bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency approximations for the radiation damping of a bubble
Authors: Spratt Kyle S. , Hamilton Mark F.
Published: November 2016

The recent work by Ainslie and Leighton [J. Acoust. Soc. Am. 126, 2163 (2009)] pointed out that there exist two different expressions in the literature for the scattering cross-section of a spherical gas bubble in liquid. The difference between the two expressions is contained in the term corresponding to the losses due to acoustic radiation. The more common expression, often attributed to R. Wildt [“Acoustic theory of bubbles,” in Physics of Sound in the Sea], is based on a low-frequency approximation and is thus only accurate when the wavelength of the incident wave is large compared to the circumference of the bubble. The purpose of the present work is to investigate specifically the accuracy of this low-frequency approximation for various physical parameters and frequencies of interest. An alternative low-frequency approximation is also suggested, which is both simpler and more accurate than the present approximation. Finally the case of a nonspherical bubble is considered, and an expression for the scattering cross-section is given that is based on the same low-frequency assumptions made by Wildt. [Work supported by the IR&D program at ARL:UT.]
Phase speed measurements of a bubbly liquid in impedance tubes using a transfer function technique
Authors: Cheyne Stanley A. , Thurman H O. , Tiblin Cecil M.
Published: November 2016

Two different impedance tube configurations were used to make phase speed measurements of a bubbly liquid. One setup consisted of a vertical water-filled tube with hypodermic needles near the top end to provide a bubbly termination. In this setup, the source was at the bottom of the tube. The second setup was a vertical tube partially filled with water with hypodermic needles at the bottom. In this setup, the source was at the top and the measurements were made in air with the bubbly termination at the bottom of the tube. In both cases, an SRS-785 spectrum analyzer was used to measure and calculate the transfer function. The transfer function technique (IS0 10534-2-1998) was used to determine the impedance of the bubbly liquid. Once the impedance was found, the phase speed was calculated. Results will be presented with a range of void fractions and bubble radii.
Room acoustics and speech perception: Considerations for the developing child
Authors: Leibold Lori
Published: November 2016

What children hear in noisy rooms is not the same thing that adults hear. Despite precocious maturation of the peripheral auditory system, the ability to hear and understand speech in the presence of competing backgrounds sounds is not fully developed until adolescence. This talk will review results of behavioral studies of auditory masking in children, with a focus on the development speech perception in complex acoustical environments. Data will be presented that support the hypothesis that children’s increased susceptibility to auditory masking relative to adults is related to immature perceptual processing such as sound source segregation and selective attention. Findings from studies investigating the extent to which children benefit from acoustic cues thought to facilitate sound source segregation will be highlighted.
Can you trust your numeric simulations—How to verify your code and validate your model
Authors: Savioja Lauri , Prepelită Sebastian , Chobeau Pierre , Botts Jonathan
Published: November 2016

In many fields where numeric simulations are utilized, there are standard practices on how to make sure that the simulation results are of high quality. In room acoustic simulations this seems to be quite rare although there are several factors that affect the accuracy of the simulations. First of all, there should be guarantees that the mathematical model, typically partial differential equations, actually model the physical phenomena under investigation. This can be made sure by validation and it can take place, for example, by comparing the simulation results to some reference solution or to measurement data. This is typically not a concern for the linearized wave equation although adding realistic boundary conditions makes it more challenging. Another essential factor affecting the correctness and reproducibility of the results is the quality of the implementation. Code verification is a procedure that aims to guarantee that an implementation is free of errors. In this paper, we review some common practices of code verification. As a practical example, we show verification studies conducted with our finite-difference time-domain solver. In addition, we show convergence rates obtained with the same solver to demonstrate the order of the accuracy of the underlying models.
Crowd noise simulation system for sound environment evaluation of public spaces
Authors: Sakuma Tetsuya , Nishimura Yukiko
Published: November 2016

Aiming at the prediction and evaluation of sound environment of public spaces, a simulation-based auralization system is developed for reproducing background crowd noise. The system combines room acoustics modeling using a ray tracing method with a six-channel sound field reproduction system in an anechoic room. As sound sources, footsteps and voices of pedestrians moving on a floor, and HVAC noise from a ceiling are modeled. In a preliminary examination simulating several existing public spaces, a general correspondence to real sound field are confirmed in noise level and auditory impressions such as noisiness, liveness, and so on. Next, simulating a variety of imaginary rooms with changing room dimensions, absorption and pedestrian density, a subjective experiment of auditory pairwise comparisons is carried out. The results show that the noisiness fairly corresponds with the noise level, whereas the feeling of reverberation does not clearly related to the reverberation time, which may be due to the continuous overlap of sounds.
Evaluation of spatial impression of sound field in a concert hall based on the sound intensity using musical sounds
Authors: Hanyu Toshiki , Matsuo Akiho , Hoshi Kazuma
Published: November 2016

