Transverse Acoustic Waves Research Articles

Dynamic X-Ray Diffraction by a Multilayer Mirror Modulated with a Transverse Acoustic Wave

Dynamic diffraction of an x-ray plane wave by a multilayer mirror modulated with a transverse acoustic wave is analyzed on the basis of rigorous multiwave mode theory. Particular attention is given to the case when λs > τ. where λs is the acoustic wavelength and τ is the extinction length. It has been derived that with increasing sound amplitude, splitting arises in every point of the kinematic branch interaction for both λs < τ and λs > τ. Accordingly the rocking curve takes the form of separate rows of peaks of Bragg diffraction into separate orders, the widths of the peaks being smaller than the width of the Bragg mirror image without modulation. The widths decrease with increasing modulation amplitude.

The properties of magnetoacoustic waves in tangentially magnetized sandwich structure

The problem of linear exitation of coupled spin waves (SW) and transversal acoustic waves (AW) was theoretically investigated for a sandwich structure, consisting of a tangentially magnetized thin film, a dielectric layer and metallic screens. An infinite system of algebraic equations was obtained for the amplitudes of SW modes, interacting with AW and the external driving field. An approximative solution, allowing to calculate parameters of the magnetoacoustic waves is presented.

Molar volume and elastic properties of multicomponent chalcogenide glasses

High purity chalcogenide glasses incorporating Ge, Sb, Se, As and Te were prepared by vacuum melting of previously distilled 5 N to 6 N pure raw materials from which the surface oxide was also removed in some cases. Molar volume and elastic properties of several isostructural chalcogenide glasses prepared by similar processing techniques were obtained from the measured values of densities and the velocities of transverse and longitudinal acoustic waves respectively. Property variations with the average coordination number, 〈 r〉, were examined. Molar volume displayed a distinct minimum at 〈 r〉 = 2.4, coincident with Phillips' ‘percolation threshold’ for each system studied. Elastic moduli, however, failed to show any dramatic changes at this threshold. Near the stoichiometric tie-line, a chemically ordered covalent network (COCN) model for the atomic arrangement in these glasses was found to be preferred over the chance coordination predicted by the random covalent network (RCN) model.

Nonlinear surface transverse waves (STW) on elastic structures

By using both a zero-thickness interface description for a “slow” thin film coating a nonlinear elastic substrate, and the Whitham-Newell theory of nonlinear, small-amplitude, almost monochromatic, dispersive waves, the existence of stable elastic solitary surface transverse acoustic waves (STW) propagating as dark or bright solitons is established. The acoustic analogue, in elastic solids, of the solitons observed for electromagnetic propagation in optical fibers is thus obtained.

Structure and dynamics of a two-component metallic glass

Computations of the frequencies of longitudinal and transverse phonon modes in a two-component metallic glass (Mg70Zn30) based on the pseudopotential approach used for the calculation of interatomic pair potential have been presented. The theory employed for these calculations is a self-consistent phonon theory as developed by Takeno and Goda (1971) for amorphous solids. The computed results are compared with molecular dynamics and neutron inelastic scattering experiments. It appears that the short-wavelength collective excitations detected in this glass arise from longitudinal phonon excitations and probably not from a diffuse Umklapp scattering from transverse acoustic waves.

On the Existence and Stability of Limit Cycles for Transverse Acoustic Oscillations in a Cylindrical Combustion Chamber. 1: Standing Modes

Abstract Nonlinear pressure oscillations in combustion chambers have been studied using an approximate analysis which treats the unsteady motions as a collection of coupled nonlinear oscillators, each corresponding to an acoustic mode of the chamber. Based on spatial and temporal averaging of the conservation equations, the formulation provides a convenient means for analyzing the nonlinear behavior of acoustic wave motions. The work addresses the linear and nonlinear characteristics of transverse acoustic waves in a cylindrical chamber, with attention focused on the conditions for the existence and stability of limit cycles. As a result of the special structure of the equations, both general and precise conclusions can be reached. Explicit results are given for the special cases of two and three standing modes. Spinning wave motions will be treated in a subsequent paper.

High-resolution Brillouin gain spectroscopy in fused silica

We report what is to our knowledge the first high-resolution Brillouin gain spectrum in a solid. Resonances corresponding to longitudinal (compressional) and transverse (shear) acoustic waves in fused silica are observed with good resolution and a high signal-to-noise ratio. Absolute gain coefficients, linewidths, and Brillouin frequency shifts are measured. The agreement with previously measured values is good.

