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Journal of the Acoustical Society of America

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Jun 1992

Volume 91, Issue 6, pp. 3099-3598

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The effect of a viscous fluid on Love waves in a layered medium

Jin O. Kim

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3099-3103 (1992); (5 pages) | Cited 1 time

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This paper describes a theoretical study pertaining to the effect of the viscosity and density of an adjacent viscous fluid on the characteristics of Love waves propagating in a layered half‐space medium. Expressions for the Love wave velocity and attenuation are obtained as functions of the viscosity and density of the fluid by exact and asymptotic analyses. The valid range of the asymptotic solution is identified by comparing it with the exact solution.
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43.20.Bi Mathematical theory of wave propagation
43.20.Fn Scattering of acoustic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Hq Velocity and attenuation of acoustic waves

On multidimensional ultrasonic scattering in an inhomogeneous elastic background

Eveline J. Aymé‐Bellegarda and Tarek M. Habashy

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3104-3115 (1992); (12 pages)

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This work is concerned with the modeling of elastic wave scattering by solid or fluid‐filled objects embedded in an inhomogeneous elastic background. The medium is probed by a monochromatic force and the scattered field is computed (forward problem) or observed (inverse problem) at some known receiver locations. Based on vector integral equations for elastic scattering, a general framework is developed, independent of both the problem geometry and the transmitter–receiver characteristics. This framework encompasses both forward and inverse modeling. In the forward model, a Born approximation for an inhomogeneous background is applied to obtain a closed form expression for the scattered field. In the inverse model, this approximation is also invoked to linearize for the mutliparameter characteristic of the object. Finally, an iterative inversion scheme alternating forward and inverse modeling is proposed to improve the resolution and accuracy of the reconstruction algorithm.
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43.20.Fn Scattering of acoustic waves
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries

Acoustic scattering by a rigid sphere in the field of waves emanating from a circular concave radiator

Takahi Hasegawa, Hideki Noda, Yasutaka Hino, Akio Annou, Masahiko Kato, and Naoki Inoue

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3116-3120 (1992); (5 pages) | Cited 1 time

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This paper presents a new method for calculating the velocity potential Φ of scattered ultrasonic waves from a rigid sphere placed in the field of waves emanating from a circular concave radiator in an infinite baffle. The solution Φ is given in the form of an infinite series of spherical surface harmonics as a function of reduced quantities ka, krc, kb, kz0, etc., where k is the wave number, a is the radius of the circular concave vibrator, rc is the radius of curvature of it, b is the radius of the sphere, and z0 is the distance from the piston to the center of the sphere. The present theoretical framework has the advantages that it includes no numerical integrations and that it is applicable to elastic or compressible sphere cases with slight modifications of the boundary conditions.
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43.20.Fn Scattering of acoustic waves

Radiation or scattering from multiple axisymmetric cylinders

Angie Sarkissian

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3121-3125 (1992); (5 pages) | Cited 1 time

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The boundary‐element method is applied to solve for the radiation or scattering from multiple cylinders having given surface normal velocity distributions. The axisymmetric case is considered where all cylinders have the same axis of symmetry with an arbitrary surface velocity field. The algorithm is applied to solve for scattering from rigid cylinders with hemispherical endcaps. Numerical results are presented for different two‐ or three‐cylinder configurations with a plane wave incident from various directions. The dependence of the scattered field on the distance between two identical cylinders is examined as well as scattering from one large and one small cylinder.
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43.20.Fn Scattering of acoustic waves
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods

Wave propagation interaction with free and fluid‐loaded piezoelectric substrates

Adnan H. Nayfeh and Hual‐Te Chien

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3126-3135 (1992); (10 pages) | Cited 3 times

