Longitudinal Acoustic Velocity Research Articles

Atomistic calculations of structural and elastic properties of serpentine minerals: the case of lizardite

The physical properties of the hydrous phyllosilicate lizardite have been investigated by atomistic simulation using the GULP code based on transferable semi-empirical interatomic potentials. Lizardite behavior was first investigated during structure relaxation at room temperature. The Helmholtz free energy is minimum for an equilibrium structure that is in agreement with experiment. The bulk, shear, and Young modulii for lizardite were calculated along with the Poisson ratio. From the shear and bulk modulii, we also calculated translational and longitudinal acoustic wave velocities that are important quantities for tectonophysics models. As expected, lizardite is stiffer in the a direction parallel to the layers than in the c perpendicular direction; the variation of the unit cell parameters with pressure is in good agreement with experiment. The cohesive energy between two successive layers along c direction was calculated at 0.33 eV (i.e., 0.11 eV per OH bond) in good agreement with recent ab initio calculations. Upon pressure and temperature variations, we evidenced that structural changes are mainly pressure induced; pressure being accommodated by a decrease of the c parameter up to 10 GPa. We also found that the change of slope in the derivative of the c cell parameter with respect to pressure occurring around 2 GPa originates from the bending of the interlayer hydroxyl groups with respect to the layer normal direction.

Forward Brillouin scattering in holey fibers

Forward Brillouin scattering behavior of a holey fiber (HF) is investigated experimentally. The shear and longitudinal acoustic velocities are evaluated from measurements of forward and backward Brillouin scattering, respectively. Experimentally obtained results reveal that the acoustic velocity ratio, given as /spl alpha/ (=shear velocity V/sub S//longitudinal velocity V/sub L/), decreases as the ratio of the total air-hole area to fiber cross-sectional area becomes large. This means that increasing the air-hole area in an HF's cross section lowers the shear velocity with respect to the mixed tortional-radial (TR/sub 2m/) modes.

Ab initio study of the structure and dynamical properties of crystalline ice

We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase, in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3× 1× 1 supercell using the direct method. So far, due to the direct method used in this calculation, the phonon spectra are obtained without taking into account the effect of polarization arising from dipole–dipole interactions of water molecules, which is expected to yield the splitting of longitudinal and transverse optic modes at the Γ point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode are in reasonable agreement with the neutron scattering data. Analysis of the vibrational density of states shows the existence of a boson peak at low energy of the translational region, a characteristic common to amorphous systems.

Application of inelastic X-ray scattering to the measurements of acoustic wave velocities in geophysical materials at very high pressure

Reference Earth global models used by geophysicists are mostly constrained by analysing seismic waves that travel in the Earth. The interpretation of these seismological models in terms of chemical composition and temperature thus relies on the knowledge of the chemical composition, structure and elastic properties of some candidate materials relevant to geophysics. We will describe some recent advances in experimental mineral physics which yield essential information on the elastic properties of pertinent materials of Earth’s mantle and core. In particular, we show that inelastic X-ray scattering (IXS) proves to be a well suited spectroscopic technique for the study of phonon dispersion in materials under high pressure. Inelastic scattering experiments carried out on polycrystalline samples provide measurements of orientationally averaged longitudinal acoustic velocities whereas investigations on single crystals yield elastic moduli. Such a technique is thus highly interesting for mineral physicists and offers a great potential in providing essential elastic data and their pressure and/or temperature dependence on most compounds of geophysical interest.

Analysis of brillouin frequency shift and longitudinal acoustic wave in a silica optical fiber with a triple-layered structure

We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO/sub 2/-doped core, P/sub 2/O/sub 5/, and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 /spl mu/m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.

Role of Am Piezoelectric Crystal Orientation in Solidly Mounted Film Bulk Acoustic Wave Resonators

To investigate the effect of AlN c-axis orientation on the resonance performance of film bulk acoustic wave resonators, solidly mounted resonators with crystallographically different AlN piezoelectric films were prepared by changing only the bottom electrode surface conditions. As increasing the degree of c-axis texturing, the effective electromechanical coupling coefficient (k eff )² in resonators increased gradually. The least 4 degree of full width at half maximum in an AlN (002) rocking curve, which corresponds to k² eff of above 5%, was measured to be necessary for band pass filter applications in wireless communication system. The longitudinal acoustic wave velocity of AㅣN films varied with the degree of c-axis texturing. The velocity of highly c-axis textured AㅣN film was extracted to be about 10200 m/s by mathematical analysis using Matlab.

Acoustooptic spectroscopy of metal structure modifications under plastic deformation due to submicrosecond impulsive shock loading

Restructuring in metals due to elastoplastic deformation produced by submicrosecond impulsive shock loading is studied experimentally. Tests are performed on 0.3ZhR iron and N1 nickel specimens with various structures. Structure modifications after shock tests are studied with acoustooptic spectroscopy. The frequency dependences of the longitudinal acoustic velocity and attenuation coefficient make it possible to estimate both the characteristic scales of restructuring in relation to the initial structure and the sensitivity of the acoustooptic method to restructuring in various materials.

