bluuebunny/crossref_metadata_2025 huggingface dataset:
A new technique for real-time freehand ultrasonic elasticity imaging
Authors: Zhu Yanning , Hall Timothy , Cook Larry
Published: February 2014

A method for high-speed, freehand ultrasonic elasticity imaging will be described. The method is based on a modified block matching technique. The modification serves two purposes. First, in order to achieve real-time performance a forward prediction mechanism is used to reduce the computational load that a conventional block matching technique requires. Second, in order to accommodate the waveform decorrelation associated with freehand scanning a statistical error detection and correction method was developed. This prevents the displacement estimation errors from propagating to affect a larger area. This new algorithm has been implemented on a Siemens Elegra (a high-end clinical ultrasound imaging system). The initial tests show that the new system can perform B-mode and strain display task at real-time frame rates. The strain images have low noise and excellent contrast. Some results obtained with this system will also be presented. [Support by USAMRAA DAMD17-00-1-0596, NSF BES-9708221, and Siemens Medical Systems is gratefully acknowledged.]
Efficient three-dimensional cylindrical-geometry ultrasound imaging
Authors: Haun Mark A. , Jones Douglas L. , O’Brien William D.
Published: February 2014

A number of new imaging modalities collect data from cylindrical platforms. In vivo imaging needles and intravascular ultrasound imaging catheters are examples of this geometry, where imager rotation and translation parallel to the cylinder axis are the only allowed motions. Efficient three-dimensional ultrasound image formation in these cases can be challenging when the aperture is small and/or highly curved. A frequency-domain imaging algorithm is obtained by approximating the free-space point spread function in cylindrical coordinates and obtaining its Fourier transform by analogy with the equivalent problem in Cartesian coordinates. We further propose an effective use of limited aperture by placing a focused transducer across the aperture, thereby creating a virtual source at the focus which is treated as a real, unfocused source by the imaging algorithm. This approach retains the simplicity and potential angular resolution of a small single element, yet permits full use of the available probe aperture and a higher energy output. Computer simulations and experimental ultrasonic results with wire targets show that this imaging technique attains the theoretical resolution dictated by the operating wavelength and transducer characteristics. [Work supported by NIH CA 079179.]
Numerical model of acoustic interactions between class IV flextensional transducers using a modal method
Authors: Blottman John B.
Published: February 2014

Acoustic projectors assembled in an array experience an interaction effect as a result of the coupling of their individual radiated powers through the acoustic medium. The acoustic interaction may be expressed as a superposition of modal–mutual radiation impedances. A hybrid modeling technique is presented that combines the boundary integral method with a piece-parts equivalent circuit. The circuit consists of assembling a motional branch for the piezoelectric driver and for a set of flexural modes of the flextensional shell. The in vacuo eigenmodes of the shell are determined using the atila finite element method. Modal radiation impedances are generated using the chief boundary integral equation method. The resulting modal–mutual impedances are applied to the motional branches through a set of source-coupling terms. The circuit then provides a set of modal participation factors. Results compare well to measurements and to full finite element models of small close-packed arrays. [Work supported by ONR and NUWC ILIR.]
Extending nearfield acoustical holography past intermediate sources
Authors: Zechmann Edward , Mann J. Adin
Published: February 2014

With planar nearfield acoustical holography (NAH), the complex acoustic pressure and the acoustic velocity vector can be estimated on a plane near a complex source surface to identify individual noise sources. However, there are often intermediate sources between the measurement plane and the primary source plane. The NAH technique in its classical form cannot be extended past the intermediate source. A method will be presented to remove the intermediate sources so that NAH can be extended to the surface of the primary source. The normal velocity at the surface of an intermediate source is used to estimate the complex pressure due to the intermediate source on the measurement plane, which is then subtracted from the measured data, providing an estimate of the measured sound pressure if the intermediate source was not present. NAH is then used to project to the surface of the primary source. The source removal process was tested with simulated and measured data. Results for two methods to estimate the pressure caused by the intermediate source, inverse NAH and a point source approximation, will be presented. The results show the effectiveness and limitations of the source removal process. [Work supported by Ford Motor Company.]
Study on acoustic transmission loss characteristics using artificial neural network approach
Authors: Ramachandraiah A. , Maheswari G.
Published: February 2014