Device for generating both transverse and longitudinal acoustic waves in a plurality of different directions

Device for generating both transverse and longitudinal acoustic waves in a plurality of different directions

Theoretical study of the anisotropic diffraction of light waves by acoustic waves in lithium niobate crystals

The anisotropic diffraction of light by high frequency longitudinal ultrasonic waves in the tangential phase matching configuration may present some definite advantages over the same interaction using transverse acoustic waves. A systematic search for favorable crystal cuts in lithium niobate was worked out. The main results of this study are reported here; they enable the choice of the best configuration for a given operating center frequency.

Effect of piezoelectricity on the excitation and radiation of acoustic waves in rotated Y-cut quartz

Recently we reported a far field theory of transverse acoustic waves radiated from an interdigital transducer deposited on a singly rotated quartz crystal. This was done by an approximation called the local decoupling approach, allowing us to consider electrical effects as forcing fields for the mechanical motion. The present analysis demonstrates that this approximation is not valid in predicting the complete spectrum of acoustic waves. It is shown that near the cutoff frequency the bulk wave may be converted into a surface wave of Bleustein–Gulyaev type in the free surface case, and that a surface metallization reinforces the strength of this conversion. Velocity of surface waves are determined by means of the effective permittivity function and correct radiation diagrams are plotted in the far field.

Acoustic and acousto-optic properties of 3-methyl 4-nitropyridine 1-oxide—a Brillouin scattering study

The complete set of elastic and photoelastic constants of 3-methyl 4-nitropyridine 1-oxide (POM) organic single crystals is measured by Brillouin scattering. The acousto-optic figures of merit are then derived and the anisotropy of the longitudinal and transverse acoustic wave velocity clearly evidenced from the knowledge of these constants. POM appears to be a promising material for acousto-optical devices as light deflectors and modulators. It is shown that a Bragg cell using POM as an interaction medium would combine several favorable technical features.

Acoustical activity in tellurium

Acoustical activity of the single crystal Te has been studied by measuring the splitting of the degeneracy of transverse acoustical waves propagating along the high symmetry direction, using the coherent inelastic neutron scattering technique. A linear relation between this splitting ( Δv) and the reduced wave vector ( q) was found in the region of q = 0.125 to the boundary of the Brillouin zone; but for q < 0.125, it seems that a quadratic relation predicted by theory was shown. A discussion of these results is also made.

Angular and temperature dependence of depolarized and polarized Rayleigh–Brillouin spectra of poly(methylphenylsiloxane)

The angular and temperature dependence of polarized and depolarized Rayleigh–Brillouin spectra of poly(methylphenylsiloxane) is studied with a Fabry–Perot interferometer. Considerable dispersion is observed in the polarized spectrum. The dispersion is interpreted as arising from structural relaxation. In the depolarized spectrum, evolution from an overdamped spectrum to the one showing shifted side peaks due to transverse acoustic waves are observed. The frequency of the transverse acoustic wave is found to decrease with increasing temperature and becomes vanishingly small at high temperature.

Electric and magnetic field structures of transverse piezoactive surface acoustic waves in crystal symmetry classes $$\bar 4$$ 3m, 23

Electric and magnetic field structures of transverse piezoactive surface acoustic waves in crystal symmetry classes $$\bar 4$$ 3m, 23

Nonlinear dynamics for proper ferroelastic transitions for which the landau condition is violated

Abstract On the basis of a lattice model the domain structure for ferroelastic transformations is examined. The model accounts for both strongly nonlinear and competing interactions which allow for, in some situations, the propagation of nonlinear excitations. The model can be mostly applied to proper ferroelastic transformations of which In-Tl, Ti-Ni, etc.… are good prototypes. The phonon dispersion of the transverse acoustic waves obtained in the linearized case is discussed and the results show first a phonon softening at nonzero wave-number and next an upwards convexity of the phonon branch near the long-wavelength limit. This can be seen as pre-transitional effects. In a fully nonlinear case we consider vanishing dilatation transformations and the continuum approximation is applied to the one-dimensional version. Then, we investigate nonlinear excitations; three main classes of solution are found: i) quasi-harmonic solutions corresponding to periodically modulated structures in space which is a precu...

