bluuebunny/crossref_metadata_2025 huggingface dataset:
Far-field superresolution imaging using shaped acoustic vortices
Authors: Guild Matthew D. , Rogers Jeffrey S. , Rohde Charles , Orris Gregory
Published: October 2018

The ability to overcome the limitations on resolution due to the effects of diffraction has attracted significant attention in recent years. Previously proposed methods to overcome this limit, and therefore achieve superresolution, have largely been restricted to operating within the near-field region of the aperture. In this work, we will describe how acoustic helicoidal waves can create acoustic vortices that are well below the resolution limit, and how this can enable far-field superresolution acoustic imaging. The acoustic vortices generated in this manner propagate from the near-field into the far-field through an arrangement of stable integer mode vortices, thereby enabling the generation of far-field superresolved features in the acoustic pressure field. In this paper, theoretical and numerical results will be presented for an acoustic aperture which is capable of generating superresolved far-field features in the radiated acoustic pressure, and results will be shown illustrating the superresolution capability of this novel technique. [Work supported by the Office of Naval Research.]
Wavefront shaping of acoustic waves in scattering media
Authors: Guo Yuning
Published: October 2018

As an essential necessity for fundamental study and a broad variety of technological applications, it is important to control the propagation of acoustic waves and select their particular wavefronts. This work is to achieve effective wavefront shaping of acoustic waves along specific paths in strongly scattering media including phononic periodic structures and random media. In the phononic crystal, a kind of artificial phononic structures, wavefront shaping, and super-resolution imaging have been achieved by designing the geometry and material parameters. Furthermore, the confocal technique of the optical beam and acoustic beam has been improved to achieve sub-wavelength imaging in random media with strongly scattering. The presented results of wavefront shaping have implications for tailoring phonon dynamics in scattering media, which offers further possibilities of controllable acoustic waves in complex materials and enlightens the interaction of multi-physics fields.
A rigid acoustic metamaterial with phase modulation and power attenuation
Authors: Gao Nansha
Published: October 2018

We introduced a rigid structure into the acoustic metasurface design, proposed labyrinth structure based on the equivalent medium theory and different media are replaced by curly labyrinth. Layered medium theory and equivalent medium theory are combined to design arbitrary acoustic metasurface structure. An acoustic metasurface studied in this paper and realised simultaneous phase modulation and power attenuation in the air, the effective range covered from 30 to 90 degrees, and power attenuation is over 40%. According to layered medium theory which could modulate acoustic wave direction, the metasurface with same function can also be applied to underwater. Its related simulation results are calculated by FEA method. Finally, by introducing the curly labyrinth theory, the underwater acoustic metasurface with simultaneous phase modulation and power attenuation is designed and verification. This paper potential applications in the rigid underwater acoustic metasurface in low frequency, adjustable direction, and sound attenuation.
Nonlinear reflection of weak shock waves from a rough surface in air
Authors: Karzova Maria M. , Lechat Thomas , Ollivier Sébastien , Dragna Didier , Yuldashev Petr V. , Khokhlova Vera , Blanc-Benon Philippe
Published: October 2018

Irregular reflection of weak acoustic shock waves occurs under the framework of the von Neumann paradox. In this study, the influence of the surface roughness on the reflection pattern was studied experimentally using spark-generated spherically divergent N-waves of 1.4 cm length reflecting from rigid rough surfaces in air. Dimensions of the roughness were varied from 20 up to 500 μm for different surfaces. A Mach-Zehnder interferometry method was used to reconstruct the pressure waveforms near the surface. The reconstruction was performed by applying the inverse Abel transform to the phase of the signal measured by the interferometer. It was shown that the height of the Mach stem became shorter for surfaces with larger dimensions of the roughness and disappeared when the surface roughness was large enough. Such tendency was also observed in simulations based on the Euler equations where the acoustic source was introduced as a Gaussian-envelope energy injection and the roughness was either sinusoidal or random and described by a Gaussian correlation function. [Work supported by RSF-17-72-10277 and by the Labex CeLyA of Université de Lyon, operated by the French National Research Agency (ANR-10-LABX-0060/ ANR-11-IDEX-0007).]
Correspondence between sound propagation in discrete and continuous random media
Authors: Ostashev Vladimir E. , Wilson D. K. , Muhlestein Michael , Attenborough Keith
Published: October 2018

