Longitudinal Acoustic Waves Research Articles

Array of piezoelectric lateral electric field excited resonators

An array containing two resonators placed on X-cut lithium niobate plate has been experimentally investigated. The resonator’s lateral electric field was directed along the Y-crystallographic axis. It has been shown that stable resonance exists for a longitudinal acoustic wave propagating along the X-axis in the area between the electrodes. A layer of special damping coating was deposited around the resonators and on the part of electrodes to suppress parasitic oscillations induced mainly by Lamb waves. Frequency dependences of the real and imaginary parts of electric impedance/admittance were measured for every resonator to find resonant frequency and Q-factor with series and parallel resonances. The optimal values of width of electrode coating for every resonator were revealed which provide good resonance quality. The measurements of parameter S12, which characterizes a degree of acoustical coupling between the resonators, have shown its value to be higher than 50dB in the absolute value in all the cases considered. This means that the resonators under study are entirely acoustically decoupled. Thus it has been demonstrated that the damping layer not only provides a sufficiently good quality of every resonator’s resonance, but it also assures their entire acoustical decoupling.

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.

Acousto-optic modulation of a fiber Bragg grating in suspended core fiber for mode-locked all-fiber lasers

The interaction of a fiber Bragg grating and longitudinal acoustic waves in a three-air-holes suspended core fiber is experimentally investigated and employed to mode-lock an ytterbium-doped fiber laser. An optimized design of an acousto-optic modulator based on two piezoelectric transducers and 1 cm grating length is also proposed. For an electrical signal strength of 10 V applied to the modulator, the results indicate output pulses with a width of less than 550 ps at a repetition rate of 10 MHz. The reduction of the grating length and the power consumed by the transducer, when compared to previous studies, points out to more efficient, compact and fast acousto-optic modulators for mode-locked all-fiber lasers.

Longitudinal dust acoustic solitary waves in a strongly coupled complex (dusty) plasma

The dynamics of the weakly nonlinear and weakly dispersive low frequency longitudinal dust acoustic waves (LDAWs) in a strongly coupled complex (dusty) plasma are investigated using generalized hydrodynamic (GH) model. In presence of strong correlation, the nonlinear wave is shown to be governed by a Korteweg–de Vries (KdV) equation with a nonlocal nonlinear forcing and a linear damping terms. This novel equation is solved numerically to show the competition between nonlinear forcing and dissipative damping in the formation of the localized structures.

Analytical study of the propagation of fast longitudinal modes along wz-BN/AlN thin acoustic waveguides.

The propagation of the fundamental symmetric Lamb mode S0 along wz-BN/AlN thin composite plates suitable for telecommunication and sensing applications is studied. The investigation of the acoustic field profile across the plate thickness revealed the presence of modes having longitudinal polarization, the Anisimkin Jr. plate modes (AMs), travelling at a phase velocity close to that of the wz-BN longitudinal bulk acoustic wave propagating in the same direction. The study of the S0 mode phase velocity and coupling coefficient (K2) dispersion curves, for different electrical boundary conditions, has shown that eight different coupling configurations are allowable that exhibit a K2 as high as about 4% and very high phase velocity (up to about 16,700 m/s). The effect of the thickness and material type of the metal floating electrode on the K2 dispersion curves has also been investigated, specifically addressing the design of an enhanced coupling device. The gravimetric sensitivity of the BN/AlN-based acoustic waveguides was then calculated for both the AMs and elliptically polarized S0 modes; the AM-based sensor velocity and attenuation shifts due to the viscosity of a surrounding liquid was theoretically predicted. The performed investigation suggests that wz-BN/AlN is a very promising substrate material suitable for developing GHz band devices with enhanced electroacoustic coupling efficiency and suitable for application in telecommunications and sensing fields.

Detailed numerical investigation of the interaction of longitudinal acoustic waves with fiber Bragg gratings in suspended-core fibers

The interaction between longitudinal acoustic waves and fiber Bragg gratings in suspended-core optical fibers is numerically investigated. The fiber core size and the air hole size are varied, and the mechanical and grating properties are simulated by means of the finite element method and the transfer matrix method, respectively. Changes of the effective index, confinement factor, silica area, strain and wavelength shift induced by the acoustic wave are evaluated, and the resultant side lobe reflectivity is estimated. A side lobe reflectivity increase of 66% compared to standard fibers is estimated, which allows reducing the modulation index or the grating length in as much as 75%. Besides, the larger reduction of the required acoustic power for achieving the acousto-optic modulation points out to more efficient modulator devices in suspended-core fibers.