High-pressure Brillouin study on methane hydrate

Acoustic velocities and adiabatic elastic constants of structure I of methanehydrate (MH) have been determined as a function of pressure up to 0.6 GPa at23°C by the high-pressure Brillouin spectroscopy developed for a singlemolecular crystal. The pressure dependence of the acoustic velocities of MH isvery similar to that of ice-Ih except for the longitudinal acoustic (LA)velocity. The value of the LA velocity along the ⟨100⟩direction of MH at 0.02 GPa is 3.63 km s−1 which is about 7% lower than theaverage of the LA velocities in the ice-Ih phase at −35.5°C and atmosphericpressure.

Sound velocities in iron to 110 gigapascals.

The dispersion of longitudinal acoustic phonons was measured by inelastic x-ray scattering in the hexagonal closed-packed (hcp) structure of iron from 19 to 110 gigapascals. Phonon dispersion curves were recorded on polycrystalline iron compressed in a diamond anvil cell, revealing an increase of the longitudinal wave velocity (VP) from 7000 to 8800 meters per second. We show that hcp iron follows a Birch law for VP, which is used to extrapolate velocities to inner core conditions. Extrapolated longitudinal acoustic wave velocities compared with seismic data suggest an inner core that is 4 to 5% lighter than hcp iron.

High Frequency Thin Film Acoustic Ferroelectric Resonators

AbstractBoth ZnO and PZT Thin Film Bulk Acoustic Resonator filters were fabricated, tested and modeled in this study. The development of an accurate Mason model allows the effect of particular parasitic components on the microwave s-parameters in the region of the series and parallel resonances to be identified. The parasitic components that limit the performance of our ZnO and PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filters are analysed. From an analysis of PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator measurements values for the longitudinal acoustic velocity and electromechanical coupling coefficient can be derived. Measured PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filter responses confirm that the larger electromechanical coupling coefficients in this material compared to ZnO give wider filter band-widths.

MICROSCALE THERMAL RELAXATION DURING ACOUSTIC PROPAGATION IN AEROGEL AND OTHER POROUS MEDIA

The longitudinal acoustic velocity in silica aerogel is presented as a function of the interstitial gas type and pressure. This was measured using air-coupled ultrasonic transducers configured for differential pulse transit time measurements. The results are interpreted in terms of the thermal relaxation of the acoustic pulse. The microscale temperature oscillations of the gas and solid phases of the aerogel due to the acoustic pulse are not identical if the rate of heat transfer between the two phases is slow compared to the period of the acoustic oscillation. The energy transferred from the gas to the solid phase is lost to the acoustic propagation and, thus, reduces the amplitude and velocity of the acoustic wave. The gas type and pressure may provide independent variables for probing these effects in aerogel.

Influence of the deposition conditions on the elastic properties of chemical vapor deposited (CVD) diamond films studied by laser ultrasonics

One of the aims in optimizing the deposition of CVD diamond is to increase the stiffness. Laser ultrasonics offers a useful tool to nondestructively investigate elastic parameters of materials. A colored liquid–transparent free-standing film configuration allowed the excitation and detection of pseudo-Lamb waves in order to simultaneously determine the longitudinal (vL) and transverse (vT) acoustic velocity of the film. The absorption of pulsed laser light by the colored liquid served as an efficient conversion mechanism of optical energy into elastic energy. The excited waves were detected with a wide bandwidth photodeflection setup. Several free-standing films, deposited under different conditions, were investigated.

Temporal deconvolution of laser-generated longitudinal acoustic waves for optical characterization and precise longitudinal acoustic velocity evaluation

The laser thermoelastic generation of ultrasound is a promising technique with many potential applications, but it is also a complicated process with many physical phenomena involved. Contrary to a conventional piezoelectric transducer generation, which is a surface phenomenon, a laser generation can activate acoustic sources within the material by optical penetration of the excitation wavelength, resulting in asynchronous wave arrivals at a given point. More generally, in the ideal case of a nondispersive isotropic material, the laser-ultrasonics displacement signals result from temporal convolutions between optical penetration, laser pulse duration, and laser spot extension effects. In this paper, a deconvolution technique is presented that extracts the laser pulse duration contribution from the experimental displacement signals. This deconvolution scheme applied to one-dimensional experiments, in which the laser excitation is spread over a sufficiently large area on the front side of the sample, allows the measurement of the optical absorption coefficient of the material at the excitation wavelength and also a precise evaluation of its longitudinal acoustic velocity.

Elastic properties of tetragonal PbTiO3 single crystals by Brillouin scattering

Brillouin light scattering was used to obtain the elastic and piezoelectric constants for tetragonal PbTiO3 single crystals at room temperature. Approximately 170 measurements of longitudinal and transverse acoustic wave velocities were inverted using literature dielectric constant values to obtain the full set of elastic and piezoelectric constants. Our data indicate a greater electromechanical anisotropy in the polar c direction than previously reported, but are otherwise in general agreement with previous studies. We discuss briefly the degree to which individual elastic and piezoelectric constants are resolved.

