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Sep 2012

Volume 132, Issue 3, pp. EL169-2094

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A quieting ocean: Unintended consequence of a fluctuating economy

M. F. McKenna, S. L. Katz, S. M. Wiggins, D. Ross, and J. A. Hildebrand

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL169-EL175 (2012); (7 pages) | Cited 3 times

Online Publication Date: 07 Aug 2012

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Simultaneous long-term monitoring of underwater sound and ship traffic provided an opportunity to study how low-frequency noise correlated with ocean-based commercial shipping trends. Between 2007 and 2010 changes in regional shipping off southern California occurred as a consequence of economic and regulatory events. Underwater average noise levels measured before and during these events showed a net reduction of 12 dB. Statistical models revealed that a reduction of 1 ship transit per day resulted in 1 dB decrease in average noise. This synthesis of maritime traffic statistics with ocean noise monitoring provides an important step in understanding the magnitude and potential effects of chronic noise in marine habitats.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
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Seasonal presence of cetaceans and ambient noise levels in polar waters of the North Atlantic

Holger Klinck, Sharon L. Nieukirk, David K. Mellinger, Karolin Klinck, Haruyoshi Matsumoto, and Robert P. Dziak

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL176-EL181 (2012); (6 pages)

Online Publication Date: 07 Aug 2012

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In 2009 two calibrated acoustic recorders were deployed in polar waters of the North Atlantic to study the seasonal occurrence of blue, fin, and sperm whales and to assess current ambient noise levels. Sounds from these cetaceans were recorded at both locations in most months of the year. During the summer months, seismic airguns associated with oil and gas exploration were audible for weeks at a time and dominated low frequency noise levels. Noise levels might further increase in the future as the receding sea ice enables extended human use of the area.
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43.30.Sf Acoustical detection of marine life; passive and active
43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
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Elastic Pekeris waveguide normal mode solution comparisons against laboratory data

Joseph D. Schneiderwind, Jon M. Collis, and Harry J. Simpson

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL182-EL188 (2012); (7 pages) | Cited 1 time

Online Publication Date: 07 Aug 2012

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Following the derivation presented by Press and Ewing [Geophysics 15, 426–446 (1950)], a normal mode solution for the Pekeris waveguide problem with an elastic bottom is outlined. The analytic solution is benchmarked against data collected in an experiment performed at the Naval Research Laboratory [Collis et al., J. Acoust. Soc. Am. 122, 1987–1993 (2007)]. Comparisons reveal a close match between the analytic solution and experimental data. Results are strongly dependent on the accuracy of the horizontal wavenumbers for the modes, and horizontal wavenumber spectra are compared against those from the experimental data.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Zk Experimental modeling
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Formant discrimination of speech and non-speech sounds for English and Chinese listeners

Chang Liu, Sha Tao, Wenjing Wang, and Qi Dong

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL189-EL195 (2012); (7 pages) | Cited 1 time

Online Publication Date: 07 Aug 2012

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Thresholds of formant discrimination of speech and non-speech sounds were compared for native listeners of English and Chinese. English listeners showed significantly better thresholds than Chinese listeners, not only for English vowels, but also for Chinese vowels. Thresholds for vowel-spectrum-shaped noise were comparable for the two groups. These results suggest that English listeners are more sensitive to formant frequency changes of vowel stimuli than Chinese listeners, possibly due to the denser vowel space for English than for Mandarin Chinese. However, the psychophysical capacity to discriminate formant frequency changes in non-speech sounds is similar for English and Chinese listeners.
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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
43.66.Fe Discrimination: intensity and frequency
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Increased intensity discrimination thresholds in tinnitus subjects with a normal audiogram

B. Epp, J. Hots, J. L. Verhey, and R. Schaette

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL196-EL201 (2012); (6 pages)