Wave propagation in random media is important in many applications such as sound propagation in a turbulent atmosphere and scattering by bubbles and microparticles in the ocean. Formulations for the statistical moments of the sound pressure field in continuous and discrete random media are usually done independently. In this presentation, it is demonstrated that the equations for the first two statistical moments in a continuous random medium have the same form as those for a discrete random medium if the scattering properties of the media are expressed in terms of the differential scattering cross section and total cross section. This analogy enables us to apply methods developed in wave propagation in continuous random media to discrete media, and vice versa. As an example, the existing theory of the interference of the direct and ground reflected waves in a turbulent atmosphere is used to study the effect of trees on the interference of these waves in a forest. The results obtained are compared with experimental data. The correspondence between wave propagation in discrete and continuous random media can also be used in other fields of physics.
Bayesian estimation of mean transmission loss along multiple paths with randomly scattered signals
Authors: Wilson D. K. , Pettit Chris L. , Ostashev Vladimir E.
Published: October 2018

A general problem is considered in which a source of unknown power transmits to multiple receiver locations. The signal is randomly scattered along each transmission path, for example, by turbulence, a forest, or buildings. At each receiver location, one or more observations of the signal power are collected. It is assumed that the functional form of the probability density function (pdf) of the received signals (an exponential pdf for strong scattering, or a gamma pdf for weak scattering) is known based on an understanding of the scattering process, although the mean transmission losses (TLs) from the source to receivers are uncertain. From the signal observations, we wish to estimate the mean power of the source and the mean TLs for each path. A Bayesian formulation for this problem is presented. An inverse gamma prior is used for the TL, which is the conjugate prior for the exponential or gamma scattered signal pdf (likelihood function). Analytical solutions are then derived for a number of limiting scenarios: (1) unscattered signals along multiple paths with dependent TLs, (2) strongly scattered signals along multiple paths with the same TL, and (3) weakly or strongly scattered signals along multiple paths with independent TLs.
Nondimensional analysis of wind noise and atmospheric surface-layer properties
Authors: Hart Carl R. , Lyons Gregory W. , Hocut Christopher M.
Published: October 2018

Wind noise is a prominent limitation to the signal to noise ratio of acoustic sensors. Realistic expectations of signal detectability can be generated by predicting the noise floor prior to a sensor deployment; however, a relationship must be established between the wind noise measured by a sensor and atmospheric surface-layer properties. Under conditions of horizontal homogeneity and quasi-steadiness, Monin-Obukhov similarity theory relates friction velocity, temperature scale, and roughness length to the near-surface profiles of mean wind speed and turbulent intensity, which in turn are known to govern wind noise. It is expected that the ratio of one-third octave band root-mean-square sound pressure to the turbulent flux of momentum, Strouhal number, and dimensionless elevation have a nondimensional relationship that collapses wind noise data as a function of Monin-Obukhov parameters. In order to establish such a relationship, we analyze a dataset of wind noise recorded in Spring 2018 within the Army Research Laboratory’s Meteorological Sensing Array on the Jornada Experimental Range, New Mexico. This dataset consists of continuous recordings of ambient noise at several sites on audio microphones up to 20 m above ground level, co-located with a suite of high-fidelity meteorological instruments, including sonic anemometers.
Calculations of low-frequency wind noise along a low two-dimensional hill surface
Authors: Lyons Gregory W. , Hart Carl R.
Published: October 2018

Measurement of outdoor sound propagation is often limited by wind noise, i.e. pressure fluctuations from atmospheric turbulence, especially for infrasound and low audible frequencies. Over a flat ground surface, the spectral density of wind noise can be predicted by the shear-turbulence mechanism for static pressure fluctuations using a mirror flow atmospheric turbulence model for the inhomogeneous surface-blocking effect. This study moves beyond a flat ground model to consider the effects of flow distortion by weak topography on surface wind noise, specifically, flow over a low two-dimensional hill, free from separation, at large Froude number. The integral solution for the pressure Poisson equation is used as a starting point, with turbulence modeled by the mirror flow in surface-following coordinates. The perturbation analysis of Hunt et al. [Q. J. R. Meteorol. Soc. 114(484), 1435–1470 (1988)] is used to model the mean shear rate as a function of elevation and distance over the hill. For upwind, downwind, and crest positions along the hill surface, the pressure correlation solution is integrated numerically to evaluate one-dimensional spectra. The relative forms of these spectra are analyzed to describe the effects of the hill crest acceleration and downwind wake deficit. Implications for microphone placement are also considered.
Improving multiple model parameters of a complex fluid-loaded structure from acoustic measurements
Authors: Liem Alyssa T. , McDaniel James G.
Published: October 2018

A method for correcting multiple mechanical and acoustical properties in a finite element model using the Neumann series is presented and demonstrated with numerical examples. In previous work, the authors developed a method for estimating a model parameter in a complex structure using a Neumann series as an approximation to system response. The method computed the sensitivity of the system response due to changes in the parameter and subsequently determined the change needed in the parameter to bring model response into agreement with vibration measurements. This previous work demonstrated the accuracy and computational efficiency of the method when correcting one model parameter. In the present work, the authors extend the analysis to compute sensitivities for multiple parameters of a system, allowing for the correction of more than one parameter. The limits and accuracies of the method are explored for a canonical acoustic system in which a complex structure interacts with an acoustic medium. Two uncertain model parameters of the system are corrected by bringing model response into agreement with acoustic measurements. Results of these examples will be reviewed and presented to illustrate the accuracy and robustness of the method.
Deterministic and statistical parameter characterization in resonant fluid-structure interaction problems
Authors: Lähivaara Timo , Göransson Peter , Cuenca Jacques
Published: October 2018