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A unified analytical treatment is presented that is supported with numerical illustrations of the interactions of ultrasonic waves with piezoelectric anisotropic half‐space substrates. The solids are allowed to possess up to monoclinic anisotropic symmetry and associated piezoelectric coupling. The solids are also assumed to be loaded with water and subjected to incident acoustic beams at arbitrary polar and azimuthal angles. Simple analytical expressions for the reflection and transmission coefficients are derived from which all propagation characteristics are identified. Such expressions contain, as a by‐product, the secular equation for the propagation of free harmonic waves on the piezoelectric substrate. It is found that piezoelectric coupling, as well as water, influence both types of modes. Higher symmetry, such as orthotropic, transverse isotropic, and cubic, are contained implicitly in this analysis. This paper also demonstrates that the motion of the surface and SH modes uncouple for propagation along axis of symmetry. For such cases, however, piezoelectric coupling can influence one of these types of modes depending upon the type of piezoelectric model adopted.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Pt Surface waves in solids and liquids
43.20.Jr Velocity and attenuation of elastic and poroelastic waves

The validity of the linear orifice impedance model for predicting the impedance of a tube

Donald F. Elger

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3136-3143 (1992); (8 pages) | Cited 3 times

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The orifice impedance model usually works well for modeling sound transmission through an orifice. However, for a long orifice or for an orifice with a large load impedance, the standard impedance model may be invalid. The goal of this paper is to establish when the orifice impedance model gives a valid estimate of the impedance of a tube in series with a load impedance. The method involved a comparison of the orifice impedance model with a transmission line model. Comparison showed that if both ‖Γkl‖<0.1 and ‖ZL/Zc‖ <0.1, then the orifice impedance model is valid (Γ is the propagation coefficient, k is the wave number, l is the tube length, and ZL/Zc is dimensionless load impedance). If either of these limits is unsatisfied, then the validity of the orifice impedance model depends on six variables. Numerical comparisons of the two models showed the effects of these variables. Computations were restricted to air, and most calculations were in the shear wave‐number range of 1≤S≤100 [S=r0(ω/ν)1/2, where r0 is tube radius, ω is frequency, and ν is kinematic viscosity]. Graphical results show the limits of validity of the orifice impedance model.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Wd Analogies
43.25.Ts Nonlinear acoustical and dynamical systems
43.55.Rg Sound transmission through walls and through ducts: theory and measurement

Harmonic generation in finite amplitude sound beams from a rectangular aperture source

Tomoo Kamakura, Meiko Tani, Yoshiro Kumamoto, and Koji Ueda

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3144-3151 (1992); (8 pages) | Cited 6 times

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Theoretical analysis and some experiments are performed on nonlinearly generated harmonic components in bounded sound beams emitted from a rectangular aperture source. The Khokhlov–Zabolotskaya–Kuznetsov equation, which takes account of nonlinearity, dissipation, and diffraction effects in the beams, is numerically solved by means of the alternating direction implicit difference method. Using a planar source of size 24×44 cm, axial sound pressures and beam patterns of the first three harmonics are measured in air for initially sinusoidal ultrasounds of 25‐ and 30‐kHz frequency, and are compared with the theory. They are in relatively good agreement. Deformation of the source face from circular to rectangular shape results in the unclear appearance of pressure peaks and dips with propagation. Within the framework of these studies, the harmonic pressure levels in the far field are almost the same as from a circular aperture source with equal face area and equal initial pressure, independent of the source levels.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Separation devices based on forced coincidence response of fluid‐filled pipes

Thomas L. Tolt and Donald L. Feke

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3152-3156 (1992); (5 pages) | Cited 8 times

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A separation process based on the acoustic radiation force created in stationary fields produced by a forced coincidence excitation at ultrasonic frequencies of fluid‐filled pipes has been developed. The efficacy of this method for the collection and manipulation of fine secondary phases in flowing suspensions will be compared to equivalent operations in stationary fields generated in acoustic interferometer chambers operated without coincidence effects. The basis for the axial translation of the phases concentrated at the pressure nodes to either end of the cell as a result of an applied periodic sweep in the driving frequency will be examined.
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43.25.Qp Radiation pressure

Simulation of drop dynamics in an acoustic positioning chamber

Shermann L. Min, R. Glynn Holt, and Robert E. Apfel

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3157-3165 (1992); (9 pages) | Cited 4 times