Online Publication Date: 07 Aug 2012

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Recent auditory brain stem response measurements in tinnitus subjects with normal audiograms indicate the presence of hidden hearing loss that manifests as reduced neural output from the cochlea at high sound intensities, and results from mice suggest a link to deafferentation of auditory nerve fibers. As deafferentation would lead to deficits in hearing performance, the present study investigates whether tinnitus patients with normal hearing thresholds show impairment in intensity discrimination compared to an audiometrically matched control group. Intensity discrimination thresholds were significantly increased in the tinnitus frequency range, consistent with the hypothesis that auditory nerve fiber deafferentation is associated with tinnitus.
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43.66.Fe Discrimination: intensity and frequency
43.66.Ki Subjective tones
43.66.Ed Auditory fatigue, temporary threshold shift
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Nonlinear ultrasound: Potential of the cross-correlation method for osseointegration monitoring

Jacques Rivière, Sylvain Haupert, Pascal Laugier, and Paul A. Johnson

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL202-EL207 (2012); (6 pages)

Online Publication Date: 07 Aug 2012

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Recently the concept of probing nonlinear elasticity at an interface prosthesis/bone has been proposed as a promising method to monitor the osseointegration/sealing of a prosthesis. However, the most suitable method to achieve this goal is a point of debate. To this purpose, two approaches termed the scaling subtraction method and the cross-correlation method are compared here. One nonlinear parameter derived from the cross-correlation method is as sensitive as a clinical device based on linear elasticity measurement. Further, this study shows that cross-correlation based methods are more sensitive than those based on subtraction/addition, such like pulse inversion and similar methods.
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43.25.Dc Nonlinear acoustics of solids
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
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Interpreting tone of voice: Musical pitch relationships convey agreement in dyadic conversation

Brooke M. Okada, Lorin Lachs, and Benjamin Boone

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL208-EL214 (2012); (7 pages)

Online Publication Date: 09 Aug 2012

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Previous research has found that the musical intervals found in speech are associated with various emotions. Intervals can be classified by their level of consonance or dissonance—how pleasant or unpleasant the combined tones sound to the ear. Exploratory investigations have indicated that in an agreeable conversation, the pitches of the last word in an utterance and the first word of a conversation partner’s utterance are consonantly related; in a disagreeable conversation, the two pitches are dissonantly related. The present results showed that the intervals between the tonics of the utterances in a conversation corresponded to the agreement between interlocutors.
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43.71.Bp Perception of voice and talker characteristics
43.75.Cd Music perception and cognition
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Coherence length as a figure of merit in multireference near-field acoustical holography

Alan T. Wall, Michael D. Gardner, Kent L. Gee, and Tracianne B. Neilsen

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL215-EL221 (2012); (7 pages)

Online Publication Date: 09 Aug 2012

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Multireference partial field decomposition (PFD) can be used to generate coherent holograms for near-field acoustical holography measurements. PFD is most successful when the reference array completely senses all independent subsources, but meeting this requirement is not straightforward when the number of subsources and their locations are ambiguous (such as in aeroacoustic sources). A figure of merit based on spatial coherence lengths, called references per coherence length (RPLC), is a useful metric to guide inter-reference spacing in the array design. For numerical, extended, arbitrarily coherent sources one reference per coherence length results in a sufficient reference array.
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43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Sx Acoustic holography
43.28.Lv Statistical characteristics of sound fields and propagation parameters
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Slow and fast ultrasonic wave detection improvement in human trabecular bones using Golay code modulation

Bahman Lashkari, Amir Manbachi, Andreas Mandelis, and Richard S. C. Cobbold

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL222-EL228 (2012); (7 pages) | Cited 2 times

Online Publication Date: 09 Aug 2012

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The identification of fast and slow waves propagating through trabecular bone is a challenging task due to temporal wave overlap combined with the high attenuation of the fast wave in the presence of noise. However, it can provide valuable information about bone integrity and become a means for monitoring osteoporosis. The objective of this work is to apply different coded excitation methods for this purpose. The results for single-sine cycle pulse, Golay code, and chirp excitations are compared. It is shown that Golay code is superior to the other techniques due to its signal enhancement while exhibiting excellent resolution without the ambiguity of sidelobes.
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43.80.Ev Acoustical measurement methods in biological systems and media
43.80.Vj Acoustical medical instrumentation and measurement techniques
43.80.Jz Use of acoustic energy (with or without other forms) in studies of structure and function of biological systems
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Radiated noise from commercial ships in the Gulf of Maine: Implications for whale/vessel collisions