The sound transmission losses of multilayer walls are determined by the physical properties of the component materials. Various analytical methods exist to evaluate the transmission loss of sound in materials. Each method has its own limitations resulting in differences of the predicted and the experimental values. Of late the neural networks have emerged as powerful pattern recognition techniques. In this approach the network learns the similarities among the patterns and infers solutions from the complex, distorted data, which generally the conventional approaches fail to do. Transmission loss of materials in building acoustics seems to be one field where the neural network can be addressed. The transmission loss characteristics of a partition are generally governed by factors like density, thickness of partition, presence of absorptive material, etc. The relation between the input and output parameters is a complex one and may at times be difficult to determine by conventional methods. A neural network has been developed to predict the transmission loss and transmission class values of composite partitions with reasonable precision. The generalization of the network is also tested. The performance of the neural network is observed and the results obtained through neural network approach are analyzed and discussed.
Contemporary ideas in musical instrument making: An overview of recent trends
Authors: Hopkin Bart
Published: February 2014

In this talk I will discuss some particularly inventive ideas that have arisen in acoustic musical instrument making in recent years. We’ll look at broad trends in instrument design as well as specific instrument types. We will cover acoustic chorusing instruments such as Sharon Rowell’s Huaca and Richard Water’s Waterphone, musical uses of longitudinally vibrating strings such as Ellen Fullman’s Long String Instrument, just intonation and harmonics-oriented instruments such as Hans Reichel’s Pick-Behind-the-Bridge Guitar and Jacques Dudon’s Photosonic Synthesizer, balloon-mounted and bowed-metal instruments from the Baschet brothers and Tom Nunn, and many more. There will be sound recordings and visuals, and I may be able to bring one or two smaller instruments along for show and tell.
The development of ‘‘21st century’’ acoustic and orchestral instruments
Authors: Ozzard-Low Patrick
Published: February 2014

The work of the Centre for New Musical Instruments (CNMI), recently established at London Guildhall University, is reported. In addition, a wide range of original slides is shown, providing an overview of international innovations relevant to the development of new versions of existing acoustic orchestral instruments, especially those offering new forms of expression to composers and performers. In view of the overwhelming majority of developments of electronic as opposed to acoustic instruments during the 20th century, the purpose of CNMI is to encourage innovations of the latter. Acoustic instruments designates not only those traditionally referred to by this term, but also those in which elements of sound generation may be electromechanical or electroacoustic, although sound diffusion is not through a loudspeaker. Three areas of innovation are discussed: (i) purely mechanical instruments; (ii) electromechanical and electroacoustic hybrids; and (iii) instruments designed for alternative tuning systems. All the orchestral families are considered. The mutually reinforcing possibilities and limitations of these elements, together with the evolving aesthetic issues of contemporary and other musics, suggests the importance of specific areas of future research and instrument making. Amongst these is the necessity of interdisciplinary perspectives and collaboration.
Prediction of vehicle passenger compartment noise due to turbulent flow excitation
Authors: Wu Sean , Wu Guoming
Published: February 2014

An engineering computer model is developed for estimating noise transmission into a vehicle passenger compartment, given the characteristic dimensions of the vehicle and turbulent flow excitation. In this model, the effects of window offset and leakage, and those of power spectral densities due to separated and reattached flows are taken into account. Empirical formulations are developed to estimate the reattachment line and the power spectral densities of separated and attached flows. The effect of leakage is accounted for by a correction factor. The computer model thus developed is validated on a greenhouse vehicle model. Experiments are conducted in a wind tunnel at the Chrysler Technology Center. Pressure fluctuations due to separated and attached flows on the side window are measured and compared with the calculated values. These pressure fluctuations are taken as input to a computer program, called VibroAcoustic Payload Environment Prediction System based on Statistical Energy Analysis, to calculate the noise spectrum, given the A-pillar angle, window size and offset, vehicle yaw angle, and wind speed. The predicted noise spectra inside the passenger compartment are compared with the measured ones under various flow speeds. Satisfactory agreements are obtained in all cases. [Work supported by a Chrysler Challenge Fund.]
Effects of brake pressure and temperature on squeal noise
Authors: Balvedi Alessandro Mattiuzi , Nashif Ahid
Published: February 2014

