Light scattering by a coated infinite cylinder in an absorbing medium

The scattering formulation for a coated infinite cylinder in an absorbing medium is presented in this paper. The cylinder is subjected to an arbitrarily polarized plane wave propagating in a general direction at the cylinder. The refractive index and magnetic permeability of the host medium, as well as those for the core and coating of the cylinder, can be real or complex. The scattering and extinction efficiencies and the scattering amplitudes are derived for both the near field and the far field. As the medium is absorbing, the "true" extinction and scattering efficiencies are derived based on the radiative energy outflow at the surface of the cylinder. The radiative efficiencies in the far field are denoted as "apparent" properties because they include absorption by the intervening medium. The influence of the refractive index and permeability of the host medium on the scattering properties of a coated cylinder is illustrated by numerical examples.     

Mie-scattering formalism for spherical particles embedded in an absorbing medium

Most of the Mie-scattering calculations have been done for a particle embedded in a nonabsorbing host medium. Generalization to an absorbing host medium can be achieved (a) by modifying the calculation of the spherical Bessel functions to account for a complex argument and (b) by accounting properly for the net rate of incident, scattered, and absorbed energy. We present an extended formalism of Mie scattering for the case of an absorbing host medium. Numerical calculations show that for a large spherical particle embedded in an absorbing host medium the extinction efficiency approaches 1 compared with 2 for a nonabsorbing host medium. We conjecture that this difference is due to the suppression of diffraction when the radius of the sphere is large.     

Mie scattering by a spherical particle in an absorbing medium

We show that the large-size parameter limit of the scattering efficiency of a spherical particle of relative refractive index m(r) embedded in an absorbing medium is equal to [m(r) - 1[2/]m(r) + 1]2 and not to zero as has been claimed in a recent article [J. Appl. Opt. 40, 1354-1361 (2001)].     

Light scattering by an infinite circular cylinder immersed in an absorbing medium

Analytic solutions are developed for the single-scattering properties of an infinite dielectric cylinder embedded in an absorbing medium with normal incidence, which include extinction, scattering and absorption efficiencies, the scattering phase function, and the asymmetry factor. The extinction and scattering efficiencies are derived by the near-field solutions at the surface of the particle. The normalized scattering phase function is obtained by use of the far-field approximation. Computational results show that, although the absorbing medium significantly reduces the scattering efficiency, it has little effect on absorption efficiency. The absorbing medium can significantly change the conventional phase function. The absorbing medium also strongly affects the polarization of the scattered light. However, for large absorbing particles the degrees of polarization change little with the medium's absorption. This implies that, if the transmitting lights are strongly weakened inside the particle, the scattered polarized lights can be used to identify objects even when the absorption property of the host medium is unknown, which is important for both active and passive remote sensing.     

Finite-difference time-domain solution of light scattering and absorption by particles in an absorbing medium

The three-dimensional (3-D) finite-difference time-domain (FDTD) technique has been extended to simulate light scattering and absorption by nonspherical particles embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition is used to truncate the computational domain. When computing the single-scattering properties of a particle in an absorbing dielectric medium, we derive the single-scattering properties including scattering phase functions, extinction, and absorption efficiencies using a volume integration of the internal field. A Mie solution for light scattering and absorption by spherical particles in an absorbing medium is used to examine the accuracy of the 3-D UPML FDTD code. It is found that the errors in the extinction and absorption efficiencies from the 3-D UPML FDTD are less than approximately 2%. The errors in the scattering phase functions are typically less than approximately 5%. The errors in the asymmetry factors are less than approximately 0.1%. For light scattering by particles in free space, the accuracy of the 3-D UPML FDTD scheme is similar to a previous model [Appl. Opt. 38, 3141 (1999)].     

Mie theory for light scattering by a spherical particle in an absorbing medium

Analytic equations are developed for the single-scattering properties of a spherical particle embedded in an absorbing medium, which include absorption, scattering, extinction efficiencies, the scattering phase function, and the asymmetry factor. We derive absorption and scattering efficiencies by using the near field at the surface of the particle, which avoids difficulty in obtaining the extinction based on the optical theorem when the far field is used. Computational results demonstrate that an absorbing medium significantly affects the scattering of light by a sphere.     