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To support experiments scheduled for the First United States Microgravity Laboratory (USML‐1) shuttle mission, experimental and computer simulation methods have been developed which allow ground‐based investigation of the translational, rotational, and vibrational motions of single and dual liquid drops in an external acoustic field in a microgravity environment. The acoustic fields used are the 3‐D orthogonal resonant modes of a rectangular chamber. Hardware and software development are described in detail. Results for the translation of single and dual drops are presented, and semi‐automated schemes for controlled translation are proposed, tested, and evaluated.
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43.25.Uv Acoustic levitation

Sonoluminescence and bubble dynamics for a single, stable, cavitation bubble

D. Felipe Gaitan, Lawrence A. Crum, Charles C. Church, and Ronald A. Roy

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3166-3183 (1992); (18 pages) | Cited 156 times

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High‐amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa (1.5 atm) at 21–25 kHz. Sonoluminescence (SL), a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius‐time curves have been obtained which confirm the absence of surface waves, which are expected at pressure amplitudes above 100 kPa. [S. Horsburgh, Ph.D. dissertation, University of Mississippi (1990)]. Also from these radius‐time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation, and sonoluminescence are discussed.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Sound propagation over a surface with varying impedance: A parabolic equation approach

James N. Craddock and Michael J. White

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3184-3191 (1992); (8 pages) | Cited 2 times

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This paper describes modifications to a finite element solution for the wide angle parabolic equation (PE). The modifications to the PE allow the computationally efficient solution of the problem of sound propagation over ground whose impedance varies with range. In particular, the set of linear algebraic equations that propagate the field outward in range is solved with a UL (upper, lower triangular) decomposition, instead of the standard LU (lower, upper triangular) scheme. This approach allows the change in impedance to affect only a single element in the decomposition. Consequently, all previous calculations in the decomposition can be saved in proceeding from one range step to the next. Results are presented for several cases, in which the ground suffers an abrupt change in acoustic impedance at some distance along the propagation path. Comparisons to existing experimental data are made and the method presented here matches the published data quite well. Other diffraction cases are presented for which no experimental data are available, however the results are fairly self‐consistent and serve to indicate the versatility of this method. The approach described in this paper represents an accurate and efficient method for solving problems involving sound propagation over ground having a range‐dependent surface impedance.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors

Examination of three‐dimensional effects using a propagation model with azimuth‐coupling capability (FOR3D)

Ding Lee, George Botseas, and William L. Siegmann

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3192-3202 (1992); (11 pages) | Cited 11 times

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A three‐dimensional wave propagation model of parabolic approximation type (FOR3D) is used to examine 3‐D ocean environmental variations. The background theory and characteristics of the model are reviewed briefly. Propagation situations that are classified as 3‐D, N×2‐D, and 2‐D are described in connection with FOR3D and are interpreted in several ways. An analytic exact solution is used to demonstrate the model’s accuracy and its capability for treating fully 3‐D propagation, when coupling exists between solutions in adjacent vertical planes of constant azimuth. It is also employed to illustrate a procedure for using approximate conditions at vertical side boundaries in a 3‐D calculation. An application is made to an Atlantic Ocean shelf‐slope environment with realistic bottom topographic variations and sound‐speed profiles. The occurrence of significant azimuthal coupling is demonstrated in propagation loss versus range curves. It follows that, while the N×2‐D approximation of no azimuthal coupling is useful in many situations, not all 3‐D ocean acoustics problems can be adequately solved without a fully 3‐D propagation model.
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43.30.Bp Normal mode propagation of sound in water

Volume scattering in a shallow channel

Mark J. Beran and Shimshon Frankenthal

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3203-3211 (1992); (9 pages) | Cited 2 times

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Using a generalization of the modal coherence equations previously developed by Sutton and McCoy [J. Math. Phys. 18, 1052 (1977)], the effect of volume scattering in a shallow channel is treated. The difference between the range behavior of the cross‐modal coherence functions and the previously studied self‐modal coherence functions is shown. In particular, calculations are made to evaluate the characteristic scales that govern the range decay of the cross‐modal coherence functions. A particular example is given to illustrate the effect of the choice of different parameters.
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43.30.Ft Volume scattering