Spatial impression is one of the most important factor for evaluating sound fields in concert halls. Objective indices, such as the lateral energy measures, for evaluating the spatial impression are standardized in the ISO-3382. These indices can be measured by using a figure-of-eight pattern microphone. On the other hand, details of spatial information of sound field can be depicted by measuring instantaneous sound intensity in the sound field. However, thus far, there is no index using the sound intensity. In this study, first the relationship between the existing objective indices and the sound intensity is examined. In particular, the existing objective indices are redefined based on the sound intensity. Secondarily, some objective indices are newly defined by using the sound intensity. These intensity-based indices can basically be calculated by using the sound intensity of impulse responses in a room. Third, potential of measuring the intensity-based indices by using musical sounds is examined. We investigated the intensity-based indices in several sound fields by using both impulse responses and musical sounds. Especially, the dependence of signals used in the measurements on the indices was examined.
The characteristics of dolphin clicks compared across recording depths and instruments
Authors: Lammers Marc , Oswald Julie N. , Kuegler Anke , Nosal Eva M.
Published: November 2016

The identification of delphinid species on the basis of the characteristics of their acoustic signals is an important aspect of many passive acoustic monitoring efforts. The development of species classifiers relies on the assumption that species-specific signal characteristics will be consistent across different recording scenarios, including depth and instrumentation. However, this assumption has largely remained untested. Here, we report on an effort to examine whether and how the properties of echolocation clicks obtained from different delphinid species vary as a function of recording depth and the instrument employed. Field recordings of seven species of dolphins were obtained off Kona, Hawaii, and San Diego, CA, using a 250 m vessel-based vertical array composed of five microMARS recorders, two SoundTrap recorders, and four C75 broadband dipping hydrophones (Cetacean Research Technology). The clicks obtained were characterized on the basis of their spectral properties and duration for each recording depth and also compared among different instruments deployed at the same depth. Both depth and recording instrumentation influenced the click characteristics observed. However, the click properties of some species varied to a greater degree than others. These results suggest that developing species-specific classifiers based on dolphin clicks should be approached with caution and carefully validated.
Role of dopamine in learning beyond reinforcement: Boost of auditory learning and transfer by orally taken or gameplay-generated dopamine
Authors: Tang Dinglan , Moore David R , Amitay Sygal , Zhang Jun-Yun , Zhang Yu-Xuan
Published: November 2016

We showed here that playing a video game, Tetris, in silence enhanced learning of contiguous auditory perceptual training and its transfer to working memory. The effect could not be explained by game play per se or the visual-spatial training involved, but rather resulted from across-time and modality interaction between game play and target training. The results led us to propose that game play releases reward signals like dopamine in the brain, which serves as a biological marker for significance of perceptual experiences and regulates learning. Consistent with this hypothesis, orally taking Madopar, a dopamine precursor, before training showed similar learning-enhancing effect as Tetris play. Madopar did not influence working memory training, indicating that the dopamine effect was perceptually but not cognitively mediated. Taken together, the results support the learning-regulating theory of dopamine, and point to a promising approach for increasing the efficiency and applicability of rehabilitative training with rewarding events like game play.
Spatial relationship between two sounds in an oddball paradigm affects responses of neurons in the auditory midbrain to the two sounds
Authors: Patel Chirag , Zhang Huiming
Published: November 2016

Neural sensitivity to a novel sound (i.e., an occasionally occurring acoustic event) is important for hearing in a natural acoustic environment. An oddball paradigm is used to study this sensitivity. Such a paradigm is a quick succession of acoustic stimuli, with each stimulus being one of two qualitatively different sounds presented at respective probabilities (i.e., high probability standard sound and low probability deviant sound). We studied action potential discharges in the rat’s auditory midbrain in response to oddball paradigms presented from free-field loudspeakers. Our results indicated that many neurons generated a stronger response to a sound presented as a deviant than as a standard stimulus when two sounds in an oddball paradigm were co-localized at the frontal midline. For many neurons, the response to a sound presented at frontal midline (either as a standard or a deviant sound) was enhanced or suppressed by relocating the other sound in an oddball paradigm from frontal midline to an off-midline angle. At extreme angles of separation, the number of neurons showing suppression exceeded that showing enhancement. Thus, a spatial separation between two sounds in an oddball paradigm affects responses to both sounds. Population results suggest that co-localization of two sounds helps maintaining neural sensitivity to both sounds.
Investigation of the processing of ambiguous melodies in the brain by behavioral and neurophysiological experiments
Authors: Yuhara Ryosuke
Published: November 2016

