bluuebunny/crossref_metadata_2025 huggingface dataset:
Mode characterization in shallow water using warping tools.
Authors: Bonnel Julien , Nicolas Barbara , Mars Jerome I. , Le Touze Gregoire , Fattaccioli Dominique
Published: October 2013

In underwater acoustics, shallow water is a complex and dispersive medium. For low frequencies, the propagation is described by normal mode theory. Modes are nonlinear structures overlapped in time, in frequency, and in time-frequency domains. Advanced signal processing methods are needed to study them. This paper presents two different warping methods allowing modal separation and estimation of parameters of the modes. As these transformations are invertible, they also allow modal filtering. Thus, they are a good preprocessing tool for source localization or tomography. This is shown on simulations and real data. Warping is a transformation of a propagated signal and is based on an environment model. Here the environment is modeled with isovelocity or Pekeris waveguide. However, both methods are quite robust to mismatches with the real environment and can be used with minimal preliminary knowledge of the real environment. The first warping method is applied on the time domain. It transforms each mode into a sinus function of frequency fm (with fm the cutoff frequency of the mode m). The second is applied on the frequency domain. It transforms a chosen mode into a dirac, which is localized on the arrival time of the mode.
Synthesis of adaptive processing of a passive fathometer.
Authors: Harrison Chris H. , Traer James , Gerstoft Peter
Published: October 2013

By using ambient noise array-processing techniques, it has been demonstrated that a passive array can be used as a fathometer [Siderius et al., JASA (2006)] and that adaptive processing gives higher temporal resolution. We show that the waveform extracted with the adaptive algorithm has a phase error of pi relative to that of conventional processing (independently observed at SIO and NURC). For the case of an array with regularly spaced hydrophone elements, the cross-spectral density (CSD) matrix is Toeplitz and the symmetry of Toeplitz matrices allows a simple analytic expression for the phase of the fathometer output. This expression is used to characterize the introduction of phase errors by adaptive processing. The effect of this phase error is investigated with simulated and real data on a vertical hydrophone array.
Representation of the musical instruments directivity using dodecahedron loudspeakers.
Authors: Behler Gottfried , Pollow Martin
Published: October 2013

Room-acoustical measurements in general are performed with omnidirectional sound sources. With respect to auralization, such an impulse response may not be ideal since it does not represent the situation playing an instrument in the room. To achieve the directivity of a real source (such as an instrument or human voice) with a technical sound source (a loudspeaker) requires either to copy the body and the surface velocity distribution of that particular source or to reproduce the directional pattern of the radiation using a multiple source configuration like a dodecahedron loudspeaker array with independent excitation of each transducer. The advantage of the latter method is obvious since one single source is able to provide different directivities by changing the excitation profile. To maintain the appropriate excitation of each individual transducer, different approaches can be made. The method described here uses spherical harmonics decomposition of the target radiation pattern and a subsequent calculation of the frequency dependent excitation coefficients for each transducer. The advantage of this method is a flexible and fast calculation delivering filters that can be used either for real time convolution or off-line processing of the measuring signals. To measure the instruments directivity an array with 32 microphones is used.
Spherical harmonic beamforming for room acoustic analysis.
Authors: Elko Gary W. , Meyer Jens
Published: October 2013

We describe the potential of using a spherical beamforming microphone array to investigate the spatial correlation of sound fields in rooms. We are building spherical microphone arrays consisting of many acoustic pressure sensors mounted appropriately on the surface of a rigid sphere. Our associated spherical eigenbeamformer decomposes the sound-field into spatially orthonormal spherical harmonics up to third-order. We refer to the signals from the eigenbeamformer as eigenbeams. All eigenbeams have phase centers at the physical center of the array. Due to the orthonormal property of the eigenbeamformer, a diffuse field ideally results in zero correlation between the eigenbeams. Therefore, by measuring the cross-correlation between the eigenbeam signals, one can investigate the proximity to the isotropy (or “diffuseness”) of the sound-field. Simultaneously, the underlying eigen-beam patterns can be steered without effecting the orthonormality property. How the cross-correlation function changes with general orientation of the eigenbeams is another potential measure for sound field diffuseness in rooms. We will show some real room measurements demonstrating the potential usefulness of this approach.
Proposed method to measure the diffusion coefficient.
Authors: D’Antonio Peter
Published: October 2013

A method to measure the uniform diffusion coefficient has been published as an AES Information Document [AES-4id-2001, JAES, Vol. 9, pp. 148–165 (March 2001)]. The method utilizes 37 fixed pressure zone microphones separated by 5 degrees located on a 1 m semicircle and a loudspeaker located on a 2 m concentric semicircle. A sample array sits at the origin. Under computer control 37 impulse responses are collected for the sample, background without sample, and a reference flat panel of similar size. The data reduction procedure will be reviewed to include all developments since the 2001 publication. In addition, experimental data will be presented along with the current presentation format. Currently the method is in the final stages of review for incorporation as Part 2 of ISO 17497-1, which describes the procedure to measure the random incidence scattering coefficient. A review and comparison between the scattering and diffusion coefficients will also be presented. A summary of this research can be found in the reference text [T. J. Cox and P. D’Antonio, Acoustic Absorbers and Diffusers: Theory, Design and Application, Spon Press 2004, second edition in press].
Analysis of in situ acoustic absorption using a spherical microphone array.
Authors: Rathsam Jonathan , Rafaely Boaz
Published: October 2013

