Normal modes of a poroelastic plate and their relation to the reflection and transmission coefficients

A poroelastic plate that obeys the Biot theory is considered. Compact new forms of its reflection and transmission coefficients, similar to those of the resonance scattering theory for an elastic plate, are derived. A numerical comparison of the reflection coefficient modulus with the plate normal modes, at low frequency, shows that a study of the reflection or transmission coefficient does not provide the same kind of information on the poroelastic plate than an investigation of guided leaky waves propagation.     

Extension of Wolter's multilayer reflection and transmission formulae for orthorhombic absorbing media

Wolter's multilayer reflection and transmission formulae are extended for the case, that the multilayer system is composed of orthorhombic media. These are oriented in such a way, that two of their principal dielectric axes lie in the surface of a layer. The third axis forms with a second one the plane of incidence. An analysis of the complex roots in the formulae, always present when dealing with absorbing media, is given to choose the correct solutions. The extended formulae are well suited for a computer program. They allow e.g. the computation of Attenuated Total Reflection (ATR)-spectra of anisotropic crystals.     

正交各向异性板液/固界面的声反射与声透射

采用Legendre正交多项式法,对液/固界面声波反射和透射系数进行求解。利用Legendre正交多项式对正交各向异性板中的位移解进行展开,推导出板中的应力和波动控制方程。联立液/固界面的边界条件和波动控制方程,建立线性无关方程组,用以计算液/固界面的反射和透射系数及Legendre多项式的展开系数,计算所得铝板液/固界面的反射和透射系数与传递矩阵法的计算结果吻合良好。以单向纤维增强复合材料板为例,在不同的方位角下,分析了反射和透射系数随斜入射角度、入射波频率的变化关系,以及板中声场的位移分布。所取Legendre正交多项式截止阶数越大,可用来计算的频厚积范围越大。研究拓展了Legendre正交多项式法的适用范围,为材料力学性能的声学测量提供了理论基础。     

正交各向异性板液/固界面的声反射与声透射

采用Legendre正交多项式法,对液/固界面声波反射和透射系数进行求解。利用Legendre正交多项式对正交各向异性板中的位移解进行展开,推导出板中的应力和波动控制方程。联立液/固界面的边界条件和波动控制方程,建立线性无关方程组,用以计算液/固界面的反射和透射系数及Legendre多项式的展开系数,计算所得铝板液/固界面的反射和透射系数与传递矩阵法的计算结果吻合良好。以单向纤维增强复合材料板为例,在不同的方位角下,分析了反射和透射系数随斜入射角度、入射波频率的变化关系,以及板中声场的位移分布。所取Legendre正交多项式截止阶数越大,可用来计算的频厚积范围越大。研究拓展了Legendre正交多项式法的适用范围,为材料力学性能的声学测量提供了理论基础。     

Geometric form of the equations for the phase changes on reflection and transmission at a thin absorbing film

Abelès' equations for the phase changes on reflection and transmission, F_s, F_p, X_s and X_p at thin films have been rearranged into geometrical form in the ε₁, ε₂ plane. The contours of constant F_s and F_p are a series of circles whilst X_s and X_p can be represented by straight lines. When considering the same functions in the n, k plane, f_s and F_p become quartics in new axes, n′ and k′, obtained by rotating the n and k axes through an angle a given by tan . A similar transformation applied to X_s and X_p generates hyperbolae in the n′, k′ plane.     

Phase relations for a sound wave at its reflection and transmission through a plane layer

A property never considered before in acoustics is established: in the case of a sound wave incidence on a plane layer bordered by two liquid media with identical elastic properties, the phase difference between the reflected and transmitted waves is equal to π/2 irrespective of the physical constants of the layer and the media contacting it, as well as of the frequency of the incident wave.     

The use of a plane parallel glass plate for determining the lens' parameters

The present article reports a shearing interferometric technique for determining the various lens' parameters, namely, the focal length, refractive index, radii of curvatures etc. The wave aberrations have also been investigated for the different values of the focal length of the same lens by immersing it in various liquids. The lens itself acts both as autocollimator and decollimator. Modified criteria for evaluating the correct position of the focal length have been adopted. The defocusing involved is observed in terms of the interference fringes. The plane parallel glass plate acts as a double shearing interferometer. The location of the point source is confirmed by testing the wavefront parallelism. A graph (refractive index versus lens' power) with various liquids has been plotted which gives the desired parameters.     

