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Journal of the Acoustical Society of America

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Jun 2010

Volume 127, Issue 6, pp. EL235-3881

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Internal waves as a proposed mechanism for increasing ambient noise in an increasingly acidic ocean

Daniel Rouseff and Dajun Tang

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL235-EL239 (2010); (5 pages)

Online Publication Date: 20 May 2010

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The effect on the ambient noise level in shallow water of the ocean growing more acidic is modeled. Because most noise sources are near the surface, high-order acoustic modes are preferentially excited. Linear internal waves, however, can scatter the noise into the low-order, low-loss modes most affected by the changes in acidity. The model uses transport theory to couple the modes and assumes an isotropic distribution for the noise sources. For a scenario typical of the East China Sea, the noise at 3 kHz is predicted to increase by 30%, about one decibel, as the pH decreases from 8.0 to 7.4.
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43.30.Bp Normal mode propagation of sound in water
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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Characterization of scattered acoustic intensity fields in the resonance region of a motionless rigid sphere

Robert J. Barton, III, Kevin B. Smith, and Harold T. Vincent, III

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL240-EL245 (2010); (6 pages)

Online Publication Date: 20 May 2010

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In this study, the properties of the scattered acoustic vector fields generated by simple rigid motionless spheres are investigated. Analytical solutions are derived from general acoustic pressure scattering models, and analyzed for wave numbers in the resonance region. The separable active and reactive components of the acoustic intensity are used to investigate the structural features of the scattered field components. Numerical results are presented. The ability to extract scattered field features is illustrated with measurements obtained from a recent in-air experiment using an anechoic chamber and acoustic intensity probes to measure the scattered acoustic vector field from motionless rigid spheres.
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43.20.Fn Scattering of acoustic waves
43.30.Vh Active sonar systems
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Acoustic emission monitoring of degradation of cross ply laminates

D. G. Aggelis, N. M. Barkoula, T. E. Matikas, and A. S. Paipetis

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL246-EL251 (2010); (6 pages) | Cited 2 times

Online Publication Date: 20 May 2010

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The scope of this study is to relate the acoustic activity of damage in composites to the failure mechanisms associated with these materials. Cross ply fiber reinforced composites were subjected to tensile loading with recording of their acoustic activity. Acoustic emission (AE) parameters were employed to monitor the transition of the damage mechanism from transverse cracking (mode I) to delamination (mode II). Wave propagation measurements in between loading steps revealed an increase in the relative amplitude of the propagated wave, which was attributed to the development of delamination that confined the wave to the top longitudinal plies of the composite.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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Measurement of thickness or plate velocity using ambient vibrations

Ros K. Ing, Nicolas Etaix, Alexandre Leblanc, and Mathias Fink

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL252-EL257 (2010); (6 pages)

Online Publication Date: 28 May 2010

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Assuming the Green’s function is linear with respect to the boundary conditions, it is demonstrated that flexural waves detected by a point receiver and a circular array of point receivers centered on the previous receiver are proportional regardless location of the source and geometry of the plate. Therefore determination of plate velocity or thickness is done from the measurement of ambient vibrations without using any emitter. Experimental results obtained with a plate of non regular geometry excited with a single transducer or a remote loudspeaker are shown to verify the theoretical approach.
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43.20.Ye Measurement methods and instrumentation
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
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Exploring the benefit of auditory spatial continuity

Virginia Best, Barbara G. Shinn-Cunningham, Erol J. Ozmeral, and Norbert Kopčo

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. EL258-EL264 (2010); (7 pages)

Online Publication Date: 28 May 2010

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Continuity of spatial location was recently shown to improve the ability to identify and recall a sequence of target digits presented in a mixture of confusable maskers [ Best et al. (2008). Proc. Natl. Acad. Sci. U.S.A. 105, 13174–13178 ]. Three follow-up experiments were conducted to explore the basis of this improvement. The results suggest that the benefits of spatial continuity cannot be attributed to (a) the ability to plan where to direct attention in advance; (b) freedom from having to redirect attention across large distances; or (c) the challenge of filtering out signals that are confusable with the target.
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43.66.Qp Localization of sound sources
43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
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Using cross-correlations of elastic diffuse fields for attenuation tomography of structural damage

