Transverse Acoustic Waves Research Articles

Spurious-free Lamb wave resonators with protrusion structures

In this letter, we demonstrate a technique to eliminate the spurious modes in aluminum nitride Lamb wave resonators (LWRs). The transverse acoustic wave characteristics are examined, and a resonance modulation theory on the regulation of mechanical boundary conditions is deducted. As examples of embodiments, vertical and lateral protrusion structures are proposed for the suppression. Finite element analysis verifies that the employment of these structures effectively restrains the transverse modes, and the measured electrical performance of the LWR with protrusions demonstrates an 11 dB reduction in the spurious response.

Acoustical activity of lithium niobate crystals

Acoustical activity in Lithium Niobate crystals was investigated by method of Bragg light diffraction. Transverse acoustic waves were excited in the range of 0.4–1.6 GHz using quartz piezoelectric plates. LiNbO3 samples were oriented at small angles to the axis Z in the crystallographic plane (010). Specific rotation of the polarization plane of transverse waves was determined from the dependence of the intensity of the diffracted light of the distance from the piezoelectric transducer along the acoustic wave propagation. The observed large specific rotation of the polarization plane of the acoustic waves can be used in devices controlling the intensity of light by the phenomenon of acoustical activity. Components of the imaginary part of the generalized Christoffel tensor taking into account the spatial dispersion have been determined also. It is shown that in crystals of class 3m the imaginary components of the Christoffel tensor for all the directions in the symmetry plane (100) are zero.

Acousto-optic investigation of acoustic anisotropy in paratellurite crystals

Propagation velocity and attenuation coefficient of acoustics waves in paratellurite crystals were measured by Bragg diffraction of light in the frequency range of 0.4–1.6 GHz. These results were used for calculation of real and imaginary components of the complex tensor of elastic constants. The analysis of the anisotropy of attenuation was carried out for the acoustic waves of different polarization propagating in the crystallographic planes, which are orthogonal to symmetry axes of second and forth order. The strongest anisotropy of acoustic attenuation and phase velocity is observed for the transverse acoustic waves propagating in the plane (1-10). It is shown that the attenuation reduces the integral efficiency of diffraction in several times in the acousto-optic deflector in which is used an oblique cut of paratellurite and the transverse acoustic wave propagating at an angle of 6 degrees to the [110] axis in the plane (1-10).

Ferrimagnetic resonance and magnetoelastic excitations in magnetoelectric hexaferrites

Static field properties of magnetoelectric hexaferrites have been explored extensively in the past five years. In this paper, dynamic properties of magnetoelectric hexaferrites are being explored. In particular, effects of the linear magnetoelectric coupling $(\ensuremath{\alpha})$ on ferrimagnetic resonance (FMR) and magnetoelastic excitations are being investigated. A magnetoelastic free energy which includes Landau-Lifshitz mathematical description of a spin spiral configuration is proposed to calculate FMR and magnetoelastic excitations in magnetoelectric hexaferrites. It is predicted that the ordinary uniform precession FMR mode contains resonance frequency shifts that are proportional to magnetoelectric static and dynamic fields. The calculated FMR fields are in agreement with experiments. Furthermore, it is predicted at low frequencies (approximately megahertz ranges), near zero magnetic field FMR frequencies, there is an extra uniform precession FMR mode besides the ordinary FMR mode which can only be accounted by dynamic magnetoelectric fields. Whereas the FMR frequency shifts in the ordinary FMR mode due to the $\ensuremath{\alpha}$ coupling scale as $\ensuremath{\alpha}$, the shifts in the new discovered FMR mode scale as ${\ensuremath{\alpha}}^{2}$. Also, magnetoelastic dispersions were calculated, and it is predicted that the effect of the $\ensuremath{\alpha}$ coupling are the following: (1) The strength of admixture of modes and splitting in energy between spin waves and transverse acoustic waves is proportional to $\ensuremath{\alpha}$. (2) The degeneracy of the two transverse acoustic wave modes is lifted even for relatively low values of $\ensuremath{\alpha}$. Interestingly, at low frequencies near zero field FMR frequencies, the surface spin wave mode branch flip-flops with the volume spin wave branch whereby one branch assumes real values of the propagation constant and the other purely imaginary upon the application of a static electric field.