Численное моделирование вибраций панели летательного аппарата при воздействии акустических пульсаций давления

Investigation vibration characteristics of thin-walled shell when excitation of random pressure fields defined of wall pressure fluctuations in a turbulent boundary layer at flow regime of maximum dynamic pressure and fluctuations induced by the noise of a jet engine at the start. Is assumed that the noise from the jet engine is described a longitudinal acoustic wave propagating along the product's enclosure and diffuse acoustic field, in particular emerging as a result reflection of acoustic waves from the launch facility. As a thin-walled structure is considered streamlined panel fairing products made of a composite materials. In structure of the panel, except shell, included reinforcing circumferential ribs with two frames. The mathematical model presented for described external effects and algorithms for determining of a random vibration characteristics when exposed to fields random pressure. The calculation of the frequency response of the system is produced by the superposition of forms. The spatial correlation function of wall pressure fluctuations in turbulent boundary layer is determined according to the expression Corcos, in which the coefficients the damping of the spatial correlation function are corrected according to the model Efimtsov. The spectral density of wall pressure fluctuations in the turbulent boundary layer is determined according to the model Efimtsov. The levels sound of acoustic pressure caused by the noise of a jet engine at the start is determined by calculating of gas dynamics, and are given as the initial data. It shows the spectral characteristics of the vibration acceleration thin-walled structure depending on the frequency and distribution of the surface of the structure in a neighborhood of the central frequency at which there is maximum loading. It is assumed that the calculated levels of loads will be used as loading conditions during experimental testing of parts.

Численное моделирование вибраций панели летательного аппарата при воздействии акустических пульсаций давления

Investigation vibration characteristics of thin-walled shell when excitation of random pressure fields defined of wall pressure fluctuations in a turbulent boundary layer at flow regime of maximum dynamic pressure and fluctuations induced by the noise of a jet engine at the start. Is assumed that the noise from the jet engine is described a longitudinal acoustic wave propagating along the product's enclosure and diffuse acoustic field, in particular emerging as a result reflection of acoustic waves from the launch facility. As a thin-walled structure is considered streamlined panel fairing products made of a composite materials. In structure of the panel, except shell, included reinforcing circumferential ribs with two frames. The mathematical model presented for described external effects and algorithms for determining of a random vibration characteristics when exposed to fields random pressure. The calculation of the frequency response of the system is produced by the superposition of forms. The spatial correlation function of wall pressure fluctuations in turbulent boundary layer is determined according to the expression Corcos, in which the coefficients the damping of the spatial correlation function are corrected according to the model Efimtsov. The spectral density of wall pressure fluctuations in the turbulent boundary layer is determined according to the model Efimtsov. The levels sound of acoustic pressure caused by the noise of a jet engine at the start is determined by calculating of gas dynamics, and are given as the initial data. It shows the spectral characteristics of the vibration acceleration thin-walled structure depending on the frequency and distribution of the surface of the structure in a neighborhood of the central frequency at which there is maximum loading. It is assumed that the calculated levels of loads will be used as loading conditions during experimental testing of parts.

Ultra-directional source of longitudinal acoustic waves based on a two-dimensional solid/solid phononic crystal

Phononic crystals (PC) can be used to control the dispersion properties of acoustic waves, which are essential to direct their propagation. We use a PC-based two-dimensional solid/solid composite to demonstrate experimentally and theoretically the spatial filtering of a monochromatic non-directional wave source and its emission in a surrounding water medium as an ultra-directional beam with narrow angular distribution. The phenomenon relies on square-shaped equifrequency contours (EFC) enabling self-collimation of acoustic waves within the phononic crystal. Additionally, the angular width of collimated beams is controlled via the EFC size-shrinking when increasing frequency.

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.

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.

Investigation of interface states distribution in metal-oxide-semiconductor structures with very thin oxides by acoustic spectroscopy

New technique of acoustic spectroscopy to study interface states in metal-oxide-semiconductor (MOS) structures with a very thin oxide layer based on the acoustoelectric effect resulting from the interaction between the longitudinal acoustic wave and semiconductor-insulator interface is presented. The essential principles and theoretical background of this acoustic spectroscopy technique that can determine the interface states distribution from the measured acoustoelectric response signal as a function of gate voltage (Uac-Ug characteristics) are described. The results obtained on the representative set of MOS structures prepared on both n- and p-type Si substrates by nitric acid oxidation of Si technology and undergone also some thermal treatment demonstrate that the introduced technique of acoustic spectroscopy can be a very useful tool for the interface states characterization.

