Experimental study of ultrasonic velocity in dispersive media

The results of an experimental study of the velocity of ultrasonic waves propagating at a 3 MHz frequency in suspensions of glass spheres in water are presented for a wide range of concentrations. It is shown that, from the variations in the concentration coefficient of the velocity of ultrasonic waves, one can extract information on the structural rearrangements in the suspension and, in the range of low concentrations, information on the elastic moduli of individual microparticles.     

Elastic properties of finite three-dimensional solid phononic-crystal slabs

We study theoretically, by means of layer-multiple scattering techniques, the propagation of elastic waves through finite slabs of phononic crystals consisting of metallic spheres in polyester matrix, embedded in air. We focus on the study of modes localized on the surfaces of the structure, investigating the physical parameters which influence and determine their appearance. Our results reveal the existence of absolute phononic frequency gaps in these finite structures, and point out the possibility, under an appropriate choice of the parameters, of tunable regions of frequency free of propagating and/or surface-localized modes. This could be very useful in the design of devices related to frequency filtering, waveguiding, etc.     

Surface acoustic waves in an elastic wedge media

We consider surface acoustic waves in an elastic wedge media. It is established that the investigated waves substantially differ from known ones. For example, the movement of surface Rayleigh wave in the direction to the edge leads to a change of its structure, accompanied by the splitting of the initial wave to two separate modes and radiation of shift and longitudinal waves. Along the edge of the wedge the surface wave is strongly localized in the transverse direction. Are discussed the properties of the wedge antisymmetric normal waves, propagating parallel to the edge of the wedge.     

Lamb waves in anisotropic plates (review)

Propagation of Lamb waves in elastic anisotropic plates is studied in the framework of the six-dimensional Cauchy formalism. Closed-form secular equations for dispersion curves for Lamb waves propagating in a plate with arbitrary elastic anisotropy are obtained.     

The influence of external tensile stress on surface elastic waves on piezoelectric ceramic plates

Experimental results on the output voltage via a propagating surface elastic wave and the convolution output of two oppositely propagating surface elastic waves on a piezoelectric ceramic plate are described as a function of external tensile stress. The convolution output increases with the cummulative load, while the output voltage via the surface elastic wave decreases. The variation of the output voltage is considered to be due to the change in nonlinearity that arises from the external load.     

Interaction of strongly nonlinear waves on the free surface of a dielectric liquid in a horizontal electric field

The nonlinear dynamics of the free surface of an ideal dielectric liquid with a large relative permittivity in a strong horizontal electric field has been considered. It has been demonstrated that the interaction between oppositely propagating solitary waves in arbitrary geometry is elastic: they conserve their energy and momentum. The interaction between waves has been numerically simulated with the use of conformal variables. It has been shown that the interaction deforms the waves; this effect is weak for waves with a relatively small amplitude: deformation for oppositely propagating waves with the identical shape is determined by the fourth power of their amplitude. At multiple collisions of strongly nonlinear waves, a tendency to the formation of singularities, i.e., points with a high energy density of the field, is observed.     

A numerical study on the propagation of Rayleigh and guided waves in cortical bone according to Mindlin's Form II gradient elastic theory

Cortical bone is a multiscale heterogeneous natural material characterized by microstructural effects. Thus guided waves propagating in cortical bone undergo dispersion due to both material microstructure and bone geometry. However, above 0.8 MHz, ultrasound propagates rather as a dispersive surface Rayleigh wave than a dispersive guided wave because at those frequencies, the corresponding wavelengths are smaller than the thickness of cortical bone. Classical elasticity, although it has been largely used for wave propagation modeling in bones, is not able to support dispersion in bulk and Rayleigh waves. This is possible with the use of Mindlin's Form-II gradient elastic theory, which introduces in its equation of motion intrinsic parameters that correlate microstructure with the macrostructure. In this work, the boundary element method in conjunction with the reassigned smoothed pseudo Wigner-Ville transform are employed for the numerical determination of time-frequency diagrams corresponding to the dispersion curves of Rayleigh and guided waves propagating in a cortical bone. A composite material model for the determination of the internal length scale parameters imposed by Mindlin's elastic theory is exploited. The obtained results demonstrate the dispersive nature of Rayleigh wave propagating along the complex structure of bone as well as how microstructure affects guided waves.     

Propagation and interaction of nonlinear waves in a liquid with gas bubbles

The propagation and interaction of nonlinear solitonlike waves in a liquid with gas bubbles are considered using the Nakoryakov-Pokusaev-Shreiber two-wave equation. It is shown that these waves exist within the “opacity” window for linear waves. The interaction of such waves propagating in opposite directions may lead to their splitting into secondary localized waves.     

Observation of the "Luxemburg-Gorky effect" for elastic waves

An experimental observation of a new nonlinear-modulation effect for longitudinal elastic waves is reported. The phenomenon is a direct elastic wave analogy with the so-called Luxemburg-Gorky (L-G) effect known over 60 years for radio waves propagating in the ionosphere. The effect consists of the appearance of modulation of a weaker initially non-modulated wave propagating in a nonlinear medium in the presence of an amplitude-modulated stronger wave that produces perturbations in the medium properties on the scale of its modulation frequency. The reported transfer of modulation from one elastic wave to another was observed in a resonator cut of a glass rod containing a few small cracks. Presence of such a small damage drastically enhances the material nonlinearity compared to elastic atomic nonlinearity of homogeneous solids, so that the pronounced L-G type cross-modulation could be observed at strain magnitude in the stronger wave down to 10(-7) and smaller. Main features of the effect are pointed out and physical mechanism of the observed phenomena is discussed.     