Melody recognition is not a mere succession of pitch and time perception but must be an active process to a make a meaningful line of tones. To investigate this process, we devised a form of illusory melody resembling but different from the ones used in the studies of streaming. A4 and E5 tones are continuously presented while another tone M (middle tone, for example, C5 or C#5) between the two continuous tones is presented intermittently (0.25 s presentation and 0.25 s rest and repeating). One may hear either an illusory continuous melody of repeated ME5 or MA4 depending on the preceding unambiguous phrase of repetition of ME5 or MA4. Assuming that this illusion reflects the active process of melody formation, we investigated 1) the transition time from the primary state (either one of the melody forms) fixed by the leading phrase behaviorally, and 2) possible neural correlates by measuring the MEG (magnetoencephalography) responses to the continuous tones separately by amplitude modulating them with different frequencies. MEG signal was filtered for the two modulation frequencies and the ASSR (auditory steady state responses) were obtained for different experimental conditions. The results so far showed wide variance among subjects but seem promising.
Level-tolerant duration selectivity in the auditory cortex of the velvety free-tailed bat Molossus molossus
Authors: Macías Silvio , Hernández-Abad Annette , Hechavarría Julio C. , Kössl Manfred , Mora Emanuel C.
Published: November 2016

It has been reported previously that in the inferior colliculus of the bat Molossus molossus, neuronal duration tuning is ambiguous because the tuning type of the neurons dramatically changes with the sound level. In the present study, duration tuning was examined in the auditory cortex of M. molossus to describe if it is as ambiguous as the collicular tuning. From a population of 174 cortical 104 (60 %) neurons did not show duration selectivity (all-pass). Around 5 % (9 units) responded preferentially to stimuli having longer durations showing long-pass duration response functions, 35 (20 %) responded to a narrow range of stimulus durations showing band-pass duration response functions, 24 (14 %) responded most strongly to short stimulus durations showing short-pass duration response functions and two neurons (1 %) responded best to two different stimulus durations showing a two-peaked duration-response function. The majority of neurons showing short- (16 out of 24) and band-pass (24 out 35) selectivity displayed “O-shaped” duration response areas. In contrast to the inferior colliculus, duration tuning in the auditory cortex of M. molossus appears level tolerant. That is, the type of duration selectivity and the stimulus duration eliciting the maximum response were unaffected by changing the sound level.
Psychophysical tuning curves as a measure of electrode position in cochlear implant listeners
Authors: DeVries Lindsay , Bierer Julie A.
Published: November 2016

Speech perception abilities vary widely among cochlear implant listeners. A potential source of this variability is electrode position; suboptimal placement has been associated with poorer outcomes. Insight into electrode position can be obtained via postoperative CT imaging, specifically the distance of each electrode from the modiolus. Additional information can be obtained with behavioral measures, which are sensitive to electrode position and neural integrity.Electrode-to-modiolus distance can explain some variability in behavioral thresholds; however, the relationship with psychophysical tuning curves (PTCs) has not been evaluated, which may provide a more detailed assessment of local variations in channel interaction. Four unilaterally implanted adults with the Advanced Bionics HiRes90K device participated. CT scans were obtained and image reconstructions were performed. Using a fast, sweep procedure, PTCs were collected for all available electrodes using the steered quadrupolar configuration within a forward-masking paradigm. Spread of neural excitation was quantified with the equivalent rectangular bandwidth (ERB). Preliminary data show a correlation between electrode-to-modiolus distance and the ERB of PTCs, suggesting poorer electrode placement may cause broader activation. The goal of this research is to develop a fast, non-radiologic method for estimating electrode position, which may lead to improved device programming by reducing unwanted channel interaction.
Sub-clinical auditory neural deficits in patients with type 1 Diabetes Mellitus
Authors: AlJasser Arwa , Uus Kai , Baker Richard , Plack Christopher
Published: November 2016

Diabetes mellitus (DM) is associated with a variety of sensory complications. Very little attention has been given to auditory neuropathic complications in DM. The aim of this study was to determine whether type 1 DM affects neural coding of the rapid temporal fluctuations of sounds, and how any deficits may impact on real-world listening tasks. Participants were 30young normal-hearing type 1 DM patients, and 30 age-, sex-, and audiogram-matched healthy controls. Tests included non-invasive electrophysiological measures of auditory nerve and brainstem function using the click-evoked auditory brainstem response (ABR), and of brainstem neural temporal coding using the sustained frequency-following response (FFR), as well as behavioural tests of temporal coding (interaural phase difference, IPD, discrimination and the frequency difference limen, FDL) and tests of speech perception in noise. There were no significant differences between DM patients and controls in the ABR. However, the DM group showed significantly lower FFR responses, higher IPD and FDL thresholds, as well as worse speech-in-noise performance. The results suggest that type 1 DM is associated with degraded neural temporal coding in the brainstem in the absence of an elevation in audiometric threshold, and that this deficit may impact on real-world hearing ability.
Binaural sensitivity in children with bilateral cochlear implants and in normal hearing children
Authors: Litovsky Ruth , Bennett Erica E.
Published: November 2016