Elastic softness of amorphous tetrahedrally bonded GaSb and(Ge2)0.27(GaSb)0.73semiconductors

We have measured the longitudinal and transverse acoustic wave velocities in bulk pressure-amorphized $a$-GaSb and $a\ensuremath{-}({\mathrm{Ge}}_{2}{)}_{0.27}(\mathrm{GaSb}{)}_{0.73}$ semiconductors and in their polycrystalline analogs. Although the densities of crystalline and amorphous states were practically equal, a significant softening of the bulk (29--35 %) and shear (41--46 %) elastic moduli has been found for amorphous phases. The ultrasonic data for bulk moduli are in good agreement with the previous direct volumetric measurements. Results of the present study combined with critical review of previous works allowed us to find specific features of elastic behavior of amorphous tetrahedral semiconductors (including group IV elements and group III-V compounds), and compare them to other classes of disordered solids.

Acoustic properties of irradiated DIGLYCINE NITRATE crystals

Abstract Temperature dependencies of longitudinal acoustic wave velocity and attenuation had been measured in crystals of DIGLYCINE NITRATE (DGN), (NH2CH3OOH)2HNO3, after and before ultraviolet (UV) and neutron irradiation. It was observed that radiation induced defects change dramatically the acoustic properties near the Phase Transition (PT) temperature.

Local, Instantaneous Heat Transfer Coefficients for Jet Impingement on a Phase Change Surface

The local variation in the heat transfer coefficient for an axisymmetric, turbulent, submerged liquid jet impinging on a nonuniform boundary of a phase-change material is measured with an ultrasonic measurement technique. The time required for an acoustic wave to traverse the phase-change material is measured with an ultrasonic transducer and the time data are converted into local thickness profiles of the phase-change material via knowledge of the longitudinal acoustic velocity in the material. An energy balance at the melt interface between the impinging jet and the phase-change material is used in conjunction with the local thickness profile data to determine the local variation in the heat transfer coefficient. The phase-change material is originally flat, but its shape changes with time as the heated jet melts a complex shape into its surface. The heat transfer rate over the surface of the melting interface is shown to vary with time as a result of the changing shape of the phase change material. A deep cavity is melted into the solid at the stagnation point and secondary cavities are melted into the interface for certain jet flow rates and surface spacings between the jet nozzle and the melt interface. When secondary cavities are produced, secondary peaks in the local heat transfer coefficient are observed. The heat transfer data are formulated into two Nusselt number correlations that are functions of the dimensionless time, dimensionless radius, dimensionless jet-to-surface spacing, and jet Reynolds number. One correlation is formulated for all locations along the surface of the phase-change material except the stagnation point, and a second correlation is valid at the stagnation point.

Theory of Transient Reflecting Grating in Fluid/Metallic Thin Film/Substrate Systems for Thin Film Characterization and Electrochemical Investigation

A general theory was developed to calculate the diffraction signals from a transient reflecting grating (TRG) at metallic thin film/substrate interfaces and liquid/solid interfaces. The TRG signals for an Au film/soda lime glass system were experimentally measured and theoretically calculated to examine their agreement. It was found theoretically and experimentally that longitudinal acoustic pulses and echoes with ultrahigh-frequency components (>10 GHz) propagating normal to the sample surfaces are generated and can be detected at the surfaces of thin films, using the TRG technique, along with surface acoustic waves. By using the time intervals of two neighboring longitudinal acoustic echoes, thicknesses or longitudinal acoustic wave velocities for opaque thin films were determinable. Furthermore, it was shown that this method is applicable to the analysis of electrochemical interfaces in situ, through changes in the thermal and longitudinal acoustic properties of electric double layers with electrochemical potentials.

High-pressure Brillouin study on the orientationally disordered phase of methane

Three elastic constants in the orientationally disordered solid phase of methane have been determined at room temperature, as a function of pressure up to 5 GPa, by Brillouin spectroscopy developed for single crystal grown in a diamond anvil cell. It is found that the velocity of the slow transverse acoustic mode in the 〈110〉 direction is insensitive to pressure as compared with other velocities, which leads to the anomalous increasing of the ratio of the longitudinal acoustic velocity to the slow transverse one in the 〈110〉 direction. This result suggests that the rotation-translation coupling has strong pressure dependence.

High-Pressure Brillouin Study on Orientationally Disordered Solid Phase I of H2S and D2S

Acoustic velocities, refractive index, and elastic constants in the orientationally disordered solid phase I of D 2 S have been determined at pressures up to 5 GPa and room temperature, by Brillouin spectroscopy developed for a single crystal grown in a diamond anvil cell. It has turned out that H 2 S and D 2 S have large values of the ratio of the longitudinal acoustic velocity to the slow transverse one in the [110] direction, i.e., 3.22 and 3.30 at 1 GPa, respectively. These results indicate the molecular rotation-translation coupling is effective in the orientationally disordered phase I. These values of this ratio decrease with increasing pressure, which means that the rotation-translation coupling becomes weak with compression, resulting in stronger hydrogen bond in H 2 S and D 2 S.