Acoustic interface waves in sandwich structures

We present a detailed analysis of acoustic interface waves in symmetrically embedded layers. In such systems generalized Lamb or shear vertical waves, polarized in the sagittal plane, and Love-type or shear horizontal waves, polarized perpendicular to the sagittal plane, can exist. The regions in the plane where these elastic interface waves can exist are discussed. The dispersion curves and the spatial dependence of the displacement fields of these acoustic phonon modes are calculated and presented in graphical form. These calculations were done for both, a general analysis in dependence of two different physical parameters and for two real systems, a Al-W-Al sandwich system and a Ga 1− x Al xAs-GaAs-Ga 1− x Al xAs double heterostructure. We show the possibility of the existence of Stoneley waves in the investigated layered systems in dependence of one of the two parameters. For the case that the speed of sound of the bulk transverse acoustic wave of the surrounding material is larger than that of the layer material, we have found that always an infinity of shear vertical waves localized within the layer exists.

Propagation of transverse bulk and surface acoustic waves in LiNbO/sub 3/ variable time-delay devices

Experimental measurements are reported on voltage-controlled acoustic time-delay lines operating at 1 GHz in the nearly pure shear-horizontal (S-H) mode in 38 degrees rotated Y-cut LiNbO(3). The high-acoustic velocity (4800 m/s) in conjunction with the large electroacoustic effect exhibited by this orientation allows high-frequency operation and optimum time-delay tuning sensitivity with a planar, single surface, device geometry. The authors demonstrate fractional time delay of 0.3x10(-6) V(-1 ) for surface electrodes that produce an in-plane E-field. However, the simultaneous excitation and propagation of both a leaky surface-acoustic wave (LSAW) and surface skimming bulk wave (SSBW), both as (nearly pure) S-H waves in these devices, seriously restricts the extent to which it is possible to maximize the time delay modulation sensitivity by reducing electrode gap spacing as done in similar SAW devices. The LSAW and surface-skimming body wave (SSBW) propagate at nearly the same velocity on a free surface, and perturbation of their velocity and relative attenuation rates by surface electrodes causes pronounced interference effects between the two modes for some device geometries.

Optical pulse compression using a TeO_2 acousto-optical light deflector

A new technique for optical pulse compression is proposed that incorporates abnormal Bragg diffraction in a TeO2 acousto-optical deflector. A transverse acoustic wave in TeO2 with a velocity as slow as 616 m/sec and a carrier frequency of 250 MHz produces a dispersion constant of 0.1 psec/nm at 600 nm. The 300-fsec optical pulse from a cavity-damped, synchronously pumped laser is successfully compressed to 70 fsec with a peak power of 83 kW.

Symmetry aspects of pretransformation behavior in metallic alloys

This paper deals with pretransformation behavior in both mineral and alloy systems. Theory that has previously been developed on the existence of local structural variants in incommensurate structures is reviewed and later applied to the study of local interactions in pretransformation phenomena. A review of the pretransformation behavior in both potassium feldspar and the mineral cordierite shows that the important feature in both cases is a very strong interaction between two orthogonal transverse acoustical waves to create a local shear structure. In the case of potassium feldspar this shear structure is the required product in the transformation, but in cordierite the first shear structure to appear in the pretransformation mechanism is not the correct one. Why this should be is explained in detail from a group theoretical analysis of the situation. Ultimately in cordierite this initial structure gives way to the correct structure with the appearance of twinning. The theory developed from the study of the mineralogical examples is then applied to the familiar cubic to tetragonal martensitic transformation in alloys such as In Tl with satisfactory results.

A new fourth-rank tensor for describing the acoustical activity of crystals

The phenomenon of acoustical activity, occurring in all noncentrosymmetric crystals, is analysed in terms of a new fourth-rank pseudotensor which is completely equivalent to the higher-rank (fifth-rank) acoustic gyrotropic tensor used so far in the literature. The nonvanishing independent components of the fourth-rank tensor are tabulated for all the crystal classes. The term 'pure ferro-acoustogyrotropy' is introduced to describe the effect in which the acoustic rotatory power of a crystal can be switched in sign for the transverse acoustic waves travelling along crystallographic axes of three-fold or higher rotational symmetry (acoustic axes). This effect can occur in ferroic crystals only. The possible ferroic species allowing it are determined and tabulated. A number of crystals are identified as candidates for demonstrating this potentially useful property, the optical analogue of which is already familiar.