Brake squeal noise has been an important issue for the automotive industry. This phenomenon is related to the modal coupling of the rotor and the pads of a brake system. When a mode of the pad matches with a mode of the rotor, the system becomes unstable. The consequence is the generation of additional vibration energy that cannot be dissipated by the system. In this manner, a solution is to improve the damping capacity of the brake system. This is accomplished by use of metal and viscoelastic materials laminates, where some of the vibrational energy is dissipated by shearing or extending the viscoelastic layer. Since the dynamic behavior of brake systems is a function of frequency, temperature, and brake pressure (friction force), it is of utmost importance to verify the influence of such parameters in order to design and select a proper multilayer treatment. This work presents a procedure to verify the influence of these parameters in the coupling of rotor and pads modes. Different conditions of pressure and temperature are applied on a brake system and the dynamic of the system related to squeal noise is evaluated.
Burst mode dither control of automotive brake squeal
Authors: Dzirasa Mawuli , Cunefare Kenneth A. , Rastelli Victor , Montbrun Nila
Published: February 2014

Brake squeal is an annoying phenomenon, generally occurring when vehicles brake at slow speeds. Significant effort is expended by the automotive industry to avoid squeal during the development of brake systems. Nonetheless, expensive warranty claims still occur when such efforts are not completely successful. Recent research demonstrated that introducing dither control into a brake is an effective means of suppressing squeal. Dither control is a method by which high-frequency disturbances are introduced into a system. This suppresses the friction induced squeal response at lower frequencies, thus eliminating the audible brake squeal. Dither control, when applied at a 100% duty cycle, is an effective means of suppressing brake squeal. This presentation focuses on the potential to use burst mode dither control for squeal suppression. Burst mode dither control is characterized by duty cycles of less than 100%. Dither is introduced to a brake by placing a piezoelectric stack actuator in the piston of a floating caliper brake. The piezoelectric stack actuator is driven by a 20-kHz burst mode signal, and the impact upon the signal is assessed. Burst mode dither with duty cycles as low as 50% are shown to be as effective in suppressing brake squeal as dithering at a 100% duty cycle.
Visualizing acoustic field inside a passenger vehicle compartment
Authors: Manmohan Moondra , Wu Sean
Published: February 2014

The objective of this study is to examine the effectiveness of the HELS method [S. F. Wu and J. Yu, J. Acoust. Am. 104, 2054–2060 (1998); S. F. Wu, ibid. 107, 2511–2522 (2000)] in visualizing the areas that are prone to noise transmission into a full-size vehicle passenger compartment due to engine, powertrain system, tires, and wind excitations. The input to the HELS formulation is the acoustic pressure measured inside the compartment. No vehicle geometry and dimensions are necessary. The optimum number of expansion functions is determined by minimizing the sum of the squared errors with respect to the measured data. Once the HELS formulation is established, the acoustic pressure anywhere including the vehicle interior surface can be determined. The normal component of the surface velocity can be reconstructed in a similar manner. Once these quantities are specified, the normal component of the time-averaged acoustic intensity and acoustic energy flow inside a vehicle passenger compartment can be visualized. This three-dimensional acoustic image can provide valuable insight into vehicle interior noise reduction. The effects of number and locations of measurements on the accuracy of reconstruction are investigated. [Work supported by the Daimler-Chryster Challenge Fund.]
Modeling acousto-gravity waves in the atmosphere of Jupiter
Authors: Lingevitch Joseph F. , Collins Michael D. , Stamoulis Catherine
Published: February 2014

The modeling of wave propagation in the atmosphere of Jupiter became a topic of great interest after the discovery of the fragments of Comet Shoemaker-Levy 9. Circular fronts were observed expanding from several of the impact sites [Hammel et al., Science 267, 1288–1296 (1995)], but the nature of these features has not yet been explained in terms of a wave model. This is due in part to a lack of data, which has been enhanced by direct measurements from the Galileo probe [Seiff et al., J. Geophys. Res. 103, 22857–22889 (1998); Atkinson et al., ibid. 103, 22911–22928 (1998)]. There have also been some recent improvements in propagation modeling using parabolic equation techniques, which can handle acousto-gravity waves [Lingevitch et al., J. Acoust. Soc. Am. 105, 3049–3056 (1999)] and the advective effects of winds [Collins et al., J. Acoust. Soc. Am. 97, 2147–2158 (1995)]. These techniques and their application using Galileo data will be presented. [Work supported by ONR.]
Temporary threshold shift in ABRs and DPOAEs following noise exposure in Long–Evans rats
Authors: Murphy William J. , van Campen Luann E.
Published: February 2014