Adelaide Duroux, Karim G. Sabra, James Ayers, and Massimo Ruzzene

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3311-3314 (2010); (4 pages) | Cited 3 times

Online Publication Date: 09 Jun 2010

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A scanning laser Doppler vibrometer is used to measure, at multiple grid points, the diffuse vibrations (50–150 kHz) propagating over a thin aluminum plate with complex geometry. These diffuse vibrations were generated by a few pulsed laser impacts randomly distributed outside of the measurement grid. The pairwise cross-correlations of the diffuse field recorded at all grid points provided an estimate of the first antisymmetric Lamb mode direct arrival between these grid points. Attenuation tomography imaging of a simulated structural damage is performed based on the relative amplitude variations of these direct arrivals between the damaged and undamaged conditions.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.Sk Inverse problems in structural acoustics and vibration
43.40.Hb Random vibration
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Detection of damage in concrete using diffuse ultrasound

Frederik Deroo, Jin-Yeon Kim, Jianmin Qu, Karim Sabra, and Laurence J. Jacobs

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3315-3318 (2010); (4 pages)

Online Publication Date: 09 Jun 2010

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This letter demonstrates the potential for using diffuse ultrasound measurements to detect damage in concrete. Two different solutions to the diffusion equation, an infinite three-dimensional (3D) volume model that neglects geometric boundaries and a finite 3D cuboid model, are used for the required curve fitting procedure to determine the influence of geometric boundaries on the solution. The measurements consider two types of microcrack damage in concrete, alkali-silica reaction and thermal damage, and show that the measured diffusivity parameter is related to the amount of damage in each specimen.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
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Finite-element modeling of depth and range dependent acoustic propagation in oceanic waveguides

Chiruvai P. Vendhan, Ganesh C. Diwan, and Subrata K. Bhattacharyya

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3319-3326 (2010); (8 pages)

Online Publication Date: 09 Jun 2010

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Finite-element models (FEMs) of ocean acoustic waveguides are capable of predicting the full wave solution including the effect of inhomogeneities and interfaces. However the method appears computationally feasible at present only for low to intermediate frequencies. The FEM discussed in this paper treats the radiation boundary condition involving multiple propagating modes using a penalty function approach. The effect of a point source has been represented as a pressure boundary condition on a small boundary surrounding the source. The FEM has been validated with a few examples of ideal waveguides. The FE results for a range and depth dependent parallel waveguide—an ASA benchmark problem [ F. B. Jensen and C. M. Ferla, J. Acoust. Soc. Am. 87, 1499–1520 (1990) ]—compare well with published results.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.30.Bp Normal mode propagation of sound in water
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Theory of compact nonporous windscreens for infrasonic measurements

Allan J. Zuckerwar

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3327-3334 (2010); (8 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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The principle of the compact nonporous windscreen is based on the great penetrability of infrasound through matter. The windscreen performance is characterized by the ratio of the sound pressure at an interior microphone, located in the center of a windscreen, to the incident sound pressure in the free field. The frequency dependence of this pressure ratio is derived as a function of the windscreen material and geometric properties. Four different windscreen geometries are considered: a subsurface, box-shaped windscreen, a cylindrical windscreen of infinite length, a cylindrical windscreen of finite length, and a spherical windscreen. Results are presented for windscreens made of closed-cell polyurethane foam and for typical dimensions of each of the above geometries. The cylindrical windscreen of finite length, featuring evanescent radial modes, behaves as a unity-gain, low-pass filter, cutting off sharply at the end of the infrasonic range. The remaining geometries reveal a pass band that extends well into the audio range, terminated by a pronounced peak beyond which the response plummets rapidly.
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43.28.Dm Infrasound and acoustic-gravity waves
43.50.Yw Instrumentation and techniques for noise measurement and analysis