Distribution of reflection coefficients in absorbing chaotic microwave cavities

The distribution of reflection coefficients P(R) for chaotic microwave cavities with time-reversal symmetry is investigated in different absorption and antenna coupling regimes. For all regimes the agreement between experimental distributions and random-matrix theory predictions is very good, provided both the antenna coupling T(a) and the wall absorption strength T(w) are taken into account in an appropriate way. These parameters are determined by independent experimental quantities.     

Air-coupled measurement of plane wave, ultrasonic plate transmission for characterising anisotropic, viscoelastic materials

Electrostatic, air-coupled, ultrasonic transducers are used to generate and detect plane waves in viscoelastic, isotropic or anisotropic solid plates. The through-transmitted field is measured and compared to numerical predictions. An inversion scheme is then applied for identifying the values of the complex Cij which are representative of the viscoelasticity properties of the materials. The issue of this work is a contact-free, ultrasonic technique for material characterisation.     

Wave reflection and transmission in beams

The vibrational behaviour of beam systems can be expressed in terms of waves of both propagating and near field types. A propagating wave incident upon a discontinuity gives rise to reflected and transmitted waves of both kinds whose amplitudes may be found from well-known reflection and transmission coefficients. In this paper the approach is extended to the case of incident near field waves, reflection and transmission matrices being derived for the cases of a point support and a change in section. Reflection at a boundary and the effects of applied excitations are also considered. It is seen that incident near fields can give rise to substantial propagating components. The application of the results to the analysis of free and forced vibration of beams is then demonstrated. By adopting this approach the effects of the interaction of the near fields with neighbouring discontinuities are fully included.     

Further study on the characteristic impedance of a new transmission line of round conductor and parallel plane with a slit

A conformal transformation for the analysis of a transmission line consisting of a cylindrical conductor placed opposite a slit in an infinite flat plate is developed. The approximate and exact expressions in closed- form of the characteristic impedance for the proposed line based on assuming only a quasi-TEM mode propagating in the line are as exact as the conventional one cited.     

Coherent reflection and transmission of close-packed scatterer monolayers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 2, pp. 299–305, August, 1990.     

Interferometric control of transmission and reflection optical elements

A simple method for interferometric control is considered that permits the control of optical elements of the transmission and reflection type. A universal control instrument is proposed. The results of experimental verification of the interferometric control method, which confirm the effectiveness of its implementation in industrial conditions, are reported.     

Coherent and incoherent reflection and transmission of multilayer structures

The complex-amplitude reflection and transmission coefficientsr andt of a pile of films are represented as a product of matrices. The matrices describe the transformation of two plane waves travelling in opposite directions between the films, and their development within the films.If one of the films is significantly thicker than the other layers (e.g., several films on a substrate), the calculated reflectanceR=rr ^* and transmittanceTt ^* show narrow Fabry-Perot oscillations which, in a lot of cases, are not observed in the experiment. Since the matrix method is equivalent to the representation of the amplitudesr andt as a coherent superposition of multiple reflected waves within the thick slab, we are able to suppress, in the calculation, the interference within this thick film by adding the absolute squares of the partial waves corresponding to an incoherent treatment. This procedure is shorter and more simple than averaging over an appropriate interval of frequency or thickness, which, in most cases, leads to the same results.     

Studying the possibility of extracting material parameters from reflection and transmission coefficients of plane wave for multilayer metamaterials based on metal nanogrids

To more adequately extract the effective refractive index and other so-called metamaterial parameters from the reflection and transmission coefficients of a wave for multilayer grid nanostructures in the near-IR spectral range, the Nicholson-Ross-Weir method was modified. The rate of convergence of each extracted metamaterial parameter to a certain limit is studied with increasing number of layers of the structure. For each frequency of the light field, this limit is obviously equal to the value of the parameter that corresponds to an infinite number of layers. The effect of a separation layer of a dielectric between pairs of grids on the convergence rate of extracted parameters is studied. Bulk electrodynamic parameters of the structure are discussed.