In conjunction with a study of reactive oxygen species induced damage in Long–Evans rats [van Campen et al., ARO abstracts (2001)], the progressions of temporary shifts in auditory brainstem response thresholds and distortion product otoacoustic emission input/output functions were analyzed. Thirty-five rats were exposed to 2 h of 120-dB SPL band-limited noise (7.5–15 kHz). ABR and DPOAE measurements were collected at 1-, 3-, 8-, 72-, and 672-h post-exposure for seven rats per condition. One sham-exposed rat was included in each exposure group. Thresholds for ABR elicited by tone bursts (2, 4, 8, 16, 32 kHz) exhibited the greatest threshold shifts for the 8-, 16- and 32-kHz stimuli. Recovery following noise exposure was greatest for the 72-h group with a lesser recovery for the 672-h group. The DPOAE thresholds (level of the f2 primary stimulus where LDPOAE was 5 dB above the noise floor) exhibited no significant difference for the 72- and 672-h groups. However, the input/output functions for the 72 group exhibited more DPOAE energy than the 672-h group.
Measurement and interpretation of stimulus frequency otoacoustic emissions: Input/output functions and transient analyses
Authors: Keefe Douglas H. , Schairer Kim S. , Zhao Fei , Simmons Jeffrey L.
Published: February 2014

A stimulus frequency otoacoustic emission (SFOAE) is a cochlear-based signal measured in the ear canal in response to sine-tone stimulation. SFOAE responses are potentially related to other auditory-system responses to sine-tone stimulation, e.g., basilar membrane input/output (I/O) functions, and behavioral studies of nonlinearity. In preliminary experiments, system distortion has been measured in an ear simulator using SFOAE and DPOAE paradigms, and different probes. SFOAE I/O functions have been measured in subjects using the double-evoked method [D. H. Keefe, J. Acoust. Soc. Am. 103, 3489–3498 (1998)] in two approaches: equal-level stimuli in each loudspeaker, or a fixed high level in one loudspeaker and varying level in the other. The latter approach is particularly helpful, because it controls for mutual suppression effects in SFOAE responses. Based on the use of transient-gated stimuli, time-frequency representations of the OAE responses enable measurement of cochlear delays and detection of possible multiple internal reflections. Results will be described in terms of the reflection emission theory of OAEs [Zweig and Shera, J. Acoust. Soc. Am. 98, 2018–2047 (1995)] extrapolated to moderate stimulus levels, in which SFOAE nonlinearities are directly related to basilar-membrane nonlinearities. [Work supported by NIH (R01 DC003784, T32 DC00013).]
Transient otoacoustic emissions and frequency selectivity
Authors: Hazelbaker Julie , Feth Lawrence
Published: February 2014

The relationship between transient evoked otoacoustic emissions (TEOAE) and frequency selectivity in the auditory system was examined. Three subjects with normal hearing sensitivity and TEOAE spectra with prominent peaks and valleys participated. Psychophysical tuning curves were measured at two pairs of frequencies: one where a robust emission occurs, and the other for an emission with a signal-to-noise ratio at least 6 dB SPL lower than the first. A forward masking paradigm with a 2AFC, 3 up – 1 down adaptive procedure was used to construct three point tuning curves. Quiet threshold for a given probe frequency was established first. The tip of the tuning curve was then obtained by determining the masker level for P(C)=79.1 with a probe at 10 dB SL. Finally, the Q—10 frequencies were acquired by adapting the frequency of the masker, which was set 10 dB above the tuning curve tip [Spetner and Olsho, 1990]. Preliminary results indicate that the Q—10 values for the tuning curves from the TEOAE peak frequencies are consistently greater than those of the tuning curves from valley frequencies. These results suggest that a relationship exists between frequency selectivity in the auditory system and the relative minima and maxima of TEOAE patterns. [Research supported by a grant from The Ohio State University College of Social and Behavioral Science.]
Stimulation rate influences frequency tuning characteristics of inferior colliculus neurons
Authors: Smalling Jeremy , Galazyuk Alexander , Feng Albert
Published: February 2014

