The propagation of ultrasonic waves in CFRP laminates

A complete survey is presented of studies of ultrasonic wave propagation in flat carbon fibre reinforced plastic (CFRP) laminates. After a summary of earlier work on uni-axial specimens, results are given for two and three-ply laminates and sandwich structures, with the current extent of interpretation. Velocities measured perpendicular to fibre directions show an interesting dependence on porosity of the matrix and the measuring technique used, which could lead to wider exploitation.     

Surface electromagnetic waves at the interface between two dielectric superlattices

The electrodynamic properties of the interface between two periodic dielectric superlattices are studied. It is shown that the interface may serve as a guide for an electromagnetic wave whose field decays exponentially on both sides of the plane of the interface. The field and power flux distributions, as well as the frequency dependence of the field penetration depth, are studied.     

Nonlinear interaction of plane ultrasonic waves with an interface between rough surfaces in contact

A theoretical investigation of the nonlinear interaction between an acoustic plane wave and an interface formed by two rough, nonconforming surfaces in partial contact is presented. The macroscopic elastic properties of such a nonlinear interface are derived from micromechanical models accounting for the elastic interaction that is characteristic of spherical bodies in contact. These results are used to formulate set of boundary conditions for the acoustic field, which are to be enforced at the imperfect interface. The scattering problem is solved for plane wave incidence by using a simple perturbation approach and the harmonic balance method. Sample results are presented for arbitrary wave polarization and angle of incidence. The relative magnitude of the nonlinear signals and their potential use toward the nondestructive evaluation of imperfect interfaces are assessed. In particular, attention is drawn to the enhanced nonlinear response of an interface insonified by a shear vertical wave in the neighborhood of the longitudinal critical angle. The motivation for this investigation is provided by the need to develop nondestructive methods to detect and localize small, partially closed cracks in metals with coarse microstructures.     

Extinction theorem and propagation of electromagnetic waves between two anisotropic materials

We systematically investigate the reflection and refraction of an electromagnetic wave between two semi-infinite anisotropic magnetoelectric materials. Using the integral formulation of Hertz vectors and the principle of superposition, we generalize the extinction theorem and derive the propagation characteristics of wave. Applying the results obtained, we find a general origin of Brewster effect. We also show that, through choosing appropriate material parameters, oblique or omnidirectional total transmission can occur to TE and TM waves. Compared to the traditional method, the method used here discloses the underlying mechanism of wave propagation between two arbitrary anisotropic materials and can be applied to other problems of propagation.     

Electroelastic field induced by thin interface electrodes between two bonded dissimilar piezoelectric ceramics

The electroelastic analysis of multiple collinear electrodes embedded at the interface of two bonded dissimilar piezoelectric ceramics is made. Within the framework of linear piezoelectricity, the Fourier transform technique is applied to reducing the problem to a singular integral equation with Cauchy kernel. Two particular cases are especially emphasized. For a single interface electrode, the electroelastic field is obtained in the entire plane of a two-phase piezoelectric composite in terms of elementary functions. For two collinear interface electrodes of equal length, a closed-form solution is determined along the interface. Obtained results reveal that near the electrode edges, the induced electroelastic field exhibits a square-root singularity, and the oscillatory singularity does not occur for arbitrary two piezoelectric ceramics poled in the same or opposite directions normal to the interface. Across the electrode, the normal component of stress is continuous, while that of strain exhibits a jump, implying strain incompatibility due to the mismatch of the material properties of two dissimilar poled ceramics.     

A numerical formulation for nonlinear ultrasonic waves propagation in fluids

A finite-difference algorithm is developed for analysing the nonlinear propagation of pulsed and harmonic ultrasonic waves in fluid media. The time domain model allows simulations from linear to strongly nonlinear plane waves including weak shock. Effects of absorption are included. All the harmonic components are obtained from only one solving process. The evolution of any original signal can be analysed. The nonlinear solution is obtained by the implicit scheme via a fast linear solver. The numerical model is validated by comparison to analytical data. Numerical experiments are presented and commented. The effect of the initial pulse shape on the evolution of the pressure waveform is especially analysed.     

Modeling laser-generated guided waves in bonded plates by the finite element method

The purpose of this research is to develop an effective model of the transient laser-generated guided waves in bonded plates by the finite element (FE) method. The FE parameters, such as the mesh density and the time step size, which are related to wave propagation, are optimized in order to set up a standard, and the correlation between these parameters is discussed. The waveforms in bonded plates with different bonded interface modeled by the spring model are obtained and then compared. The results show that the transient responses are sensitive to the stiffness coefficients characterizing the cohesive quality. Finally, these FE results are compared with analytical and experimental results. All these comparisons confirm the accuracy of the FE method for modeling laser-generated guided waves in bonded plates.     

Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates

This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations: a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties (elastic modulus, viscoelastic modulus, and thickness) of the adhesive layer has been studied in detail.     

The rate of propagation of ultrasonic waves in ADP in voigt's theory

The difference measured in the rates of propagation of shear ultrasonic wavesv _zx andv _zx in an ADP crystal is one of the bases of the Laval-Raman theory of the elastic properties of crystals. In the present paper an attempt is made to obtain by calculation a similar difference in rates within the old Voigt theory by using the more perfect methods of computation of Lawson and Paillouxe. The calculations, together with an estimate of the influence of second-order effects, however, indicate that the measured differences in rates cannot be explained even in this way by means of Voigt's theory.In conclusion, the author would like to express his sincere thanks to Senior Lecturer L. Janík for cooperation in the measurements, Assistant Professor J. Tichý for kindly lending the results of his own measurements and less accessible literature, and Technician R. Suchy for assistance in adapting the experimental equipment. He is also indebted to Professor P. A. O'Brien and the head of the Czechoslovak Commercial Section in Khartoum, B. Sychra, for help in elaborating this contribution.     