Acoustic absorption of materials typically depends on the characteristics of the incident sound field. Differences in the incident sound field between one laboratory and another, or between the laboratory and in situ, may therefore lead to differences in the measured absorption for the same material. To overcome this problem, a new method is proposed to measure acoustical absorption using a spherical microphone array. With this method one measures simultaneously the acoustic absorption as well as the incident sound field. The incident sound field and the reflected sound field are separated by the spherical microphone array using spatial filtering, or beamforming. The acoustic absorption is then determined from the amplitudes of the incident and the reflected fields. The measurement method may also be useful for verifying sound field diffusivity in a reverberation chamber when measuring diffuse-field absorption. Furthermore, absorption coefficients measured under in-situ sound fields may yield more accurate computer-based sound field simulations than diffuse-field absorption coefficients when the in-situ sound field is not diffuse. [Work supported by the National Science Foundation.]
Speech intelligibility improvement in rooms using microphone arrays.
Authors: Stinson Michael R. , Gover Bradford N. , Daigle Gilles A.
Published: October 2013

Microphones arrays reduce the effects of reverberation and background noise as compared to a single microphone. The resulting improvement in speech intelligibility in rooms is investigated here, following the approach discussed by Houtgast et al. [Acustica 46, 60–72 (1980)]. Room characteristics (volume, reverberation time), the background noise spectrum, and the source-receiver separation are used to compute a modulation transfer function. This function is input into the procedure described in IEC standard 60268-16(2003) to arrive at an objective measure of speech intelligibility, the speech transmission index (STI). Doing this for both omnidirectional and microphone array receivers, the improvement in intelligibility is determined. The signal source has the spectral shape of a human talker, as given in the IEC standard; the background noise spectrum is based on measurements made in a restaurant. The benefit of using microphone arrays is discussed for various conditions.
A new method for the measurement of directional sound arrivals in rooms.
Authors: Thornock Brian T. , Leishman Timothy W.
Published: October 2013

In room acoustics, directional measurements have the ability to more fully detail room effects than common nondirectional measurements. The extraction of directional information has been a subject of considerable interest for years and has resulted in the development of several interesting approaches to the problem. However, past methods have often suffered from inaccuracies, difficult implementation, lengthy procedures, extensive computational requirements, or the need for large amounts of equipment. A practical new method will be presented that extracts directional information of sound arrivals through a single multichannel measurement and a new cross-correlation technique. A direct comparison of numerical simulations will demonstrate that the method is more accurate than other well-established methods. Advantages and limitations of the new approach will be discussed.
Microphone array beamforming with near-field correlated sources.
Authors: Odom Jonathan L. , Krolik Jeffery
Published: October 2013

As the price of omnidirectional microphone arrays has fallen, new applications have emerged for large room audio capture. Further, large room acoustics use loudspeakers, which create correlated sources and severely limit the use of optimum beamformers. Most sources are in the near field due to the large wavelength of speech. Widrow and Kailath’s work on correlation in sonar and radar assumed far field, but it cannot be directly applied to near-field acoustics. A new beamforming method has been devel-oped, which incorporates near field and correlation. The source bearings are estimated and an uncorrelated model is formed. A better DOA estimator was developed for the near-field correlated case limited by the width of the mainlobe. The new beamformer is able to null strong, perfectly and nearly perfectly correlated signals using the uncorrelated model and minimum variance distortionless response beamforming.
Prediction and measurement of reverberation increase from electroacoustic architecture systems.
Authors: Schwenke Roger , Ellison Steve , Poletti Mark
Published: October 2013

Electroacoustic architecture (EA) systems increase the reverberation time (RT) of rooms by regenerating the physical reverberation of the room, and/or adding electronic reverberation to the direct sound. In regenerative systems, the amount of regeneration is controlled by the loop gain of the system. Increasing loop gain is analogous to reducing the effective absorption in the room. The RT of the electronic reverberator is analogous to the decay time of a physically coupled room, and, therefore, analogous to adding cubic volume to the room. As the electronic RT is increased, there is a point above which the resulting reverberation will begin to be double sloped. This point depends on the gain. The higher the gain, the higher the electronic RT before the resulting reverberation double slopes. In previous work, the gain before feedback of EA systems has been predicted in a statistical approach based on the bulk properties of the room such as RT and cubic volume. This, in turn, can be used to predict the maximum possible power gain and RT increase before double sloping. In this paper, we measure systems in use in the field and compare the achieved performance with predictions.
A survey of remote underwater autonomous acoustic recorders.
Authors: Au Whitlow W. L. , Lammers Marc O. , Richlen Michael F.
Published: October 2013