This research focuses on developing computational methods to estimate model parameters in resonant fluid-structure interaction problems over a wide frequency range by means of model inversion approaches. The considered problems are widely known to be subjected to local minima, which represent a major challenge in the field of parameter identification. In the proposed method, the frequency spectrum is divided into successive substeps allowing to efficiently guide the estimation towards the global minimum, i.e., the true model parameters. The estimation is performed through two frameworks, namely, the deterministic using gradient-based optimization and Bayesian using Markov chain Monte Carlo method. Proposed numerical examples illustrate the effectiveness and potential of the proposed stepwise scheme to find the global minimum and reduce the overall computational burden.
On the use of model truncation to extend the applicability of the finite element method to higher frequencies
Authors: Bonomo Anthony L. , McWaters Joshua , Wu Kuangcheng
Published: October 2018

Many structural acoustics problems of interest can be modeled as a vibrating elastic structure situated in and fully coupled to an infinite acoustic fluid domain. To model such problems using the finite element method, techniques have been developed to approximately enforce the Sommerfeld radiation condition at the boundary of the computational domain and prevent spurious boundary reflections from adversely affecting the calculated solution. These techniques include radiation boundary conditions, infinite elements, and perfectly matched layers. It is well known that due to computational constraints, the finite element method is often restricted to relatively low frequencies. However, many of the same techniques that have been used to enforce the Sommerfeld radiation condition can also be used to truncate the computational domain further and allow the finite element method to be used to study higher frequency problems where the structural acoustic response is relatively localized. This talk explores this model truncation application.
Acoustic wave scattering from a wave-bearing cavity in a rectangular waveguide
Authors: Afzal Muhammad , Bilal Hazrat
Published: October 2018

This article discusses the acoustic scattering in a waveguide containing flexible cavity bridged by vertical membranes. A tailored-Galerkin approach is adopted for the solution of governing boundary value problem. Unlike to the usual Mode-Matching (MM) technique, the schemes adopted here for solution modify the MM procedure by using Galerkin and Modal approaches. In Galerkin process, the displacement of vertical membrane is expanded by means of the usual orthogonal modes whilst in the later case, this displacement is found by utilizing the non-orthogonal modes of wave-bearing cavity. The results for scattering powers and transmission loss are shown against frequency and the dimensions of the chamber. A good agreement in results obtained via Galerkin and Modal approaches for different sets of edge conditions is seen. The numerical results show that the choices of edge conditions significantly affect the transmission loss and scattering powers.
Multi-layer actuator array to render a vibration field on a point-excited panel speaker
Authors: Lee Ki-Ho , Ih Jeong-Guon , Park Youngjin
Published: October 2018

Panel speakers often adopts the vibration actuator attached to a plate center to excite the whole panel. When a thin rectangular plate is excited by a point force, the generated bending wave is reflected quickly from the edges, so the plate is governed by the reverberant field. Because many vibrational modes participate even in the low frequencies, the radiated sound spectrum is involved with many peaks and troughs resulting a poor sound quality. To minimize the modal participation, the vibration is rendered to be confined and in-phase within a circular area enclosing the actuator point, and the vibration is being suppressed outside of it. An additional multi-layer actuator array surrounding the speaker zone is employed to control the vibration, thus fulfilling the rendered field. The study aim is now to obtain an appropriate gain of the actuators by solving the inverse problem consisting of the transfer matrix between field points and control actuators. The effect of the number of arrays is tested for the radius of 0.05–0.2 m. The control result reveals that the signal-to-noise ratio in the speaker and baffle zone is improved 8–11 dB by the three-layer array than by the single-layer array with the same size.
Deflectometry, a full field slope measurement technique: General perspectives and application to loading identification using the virtual fields method
Authors: Robin Olivier , O'Donoughue Patrick , Berry Alain
Published: October 2018

The ability of photographic techniques to quickly record high volumes of scientific data has been understood since the early 1900s. It is only following the advent of digital imaging and data processing systems that so-called full-field optical measurement techniques became sufficiently reliable for performing high spatial density structural vibration measurements. In particular, the deflectometry technique directly provides a spatially and temporally resolved measurement of slope fields on plane structures using a single high-speed camera. The presentation first demonstrates the principles of this technique and explores some direct applications of such full-field measurements. The advantages and drawbacks of deflectometry are compared with other optical techniques like digital image correlation or scanning laser Doppler vibrometry. A key aspect of several engineering domains consists in the identification of dynamic loads acting on structures by inverse methods. It is shown that coupling deflectometry measurements with the virtual fields method enable the reconstruction of stationary and transient excitations without any specific regularization. Experimental reconstruction results on an aluminum panel are presented for two different transient mechanical loadings: instrumented impact hammer and impacting metal marbles (multiple unknown excitations). Finally, the identification of random excitations is considered using a plate and a membrane.
Predicting transmission loss errors through machine learning
Authors: Cooper Jennifer , Della Porta C. J. , Ott Olivia
Published: October 2018