Children with bilateral cochlear implants (CIs), and normal hearing (NH) children were studied. One goal was to understand if sensitivity to interaural time difference (ITD) and interaural level difference (ILD) is attained at young ages with acoustic hearing. A second goal was to determine if children who hear through electrical stimulation of the auditory nerve are also sensitive to ITD and ILD cues. The bilaterally implanted children received stimulation through synchronized research processors, which is unlike the clinical speech processors that they use every day, which lack interaural synchronization. Sensitivity to ILDs was adult-like in NH children, and all children with CIs were able to use ILDs. Sensitivity to ITDs was, on average, adult-like in NH children, but many of the CI users were unable to use ITDs to determine if a sound was presented to the right or left. This contrasts with prior findings that children with CIs can detect the presence of a stimulus with a binaural cue, regardless of whether they could discriminate ITDs or not. Results underscore the importance of task selection in evaluating binaural sensitivity. Data are interpreted in the context of auditory plasticity and peripheral integrity for the development of binaural coding.
Dynamic representation of acoustic features in neural responses to continuous speech
Authors: Khalighinejad Bahar , Da Silva Guilherme , Mesgarani Nima
Published: November 2016

Humans are unique in their ability to communicate using spoken language. However, it remains unclear how distinct acoustic features of speech sounds are represented in the auditory pathway over time. In this study, we applied a novel analysis technique to electroencephalography (EEG) signals as subjects listened to continuous speech and characterize the neural representation of acoustic features and the progression of responses over time. We averaged the time-aligned neural responses to phoneme instances and calculated a phoneme-related potential (PRP). We show that phonemes in continuous speech evoke multiple observable responses which are clearly separated in time. These recurrent responses have different scalp distributions, and occur as early as 50 ms, and as late as 400 ms after the phoneme onset. We show that the responses explicitly represent the acoustic distinctions of phonemes, and that linguistic and non-linguistic information appear at different time intervals. Finally, we show a joint encoding of phonetic and speaker information, where the neural representation of speakers is dependent on phoneme category. This study provides evidence for a dynamic neural transformation of low-level speech features and form an empirical framework to study the representational changes in learning, attention, and speech disorders.
Influence of stiffeners and internal structures on the vibroacoustic behavior of submerged cylindrical shells under random excitations
Authors: Meyer Valentin , Maxit Laurent , Audoly Christian , Renou Ygaäl
Published: November 2016

The vibroacoustic behavior of structures excited by random pressure fields such as turbulent boundary layers or diffuse sound fields is of great interest for industrial applications. Many works have been carried out for periodically stiffened plates. In particular, the influence of Bloch-Floquet waves on the panel radiation has been highlighted. However, few studies have investigated more complex structures under random excitations. The present work studies the influence of internal structures on the vibro-acoustic behavior of submerged cylindrical shells. The geometric complexity is successively increased by including periodic, non-periodic stiffeners and various internal frames. The numerical prediction is based on the combination of two methods developed by the authors. The first one is the wavenumber-point (k,M) reciprocity technique. This method estimates the response of the system at point M from the shell velocity in the wavenumber space under a point excitation at M. The velocity field is estimated with the second method, called the Condensed Transfer Function method. It is a substructuring approach which couples a semi-analytical model of a submerged cylindrical shell with Finite Element models of axisymmetric and non-axisymmetric frames. Numerical results are analyzed to evaluate the influence of the stiffeners and the internal structures on the shell radiation.
Exhaustive optimization of rib-stiffened, layered plate structures for acoustic response
Authors: Reed Heather M. , Cipolla Jeffrey
Published: November 2016

A previously reported structural-acoustic frequency-domain formulation for layered, ribbed structures is used here as the basis for an approach to optimize these systems. We will review a previously reported singular perturbation approach to resolve convergence difficulties in both planar and cylindrical configurations, and discuss verification and validation. The significant successes of topological structural optimization for strength, weight, and efficiency are more challenging to repeat in coupled wave-bearing systems with many modes present. This is due, at least, to the difficulties of defining appropriate cost and regularization functions applicable across frequency ranges of interest and across the orders of magnitude of response characteristic of vibroacoustic systems. We discuss overcoming these difficulties by evading them entirely: the layered ribbed structural-acoustic model we use is sufficiently fast that sophisticated optimization algorithms are not required. To understand the dependence of critical solution performance metrics on the input parameters, we simply sample the design space exhaustively and develop graphical representations of the relative optimality of solutions. By using sensitivity analysis (effected through Fisher Information) and uncertainty quantification (UQ), optimal layered designs are obtained and balanced by performance robustness. In this talk, we will present examples of applying the approach to realistic systems of interest.
Prediction of reflection and transmission by an elastic barrier with periodic structural discontinuities forced by oblique acoustic waves
Authors: Bliss Donald B. , Villa Mauricio , Franzoni Linda P.
Published: November 2016