There has been a proliferation of different types of remote underwater autonomous acoustic recorders in recent years. Many were designed for a specific purpose to measure sounds from specific organisms. Others were designed for general application to encompass a wide variety of sounds. Many have fancy acronyms such as ARP, BPROBE, DTAG, EAR, EARS, HARP, MARU, PALs, RUDAR, and TPOD, to name a few. All have essentially the same subsystems consisting of a hydrophone and amplifier assembly, an analog-to-digital converter, data storage, and a microcontroller to handle the data acquisition and storage operations and to control the overall functioning of the unit. The differences are in the bandwidth of the system, amount of storage available, amount of power required, and duration of deployment possible. Some can be purchased commercially, some can only be leased, while others can only be used in a collaborative research project. The prices also vary considerably. Some have been used for many years while others have come into play within the last few years. The sum total of all these acoustic recorders have contributed tremendously to our understanding of the marine ecosystem in ways that we could not have imagined several years ago.
Acoustic tracking of whistling dolphins offshore of Southern California.
Authors: Frasier Kaitlin E. , Wiggins Sean M. , Hildebrand John A.
Published: October 2013

Dolphin whistles were recorded near San Clemente Island, offshore of Southern California, by four autonomous high-frequency acoustic recording packages (HARPs) deployed in a sea-floor array (dimensions: 2 km × 2 km) centered around the R/P FLIP. This array layout allowed localization of the calling animals using time difference of arrivals (TDOAs) from the same calls simultaneously recorded on the four instruments. Whistle TDOAs were calculated using cross-correlations of spectrograms. A matched-field least-squares minimization procedure used whistle TDOAs to localize the animals. Successive localizations were combined to track movement over time, revealing local movements of presumably common dolphins (Delphinus spp.), typically during elevated nocturnal activity. These tracks, coupled with the animals’ acoustic activity, provide insight into their behavior and could potentially be used to study their response to various stimuli including anthropogenic sources such as sonar. [This research is supported by CNO-N45.]
A high-resolution pressure tag for ocean depth measurements.
Authors: John Prajas , Peter Jaison , Correya Adrine Antony , Supriya M. H. , Pillai P. R. Saseendran
Published: October 2013

Data Storage Tags form an important class of electronic tags, used for studying the migratory patterns of highly migratory marine species. In such tags, the parameters to estimate the position of the species are recorded in the tag memory and are retrieved subsequently upon recapturing the tag. The vertical and spatial migration of such marine species can be analyzed in detail using the pressure measurements made by the tags. The migratory behavior of marine species can be attributed to the light intensity variations and temperature profile as well as the search of food and suitable environmental conditions. The depth measurements can be made more accurate, if the resolution of the pressure sensor is significantly high. An absolute pressure measurement with a resolution of 1.2 mbar (approx. 1.2 cm in depth measurements) has been achieved with a pressure tag, capable of recording pressures at preset time intervals. Conversion of the hydrostatic pressure measurements into linear depth variation is carried out using the well-known equations. Pressure measurements were carried out using the pressure tag in the laboratory conditions as well as in the open ocean and the depth variations were computed using a user-friendly interactive software.
Theoretical models for imaging distributed fish groups in an ocean waveguide with wide-area sonar including multiple scattering.
Authors: Andrews Mark , Ratilal Purnima
Published: October 2013

Wide area sonar has been shown to be a useful tool for instantaneously imaging shoals of fish distributed over large areas on the continental shelf. Numerical models are applied to simulate the active imaging system and determine the statistics of the received matched filtered intensity scattered off remote fish groups in the ocean waveguide environment. The model includes multiple scattering of the dense fish groups and uses a range-dependent acoustic model to simulate the ocean environment. The numerical model results are compared to analytic models, which make a single scattering assumption. We find the conditions for when multiple scattering is important and show that it is a function of both the fish density and mean target strength for a given distribution of fish. We use Monte Carlo simulations to explore the effects on the statistics of the received matched filtered intensity for an ocean waveguide randomized by internal waves. The model can be used to infer fish densities and abundances in wide area sonar imagery as well as provide error analysis of these estimates.
Midfrequency backscatter imaging of fish schools in a shallow water waveguide.
Authors: Jones Christopher D. , Jackson Darrell R.
Published: October 2013