Uncertainty in a sound speed profile can lead to uncertainty in the associated prediction of transmission loss (TL). In order to better quantify the effect of imperfect knowledge of the sound speed profile on the acoustic propagation, a study was done comparing pairs of sound speed profiles. In each pair, one profile was treated as ground truth and the second profile was a perturbed version of the first. No single metric on the sound speed profiles, such as mixed layer depth or surface layer characteristics, correlated well with the errors in resulting TL. Several attempts at creating a more complex metric on the profile that could predict errors in the TL were also unsuccessful. However, even a rather simple machine learning approach was able to reliably predict TL errors. Results of the study will be presented and implications discussed.
Grating lobe prediction and deconvolution for synthetic aperture sonar
Authors: Dillon Jeremy
Published: October 2018

Synthetic aperture sonar (SAS) arrays are typically undersampled in the sense that the array element spacing is much larger than the acoustic wavelength. Grating lobes are suppressed by making a judicious choice of beampattern nulls for the transmit and receive elements, such as a 3:2 ratio for the length of the transmit and receive elements. However, grating lobe artifacts can appear in SAS imagery when the target strength difference between a highly reflective object and the surrounding seabed exceeds the sidelobe level of the synthetic array. We present a theoretical model of the SAS point scattering function (PSF) that takes into account shaded element beampatterns for a multichannel SAS array. The PSF model is validated using experimental data from AquaPix, a wideband 300 kHz interferometric SAS. In practice, observed SAS images are described by the convolution of the seabed reflectivity with the PSF. Therefore, knowledge of the PSF facilitates the removal of grating lobe artifacts using deconvolution techniques such as the Richardson-Lucy algorithm. Conventional and deconvolved SAS images of a highly reflective target are presented to demonstrate the effectiveness of deconvolution based on the modeled PSF.
Measurement matrix design for sparse spatial spectrum estimation in Khatri-Rao subspace
Authors: Shen Jiajun , Zhou Tian
Published: October 2018

Compressive (or namely compressed) sensing (CS) exhibits superior performance in sparse spatial spectrum estimation from a predefined vandermonde based dictionary. The CS theory requires that dictionary is as incoherent (orthogonal) as possible since the number of atoms is generally much more than observation vectors, and, namely, the dictionary is over-complete or redundant. Previous researches focus on designing sensing matrix to reduce the mutual coherence of dictionary. However, according to Grassmannian frames, it is still a problem that the coherence of a given dictionary is hard to break through an equiangular tight frame (ETF). To address the problem, we proposed and proved a KR-KSVD method to break through the original lower bound of mutual coherence. In the Khatri-Rao subspace, measurement matrix is designed by minimizing the cost function between the Gram matrix of the equivalent dictionary and an identity matrix with the KSVD method. Simulations demonstrate that the method can produce a better performance in terms of mutual coherence property and sparse recovery accuracy.
Vector intensity properties from direct and reverberant field from a mid-frequency sonar in shallow water
Authors: Dahl Peter H. , Dall'Osto David R.
Published: October 2018

The Intensity Vector Autonomous Recorder (IVAR) is a benthic lander system that coherently measures 3-axis acoustic particle velocity and pressure (combined sensor). Results using IVAR in a mid-frequency propagation and reverberation study conducted near Geoje Island, Republic of Korea, are presented. The measurements were made within shallow semi-circular bay (depth ~25 m) with bay opening to deeper waters, and with directional wave measurements made within the bay waters. This presentation will focus on measurements made at a fixed range (100–1000 m, depending on test) from the Autonomous Reverberation Measurement System (ARMS), a benthic lander with a source and receive array mounted on a rotation stage in order to collect reverberation data as a function of bearing angle. Several vector and scaler metrics emerge based on different combinations of second-order acoustic fields are discussed, such as rate of energy transport and active and reactive intensity that lend insight into the process of shallow water reverberation. For example, in one continuous measurement made over a 12 hour period, there is high correlation between wave slope and horizontal beam width as determined with horizontal active intensity. This and other effects related to variability in shallow water reverberation will be discussed.
Oceanographic effects on mid-frequency acoustics during KOREX-17
Authors: Shim Taebo , Hefner Brian T. , Son Su-Uk , Na Youngnam , Tang Dajun
Published: October 2018