Акустооптические свойства метаматериалов

The possibility of the effective use of metamaterials in acousto-optics is demonstrated. It is shown that photoelastic constants that determine a change in the dielectric constant of a heterogeneous medium under the action of a sound wave can significantly exceed the corresponding constants for conventional crystals. We have analysed the mechanisms of the dielectric constant variation in a heterogeneous medium consisting of nanoparticles in the form of ellipsoids and have found explicitly the values of the photoelastic constants. It is shown that the mechanism of the dielectric constant variation in a longitudinal sound wave is reduced to a change in the local concentration of nanoparticles in the bulk and in a transverse acoustic wave – to a local rotation of space-oriented nanoellipsoids. It is also shown that the use of metamedia with a nonuniform distribution of nanoparticles provides a unique opportunity for designing qualitatively new instruments and devices that cannot be produced on the basis of conventional crystals. It is noted that metamaterials open ample opportunities for creating devices of the IR region of the spectrum due to the absence of restrictions on the size of such media.

Boundary scattering of phonons: Specularity of a randomly rough surface in the small-perturbation limit

Scattering of normally incident longitudinal and transverse acoustic waves by a randomly rough surface of an elastically isotropic solid is analyzed within the small perturbation approach. In the limiting case of a large correlation length $L$ compared with the acoustic wavelength, the specularity reduction is given by $4\eta^2k^2$, where $\eta$ is the RMS roughness and $k$ is the acoustic wavevector, which is in agreement with the well-known Kirchhoff approximation result often referred to as Ziman's equation [J. M. Ziman, Electrons and Phonons (Clarendon Press, Oxford, 1960)]. In the opposite limiting case of a small correlation length, the specularity reduction is found to be proportional to $\eta^2k^4L^2$, with the fourth power dependence on frequency as in Rayleigh scattering. Numerical calculations for a Gaussian autocorrelation function of surface roughness connect these limiting cases and reveal a maximum of diffuse scattering at an intermediate value of $L$. This maximum becomes increasingly pronounced for the incident longitudinal wave as the Poisson's ratio of the medium approaches 1/2 as a result of increased scattering into transverse and Rayleigh surface waves. The results indicate that thermal transport models using Ziman's formula are likely to overestimate the heat flux dissipation due to boundary scattering, whereas modeling interface roughness as atomic disorder is likely to underestimate scattering.

Acoustic anisotropy of acoustooptic TI(3)AsS(4) crystals.

We present comprehensive experimental measurements and analysis of anisotropy of the acoustic wave velocities for TI(3)AsS(4) crystals, including the obliquity and nonorthogonality of the acoustic waves, and the deviations from purely longitudinal and transverse polarization types. We have found that the crystals under analysis are characterized by rather low transverse wave velocities v(23) and v(32), which are both equal to 630 m/s. It is shown that the efficiency of acoustooptic (AO) interactions in TI(3)AsS(4) can be notably increased when providing anisotropic interaction with the slowest transverse acoustic wave. Under the previously mentioned conditions, the AO figure-of-merit can be estimated to be extremely high, i.e., approximately 3×10(-12) s(3)/kg.

Electrical manipulation of crystal symmetry for switching transverse acoustic phonons.

We experimentally explore the use of a novel device where lateral electric fields can be applied to break the translational symmetry within the isotropic plane and hence change the selection rules to allow normally forbidden transverse acoustic (TA) phonon generations. The ultrafast screening of the lateral electric field by the photocarriers relieves shear strain in the structure and switches on the propagating TA waves. The amplitude and on-state time of the TA mode can be modulated by the external field strength and size of the laterally biased region. The observed frequency shift with an external bias as well as the strong geometrical dependence confirm the role of the asymmetric potential distribution in electrically manipulating the crystal symmetry to control modal behavior of acoustic phonons.

Coefficients of Reflection and Transmission of Transverse and Longitudinal Acoustic Wave in the Blatz-Ko Material

Abstract The purpose of this paper is to analyze the propagation of transverse and longitudinal acoustic wave in a composite made of hyperelastic Blatz-Ko material. Composite consists of a homogeneous layer of predetermined thickness d separating two infinite homogeneous material areas. In the paper it is assumed that the middle layer is filled with a homogeneous rubber (ƒ=1), whereas the external areas with foam rubber (ƒ=0). The final effect of paper are graphs of coefficients reflection of transverse and longitudinal acoustic wave, propagating in this composite.

Mechanisms of anomalous compressibility of vitreous silica

The anomalous compressibility of vitreous silica has been known for nearly a century, but the mechanisms responsible for it remain poorly understood. Using GHz-ultrasonic interferometry, we measured longitudinal and transverse acoustic wave travel times at pressures up to 5 GPa in vitreous silica with fictive temperatures $({T}_{f})$ ranging between 985 \ifmmode^\circ\else\textdegree\fi{}C and 1500 \ifmmode^\circ\else\textdegree\fi{}C. The maximum in ultrasonic wave travel times--corresponding to a minimum in acoustic velocities--shifts to higher pressure with increasing ${T}_{f}$ for both acoustic waves, with complete reversibility below 5 GPa. These relationships reflect polyamorphism in the supercooled liquid, which results in a glassy state possessing different proportions of domains of high- and low-density amorphous phases (HDA and LDA, respectively). The relative proportion of HDA and LDA is set at ${T}_{f}$ and remains fixed on compression below the permanent densification pressure. The bulk material exhibits compression behavior systematically dependent on synthesis conditions that arise from the presence of floppy modes in a mixture of HDA and LDA domains.