Meteorological influence on sound propagation between adjacent city canyons: A real-life experiment

Timothy Van Renterghem and Dick Botteldooren

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3335-3346 (2010); (12 pages)

Online Publication Date: 09 Jun 2010

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Sound propagation between a courtyard and an adjacent street canyon, as influenced by a wide range of meteorological conditions, was investigated by means of a real-life experiment in a dense urban setting. During several months, test signals were emitted on a regular base by an outdoor loudspeaker in the courtyard and recorded by wall-mounted microphones in the courtyard and the street canyon. Detailed meteorological observations were made at nearby buildings with sensors at roof level. A thorough quality check of the recorded signals was performed, given the large amount of shielding and the presence of background noise. With increasing wind speed and sound frequency, a strong increase in coherence loss was observed. The wide variety of measured vertical temperature lapses was shown to have no effect given the short propagation distance. With increasing downwind wind speed, refraction into the shielded canyon was observed to a limited degree only. The rather small effect of building-induced refraction of sound by wind could be qualitatively explained by the geometry of the city canyons under study.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics

Predicting transmission of shaped sonic booms into a residential house structure

Natalia V. Sizov, Kenneth J. Plotkin, and Christopher M. Hobbs

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3347-3355 (2010); (9 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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Human perception of sonic booms is a major impediment to commercial supersonic flight. Shaping, which reduces the audible shock waves of a boom, can make outdoor perception of booms acceptable. Perception of sonic booms experienced indoors is of concern, and it is not yet established whether shaped booms offer benefit to indoor listeners. A better understanding of the transmission of shaped booms into building structures is needed. In the authors’ earlier work the vibration response of house elements subjected to different sonic boom wave shapes was evaluated using a single degree of freedom model. This paper expands that approach with a modal analysis model. The acceleration of building elements and the resulting sound pressure inside a room are computed in the time and frequency domains. Analytical results are compared with experimental data measured by NASA during sonic boom tests conducted at Edwards Air Force Base in 2007. The effects of wave signature parameters on transmission are studied to evaluate the advantages of various kinds of minimized boom shapes.
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43.28.Mw Shock and blast waves, sonic boom
43.55.Rg Sound transmission through walls and through ducts: theory and measurement
43.40.Dx Vibrations of membranes and plates
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Acoustic scattering from a solid aluminum cylinder in contact with a sand sediment: Measurements, modeling, and interpretation

Kevin L. Williams, Steven G. Kargl, Eric I. Thorsos, David S. Burnett, Joseph L. Lopes, Mario Zampolli, and Philip L. Marston

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3356-3371 (2010); (16 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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Understanding acoustic scattering from objects placed on the interface between two media requires incorporation of scattering off the interface. Here, this class of problems is studied in the particular context of a 61 cm long, 30.5 cm diameter solid aluminum cylinder placed on a flattened sand interface. Experimental results are presented for the monostatic scattering from this cylinder for azimuthal scattering angles from 0° to 90° and frequencies from 1 to 30 kHz. In addition, synthetic aperture sonar (SAS) processing is carried out. Next, details seen within these experimental results are explained using insight derived from physical acoustics. Subsequently, target strength results are compared to finite-element (FE) calculations. The simplest calculation assumes that the source and receiver are at infinity and uses the FE result for the cylinder in free space along with image cylinders for approximating the target/interface interaction. Then the effect of finite geometries and inclusion of a more complete Green’s function for the target/interface interaction is examined. These first two calculations use the axial symmetry of the cylinder in carrying out the analysis. Finally, the results from a three dimensional FE analysis are presented and compared to both the experiment and the axially symmetric calculations.
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43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.40.Fz Acoustic scattering by elastic structures

Dispersion and attenuation due to scattering from heterogeneities of the frame bulk modulus of a poroelastic medium

