Transverse Acoustic Waves Research Articles

Aeroacoustical coupling in a ducted shallow cavity and fluid/structure effects on a steam line

A pure tone phenomenon has been observed at 460 Hz in a piping steam line. The acoustical energy has been identified to be generated in an open gate valve and to be of cavity noise type. This energy is then transmitted to the main pipe by fluid/structure coupling. The objectives here are to display the mechanism of the flow acoustic coupling in the cavity and in the duct through an aeroacoustical analysis and to understand the way of energy transfer from the fluid to the main pipe through a vibroacoustical analysis. Concerning the first objective, an experimental study by means of 2/7 scale models in air is analysed by means of numerical flow simulation. The flow acoustic phenomena are modelled by computing the Euler equations. Two different computations are carried out: in the first one, a pure Euler modelling is used, in the second one, a boundary layer obtained from experimental data is introduced in the computation in order to have a realistic flow profile upstream the cavity. The boundary layer flow profile appears to be essential to recover the experimentally observed coupling between the shear-layer instability and the acoustical transverse mode of the pipe. The numerical results confirm that the second aerodynamic mode is responsible for the oscillation. While the predicted frequency agrees about 1% with the scale model experiments, the predicted amplitude is approximately 15 dB too low. For the second objective, fluid/structure coupling in the main pipe is studied using two fully coupled methods. The first method consists in a modal analysis of the line using a fluid–structure finite element model. The second one is based on the analysis of dispersion diagrams derived from the local equations of cylindrical shells filled with fluid. The way of energy transfer in transverse acoustical waves coupled with flexion-ovalization deformations of the pipe is highlighted using both methods. The dispersion diagrams allow a fast and accurate analysis. The modal analysis using a finite-element model may complete the first one with quantitative data. The link between the fluid/acoustic and the fluid/structure analysis is then the excitation of the transverse acoustical mode of the duct.

Acousto-optic-induced cladding-mode reflection in a blazed-superstructure fiber grating

The coupling phenomenon between the cladding mode and the core mode in a blazed-superstructure fiber grating is experimentally demonstrated in this letter by applying both transverse and longitudinal acoustic waves. This is based on the difference between the cladding-mode wave vector and the core-mode wave vector, which is equivalent to the acoustic wave vector. By this means, a reflectivity-tunable multiwavelength switchable comb filter would be developed for the applications in fiber optics.

Dry Coupling Ultrasonic High Frequency (10–100 MHz) Sensors for Detection of Surface and Tribological Properties at a Submicrometric Scale

Acoustic plane sensors adequately pressed against materials are suitable to measure elastic constants from flight-time measurement, without any coupling fluid for high temperature, with longitudinal and transverse acoustic waves in the megacycle range. Soft delay lines are generally used to match the sample roughness and to make mechanical play correction easier. At the opposite, our sensors use a hard delay line with a mirror-polished end surface. An experimental set-up is presented to perform acoustic reflection measurement in various contact conditions by increasing the applied mechanical load. The frequency dependence of this parameter is also measured in the 10- to 100-MHz range. Reproducibility tests are presented to validate this experimental set-up, but the main results concern the surprising ability of this technique to detect surface property modifications limited to thickness less than 1 μm. Indeed, surface modification induced by different solvents on glass substrates has been detected by this means. This technique has also been used to detect surface property modifications of lixiviated glasses. In this case, atomic force microscopy and inductively coupled plasma analyses have demonstrated that the earlier stage of the surface damage had been detected whereas the thickness altered by ionic diffusion was less than 100 nm with almost no roughness variation. Similarly, tests on mechanically scratched glasses have shown that samples with an average roughness, respectively, of 4 and 120 nm were easily identified from their reflection coefficient versus load curves. Moreover, the pressure dependence of the acoustic reflection is used to estimate the contact stiffness and the contact area between the sensor and the material as a function of the applied compressive stress for contact, adhesion, and friction investigations.

Reflection and refraction of acoustic waves from the insulator-magnetoacoustic material interface

The reflection and refraction of longitudinal and transverse acoustic waves by the plane interface between an insulator and an easy-plane antiferromagnet undergoing a magnetic-field-induced orientational phase transition are analyzed. The angles of refraction, as well as all four coefficients of wave conversion, can be effectively controlled by varying the field. Conditions for the appearance of the critical angles of internal reflection and the effect of the magnetic field on these angles are considered. A glancing wave radiated into the material is shown to be a possibility near the phase transition.