An analysis method is developed for acoustic reflection and transmission from an infinite fluid-loaded flexible barrier with spatially periodic discontinuities. The barrier has acoustic fluids on both sides, which can be dissimilar. The structure is excited by an oblique-wave incident acoustic field. The fully-coupled structural/acoustic problem is treated by the method of Analytical-Numerical Matching (ANM). The ANM framework separates the problem into a global numerical solution and local analytical solutions. ANM handles rapid spatial around the structural discontinuities, improving the accuracy and convergence rate of reflected and transmitted pressures. Furthermore, the ANM approach offers a way to handle the mathematical difficulties associated with coincidence frequencies. The periodic spatial discontinuities create variations from simple specular-like directivity with multiple reflection and transmission angles, the effect being most pronounced at structural resonances. The periodic discontinuities can be thought of as redirecting a portion of the structural energy into resonant substructures having wavenumbers different from the oblique wave forcing, reradiating reflection and transmission fields with different directivity patterns. Discrete frequency and broadband results are presented. The goal is to develop efficient first-principles methods for structural-acoustic reflection and transmission between coupled acoustic spaces and into surrounding media.
Investigating the sliding template model of vowel perception
Authors: Barreda Santiago
Published: November 2016

According to the sliding-template model of vowel perception, vowel quality is specified by the frequencies of the first three formants, and within-category variability in formant-patterns is primarily according to a single scaling-parameter [Nearey, J. Acoust. Soc. Am. 85, 2088-2113, 1989]. In this view, speaker normalization in vowel perception centers on the estimation of the spectral-scaling parameter for a speaker. This process may include consideration of “indirect” evidence such as fundamental frequency (f0), or information about speaker size or sex. This model also suggests the potential integration of vowel perception and speaker-size estimation via shared use of the estimated scaling parameter, which is related to speaker vocal-tract length and height. An experiment is presented where listeners were asked to listen to vowel stimuli whose formant patterns were potentially ambiguous between the /æ/ of a larger speaker and the /ʌ/ of a smaller speaker. Listeners were asked to make a vowel-category judgment, and to estimate the height of the apparent speaker in feet and inches. Results are consistent with predictions made by the sliding template model: apparent speaker size was predictive of perceived vowel quality independently of the acoustic characteristics of a sound, and f0 appears to affect vowel quality primarily indirectly.
What does sinewave speech tell us about phonetic perception?
Authors: Hillenbrand James
Published: November 2016

It has been 35 years since the striking demonstration that intelligible speech can be created by mixing sinusoids that follow the formants of natural speech [Remez et al. (1981) Science 212, 947-950]. A good deal has been written about what sinewave speech (SWS) might reveal about the mechanisms underlying phonetic perception. However, most of the experimental work on SWS has been carried out using well-formed sentences whose intelligibility depends on many factors other than phonetic identification. Results will be reported for experiments designed to measure SWS intelligibility explicitly at the phonetic level. For example, listeners were asked to identify the vowel in SW /hVd/ syllables. Intelligibility was far above chance (55%) but dramatically lower than that of the original utterances. Further tests showed: (1) intelligibility increased substantially when the SW syllable was preceded by a brief SW carrier phrase (CP); (2) tests that alternated trials with and without the SW CP showed that CP enhancement is a real-time effect; (3) SW vowels can be classified using a template-matching algorithm trained on naturally spoken vowels at rates exceeding those of human listeners. Preliminary results will be reported for consonant recognition using SW nonsense syllables. [Work supported by NIH.]
Toward a triple-weak theory of phonology/phonetics
Authors: Port Robert
Published: November 2016

Almost 20 years ago, Nearey proposed the Double-Weak theory of speech production and perception. He pointed to three dominant theories of speech production and perception. All begin by assuming the memory representations of language consist of phonemes made from segmental distinctive features. He called the linguistic approach “double-strong” since it assumed each phoneme has a simple set of articulatory correlates as well as acoustic correlates. The other two theories assume either that the articulatory definitions are simple and strong while the acoustics is messy. Or that acoustics plays the strong role while articulation is messy. However, Nearey's double-weak theory assumed no simple relation of either articulation or acoustics to phonemes was possible. In contrast, my theory agrees with Nearey but further argues there is no fixed, invariant set of discrete, non-overlapping phonemes for spelling words (Port, Lang Sci, 2010). This presentation will also discuss recent attempts to salvage the phoneme noting they include so many caveats and revisions that they basically cede the issue.
Double weak theory as a framework for discovery
Authors: Nearey Terrance M.
Published: November 2016