In this experimental effort, field data and modeling are used to investigate backscatter imaging of schools of pelagic fish in a shallow water oceanic waveguide. Two-dimensional (2-D) circular images of an oceanic waveguide are created using a monostatic circular receiving array and vertical line array source (12 kHz) deployed from a stationary ship. Horizontal multibeam images of a radial (depth integrated) cross section of the ocean are formed with targets and reverberation structure observed at ranges up to several Km. Examples of waveguide images are presented for data taken in the Puget Sound of Washington state. In some instances, the backscatter from aggregations of fish was observed to be higher than the reverberation; in other cases, fish schools could not be resolved. Fish school locations were independently observed by vertical echo sounding. Preliminary experimental results are shown to illustrate the potential of resolving the 2-D horizontal structure of aggregations of fish using such methods. Modeling is used to interpret the effects of waveguide propagation on imaging. Operational issues related to using waveguide imaging for fisheries’ research and signal processing issues related to waveguide imaging will be discussed. [Work funded by NOPP with support from ONR and NOAA-OE.]
Humboldt squid distribution in three-dimensional space as measured by acoustics in the Gulf of California.
Authors: Matteson Robyn S. , Benoit-Bird Kelly J. , Gilly William F.
Published: October 2013

The Humboldt squid, Dosidicus gigas, is a voracious migratory predator, important prey for many species, and the target of an economically important fishery. However, information on the behavior, life history, and biomass of this species is limited. Current knowledge is based almost exclusively on fisheries records, which only contain nighttime observations and provide no information on squid distribution and behavior outside of heavily fished areas. Acoustic measurements have long been used to study fish. Development of this method for application to squid provides a noninvasive technique to assess squid numbers and sizes. This method was applied in March and April of 2007 and November of 2008 in the Gulf of California, with a focus on the Santa Rosalia region. Squid densities were as high as 25 000 per km3. Larger numbers of squid were observed at shelf breaks relative to other areas. Squid exhibited a marked diel vertical migration, with daytime depths of 300–400 m, bathymetry allowing, and nighttime depths of 0–200 m. In shallower coastal areas, the distribution of squid closely mirrored the shape of the bottom topography. This new technique is providing previously unattainable insights into the behavior and biology of this commercially and ecologically important squid species.
Acoustical and optical measurements provide evidence of ecological interactions in planktonic thin layers.
Authors: Benoit-Bird Kelly J. , Cowles Timothy J.
Published: October 2013

Coincident physical, optical, and acoustical data were obtained in Monterey Bay, CA during an extensive study of planktonic layers. These concurrent data describing the distributions of phytoplankton, zooplankton, and small fish as well as gradients in the physical habitat were used to examine the interactions between vertically compressed plankton structures (thin layers), their consumers, and the local physical forces they experience. The steepness of the vertical gradient on the top versus the bottom of the plankton layer was correlated to the difference in the relative abundance of consumers above and below the layer. Phytoplankton layer gradients were steeper when more zooplankton were present on one side of the layer versus the other while zooplankton layers were more diffuse with a greater number of fish adjacent to one side of the layer than the other. Both layer types showed nearly symmetrical gradients when predators were in low abundance or absent. Differences in phytoplankton and zooplankton layer “shape” were not correlated with vertical gradients in shear or mixing potential surrounding layers. The consequences of trophic interactions within aggregations can be detected and assessed, and in the absence of strong physical gradients, grazers can play an important role in structuring plankton thin layers.
Pilot work using a codend video camera for improved acoustic interpretation of backscatter observed during fisheries acoustic surveys.
Authors: Bonacci Lisa A. , Wakefield W. Waldo
Published: October 2013

One challenging but crucial element of fisheries acoustic surveys is accurate groundtruthing of the echo return. Assignment and proportioning of areas of backscatter to the correct species or mix of species affects fish biomass calculations. Typically, survey groundtruthing is done by midwater trawls targeting a single scattering layer of interest. However, the depth at which each species is caught is unknown. Therefore, this method is problematic when multiple scattering layers are present. Small scatters are also missed, which may be important contributors to the echo intensity. To address these issues, we conducted pilot work using a video camera mounted in the codend of an open midwater trawl, which enabled us to look at several scattering layers during each tow. For comparison, we conducted tows with a closed net and no camera at the same location. We then examined each acoustic echogram and the corresponding tow in order to compare backscatter calculations attributable to our species of interest. We found that there were some differences in these measurements between the two types of tows. We conclude that this method appears to provide improved knowledge of acoustic backscatter observed during fisheries acoustic surveys and plan to integrate this method into future surveys.
Radiation torque on a sphere centered on an acoustic helicoidal (vortex) Bessel beam.
Authors: Zhang Likun , Marston Philip L.
Published: October 2013

Circularly polarized electromagnetic waves carry axial angular momentum and analysis shows that the axial radiation torque on an illuminated sphere is proportional to the power absorbed by the sphere [P. L. Marston and J. H. Crichton, Phys. Rev. A. 30, 2508–2516 (1984)]. Hefner and Marston [J. Acoust. Soc. Am. 106, 3313–3316 (1999)] proposed that a helicoidal acoustic beam (an acoustic vortex) also carries axial angular momentum and noted that absorption of such a beam should also produce an axial radiation torque. In the present work the acoustic radiation torque on a sphere centered on an acoustic helicoidal Bessel beam is analyzed and the torque is predicted to be proportional to the ratio of the power absorbed as a result of the interaction of sound with the sphere to the acoustic frequency. The torque is also proportional to the topological charge of the beam. Depending on the beam helicity, the torque is parallel or anti-parallel to the beam axis. The analysis uses a relation between the scattering and the partial wave coefficients for a sphere in a helicoidal Bessel beam [P. L. Marston, J. Acoust. Soc. Am. 124, 2905–2910 (2008)]. [This research was supported in part by ONR and NASA.]
Shear wave dispersion ultrasound vibrometry of gel dosimetry phantoms.
Authors: Vieira Silvio , Urban Matthew , Baggio Andre , Carneiro Antonio , Fatemi Mostafa
Published: October 2013