A 9-day mid-frequency, shallow water experiment was conducted off Geoje Island, Republic of Korea, in May 2017. The experiment consisted of transmission, reverberation, and backscatter measurements. The experiment site includes a shallow bay, with water depth less than 30 m, which opens to the Korea Strait where the depth reaches 60 m at a range of a few kilometers from the bay entrance. While the bathymetry of the site is well documented, the geo-acoustic properties of the area is complex, comprised of mud with rock outcrops and regions of sand. The oceanography during the experiment was dominated by tidal forcing and this is expected to be the main source of temporal variability in propagation and reverberation at the site. This paper focus on understanding the variability of the water column in space and time by analyzing data from CTD casts and from a CTD chain, supplemented by data from a nearby oceanographic buoy. A preliminary assessment of the impact of this variability on transmission loss is also examine. [Work supported by the Office of Naval Research and the Agency for Defense Development.]
Geoacoustic inversion of 3.5-kHz towed receiver data from the KOREX-17
Authors: Kwon Hyuckjong , Choi Jee Woong , Son Su-Uk , Na Youngnam , Jung Seom-Kyu , Tang Dajun , Shim Taebo
Published: October 2018

The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters obtained by the empirical relationship to mean grain size and a sediment layering information obtained by a chirp sonar survey. [Work supported by Agency for Defense Development, Korea (UD170014DD).]
Rocky outcrops as clutter in mid-frequency reverberation measurements
Authors: Hefner Brian T. , Tang Dajun , Choi Jee Woong , Shim Taebo
Published: October 2018

Scattering by isolated rock outcrops stand out as prominent features in mid-frequency reverberation measured during KOREX-17, a shallow water experiment conducted off Geoje Island, Republic of Korea, in May 2017. The reverberation data were collected using the Autonomous Reverberation Measurement System (ARMS), a benthic lander with a directional source and receive array mounted on a rotation stage. This stationary system was deployed in roughly the same position on the seafloor over the course of the 9-day experiment. A side-scan sonar survey of the seafloor was conducted to identify the location and rough spatial extend of the exposed portions of the rock outcrops. This talk examines scattering by the rock outcrops as a function of time, signal waveform, and changing oceanographic conditions, with an eye toward detection in clutter environments. Since the ARMS is a fully-calibrated sonar system, with known source level and directivities, the target strengths of the outcrops are also estimated with the long-term goal of developing a scattering model of the most prominent rock outcrop which extends 7-8 m above the seafloor. [Work supported by ONR.]
Analysis of sonar clutter using backscattered spatial correlation
Authors: Smith Chad M. , Brown Daniel C. , Preston John R.
Published: October 2018

Sonar clutter events are one of the primary limitations of long-range active sonar systems within the littoral environment. For this reason, research towards understanding their acoustic return characteristics and ultimately their mitigation are of high importance. This paper discusses measurements and modeling of the backscattered horizontal correlation function from clutter events and comparison with returns from the littoral environment. A statistical model for returns from boundaries, as well as general expectations of returns from common clutter sources will be discussed. The horizontal correlation function is estimated via sub-aperture beamforming of the Five Octave Research Array (FORA), a towed line array system owned and operated by Penn State and funded by the Office of Naval Research. [Work supported by Office of Naval Research.]
Recent acoustic designs in China, commissioning results
Authors: Scelo Thomas , Fearnside Peter , Exton Peter
Published: October 2018

Marshall Day Acoustics has recently completed three large performing arts centres in China. Some of the challenges and design approaches are presented in an accompanying paper. These include the Jiangsu Grand Theatre with a 1,500-seat concert hall, 2,300-seat opera house and a 1,000-seat drama theatre. Also included is the 2,000-seat Qingdao Grand Theatre and the 2,040-seat opera house at Shaanxi Grand Theatre. The present paper will provide details on the commissioning measurement results for room acoustics. First the principles of the measurement system and room setup will be briefly presented before the actual measurement data and derived acoustic parameter are revealed.
Underwater ecoacoustics as a monitoring tool in freshwater environments
Authors: Desjonquères Camille , Rybak Fanny , Gifford Toby , Linke Simon , Sueur Jérôme
Published: October 2018