Brian T. Hefner and Darrell R. Jackson

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3372-3384 (2010); (13 pages)

Online Publication Date: 09 Jun 2010

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While Biot theory can successfully account for the dispersion observed in sand sediments, the attenuation at high frequencies has been observed to increase more rapidly than Biot theory would predict. In an effort to account for this additional loss, perturbation theory is applied to Biot’s poroelastic equations to model the loss due to the scattering of energy from heterogeneities in the sediment. A general theory for propagation loss is developed and applied to a medium with a randomly varying frame bulk modulus. The theory predicts that these heterogeneities produce an overall softening of the medium as well as scattering of energy from the mean fast compressional wave into incoherent fast and slow compressional waves. This theory is applied to two poroelastic media: a weakly consolidated sand sediment and a consolidated sintered glass bead pack. The random variations in the frame modulus do not have significant effects on the propagation through the sand sediment but do play an important role in the propagation through the consolidated medium.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves

Wind-generated ambient noise in a shallow brackish water environment in the archipelago of the Gulf of Finland

Ari Poikonen and Seppo Madekivi

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3385-3393 (2010); (9 pages) | Cited 3 times

Online Publication Date: 09 Jun 2010

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Underwater ambient noise measurements were carried out in a shallow (15–20 m) brackish water in the archipelago of the Gulf of Finland for period of 1 year. The absence of traffic noise made it possible to study wind driven effects in ambient noise at lower frequencies. The ambient noise comes mostly from local sources and the propagation effects are shown to be negligible. The ambient noise develops bubble type spectral features above 100 Hz as wind speed increases. Sharp spectral declines are observed below 500 Hz, which are most likely due to resonances from oscillating bubble clouds created by breaking waves. The low frequency range of the observed declines may partly be attributed to the larger bubble size in fresh and brackish waters. In the present study the wind speed dependence factor was ∼ 2.4 at 200 Hz, which is significantly higher than the typical factor of ∼ 1.5 for the ocean environment. The average high-frequency spectral slope was −4.9 dB/octave which is ∼ 1 dB/octave less than for typical deep water slopes. No significant seasonal effects were found in any parameter calculated from the ambient noise spectra.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Model calculations of the underwater noise of breaking waves and comparison with experiment

Grant B. Deane and M. Dale Stokes

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3394-3410 (2010); (17 pages) | Cited 4 times

Online Publication Date: 09 Jun 2010

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A model for the underwater noise of whitecaps is presented and compared with the noise measured beneath plunging seawater laboratory waves. The noise from a few hundred hertz up to at least 80 kHz is assumed to be due to the pulses of sound radiated by bubbles formed within a breaking wave crest. The total noise level and its dependence on frequency are a function of bubble creation rate, bubble damping factor and an ‘acoustical skin depth’ associated with scattering and absorption by the bubble plume formed within the crest. Calculation of breaking wave noise is made using estimates of these factors, which are made independently of the noise itself. The results are in good agreement with wave noise measured in a laboratory flume when compensated for reverberation. A closed-form, analytical expression for the wave noise is presented, which shows a −11/6 power-law dependence of noise level on frequency, in good agreement with the −10/6 scaling law commonly observed in the open ocean.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Inversion for range-dependent water column sound speed profiles on the New Jersey shelf using a linearized perturbative method

Megan S. Ballard and Kyle M. Becker

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3411-3421 (2010); (11 pages) | Cited 3 times

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The environment of the New Jersey shelf is characterized by high spatial and temporal variability of water column properties caused by intrusions of warm, salty water from the continental slope. These intrusions cause fluctuations in the water column sound speed profile which can have significant effects on acoustic propagation in shallow water. In this work, a linearized perturbative inverse technique is applied to estimate range-dependent water column sound speed profiles. This method utilizes estimates of horizontal wave numbers to determine sound speed as a function of depth. This technique is appropriate for the range-dependent shallow-water environment as horizontal wave numbers can be measured semilocally (1–2 km aperture) and their values are a direct measurement of the local environmental parameters. Difficulty is encountered in application of the perturbative inverse technique because the wave number data are insensitive to some portions of the waveguide and, as a result, the solution can deviate wildly from true values. This issue is addressed by application of approximate equality constraints which force the solution to be close to likely values at prescribed locations.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Bp Normal mode propagation of sound in water