Finite-difference time-domain solution of light scattering by an infinite dielectric column immersed in an absorbing medium

The two-dimensional (2-D) finite-difference time-domain (FDTD) method is applied to calculate light scattering and absorption by an arbitrarily shaped infinite column embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition is used to truncate the computational domain. The single-scattering properties of the infinite column embedded in the absorbing medium, including scattering phase functions and extinction and absorption efficiencies, are derived by use of an area integration of the internal field. An exact solution for light scattering and absorption by a circular cylinder in an absorbing medium is used to examine the accuracy of the 2-D UPML FDTD code. With use of a cell size of 1/120 incident wavelength in the FDTD calculations, the errors in the extinction and absorption efficiencies and asymmetry factors from the 2-D UPML FDTD are generally smaller than approximately 0.1%. The errors in the scattering phase functions are typically smaller than approximately 4%. With the 2-D UPML FDTD technique, light scattering and absorption by long noncircular columns embedded in absorbing media can be accurately solved.     

Evolution of microstructures and thermal properties with heat treatment for absorbing, emitting and scattering fibrous medium

The microstructure changes of a fibrous insulation for thermal protection system were examined before and after thermal exposures at different temperatures between 1000 °C and 1400 °C. The consequent thermal properties, i.e., thermal conductivity, extinction coefficient, albedo of scattering, and linear coefficient of phase function at different stages were measured by using a developed experimental device and data processing method. The effects of microstructure changes on the thermal properties degradation were discussed. It was found that the devitrification of mullite and the microstructure changes induced by heat treatment had a significant influence upon the thermal properties, and higher temperature treatment yielded a strong increase in thermal conductivity of fibrous insulation. The results also indicated that the relative contribution of conductive and radiative heat transfer would be re-regulated after high temperature thermal annealing.     

Polarization properties and fractional-power analysis of coated and uncoated parallel-slab multireflection beam splitters

The polarization properties of coated and uncoated parallel-slab multireflection beam splitters are investigated. In a recent study [Opt. Lett. 21, 1709 (1996)] it was shown that the parallel-slab beam splitter is a basic optical component of the parallel-slab division-of-amplitude photopolarimeter. The ellipsometric parameters and the fractional powers for multireflected components generated by this system are analyzed. Interesting new observations with respect to the polarization properties at the Brewster angle of incidence and the distribution of powers among the multireflected components are presented.     

Photon diffusion coefficient in an absorbing medium

A number of investigators have recently claimed, based on both analysis from transport theory and transport-theory-based Monte Carlo calculations, that the diffusion coefficient for photon migration should be taken to be independent of absorption. We show that these analyses are flawed and that the correct way of extracting diffusion theory from transport theory gives an absorption-dependent diffusion coefficient. Experiments by two different sets of investigators give conflicting results concerning whether the diffusion coefficient depends on absorption. The discrepancy between theory and the earlier set of experiments poses an interesting challenge.     

Reflection and transmission properties of a wire grid embedded in a SNG or SZ medium

The reflection and transmission properties of a wire grid embedded in lossless Single Negative (SNG) or Single Zero (SZ) medium have been analytically studied. The wires of the grid are taken to be lossless as well as lossy. It is shown that a lossy grid has approximately identical reflection characteristics for the Transverse Magnetic incident wave with Epsilon Negative and Mu Negative background medium. The lossy grid with Epsilon Zero background medium acts as a perfect reflector for the normally incident wave. Likewise, it is further studied that a lossy wire grid embedded in Mu Zero medium can be cloaked for the incoming normally incident wave.     

Electromagnetic scattering by an aggregate of spheres

We present a comprehensive solution to the classical problem of electromagnetic scattering by aggregates of an arbitrary number of arbitrarily configured spheres that are isotropic and homogeneous but may be of different size and composition. The profile of incident electromagnetic waves is arbitrary. The analysis is based on the framework of the Mie theory for a single sphere and the existing addition theorems for spherical vector wave functions. The classic Mie theory is generalized. Applying the extended Mie theory to all the spherical constituents in an aggregate simultaneously leads to a set of coupled linear equations in the unknown interactive coefficients. We propose an asymptotic iteration technique to solve for these coefficients. The total scattered field of the entire ensemble is constructed with the interactive scattering coefficients by the use of the translational addition theorem a second time. Rigorous analytical expressions are derived for the cross sections in a general case and for all the elements of the amplitude-scattering matrix in a special case of a plane-incident wave propagating along the z axis. As an illustration, we present some of our preliminary numerical results and compare them with previously published laboratory scattering measurements.     

