Scattering of a Rayleigh surface acoustic wave by a small-size inhomogeneity in a solid half-space

We use the Born approximation of the perturbation method to solve the problem of scattering of a harmonic Rayleigh surface acoustic wave by a weak-contrast inhomogeneity that is small compared with the wavelength and is located in a solid half-space near its boundary. The material of the inhomogeneity differs from the material of the half-space only in its density. The Rayleigh wave incident on the inhomogeneity is excited by a monochromatic surface force source acting normally to the half-space boundary. We derive expressions for the displacement fields in the scattered spherical compressional and shear (SV- and SH-polarized) waves. Scattering of the Rayleigh wave into a Rayleigh wave is studied in detail. We find expressions for the vertical and horizontal components of the displacement vector in the scattered Rayleigh wave as well as its radiated power. It is shown that the field of the scattered surface wave is mainly formed by vertical oscillations of the inhomogeneity in the field of the incident wave. In this case, the radiated power for the scattered Rayleigh wave formed by vertical motion of the inhomogeneity in the incident-wave field depends on the depth of the inhomogeneity as the fourth power of the function describing the well-known depth dependence of the vertical displacements in the Rayleigh surface wave. Correspondingly, the dependence of the radiated power for the scattered Rayleigh wave formed by horizontal motion of the inhomogeneity depends on its location depth as the fourth power of the depth dependence of the horizontal displacements in the Rayleigh surface wave. We perform calculations of the ratio between the powers of the scattered and incident Rayleigh waves for different ratios between the velocities of the compressional and shear waves in a solid. It is shown that the radiated power for the scattered surface wave decreases sharply with increasing depth of the subsurface-inhomogeneity location. Thus, the scattering of a Rayleigh wave into a Rayleigh wave is fairly efficient only when the location depth of the inhomogeneity does not exceed about one-third of the wavelength of the shear wave in an elastic medium.     

Absorption of bending waves in a plate driven by a normal force source encircled with monopole-dipole resonators

The field produced by a harmonic point source of normal force in a plate with resonators is studied. The origin of the force is encircled with a ring of closely spaced identical monopole-dipole resonators responsive to both the displacement and tilt of the plate. For these resonators, parameters are determined that ensure the complete absorption of the divergent cylindrical bending wave generated in the plate by the point source of normal force.     

Surface electron states produced by a Rayleigh wave

The electronic properties of a semiconductor bounded by an uneven surface representing an infinitely high potential barrier are investigated. The surface irregularities are produced by a Rayleigh acoustic wave. It is shown that, on the boundary of a semiconductor, surface electron states (waves) may arise whose dispersion laws are obtained under the conditions when conduction electrons are located either in or outside the field of the acoustic wave. Existence domains of surface electron states are found that are distinguished by their physical properties. These domains are separated by a band gap whose width is determined by the height of irregularities.     

Scattering of a sound wave by a vibrating surface

We report an experimental study of the scattering of a sound wave of frequency f by a surface vibrating at frequency F. Both the Doppler shift at the vibrating surface and acoustic nonlinearities in the bulk of the fluid, generate the frequencies f±nF (n integer) in the spectrum of the scattered wave. We show that these two contributions can be separated because they scale differently with respect to the vibration frequency and to the distance between the vibrating scatterer and the detector. We determine the parameter ranges in which one or the other mechanism dominates and present quantitative studies of these two regimes. Received 2 December 2002 / Received in final form 27 March 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: fauve@physique.ens.fr RID="b" ID="b"UMR 8550     

介质球的各向异性瑞利散射

基于电磁场的多尺度理论,研究了各向异性介质球内、外电场的规律,导出了各向异性目标散射场的表达式,得到了各向异性介质目标散射振幅、散射截面等的解析表达式,并对其正确性进行了检验.仿真结果表明:各向异性介质球的散射具有偶极辐射的特点,介电常量越大,产生的偶极矩也愈大,散射也越强.其结果可为各向异性目标监测、各向异性光散射研究等提供理论支持.     

Scattering of Rayleigh waves by a statistical inhomogeneity of the mass density

The problem of the scattering of a Rayleigh wave by a surface inhomogeneity of the mass density of an isotropic solid is solved in the Born approximation of perturbation theory. The inhomogeneity is statistical with a Gaussian correlation function in the plane parallel to the surface and is deterministic with an exponentially decaying dependence on the coordinate perpendicular to the surface. Expressions are derived for the displacement fields in the scattered longitudinal (P), transverse (SV and SH), and Rayleigh (R) waves at large distances from the inhomogeneity. The Rayleigh wave energy scattering coefficients are calculated as functions of the wavelength λ, the correlation length a of the inhomogeneity, the depth d of the defective layer, and the Poisson ratio of the medium, σ. The angular distribution of the scattered Rayleigh wave energy is determined. Asymptotic expressions are obtained for the scattering coefficient in various limiting cases with respect to the parameters a/λ and λ/d. The relation between the energies in the scattered P, SV, SH, and R waves is established. The resulting equations are used to calculate the scattering coefficients numerically over a wide range of variation of the parameters a/λ, λ/d, and σ; the results are presented in the form of graphs and a table. A physical pattern of the scattering process is constructed and used as a basis for interpreting the results of the study. Fiz. Tverd. Tela (St. Petersburg) 39, 267–274 (February 1997)     

Sound absorption by a planar array of monopole-dipole scatterers

The scattering of a plain sound wave by an array of small monopole-dipole scatterers (Helmholtz resonators vibrating on small bars) is considered. It is shown that, at a certain friction in the resonators, an array whose spatial periods do not exceed the half-wavelength of sound serves as an efficient absorber for resonance-frequency sound.     