A deterministic (non-stochastic) low frequency method for geoacoustic inversion

A. Tolstoy

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3422-3429 (2010); (8 pages)

Online Publication Date: 09 Jun 2010

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It is well known that multiple frequency sources are necessary for accurate geoacoustic inversion. This paper presents an inversion method which uses the low frequency (LF) spectrum only to estimate bottom properties even in the presence of expected errors in source location, phone depths, and ocean sound-speed profiles. Matched field processing (MFP) along a vertical array is used. The LF method first conducts an exhaustive search of the (five) parameter search space (sediment thickness, sound-speed at the top of the sediment layer, the sediment layer sound-speed gradient, the half-space sound-speed, and water depth) at 25 Hz and continues by retaining only the high MFP value parameter combinations. Next, frequency is slowly increased while again retaining only the high value combinations. At each stage of the process, only those parameter combinations which give high MFP values at all previous LF predictions are considered (an ever shrinking set). It is important to note that a complete search of each relevant parameter space seems to be necessary not only at multiple (sequential) frequencies but also at multiple ranges in order to eliminate sidelobes, i.e., false solutions. Even so, there are no mathematical guarantees that one final, unique “solution” will be found.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Jn Source localization and parameter estimation
43.60.Kx Matched field processing

Experimental demonstration of a high-frequency forward scattering acoustic barrier in a dynamic coastal environment

Karim G. Sabra, Stephane Conti, Philippe Roux, Tuncay Akal, William A. Kuperman, J. Mark Stevenson, Alessandra Tesei, and Piero Guerrini

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3430-3439 (2010); (10 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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Detecting a target by measuring its forward scattered field is of interest for harbor surveillance because target strength levels are generally higher in the forward direction than in the backward direction for simple geometries. An acoustic barrier based on forward scattering was demonstrated in a nearly range-independent shallow water environment. The experimental location was characterized by high reverberation, low temporal signal coherence, and, as a result, few stable multipath arrivals due to the fluctuating sea surface. This high-frequency experiment utilized a vertical source array, broadcasting broadside pulses, and a vertical receiver array spanning the water column. The signal of interest was the aberration (in space and time) caused by the acoustic forward scattering field of crossing targets (2-m-long aluminum cylinder, 1-m-diameter steel sphere and pair of scuba tanks). Hence, the spatial and temporal coherence of the recorded acoustic signals was first investigated to assess the stability of the early acoustic arrivals in this rapidly fluctuating coastal environment. A principal component analysis of the stable portion of the recorded acoustic signals was then used to determine the crossing time of the target and to isolate some of its scattered wavefield components.
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43.30.Vh Active sonar systems
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.60.Fg Acoustic array systems and processing, beam-forming
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The scattering of the fundamental torsional mode from axi-symmetric defects with varying depth profile in pipes

R. Carandente, J. Ma, and P. Cawley

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3440-3448 (2010); (9 pages)

Online Publication Date: 09 Jun 2010

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Guided ultrasonic waves have been successfully applied to detect defects and corrosion in plates and pipes; however, defect sizing remains challenging due to the complex profiles of the defects encountered in practice. A study of the reflection of the fundamental torsional mode T(0,1) from an axi-symmetric defect with varying depth profile has been carried out via finite element modeling and experimental validation. Defects with gradually varying depth are represented by a series of tapered steps. It is revealed that, for both tapered up- and down-steps, the wave packet is reflected only at the start and end of the steps. The reflections from the start and end of the step have been predicted, and the frequency dependence of the overall reflection from the step has been studied. The study shows that the reflection coefficient varies as a function of the ratio of the average length of the tapered defect to the wavelength due to the interference between the waves reflected from the two ends of the defect. The reflection coefficient maxima decrease as the slope of the taper becomes more gradual, this effect being more pronounced when the ratio of the average defect length to the wavelength increases.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.20.Mv Waveguides, wave propagation in tubes and ducts

