Wave field localization in a prestressed functionally graded layer

Characteristic features of wave field formation caused by a surface source of harmonic vibration in a prestressed functionally graded layer are investigated. It is assumed that the elastic moduli and the density of the material vary with depth according to arbitrary laws. The initial material of the medium is represented by a model hyperelastic material with third-order elastic moduli. The boundary-value problem for a set of Lamè equations is reduced to a set of Cauchy problems with initial conditions, which is solved by the Runge–Kutta–Merson method modified to fit the specific problem under study. Considering shear vibrations of a functionally graded layer as an example, effects of the type of its inhomogeneity, variations in its properties, and nature of its initial stressed state on the displacement distribution in depth are investigated. Special attention is paid to characteristic features of displacement localization in a layer with an interface-type inclusion near critical frequencies. A direct relation between the inhomogeneous layer structure and the type of displacement localization in depth is demonstrated. It is found that the role of initial stresses and variations in material parameters considerably increases in the vicinities of critical frequencies.     

用有限元法解龟磁波穿透非均匀有耗等离子体鞘套时的损耗

本文用有限无法求解了电磁波穿透具有任意密度剖面的非均匀等离子体鞘套时的反射和透射问題。鞘套的剖面参数选自典型再入飞行器的粘性激波层平衡流场数据^[1]。利用虚功原理和线性插值函数从Helmholtz方程导出有限元方程。鞘套按对数剖分为31个单元。然后,分别对频率f=400MHZ,4000MHZ和10GHZ时,计算了鞘套内的场值及反射,透射和吸收系数。并估算了信号的总功耗。误差分析表明,计算结果是令人满意的。与其它方法相比较,本文所给出的有限无法是简捷而精确的,所以该方程适于计算波穿透具有任意的而且变化剧烈的剖面的等离子体鞘套时的损耗     

Focused antenna array in a strongly inhomogeneous medium

A focused acoustic antenna array is considered in a strongly inhomogeneous stationary medium. An opportunity is indicated to determine the coordinates of a number of objects by active location. It is assumed that, in insonifying the objects by a wave with an arbitrary wave front, they scatter spherical waves and are sufficiently separated in distance and angle to be resolved by the same array in a homogeneous medium. The procedure of determining the coordinates of the objects involves a wave front inversion for distinguishing between the signals from different objects. The coordinates are determined by estimating the parameters for each individual object. The parameter estimation procedure is shown to provide a high efficiency of extracting the argument of a complex signal. The results of the numerical modeling and solution of the problem are presented.     

Material parameter computation for multi-layered vocal fold models

Today, the prevention and treatment of voice disorders is an ever-increasing health concern. Since many occupations rely on verbal communication, vocal health is necessary just to maintain one's livelihood. Commonly applied models to study vocal fold vibrations and air flow distributions are self sustained physical models of the larynx composed of artificial silicone vocal folds. Choosing appropriate mechanical parameters for these vocal fold models while considering simplifications due to manufacturing restrictions is difficult but crucial for achieving realistic behavior. In the present work, a combination of experimental and numerical approaches to compute material parameters for synthetic vocal fold models is presented. The material parameters are derived from deformation behaviors of excised human larynges. The resulting deformations are used as reference displacements for a tracking functional to be optimized. Material optimization was applied to three-dimensional vocal fold models based on isotropic and transverse-isotropic material laws, considering both a layered model with homogeneous material properties on each layer and an inhomogeneous model. The best results exhibited a transversal-isotropic inhomogeneous (i.e., not producible) model. For the homogeneous model (three layers), the transversal-isotropic material parameters were also computed for each layer yielding deformations similar to the measured human vocal fold deformations.     

Determination of thermophysical characteristics of materials at thermal effect of constant power

On the basis of the solution to the coefficient inverse problem of heat conductivity we have proposed a method for determination of thermophysical characteristics of material according to temperature measurement in its depth as an approximation of semi-infinite solid, plate of finite thickness, and plate with a layer of ideal conductor at thermal effect of constant power on their surface. The method does not require experimental data smoothing, serves to remove restrictions for heating mode selection, and increases accuracy of thermophysical parameters determination.     

