Attenuation Of Acoustic Waves Research Articles

Acoustic characterization of AlN films using a High Overtone Bulk acoustic wave resonator

Using the composite resonator with additional thick AlN film with the FWHM of rocking curve of 2.53° under investigation, the bulk acoustic wave attenuation constant and sound velocity along c-axis were directly measured. The method of High Overtone Bulk acoustic wave Resonator (HBAR) spectroscopy based on frequency, measurements of the positions of the resonator peculiarities of phase and amplitude of electromagnetic wave reflection coefficient from composite resonator structure was applied. The method provides attenuation and velocity measurement in a wide frequency band, using the same sample. For the measurements, standard and modified HBAR spectroscopy based on the analysis of only parallel resonance properties of composite resonator structures were used.

Imaging the permeability structure within near-surface sediments by acoustic crosswell tomography

Permeability structure within near-surface sediments is imaged by analytically inverting the measured fields of acoustic wave velocity and attenuation. The acoustic velocity and attenuation fields at 1000 Hz were previously measured by a pseudorandom binary sequence (PRBS) based crosswell acoustic tomography device [T. Yamamoto, J. Acoust. Soc. Am. 98, 2235–2248 (1995)]. A quadratic equation of permeability derived from the Biot theory is used for the permeability imaging. The porosity and shear modulus images are also extracted from the velocity and attenuation fields using the newly derived quadratic dispersion equation and an empirical shear modulus porosity depth of burial relation. The acoustically measured images of permeability, porosity, and shear modulus are favorably compared with the engineering tests performed on the cores and boreholes.

High-frequency hopping conductivity in the quantum Hall effect regime: Acoustical studies

The high-frequency conductivity of Si delta-doped GaAs/AlGaAs heterostructures is studied in the integer quantum Hall effect (QHE) regime, using acoustic methods. Both the real and the imaginary parts of the complex conductivity are determined from the experimentally observed magnetic field and temperature dependences of the velocity and the attenuation of a surface acoustic wave. It is demonstrated that in the structures studied the mechanism of low-temperature conductance near the QHE plateau centers is hopping. It is also shown that at magnetic fields corresponding to filling factors 2 and 4, the doped Si delta- layer efficiently shunts the conductance in the two-dimensional electron gas (2DEG) channel. A method to separate the two contributions to the real part of the conductivity is developed, and the localization length in the 2DEG channel is estimated.

Surface acoustic waves and magnetotransport in an embedded modulated two-dimensional electron gas

The attenuation and frequency shift of surface acoustic waves of Rayleigh and Sezawa types are calculated, which propagate in a layered semiconductor heterostructure containing an embedded spatially modulated two-dimensional electron gas (2DEG). The surface waves couple to the 2DEG via the piezoelectric effect. The electron gas is subjected to a static magnetic field directed normal to the interfaces of the layered system. The one- and two-dimensional periodic spatial modulations are due either to an electrostatic external potential or to a spatially varying magnetic field. The effects of the anisotropy of the elastic media as well as the two-dimensionally modulated electron gas are studied on the Weiss oscillations occurring in this system.

The effects of interfacial viscosity on the attenuation and phase speed of acoustic waves in bubbly liquids

The attenuation and phase speed of bubbly fluids have been shown to be highly dispersive due in part to the resonance response of individual bubbles. Surface-active materials, or surfactants, are known to dramatically alter the viscoelastic dynamics of an interface without affecting the bulk fluid properties. In this theoretical model the effects of surface viscosity on the propagation of linear pressure waves through a bubbly fluid are examined. The attenuation and phase speed are calculated for varying radii, void fraction, and interfacial viscosity for air bubbles in water. The results show an increase in attenuation for frequencies far removed from the bubble resonance for radii less than 100 microns. There is no significant increase in attenuation for larger bubbles (order 1 mm). Interestingly, near resonance, the interfacial viscous case has a lower attenuation than the clean interface, most likely due to the reduced radiation damping associated with smaller radial excursions. Likewise, resonance effects on the phase speed dispersion curve are also significantly diminished due to the interfacial viscosity. These results could be important for understanding propagation near the surface of the ocean, where surface-active materials can dramatically affect the dynamics of micron-sized bubbles and bubble distributions. [Work supported by ONR.]