Determination of postexcitation thresholds for single ultrasound contrast agent microbubbles using double passive cavitation detection

Daniel A. King, Michael J. Malloy, Alayna C. Roberts, Alexander Haak, Christian C. Yoder, and William D. O’Brien, Jr.

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3449-3455 (2010); (7 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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This work presents experimental responses of single ultrasound contrast agents to short, large amplitude pulses, characterized using double passive cavitation detection. In this technique, two matched, focused receive transducers were aligned orthogonally to capture the acoustic response of a microbubble from within the overlapping confocal region. The microbubbles were categorized according to a classification scheme based on the presence or absence of postexcitation signals, which are secondary broadband spikes following the principle oscillatory response of the ultrasound contrast agent and are indicative of the transient collapse of the microbubble. Experiments were conducted varying insonifying frequencies (0.9, 2.8, 4.6, and 7.1 MHz) and peak rarefactional pressures (200 kPa to 6.2 MPa) for two types of contrast agents (Definity® and Optison™). Results were fit using logistic regression analysis to define pressure thresholds where at least 5% and 50% of the microbubble populations collapsed for each frequency. These thresholds were found to occur at lower pressures for Definity than for Optison over the range of frequencies studied; additionally, the thresholds occurred at lower pressures with lower frequencies for both microbubble types in most cases, though this trend did not follow a mechanical index scaling.
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43.35.Ei Acoustic cavitation in liquids

Transient cavitation in high-quality-factor resonators at high static pressures

D. Felipe Gaitan, Ross A. Tessien, Robert A. Hiller, Joel Gutierrez, Corey Scott, Henry Tardif, Brant Callahan, Thomas J. Matula, Lawrence A. Crum, R. Glynn Holt, Charles C. Church, and Jason L. Raymond

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3456-3465 (2010); (10 pages) | Cited 6 times

Online Publication Date: 09 Jun 2010

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It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye [sonoluminescence (SL)]. Considerable attention has been devoted to the phenomenon of “single bubble sonoluminescence” (SBSL) in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa (1 bar), and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa (300 bars). This system generates bursts of violent inertial cavitation events lasting only a few milliseconds (hundreds of acoustic cycles), in contrast with the repetitive cavitation events (lasting several minutes) observed in SBSL; accordingly, these events are described as “inertial transient cavitation.” Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.
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43.35.Ei Acoustic cavitation in liquids
43.35.Hl Sonoluminescence

Optical Bragg imaging of acoustic fields after reflection

Nico F. Declercq, Michael S. McPherson, Mack A. Breazeale, and Alem A. Teklu

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3466-3469 (2010); (4 pages) | Cited 1 time

Online Publication Date: 09 Jun 2010

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Bragg diffraction of x-rays occurs when the rays interact with a crystalline lattice at the appropriate angle. Bragg diffraction of visible light occurs when the light interacts at the Bragg angle with an ultrasonic field of the appropriate frequency. (The spacing between acoustic condensations and rarefactions acts like the planes in an atomic lattice.) If a beam of light is Bragg diffracted by an ultrasonic beam that previously has passed through an object, an image of the structure of the object is made visible in the diffraction field of the optical beam since there is a one-to-one mapping of the ultrasonic field onto the diffraction order. In many acoustic Bragg imaging applications, the sound field must pass through the object which is to be imaged. Ultrasonic attenuation at the very high acoustic frequencies needed for Bragg imaging (typically ∼ 25–30 MHz) severely limits the nondestructive testing (NDT) applications of traditional acoustic Bragg imaging. In this paper, a reflection-based application of acoustic Bragg imaging is discussed which may have useful industrial and biomedical NDT applications.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Fn Scattering of acoustic waves