J. Kaitlyn Allen, Michael L. Peterson, George V. Sharrard, Dana L. Wright, and Sean K. Todd

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL229-EL235 (2012); (7 pages)

Online Publication Date: 09 Aug 2012

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To understand mysticete acoustic-based detection of ships, radiated noise from high-speed craft, cruise ships, catamarans and fishing vessels was recorded June–September 2009. Calibrated acoustic data (<2500 Hz) from a vertical hydrophone array was combined with ship passage information. A cruise ship had the highest broadband source level, while a fishing vessel had the lowest. Ship noise radiated asymmetrically and varied with depth. Bow null-effect acoustic shadow zones were observed for all ship classes and were correlated with ship-length-to-draft-ratios. These shadow zones may reduce ship detection by near-surface mysticetes.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.50.Cb Noise spectra, determination of sound power
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.80.Nd Effects of noise on animals and associated behavior, protective mechanisms
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A numerical study of a method for measuring the effective in situ sound absorption coefficient

Erwin R. Kuipers, Ysbrand H. Wijnant, and André de Boer

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL236-EL242 (2012); (7 pages)

Online Publication Date: 21 Aug 2012

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The accuracy of a method [Wijnant et al., Proc. of ISMA 31, Leuven, Belgium (2010), Vol. 31] for measurement of the effective area-averaged in situ sound absorption coefficient is investigated. Based on a local plane wave assumption, this method can be applied to sound fields for which a model is not available. Investigations were carried out by means of finite element simulations for a typical case. The results show that the method is a promising method for determining the effective area-averaged in situ sound absorption coefficient in complex sound fields.
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43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.55.Dt Sound absorption in enclosures: theory and measurement; use of absorption in offices, commercial and domestic spaces
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Ye Measurement methods and instrumentation
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Ultrasonic Doppler methods to extract signatures of a walking human

Asif Mehmood, James M. Sabatier, and Thyagaraju Damarla

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL243-EL249 (2012); (7 pages)

Online Publication Date: 21 Aug 2012

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Extraction of Doppler signatures that characterize human motion has attracted a growing interest in recent years. These Doppler signatures are generated by various components of the human body while walking, and contain unique features that can be used for human detection and recognition. Although, a significant amount of research has been done in radio frequency regime for human Doppler signature extraction, considerably less has been done in acoustics. In this work, 40 kHz ultrasonic sonar is employed to measure the Doppler signature generated by the motion of body segments using different electronic and signal processing schemes. These schemes are based on both analog and digital demodulation with homodyne and heterodyne receiver circuitry. The results and analyses from these different schemes are presented.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.60.Vx Acoustic sensing and acquisition
43.60.-c Acoustic signal processing
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Measurement of stop consonant identification using adaptive tracking procedures

Chang Liu and David A. Eddins

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. EL250-EL256 (2012); (7 pages)

Online Publication Date: 23 Aug 2012

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The purpose of this study was to establish the potential utility of adaptive tracking procedures, relative to the method of constant stimuli, when examining consonant identification in cafeteria noise or four-talker babble. Thresholds for consonant identification were comparable for the two methods, while psychometric function slopes derived from the two methods were statistically different. To obtain accurate slope estimates from adaptive procedures, the target percent correct and change in variability with signal-to-noise ratio should be considered carefully. However, adaptive procedures are accurate and more efficient than the method of constant stimuli when the purpose is to estimate phoneme identification threshold.
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43.71.Gv Measures of speech perception (intelligibility and quality)
43.71.An Models and theories of speech perception
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Combining time of flight and diffraction tomography for high resolution breast imaging: Initial invivo results (L)

P. Huthwaite, F. Simonetti, and N. Duric

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1249-1252 (2012); (4 pages)