Influence of static and dynamic internal actions on elastic nonlinear properties of a granulated unconsolidated medium

We have studied the influence of external static (pressure) and dynamic (caused by an elastic wave with a finite amplitude) actions on the linear and nonlinear elastic properties of a granulated unconsolidated medium, which was simulated by steel spheres with diameters of 2 and 4 mm. We have analyzed the equation of state for such a medium taking into account the presence of weakly and strongly deformed contacts between individual spheres. We have obtained expressions for the elasticity coefficient and second- and third-order nonlinear elastic parameters, and we have experimentally studied the influence of external static pressure on their values. We have measured the dependence of the velocity of elastic waves on external static pressure and the probing signal amplitude. In the studied medium, a number of structural phase transitions were observed, related to rearrangement of the packing of spheres, which were caused by both static and dynamic actions. The structural phase transition was accompanied by an anomalous change in the nonlinear elastic parameters of the medium and the velocity of elastic waves. We have analyzed the results based on the Hertz theory of contact interaction.     

Dispersion relations of waves in a rod embedded in an elastic medium

The dispersion relations of waves propagating in a system consisting of an elastic rod of radius a embedded in a linear elastic medium are investigated, and phase speeds of waves of wavelength λ which propagate under steady state conditions are determined. The dispersive behaviour is found to be dependent on several non-dimensional parameters defined by the geometric ratio $\text{a}\text{λ}$, as well as on non-dimensional ratios of the rod-medium properties. It is shown that the resulting waves which can propagate under steady state conditions are surface waves which decay with the radial distance and which permit no radiation damping of energy. It is further shown that such waves can propagate freely only if the propagation speed of longitudinal waves in the corresponding free rod is less than that of shear waves propagating in the medium. Results are presented by means of dispersion curves and surfaces. From a study of the analytical results obtained, lower and upper bounds on the phase speeds are established.     

First laboratory observation of freely propagating electrostatic waves produced by intense, localized field structures

Freely propagating electrostatic waves (free modes) are observed to be produced by intense, localized field structures in laboratory measurements performed in an unmagnetized plasma in a state of strong Langmuir turbulence. The freely traveling waves conform to the Langmuir dispersion relation and have an average frequency which is approximately 11% higher than the average frequency of the localized field structures. The observations are consistent with the predictions of strong Langmuir turbulence theory.     

Nonlinear wave processes in media containing cracks partially filled with a viscous liquid

A nonlinear (in the cubic approximation) relaxation equation of state is derived for a rod containing cracks partially filled with an incompressible viscous liquid. The nonlinear effects of the self-action and interaction of low-and high-frequency longitudinal elastic waves propagating in such a rod are studied for the cases of identical and size-varied cracks. Linear and nonlinear acoustic parameters characterizing the self-action and interaction of elastic waves in a cracked rod are determined.     

The anisotropy of elastic waves in a tellurium crystal

For acoustic waves propagating in an acoustooptic tellurium crystal, the dependence of their polarization on the propagation direction with respect to the crystal axes is discussed. The characteristic features of waves propagating in the crystal are considered; these features manifest themselves in an excess of the phase velocity of shear acoustic modes over the velocity of longitudinal modes. The change in the wave type from quasi-longitudinal to quasi-transverse as a result of the variation in the propagation direction of ultrasound is investigated. It is shown that such a behavior of bulk acoustic waves is caused by the specific relation between the elastic moduli, which differs from the corresponding relations observed in other acoustooptic materials.     

Stresses in Pochhammer–Chree Axisymmetric Waves in the Medium-Wavelength Range

Acoustical Physics - Pochhammer–Chree axisymmetric waves propagating along an elastic rod with a circular cross section are analytically investigated. The stress-strained state of the rod is...     

Localization of nonlinear waves between interfaces

Stationary localized states of nonlinear waves propagating in a focusing medium along two plane-parallel interfaces repulsing the wave flux are investigated analytically. It is established that the nonlinear wave beam can be localized in the region between these interfaces.     

Peculiarities of ultrasound propagation through layered structurally inhomogeneous solid bodies

The results of measuring the velocities of quasi-longitudinal elastic waves propagating through two-phase layered model samples are presented. These samples are fabricated from powders of different crystalline minerals and epoxy. The influence of foliation and powder grain sizes on the elastic anisotropy of the samples is analyzed. It has been revealed that samples with muscovite and quartz fillers have different relations between the layered structure and the spatial distribution of the velocities of quasi-longitudinal elastic waves.     

Diffraction of SH waves at a mixed interface

Summary We study the diffraction of SH-type elastic waves propagating along the plane interface between two dissimilar elastic half-spaces. It is assumed that the contact between the half-spaces is perfect except for a part of semi-infinite extension where the contact is loosely coupled. We use the Wiener-Hopf technique to obtain the diffracted field in a closed form.     

A Study of the Acoustic Properties of a Body of Heterogeneous Rocks and Concrete Lining under Natural Conditions

Technical Physics - The field of velocities of elastic waves propagating in a body of heterogeneous rocks is measured. The spectral composition of the response of the bodies of heterogeneous rocks...     

弹性波通过一维复合材料系统的透射性质

提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器 关键词： 弹性波复合材料 局域化