Biodiversity in freshwater habitats is decreasing faster than in any other environment, mostly due to human activities. Monitoring these losses can help guide mitigation efforts. In most comparative or focal studies, sampling strategies predominantly rely on collecting animal and vegetal specimens. Although these techniques have produced valuable data, they are invasive, time-consuming, and typically have limited spatial and temporal replication. There is therefore a need for the development of complementary methods. As with other ecosystems and landscapes, freshwater environments host animals producing sounds, either to communicate or as a byproduct of their life activity. Animals and processes can be recorded, remotely, by unattended equipment and provide global information on local diversity and ecosystem health. We review practical examples of progress in experimentally addressing six main challenges that freshwater ecoacoustic monitoring faces: (1) associating each sound to its emitter, (2) estimating intra-specific sound variations, (3) evaluating diurnal variation, (4) modeling sound propagation, (5) deriving links between ecological condition and sounds, and (6) developing a repository for freshwater sounds. Passive acoustics represents a potentially revolutionary development in freshwater ecology, enabling dynamic monitoring of biophysical processes to inform conservation practitioners and managers.
Spatial mapping of the biophony of the fishes living in seagrass meadows
Authors: Gervaise Cédric , Lossent Julie , Iorio Lucia D. , Valentini Poirier Cathy Anna , Boissery Pierre
Published: October 2018

Passive acoustics is well suited to assess the diversity and/or activity of marine animals, particularly if cryptic or difficult to observe as in seagrass Posidonia oceanica meadows. The ability to locate the emitters allows not only to detect the presence of a specific sound or specie but also to estimate source levels, the communicative space with respect to ambient noise and anthropogenic impact, the density of vocalizing animals, their movements and potentially home ranges, etc. Here, we located fishes in seagrass meadows (Calvi, France). Two particular sounds dominated the acoustic scene of seagrass meadows: the: 300 Hz drums of Ophidion rochei and the ubiquitous 800Hz /kwa/ sound of unknown origin. The wavelengths of these fish sounds range from 5 m to 2 m. During six 48-hours period, we deployed a squared array of 4 hydrophones (20 x 50 x 50 m). Here, we describe the algorithm for automated fish sound detection and 3D localization of the sources and assess their performances on our real data. Over 1000 fish sounds were detected per night. These detections were used to create localization maps and study the spatial distribution of fish sound production, estimate source levels and the density of the vocalizing fishes within the meadow and their limits.
Automatic detection and localization of croaker’s fish calls using beamforming
Authors: Matsuo Ikuo , Yamato Kazuki , Takahashi Ryuzo , Imaizumi Tomohito , Akamatsu Tomonari
Published: October 2018

Many kinds of fish, including croaker, produce species-specific low-frequency sounds associated with courtship and spawning. A recording system was used to monitor underwater fish call sounds. We have proposed the method to detect croaker calls from data measured by a single hydrophone. However, it was difficult to detect the desired calls at a high detection rate because of a low signal-to-noise ratio. We proposed the method using beamforming to improve the detection rate. At first step, fish calls are detected from data measured on one hydrophone using the previous method, which detects calls automatically using the acoustic features, that is, duration and periodicity. At second step, additional calls are detected by beamforming the four-channel data. At third step, detected calls are localized by using the time differences of arrivals. It was clarified that the detection rate using the proposed beamforming method was higher than that under the previous method with a single data channel. In addition, it was shown that fish calls could be localized from the acoustic data measured during several weeks. Therefore, this method could monitor sounds from croaker in the ocean.
Sounds from the Amazon: Piranha and prey
Authors: Rountree Rodney A. , Juanes Francis
Published: October 2018

The underwater soundscape of an upper tributary of the Amazon River was studied in a four-week survey from 3 to 26 July 2012 within the Pacaya-Samiria National Reserve, Peru. Over 550 individuals representing over 70 species of fishes were auditioned for sound production. In addition, over 641 minutes of natural sounds from the river were recorded from 22 sites. We demonstrate that closely related species of piranha can be distinguished by their hand-held disturbance sounds. Similar piranha sounds were recorded in the wild at locations where piranha were known to be actively feeding. Sounds of catfishes and other fishes were significantly more frequent at piranha feeding sites. Thus, piranha sounds appear to be excellent indicators of local piranha feeding activity and suggest that passive acoustic monitoring (PAM) can be an effective tool for studies on piranha behavior, feeding activity, and impact on prey fishes.
Acoustic recordings of Pacific salmon (Oncorhynchus spp.) from a hatchery on Vancouver Island
Authors: Murchy Kelsie , Mouy Xavier , Juanes Francis
Published: October 2018

Sound production in fish has been documented; however, the diversity of species that create sound is not fully understood. Pacific salmon (Oncorhynchus spp.) are ecologically, economically, and culturally important in the northeast Pacific. Recent declines in specific species and stocks have increased their public interest. Other species from the family Salmonidae produce sounds, but there is little evidence of any species of Pacific salmon producing sounds. Recording salmon in the wild would be difficult but local hatcheries allow for a unique opportunity to listen for salmon sounds in a semi-natural environment. Chinook salmon (O. tshawytscha), pink salmon (O. gorbuscha), and coho salmon (O. kisutch) were recorded using two stationary acoustic recorders that were deployed at a salmon hatchery in Qualicum beach Vancouver Island, British Columbia, for three consecutive weeks in September and October 2017. Audio files were collected in 5 minute subsections and examined for salmon sounds. Here, we present spectrograms and time-frequency composition of potential sounds found for Chinook, pink, and coho salmon. All sounds were then compared to sounds produced by other soniferous fish and to the hearing range of Pacific salmon.
Various approaches for designing phased arrays for high-intensity focused ultrasound therapies: From sparse to fully-populated configurations
Authors: Sapozhnikov Oleg , Khokhlova Vera , Rosnitskiy Pavel , Gavrilov Leonid
Published: October 2018