二氧化锰涂覆EPS方法与效能分析

采用直接涂覆法将二氧化锰涂覆在EPS表面制成吸波球体。实验证实，这种方法有能力涂覆大密度导电粉末，且效果良好。在反射阻抗的测试中，当试样厚度为10mm时，其反射损耗在8～18GHz频率范围内为-7～-15dB，发现随着吸波颗粒中二氧化锰含量和试样厚度的增加，在8～18GHz频段内，试样的反射损耗增加。二氧化锰层吸波球体效能略低于同等导电层厚度的炭粉层吸波球体。     

含Minkowski活性碳毡电路屏复合材料的吸波性能研究

研究了含Minkowski活性碳毡电路屏复合材料的微波吸收特性,并对电路屏的吸波机理进行了初步的探讨。结果表明,含Minkowski活性碳毡电路屏复合材料的吸波性能与电路屏阵列单元的尺寸密切相关,经合理设计,复合材料在5.3～18GHz频率范围内有-10dB以下的吸收,有效带宽达12.7GHz。复合材料对电磁波的主要吸收机制是电磁波在电路屏和反射板之间的多次反射、衰减。     

Methods of examining beam diffusion in an absorbing and scattering material

An apparatus and method are presented for measuring the effective cross section of a radiation beam subject to reflection and transmission by layers of absorbing and scattering material.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 2, pp. 264–269, February, 1977.     

The compression of spheres coated with an aqueous ethylcellulose dispersion

Tablets were compressed from commercial samples of Sugar Spheres NF, Sucrose NF, Corn Starch NF, as well as ground spheres and a physical mixture of ground sucrose plus cornstarch. Additional tablets were compressed from spheres that had been coated with a water-soluble cellulosic polymer solution followed by an aqueous ethylcellulose dispersion. Tableting parameters measured “in-die” included work of compression, peak offset time, tablet density, and Young's modulus. Following ejection, tensile strength was determined under diametrical loading. Dissolution of a marker contained in the water-soluble layer was determined for both compressed and uncompressed spheres. Porosities at peak pressure and peak offset times or tensile strength as functions of peak pressure did not differ between tablets compressed from pristine spheres or from ground spheres. Tablets compressed from spheres had higher values for porosity, tensile strength, and peak offset time than those compressed from sucrose or the sucrose:starch mixture. Values for work of compression were higher for tablets compressed from pristine spheres or from starch. This was attributed to the work required for particle deformation and for breaking of the spheres. The greatest elastic recovery during decompression was observed for tablets compressed from pristine spheres or starch. More brittle behavior was observed for tablets compressed from sucrose or the sucrose:starch mixture. Tablets compressed from ground spheres were more brittle than those compressed from the pristine spheres, indicating an effect due to grinding. Most mechanical properties of tablets compressed from the coated spheres were comparable to those of tablets compressed from uncoated spheres. An exception was diametric strain for tablets compressed from spheres coated with the aqueous ethylcellulose dispersion. These values increased since the plasticized ethylcellulose allowed greater distortion of the tablet before failure occurred. The dye marker was released more rapidly from tablets compressed from spheres coated with the aqueous ethylcellulose dispersion than from comparable uncompressed spheres. At both the 5% and 10% coating levels, spheres coated with the aqueous ethylcellulose dispersion fused into nondisintegrating matrices during compression. Little difference in release rates was seen between the two tablets.     

Efficiency factors and radiation characteristics of spherical scatterers in an absorbing medium

The radiative properties of bubbles or particles embedded in an absorbing medium are investigated. We aim first to determine the conditions under which absorption by the surrounding medium must be accounted for in the calculation of the efficiency factors by comparing results from Mie theory and the far-field and near-field approximations. Then, we relate these approximations for a single particle to the effective radiation characteristics required for solving the radiative transfer in an ensemble of scatterers embedded in an absorbing medium. The results indicate that the efficiency factors for a spherical particle can differ significantly from one model to another, in particular for large particle size parameter and matrix absorption index. Moreover, the effective scattering coefficient should be expressed based on the far-field approximation. Also, the choice of the absorption efficiency factor depends on the model used for estimating the effective absorption coefficient. However, for small void fractions, absorption by the matrix dominates, and models for the absorption coefficient and efficiency factor are unimportant. Finally, for bubbles in water, the conventional Mie theory can be used between 0.2 and 200 mum except at some wavelengths at which absorption by water must be accounted for.