Short- and long-term dynamic modes of turbulent swirling premixed flame in a cuboid combustor

Direct numerical simulation (DNS) of hydrogen–air turbulent swirling premixed flame in a cuboid combustor is conducted to investigate thermoacoustic instability and dynamic modes of turbulent swirling premixed flame in combustors. A detailed kinetic mechanism and temperature dependency of physical properties are considered in DNS. Two swirl number cases of 0.6 and 1.2 are investigated. Large-scale helical vortical structures are generated near the inlet of combustion chamber, and a lot of fine-scale vortices emerge downstream. Flame structure is engulfed by the vortical structures and depends largely on the swirl number. Spectral analysis of pressure oscillation on walls shows that quarter-wave mode of longitudinal acoustics has the largest energy, and that characteristic oscillations are found at higher frequencies. To investigate oscillation modes of pressure and heat release rate fields, dynamic mode decomposition (DMD) is applied to DNS results. It is shown that there are differences between dominant frequencies in spectral analysis of time-series pressure data at one point of walls and DMD of time-series pressure field data. DMD of pressure field reveals that the quarter-wave mode in longitudinal acoustics has the largest energy for the case of S=0.6. Furthermore, it is clarified that the transverse acoustic plane waves and pressure oscillations induced by large-scale vortical motions play important roles for the pressure oscillations in combustors. DMD of heat release rate field reveals that the DMD modes of pressure with high amplitude do not necessarily have coupling with fluctuations of heat release rate. Interactions between dynamic modes of pressure and heat release rate are also discussed.

Fundamental Understanding of Ferroelectric Properties in Piezoelectric Ceramics from Viewpoints of Domain Alignment

Research and development of controlling and evaluation on ferroelectric domain structures are described in piezoelectric ceramics composed of lead zirconate titanate, lead titanate, barium titanate, alkali bismuth niobate and alkali bismuth titanate. Ferroelectric domain switching and domain rotation could be explained by DC poling field dependence of dielectric and piezoelectric properties. In addition, Young's modulus and Poisson ratio toward poling field in piezoelectric ceramics were investigated by measuring longitudinal and transverse acoustic wave velocities to clarify the relationships between high piezoelectricity and the values. Increasing domain alignment by applying poling field, basically, the Young's modulus decreased and Poisson ratio increased.

Abnormal elastic and vibrational behaviors of magnetite at high pressures.

Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.

Giant ultrafast photo-induced shear strain in ferroelectric BiFeO3.

Generation of strain using light is a key issue for future development of ultrasonic devices. Up to now, photo-induced GHz-THz acoustic phonons have been mainly explored in metals and semiconductors, and in artificial nanostructures to enhance their phononic emission. However, despite their inherent strong polarization (providing natural asymmetry) and superior piezoelectric properties, ferroelectric oxides have been only poorly regarded. Here, by using ultrafast optical pump-probe measurements, we show that photogeneration/photodetection of coherent phonons in BiFeO3 ferroelectric leads, at room temperature, to the largest intensity ratio ever reported of GHz transverse acoustic wave versus the longitudinal one. It is found that the major mechanism involved corresponds to screening of the internal electric fields by light-induced charges, which in turn induces stress by inverse piezoelectric effect. This giant opto-acoustic response opens new perspectives for the use of ferroelectric oxides in ultrahigh frequency acoustic devices and the development of new GHz-THz acoustic sources.

Application of a layered rubber composite to reduce dynamic effects on steel structures

The purpose of paper is to analyze a layered rubber composite aimed at significant reduction in dynamic effects on steel structures. In the first part of the paper there is presented an analytical analysis of transverse and longitudinal acoustic wave propagating in a layered rubber composite made of a material with elastic potential Blatz - Ko. The second part discusses a numerical example showing the behavior of the surface discontinuities propagating in this layered composite, showing the distribution of stresses for the assumed potential and constant material from the first part of the paper. In the paper seeking possibilities of application of the composite inter alia in order to reduce the dynamic effects generated in the process of emptying silos from granular materials which can cause their failures and for the group of silos can lead to the creation and propagation of dynamic oscillations in the subsoil which threaten building located nearby. Issue adopted at work and the obtained results provide the basis for the further numerical study expanding the results.