Sounds in real world environments such as animal calls and human speech are complex and often occur in rapid succession. In light of this, it is important to gain an understanding of how the rate of acoustic stimulation influences the units’ basic response properties. Previous studies of frequency tuning were generally based on investigating neuronal responses to tonal stimuli presented in isolation, and the results derived therefrom were assumed to accurately portray the cell’s response range. However, the firing history of an auditory neuron has been shown to shape its response to subsequent sounds. The goal of the present study was to investigate the frequency tuning characteristics of neurons in the inferior colliculus (IC) of the little brown bat to tone pulses presented at various rates. Eighty-five percent of the IC neurons studied showed rate-dependent changes in their frequency selectivity. Half of these neurons exhibited narrowing of their frequency response range at higher rates. These results indicate that the response properties of central auditory neurons at low stimulation rates do not necessarily reflect the units’ response properties to sounds presented at high and behaviorally relevant rates. The possible cellular mechanisms and behavioral importance of this effect are discussed.
Noninvasive recording of fetal auditory evoked responses using a new 151 channel sensor array (SARA)
Authors: Eswaran Hari , Wilson James , Preissl Hubert , Murphy Pamela , Lowery Curtis
Published: February 2014

The goal was to successfully record fetal auditory evoked responses (AERs) using the newly developed noninvasive fetal magnetoencephalographic (MEG) system called SARA. 131 AER measurements were performed on 31 fetuses starting at 27 weeks. The SARA system, equipped with an array of 151 SQUID (superconducting quantum interference device) sensors spread over an area of 1300 cm2, is curved to fit the shape of the pregnant abdomen. The auditory stimulus was—1 kHz tone; duration—100 ms; rate—0.5 tones/s.; intensity (external)—100-dB SPL in air. The data were collected at a sampling rate of 312.5 Hz. The AERs were averaged over a period of 700-ms window after removing interfering maternal and fetal heart signals. Control recordings were performed on the same fetus with the same parameters but without any sound stimulation. The peak of the evoked responses was around 250 ms with amplitudes of about 20 fT. No evident evoked response was seen in the control recordings on the same fetus. In summary, it is feasible to noninvasively acquire MEG auditory evoked responses from the fetus using SARA. AER can be a useful tool for the neurological assessment of fetal well-being throughout gestation. [Work funded by NIH.]
A coincidence-detection model for level discrimination of tones in roving-level noise
Authors: Zhang Xuedong , H. Carney Laurel
Published: February 2014

This study describes a monaural cross-frequency coincidence-detection mechanism to model level discrimination performance for a tone in the presence of noise in a roving-level paradigm. Model coincidence detectors receive population input from model auditory-nerve (AN) fibers from the same ear with different characteristic frequencies (CFs). The response of each model coincidence detector is sensitive to both the rate and the phase of its AN fiber inputs. A set of model coincidence detectors was constructed that received input from a population of model AN fibers. To detect intensity increments of tones in wideband noise, the most sensitive coincidence detector was one that received the inputs from two AN fibers with tone responses that were opposite in phase (phase opponency); this mechanism was robust in the presence of roving-level maskers. For narrow-band noise, detectors that were sensitive to changes in rate also contributed information to the detection task; this rate-based mechanism was affected by a roving-level paradigm. The difference in the effect of the rove on model performance with different masker bandwidths was similar to that observed for human subjects [Kidd et al., J. Acoust. Soc. Am. 86, 1310 (1989)].
Effect of reverberation on the masking of narrow-band signals
Authors: Freyman Richard , Balakrishnan Uma , Zurek Patrick
Published: February 2014

This study explores the factors that influence the masking of narrow-band signals in reverberant sound fields. Rectangular rooms were simulated using the image method with a rigid sphere modeling the head. The signals were third-octave noise bands presented in a continuous broadband noise masker. For a given room simulation, the signals and masker were convolved with impulse responses obtained in the room at multiple azimuth angles and distances, for subsequent presentation via headphones. Adaptive forced-choice procedures were used with the resulting signals to find monaural and binaural thresholds in listeners with normal hearing. The benefit of separating the masker and signal spatially in the simulation was reduced by reverberation, as expected, although the effects were complex. Among the predictions confirmed by these experiments is that reverberation actually improves thresholds when the masker is closer to the listener than the signal, apparently due to both an increase in monaural signal power a decrease in interaural signal correlation. With masked thresholds obtained over the frequency range of the articulation index, the results of these experiments will allow quantitative predictions of speech intelligibility as a function of room charcteristics and speech and noise source locations. [Work supported by NIH.]
Interaction of Lamb wave with a welded rib
Authors: Morvan Bruno , Duclos Jean , Duflo Hugues , Tinel Alain
Published: February 2014

