Solving the diffraction problem of electromagnetic waves on objects with a complex geometry by the pattern equations method

A new efficient method for solving the problems of waves diffraction on complex-shaped objects with the use of their replacement by a group of bodies with more simple form (fragments of complex objects) is offered. By the expansion of the scattering patterns of separate bodies in the series of vector spherical harmonics, the problem is reduced to solving the algebraic system of equations. It is shown that the method possesses a high convergence rate. Examples of modeling the scattering patterns of various complex objects are considered. Reliability of the results obtained is validated using the Optical theorem.     

The application of a modified method of discrete sources for solving the problem of wave scattering by group of bodies

A new universal and effective algorithm for solving the problems of wave diffraction on complicated structures composed of bodies of revolution is presented. The method is applied to diffraction on a group made of two impedance bodies of revolution. The method permits to get the pattern and the field with high accuracy.     

基于递归T矩阵的离散随机散射体散射特性研究

本文根据电磁场矢量球波函数多极点展开原理及矢量叠加定理提出了递归T矩阵算法的矢量形式,并且基于矢量递归T矩阵算法建立了多散射球模拟离散随机散射体散射的三维电磁散射模型.通过计算不同尺寸、随机分布散射球的散射以及分析散射球间的高阶散射效应,结果表明:矢量递归T矩阵算法具有很高的计算精度,算法中包含多散射体间的高阶散射效应,因此能够精确计算多散射体总的散射效应.本文所建模型可应用于土壤湿度探测工程中评估地表下掩埋离散随机散射体散射对雷达回波信号产生的影响.     

Physical optics theory for the scattering of waves by an impedance strip

The physical optics integral of the scattered waves by an impedance strip is derived by using the modified theory of physical optics. The surface currents of the physical optics integral, which was introduced for the scattered waves by an impedance half-plane, are taken into account. The uniform diffracted fields of the impedance strip are evaluated asymptotically. The second order diffraction terms are also obtained. The total scattered field and its subcomponents are plotted and the effect of the second order diffraction and strip width to the scattering is investigated numerically.     

Light scattering and absorption by densely packed groups of spherical particles

Light scattering by clusters of spheres is investigated using numerical light scattering simulations. We consider clusters with density of 0.1-30%. Simulations are carried out for various real part of refractive indices (i.e., 1.01, 1.10, 1.31, 1.60, and 2.00) and for two values of the imaginary part of the refractive index (0 and 0.01) of spheres in the cluster. All spheres in the cluster have the same size (kr=4, k=2π/λ, r is the radius of the sphere, λ is the wavelength of the incident light).The obtained results include behaviors of cross sections as functions of densities (up to 30%), investigation of the influence of multiple scattering inside the media on the cross sections, and influence of densities on phase matrix elements (PMEs) and parameters obtained from the PMEs such as the cross polarization ratio, degree of linear depolarization, entropy, etc.In addition, we also investigate the influence of particle size for the same total volume of the cluster on cross sections. The outer radius R of the cluster of spheres was constant and equal to 40/k in all calculations.     

Simulation of detection and scattering of sound waves by the lateral line of a fish

A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks,as well as the cross section of sound scattering on both the lines,strongly depends on angles of incidence of incoming sound waves.The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.     

Visualization of the sound scattering by a cylinder

The schlieren method is applied to visualizing the sound scattering ofa cylinder immersed in the liquids.Images of the echoes,caused by normal andoblique incidence from a cylinder,are obtained for two kinds of liquids:(1)theliquid is composed of a transparent liquid;and(2)the liquid is composed of twonon-mixable transparent liquids.It is found experimentally that the echo canbe caused by the discontinaites in the shadow zone.This fact is utilized to dem-onstrate the locus of the helical surface wave creeping along the surface of thecylinder.For such cases the three-dimensional image can be described by thismethod and has not to use the system with special appliances and complexalgorithm.     

Analysis of mutiple-shepers radiation and scattering problems by using a null-field integral equation approach

A systematic approach using the null-field integral equation in conjunction with the degenerate kernel is employed to solve the multiple radiation and scattering problems. Our approach can avoid calculating the principal values of singular and hypersingular integrals. Although we use the idea of null-field integral equation, we can locate the point on the real boundary thanks to the degenerate kernel. The proposed approach is seen as one kind of semi-analytical methods, since the error is attributed from the truncation of spherical harmonics. Finally, the numerical examples including one and two spheres are given to verify the validity of proposed approach.     

Appearance of extrema in the frequency shift produced by scattering from a rotational anisotropic particle

We investigate the analytical expression of the spectrum that is produced by scattering of a polychromatic plane light wave incident upon a rotational anisotropic particle. It is found that the appearance of extrema in the frequency shift of the scattered field can be exactly predicted by our derived equations of the rotation angle. Numerical examples are presented to illustrate the theoretical results and also to show the impact of the effective radius of the scattering potential on the frequency shift.     

On the use of stimulated Brillouin scattering as a calibration method for group delay and differential group delay measurements

We propose a novel group delay and differential group delay calibration method for polarization-dependent optical spectral characterization measurements. The calibration method is based on the dispersive nature of stimulated Brillouin scattering and its polarization dependent spectral response. The main advantage of the calibration method is its tunability in wavelength, bandwidth and magnitude, what makes it suitable for different measurement setups.     