A weak theory is not very attractive, a double-weak one even less so. The double-weak theory of speech perception serves mainly as a cover story for postponing rumination on the deeper principles that ultimately underlie human speech communication. Instead, it adopts minimal assumptions about the relation among symbols, sounds, and gestures that provides a rationale for immediately pursuing some hunches about empirical generalizations, or primitive “laws.” It is hoped that some of these may be akin to Kepler's laws of planetary motion or eighteenth century “gas laws” that may serve as grist for later, more deeply explanatory theories. The active search for such empirical laws in speech perception starts from existing hypotheses about the general structure of surface phonological representations (e.g., features, phonemes, syllables) and proceeds by constructing detailed statistical models that accord with the fine structure of human responses in parametrically controlled speech perception experiments. Some examples and possible extensions of existing models are presented.
Nonlinear Coda Wave Interferometry: Detecting, quantifying, and locating damage in complex solids
Authors: Tournat Vincent , Abraham Odile , Zhang Yuxiang , Legland Jean-Baptiste , Hilloulin Benoit , Durand Olivier , Letourneur Stéphane , Brasseur Emmanuel , Chekroun Mathieu
Published: November 2016

In this talk, we report results on the nonlinear interactions of ultrasonic coda waves with lower pump waves, in reverberating or multiple scattering mesoscopic solid media. Using the method of coda wave interferometry (CWI), we analyze the effect of mixing a coda wave with an additional lower frequency pump wave. The extracted CWI parameters, known to be highly sensitive to small geometric or elastic modifications of the tested medium, are shown to be pump-amplitude dependent and to capture finely the results of the nonlinear interactions. Although nonlinear self-action effects with coda waves have been reported in unconsolidated granular media, they are difficult to implement in cracked solids or concrete. Instead, the reported nonlinear CWI class of methods (NCWI) shows robustness, a high sensitivity, and has been applied successfully to various complex media and structures. We show through several examples on « model » media (cracked glass plates) and on concrete structures, that NCWI can be useful for the nondestructive evaluation of complex solids that are strongly scattering at usual probing frequencies. Preliminary results and prospects in nonlinear elastic properties imaging and quantitative evaluation with NCWI are discussed.
Quantitative evaluation of strength degradation by using linear-nonlinear ultrasonic techniques
Authors: Jhang Kyung-Young , Kim Jongbeom , Lee Ju-ho
Published: November 2016

The ultrasonic nonlinear parameter, β, has been known as effective for the evaluation of material degradation, and its correlation with material degradations such as thermal aging, fatigue, creep, and plastic deformation has been reported. However, most studies were limited to the relative measurements that is effective only for the relative comparison and not able to evaluate the degradation in quantitative. To overcome this limit, this study proposes a new algorithm which is able to evaluate the quantitative strength degradation. The proposed method mainly consists of four steps: 1) Measure the linear elastic modulus (E) from the longitudinal and shear wave velocities by using pulse echo method. 2) Measure the absolute ultrasonic nonlinear parameter, β, by using piezoelectric detection method. 3) Construct the stress-strain curve by substituting the measured linear elastic modulus (E) and absolute ultrasonic nonlinear parameter β to the nonlinear stress-strain equation. 4) Estimate the 0.01% offset yield strain and yield strength. The yield strengths estimated by the proposed technique in the heat-treated Al6061-T6 and SA508 showed good agreement with the yield strength obtained by tensile test. Consequently, the proposed method makes the quantitative evaluation of strength degradation using ultrasonic measurement possible. [This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (NRF-2013M2A2A9043241).]
How to improve detectability of crack size in nonlinear sub-harmonic imaging
Authors: Park Choon-Su , Cho Seunghyun , Seo Dae-Chul , Kim Jun-Woo
Published: November 2016

Crack growth is regarded as an important monitoring parameter for structural degradation. To precisely estimate crack size, therefore, has been highly demanded to monitor structural healthiness and to assess residual life of various structures from small components to huge plants. Conventional non-destructive inspections have been successfully detected cracks, but some deficiencies for accuracy still remain. Nonlinear sub-harmonic generation was well proved to detect closed cracks that could cause underestimation of crack size. Moreover, sub-harmonic phased array (PA) imaging was proposed to visualize where the closed cracks are. The sub-harmonic PA images, however, has lower spatial resolution than the fundamental frequency PA images due to its longer wavelength, which often prevents from clearly observing closed cracks. Many of signal processing techniques have been developed to improve spatial resolution of images for more than half a century, and some resolution enhancing techniques such as deconvolutions and an eigen-analysis based technique are employed to make the resolution of sub-harmonic imaging better. Point spread function issues for deconvolution have been also investigated theoretically and experimentally. In addition, some experiments with CT specimens have been done to prove closed-crack localization by improving spatial resolution of sub-harmonic imaging.
Extraction of nonlinear elastic material parameters from single-impact nonlinear ring-down spectroscopy
Authors: Shokouhi Parisa , Jin Jiang , Riviere Jacques
Published: November 2016