High Temperature Acoustic Anomalies in PMN-PSN Solid Solution

We present an acoustic study of 0.55 PbMg1/3Nb2/3O3 - 0.45 PbSc1/2Nb1/2O3 relaxor ferroelectric solid solution in a wide temperature range, from 150 to 750 K. The longitudinal acoustic wave velocity and attenuation were measured by the ultrasonic pulse-echo technique at frequency 10 MHz. The strong anomalies observed in the longitudinal sound velocity and attenuation versus temperature were found to correlate with the temperature range of the relaxor ferroelectric state. Attenuation peaks were observed at characteristic temperatures of relaxors, i.e., at TB (Burns temperature) and T* (an additional significant temperature). The results are compared with the acoustic behavior of PbMg1/3Nb2/3O3.

Quasi-periodic Fibonacci and periodic one-dimensional hypersonic phononic crystals of porous silicon: Experiment and simulation

A one-dimensional Fibonacci phononic crystal and a distributed Bragg reflector were constructed from porous silicon. The structures had the same number of layers and similar acoustic impedance mismatch, and were electrochemically etched in highly boron doped silicon wafers. The thickness of the individual layers in the stacks was approximately 2 μm. Both types of hypersonic band gap structure were studied by direct measurement of the transmittance of longitudinal acoustic waves in the 0.1–2.6 GHz range. Acoustic band gaps deeper than 50 dB were detected in both structures. The experimental results were compared with model calculations employing the transfer matrix method. The acoustic properties of periodic and quasi-periodic structures in which half-wave retarding bi-layers do not consist of two quarter-wave retarding layers are discussed. The strong correlation between width and depth of gaps in the transmission spectra is demonstrated. The dominant mechanisms of acoustic losses in porous multilayer structures are discussed. The elastic constants remain proportional over our range of porosity, and hence, the Grüneisen parameter is constant. This simplifies the expression for the porosity dependence of the Akhiezer damping.

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.

Localization of acoustic modes in periodic porous silicon structures.

The propagation of longitudinal acoustic waves in multilayer structures based on porous silicon and the experimental measurement of acoustic transmission for the structures in the gigahertz range are reported and studied theoretically. The considered structures exhibit band gaps in the transmission spectrum and these are localized modes inside the band gap, coming from defect layers introduced in periodic systems. The frequency at which the acoustic resonances appear can be tuned by changing the porosity and/or thickness of the defect layer.

Surface acoustic waves in semi-insulating Fe-doped GaN films grown by hydride vapor phase epitaxy

The propagation properties of surface acoustic waves (SAWs) in semi-insulating Fe-doped GaN films grown on sapphire substrates by hydride vapor phase epitaxy are investigated. Compared with native n-type GaN, Fe-doped GaN exhibits a higher electromechanical coupling coefficient due to its high electrical resistivity. In addition, guided longitudinal leaky surface acoustic wave (LLSAW) was observed experimentally with a very high phase velocity (about 7890 m/s), and this mode was verified by numerical simulations. The small propagation attenuation of LLSAW along liquid/solid interfaces was demonstrated in glycerol solutions, which implies the potential applications in high-frequency chemical sensing.

Second-order and third-order elastic constants of B4C ceramics

The linear and nonlinear elastic properties of B4C boron carbide ceramics have been studied. The second-order elastic constants and other parameters of the theory of elasticity in the linear approximation have been calculated based on the experimentally measured density and velocity values of longitudinal and shear bulk acoustic waves in the samples. The Thurston-Brugger method has been used to determine the third-order elastic constants of B4C. To achieve this, we have measured the relative changes of the longitudinal and shear bulk acoustic wave velocities depending on the uniaxial compression applied to the sample.

Quasi-Linear Polarized Modes in Y-Rotated Piezoelectric GaPO4 Plates

The propagation of both surface and flexural acoustic plate modes along y-rotated x-propagation GaPO4 piezoelectric substrates was studied for several y-cut angles: the phase velocity and coupling coefficient dispersion curves were theoretically calculated for two different electroacoustic coupling configurations. The investigation of the acoustic field profile across the plate thickness revealed the presence of thin plate modes having polarization predominantly oriented along the propagation direction, and hence suitable for operation in liquid environment. These modes include the linearly polarized Anisimkin Jr. and the quasi longitudinal plate modes, AMs and QLs, showing a phase velocity close to that of the longitudinal bulk acoustic wave propagating in the same direction. The temperature coefficient of delay (TCD) of these longitudinal modes was investigated in the −20 to 420 °C temperature range, in order to identify thermally stable or low TCD cuts. The power flow angle, i.e., the angle between the phase and group velocity vectors, was also estimated to evaluate the substrate anisotropy effect on the acoustic wave propagation. The GaPO4 intrinsic properties, such as its resistance to high temperature and its chemical inertness, make it especially attractive for the development of acoustic waves-based sensors for applications in harsh liquid environment.