Transverse acoustic waves in piezoelectric ZnO/MgO and GaN/AlN Fibonacci-periodic superlattices

This work studies the transverse acoustic waves, including the piezoelectric coupling, in Fibonacci superlattices formed by wurtzite ZnO/MgO and GaN/AlN, respectively. We examine also other superlattice structures formed by combining different kinds of Fibonacci sequences and finite periodic systems. The possibility to use different Fibonacci sequences including layers with double length of one of the constituent materials produces important modifications in the dispersion curves. The effect is more important in the lower frequency range and affects the gaps appearing in this frequency range. It is also possible to find narrow and flat bands cutting the original gaps and producing narrower ones. There are modes at different frequency ranges having spatial confinement in one of the constituent parts of the superlattice period.

Acoustic evidence of distinctive temperatures in relaxor-multiferroics

We present an acoustic study of relaxor ferroelectrics with magnetic ordering PbFexB1−xO3 (B = Nb, Ta, W) in the wide temperature range from 100 to 750 K as well as relaxor PbMg1/3Nb2/3O3 at temperatures from 300 to 750 K. The longitudinal and transverse acoustic wave velocity and attenuation have been measured by the ultrasonic pulse-echo technique at frequencies of 5 and 10 MHz. The strong anomalies observed in the longitudinal sound velocity and attenuation versus temperature are correlated with a temperature range of the coexistence of relaxor ferroelectric and antiferromagnetic states. Attenuation peaks have been observed at distinctive temperatures for relaxors, i.e., at TB (Burns temperature) and T* (an additional distinctive temperature). Fluctuations of the polar nanoregion boundaries are considered as the source of the acoustic anomalies.

Ultraweak long-range interactions of solitons observed over astronomical distances

We report what we believe is the weakest interaction between solitons ever observed. Our experiment involves temporal optical cavity solitons recirculating in a coherently-driven passive optical fibre ring resonator. We observe two solitons, separated by up to 8,000 times their width, changing their temporal separation by a fraction of an attosecond per round-trip of the 100 m-long resonator, or equivalently 1/10,000 of the wavelength of the soliton carrier wave per characteristic dispersive length. The interactions are so weak that, at the speed of light, they require an effective propagation distance of the order of an astronomical unit to fully develop, i.e. tens of millions of kilometres. The interaction is mediated by transverse acoustic waves generated in the optical fibre by the propagating solitons through electrostriction.

Velocity and Flame Wrinkling Characteristics of a Transversely Forced, Bluff-Body Stabilized Flame, Part II: Flame Response Modeling and Comparison with Measurements

This article analyzes the response of bluff-body stabilized flames to transverse acoustic waves. Data were obtained for bluff-body flames at flow velocities of 50 m/s and 100 m/s with inlet air temperatures ranging from 475–750 K. Two different modes of acoustic excitation were applied, corresponding to velocity and pressure nodes/antinodes along the combustor centerline. High-speed imaging and phase-locked particle image velocimetry (PIV) were used to characterize the spatio-temporal flame front and velocity field response. The key objective of the study is to compare measurements of the fluctuating velocity and flame wrinkling using the G-equation, e.g., to compare how the ensemble averaged unsteady flame wrinkling gain/phase predicted by solving the G-equation using the measured velocity field as inputs compares to the measured values. These results show good qualitative agreement between the comparisons and measurements, and quite good quantitative accuracy in many of the cases. These comparisons also enable insight into the features controlling the unsteady flame wrinkling; for example, it enables insight into the relative contributions of acoustic and vortical disturbances on the flame wrinkling characteristics, whose different propagation velocities lead to interference patterns and oscillatory flame wrinkle amplitude characteristics.

Velocity and Flame Wrinkling Characteristics of a Transversely Forced, Bluff-Body Stabilized Flame, Part I: Experiments and Data Analysis

This article describes measurements of the response of bluff-body stabilized flames subjected to transverse acoustic waves. It is the first of a two-article series. The objective of this work was to extend prior studies of this nature to much higher Reynolds numbers and more severe environments that more closely mimic conditions encountered in applications. To this end, experiments were performed at flow velocities of 50 m/s and 100 m/s with inlet air temperatures ranging from 475–750 K. Two different modes of acoustic excitation were applied, corresponding to velocity and pressure nodes/antinodes along the combustor centerline. High-speed imaging and phase-locked particle image velocimetry (PIV) were used to characterize the spatio-temporal flame front and velocity field response. The data show that the disturbance field and the flame front response amplitude exhibit a nonmonotonic spatial distribution with interference patterns. The phase of the flame front response at the forcing frequency varies nearly linearly with downstream distance, and corresponds to a phase speed that is slightly less than the mean flow velocity. Significantly, these results show that the key features of the flame's magnitude and phase characteristics are quite similar to those observed in much lower flow velocities.