The evolution of longitudinal and transverse acoustic waves in a medium with paramagnetic impurities

We study the bipartial interaction of longitudinal and transverse acoustic pulses with a system of paramagnetic impurities with an effective spin S=1/2 in a crystalline layer or on a surface in the presence of an arbitrarily directed external constant magnetic field. We derive a new system of evolution equations that describes this interaction and show that, in the absence of losses, for equal phase velocities of these acoustic components, and under the condition of their unidirectional propagation, the original system reduces to a new integrable system of equations. The derived integrable system describes the pulse dynamics outside the scope of the slow-envelope approximation. For one of the reductions of the general model that corresponds to the new integrable model, we give the corresponding equations of the inverse scattering transform method and find soliton solutions. We investigate the dynamics and formation conditions of the phonon avalanche that arises when the initial completely or incompletely inverted state of the spin system decays. We discuss the application of our results to describing the interaction dynamics of spins and acoustic pulses in various systems with an external magnetic field.

Acoustic Fields of Bulk Acoustic Waves Excited by Phase Velocity Scanning of Laser Interference Fringes

Directivity and generation efficiency of transverse and longitudinal bulk acoustic waves (BAWs) excited by phase velocity scanning (PVS) of laser interference fringes were theoretically investigated. Formulas were derived for the BAW generation based on scanning interference fringes (SIF) which were produced by intersecting two coherent laser beams with different frequencies on an opaque specimen. It was deduced that the amplitude of the BAW was proportional to the product of the scanning length of the SIF and the directivity pattern due to the thermoelastic line source. Unidirectionality of the BAW generated by the SIF was theoretically verified in an ideal state.

Anomalies of the Boundary Reflection of Ultrasound from the Film of a Dissipative Medium

Theoretical consideration has been given to the reflection of continuous and pulsed longitudinal and transverse acoustic waves from the film of a dissipative medium which is in contact with a solid-state half-space. It has been shown that the reflection coefficient and its phase substantially depend on the coefficient of attenuation of ultrasound in the dissipative-medium film and on its phase thickness. The shape of the reflected acoustic pulsed signal has been calculated using software. The application of the results obtained to investigation of the acoustic properties of viscous fluids is discussed.

Acoustoelastic effect in stressed heterostructures.

Mechanical stresses influence the phase velocity of acoustic waves, known as the AE (acoustoelastic) effect. In order to calculate the AE effect of biaxially stressed layered systems, we extended the transfer matrix method for acoustic wave propagation by considering the change of the density, the influence of residual stress, and the modification of the elastic stiffness tensor by residual strain and by third-order constants. The generalized method is applied to the calculation of the angular dispersion of the AE effect for transverse bulk modes and surface acoustic waves on Ge(001). Our calculations reveal that the AE effect significantly depends on the propagation direction and can even change sign. The maximal velocity change occurs for transversally polarized waves propagating parallel to the [110] direction. For the layered Ge/Si(001) system, the AE effect is investigated for Love modes propagating in the [100] and [110] directions. The AE effect increases rapidly with increasing layer thickness and almost reaches its maximal value when the wave still penetrates into the unstressed substrate.

Shear horizontal acoustic waves at the boundary of two piezoelectric crystals separated by a liquid layer

Transverse acoustic waves that occur at the boundary of two piezoelectric halfspaces separated by a viscoelastic liquid layer are studied theoretically. Three variants of layered structures with different numbers of metallized interfaces are considered. It is demonstrated that two types of waves exist in each of these structures. The waves are localized near the boundaries and differ in both their structure and the dependences of the complex wave numbers on the frequency or the gap width. The properties of this family of shear horizontal waves are described.

Structure of the charge-density wave in(TaSe4)2I

(TaSe4)2I is a quasi-one-dimensional (1D) electrical conductor.It exhibits a phase transition at TCDW = 263 K towards acharge-density-wave (CDW) state at low temperatures. We report afull structure refinement of the incommensurately modulatedstructure in the CDW state at T = 110 K against synchrotronradiation, single-crystal x-ray diffraction data. At roomtemperature the crystal structure has tetragonal symmetry with spacegroup I422. In the CDW state each main reflection in the x-rayscattering is surrounded by eight incommensurate satellites at (±0.064,±0.064,±0.151). The CDW state is found to comprisefour domains, and it is characterized by one modulationwavevector. With respect to a √2×√2×1supercell it has the symmetry of the superspace groupF2(0,β,γ) with β = 0.128 and γ = 0.151. Thefirst part of the modulation is found to be a transverse acousticwave, involving amplitudes of similar magnitudes of about 0.13 Å on all atoms. The second part of the modulation involvesdisplacements of the Ta atoms of about 0.03 Å, that are parallelto the 1D chains. These are interpreted as reflecting the CDW. ALandau free-energy model is developed, that shows that symmetryarguments allow the phase transition to be second order.