Ocean acoustics turbulence study: Acoustic scattering from a buoyant axisymmetric plume

L. Goodman, J. Oeschger, and D. Szargowicz

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3212-3227 (1992); (16 pages) | Cited 6 times

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Limited in situ measurements from high‐frequency underwater acoustic echosounders have suggested that there may be circumstances in which acoustic scattering from ocean temperature variability is sufficiently intense to be observable over volume reverberation due to biologics. A new laboratory program, the ocean acoustics turbulence study (OATS), has been undertaken to quantify such scattering. The laboratory employs a very precise computer‐controlled positioning system and allows a scattering geometry from a near forward‐scattering angle, 5°, to a near backscattering angle, 160°. This article reports on results of an initial set of experiments utilizing a 1‐MHz, 1‐cycle transmitted pulse scattering from a temperature anomaly field produced by a laminar buoyant plume. The objective of this experiment is to compare observations of acoustic scattering from the temperature anomaly with that predicted by the Bragg scattering condition. A parameter regime is chosen such that the laminar plume has an approximately axisymmetric and Gaussian temperature profile. For the two‐dimensional axisymmetric case, the Bragg scattering condition allows prediction of an acoustically derived two‐dimensional Fourier transform of the temperature field. The acoustically derived two‐dimensional Fourier transform and the one derived directly from in situ temperature measurements are in good agreement, except at the higher frequency range of the bandwidth of the scattered signal. Discussion of the possibility of inverting such measurements for a direct calculation of the temperature field is presented.
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43.30.Ft Volume scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Waveform inversion for the geoacoustic parameters of the ocean bottom

Subramaniam D. Rajan

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3228-3241 (1992); (14 pages) | Cited 4 times

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The geoacoustic properties of ocean sediments in deep water environments are important parameters necessary to predict low‐frequency acoustic fields in the water column. A full wave method for obtaining the geoacoustic parameters from the acoustic field measured as a function of range with a cw source is presented. By assuming horizontal stratification, the unknown geoacoustic parameters are reduced to functions of one variable, i.e., depth. The problem of estimating the geoacoustic properties of the ocean floor is then cast as a parameter estimation problem in which a cost function ϕ(m), where m is a vector containing the unknown parameters, is minimized. This problem is then solved using a nonlinear optimization algorithm. This algorithm requires the determination of the derivative ∂ϕ/∂m. For a fluid bottom model an efficient algorithm for obtaining these partial derivatives is presented. The performance of the inversion algorithm is studied using noise free and noisy synthetic data. These inversions are carried out using the complex pressure field and the magnitude of the field as data. For the noise‐free case, both approaches yield estimates close to the true value.
In the case of noisy data, inversions carried out using the magnitude of the pressure field as data do not perform as well as inversions where the data are the complex pressure field. However, in both cases the algorithm is stable. The effect of modeling errors on the estimates is studied and it is shown that even small errors in source/receiver location lead to significant errors in the estimates. The effect of modeling the sediment as a fluid on the estimation of its geoacoustic properties is studied. In the case where the sediment shear speed is much smaller than compressional wave speed, the fluid approximation has no significant effect on the estimate of the compressional wave speeds. On the other hand, if the shear speed is such that considerable conversion exists, the fluid bottom model leads to a poor estimate of the compressional wave speed. In both cases the estimates of compressional wave attenuation and density are significantly affected by the fluid approximation. Finally this method is applied to data obtained in a field experiment and an estimate of the compressional wave speed profile in the sediment layers is obtained. This result is compared with the model obtained by iteration of forward models [G. V. Frisk et al., J. Acoust. Soc. Am. 80, 591–600 (1986)].
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Estimation of sediment volume scattering cross section and absorption loss coefficient

Robert A. Stewart and Nicholas P. Chotiros

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3242-3247 (1992); (6 pages)

