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Journal of the Acoustical Society of America

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Mar 2011

Volume 129, Issue 3, pp. EL57-1675

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Dutch and English listeners’ interpretation of vowel duration

Suzanne V. H. van der Feest and Daniel Swingley

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL57-EL63 (2011); (7 pages)

Online Publication Date: 02 Mar 2011

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Dutch and English listeners’ interpretation of vowel duration changes was examined in a word transcription task. Listeners were presented with spoken words realized with canonical or altered vowel durations. Dutch listeners often misperceived lengthened short vowels and shortened long vowels, identifying them as the short/long counterpart of the target, whereas English listeners more rarely misidentified words with altered vowel duration. Although Dutch and English are similar prosodically and phonologically, listeners’ treatment of vowel duration in clear speech is different across the two languages.
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43.71.Hw Cross-language perception of speech
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.Sy Spoken language processing by humans
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Impact of wall rotation on supraglottal jet stability in voiced speech

Byron D. Erath and Michael W. Plesniak

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL64-EL70 (2011); (7 pages) | Cited 3 times

Online Publication Date: 02 Mar 2011

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Supraglottal jet variability was investigated in a scaled-up flow facility incorporating driven vocal fold models with and without wall rotation. Principle component analysis was performed on the experimental supraglottal flow fields to ascertain the roll of glottal wall motion on the development of the supraglottal jet. It is shown that intraglottal flow asymmetries that develop due to wall rotation are not the primary mechanism for generating large-scale cycle-to-cycle deflection of the supraglottal jet. However, wall rotation does decrease the energy content of the first mode, redistributing it to the higher modes through an increase in unstructured flow variability.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
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Long-range acoustic communication in deep water using a towed array

H. C. Song, S. Cho, T. Kang, W. S. Hodgkiss, and J. R. Preston

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL71-EL75 (2011); (5 pages)

Online Publication Date: 02 Mar 2011

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In September 2010 a long-range acoustic communication (LRAC10) experiment was carried out in deep water off the Southern California Coast. The experiment involved two mobile components: (1) a source towed slowly at a speed of 2–3 knots at ∼75-m depth and (2) a horizontal line array towed at 3.5 knots at a depth of ∼200 m. Phase-coherent communication sequences were transmitted in the frequency band of 200–300 Hz at various ranges (100–700 km). Initial analysis of the LRAC10 data demonstrates that an information rate of 50 bits/s can be achieved over ∼550-km range using quadrature-phase shift-keying (QPSK) modulation and error-correction coding combined with beamforming.
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43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
43.60.Fg Acoustic array systems and processing, beam-forming
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Effect of bubble shell nonlinearity on ultrasound nonlinear propagation through microbubble populations

Meng-Xing Tang, Jonathan Loughran, Eleanor Stride, Dong Zhang, and Robert J. Eckersley

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL76-EL82 (2011); (7 pages) | Cited 1 time

Online Publication Date: 04 Mar 2011

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Nonlinear propagation of ultrasound through microbubble populations can generate artifacts and reduce contrast to tissue ratio in ultrasound imaging. The existing propagation model, which underestimates harmonic generation by an order of magnitude, was revised by incorporating a nonlinear constitutive equation for the coating into the description of the microbubble dynamics. Significantly better agreement with experiments was obtained, indicating that coating nonlinearity represents an important contribution to nonlinear propagation of ultrasound in microbubble populations. The results were found to be sensitive to the parameters characterizing the coating nonlinearity and thus accurate measurement of these parameters is required for accurate quantitative predictions.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.80.Qf Medical diagnosis with acoustics
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A candidate mechanism for exciting sound during bubble coalescence

Helen Czerski

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL83-EL88 (2011); (6 pages)

Online Publication Date: 04 Mar 2011

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Coalescing bubbles are known to produce a pulse of sound at the moment of coalescence, but the mechanism driving the sound production is uncertain. A candidate mechanism for the acoustic forcing is the rapid increase in the bubble volume, as the neck of air joining the two parent bubbles expands. A simple model is presented here for the volume forcing caused by the coalescence dynamics, and its predictions are tested against the available data. The model predicts the right order of magnitude for the acoustic amplitude, and the predicted amplitudes also scale correctly with the radius of the smaller parent bubble.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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Deduction of static surface roughness from complex excess attenuation