Self-induced acoustic transparency in the long-short-wave resonance mode

The effect of self-induced acoustic transparency for transverse-longitudinal pulses propagating along an external magnetic field in a system of resonance paramagnetic impurities with the effective spin S=1/2 is theoretically investigated. In this case, the short-wave transverse component of the pulse causes quantum transitions, and the longitudinal long-wave component dynamically shifts the frequency of those transitions. When the speeds of the longitudinal and transverse acoustic waves in the crystal matrix are close to each other, both components interact in the mode of the long-short-wave resonance, which is described by a system of nonlinear integro-differential equations. It is shown that this interaction results, in particular, in the modulation of the carrier frequency of the circular-polarized component of the pulse. More precisely, the frequency in the neighborhood of the signal’s maximum is less than in the vicinity of its edges. Solutions in the form of traveling 2π-pulses are analyzed analytically and numerically. It is shown that there exist solutions that include a longitudinal component and cannot be reduced to well-known transverse solitons of the sinus-Gordon equation.

Transverse Brillouin Effect Produced by Electrostriction in Optical Fibers and Its Impact on Soliton Transmission Systems

Large radial gradient of light intensity in single-mode fibers leads to excitation of transverse acoustic waves through electrostriction mechanism. The nanosecond range for the acoustic effect introduces a time-dependent index evolution for the optical pulses following and results in an additional temporal shift. The dynamic frequency shift of optical pulses in optical fibers is evaluated by a time-domain resolution technique using copropagated pump and probe signals arrangement. Complete electrostrictive response measurements including excitation of pure radial and mixed torsional–radial acoustic modes are presented. In a second time, the acoustic effect is incorporated in the nonlinear Schrödinger equation as a perturbative term. We have investigated the evolution of timing jitter, taking into account both the Gordon–Haus and the acoustic interaction contributions for different dispersion management soliton system configurations in order to evaluate the induced penalties.

Investigations on plasma-polymer-coated SAW and STW resonators for chemical gas-sensing applications

Results from gas probing with various analyte vapors on high-Q low-loss surface transverse wave (STW) and surface acoustic wave (SAW) resonators coated with thin plasma-polymer films of hexamethyldisiloxane (HMDSO), styrene, and allyl alcohol at different polymerization conditions are presented in this paper. At the same acoustic wavelength of 7.22 /spl mu/m and identical film thicknesses, HMDSO-coated STW devices feature substantially higher relative sensitivities to all analytes compared to their SAW counterparts. When operated in a microwave oscillator loop, plasma-poly-styrene and allyl-alcohol-coated STW devices generate strong sensor signals, even at low analyte concentrations, retaining an oscillator short-term stability in the 1/spl times/10/sup -9//s to 1/spl times/10/sup -8//s range. A 250 kHz sensor signal with 7/spl times/10/sup -9//s stability was obtained from a styrene coated 700 MHz STW resonator oscillator at a 1400 parts per million concentration of xylene vapor, which results in a measurement resolution of less than 40 parts per billion for xylene in the ambient air. It is shown that, with respect to sensitivity and stability over long probing periods, plasma-polymer films may become a serious competitor to the more or less unstable soft polymer coatings currently used in SAW-based gas sensors for applications in wireless systems for environmental control and protection.

Interaction of collinear transverse acoustic waves in cubic crystals

In isotropic solids, transverse acoustic waves propagate undistorted and the interaction of collinear transverse waves is forbidden. We stress here that transverse waves behave differently in anisotropic solids and we give experimental evidence for the interaction of transverse acoustic waves propagating along the threefold axis of a cubic crystal.

Intramolecular origin of the fast relaxations observed in the brillouin light scattering spectra of molecular glass formers

The Brillouin light scattering spectra of the o-terphenyl single crystal are compared with those of the liquid and the glass phases. This shows (i) the direct evidence of a fast relaxation at frequencies nu approximately 5 GHz in both the single crystal and the glass; (ii) a similar temperature dependence for the attenuation of the longitudinal sound waves in the single crystal and the glass; and (iii) the absence of coupling between the fast relaxation and the transverse acoustic waves. These results allow us to assign such a relaxation to the coupling between the longitudinal acoustic waves and intramolecular vibrations, and therefore to exclude any relationship between it and the glass transition.