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Ultrasound tomography (UST) is being developed to address the limitations of mammography in breast cancer detection. Central to the success of UST is the possibility of obtaining high-resolution images of tissue mechanical properties across the whole breast. A recent paper [Huthwaite and Simonetti, J. Acoust. Soc. Am. 130, 1721–1734 (2011)] made use of a numerical phantom to demonstrate that sufficient image resolution can be obtained by simply treating refraction and diffraction effects in consecutive steps through the combination of ray-based time of flight and diffraction tomography. This letter presents the first experimental demonstration of the method using phantom and invivo data from a cancer patient.
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43.80.Qf Medical diagnosis with acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems
43.60.Qv Signal processing instrumentation, integrated systems, smart transducers, devices and architectures, displays and interfaces for acoustic systems
43.20.Fn Scattering of acoustic waves

Architectural shape and early acoustic efficiency in concert halls (L)

Yann Jurkiewicz, Thomas Wulfrank, and Eckhard Kahle

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1253-1256 (2012); (4 pages)

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Supplying sufficient early reflections to audience members is an important prerequisite to good acoustic quality in performing arts spaces. However, the relationship between the geometry of a room and its acoustic efficiency in terms of early energy has rarely been investigated using basic geometrical principles. The present study demonstrates the possibility of predicting the average value of early reflected energy across the audience area using solid angles. The formulas obtained display the influence of various factors on average early energy; in particular, the direction of arrival of early reflections is found to play a significant role, which highlights interesting implications for the acoustic design of concert halls.
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43.55.Fw Auditorium and enclosure design
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response

A Bayesian inference model for speech localization (L)

José Escolano, José M. Perez-Lorenzo, Ning Xiang, Máximo Cobos, and José J. López

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1257-1260 (2012); (4 pages)

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The localization of active speakers with microphone arrays is an active research line with a considerable interest in many acoustic areas. Many algorithms for source localization are based on the computation of the Generalized Cross-Correlation function between microphone pairs employing phase transform weighting. Unfortunately, the performance of these methods is severely reduced when wall reflections and multiple sound sources are present in the acoustic environment. As a result, estimating the number of active sound sources and their actual directions becomes a challenging task. To effectively tackle this problem, a Bayesian inference framework is proposed. Based on a nested sampling algorithm, a mixture model and its parameters are estimated, indicating both the number of sources—model selection—and their angle of arrival—parameter estimation, respectively. A set of measured data demonstrates the accuracy of the proposed model.
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43.60.Jn Source localization and parameter estimation
43.72.Ne Automatic speech recognition systems
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Generalized method of moments: A boundary integral framework for adaptive analysis of acoustic scattering

N. V. Nair, B. Shanker, and L. Kempel

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1261-1270 (2012); (10 pages)

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Boundary integral equations (BIEs) find applications in problems ranging from sonar to medical diagnostics. The two ingredients of the BIE solution technique are (1) representation of the domain and (2) design of approximation spaces to represent physical quantities on the domain. These, in concert, affect accuracy and convergence of the simulation. This paper presents a framework that permits the development of a scheme for refinement (of size and order) in both geometry and function representations. Further, this permits flexibility in the types of basis functions that can be used. Capabilities of the proposed framework are shown via a number of numerical examples.
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43.20.Fn Scattering of acoustic waves
43.58.Ta Computers and computer programs in acoustics

A first-order k-space model for elastic wave propagation in heterogeneous media

K. Firouzi, B. T. Cox, B. E. Treeby, and N. Saffari

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1271-1283 (2012); (13 pages)

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A pseudospectral model of linear elastic wave propagation is described based on the first order stress-velocity equations of elastodynamics. k-space adjustments to the spectral gradient calculations are derived from the dyadic Green’s function solution to the second-order elastic wave equation and used to (a) ensure the solution is exact for homogeneous wave propagation for timesteps of arbitrarily large size, and (b) also allows larger time steps without loss of accuracy in heterogeneous media. The formulation in k-space allows the wavefield to be split easily into compressional and shear parts. A perfectly matched layer (PML) absorbing boundary condition was developed to effectively impose a radiation condition on the wavefield. The staggered grid, which is essential for accurate simulations, is described, along with other practical details of the implementation. The model is verified through comparison with exact solutions for canonical examples and further examples are given to show the efficiency of the method for practical problems. The efficiency of the model is by virtue of the reduced point-per-wavelength requirement, the use of the fast Fourier transform (FFT) to calculate the gradients in k space, and larger time steps made possible by the k-space adjustments.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Bi Mathematical theory of wave propagation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Px Transient radiation and scattering
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Acoustoelastic Lamb wave propagation in biaxially stressed plates