基于等效衰减矢方法的非均匀光波导色散方程

利用转换矩阵理论和等效衰减矢的概念，以此为根据分析了任意折射率分布平板波导的模式传输特性，导出了意义明确的非均匀平板波导的色散方程的严格的解析解，并指出了ＷＫＢ法的局限性，数值计算的结果表明本文所得公式的结果和严格的数值解非常接近，表明本文所得的公式是严格的。     

Analysis of conditions for determining the thermophysical characteristics of energetic materials by the laser pulse method

An analysis of conditions for determining the thermophysical characteristics of energetic materials by the laser pulse method is performed. Based on the results of numerical solution of the heat conduction problems for a sample of a material irradiated with a short heating laser pulse corresponding to actual experimental conditions, the time dependences on the sample surface temperature are determined. The heat pulse duration required to determine the thermophysical properties of materials and the ignition delay time are compared. It is shown that the determination of the thermophysical characteristics of a typical energetic material by the laser pulse method is possible at pulse durations of no longer than 0.24 s.     

Statistical characteristics of an intense wave behind a two-dimensional phase screen

An analysis of the parameters of nonlinear waves transmitted through a layer of a randomly inhomogeneous medium is carried out. The layer is modeled by a two-dimensional phase screen. Passing through the screen plane, the wave acquires a random phase shift. The wave front becomes distorted, and randomly located regions of ray convergence and divergence are formed, in which the nonlinear evolution of the wave alters profoundly. The problem is solved in the approximation of geometrical acoustics. The ray pattern of a plane wave transmitted through the regular screen is constructed. The solution that describes the spatial structure of the field and the evolution of an arbitrary temporal wave profile behind the screen is obtained. Statistical characteristics of the discontinuity amplitude are calculated for different distances from the screen. A random modulation is shown to result in a faster (in comparison with the case of a homogeneous medium) nonlinear attenuation of the wave and in the smoothing of the shock profile. The distribution function of the wave field parameters becomes broader because of random focusing effects.     

Visualization of blood flow by ultrasound speckle interferometry

A new method for the visualization of flowing liquids is suggested. The method makes it possible to obtain images of dynamic objects located in an inhomogeneous medium. The main requirement for the realization of this method is the stability of the field during two successive measurements. The dimensions of the irradiating beam depend on the value of the spatial correlation interval characterizing the inhomogeneities of the medium, while the amplitude distribution in the beam can be arbitrary. A numerical modeling of the method is performed, and images of the models of blood vessels lying under an inhomogeneous layer are presented.     

Asymmetric Fabry-Perot resonator containing an arbitrary inhomogeneous layer

A new method for determining the transmission and reflection coefficients for an arbitrarily polarized electromagnetic wave incident obliquely on an inhomogeneous insulating layer inside an asymmetric Fabry-Perot resonator is proposed. Algebraic relationships between these coefficients for a layer bounded by different homogeneous semi-infinite media and for the same layer in a vacuum are derived. Three examples corresponding to real situations are analyzed, and the results of corresponding numerical calculations are discussed.     

Near-stoichiometric Ti:LiNbO3 strip waveguide with varied substrate refractive index in waveguide layer

We report the near-stoichiometric Ti:LiNbO3 strip waveguides fabricated by vapour transport equilibration (VTE) at 1060 C for 12 h and co-diffusion of 4-8 μm wide, 115-nm thick Ti-strips. Optical studies show that these waveguides are monomode at 1.5 μm and have losses of 1.3 and 1.1 dB/cm for the TM and TE modes, respectively. In the waveguide width/depth direction, the mode field follows a Gauss/Hermite-Gauss profile. A secondary ion mass spectrometry study reveals that the Ti profile follows a sum of two error functions along the width direction and a complementary error function in the depth direction. Micro-Raman analysis shows that the Li-composition in the depth direction also follows a complementary error function. The mean Li/Nb ratio in the waveguide layer is about 0.98. The inhomogeneous Li-composition profile results in a varied substrate index in the guiding layer, and the refractive index profile in the guiding layer is given.     

X-ray rocking curves on inhomogeneous surface layers on Si single crystals

Two cases of inhomogeneous surface layers are considered — diffusion layers as well as implanted layers. The parameters of the layers are investigated by means of an X-ray rocking curve analysis. In this paper the concentration profile of a diffusion layer in Si is determined from X-ray rocking curves, the rocking curves on implanted layers will be discussed in the next paper. A graph is constructed for determining approximate values of surface concentrationC ₀ and diffusion lengthL from subsidiary maxima on the X-ray rocking curve. The dependence of the shape of the rocking curves on the type of the concentration profile and on the values ofC ₀ andL was shown. The influence of crystal thickness and curvature is studied theoretically and experimentally. As an example of using this method a rocking curve of a crystal with a boron diffusion layer is measured and the parameters of the concentration profile are determined. The parameters found are proved by multiplied measurement of rocking curves after anodic oxidation and by comparing these rocking curves with theoretical ones.     