High-intensity focused ultrasound (HIFU) therapies are often performed using multi-element phased arrays. Independent variation of the amplitudes and phases at the array elements allows electronic steering of the focus and compensation for aberrations. To suppress the formation of grating lobes, the arrangement of the array elements should be non-periodic. Three approaches that have been recently employed in our studies to solve this problem are presented and discussed: a random element arrangement [L.R. Gavrilov and J.W. Hand, IEEE Trans. UFFC 2000], a multi-armed spiral arrangement [V.A. Khokhlova et al., Physics Procedia 2016], and recently proposed array design with tight packing of the elements based on the capacity-constrained tessellation [P.B. Rosnitskiy et al., IEEE UFFC 2018]. The efficiency of two arrays with the same geometric and physical parameters is compared: a 256-element array with a compact 16-spirals layout of circular elements and a fully populated array comprising polygonal elements of equal area. It is shown that for the same intensity at the elements, the fully-populated array provides twofold higher total power while maintaining the same electronic focusing capabilities as compared to the spiral one which can be beneficial for high-power applications such as histotripsy. [The work was supported by NIH R01EB7643 and R01EB025187, RFBR 17-02-00261, and Ph.D. student stipends from the “Basis” Foundation and of the President of Russia SP-2644.2018.4.]
Development of a freely available simulator with graphical interface for modeling nonlinear focused ultrasound fields with shocks
Authors: Khokhlova Vera A. , Yuldashev Petr V. , Mezdrokhin Ilya , Rosnitskiy Pavel , Karzova Maria M. , Kreider Wayne , Sapozhnikov Oleg
Published: October 2018

Measurement-based modeling is gaining acceptance as a standard tool for characterizing the nonlinear fields of existing therapeutic ultrasound devices and designing new ones. Here, a freely available simulation tool is presented for modeling axially symmetric, strongly nonlinear HIFU beams with shocks in a layered propagation medium such as water and different types of tissue. Two nonlinear wave equations are included in the simulator: the KZK equation generalized to include an equivalent source boundary condition for strongly focused beams and the Westervelt equation in a nonlinear wide-angle parabolic representation. Both equations are solved in the frequency domain and permit definition of the HIFU transducer as an annular array. The geometrical parameters and power output of the array, electronic focus steering along the beam axis, and acoustic properties of the layered propagation medium can be configured via graphical interface. Visualization and output of various acoustic field parameters such as peak positive and negative pressures, shock amplitude, intensity, heat deposition rate, and total power of a beam are also provided. The simulator can be used for transducers without ideal symmetry through definition of an equivalent radially symmetric source. Widespread availability of such simulation tools will help advance standardized utilization of measurement-based modeling and facilitate the adoption of such approaches for HIFU treatment planning. [Work supported by NIH R01EB7643, R01EB025187, and RSF №14-12-00974.]
Nonlinear ultrasound fields generated by a 256-element spiral array for boiling histotripsy
Authors: Khokhlova Tatiana D. , Kreider Wayne , Hunter Christopher , Ghanem Mohamed A. , Cunitz Bryan , Sapozhnikov Oleg A. , Khokhlova Vera A.
Published: October 2018

Boiling histotripsy (BH) is a HIFU approach that uses millisecond-long ultrasound bursts with high-amplitude shocks to mechanically fractionate tissue. In this work, the performance of a BH pre-clinical system operating at 1.5 MHz was characterized by hydrophone measurements in water and lesion formation capabilities were tested in ex vivo tissue. The system comprises a 256 element array driven by Verasonics Ultrasound Engine with a 1.2 kW external power source enhanced by an additional capacitor bank. The maximum pulse average acoustic power of the system was 2.2 kW (as measured by radiation force balance), sustained for 10 ms with <15% drop in amplitude. At the focus, a fully developed shock of 100 MPa amplitude formed at 275 W acoustic power. The steering range defined at -3 dB in both linear and nonlinear beam was 19 mm laterally and 38 mm axially forming the region where 100 MPa shocks can be achieved with less than twofold increase in acoustic power. Within the axial steering range, shock formation characteristics varied substantially due to changes in the effective transducer F-number. The system was successfully used to produce volumetric BH lesions in ex vivo tissue using electronic steering only. [Work supported by NIH R01EB7643, R01GM122859, and R01EB025187.]
Using and selecting small condenser format microphones for impulsive noise measurement
Authors: Weir James
Published: October 2018