Navneet Gandhi, Jennifer E. Michaels, and Sang Jun Lee

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1284-1293 (2012); (10 pages) | Cited 2 times

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Acoustoelasticity, or the change in elastic wave speeds with stress, is a well-studied phenomenon for bulk waves. The effect of stress on Lamb waves is not as well understood, although it is clear that anisotropic stresses will produce anisotropy in the Lamb wave dispersion curves. Here the theory of acoustoelastic Lamb wave propagation is developed for isotropic media subjected to a biaxial, homogeneous stress field. It is shown that, as expected, dispersion curves change anisotropically for most stresses, modes, and frequencies. Interestingly, for some mode-frequency combinations, changes in phase velocity are isotropic even for a biaxial stress field. Theoretical predictions are compared to experimental results for several Lamb wave modes and frequencies for uniaxial loads applied to an aluminum plate, and the agreement is reasonably good.
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43.25.Dc Nonlinear acoustics of solids
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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An exact frequency-domain solution of the sound radiated from the rotating dipole point source

Yijun Mao, Yuanyuan Gu, Datong Qi, and Hongtao Tang

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1294-1302 (2012); (9 pages)

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An exact solution of the acoustic field around the rotating dipole source has been derived by using a series expansion method and the gradient calculation in the spherical and cylindrical coordinate systems which extends a previously published solution for a rotating monopole source. The proposed exact solution establishes an analytical method to predict the sound radiated from the rotating blades once the acoustic sources have been known.
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43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts
43.20.Bi Mathematical theory of wave propagation
43.50.Nm Aerodynamic and jet noise
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
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Consistent modeling of boundaries in acoustic finite-difference time-domain simulations

Jon Häggblad and Björn Engquist

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1303-1310 (2012); (8 pages)

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The finite-difference time-domain method is one of the most popular for wave propagation in the time domain. One of its advantages is the use of a structured staggered grid, which makes it simple and efficient on modern computer architectures. A drawback, however, is the difficulty in approximating oblique boundaries, having to resort to staircase approximations. In many scattering problems this means that the grid resolution required to obtain an accurate solution is much higher than what is dictated by propagation in a homogeneous material. In this paper zero boundary data are considered, first for the velocity and then the pressure. These two forms of boundary conditions model perfectly rigid and pressure-release boundaries, respectively. A simple and efficient method to consistently model curved rigid boundaries in two dimensions was developed in Tornberg and Engquist [J. Comput. Phys. 227, 6922–6943 (2008)]. Here this treatment is generalized to three dimensions. Based on the approach of this method, a technique to model pressure-release surfaces with second order accuracy and without additional restriction on the timestep is also introduced. The structure of the standard method is preserved, making it easy to use in existing solvers. The effectiveness is demonstrated in several numerical tests.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves
43.30.Ft Volume scattering

Parabolic equation modeling of high frequency acoustic transmission with an evolving sea surface

J. Senne, A. Song, M. Badiey, and K. B. Smith

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1311-1318 (2012); (8 pages)

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The present paper examines the temporal evolution of acoustic fields by modeling forward propagation subject to sea surface dynamics with time scales of less than a second to tens of seconds. A time-evolving rough sea surface model is combined with a rough surface formulation of a parabolic equation model for predicting time-varying acoustic fields. Surface waves are generated from surface wave spectra, and stepped in time using a Runge–Kutta integration technique applied to linear evolution equations. This evolving, range-dependent surface information is combined with other environmental parameters and input to the acoustic model, giving an approximation of the time-varying acoustic field. The wide-angle parabolic equation model manages the rough sea surfaces by molding them into the boundary conditions for calculations of the near-surface acoustic field. This merged acoustic model is validated using concurrently-collected acoustic and environmental information, including surface wave spectra. Data to model comparisons demonstrate that the model is able to approximate the ensemble-averaged acoustic intensity at ranges of about a kilometer for acoustic signals of around 15 kHz. Furthermore, the model is shown to capture variations due to surface fluctuations occurring over time scales of less than a second to tens of seconds.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Hw Rough interface scattering
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Cross-imaging system comparison of backscatter coefficient estimates from a tissue-mimicking material