Shear wave dispersion ultrasound vibrometry (SDUV) has been introduced to use the dispersive nature of shear wave speed to locally estimate the material properties or tissue. Shear waves were created using a mechanical shaker and pulsed radiation force. Using the information from the phase one can estimate the shear velocity. A theoretical Voigt model allows us to find, at different frequencies (100–400 Hz), the viscosity and shear elasticity of the polymer gel dosimeter. The aim of this work was to perform the SDUV and mechanical vibrometry techniques to study the viscoelastic properties of absorbed dose phantoms. The experiments were performed using five phantoms of different absorbed doses varying 10 up to 50 Gy, while a nonirradiated phantom was kept as a control. The SDUV technique was performed using a pulsed radiation force to vibrate the gel provide by a confocal transducer with a focal depth of 70 mm, nominal frequency of 3 MHz. For the mechanical vibrometry and SDUV experiments, shear wave motion measurements were made with a commercial ultrasound machine with a research using a 10 MHz linear array transducer. The quantitative elasticity and viscosity results for these two experiments were compared.
Targeted ultrasound contrast agents—Mediated endothelial permeability.
Authors: Anastasiadis Pavlos , Layman Chris N. , Allen John S.
Published: October 2013

Endothelial cell dysfunction is considered to play a major role in the early stages of atherosclerosis. Targeted ultrasound contrast agents offer potential for therapeutic treatment though the mechanisms for enhanced ultrasound and microbubble mediated transport across endothelial layers are not well understood. In this study, we evaluate the endothelial cell-to-cell and cell-to-substrate gaps with the electric cell-substrate impedance sensing system (ECIS, Applied BioPhysics, Troy, NY). ECIS can detect the nanometer order changes of cell-to-cell and cell-to-substrate distances separately. Targeted ultrasound contrast agents (UTC) were employed in conjunction with the application of ultrasound, while continuous measurements of electrical resistance across the endothelial monolayers were conducted in real-time for the determination of permeability. The measurements were performed in both, the presence and absence of UCA. Additional complementary, noninvasive acoustic measurements of local changes in the mechanical properties of the endothelial monolayers were conducted at high-frequency (100 MHz) with a time-resolved scanning acoustic microscope. [This work was supported by the National Institutes of Health Grants NIH 2 P20 RR016453-05A1 and NIH 2 G12 RR0030161-21.]
Transcutaneous acoustic palpation (TAP) for the localization of peripheral, painful tissue.
Authors: Mourad Pierre D. , Kliot Michel , Jarvik Jeffrey G.
Published: October 2013

Localizing painful tissue (pain generators) is central to medicine. Here we sought to demonstrate that intense focused ultrasound (iFU) can successfully differentiate normal from painful tissue. Rats were injected with complete Freunds adjuvant in a hind paw to create an inflammatory injury, or underwent a surgical procedure that damaged the nerve enervating the paw, creating a neuropathic injury. Each created a paw sensitive to external stimulation relative to the contralateral paw. iFU was applied individually to each hind paw in increasing doses until the animal withdrew either paw consistently from the iFU stimulus, thereby defining the iFU threshold dose for that animal. This data was correlated with paw withdrawal latencies to a heat lamp (Hargreaves) test. Sensitized paws responded to lower intensities and doses of iFU than control paws greater than 95 percent of the time with sensitivities and specificities generally greater than 90 percent. In general, iFU threshold tests and Hargreaves tests did not affect one another, a functional test of the safety of iFU. This preliminary evidence supports the hypothesis that iFU can safely discriminate between painful and normal tissue. Future work will use image-guided iFU to localize deep rather than superficial pain generators.
Acquiring acoustic data using a scanning laser vibrometer.
Authors: Boober Walter H. , Benjamin Kim C. , Forsythe Stephen E. , Walsh Kenneth M.
Published: October 2013

Scanning laser vibrometers have been in use for many years in acoustic measurements. Unique methods of characterizing both active and passive devices or structures with vibrational modes have been developed by NUWC personnel; these are combinations of signal generation techniques and physics-based data analysis tools. The signal generation techniques reduce the time for potentially lengthy scans at multiple frequencies through the use of a “comb” waveform, [J. Acoust. Soc. Am. 116(5), (2004)], if the device under test is known to be linear. Scans can be done in either air or water. An analysis technique using the Helmholtz integral (using NUWC’s MATLAB-based CHIEF code; Schenck and Benthein, NOSC 1970, 1988) allows analysis from an in-air scan of a transducer face (before encapsulation) to predict the transducer’s far-field beam patterns under some conditions. This is especially valuable as a time-saving tool to ensure that the transducer is on track to achieve the final design intent. Examples of the techniques applied to various transducer designs will be presented; for comparison, single-tone results also will be shown.
Measurement and imaging of high-frequency sonar fields using acousto-optic tomography.
Authors: Theobald Pete , Robinson Stephen , Koukoulas Triantafillos , Hayman Gary
Published: October 2013