Andrew Nichols, Keith Attenborough, and Shahram Taherzadeh

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL89-EL93 (2011); (5 pages)

Online Publication Date: 09 Mar 2011

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Data for complex excess attenuation have been used to determine the effective surface admittance and hence characteristic roughness size of a surface comprising a random distribution of semi-cylindrical rods on an acoustically hard plane. The inversion for roughness size is based on a simplified boss model. The technique is shown to be effective to within 4%, up to a threshold roughness packing density of 32%, above which the interaction between scattering elements appears to exceed that allowed by the model.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.58.Bh Acoustic impedance measurement
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Mapping the sound field of an erupting submarine volcano using an acoustic glider

Haru Matsumoto, Joseph H. Haxel, Robert P. Dziak, Delwayne R. Bohnenstiehl, and Robert W. Embley

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. EL94-EL99 (2011); (6 pages)

Online Publication Date: 09 Mar 2011

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An underwater glider with an acoustic data logger flew toward a recently discovered erupting submarine volcano in the northern Lau basin. With the volcano providing a wide-band sound source, recordings from the two-day survey produced a two-dimensional sound level map spanning 1 km (depth) × 40 km(distance). The observed sound field shows depth- and range-dependence, with the first-order spa tial pattern being consistent with the predictions of a range-dependent propagation model. The results allow constraining the acoustic source level of the volcanic activity and suggest that the glider provides an effective platform for monitoring natural and anthropogenic ocean sounds.
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43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Zk Experimental modeling
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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Evidence for the central origin of lexical tone normalization (L)

Jingyuan Huang and Lori L. Holt

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1145-1148 (2011); (4 pages)

Online Publication Date: 09 Mar 2011

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Huang and Holt [(2009). J. Acoust. Soc. Am. 125, 3983–3994] suggest that listeners may dynamically tune lexical tone perception via general auditory sensitivity to the mean f0 of the preceding context, effectively normalizing pitch differences across talkers. The present experiments further examine the effect using the missing-f0 phenomenon as a means of determining the level of auditory processing at which lexical tone normalization occurs. Speech contexts filtered to remove or mask low-frequency f0 energy elicited contrastive context effects. Central, rather than peripheral, auditory processes may be responsible for the context-dependence that has been considered to be lexical tone normalization.
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43.71.An Models and theories of speech perception
43.66.Ba Models and theories of auditory processes
43.71.Hw Cross-language perception of speech

Vowel-related tongue movements in speech: Straight or curved paths? (L)

Anders Löfqvist

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1149-1152 (2011); (4 pages)

Online Publication Date: 09 Mar 2011

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This paper examines tongue movements between the two vowels in sequences of vowel-labial consonant-vowel, addressing the question whether the movement is a straight line or a curved path. Native speakers of Japanese and Italian served as subjects. The linguistic material consisted of words where the bilabial consonant was either long or short. The inclusion of words with different consonant lengths was motivated by earlier findings that the tongue movement is often longer when the consonant is long, which may be due to a more curved movement path. Tongue movements were recorded using a three-transmitter magnetometer system. To assess the movement path, the movement magnitude was calculated in two ways, as a straight line, the Euclidean distance, and as the actual path, obtained by summing the individual Euclidean distances between successive samples from movement onset to offset. The ratio between the path and the Euclidean distance is 1 when the movement is a straight line and greater than 1 when the path is curved. Results show that in virtually all 21 cases examined the ratio was very close to 1 and in most cases 1.2 or less. There was no reliable influence of consonant length on the ratio.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

The effect of the coupling between the top plate and the fingerboard on the acoustic power radiated by a classical guitar (L)

Héctor García-Mayén and Arturo Santillán

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1153-1156 (2011); (4 pages)

