applicable to axially symmetric scatterers of different shape but is inefficient if the ratio of the maximum to the minimum size of the particles exceeds 3–5; the other is applicable only to spheroids, but the ratio of the major semiaxis to the minor one can be considerable, for example, 100 and larger. 相似文献
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An exact solution to the problem of light scattering by multilayer axially symmetric particles is derived and some aspects of its computer-aided implementation are discussed. The main specific features of the solution are (i) separation of the incident, scattered, and internal fields into two parts and special selection of the scalar potentials for each of them; (ii) expansion of the potentials in terms of spherical wave functions; (iii) formulation of the problem in the form of surface integral equations; and (iv) solution of the reduced systems of the linear algebraic equations for the coefficients of the potential expansions. Mathematical justification of the solution is discussed, which is formulated in the recursive and nonrecursive form (for the T-matrix). The developed computer program has shown that the proposed approach makes it possible to consider axially symmetric particles with essentially different internal structures (i.e., with a spherical core, oblate spheroidal shell, or prolate spheroidal intermediate layer). The results of calculations of the optical properties of the multilayer nonspherical particles are presented and discussed. 相似文献
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Multiple optical trapping with high-order axially symmetric polarized beams(ASPBs) is studied theoretically,and a scheme based on far-field optical trapping with ASPBs is first proposed.The focused fields and the corresponding gradient forces on Rayleigh dielectric particles are calculated for the scheme.The calculated results indicate that multiple ultra-small focused spots can be achieved,and multiple nanometer-sized particles with refractive index higher than the ambient can be trapped simultaneously near these focused spots,which are expected to enhance the capabilities of traditional optical trapping systems and provide a solution for massive multiple optical trapping of nanometer-sized particles. 相似文献
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Light scattering by small dielectric particles of an arbitrary axially symmetric shape is analyzed. A simple approximate expression
that governs the polarizability of the particle is found under the assumption of field homogeneity inside of these particles.
The expression includes four relatively simple one-dimensional integrals that can be calculated analytically for some types
of particles (except for spheroids). A comparison with the numerical data obtained for various Chebyshev particles and finite
cylinders showed that the obtained approximation yields acceptable results, even when the shape of scatterers is significantly
different from spheroidal. For spheroids, our approximation coincides with the Rayleigh one. 相似文献
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Small particle light scattering can produce light with polarization characteristics different from those of the incident beam. An analytical solution to the scattering by a spheroid with inclusion for an on-axis polarized Gaussian beam incidence is provided within the generalized Lorenz-Mie theory framework. The shapes of the inclusion can be spherical, confocal spheroid, or non-confocal spheroid. The Muller scattering matrix elements are computed for plane wave incidence or Gaussian light beam incidence. The effect of the size and shape of the inclusion or the coating on the polarized Oaussian light scattering characteristics by a spheroidal water coating aerosol Darticle are commlted and a,nalvzed. 相似文献
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S.-C. Lee 《Physics letters. [Part B]》1985,158(5):413-416
We point out that the nonlinear sigma models on symmetric spaces as considered by Eichenherr and Forger can be generalized to include a larger class of models possessing dual symmetry. The well-known axially symmetric gravitational vacuum and electrovac problems as well as the axially symmetric Kaluza-Klein dyons fall into this class. 相似文献
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Boost-rotation symmetric spacetimes are the only locally asymptotically flat axially symmetric electrovacuum spacetimes with a further symmetry that are radiative. They are realized by uniformly accelerated particles of various kinds or black holes. Their general properties are summarized. Several examples of boost-rotation symmetric solutions of the Maxwell and Einstein equations are studied: uniformly accelerated electric and magnetic multipoles, the Bonnor-Swaminarayan solutions, the C-metric and the spinning C-metric. 相似文献