The acoustic near-field of a high-frequency sonar array transducer has been measured using a laser scanning acousto-optic method and reconstructed using a tomographic technique similar to that used for x-ray computed tomography. This measurement, using a laser interferometer to scan a plane in front of the transducer for a series of transducer rotations, provides an image of the acoustic field for a plane in front of the transducer array. This method allows measurement of the acoustic field without perturbing the field being measured, which can occur when using the planar hydrophone scanning method, provides high spatial resolution with minimal phase averaging across the measurement aperture and provides potential for significantly decreasing the scan time. Measurements have been performed on two 1–3 composite transducer arrays at frequencies between 330 and 500 kHz. These are compared with planar hydrophone scans obtained using a 1.5-mm probe hydrophone. Both parallel and fan beam tomographic scan geometries have been considered along with the effect of lateral scan resolution versus angular rotation resolution.
Laser light scattering by bubbles in water: Fundamentals and applications to acoustics.
Authors: Marston Philip L.
Published: October 2013

Laser light scattering is sometimes used as an alternative to acoustical methods for monitoring bubbles in seawater. There has also been interest in using lasers to investigate bubbles in wakes. In some cases light scattering by bubbles has been used in conjunction with acoustical measurements to characterize dynamics of bubbles radiating sound [J. S. Stroud and P. L. Marston, J. Acoust. Soc. Am. 94, 2788–2792 (1993)]. In applications such as these it is important to understand the optical properties of bubbles that differ significantly from drops and particles. Examples include critical angle scattering and the transition to total reflection [D. S. Langley and P. L. Marston, Appl. Opt. 23, 1044–1054 (1984)], forward scattering and extinction [D. S. Langley and P. L. Marston, Appl. Opt. 30, 3452–3458 (1991); J. S. Stroud and P. L. Marston, cited previously], glory back-scattering enhancements and shape effects [W. P. Arnott and P. L. Marston, J. Opt. Soc. Am. A5, 496–506 (1988); Appl. Opt. 30, 3429–3442 (1991)] and Brewster angle scattering. Some optical effects of coatings on bubbles (which can occur naturally) have also been modeled [P. L. Marston, Appl. Opt. 30, 3479–3484 (1991)]. [Research supported by ONR between 1980 and 1995.]
Remote, aerial, translayer, nonlinear downlink underwater acoustic communication.
Authors: Blackmon Fletcher A. , Antonelli Lynn T.
Published: October 2013

The nonlinear mechanism for optical to acoustic energy conversion is explored for optoacoustic communication from an in-air platform to a submerged platform. This downlink communication can provide a bell ringer function and transmission of text and data. The nonlinear conversion mechanism, also known as the nonlinear optoacoustic regime where focused laser energy is converted to sound at the air-water interface, involves a phase change of the water medium through evaporation and vaporization leading to plasma production. The nonlinear conversion mechanism provides a more efficient, i.e., higher source level, controllable method for producing underwater acoustic signals. A means of deterministically controlling the spectrum of the underwater acoustic signal has been investigated and demonstrated by varying the laser-pulse repetition rate to provide M-ary frequency shift keyed signaling. This physics-based conversion process provides a methodology for providing low probability of intercept signals whose information is embedded in noiselike signals. These laser generated signals can then be used in a frequency hopped spread spectrum technique with the use of the proper receiver structures to take advantage of the frequency diversity and periodicity inherent in this type of signal structure that could also be used to combat frequency selective fading in underwater acoustic channels.
Intense underwater laser acoustic source for Navy applications.
Authors: Jones Theodore G. , Hornstein Melissa K. , Ting Antonio C. , Wilkes Zachary W.
Published: October 2013

An intense remote underwater laser acoustic source is under development at the Naval Research Laboratory. In a novel configuration, a tailored intense laser pulse can be designed to propagate many meters underwater and compress at a predetermined remote location. Controlled compression of these optical pulses is governed by a combination of optical group velocity dispersion and nonlinear Kerr self-focusing. Optical compression can result in laser-induced breakdown, localized heating, and acoustic shock generation. Recent experiments include near-field acoustic source characterization using lens-focused 400 and 800 nm pulses of a Ti:sapphire laser, as well as 532 and 1064 nm pulses of a YAG laser. Sound pressure levels over 210 dB were achieved using a compact laser. Acoustic source characterization includes measurements of photoacoustic energy conversion efficiency, acoustic power spectrum, and directivity. Nonlinear optical studies included the precise measurement of the Kerr index of water at 400 and 800 nm, as well as conditions for optical filament generation, and their effects on acoustic signals. Planned experiments include tests in a bubbly salt water tank. Experimental results will be presented, and laser sources and techniques for underwater acoustic generation will be compared. [This work is supported by the U.S. Office of Naval Research.]
Measurement of the resonance frequency of a bubble using a laser Doppler vibrometer.
Authors: Argo Theodore F. , Wilson Preston S.
Published: October 2013