Online Publication Date: 09 Mar 2011

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An experimental investigation on the coupling between the fingerboard and the top plate of a classical guitar at low frequencies is presented. The study was carried out using a finished top plate under fixed boundary conditions and a commercial guitar. Radiated sound power was determined in one-third octave bands up to the band of 1 kHz based on measurements of sound intensity. The results provide evidence that the way in which the fingerboard and top plate are coupled is not a relevant factor in the radiated acoustic power of the classical guitar in the studied frequency range.
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43.75.Gh Plucked string instruments

Temperature effects on the band gaps of Lamb waves in a one-dimensional phononic-crystal plate (L)

Y. Cheng, X. J. Liu, and D. J. Wu

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1157-1160 (2011); (4 pages) | Cited 1 time

Online Publication Date: 09 Mar 2011

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This study investigates the temperature-tuned band gaps of Lamb waves in a one-dimensional phononic-crystal plate, which is formed by alternating strips of ferroelectric ceramic Ba0.7Sr0.3TiO3 and epoxy. The sensitive and continuous temperature-tunability of Lamb wave band gaps is demonstrated using the analyses of the band structures and the transmission spectra. The width and position of Lamb wave band gaps shift prominently with variation of temperature in the range of 26 °C–50 °C. For example, the width of the second band gap increases from 0.066 to 0.111 MHz as the temperature is increased from 26 °C to 50 °C. The strong shift promises that the structure could be suitable for temperature-tuned multi-frequency Lamb wave filters.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.40.Dx Vibrations of membranes and plates

Comment on “Increase in voice level and speaker comfort in lecture rooms” [J. Acoust. Soc. Am. 125, 2072–2082 (2009)] (L)

David Pelegrín-García

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1161-1164 (2011); (4 pages) | Cited 2 times

Online Publication Date: 09 Mar 2011

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Recently, a paper written by Brunskog Gade, Payá-Ballester and Reig-Calbo, “Increase in voice level and speaker comfort in lecture rooms” [J. Acoust. Soc. Am. 125, 2072–2082 (2009)] related teachers’ variation in vocal intensity during lecturing to the room acoustic conditions, introducing an objective parameter called “room gain” to describe these variations. In a failed attempt to replicate the objective measurements by Brunskog et al., a simplified and improved method for the calculation of room gain is proposed, in addition with an alternative magnitude called “voice support.” The measured parameters are consistent with those of other studies and are used here to build two empirical models relating the voice power levels measured by Brunskog et al., to the room gain and the voice support.
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43.55.Hy Subjective effects in room acoustics, speech in rooms
43.70.Mn Relations between speech production and perception
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Acoustic iridescence

Trevor J. Cox

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1165-1172 (2011); (8 pages)

Online Publication Date: 09 Mar 2011

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An investigation has been undertaken into acoustic iridescence, exploring how a device can be constructed which alter sound waves, in a similar way to structures in nature that act on light to produce optical iridescence. The main construction had many thin perforated sheets spaced half a wavelength apart for a specified design frequency. The sheets create the necessary impedance discontinuities to create backscattered waves, which then interfere to create strongly reflected sound at certain frequencies. Predictions and measurements show a set of harmonics, evenly spaced in frequency, for which sound is reflected strongly. And the frequency of these harmonics increases as the angle of observation gets larger, mimicking the iridescence seen in natural optical systems. Similar to optical systems, the reflections become weaker for oblique angles of reflection. A second construction was briefly examined which exploited a metamaterial made from elements and inclusions which were much smaller than the wavelength. Boundary element method predictions confirmed the potential for creating acoustic iridescence from layers of such a material.
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43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Fn Scattering of acoustic waves

Noise control by sonic crystal barriers made of recycled materials

José Sánchez-Dehesa, Victor M. Garcia-Chocano, Daniel Torrent, Francisco Cervera, Suitberto Cabrera, and Francisco Simon

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1173-1183 (2011); (11 pages) | Cited 6 times

Online Publication Date: 09 Mar 2011

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A systematic study of noise barriers based on sonic crystals made of cylinders that use recycled materials like absorbing component is reported here. The barriers consist of only three rows of perforated metal shells filled with rubber crumb. Measurements of reflectance and transmittance by these barriers are reported. Their attenuation properties result from a combination of sound absorption by the rubber crumb and reflection by the periodic distribution of scatterers. It is concluded that the porous cylinders can be used as building blocks whose physical parameters can be optimized in order to design efficient barriers adapted to different noisy environments.
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43.20.Fn Scattering of acoustic waves
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.40.Fz Acoustic scattering by elastic structures
43.20.Hq Velocity and attenuation of acoustic waves