Acoustic Faraday effect and transverse waves in a superfluid

Acoustic waves provide a powerful tool for studying the structure of matter. The speed, attenuation, and dispersion of acoustic waves give useful details of the molecular forces and microscopic mechanisms for absorption and scattering of acoustic energy. In solids, both compressional and shear waves occur, so-called longitudinal and transverse sound. However, normal liquids do not support shear forces and consequently transverse waves do not propagate in liquids with one notable exception, the quantum liquid phase of 3He. We have observed rotation of the polarization of transverse sound waves in superfluid 3He−B in a magnetic field. This magneto–acoustic effect is the direct analog to the magneto–optical effect discovered by Michael Faraday in 1845, where the polarization of an electromagnetic wave is rotated by a magnetic field along the propagation direction. Our experiment [Nature 400, 431 (1999)], is the first demonstration of the existence of propagating shear waves in a liquid.

Nonlinear Distortion and Attenuation of Intense Acoustic Waves in Lossy Media Obeying a Frequency Power Law

Nonlinear Distortion and Attenuation of Intense Acoustic Waves in Lossy Media Obeying a Frequency Power Law

Connection between Near Millimeter Range Dielectric Loss and High Frequency Acoustic Attenuation

ABSTRACTA series of crystalline isomorphic solid solutions of Yttrium-Lutetium Aluminum Garnets (Y1−cLuc)3Al5O12 (c = 0 – 1) has been studied. The measurements of dielectric loss (DL) tangent tgδ has been performed at electromagnetic wavelengths 1 – 0.6 mm and temperature T = 300 K. The results obtained has been compared with longitudinal acoustic waves (AW) attenuation data for frequencies f = 1 – 9.4 GHz, T = 4.2 – 300 K and with theory. The correlation between the DL and the AW attenuation is observed. The dependencies of DL (at T = 300 K) and AW attenuation (at T > 77 K) on concentration c are qualitatively identical in the whole interval c = 0 – 1. From comparison with theory it follows that the observed DL is due to the two-phonon intrinsic lattice loss. It is caused by the lattice anharmonicity as well as the AW attenuation at not too low temperatures. Also the prediction for concentration dependence of DL at very low temperatures is discussed that follows from comparison with the results of “heat pulse” propagation experiments for the same samples at T = 2 K and theory.

Tunneling states in a single-grain Al-Cu-Fe quasicrystal

Velocity and attenuation of acoustic waves (190 Mhz) have been measured in a phason-free single grain of i-AlCuFe between 40 mK and 30 K. The results reveal the existence of tunneling states (TS's). The coupling parameter $P{\ensuremath{\gamma}}^{2}$ (where P is the TS density of states and $\ensuremath{\gamma}$ is the phonon-TS coupling) is close to the one in metallic glasses. The crossover temperature from the ${T}^{3}$ law to the plateau regime in the attenuation is well defined. Hence, within the TS model, both P and $\ensuremath{\gamma}$ can be calculated. The TS's seem to be intrinsic to the quasicrystal structure.

Attenuation of acoustic emission body waves in acrylic bone cement and synthetic bone using wavelet time-scale analysis.

This article addresses acoustic emission (AE) wave attenuation in acrylic bone cement and wave attenuation due to the existence of material interface between acrylic bone cement and sawbone. In this article, a series of tests were performed using standard pencil lead break sources. The attenuation features inside acrylic bone cement and sawbone materials and the attenuation due to the existence of material interfaces such as cement-cement and cement-sawbone were studied. In addition, the discrete wavelet-based signal energy decomposition method was introduced to examine detail breakdown of signal energy distribution of attenuation. From the tests, it was observed that the attenuation of AE signal was linear with respect to the wave travel distance for both energy and amplitude. Furthermore, AE energy attenuation was more sensitive than AE amplitude attenuation. In the analysis of attenuation due to material interfaces, the couplant plays a major role in reducing the attenuation at the interfaces. The attenuation at an interface composed by different material is less compared with an interface composed by the same material.