Knowledge of the behavior of bubbles that are confined within tubes or channels has a direct impact on the development of various medical applications and industrial processes. In such confined spaces, bubbles are not easily observed by traditional experimental means, such as acoustically with hydrophones, or optically with Mie scattering or stroboscopy. Further, facilitating observation with these methods may significantly perturb the system. A laser Doppler vibrometer (LDV) requires only a narrow (∼1 mm diam) line-of-sight access for the beam and illumination of the bubble does not perturb its dynamics. LDV measurements of the resonance frequency and quality factor of an air bubble suspended in a small water tank are presented to demonstrate the utility of this technique. The measurements are compared to a model that includes the acoustic effect of the tank walls. The precision of the technique was found to be similar to the precision of a traditional hydrophone-based acoustic technique.
Spectral component relationships in wind instrument transients.
Authors: Hoekje Peter L.
Published: October 2013

Playing characteristics of a wind musical instrument are related to its transient response, the efficiency of its sound production, and the stability of its sustained tones, as determined partly by the acoustical resonances of the instrument, and their nearly harmonic relationships. These can be explored using analysis of instrument attack transients by tracking development of the spectral components. A coupled oscillator model is used to explain the benefits to an instrument’s response due to resonances at harmonics of the playing frequency. Furthermore, the slight deviation from harmonic relationships of an instrument’s resonances leads to a shift in its tone center during a crescendo. A resonance at a frequency above the tone-hole lattice cutoff can affect the playing behavior of flutes and cornettos. The player’s airway in reed woodwinds and brasses is as much a part of the acoustic system as the instrument proper, and its resonances can have a correspondingly important effect.
Impulse response reverb as a tool for voicing organs.
Authors: Steppat Michael
Published: October 2013

The sound of a flue pipe can be adjusted by voicing. With parameters like the cut-up of the upper lip and their width, the opening in the foot, the height of the languid, and the width of the slit the voicer can influence the promptness of speech and adjust the intensity of the starting transient. The acoustical environment (especially the reverberation time) plays an important role in the reception of the starting transient, therefore the organ builder has to also take the architecture into account. Convolution reverb allows a simulation of the reverb at different positions. Sampled organ sounds with modified starting transients or modeled sounds can be played on a computer and mixed with a convolution reverb using measured impulse responses from different positions of the room. This computer model can be used during the design process to estimate the parameters for the voicing. Results of measurements in a church building and different modeling techniques will be presented
The influence of curvature on the vibration and tone quality of pipe organ reed tongues.
Authors: Plitnik G. R. , Angster J.
Published: October 2013

Given certain design constraints, such as the type of stop being voiced and the desired tone quality, organ reed voicers must curve each tongue so as to produce the best and most stable tone, as well as maintaining a consistent tone quality across an entire rank of pipes. This study investigated the effects of varying tongue curvatures on two pipes, an F2 Trompette and an F2 Clarinet. Reed vibration was measured under typical conditions by laser vibrometer; the pressure waves in the boot and shallot were measured by means of one-eighth inch microphones and the emitted sound was recorded at the egress. By integrating the velocity data, the displacement of the reed may be plotted in tandem with the pressure difference across the reed, allowing tongue position to be plotted versus the pressure variation during one steady-state cycle for each reed while vibrating. These graphs can then be compared and correlated to the observed tone quality for each of the differently curved reeds.
Acoustics of single-reed duck calls.
Authors: Goodweiler Nicholas P. , Cottingham James P.
Published: October 2013

A single-reed duck call features a reed of Mylar or similar elastic material mounted above a curved tone channel. The arrangement resembles that of a clarinet, except that the extreme curve of the tone channel (compared to the relatively flat lay of the clarinet) allows for a rather large volume airflow. In addition, the flexibility of the reed results in a low fundamental frequency (typically 100–140 Hz) so that the pitch of the call is close to the natural frequency of the reed, modified only slightly by the short resonating barrel. As the blowing pressure is increased, there is a gradual rise in pitch, punctuated by periodic jumps from one apparent regime of vibration to another. As the blowing pressure is lowered, some hysteresis effects are observed. Several calls built by different makers have been studied, each with a differently proportioned barrel and tone channel. Some of the phenomena observed include reed velocity and displacement, changes in effective reed length as a function of blowing pressure, and effects of barrel design on tone quality. Some observations have also been made of the volume airflow and effects of attaching pipe resonators.
Laser-induced dielectric breakdown as a method for noncontact pressure measurement.
Authors: Sukovich Jonathan R. , Murray Todd W. , Holt R. Glynn
Published: October 2013