A real-time plane-wave decomposition algorithm for characterizing perforated liners damping at multiple mode frequencies

Dan Zhao

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1184-1192 (2011); (9 pages) | Cited 2 times

Online Publication Date: 09 Mar 2011

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Perforated liners with a narrow frequency range are widely used as acoustic dampers to stabilize combustion systems. When the frequency of unstable modes present in the combustion system is within the effective frequency range, the liners can efficiently dissipate acoustic waves. The fraction of the incident waves being absorbed (known as power absorption coefficient) is generally used to characterize the liners damping. To estimate it, plane waves either side of the liners need to be decomposed and characterized. For this, a real-time algorithm is developed. Emphasis is being placed on its ability to online decompose plane waves at multiple mode frequencies. The performance of the algorithm is evaluated first in a numerical model with two unstable modes. It is then experimentally implemented in an acoustically driven pipe system with a lined section attached. The acoustic damping of perforated liners is continuously characterized in real-time. Comparison is then made between the results from the algorithm and those from the short-time fast Fourier transform (FFT)-based techniques, which are typically used in industry. It was found that the real-time algorithm allows faster tracking of the liners damping, even when the forcing frequency was suddenly changed.
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43.20.Ye Measurement methods and instrumentation
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.58.Bh Acoustic impedance measurement
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Statistical model of clutter suppression in tissue harmonic imaging

Xiang Yan and Mark F. Hamilton

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1193-1208 (2011); (16 pages)

Online Publication Date: 09 Mar 2011

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A statistical model is developed for the suppression of clutter in tissue harmonic imaging (THI). Tissue heterogeneity is modeled as a random phase screen that is characterized by its correlation length and variance. With the autocorrelation function taken to be Gaussian and for small variance, statistical solutions are derived for the mean intensities at the fundamental and second-harmonic frequencies in the field of a focused sound beam that propagates through the phase screen. The statistical solutions are verified by comparison with ensemble averaging of direct numerical simulations. The model demonstrates that THI reduces the aberration clutter appearing in the focal region regardless of the depth of the aberrating layer, with suppression of the clutter most effective when the layer is close to the source. The model is also applied to the reverberation clutter that is transmitted forward along the axis of the beam. As with aberration clutter, suppression of such reverberation clutter by THI is most pronounced when the tissue heterogeneity is located close to the source.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Scattering of ultrasonic shock waves in suspensions of silica nanoparticles

Michael Baudoin, Jean-Louis Thomas, François Coulouvrat, and Corinne Chanéac

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1209-1220 (2011); (12 pages) | Cited 1 time

Online Publication Date: 09 Mar 2011

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Experiments are carried out to assess, for the first time, the validity of a generalized Burgers’ equation, introduced first by Davidson [J. Acoust. Soc. Am. 54, 1331–1342 (1973)] to compute the nonlinear propagation of finite amplitude acoustical waves in suspensions of “rigid” particles. Silica nanoparticles of two sizes (33 and 69 nm) have been synthesized in a water–ethanol mixture and precisely characterized via electron microscopy. An acoustical beam of high amplitude is generated at 1 MHz inside a water tank, leading to the formation of acoustical shock waves through nonlinear steepening. The signal is then measured after propagation in a cylinder containing either a reference solution or suspensions of nanoparticles. In this way, a “nonlinear attenuation” is obtained and compared to the numerical solution of a generalized Burgers’ equation adapted to the case of hydrosols. An excellent agreement (corresponding to an error on the particles size estimation of 3 nm) is achieved in the frequency range from 1 to 40 MHz. Both visco-inertial and thermal scattering are significant in the present case, whereas thermal effects can generally be neglected for most hydrosols. This is due to the value of the specific heat ratio of water–ethanol mixture which significantly differs from unity.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.20.Fn Scattering of acoustic waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

A contrast source method for nonlinear acoustic wave fields in media with spatially inhomogeneous attenuation