Volumetric microcracking is one of the early symptoms of distress in cementitious materials caused by excessive mechanical stress, chemical attacks, and environmental influences. The microcracks widen, coalesce, and develop into larger cracks with the progress of damage. Visible macro-cracks indicate severe damage that often cannot be mitigated. As such, detection of damage at the early stages of development is essential for designing optimal preventive maintenance programs for concrete structures. Nonlinear acoustics-based nondestructive testing techniques have shown great promise in identification of microscopic cracks in diverse materials including concrete. Impact-based alternatives of conventional techniques are gaining popularity for concrete testing mainly due to their field transportability. In this study, we focus on impact-based nonlinear resonance acoustic spectroscopy (INRAS). We compare the results from multi-impact INRAS, where several impacts of increasing intensities are applied, to those from single impact ring-down spectroscopy where only one impact of large intensity is used. Hilbert Huang Transform (HHT) is used to obtain the time-dependent frequency content of the single-impact ring-down. We propose several models for fitting the entire ring-down in order to extract nonlinear elastic material parameters. We demonstrate that our proposed approach for analyzing single-impact INRAS data yields material parameters compatible with those obtained from conventional testing and analysis.
Characterizing nonlinear systems with memory while combating and reducing the curse of dimensionality using new volterra expansion technique
Authors: Nuttall Albert H. , Hughes Derke , Katz Richard A. , Koch Robert M.
Published: November 2016

A generalized model for characterizing nonlinear systems was originally proposed by Italian mathematician and physicist Vito Volterra (1860-1940). A further development by American mathematician and MIT Professor Norbert Wiener (1894-1964) was published in 1958. After direct involvement with Norbert Wiener publication, Albert H. Nuttall has recently made new inroads along with his coauthors in applying the Wiener-Volterra model. A general description of a nonlinear system to the third order is termed the Nuttall-Wiener-Volterra model (NWV) after its co-founders. In this formulation, two measurement waveforms on the system are required in order to characterize a specified nonlinear system under consideration: an excitation input, x(t) (the transmitted signal) and a response output, z(t) (the received signal). Given these two measurement waveforms for a given system, a kernel response, h= [h0,h1,h2,h3] between the two measurement points, is computed via a least squares approach that optimizes modeled kernel values by performing a best fit between measured response z(t) and a modeled response y(t). New procedures developed by A. Nuttall are invoked to significantly diminish the exponential growth of the computed number of kernel coefficients with respect to third order and higher orders to combat and reasonably reduce the curse of dimensionality.
Superdirective non-linear beamforming with deep neural network
Authors: Mizumachi Mitsunori , Origuchi Maya
Published: November 2016

Beamforming has been one of important issues in acoustic signal processing, since it can achieve signal enhancement and sound source localization. In general, traditional beamformers are designed by an analytical approach or an adaptive approach. It is, however, difficult to properly optimize the beamformers under the complicated acoustical scene. An alternative non-linear beamforming can be substituted for the linear beamforming. In this study, a flexible framework for optimizing the beamformer is introduced based on a deep neural network. Capturing acoustic signals using a microphone array is regarded as spatial sampling, so that annoying grating lobes appear in beam-pattern when the relationship between the wavelength and the microphone spacing does not satisfy the sampling theorem. The proposed method achieves sub-band beamforming using the non-uniform microphone array with eight nesting microphones, which are carefully designed not to cause spatial aliasing. Feasibility of the proposed method has been confirmed by computer simulation. The proposed non-linear beamformer could successfully achieve superdirectivity compared with conventional beamformers.
Compiling the air situation picture from a submerged submarine
Authors: Ferguson Brian G. , Speechley Gary C.
Published: November 2016

The transmission of sound through the air-water interface produces an underwater sound field that can have as many as four separate contributions from an airborne acoustic source. These contributions are identified as: direct refraction, one or more seafloor reflections, the evanescent wave, and sound scattered from a rough sea surface. The relative importance of each contribution depends on the horizontal distance of the source from the receiver, the water depth, the depth of the receiver in relation to the wavelength of the signal radiated by the source, and the roughness of the sea surface. This paper demonstrates how a submerged submarine towing an array of hydrophones is able to detect, classify, localize and track maritime patrol aircraft and helicopters, whilst at depth, by exploiting the direct and indirect sound propagation paths of the aircraft’s radiated noise (acoustic signature). As the airborne source is in relative motion with respect to the array, the received signal at each hydrophone is Doppler-shifted in frequency. It is shown that the variation with angle of arrival of the observed Doppler-shifted propeller blade passing frequency is in close agreement with that predicted for the direct refraction path. Similar observations are also made for the seafloor reflected propagation paths. Early warning/long range detection of threat aircraft is enabled by one or more reflections from the sea floor.
Light aircraft sound for underwater acoustics experiments
Authors: Buckingham Michael J.
Published: November 2016