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A simple theoretical model for estimating the sediment volume scattering cross section and the absorption loss coefficient from the reverberation tail of an acoustic pulse observed by a point receiver within the ocean sediment is described. This model assumes an infinite plane wave entering the sediment at normal incidence and scattering isotropically from a uniform field of random point scatterers. The model predicts the magnitude and decay rate of the volume scattering at a point receiver in terms of the volume scattering cross section and the absorption coefficient of the medium. Experimental data were obtained from an array of in‐sediment acoustic probes deployed at a site near Jacksonville, Florida, and Kings Bay, Georgia. By fitting the predictions of the model to experimentally observed volume scattering data, the volume scattering cross sections and absorption coefficients of real sediments were inferred. The absorption coefficient and volume scattering cross‐section results were compared with attenuation measurements from core samples and with theoretical and experimental data from Hamilton [J. Acoust. Soc. Am. 68, 1313 (1980)], Nolle [J. Acoust. Soc. Am. 35, 1394–1408 (1963)], Turgut and Yamamoto [J. Acoust. Soc. Am. 87, 2376 (1990)], and Jackson et al. [J. Acoust. Soc. Am. 79, 1410 (1986)].
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Ft Volume scattering

An equivalent fluid approximation for a low shear speed ocean bottom

C. T. Tindle and Z. Y. Zhang

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3248-3256 (1992); (9 pages) | Cited 4 times

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The acoustic reflection coefficient for a homogeneous fluid over a homogeneous solid with a low shear speed is shown to be well approximated by replacing the solid with a fluid of different parameters. Explicit formulas for the density and attenuation coefficient of the equivalent fluid are given. Since the acoustic field in the upper fluid depends only on the reflection coefficient of the bottom, a uniform solid bottom with low shear speed can be approximated by assuming a fluid bottom with suitably chosen parameters. Shallow water examples are given.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Narrow‐band performance of phase‐conjugate arrays in dynamic random media

David R. Dowling and Darrell R. Jackson

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3257-3277 (1992); (21 pages) | Cited 25 times

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The theoretical narrow‐band performance of acoustic phase‐conjugate arrays in the presence of static and dynamic random media is presented. For a static random medium, analytical formulas are derived for the mean focus field of a Gaussian‐shaded volumetric phase‐conjugate array. The results suggest that random refraction allows phase‐conjugate arrays to ‘‘super focus,’’ that is, produce a focal region smaller than the free‐space diffraction limit. More specifically, vertical phase‐conjugate arrays are predicted to have horizontal directivity. In a dynamic random medium, phase‐conjugate array performance is degraded by changes in the medium that occur between the time that the acoustic signal is launched from its source and the time that the array’s transmission is received back at the source location (the round‐trip time delay). Formal results are obtained for an intrinsic signal‐to‐noise ratio for the signal sent from the phase‐conjugate array based on a combination of multiple scattering from static random refraction and single scattering from dynamic random refraction in the acoustic medium. These formal results are reduced to analytical formulas for a random medium characterized by the statistics of oceanic internal waves. The intrinsic signal‐to‐noise ratio is found to be proportional to: the inverse square of the round‐trip time delay, the inverse square of the acoustic frequency, the inverse first power of the array‐source range, and a simple function that combines the size of the array and the parameters of the random medium. For a typical deep‐water oceanic medium at acoustic frequencies near 10 kHz, phase‐conjugate array performance may be unaffected for round‐trip time delays as long as a minute.
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43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
43.30.Vh Active sonar systems
43.30.Ft Volume scattering
43.20.Fn Scattering of acoustic waves

Power‐law relationships between the dependence of ultrasonic attenuation on wavelength and the grain size distribution

Denise Nicoletti, Nihat Bilgutay, and Banu Onaral

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3278-3284 (1992); (7 pages) | Cited 2 times

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Grain size is one of the factors that influence mechanical properties of metals like strength and fracture toughness. Ultrasonic waves propagating in polycrystalline materials are subject to attenuation dominated by grain boundary scattering. The importance of grain size estimation for industrial applications warrants the investigation of alternative methods of nondestructive grain size determination. Analysis of the power‐law behavior of ultrasonic attenuation experimental data is used to link the wavelength dependence of the attenuation coefficient directly to the grain size distribution. The outcome is a simple relationship between the power law that describes the grain size distribution and the power‐law dependence of attenuation on wavelength. Careful attention is given to the limitations in terms of a practical grain size distribution with finite limits. Two types of measurements are presented to verify the theoretical development: grain size distribution and ultrasonic attenuation. Nickel samples were prepared using three different annealing durations. The attenuation exponent is experimentally shown to be an appropriate nondestructive measurement of the grain size distribution exponent.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