L. Demi, K. W. A. van Dongen, and M. D. Verweij

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1221-1230 (2011); (10 pages) | Cited 2 times

Online Publication Date: 09 Mar 2011

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Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.80.Qf Medical diagnosis with acoustics

Buckling resistance of solid shell bubbles under ultrasound

Philippe Marmottant, Ayache Bouakaz, Nico de Jong, and Catherine Quilliet

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1231-1239 (2011); (9 pages) | Cited 1 time

Online Publication Date: 09 Mar 2011

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Thin solid shell contrast agents bubbles are expected to undergo different volume oscillating behaviors when the acoustic power is increased: small oscillations when the shell remains spherical, and large oscillations when the shell buckles. Contrary to bubbles covered with thin lipidic monolayers that buckle as soon as compressed: the solid shell bubbles resist compression, making the buckling transition abrupt. Numerical simulations that explicitly incorporate a shell bending modulus give the critical buckling pressure and post-buckling shape, and show the appearance of a finite number of wrinkles. These findings are incorporated in a model based on the concept of effective surface tension. This model compares favorably to experiments when adjusting two main parameters: the buckling tension and the rupture shell tension. The buckling tension provides a direct estimation of the acoustic pressure threshold at which buckling occurs.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Ei Acoustic cavitation in liquids
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A coupled modal-finite element method for the wave propagation modeling in irregular open waveguides

Adrien Pelat, Simon Felix, and Vincent Pagneux

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1240-1249 (2011); (10 pages)

Online Publication Date: 09 Mar 2011

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In modeling the wave propagation within a street canyon, particular attention must be paid to the description of both the multiple reflections of the wave on the building facades and the radiation in the free space above the street. The street canyon being considered as an open waveguide with a discontinuously varying cross-section, a coupled modal-finite element formulation is proposed to solve the three-dimensional wave equation within. The originally open configuration—the street canyon open in the sky above—is artificially turned into a close waveguiding structure by using perfectly matched layers that truncate the infinite sky without introducing numerical reflection. Then the eigenmodes of the resulting waveguide are determined by a finite element method computation in the cross-section. The eigensolutions can finally be used in a multimodal formulation of the wave propagation along the canyon, given its geometry and the end conditions at its extremities: initial field condition at the entrance and radiation condition at the output.
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43.28.Js Numerical models for outdoor propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts

Diffraction of sonic booms around buildings resulting in the building spiking effect

Sang-Ik T. Cho and Victor W. Sparrow

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1250-1260 (2011); (11 pages)

Online Publication Date: 09 Mar 2011

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The diffraction of a sonic boom around a building of finite dimensions yields amplification of the front shock and a positive spike that follows the tail shock in the pressure waveform recorded at the incident side of the building’s exterior surface. This physical phenomenon is consistently found both in the data obtained from a 2006 NASA flight test and field experiment, and in the finite-difference time-domain simulation that models this particular experiment, and the authors call it the “building spiking” effect. This paper presents an analysis of the numerical and the accompanying experimental results used to investigate the cause of this effect. The simulation assumes linear acoustics only, which sufficiently describes the physics of interest. Separating the low and high frequency components of boom recordings using optimal finite impulse response filters with complementary magnitude responses shows that the building spiking effect can be attributed to the frequency dependent nature of diffraction. A comparison of the building spiking effect of a conventional N-wave and a low-amplitude sonic boom shows that a longer shock rise time leads to less pronounced amplification of the exterior pressure loading on buildings, and thus reveals an advantage of shaping a boom to elongate its rise time.
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43.28.Mw Shock and blast waves, sonic boom
43.28.Js Numerical models for outdoor propagation
43.20.El Reflection, refraction, diffraction of acoustic waves

Investigation of non-linear acoustic losses at the open end of a tube

James M. Buick, M. Atig, D. J. Skulina, D. M. Campbell, J. P. Dalmont, and J. Gilbert

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1261-1272 (2011); (12 pages) | Cited 2 times