Thermoacoustic properties of fibrous materials

Carl Jensen and Richard Raspet

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3470-3484 (2010); (15 pages)

Online Publication Date: 09 Jun 2010

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The thermoacoustic properties of fibrous materials are studied using a computational fluid simulation as a test of proposed analytical models for propagation in porous materials with an ambient temperature gradient. The acoustic properties of porous materials have been understood in terms of microstructural models that approximate the material as an array of pores with empirical shape factors used to fit the pore theory to the material. An extension of these theories of acoustics to the thermoacoustic case with an ambient temperature gradient has been proposed by Roh et al. [J. Acoust. Soc. Am. 121, 1413–1422 (2007)] and a model based on Wilson’s relaxation approximation for porous acoustics [ J. Acoust. Soc. Am. 94, 1136–1145 (1993) ] is proposed herein, but the predictions of these analytical models have not been tested successfully against measurements. Accurately characterizing the effects of the applied temperature gradient in a wide bandwidth laboratory setup have proven difficult; as a result, the authors conducted a numerical simulation of propagation within a fibrous geometry in order to test the predictions of the analytical models. The results for several fibrous samples show that the models yield a reliable prediction of thermoacoustic performance from the shape factors and relaxation times.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts

Low-frequency pulse echo reflection of the fundamental shear horizontal mode from part-thickness elliptical defects in plates

J. Ma and P. Cawley

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3485-3493 (2010); (9 pages)

Online Publication Date: 09 Jun 2010

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Defect characterization using guided ultrasonic waves remains a challenging subject and requires a full understanding of the interaction of guided waves with a realistic representation of the defect. The characteristics of pulse echo reflection of the SH0 mode from part-thickness elliptical defects in plates is studied via finite element analysis and experimental measurements. The study shows that the reflection ratio spectrum of the SH0 mode from an elliptical defect exhibits periodic pattern due to interference between reflections from the two edges of the defect. The pattern of the reflection ratio spectrum is determined by the ratio of defect length in the incidence direction to wavelength, while the magnitude is affected by the maximum depth and the effective aspect ratio of the defect. Both the pattern and magnitude of the reflection ratio spectrum are found to be highly sensitive to the incidence angle, and the form of the variation of the reflection with angle is a strong function of the defect shape. In addition, a study of circular defects with tapered depth profiles reveals that the reflection is a function of average length of the tapered defect to wavelength ratio, and the magnitude of the reflection diminishes as the ratio increases.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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A stepped-plate bi-frequency source for generating a difference frequency sound with a parametric array

Yub Je, Haksue Lee, Jongkyu Park, and Wonkyu Moon

J. Acoust. Soc. Am. Volume 127, Issue 6, pp. 3494-3502 (2010); (9 pages)

Online Publication Date: 09 Jun 2010

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An ultrasonic radiator is developed to generate a difference frequency sound from two frequencies of ultrasound in air with a parametric array. A design method is proposed for an ultrasonic radiator capable of generating highly directive, high-amplitude ultrasonic sound beams at two different frequencies in air based on a modification of the stepped-plate ultrasonic radiator. The stepped-plate ultrasonic radiator was introduced by Gallego-Juarez et al. [Ultrasonics 16, 267–271 (1978)] in their previous study and can effectively generate highly directive, large-amplitude ultrasonic sounds in air, but only at a single frequency. Because parametric array sources must be able to generate sounds at more than one frequency, a design modification is crucial to the application of a stepped-plate ultrasonic radiator as a parametric array source in air. The aforementioned method was employed to design a parametric radiator for use in air. A prototype of this design was constructed and tested to determine whether it could successfully generate a difference frequency sound with a parametric array. The results confirmed that the proposed single small-area transducer was suitable as a parametric radiator in air.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
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