A modified ray theory for predicting the V(x,z) response of a point‐focus acoustic microscope in the presence of a crack

Dmitry Chizhik, Douglas A. Davids, Henry L. Bertoni, and Michael G. Somekh

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3285-3290 (1992); (6 pages)

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A modified geometric ray approach is used to predict the V(x,z) or the acoustic material signature of a circular point‐focus scanning acoustic microscope for an isotropic surface containing a surface‐breaking crack. The microscope response is assumed to consist of a specularly reflected geometric contribution, and the leaky contribution due in part to surface waves scattered from the crack. The long thin straight crack is presumed to be characterized by symmetric reflection and transmission coefficients. This approach is numerically simple and can be used to evaluate the response of acoustic lenses of various geometries. The method is used to predict line scan V(x,z0) response of a microscope in the vicinity of the crack for several defocus distances z0 and the results are compared with measurements.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Development of the active doublet method for measuring small velocity and attenuation changes in solids

Peter M. Roberts, W. Scott Phillips, and Michael C. Fehler

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3291-3302 (1992); (12 pages) | Cited 9 times

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The measurement of small changes in elastic wave velocity and attenuation is important to a broad range of problems, such as earthquake prediction and early detection of rock failure in mines. Previous authors proposed a method for estimating small temporal velocity changes in the earth’s crust by analyzing progressive relative phase delays between the scattered waves of two signals generated by nearly identical earthquake sources, called doublets, recorded at different times at the same receivers. Several improvements have been made to the original method and are presented here. The reliability of measured velocity changes has been increased by using active, repeatable sources instead of natural earthquakes. The robustness of the analysis technique has been improved by eliminating unnecessary intermediate phase regression steps and thus reducing the sensitivity to spurious data. Finally, the phase‐delay algorithm has been extended to allow measurement of small attenuation changes from relative amplitude decay rates. Using ultrasonic source and receiver transducers embedded in Plexiglas test samples, velocity changes as small as 0.01%, caused by ambient temperature variations in the Plexiglas, have been measured. Changes in attenuation on the order of 10%, due to permanent damage induced in one of the samples, have also been measured.
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43.35.Pt Surface waves in solids and liquids
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.40.Ph Seismology and geophysical prospecting; seismographs

Double through‐transmission bulk wave method for ultrasonic phase velocity measurement and determination of elastic constants of composite materials

S. I. Rokhlin and W. Wang

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3303-3312 (1992); (10 pages) | Cited 18 times

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This paper describes a modification of a nondestructive ultrasonic method for measurements of the phase velocity of bulk waves in arbitrary directions in generally anisotropic materials. In the conventional method the through‐transmission technique is used for velocity measurements at a specified angle of incidence. When this angle is changed by rotation of the sample, the transmitted beam changes position, and so the position of the receiving transducer must be changed. This leads to experimental difficulties and loss of precision. In the double‐transmission technique, the ultrasonic wave is reflected from reflector plates behind the sample and returns via the same path to the same position on the transmitter/receiver working in pulse‐echo mode, which eliminates the necessity of readjusting the receiver position. It is also shown that for arbitrary direction of measurement in anisotropic materials, time‐delay measurements give phase velocity regardless of the angle of deviation between phase and group velocities. The physical basis of this phenomenon is explained. An example of velocity measurement and elastic‐constant determination is given for unidirectional graphite–epoxy composite. Stability of the nonlinear least‐square algorithm used for reconstruction of the elastic constants from the velocity data is demonstrated by computer simulation on a synthetic set of data.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Yb Ultrasonic instrumentation and measurement techniques

Experiments on active control of structurally radiated sound using multiple piezoceramic actuators

Robert L. Clark and Chris R. Fuller

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3313-3320 (1992); (8 pages) | Cited 11 times