Dispersion and attenuation of acoustic waves in randomly heterogeneous media

We derive the effective displacement relation for acoustic waves in a spatially random heterogeneous one-dimensional medium. This relationship is expressed in terms of parameters σ R and σ A which represent the standard deviations of the randomly varying density ρ( x) and the randomly varying Young's modulus α( x), of the medium. In this way, we build the contributions into the total displacement relationship for the spatially random heterogeneous medium and apply this result to determine the dispersion and attenuation of acoustic waves propagating in the random heterogeneous medium. Attenuation and dispersion of waves propagating in media with randomly varying properties has been the subject of much study. Most of this work has neglected the effects of intrinsic dispersion and attenuation in order to concentrate on the effects of the medium inhomogeneities. We demonstrate how intrinsic attenuation may be easily included in the theoretical development, and explore the combined effects of scattering-based and intrinsic attenuation and dispersion on wave propagation. We apply the solution to model interwell acoustic waves propagating in the Kankakee formation at the Buckhorn Test Site, IL. The modeling results show that the strong dispersion in the frequency range of 500–2000 Hz is due to the reservoir heterogeneity. Alternatively, the velocity dispersion for frequencies greater than 2000 Hz corresponds to the intrinsic properties of the reservoir.

Surface acoustic wave NO 2 sensing using attenuation as the measured quantity

In this paper, we present a new method for gas sensing using the attenuation of surface acoustic waves (SAWs) as the measured quantity. For a NO 2-sensor employing this technique, simple delay lines on LiNbO 3 substrates were coated with copper or lead phthalocyanine as sensitive layer. The sensor signal is a change of the attenuation originating from surface conductivity changes induced by the adsorbed NO 2. The advantage of monitoring attenuation is that the amplitude of a surface wave is much less sensitive to temperature fluctuations of the device than the customarily employed SAW velocity. Therefore, high stability and sensitivity of the sensor to atmospheric NO 2 concentrations in the ppb range could be achieved. For field measurements, a compact electronic system was developed. Comparisons of the SAW sensor with other techniques like optical absorption spectroscopy or chemoluminiscence in several ambient air measurement campaigns were carried out. The results of the comparative measurements were found to agree well.

Surface acoustic wave resonances in the spreading of viscous fluids

Reflection and attenuation of a Rayleigh surface acoustic wave from a small stripe of viscous fluid spreading across the acoustic path have been observed. As the stripe spreads across the acoustic path, with an accompanying decrease in stripe height to conserve volume, the reflected and attenuated acoustic signals show a distinct pattern of resonances. This paper reports experimental results for the spreading of highly viscous poly(dimethyl)siloxane oils (100 000 cS) in the propagation path of a 169 MHz Rayleigh wave operating in pulse mode and develops a model to explain the observed resonances of the transmission coefficient. Simultaneous optical observations enable the time evolution of the shape of the stripe to be converted into changes in geometric parameters (contact width, spherical radius, height, and contact angle). To model the acoustic attenuation, an approach treating the fluid as a viscoelastic fluid with a single relaxation time (Maxwell model) is developed. This approach is able to explain the structure of the observed transmitted signal. Resonances in the transmission coefficient occur cyclically and correspond to the stripe height matching $n{\ensuremath{\lambda}}_{s}/4,$ where n is odd and ${\ensuremath{\lambda}}_{s}$ is the shear wavelength in the fluid.

Saw attenuation in C 60 thin films at transition temperature

Surface acoustic wave (SAW) attenuation of microcrystalline C 60 film prepared by vacuum evaporation is measured in the temperature range 150–300 K. A strong attenuation is observed near the temperature of the fcc–sc transition, at about 260 K. The attenuation may be related to a thermal activated relaxation mechanism having an activation energy of about 68 meV. No thermal hysteresis in the attenuation is observed in the temperature range.

Particle Sizing in Colloidal Dispersions by Ultrasound. Model Calibration and Sensitivity Analysis

In this paper, the use of ultrasonics for the determination of particle size distributions (PSDs) in suspensions and emulsions is discussed. Focusing on systems with a large density difference between the dispersed and continuous phases, a mathematical model is used to correlate the primary measurementthe attenuation of acoustic waves as a function of frequencyto the PSD, and it becomes clear that the quality of the PSD thus obtained is directly related to the accuracy of the model parameters. To overcome possible problems in the case of incomplete physical-property information, we have developed a generalized procedure for particle sizing, based on a parametric sensitivity analysis and parameter calibration. The latter allows for computation of physical properties from acoustic data provided that the PSD is known. Moreover, particle sizing results are presented for dispersions of different sizes and materials, and compared to the findings of electron microscopy and dynamic light scattering.