A propeller-driven light aircraft produces sound in the form of a sequence of harmonics from the propeller and from the reciprocating engine. The lowest frequency, from a two-bladed propeller, is around 80 Hz with detectable harmonics extending up to about 1 kHz. When flying over the shallow ocean at low level, some of the aircraft sound penetrates the air-sea interface to undergo multiple reflections between the seabed and the sea surface as it propagates through the channel. On approach to a sub-surface receiver station, the frequency of a given harmonic is Doppler upshifted, whereas on departure it is downshifted. Since these Doppler shifts depend not only on the speed of the aircraft but also on the geo-acoustic properties of the seabed, they provide the basis of a rapid and efficient inversion technique for surveying the seabed. To develop the technique, shallow-water experiments have been performed using various types of light aircraft as the sound source and a single hydrophone as the receiver. It was found that, with the aid of the grain-shearing theory of wave propagation in unconsolidated sediments, it is possible to recover the sediment geo-acoustic parameters from the Doppler-shifted aircraft harmonics. [Research supported by ONR.]
A geoacoustic inversion technique using the low-frequency sound from the main rotor of a Robinson R44 helicopter
Authors: Bevans Dieter A. , Buckingham Michael J. , Hursky Paul
Published: November 2016

A series of underwater acoustic experiments utilizing a Robinson R44 helicopter and an underwater receiver station has been conducted in shallow (16.5 m) water. The receiver station consisted of an 11-element nested hydrophone array with a 12 m aperture configured as a horizontal line (HLA) 0.5 m above the seabed. An in-air microphone was located immediately above the surface. The main rotor blades of the helicopter produce low-frequency harmonics, the fundamental frequency being ~13 Hz. The tail rotor produces a sequence of harmonics approximately six times higher in frequency. The first experiment characterized the underwater sound signature of the helicopter with altitude and range. Using analytical and numerical 3-layer (atmosphere-ocean-sediment) acoustic propagation models a sediment geoacoustic inversion technique has been developed. This technique, requiring only knowledge of the relative location of the sensors and sound source (helicopter), uses the cross-correlation between HLA sensor pairs to produce the estimated time delay of the head wave. The results from the simulations and the latest experiment are presented. [Research supported by ONR, SMART(DOD), NAVAIR, and SIO.]
A spectral approach to geoacoustic inversion from sparse impulsive sources
Authors: Yudichak Thomas W. , Stotts Steven A. , Koch Robert A. , Jacobellis Dan G. , Ruditskiy Daniil
Published: November 2016

A common approach to geoacoustic inversion is to match the temporal structure displayed by modeled and measured acoustic data produced at a small number of frequencies by range sampling source emissions over a broad interval between a source and a receiver. An alternative approach is to match spectral structure in modeled and measured acoustic data for a small number of source-receiver separations from a fine frequency sample over a broad bandwidth. The latter approach is demonstrated with Shallow Water '06 experiment data in which the acoustic sources were imploding light bulbs. Geoacoustic parameter values obtained by this approach are compared to values obtained from previous inversions, and the limits of validity of the approach are discussed.
Prediction of array gain in directional noise field
Authors: Park Jisung , Choi Yonghwa , Kim Jeasoo , Cho Sungho , Park Jungsoo
Published: November 2016

The Array Gain(AG) is a metric to assess the performance of an array and is dependent on the configuration of array, frequency, as well as on the directionality of noise. In this study, AG is calculated based on the spatial coherence between sensor elements in directional noise environment for a given array shape. The estimated AG is then compared with AG derived from the sea going data based on the signal to noise ratio. The results are presented and discussed.
Research for the position detection of the object within the tube liquid using sound wave
Authors: Muto Seijun , Fukuda Katsumi , Nishimura Yoshihiro
Published: November 2016

The purpose of detecting using sound waves the position of an object in the tube filled with liquid. Experiments were carried out taking into account the frequency and oscillation of the process of the sound. As a result, good results for the position detection of the object to obtain a new knowledge.
Acoustic characterization of a wave energy converter
Authors: Polagye Brian L. , Murphy Paul , Bethune Keith , Cross Patrick , Vega Luis
Published: November 2016

As progress toward the commercial deployment of wave energy converters accelerates, it is important to ensure that these renewable energy systems do not have unintended, adverse environmental consequences. While the sound from wave energy converters is unlikely to cause acoustic injury to marine animals, it may affect their behavior. Here, we present measurements from a point-absorber wave energy converter at the U.S. Navy Wave Energy Test Site in Kaneohe Bay, HI. Measurements of wave converter sound are obtained for a range of sea states using a combination of free-drifting near-surface measurements and stationary bottom packages. The relative effectiveness of these systems are contrasted and the unique challenges associated with acoustic measurements at energetic sites discussed. For example, fixed measurements are found to be substantially contaminated by flow-noise (non-propagating sound) during long-period ocean swell, while free-drifting measurements require significant post-processing to avoid convolving flow-noise or self-noise with wave converter sound. Preliminary results of parabolic equation modeling is also presented and used to interpret spatially distributed measurements.