Acoustoelastic effect in anisotropic layered structures

Mechanical stress alters the velocity of acoustic waves, a phenomenon known as AE (acoustoelastic) effect, which is of particular importance for the wave propagation in layered heterostructures. In order to calculate the AE effect of layered systems in the presence of stress we extended the transfer-matrix method for acoustic wave propagation by considering the change of the density, the influence of residual stress, and the modification of the elastic stiffness tensor by residual strain and by third-order constants. The generalized method is applied to the calculation of the angular dispersion of the AE effect for transverse bulk modes and surface acoustic waves on the Ge(001) crystal cut. The AE effect is found to depend significantly on the propagation direction and can even change sign. The maximum velocity change occurs for transversally polarized waves propagating parallel to the [110] direction. For the layered Ge/Si(001) system the AE effect is investigated for Love modes propagating in the [100] and [110] directions. The AE effect increases rapidly with increasing layer thickness and reaches almost its maximum value when the wave is still penetrating into the unstressed substrate. For higher-order Love modes the increase of the AE effect is even steeper and, furthermore, can reach higher values.

Anisotropic Nonlinear Elastic Properties of an Icosahedral Quasicrystal

We show that the nonlinear behavior of transverse acoustic waves can reveal the anisotropic structure of an icosahedral quasicrystal, at the macroscopic level. We report experiments performed in i-Al-Pd-Mn. We observe that a primary transverse acoustic wave can generate a second harmonic transverse acoustic wave. We also observe a specific relation between the polarization directions of those waves. These observations are manifestations on a macroscopic scale of the long-range order in quasicrystals.

Acousto-electric effect induced by transverse acoustic waves in a mixed state of type-II superconductors

A transverse ultrasonic wave should drag the vortex structure of superconductors at an acute angle with respect to the direction of wave propagation. The oscillation of the vortex density and the directed motion of the vortices give rise to a constant component of electric field in a bulk of the superconductor. The effect should be observed in all type-II superconductors above the irreversibility line.

Transverse elastic waves in superlattices: The Brewster acoustic angle

We use a plane wave basis to study the transverse acoustic waves in elastic superlattices---artificial binary structures of periodic mass density $\ensuremath{\rho}(z)$ and periodic transverse elastic velocity ${c}_{t}(z).$ The bulk frequency bands for oblique propagation support minigaps that can close due to the edge crossing of subsequent bands. Some of these crossings are explained in terms of the acoustic Brewster angle ${\ensuremath{\theta}}_{a\mathrm{B}}$ that is a function of the material parameters only. A second condition for the complete shrinking of the gaps that involves the structural parameters is also discussed. The surface waves in the corresponding truncated superlattices are obtained by use of the supercell method. The dispersion curves of these waves are strongly dependent on the material of the layer at the surface---the surface waves that appear for a selected layer at the surface can completely disappear when the last layer is the other one. Specific applications are given for Zn/Fe, Pb/Ge, and Si/Au superlattices.

Interfacial Properties and the Response of the Transverse Acoustic Wave Device in Electrolytes

An analysis of electrical effects associated with the operation of thickness-shear-mode acoustic wave sensors in liquid is presented. A frequent observation found for this system is that the magnitude and the sign of frequency changes cannot be explained by the previously developed mass- and the viscous-loading formulations. These discrepancies are attributed, in part, to the electric properties of the liquid layers in the vicinity of the device electrode. Using network analysis, the resonance frequencies and the equivalent circuit parameters of the device were monitored for a variety of electrolytes in the concentration range 1 to 3000 mM. A nonlinear and periodic dependence was found between both the series resonance frequency and the motional resistance parameter of the device with respect to concentration of electrolyte. Unlike the case of viscous-loading of the sensor, which is known to exhibit a linear and inversely proportional relationship between frequency change and motional resistance, the electrolyte loading of the device yields an unexpected spiral dependence of the two quantities. The spiral dependence provides further proof for the periodicity of the dependence of the series resonance frequency and motional resistance parameter on electrolyte concentration. This finding has important implications for the development of acoustic wave biosensors, since solutions of biochemical species usually involve electrolytes of variable composition, which may affect the electrical double layer structure and, in turn, the response of the sensor.