Attenuation Of Acoustic Waves Research Articles

Random propagation times in ultrasonics

The attenuation of acoustic waves is often in the form exp with 0 < b ≤ 2. For b = 2, experiments show negligible dispersion. For b = 1, the variation of the velocity is well-fitted by a logarithmic function, and by power functions when b ≠ 1. An explanation of theses results has been provided by T.L. Szabo by extensions of the Kramers–Kronig relations. In this paper, we show that a random propagation time leads to similar results. This model explains the loss of power by the existence of noise which cannot be taken into account by the devices. Also, it explains the redshift linked to the wave bandwidth.

Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure

Measurement results of the acoustoelectric effects [surface acoustic waves (SAW) attenuation and velocity] in a high-mobility p-SiGe/Ge/SiGe structure are presented. The structure was low-energy plasma-enhanced chemical vapor deposition grown with a two-dimensional (2D) channel buried in the strained Ge layer. The measurements were performed as a function of temperature (1.5–4.2 K) and magnetic field (up to 8.4 T) at different SAW intensities at frequencies 28 and 87 MHz. Shubnikov–de Haas-like oscillations of both SAW attenuation and the velocity change have been observed. Hole density and mobility, effective mass, quantum and transport relaxation times, as well as the Dingle temperature were measured with a method free of electric contacts. The effect of heating of the 2D hole gas by the electric field of the SAW was investigated. Energy relaxation time τε and the deformation potential constant determined.

Dispersion and attenuation of surface acoustic waves of shear horizontal polarization on a free surface of a hexagonal crystal with a structurally damaged isotropic surface layer

The phase velocity dispersion and the inverse attenuation length of surface acoustic waves of shear horizontal polarization propagating along a free flat (smooth) surface of a hexagonal crystal (Z cut) in the presence of a thin (compared to the wavelength) structurally damaged surface layer are found in the analytical form. It is shown that, in the long-wavelength limit (the wavelength is large compared to the characteristic size of layer inhomogeneities), which is of the greatest interest to experimenters, the change in the phase velocity dispersion and the change in the inverse attenuation length are proportional to the third and sixth powers of the wave frequency, respectively. The inverse attenuation length is numerically calculated.

Su-8-based nanocomposites for acoustical matching layer

SU-8, an epoxy-based photoresist, was introduced as the acoustical matching layer between silicon and water for lab-on-chip applications integrating acoustic characterization. Acoustical performances, including the acoustic longitudinal wave velocity and attenuation of the SU-8-based matching layer, were characterized at a frequency of 1 GHz at room temperature. The gain in echo characterization with a SU-8/SiO2 bilayer and with different nanocomposite monolayers made of SU-8 and TiO2 nanoparticles (size around 35 nm) between silicon and water was characterized as being above 10 dB in each case. With the increase of concentration of TiO2 in SU-8 based composites from 0 to 30 wt%, acoustical impedance of the nanocomposites increased from about 3 to 6 MRayls, respectively. The acoustical attenuation in the nanocomposites is between 0.5 and 0.6 dB/microm. The most efficient matching was obtained with the nanocomposite integrating 30 wt% TiO2 nanoparticles, with which the enhanced loss is about 0.34 dB as the attenuation is about 0.5 dB/microm. This type of matching layer has potential applications in lab-on-chip technology for high frequency transducers or in the fabrication of high frequency piezocomposites.

Leaky-Surface-Acoustic-Wave Properties on Reverse-Proton-Exchanged LiNbO3

A proton-exchanged (PE) layer with an elastically soft property can be buried into a substrate by a reverse proton exchange (RPE) process. It is expected that an RPE layer with a property similar to that of bulk LiNbO3 will prevent the degradation of coupling factor, and that the buried PE layer will change the anisotropy of the substrate effectively and reduce the leaky surface acoustic wave (LSAW) attenuation as compared with bulk LN. In this study, first, a layered structure of air/bulk LN/softened LN was assumed for rotated Y–X LN and LSAW attenuation was calculated. By controlling the elastic constant of the softened LN, the rotation angle from the Y-axis giving zero attenuation shifted from 64 to 5° for a metallized surface, and the rotation angle at which the attenuation decreases as compared with bulk LN was drastically changed for a free surface. Next, the LSAW propagation loss PL was measured on 41° Y–X LN. The PL for the metallized surface was decreased by carrying out the RPE process from 0.036 dB/λ of a virgin sample to 0.015 dB/λ. The decrease in PL for the free surface was also observed.