The small format condenser microphone is the most often used transducer for impulsive measurements of firearms and suppressors. In this paper, the properties and characteristics of these microphones will be detailed and how the selection and use of these condenser microphones will affect the consistency and accuracy of measurements. The goal is to raise awareness and measurement consistency for developers, regulators, and user/hobbyists. The short wavelengths of sound at high frequencies are physically manipulated by the physical design of the transducers. A thorough testing of these products reveal these characteristics and their effect on the accuracy of the resulting measurement. The directivity, frequency response, impulse response, and damping characteristics will be compared. Results will be represented, along with anecdotal stories of real life implementation.
Estimation of atmospheric sound transmission loss due to sea roughness by mean of an effective impedance: A numerical validation
Authors: Turo Diego , Ryan Teresa J. , Vignola Joseph F.
Published: October 2018

Preliminary numerical studies have been demonstrated that sea roughness introduces an excess of transmission loss of atmospheric sound propagation. However, numerical solution of the parabolic equation that describes this phenomenon is computationally intensive, particularly when the spatial domain is large (>1 km). This study evaluates the validity of implementing an effective impedance (a flat absorbing surface) in the place of a rough surface. The effective impedance is a parametric complex quantity that is different for each sea state. The parameters of the impedance are estimated by best fitting the numerical solution of a two-dimensional finite-difference time-domain solver. The effectiveness and validity of using this impedance in place of a rough surface is evaluated by direct comparison of the solutions of the Crank-Nicolson parabolic equation obtained with and without the impedance.
Time-series analysis of binaural perception and uncertainty using eye movements
Authors: Winn Matthew , O'Brien Gabrielle
Published: October 2018

Uncertainty affects sensory perceptions, even for stimuli well above detection thresholds. Using an anticipatory eye-movement paradigm popularized in studies of linguistic perceptual certainty and competition, we measured perception of binaural cues in dichotic narrowband noises that varied by center frequency, bandwidth, envelope fluctuations and interaural correlation. Participant’s eye gaze served to mark detection of change in the ILD or ITD. We tracked the timing and direction of saccades, as well as the number of saccades (“guesses”) as a metric of perceptual uncertainty. Results showed gradually increasing performance accuracy for greater cue magnitude, coupled with fewer saccades overall. There was also a change in the distribution of saccade timings and number of saccades depending on whether cues were low-frequency ITD, high-frequency envelope ITD, correlated-noise ILD, or uncorrelated-noise ILD. All ILD results were consistent with a model of detection based on interaural envelope decorrelation; performance was particularly poorer, slower, and more variable for stimuli whose envelopes had greater fluctuation, but only when channels were uncorrelated. Comparison with behavioral accuracy and reaction time will be discussed. This study highlights the potential benefits of time-series analysis in psychoacoustic experiments in order to reveal some subtle effects of stimulus properties on perceptual judgments and certainty.
Thermoacoustic waste heat recovery engine. Comparison of simulation and experiment
Authors: Steiner Thomas W. , Elferink Maarten
Published: October 2018

A thermoacoustic engine heated with a 10–20 kW 600C waste heat exhaust stream was designed and built. The heat is extracted from the exhaust with a microchannel counter flow heat exchanger and delivered to the hot side of the regenerator with a self-ciculating loop. This loop is driven using Venturi driven streaming of the helium working gas so that no high pressure and high temperature pump is required. The prototype system performed close to simulated expectations. A peak of 570 W electrical power was measured as was a peak conversion efficiency of waste heat enthalpy to electrical energy of 5%.
Variability in speaking rate of native and non-native speakers
Authors: Baese-Berk Melissa M. , Walker Kayla , Bradlow Ann
Published: October 2018

The bulk of the work on non-native speech has focused on average differences between L1 and L2 speakers. However there is growing evidence that variability also plays an important role in distinguishing L1 from L2 speech. While some studies have demonstrated greater variability for non-native than native speech (e.g., Baese-Berk & Morrill, 2015; Wade et al., 2007), others have demonstrated that under some circumstances non-native speech maybe lessvariable and that variability in non-native speech may shift as a function of many factors, including task (Baese-Berk & Morrill, to appear; Baese-Berk, Morrill, & Bradlow, 2016) and L1-L2 pairing (Vaughn, Baese-Berk, & Idemaru, to appear). In this study, we ask how variability manifests in L1 and L2 speech by speakers from a variety of language backgrounds. Specifically, we ask whether a speaker whose L1 speaking rate is highly variable is also highly variable in their L2. We also ask whether variability in speaking rate in L1 or L2 differs as a function of task (e.g., read vs. spontaneous speech) and complexity of the task (e.g., more or less complicated reading passages). The results of this study will inform our understanding of the myriad complex factors that influence non-native speech.