Methods of ellipsometric analysis of polarization optical properties of inhomogeneous surface layers of optoelectronics elements

The basic regularities of changes in the main ellipsometric parameters of a light beam reflected from inhomogeneous surface layers of silicate glasses have been described on the basis of the Drude-Born theories of polarized light reflection. A method of physicomathematical modeling of the refractive index profile in an inhomogeneous surface layer of silicate glasses is reported, which makes it possible to determine, with the lowest second-kind error probability, a model of an inhomogeneous reflecting system that is adequate to the object of study.     

Methods of Determining the Characteristics of Dispersed Media at a Phase Transition

Gradient methods of determining the thermophysical characteristics of dispersed media at phase transitions are suggested. The reliability and the rate of convergence of the suggested methods are tested for a model problem. A comparison of the results of reconstructing the thermophysical characteristics by the numerical and conventional quasi-stationary methods demonstrates their good agreement. The influence of the number and arrangement of sensors on the accuracy of reconstruction of the thermophysical characteristics is studied.     

多层不均匀材料中光吸收系数深度分布计算的理论处理

提出了一种通过光热法测定与样品表面温度有关的光热信号，重构反映多层不均匀材料中光吸收系数深度分布的理论处理和新的有效数值计算方法，数值模拟显示了较好的逼近效果。     

Modeling the Effect of Thermophysical Properties on Pyrolysis of Intumescent Fire-retardant Materials

Thermophysical properties of intumescent fire-retardant (IFR) materials are important input parameters to simulate the pyrolysis process of IFR materials in fire scenarios. In this article, the effects of the thermophysical properties on pyrolysis of IFR materials are simulated based on a pyrolysis model of IFR materials. The selected thermophysical properties here are the specific heat capacity of the virgin material, thermal conductivity of the virgin material and char layer, heat of decomposition, density of virgin material, intumescent temperature, and surface emissivity of virgin material and char layer. Simulated mass loss rates (MLR) for the IFR materials at an incident heat flux of 50 kW/m² are investigated for the varied thermophysical parameter values. The results show that changes in these property values can affect the pyrolysis behavior of materials profoundly. Comparison with experimental results indicates that the simulations of MLR are in reasonably good agreement with the experiments.     

The determination of dislocation density depth profiles in surface layers from broadening of X-ray diffraction profiles

A method is proposed for the determination of dislocation density depth profiles in the thin surface layers comparable to the penetration depth of X-rays, with no need to remove the surface layers by chemical or electrolytic polishing. The dislocation density depth profile is modelled mathematically and the parameters determining the profile can be evaluated from the Fourier transform of the X-ray diffracted profiles with various wavelengths of radiation.     

Two-dimensional thermoelasticity solution for functionally graded thick beams

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.     

Investigation of the electromagnetic fields at a jump in the dielectric constant

The passage of a plane wave through an inhomogeneous flat insulator layer of arbitrary thickness without absorption is considered. A method is given for solving the problem in terms of elementary functions, which reduces the number of independent parameters of the layer. A similarity principle for layers having equivalent reflectivities is described. It is shown that the electric field intensity can increase to infinity near the critical point where ɛ=0. Zh. Tekh. Fiz. 69, 5–9 (August 1999)     

Sound Propagation in Shallow Water with an Inhomogeneous GAS-Saturated Bottom

We present the methods and results of numerical experiments studying the low-frequency sound propagation in one of the areas of the Arctic shelf with a randomly inhomogeneous gas-saturated bottom. The characteristics of the upper layer of bottom sedimentary rocks (sediments) used in calculations were obtained during a 3D seismic survey and trial drilling of the seafloor. We demonstrate the possibilities of substituting in numerical simulation a real bottom with a fluid homogeneous half-space where the effective value of the sound speed is equal to the average sound speed in the bottom, with averaging along the sound propagation path to a sediment depth of 0.6 wavelength in the bottom. An original technique is proposed for estimating the sound speed propagation in an upper inhomogeneous sediment layer. The technique is based on measurements of acoustic wave attenuation in water during waveguide propagation.