基于法布里-珀罗干涉仪的瑞利散射测速技术研究

基于法布里-珀罗干涉仪的干涉瑞利散射测速技术原理,结合种子注入Nd∶YAG脉冲激光器、ICCD相机和高光谱分辨法布里-珀罗干涉仪,建立了一套干涉瑞利散射速度测量系统,系统的速度测量准确度为10m/s.对拉瓦尔喷管产生的超声速自由射流开展干涉瑞利散射速度测量,得到气流的流动速度为366m/s.在不需要外加任何示踪粒子的条件下,利用流场气体分子本身的瑞利散射,实现了对超声速流场速度的非接触测量.     

Molecular Resonance Raman and Rayleigh Scattering Stimulated by a Short Laser Pulse

We study a simple model for a molecule subjected to a short laser pulse. We derive very simple expressions for resonance Raman and resonance Rayleigh scattering amplitudes to leading order in the strength μ of the laser and the Born–Oppenheimer parameter ? for the molecule. We also briefly consider the situation where the incident light is close to, but not exactly at the resonance frequency for an electronic transition of the molecule.     

表面垂直裂痕诱发瑞利波散射的数值分析

激光激发的声表面波为材料表面缺陷的检测提供了有力的工具.针对含缺陷材料在模型边界上的复杂性,建立了基于平面应变的有限元模型并选取了相同厚度但含有不同深度的表面裂痕的单层铝板进行了对比计算,得到了声表面波经过不同深度的表面裂痕时产生的反射及透射信号波形的时域特征.进而引入了基于Wigner-Ville分布理论的时-频分析方法计算裂痕前、后散射的瞬态表面波的能量在时间-频率平面内分布的情形.结果显示：声表面波接近中心频率的某一频率成分在经过深度小于其中心波长的表面缺陷时,随着裂痕深度的增加,对应于该频率的反射系数呈现单调递增的趋势;而透射系数呈现递减的特征,这一结果可以为激光超声检测表面缺陷提供一种定量的表征手段.     

激光激发声表面波在缺陷板材中散射过程的有限元分析

利用有限元法模拟了金属板材中激光激发的声表面波经过缺陷位置时发生散射的瞬态过程,采用线状激光源作为超声导波的激发源.针对三种不同深度的表面缺陷以及三种亚表面缺陷的模型进行了对比计算,结果显示缺陷的深度及位置对声表面波的时域特征存在显著的影响.表面缺陷深度越深将产生较大幅度的表面反射回波,亚表面缺陷的影响将取决于缺陷上顶面距离板材上表面的距离.因此,数值模拟结果表明通过分析激光产生的表面波形可以判定近表面缺陷的尺寸和所处的位置.     

新的光散射体系测定蛋白质的研究

以1,6-己二胺二吖啶为荧光探针,建立了一种新的蛋白质共振散射检测体系。实验考察了该吖啶荧光探针的共振散射特征光谱、散射反应稳定性,研究了缓冲介质pH、探针浓度等参数对测定蛋白质的影响。结果表明,当pH 8.9时,1,6-己二胺二吖啶染料的散射波长为470 nm;加入BSA,反应约9 min后,体系光散射强度达到最大并维持稳定,2 h内无明显变化。当1,6-己二胺二吖啶探针(浓度1.00×10-4mol·L-1)用量为3.00 mL时,蛋白质与1,6-己二胺二吖啶的光散射增强作用显著,共振散射强度随着BSA的增加而明显增强,光散射强度与蛋白质浓度成良好线性关系,线性浓度范围为1.00～5.00 μg·mL-1,检测限(3σ/K)为0.085 μg·mL-1。测定了血清样品,浓度为2.00～4.00 μg·mL-1,回收率为98.0%～101.7%,测定偏差小于1.7％。     

Scattering of a plane inhomogeneous electromagnetic wave by a spherical particle

We extend an analytical solution for the problem of diffraction of a plane wave by a spherical particle to the case of an inhomogeneous wave. Numerical examples showing a significant change in the scattered-wave structure compared with the case of diffraction of a homogeneous wave are presented. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 1, pp. 72–81, January 2006.     

Scattering of a spherical wave by a statistically irregular dielectric surface

The scattering of a spherical wave by a static irregular dielectric surface, separating two subspaces with dielectric constant close to the permittivity of free space, is investigated by the Kirchhoff method. The irregularities of the surface — large-scale with small angles of inclination, and their heights are distributed according to a normal law. Self-shadowing and the set of spots associated with scattering on such a surface are taken into account. The polarization matrix of second moments of the components of the scattered field is calculated. The dependence of the matrix elements on the statistical parameters of a randomly irregular surface are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 7–10, May, 1974.