Capillary waves on the liquid-vapour interface, and propagation near boundaries

The paper will outline the thermally-excited-capillary-wave model for the liquid-vapour interface, and then discuss some factors which are neglected which may well be important when comparing with experiment. To learn about the properties of capillary waves in thin liquid layers we have made a study of the propagation of waves up an inclined beach and preliminary results of this study will be described.     

骨折长骨中超声导波传播特性的仿真研究

采用超声导波评价长骨骨折已成为近两年来的一个研究热点.本文采用混合边界元方法(HBEM)对超声导波在骨裂长骨中的传播情况以及各导波模式的反射系数和透射系数进行了数值分析.研究结果表明,入射导波模式经由裂纹处模式转换后依然保持为主要接收模式不变.对某一裂纹,各模式透射系数常在相近的频率点上达到局部峰值.对于不同深宽比(d/w)裂纹,某些模式透射系数曲线局部峰值所对应的频率存在着相互错开的现象,这些结果可用于选择最优入射导波模式和频率,以便更好地定量评价骨质以及骨裂状况.     

双层杆结构中纵向模态的超声导波

通过分析应力和位移边界条件得到了双层杆结构中纵向模态的频散方程，并进行数值求解，得到相应的频散曲线。对该结构中纵向模态的主要传播特性进行了分析。然后，利用长度伸缩型压电陶瓷片在内层为冰外层为钢的双层杆结构中进行了激励接收纵向模态的实验。实验结果与理论分析较为吻合。结果表明，双层杆结构的频散曲线可用作模态选取的理论指导，用于该结构的缺陷检测。     

Modeling of the propagation of electromagnetic waves in 2D labyrinthine photonic structures

The features of electromagnetic wave propagation in photonic structures with a labyrinthine distribution of the refractive index have been analyzed based on the direct numerical solution of Maxwell’s equation. It is shown that the distribution of the energy density of the electromagnetic field is characterized by a complex branching structure, and the transmission nonlinearly depends on the size of the photonic cell.     

Detection and location of cracks using loss of reciprocity in ultrasonic waves propagation

The reciprocity theorem is a general statement valid for elastic media, and it has been applied to the solution of elastic wave equations, transducers calibration, time reversal acoustics, etc. However, localized nonlinear scatterers are expected to break reciprocity even though the effect is, in several cases, negligible. Here the dependence of the reciprocity break on the presence of a localized damage and the influence of its relative position has been experimentally investigated. It will be shown that the break of reciprocity, usually considered a disadvantage, can be exploited as an imaging tool for localized cracks detection.     

On the structure of waves at the charged interface between two viscous liquids at the solid bottom

The solutions to the equation describing the wave motion in a bilayer system of immiscible liquids are obtained in the first order of the theory of approximations. The hydrodynamic potentials, current functions, generatrix of the shape, and electrostatic potential of the charged interface between two viscous liquids, one of which conducts current and the other being a dielectric, on the solid bottom, are determined. It is shown that in the case when the density of the upper medium is three or more orders of magnitude lower than that of the lower liquid or when the kinematic viscosity of the upper medium is negligibly low as compared to that of the lower medium, the effect of the upper medium on the flow of the liquid in the lower medium is negligibly small. The structure of the wave motion generated by the interface between the two media is analyzed.     

The propagation in metal tubing of ultrasonic wave modes equivalent to Lamb waves

The generation of ultrasonic wave modes in thin-walled metal tubing has been investigated experimentally using piezoelectric ultrasonic probes. It is shown that the L(0, 1) mode, which is comparable to the A₀ Lamb wave mode in flat plate, can be generated with acceptable efficiency. The L(0, 2) mode (compare the S₀ Lamb wave mode) is generated rather less efficiently, while its greater group velocity tends to enhance the resolution problems so caused.The initial probe designs were inefficient in that a considerable amount of ultrasonic ‘noise’ was also present which could mask ultrasonic pulses of interest. This would be especially so for short range operation. An improved probe design reduced this background noise to a more acceptable level.The propagation of the L(0, 1) mode around a length of bent (U-form) tubing has also been investigated and it is shown that the ultrasonic pulse is both attenuated and lengthened, while structure has also been introduced. The theoretical implications of this are discussed. Finally a small amount of work is presented on the interaction of both modes with artificial defects.     

Modeling the propagation of electromagnetic waves over the surface of the human body

The results of modeling and an experimental study of electromagnetic (EM) waves in microwave range propagating along the surface of the human body have been presented. The parameters of wave propagation, such as the attenuation and phase velocity, have also been investigated. The calculation of the propagation of EM waves by the numerical method FDTD (finite difference time domain), as well as the use of the analytical model of the propagation of the EM wave along flat and curved surfaces has been fulfilled. An experimental study on a human body has been conducted. It has been shown that creeping waves are slow and exhibit a noticeable dispersion, while the surface waves are dispersionless and propagate at the speed of light in free space. A comparison of the results of numerical simulation, analytical calculation, and experimental investigations at a frequency of 2.55 GHz has been carried out.