The solution of the neutron transport equation in a slab with anisotropic scattering

The neutron transport equation for a slab geometry with the extremely anisotropic scattering kernel is considered. The albedo and transmission factors are calculated using the variation method. The effect of the extremely anisotropic parameter on the variation of the slab albedo and transmission factor is calculated. The obtained results are compared with the published data.     

Analytical study of the propagation of acoustic waves in a 1D weakly disordered lattice

This paper presents an analytical approach of the propagation of an acoustic wave through a normally distributed disordered lattice made up of Helmholtz resonators connected to a cylindrical duct. This approach allows to determine analytically the exact transmission coefficient of a weakly disordered lattice. Analytical results are compared to a well-known numerical method based on a matrix product. Furthermore, this approach gives an analytical expression of the localization length apart from the Bragg stopband which depends only on the standard deviation of the normal distribution disorder. This expression permits to study on one hand the localization length as a function of both disorder strength and frequency, and on the other hand, the propagation characteristics on the edges of two sorts of stopbands (Bragg and Helmholtz stopbands). Lastly, the value of the localization length inside the Helmholtz stopband is compared to the localization length in the Bragg stopband.     

Simple expressions of the reflection and transmission coefficients of fundamental Lamb waves by a rectangular notch

The scattering of Lamb waves by a two-dimensional rectangular notch is investigated for rapid inspection of defects in a structure. To derive the reflection and transmission coefficients of the scattered waves in a simple way, the scattering caused by the notch is analyzed through the composition of individual scattering processes. Linear equations corresponding to the reflection and transmission coefficients are constructed along with scattering graphs. For an illustration of the efficacy of the presented method, the scattering of fundamental symmetric and anti-symmetric modes are inspected according to the depth and width of a notch in a plate. Validity of these expressions is demonstrated by the comparison of the theoretical analysis results with those from the finite element analysis.     

Determination of the refractive index profile of a symmetric fiber preform by the transport of intensity equation

The refractive index profile of an axially symmetric fiber preform is determined by using the transport of intensity equation. In this method the preform is immersed in an index-matching liquid, and a collimated light beam impinges on it laterally. The intensity distributions of the transmitted light are measured on two close parallel planes inside the preform core. From the recorded intensity distributions, the deflection function is calculated by the transport of intensity equation. The refractive index profile is obtained by means of Abel inversion. Also, for comparison, the refractive index profile of the preform is measured by the focusing method and the results are in agreement with less than 3% error.     

Investigation the spectral scattering characteristics of a nanohole in a film

Based on the method of discrete sources, an analysis is made of the spectral scattering characteristics of a nanohole in a metal film applied onto a glass prism. An effect of extremal electromagnetic energy leakage through the hole is discovered in the evanescent wave formation region.     

圆棒介质波导的电磁波传播特性

通过简单的数学分析,推导圆棒介质波导的导模传播条件及特征方程,讨论电磁波在圆棒介质波导中的传播特性。     

Accurate calculation of the scattering length for the cooling of hydrogen atoms by lithium atoms

An improved ab initio calculation has been performed for the potential for the LiH a ³Σ⁺ state, using two very large basis sets. The Basis Set Superposition Error (BSSE) correction has been determined for both basis sets and the non-Born-Oppenheimer correction estimated to be negligible. The best potential is approximately 10% deeper than the previous estimate. Vibrational energies and scattering lengths have been calculated for ^6,7LiH(D) with both potentials, with and without the BSSE correction, and also with an estimated potential expected to bracket the true potential. The ⁷LiH scattering length is estimated to be (45 ± 4)a₀ and hence the low-energy cross-section in the best a ³Σ⁺ potential is about half that calculated previously. Enhanced cooling by ⁷Li of trapped H atoms remains feasible. Received 30 April 2001     

Higher order contribution to the propagation characteristics of low frequency transverse waves in a dusty plasma

Characteristic features of low frequency transverse wave propagating in a magnetised dusty plasma have been analysed considering the effect of dust-charge fluctuation. The distinctive behaviours of both the left circularly polarised and right circularly polarised waves have been exhibited through the analysis of linear and non-linear dispersion relations. The phase velocity, group velocity, and group travel time for the waves have been obtained and their propagation characteristics have been shown graphically with the variations of wave frequency, dust density and amplitude of the wave. The change in non-linear wave number shift and Faraday rotation angle have also been exhibited with respect to the plasma parameters. It is observed that the effects of dust particles are significant only when the higher order contributions are considered. This may be referred to as the ‘dust regime’ in plasma.     

氧化石墨烯猝灭罗丹明6G荧光的机理研究

The fluorescence quenching of Rhodamine 6G (R6G) by graphene oxide (GO) was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher.The carbonyl groups on the GO nanosheet turned to play a dominant role in quenching the R6G fluorescence.The quenching in the static regime can be described by the "sphere of action" model.The significant absorption of the R6G fluorescence by the ground-state complex formed between R6G and GO was identified to be responsible for the static quenching.This work offers helpful insights into the fluorescence quenching mechanisms in the R6G/GO system.     

A diagnostic tool for the study of stochastic properties of density striations excited by powerful electromagnetic waves in the ionospheric plasma

Powerful electromagnetic waves illuminating the ionospheric plasma generate small-scale density irregularities elongated in the direction of the geomagnetic field. Stochastic motion of these irregularities results in fluctuations of HF radio signals backscattered by the illuminated region. Observations of the full wave form of the radio signals make it possible to reconstruct the distribution function of the irregularities over their velocities. An experiment with such a reconstruction is proposed.