Dynamic Effective Mass of Granular Media

We develop the concept of frequency dependent effective mass, M[over ](omega), of jammed granular materials which occupy a rigid cavity to a filling fraction of 48%, the remaining volume being air of normal room condition or controlled humidity. The dominant features of M[over ](omega) provide signatures of the dissipation of acoustic modes, elasticity, and aging effects in the granular medium. We perform humidity controlled experiments and interpret the data in terms of a continuum model and a "trap" model of thermally activated capillary bridges at the contact points. The results suggest that attenuation of acoustic waves in granular materials can be influenced significantly by the kinetics of capillary condensation between the asperities at the contacts.

Erratum: “Low-frequency attenuation of acoustic waves in sandy/silty marine sediments” [J. Acoust. Soc. Am., 124, EL308–EL312 (2008)

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HIGH-FREQUENCY ACOUSTIC PHENOMENON IN QUASI-TWO-DIMENSIONAL ORGANIC CONDUCTORS

The propagation of a monochromatic high-frequency longitudinal acoustic wave along the normal to the layer (z-axis) in a bulk quasi-two-dimensional conductor (Q2D), in the absence of an external magnetic field under assumption of arbitrary scattering of the charge carriers from the boundary surface, is studied theoretically. The effect of the Q2D electron energy spectrum features on the attenuation of an ordinary acoustic wave (OAW) and of an anomalous acoustic wave (AAW) is discussed. It is shown that for certain values of the characteristic parameters, the OAW in Q2D is strongly attenuated, and the asymptotic form of the acoustic field in the conductor is determined by the AAW. In the case of a Q2D conductor, the anomalous acoustic field is transmitted by electrons belonging to the belt points of the Fermi surface.

Calculation of Anharmonic Coupling Constants between Phonon Modes in GaAs

Anharmonic coupling between phonon modes of a crystal determine many of its properties, thermal conductivity being a standard example. Although anharmonicity-related effects observed in bulk crystals (decay of the zone-center longitudinal optical (LO) phonon or acoustic wave attenuation) rely only on a small subset of anharmonic couplings, the full set of such constants is needed for a complete description of phonon-induced dephasing and relaxation of electrons and excitons in quantum dots [1–4]. The reason for this is that breaking of the translational symmetry and appearance of a quantized spectrum completely changes the energy-momentum conservation conditions and opens decoherence (relaxation and dephasing) paths which are not allowed in a bulk crystal. So far, only the anharmonic couplings between acoustic branches have been completely described [5], while the only known coupling involving optical phonons is that between the LO phonon and two longitudinal acoustic (LA) phonons, which seems to be responsible for the decay of the zone-center LO phonon in a bulk crystal [6] and is therefore accessible experimentally [7]. In this paper, we derive third-order anharmonic coupling constants between various phonon modes in a zinc-blende crystal. We use a model combining the

Band gaps and Brekhovskikh attenuation of laser-generated surface acoustic waves in a patterned thin film structure on silicon

Surface acoustic modes of a periodic array of copper and ${\text{SiO}}_{2}$ lines on a silicon substrate are studied using a laser-induced transient grating technique. It is found that the band gap formed inside the Brillouin zone due to ``avoided crossing'' of Rayleigh and Sezawa modes is much greater than the band gap in the Rayleigh wave dispersion formed at the zone boundary. Another unexpected finding is that a very strong periodicity-induced attenuation is observed above the longitudinal threshold rather than above the transverse threshold.

Low-frequency attenuation of acoustic waves in sandy/silty marine sediments

Sandy/silty marine sediments are water saturated and consist of diverse tiny rock pebbles. The weight of higher pebbles holds lower pebbles in contact. For low-frequency acoustic disturbances, the no-slip condition and viscosity cause the local water displacement near solid surfaces to be nearly the same as that of the neighboring pebbles. Water farther from surfaces oscillates relative to solid matter because of mass density difference, and viscosity limits the oscillation amplitude. Derived dissipative wave equation predicts attenuation proportional to frequency squared, proportional to the square of the difference of the densities, and inversely proportional to viscosity.

Laboratory measurements of sound speed and attenuation in water‐saturated artificial sediments as a function of porosity.