Saw attenuation by the localised states of a 2D carrier system in a magnetic field

The surface acoustic wave attenuation and dispersion have been measured as a function of magnetic field for both a 2D electron system and a 2D hole system at frequencies between 100 and 1100 MHz. The experiments were made at 350 mK in the quantum Hall regime. In the region of filling factor one where the quasi-DC conductivity becomes very small, an attenuation and dispersion is found which we attribute to localised carrier states. We estimate that the relaxation time of the localised electrons is about 60 ps while the relaxation time for localised holes is about 20 ps.

Determination of specific surface area and mean grain size from well-log data and their influence on the physical behavior of offshore reservoirs

Specific surface area ( s s) is one of the most important and effective geometrical parameters in defining and interpreting petrophysical relationships, textural framework, and fluid–solid interactions in porous media. It is defined as the interstitial surface area of the pores and pore channels for each unit of bulk volume, grain volume, or pore volume, or for a unit of weight of a material. Variations in the specific surface area ( s s) and mean grain size ( G s) influence the physical parameters controlling electric current and hydraulic flow, as well as acoustic and seismic wave propagation and attenuation. In this study, the specific surface area per unit of pore volume ( s p) and the mean grain size ( G s) were numerically determined from well-log data for 14 wells penetrating the Hibernia and Terra Nova reservoirs of the Jeanne d'Arc Basin (JDB), offshore Newfoundland, Canada. Both parameters ( s p and G s) were derived using the formation resistivity factor, porosity, and permeability. Mathematical and physical concepts of s s (including s p) and G s were analyzed, and empirical equations linking s p and G s with various petrophysical parameters were obtained. The lithological components (shale, sandstone, silt, limestone, and marl) were also obtained. The rocks in both reservoirs are generally characterized by fine- to medium grain size and high values of s p.

Electromechanical coupling coefficient for surface acoustic waves in proton-exchanged 128°-rotated Y-cut lithium niobate

The attenuation of surface acoustic waves propagating along crystallographic X axis in proton-exchanged 128° rotated Y-cut lithium niobate during the evaporation of copper film on the crystal surface has been measured as a function of sheet resistivity of the film. From the magnitude of attenuation maxima, the effective electromechanical coupling coefficients for samples with different thicknesses of HxLi1−xNbO3 layers have been evaluated, and from the position of maxima in the resistivity scale, the effective dielectric permittivities of the structure have been estimated. The electromechanical coupling coefficient is found to be reduced practically to zero with increasing thickness of protonated layer and acoustic frequency, and the dielectric permittivity is not significantly affected by the proton exchange.

Anomalies of attenuation and phase velocity of surface acoustic waves in thin films in the vicinity of

We present measurements of the attenuation and phase velocity of surface acoustic waves in thin YBa2Cu3O YBa2Cu3O7‒δ films as a function of temperature, in magnetic fields up to 3.6 T applied parallel to the c-axis of the films. We have observed anomalies in both, the attenuation and the phase velocity in the vicinity of the superconducting critical temperature which do not depend on the magnetic field. Possible origins of these anomalies, observed, to our knowledge, for the first time in YBa2Cu3O7‒δ thin films, are discussed and compared to bulk acoustic wave experiments. We present a kind of feedback technique for surface acoustic waves which improves the sensitivity of this type of measurement. The actual sensitivity limits are mentioned.

Attenuation of surface acoustic waves by quantum dots

Abstract The attenuation Γ of surface acoustic waves (SAWs) by an array of quantum dots is considered. The processes contributing to Γ, direct and intralevel (Debye) absorption and (elastic) scattering off the direction of the SAW are discussed for two limiting cases of the energy spectra of the dots: firstly a continuous spectrum, which is realized when the SAW frequency ω is much larger than the mean level spacing Δ or when the broadening of the levels is sufficiently strong, Δ < τφ -1, τφ -1 being the phase breaking rate; secondly a discrete spectrum, obtained for ω, τφ -1 < Δ. The results show that the sensitivity of Γ to weak-localization effects such as magnetic fields, spin-orbit scattering and temperature, are considerably enhanced for a discrete spectrum. It is argued that the non-invasive character of the measurement of Γ makes the SAW experiments especially suitable for the determination of the temperature dependence of τφ -1 and the equilibration rate of the electronically isolated dots.