Kibo Nam, Ivan M. Rosado-Mendez, Lauren A. Wirtzfeld, Viksit Kumar, Ernest L. Madsen, Goutam Ghoshal, Alexander D. Pawlicki, Michael L. Oelze, Roberto J. Lavarello, Timothy A. Bigelow, James A. Zagzebski, William D. O’Brien, Jr., and Timothy J. Hall

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1319-1324 (2012); (6 pages)

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A key step toward implementing quantitative ultrasound techniques in a clinical setting is demonstrating that parameters such as the ultrasonic backscatter coefficient (BSC) can be accurately estimated independent of the clinical imaging system used. In previous studies, agreement in BSC estimates for well characterized phantoms was demonstrated across different laboratory systems. The goal of this study was to compare the BSC estimates of a tissue mimicking sample measured using four clinical scanners, each providing RF echo data in the 1-15 MHz frequency range. The sample was previously described and characterized with single-element transducer systems. Using a reference phantom for analysis, excellent quantitative agreement was observed across the four array-based imaging systems for BSC estimates. Additionally, the estimates from data acquired with the clinical systems agreed with theoretical predictions and with estimates from laboratory measurements using single-element transducers.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.20.Fn Scattering of acoustic waves

Application of the distributed point source method to rough surface scattering and ultrasonic wall thickness measurement

A. J. C. Jarvis and F. B. Cegla

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1325-1335 (2012); (11 pages)

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The distributed point source method is commonly used to predict the complex acoustic field emitted by ultrasonic transducers. In this paper, it is presented as an alternative to conventional approaches often used when solving rough surface scattering problems. Surface shadowing and multiple scattering effects are inherently included in the mesh-free semi-analytical simulation method through matrix manipulation making it very efficient and simple to implement. Results are presented which illustrate the improvement in accuracy gained over the Kirchhoff approximation and the decrease in computational load over the finite element method, culminating in greater than an order of magnitude decrease in required simulation time. The method is applied to the practical problem of online wall thickness monitoring within corrosive environments, illustrating the variability in reflected pulse shape that could be expected from rough surfaces with similar statistics. Three commonly implemented time-of-flight algorithms are used to analyze a large number of simulated signals from which it is concluded that those based on first arrival time are more stable under increasing roughness conditions than those which are based on reflected pulse shape.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.60.Cg Statistical properties of signals and noise
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Surface waves on a half space with depth-dependent properties

Oluwaseyi Balogun and Jan D. Achenbach

J. Acoust. Soc. Am. Volume 132, Issue 3, pp. 1336-1345 (2012); (10 pages)

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The dispersive properties of surface waves on an isotropic elastic body with elastic moduli and mass density that depend on depth have been analyzed in the high frequency range, for the case of axially symmetric surface waves, which are of interest for point loading of a body. The method of approach requires some simplifications, but the final analysis yields simple expressions for the displacements, for the case that the two elastic moduli and the mass density each have different dependencies on depth. In a high-frequency approximation expressions are obtained for the displacements and the stresses. The condition that the surface tractions vanish at the free surface yields the dispersion equation which relates the surface wave velocity to the wavenumber. Conditions have been derived for a class of examples for which this equation yields a real valued surface wave velocity, and the displacement amplitudes decay exponentially with depth. Results for the surface wave velocity as a function of the wavenumber have been compared with numerical results which were obtained when the continuous inhomogeneity with depth is replaced by an equivalent layering. For some typical cases of increasing and decreasing material properties with depth, excellent agreement has been obtained between analytical and numerical results.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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