Several models have been proposed to describe the sound speed and attenuation of acoustic waves in water‐saturated granular sediments. The difference between the predictions of competing models can be only a few percent, and it is difficult to obtain both sufficient knowledge of the sediment physical parameters and sufficiently small measurement uncertainty to adequately verify competing models. Furthermore, the inhomogeneity of natural sediments causes additional measurement and interpretation uncertainty. Therefore, well‐controlled laboratory measurements are useful for model validation and also facilitate exploration of the effects of sediment physical parameter variation. A method for controlling the porosity of an ensemble of water‐saturated granular particles [Schroter et al., Phys. Rev. E 71, 030301(R) (2005)] was used to prepare columns of artificial sediments, composed of monodisperse 280‐μm‐diameter glass spheres and distilled water of varying porosity. Acoustic time‐of‐flight measurements were ...

The physical mechanism (viscosity related) of low‐frequency acoustic wave attenuation in sandy/silty sediments.

Considered saturated sediments contain diverse rock pebbles (characteristic size of 0.1 mm). The weight of higher pebbles holds lower pebbles in contact sufficiently that acoustically induced solid displacements vary slowly over several adjacent pebbles. Apart from contact areas, each is nearly surrounded by water at a nearly uniform pressure. An appropriate first approximation predicts that the elastic stress tensor in the pebbles is diagonal, with components equal to the negative of the acoustic pressure in the neighboring fluid. The assumptions of Mallock and Wood apply: the mass weighted local average velocity is proportional to the negative gradient of the pressure in the water. The no‐slip condition at the interfaces tends to force the water to move with the pebbles, but the finite viscosity allows the fluid at small distances from the interfaces to move at a different velocity than the pebbles. The apparent driving force for the oscillations of the interstitial water relative to the pebbles is associated with the inertia of the water and is proportional to the difference in densities. The derived approximate wave equation predicts attenuation proportional to frequency squared, proportional to the square of the difference of the densities, and inversely proportional to viscosity. The derived dimensionless proportionality constant is consistent with recent experiments.

Elastic properties of aspirin in its crystalline and glassy phases studied by micro-Brillouin scattering

The acoustic waves propagating along the direction perpendicular to the (1 0 0) cleavage plane of aspirin crystal were investigated using micro-Brillouin spectroscopy from which C 11 , C 55 and C 66 were obtained. The temperature dependence of the longitudinal acoustic waves could be explained by normal anharmonic lattice models, while the transverse acoustic waves showed an abnormal increase in the hypersonic attenuation at low temperatures indicating their coupling to local remnant dynamics. The sound velocity as well as the attenuation of the longitudinal acoustic waves of glassy aspirin showed a substantial change at ∼235 K confirming a transition from glassy to supercooled liquid state in vitreous aspirin.

Scattering and attenuation of surface acoustic waves in droplet actuation

This paper presents an analytical model for surface acoustic waves (SAW) in actuating a single liquid droplet on a piezoelectric substrate. Both scattering waves outside the droplet and attenuation waves beneath the droplet are obtained, and the energy transfer from SAW to droplet in the process of actuation is calculated. The results from this analytical model can provide qualitative explanations to some experimental observations, such as the weak actuation behind the droplet and flow patterns inside the droplet. It is found that effective actuation wavelength is around 1/5 of the droplet radius, at which the droplet absorbs the maximum incident SAW energy.

Anomalies of low-intensity acoustic wave attenuation in rocks

It is experimentally established that acoustic waves in rocks attenuate abnormally depending on varying amplitude. The amplitude growth results in the increase in elastic wave velocities and decrease in the attenuation decrement. The attenuation rather than wave velocity is more sensitive to the amplitude variations. The obtained data are applicable to diagnose the states of fractured and porous rocks.

Effect of soil texture and excitation frequency on the propagation and attenuation of acoustic waves at saturated conditions