Being able to accurately measure pressure fields in acoustic experimentation is of critical importance for understanding and describing observed acoustical phenomena. However, in many experimental situations, it is undesirable or impossible to measure the acoustic field using a transducer in contact with the acoustic host medium. It becomes useful then to have alternative, noncontact, methods for reliably and accurately measuring pressure fields in experiments. One alternative to traditionally invasive means, such as the use of a hydrophone, to measure pressure, is to use focused, short (5–7 ns), high power laser pulses to cause dielectric breakdown. Breakdown events can be detected by looking for the signature, near instantaneous, flash of broadband light generated by the subsequent ionization cascade. This procedure can then be repeated under different known hydrostatic pressures to establish pressure’s effect on the breakdown strength of water. Once a relationship is established, the process can be used to map local pressures in acoustic fields of sufficiently long period as to be considered hydrostatic in relation to the laser pulse duration. [Work supported by the US Army Space and Missile Command.]
Acoustic measurement of bubble size and position in an ink jet printhead.
Authors: van der Bos Arjan , Jeurissen Roger , Versluis Michel , Lohse Detlef , Reinten Hans , Wijshoff Herman , van den Berg Marc , de Jong Jos
Published: October 2013

A bubble can be entrained in the ink channel of a piezo-driven ink jet printhead leading to malfunction. Here, an acoustic sizing method for the volume and position of the bubble is presented. The influence of the bubble on the channel acoustics is detected by the piezo-actuator operating in a sensing mode. The acoustic response is also modeled in a linearized bubble dynamics model and it is demonstrated how the size of the bubble and its position within the channel can be inferred from the inverse problem. The validity of the presented method is supported by time-resolved optical observations of the bubble dynamics visualized in a glass connection channel. The combined optical and acoustical recordings are compared to the model, where a very good agreement is found. [This work is part of the research program of the Technology Foundation STW and financially supported by Océ Technologies B.V.]
Collapse dynamics of laser-nucleated bubble clusters in a spherical resonator.
Authors: Anderson Phillip A. , Murray Todd W. , Holt R. Glynn
Published: October 2013

The collective collapse of bubble clouds or clusters is important to many applications, including underwater sound propagation, shock-wave lithotripsy, and focused ultrasound therapy. Energetic collective cluster collapses appear to happen only when there is sufficient nuclei density. In order to study this phenomenon, we have implemented a laser-based method for creating clusters consisting of planar or cubic arrays of bubbles with controllable interbubble spacing. The growth and collapse of the arrays are observed using ultrahigh-speed photography and other diagnostics. Effects of interbubble spacing and nucleation phase with respect to the acoustic period are studied. [Work supported by the US Army Space and Missile Command.]
Motion of dissolved gas in a cavitating fluid.
Authors: Mastikhin I. V. , Newling B. , Kristoffersen S.
Published: October 2013

A strong acoustic field in a liquid separates the liquid and dissolved gases by the formation of bubbles (cavitation). Bubble growth and collapse is the result of active exchange of gas and vapor through the bubble walls with the surrounding liquid. This work investigates a new approach to the study of cavitation, not as an evolution of discrete bubbles, but as the dynamics of molecules constituting both the bubbles and the fluid. Direct Magnetic Resonance Imaging measurements of dynamics of the liquid and the dissolved gas show that the motions of dissolved gas (freon-22, CHClF2) and liquid (water) can be very different during acoustic cavitation and are strongly affected by the ultrasonic power, filtration, or previous cavitation of the solvent. The observations suggest that bubbles can completely refresh their content within two acoustic cycles and that long-lived (∼minutes) microbubbles act as nucleation sites for cavitation. The technique is complementary to the traditional optical and acoustical techniques. [V. Mastikhin and B. Newling, Physical Review E (2005, 2008).] [Authors thank the Natural Science and Engineering Research Council of Canada for funding.]
Simultaneous, noninvasive determination of fluid viscosity and density from acoustical resonances.
Authors: Osterhoudt Curtis F. , Sinha Dipen N.
Published: October 2013

U-tube densitometers make fluid density measurements based on eigenfrequency shifts, which depend on the fluids contained within the densitometer. This measurement method is the current standard for density measurements in industrialized settings. However, ruggedized densitometers have several drawbacks. They are expensive, and require diverting fluids into the apparatus to make their measurements. Viscometers, too, are considered invasive, or require diverting fluid into a measurement chamber (the one exception is the “OSCAR” viscometer, which cannot make measurements on flowing systems). In contrast, a simultaneous density/viscosity measurement can be made without diverting fluid from the container or pipe carrying it. The measurement, in which the container (e.g., pipe section) itself becomes the sensor, is based on acoustical frequency resonance shifts and resonance width changes. Such measurements can in principle be made at a standoff from the container, reducing price and requiring no further contact with the fluids. This presentation will address the technique, give the theoretical background for it, and present experimental validation.