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Active control of sound radiation from a vibrating rectangular plate excited by a steady‐state harmonic point force disturbance is experimentally studied. Control structural inputs are achieved by three piezoceramic actuators bonded to the surface of the panel. Microphones were implemented as error sensors in the radiated field, while the control approach was based upon a filtered‐X version of the adaptive least‐mean‐squares (lms)algorithm. Both position and number of piezoceramic actuators were varied during the test to determine the effects on control authority. A variety of test cases were studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that piezoceramic elements provide an efficient method for distributed modification of structural response to attenuate sound radiation. In addition, the adaptive lms algorithm is shown to be an effective narrow‐band controller, which in contrast to feedback approaches, requires little system modeling.
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43.40.Dx Vibrations of membranes and plates
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

Modal sensing of efficient acoustic radiators with polyvinylidene fluoride distributed sensors in active structural acoustic control approaches

Robert L. Clark and Chris R. Fuller

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3321-3329 (1992); (9 pages) | Cited 13 times

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An experimental investigation was performed to determine the feasibility of implementing polyvinylidene fluoride (PVDF) piezoelectric distributed sensors on the surface of a structure as error sensors in an adaptive least‐mean‐squares (lms) control approach to minimize acoustic radiation. While much research has been devoted to controlling vibration of structures with these sensors, they have yet to be implemented in structural acoustic control. To this end, two narrow strip PVDF sensors were positioned on a simply supported plate such that the dominant observed response was due to the odd–odd modes of the plate (i.e., the more efficient acoustic radiators). The error sensors in effect act as spatial wave‐number filters and only observe those components that contribute significantly to far‐field sound radiation. A variety of test cases were studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that PVDF sensors and piezoceramic actuators show much promise for controlling acoustic radiation from structures, to a large degree overcoming the need for error microphones in the far field.
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43.40.Dx Vibrations of membranes and plates
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

Annoyance caused by simultaneous impulse, road‐traffic, and aircraft sounds: A quantitative model

Joos Vos

J. Acoust. Soc. Am. Volume 91, Issue 6, pp. 3330-3345 (1992); (16 pages) | Cited 4 times

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In this study, total annoyance caused by different simultaneous environmental sounds is investigated. In spite of a number of puzzling data in the literature, it is fairly well established that in combinations in which the annoyance of one source is considerably higher than that of another source, total annoyance is equal to the maximum annoyance of the separate sources. For combinations in which both sounds are about equally annoying, total annoyance seems to be higher than the maximum source‐specific annoyance. The available data, however, are too rough to model total annoyance in these conditions. The present laboratory studies were therefore designed to explore further possible procedures to quantify total annoyance. Subjects rated the (total) annoyance caused by various combinations of impulse, road‐traffic, and aircraft sounds.
The results support a simple model which predicts the overall or total rating sound level Lt for combinations of several types of sounds. Here, Lt is numerically equal to the A‐weighted equivalent sound level Leq of road‐traffic sound with the same annoyance as caused by the combination of sounds. In the model, the sound exposure caused by the impulse and/or aircraft sounds is first expressed in the Leq of equally annoying road‐traffic sound. With the help of source‐specific dose–effect relationships, this is achieved by adding level‐dependent penalties to the Leq of the respective sources. Weighted summation of the corrected Leq’s of the various sources then results in Lt. An optimal overall fit of the data from two separate experiments was obtained when the weighted summation of the corrected Leq’s was performed with the parameter k in k log{∑10(corrected Leq of source j)/k} set to 15. The standard deviation of the differences between the experimental results and the model predictions with k=15 was equivalent to the small change in annoyance produced by a 1.5‐dB shift in the Leq of road‐traffic sound. Adoption of k=15 implies that after correction, two equal Leq’s yield a total rating sound level which is 4.5 dB higher than each single‐source corrected Leq.
Show PACS
43.50.Ba Noisiness: rating methods and criteria
43.50.Pn Impulse noise and noise due to impact
43.50.Qp Effects of noise on man and society
43.50.Sr Community noise, noise zoning, by-laws, and legislation
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