The study of the propagation and dissipation of acoustic waves through a fluid-containing porous medium is crucial for the successful application of seismic methods to characterize subsurface hydrological properties. To gain a better understanding of changes in two important acoustic wave characteristics (speed and attenuation) due to the effect of soil texture and excitation frequency, a complex-valued dispersion relation obtained from the Biot theory of poroelasticity was solved numerically for eleven soil texture classes whose pore space is fully saturated by one of two very different fluids, air or water. Two modes of acoustic motion can be demonstrated to exist, known as the Biot fast and slow waves. Five lower excitation frequencies (100–500 Hz) were selected for numerical simulation, below which Darcy’s law remains valid for describing porous media flow under wave perturbation. Numerical results show that in the frequency range we examined, the predicted phase speed of the Biot fast wave takes the same value as the Biot reference speed. The variation in speed is not obvious in a water-filled system, but becomes more significant in an air-filled system. When the pore fluid is water, an inverse linear relation exists between the phase speed of the Biot fast wave and porosity. An important physical parameter controlling its attenuation coefficient is intrinsic permeability, which renders a positive impact. A statistical analysis indicates that the attenuation coefficient of the Biot fast wave linearly increases with an increase in intrinsic permeability. In an air-saturated system, the phase speed of the Biot slow wave is found to be quadratically proportional to intrinsic permeability, whereas the attenuation coefficient of the Biot slow wave bears a quadratic relation with the inverse of intrinsic permeability. A study on the influence of pore fluid reveals that the Biot fast wave attenuates more in the water-saturated system than in the air-saturated system; an exception occurs in clay. A reverse trend is observed for the Biot slow wave. As far as the effect of excitation frequency is concerned, the attenuation coefficient of the Biot fast wave is essentially proportional to the square of excitation frequency, whereas the phase speed and attenuation coefficient of the Biot slow wave are both proportional to the square root of excitation frequency. The phase speed of the Biot fast wave is frequency independent.

Micro‐viscometer using acoustic wave absorption in micro‐chamber and channel

A micro‐viscometer is designed for real‐time measurement on the viscosity change of biomaterial including DNA or RNA, etc. It is composed of two chambers and several micro‐channels connecting between them. Each chamber has a PZT unimorph membrane for generating and sensing the sound waves. Namely, one is regarded as an actuator, the other as a sensor. Micro‐channels, which have the large attenuation of acoustic waves caused by wall effect, are applied to the micro‐viscometer for increasing viscosity effect. When the actuator is driven at a resonance frequency under the condition of continuous flowing of liquid through an inlet/outlet hole, the sensor can detect the amplitude differences caused by viscosity change. Therefore, it is possible to measure the viscosity change in real time by detecting the signal change of sensor. The micro‐viscometer can be also applied to the integration kit such as LOC (Lab‐On a Chip) to detect whether DNA is amplified by micro‐PCR (Polymerase Chain Reaction) and it will giv...

Time-Resolved Spectroscopy of Water confined in Vycor

We present measurements on water confined in Vycor 7930 by heterodyne-detected transient grating experiments (HD-TG) [1]. We studied the acoustic wave propagation, the thermal diffusion and the liquid viscous flow through the pores as a function of temperature (-15 - 90 °C) and of the exchanged q-vector (0.63 - 2.5 μm-1). The data show interesting aspects due partly to the confinement effects and partly to the peculiarities of bulk water. Acoustic results are compared with the predictions of the Biot theory finding a good agreement only for the sound velocity data, while the predictions for the acoustic wave attenuation is poor as just reported in [2]. Our technique is able to induce a thermal grating inside the sample. The analysis of the data requires an extension of the Biot theory, that takes into account the temperature variations. Surprisingly, our data show that the acoustic oscillation are not affected by the temperature. The induced thermal grating is also used to analyze the viscous flow of water inside the pores and the thermal diffusion. [1] Time-resolved spectroscopy of complex liquids, edited by Torre R. (Springer, New York) 2008 [2] A. Taschin, R. Cucini, P. Bartolini, R. Torre, Europhys. Lett., in press.

Influence of a structurally damaged surface layer of the hexagonal crystal on the dispersion and attenuation of Rayleigh surface acoustic waves

Analytical expressions for the dispersion of the phase velocity and the inverse attenuation length of Rayleigh waves are derived with allowance made for a thin (as compared to the length of the surface wave) isotropic damaged surface layer that is contiguous with vacuum and located on the surface of a hexagonal crystal with the sixfold axis perpendicular to the surface. It is demonstrated that, in the limit of long wavelengths (as compared to the characteristic inhomogeneity size), which is of greatest interest for experimenters, the change in the dispersion of the phase velocity of Rayleigh waves is proportional to the second power of the frequency, whereas the inverse attenuation length of Rayleigh waves is proportional to the fifth power of the frequency. The inverse attenuation length of the Rayleigh wave is calculated numerically. The calculation method previously proposed by one of the authors (Kosachev, 1998) is generalized to the case of an isotropic damaged layer on an anisotropic (hexagonal) substrate.