This work deals with Lamb wave conversion on a rib stiffened plate. Some previous work has studied the scattering of plane waves at a T junction at low frequency (FE<200 kHzmm) for which the wavelengths are higher than the plate thickness. In this study, the conversion phenomenon is investigated in the case of an A1 incident Lamb wave (FE=4 MHzmm). The experimentation is done with a stainless steel T structure, and the plate and rib are 2 mm thick. The normal surface displacement is related theoretically to the power flow. Then, the energy of the converted waves is obtained from measurement of the plate normal displacements by means of a laser interferometer. Next, we compute a finite-element simulation on two various meshes: the plates are connected perpendicular to each other either with or without a weld. The comparison between experimental and numerical methods shows the importance of the weld shape on the wave transmission to the rib. The weld funnels the incident wave and improves the energy transmission on the rib. Moreover, the experimental and MEF results are in a good agreement.
Improvement of the solution convergence rate for an elastic shell driven by a vibratory constraint using analytical-numerical matching
Authors: Park Christopher , Franzoni Linda , Bliss Donald
Published: February 2014

A three-dimensional elastic shell is driven by the motion of an attached support and the solution is constructed using the method of analytical-numerical matching (ANM) with finite-element analysis and the structural-acoustic scattering code sonax. First, the area around the structural constraint is resolved in great detail as a separate local three-dimensional FEA solid model. Second, a Love–Timoshenko shell-type model of the local region is solved analytically for a set of smooth forces that will be applied to the full three-dimensional shell in place of the constraint. Third, the model of a full three-dimensional shell with end caps is analyzed in sonax, with the smooth forces applied on a mode-by-mode basis. The complete solution to the original problem is the superposition of the solutions of each of the subproblems described. Note that the high modal content of the original problem is contained in the high-resolution separate local problem (small domain), leaving only low modal content in the global (large domain) problem that is solved using sonax. This sample problem demonstrates the ability of ANM to enhance the capabilities of sonax and to improve the convergence rate (and overall computation time) for problems of this type. [Work sponsored by ONR.]
Circumferential-wave phase velocities for empty, fluid-immersed spherical metal shells
Authors: Überall Herbert , Ahyi A. Claude , Raju P. K. , Bjo/rno/ I. K. , Bjo/rno/ L.
Published: February 2014

Our earlier studies regarding acoustic scattering resonances and the dispersive phase velocities of the surface waves that generate them, have demonstrated the effectiveness of obtaining phase velocity dispersion curves from the known acoustic resonance frequencies, and their accuracy. This possibility is offered by the picture of phase matching after each complete circumnavigation of these waves, which leads to close agreement of resonance results with those calculated from 3-D-elasticity theory whenever the latter are available. The present investigation is based on the mentioned resonance frequency/elasticity-theory connection, and we obtain comparative dispersion-curve results for water-loaded, evacuated spherical shells of various metals. In particular, the characteristic upturn of the dispersion curves of low-order shell-borne circumferential waves (A or A0 waves) which takes place on spherical shells when the frequency tends towards low values, is demonstrated here for all the metals under consideration.
Scattering and radiation from a fluid-loaded coated cylindrical shell
Authors: Cuschieri J. M. , Treffot C.
Published: February 2014

A common question when dealing with fluid-loaded coated structures is how well a normally reacting coating layer models the radiation and scattering from a fluid-loaded coated cylindrical. Modeling with a normally reacting layer simplifies the model which therefore allows more complex conditions to be analyzed. To explore this question analytic solutions are obtained for the scattering from a fluid-loaded cylindrical shell with a compliant coating using both multilayer shell theory [L. Flax and W. G. Neubauer, J. Acoust. Soc. Am. 61, 307 (1977)], and a normally reacting coating solution [J. M. Cuschieri and D. Feit, J. Acoust. Soc. Am. 107, 3196 (2000)]. The similarities and differences in the scattering results that are obtained using either of these two approaches are presented for different coating thicknesses and characteristics.
Large coated plates under random excitation: Spatial-domain insights into radiation efficiency
Authors: Martinez R. , Garrelick J. M.
Published: February 2014