Online Publication Date: 09 Mar 2011

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At high acoustic level, non-linear losses at the end of a tube are usually interpreted as the consequence of a jet formation at the tube end resulting in annular vortices dissipating part of the acoustic energy. Previous work has shown that two different regimes may occur. The present work, using particle image velocimetry visualization, lattice Boltzmann method simulation in 2D, and an analytical model, shows that the two different regimes correspond to situations for which the annular vortices remain attached to the tube (low acoustic particle velocity) or detached (high acoustic particle velocity).
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43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
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Finite element modeling of reverberation and transmission loss in shallow water waveguides with rough boundaries

Marcia J. Isakson and Nicholas P. Chotiros

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1273-1279 (2011); (7 pages)

Online Publication Date: 09 Mar 2011

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A finite element model for the reverberation and propagation in a shallow water waveguide with a sandy bottom was calculated for five different environments at a center frequency of 250 Hz. The various environments included a rough water/sediment interface, a rough air/water interface, roughness at both interfaces and downward and upward refracting sound speed profiles with roughness at both interfaces. When compared to other models of reverberation such as ray theory, coupled modes, and parabolic equations, finite elements predicted higher levels of reverberation. At early times, this is due to the “fathometer” return, energy that is normally incident on the boundaries at zero range. At later times, the increased reverberation was due to high angle scattering paths between the two interfaces. Differences in reverberation levels among the environments indicated that scattered energy from the air/water interface is transmitted into the bottom at steep angles. This led to a large decrease in reverberation for a rough air/water interface relative to a rough water/sediment interface. Sound speed profile effects on reverberation were minimal at this frequency range. Calculations of the scintillation index of the different environments indicated that most of the reverberation was relatively Rayleigh-like with heavier tailed distributions at longer ranges.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Hw Rough interface scattering
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Influence of stacking sequence on scattering characteristics of the fundamental anti-symmetric Lamb wave at through holes in composite laminates

Martin Veidt and Ching-Tai Ng

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1280-1287 (2011); (8 pages)

Online Publication Date: 09 Mar 2011

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This paper investigates the scattering characteristics of the fundamental anti-symmetric (A0) Lamb wave at through holes in composite laminates. Three-dimensional (3D) finite element (FE) simulations and experimental measurements are used to study the physical phenomenon. Unidirectional, bidirectional, and quasi-isotropic composite laminates are considered in the study. The influence of different hole diameter to wavelength aspect ratios and different stacking sequences on wave scattering characteristics are investigated. The results show that amplitudes and directivity distribution of the scattered Lamb wave depend on these parameters. In the case of quasi-isotropic composite laminates, the scattering directivity patterns are dominated by the fiber orientation of the outer layers and are quite different for composite laminates with the same number of laminae but different stacking sequence. The study provides improved physical insight into the scattering phenomena at through holes in composite laminates, which is essential to develop, validate, and optimize guided wave damage detection and characterization techniques.
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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

Scattering of the fundamental anti-symmetric Lamb wave at delaminations in composite laminates

Ching-Tai Ng and Martin Veidt

J. Acoust. Soc. Am. Volume 129, Issue 3, pp. 1288-1296 (2011); (9 pages)

Online Publication Date: 09 Mar 2011

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An analysis of the scattering characteristics of the fundamental anti-symmetric (A0) Lamb wave at a delamination in a quasi-isotropic composite laminate is presented. Analytical solutions for this problem do not exist due to the anisotropic nature and multilayer characteristics of composite laminates. This study uses a three-dimensional finite element (FE) method and experimental measurements to provide physical insight into the scattering phenomena. Good agreement is found between simulations and experimental measurements. The results show that the A0 Lamb wave scattering at a delamination in composite laminates is much more complicated than the scattering at a defect in isotropic plates. Scatter amplitudes and scatter directivity distributions depend on the delamination size to wavelength ratio and the through-thickness location of the delamination damage. The study also investigates the feasibility of the common experimental practice of simulating delamination damage by bonding masses to the surface of composite laminates for guided wave damage detection and characterization methodologies verifications. The results suggest that care is required to use bonded masses to simulate delamination damage for verifying and optimizing damage characterization techniques. In summary, the results of the investigation help to further advance the use of the A0 Lamb wave for damage detection and characterization.
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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
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