A formal spatial-domain analysis of a large plate’s cross-spectral response to TBL-like excitations yields the following two results, unified and in closed form: (1) a part that contains a moderate area effect (from the acoustic field’s point of view, despite the plate being below coincidence by choice) and a stronger edge effect; and (2) a second part with a weak edge effect and a potentially strong area effect. The strong-edge/moderate-area part contains as coefficient the inverse of the plate’s effective loss factor. The strong-area part does not, enabling it to dominate the former with rising frequency particularly over that range in the frequency spectrum encompassing the typically broad (lossy) thickness resonances of the plate’s coating. Use of this unified cross-spectral response function to compute the plate’s acoustic field confirms the expected rise in radiation efficiency at higher loss factors and frequencies, as brought about by the relative growth of the strong-area effect under both of those conditions. [Work supported by NSWC/Carderock Division.]
Eigenfrequencies of fluid waves entrained in elastic shells
Authors: Uberall H. , Werby M. F.
Published: February 2014

Acoustic signals that scatter from an elastic shell may excite elastic shell resonances. If the shell is evacuated then these as well as the pseudo-Stoneley resonances are the only ones allowed. However, if there is a fluid inside then the eigenfrequencies of the enclosed fluid may be excited. Further, the presence of the fluid may alter the elastic body resonances. When the impedance of the enclosed fluid is not much smaller than the mechanical impedance of the elastic material then the scattered signal is greatly influenced by the enclosed fluid, but only at the allowed eigenfrequencies. Since the fluid is enclosed this leads to a discrete spectrum and an eigenvalue problem which is quite manageable. In this work we outline a method for determining the eigenfrequencies as well as their nature and use their values to isolate the actual body resonances due to the elastic material. We also illustrate the influence of the presence of the enclosed fluid on the elastic resonance frequencies.
Bayesian estimation framework for source separation with mixture densities
Authors: Mohammad-Djafari Ali , Snoussi Hichem
Published: February 2014

One of the main signal processing problems in acoustics applications is the sources separation. This problem is inherently an ill-posed problem. The Bayesian inference framework is a coherent way to solve such problems by modeling sources and canals and by combining prior information coming from these probabilistic modeling and information included in the data. In this contribution, after a brief presentation of general source separation problems and the Bayesian inference framework, we present new algorithms to source separation for the case of noisy instantaneous linear mixture, within the Bayesian estimation framework. The prior source distribution is modeled by a mixture of Gaussians and the mixing matrix elements distributions by a Gaussian. We model the mixture of Gaussians hierarchically by means of hidden variables representing the labels of the mixture. Then, we consider the joint a posteriori distribution of sources, mixing matrix elements, labels of the mixture, and other parameters of the mixture with appropriate prior probability laws to eliminate degeneracy of the likelihood function of variance parameters and we propose iterative algorithms to estimate jointly sources, mixing matrix, and hyperparameters: Joint MAP (maximum a posteriori) algorithms.
Does semiclassical ray theory work for megameter propagation?
Authors: Henyey Frank S.
Published: February 2014

In the presence of internal waves, a very large number of rays connect any source to a distant receiver. The ray intensities vary by orders of magnitude, causing the scintillation index predicted by semiclassical ray theory to be very large. In this talk, possible diffractive effects at frequencies at or below 100 Hz are considered. One effect is caustics. A region where Airy functions must be used can be identified; if this region contains additional caustics, Airy functions do not suffice. This caustic region is identified and characterized from numerical ray-tracing simulations. The rays that are high intensity occur in narrow beams. The diffraction of these beams is estimated from the same numerical simulations. [Work supported by ONR.]
Computer modeling and prediction in the design of coupled volumes for a 1000-seat concert hall at Goshen College, Indiana
Authors: Harrison Byron W. , Madaras Gary , Celmer Robert D.
Published: February 2014

The effects of specific architectural parameters (volume, shape, location, aperture size, and location) on the acoustic characteristics of variable-acoustic coupled volumes were analyzed using the computer modeling application, CATT-Acoustic. The purpose of the study was to optimize design and determine the effectiveness of coupled volumes for use in the Goshen College Concert Hall, Goshen, Indiana. The computer modeling technique allowed specific variables to be isolated and parameters to be analyzed. Prototype models were evaluated by a visual inspection of decay curves, comparisons of T15, T30, and T60, and auralizations. The goal was to preserve the early decay rate of the main hall while achieving a slower decay rate after 750 ms. The analysis confirmed the use of computer modeling and prediction in studying the acoustic performance of coupled volume designs. Chamber volumes were found to be the most influential factor in realizing the double-sloped decay. Shape, location, and aperture configuration had noticeable, but lesser, effects on acoustic performance than did chamber volume. To realize efficient acoustic variability for the small-volume hall researched, the chambers required volumes that compared to large percentages of the main enclosure volume (50–75 percent).
Applications of physical and mathematical modeling in concert hall design
Authors: Calamia Paul , Larson Martha
Published: February 2014

A variety of testing methods were employed throughout the early and mid stages of design for an eighteen-hundred-seat flexible-use concert hall. Full-scale laboratory testing, model-scale measurements, and mathematical modeling were undertaken to provide guidance on particular design decisions. Mathematical techniques were used to guide the full-scale laboratory testing, and full-scale testing results were applied in the model-scale measurements. Auralization techniques were implemented to study specific effects.
Spatial and temporal variation of sperm whale (Physeter macrocephalus) codas in the northern Gulf of Mexico
Authors: Apple Trent C.
Published: February 2014

Sperm whale (Physeter macrocephalus) codas, short rhythmic patterns of clicks, were recorded annually from a towed linear array throughout the northern Gulf of Mexico during 2-week cruises spanning October 1991–August 1997. Codas were sampled and classified according to their temporal pattern and the number of clicks they contained. Regular codas, with equally spaced intervals between clicks, were analyzed along with irregular codas, with double intervals between the last two clicks. In this sample, short codas (less than five clicks) were more common than long codas (greater than six clicks). Preliminary analysis (n=11), using Student’s t-test, suggests that irregular codas may not vary in the northern Gulf of Mexico. When comparing interclick intervals, irregular coda types did not differ significantly across multiple years, and no spatial variation was observed. This pattern of similarity in coda types, if upheld with additional analyses, may suggest that coda repertoires remain stable over periods of years or that a resident population of animals may inhabit this area. Further analysis, however, is required to substantiate this supposition. [Work supported by Texas A&M University at Galveston.]
An ‘‘acoustic niche’’ for Antarctic killer whale and leopard seal sounds
Authors: Mossbridge Julia A. , Thomas Jeanette A.
Published: February 2014

It is not known whether species that share the same acoustic environment develop an ‘‘acoustic niche’’ to reduce competition. To address this issue, spectrograms were used to analyze underwater killer whale (Orcinus orca) and leopard seal (Hydrurga leptonyx) sounds from recordings made in December and January 1977/1978 in Antarctica. Forty-seven leopard seal sounds were found in December recordings; no leopard seal sounds were found in January recordings. FM points were defined as the frequency within a sound at which a detectable change in the frequency slope occurred. The FM-point distribution for December killer whale sounds showed a gap between 2500 and 3750 Hz, which is near the frequency range of the most common leopard seal sound (2777–3802 Hz). No gap was found in January’s FM-point distribution. The FM-point distributions differed significantly between months, while the number of FM points per sound and the duration of killer whale sounds did not differ between months. December killer whale sounds did contain frequencies between 2500 and 3750 Hz, but frequency modulations were uncommon in this frequency range. It seems that killer whales may have used frequency modulation to adapt their acoustic niche when leopard seal sounds were present. [Work supported by NSF.]
Analysis of surface vocalizations from mother and pup Weddell seals (Leptonychotes weddellii)
Authors: Noe Beth A. , Thomas Jeanette
Published: February 2014

The antarctic Weddell seal (Leptonychotes weddellii) is a vociferous species with an extensive underwater repertoire, but little is documented about their airborne sounds. Weddell seals return to traditional pupping colonies, are approached easily, and recordings of individual seals are available from a tagging study conducted since the early 1970’s. Therefore, this study on airborne vocalizations of Weddell seal mothers and their pups provides a unique opportunity for detailed analysis of calls. During 1976, 1977, 1979, and 1996, surface vocalizations of mother and pup Weddell seals were recorded. Analysis variables included beginning, ending, maximum, and minimum frequency, fundamental harmonic interval, components per call, intercall interval, and duration. This study determined that surface calls of Weddell seal pups changed as the pup grew older. Although pups within an age bracket showed little variability in call structure, adult vocalizations varied among individuals. Relatedness of mothers and pups could not be concluded solely by the call variables examined. Further studies need to be conducted to determine the extent of the change that pup vocalizations undergo as they mature and to identify the acoustic variables influencing mother/pup vocalizations. [Acknowledgments: Dr. Jeanette Thomas, Dr. Douglas Quin, Bart Jones.]
Blue whale calling off the Western Australian coast
Authors: McCauley Robert D. , Jenner Curt , Bannister John L. , Cato Douglas H.
Published: February 2014

Throughout 2000, aerial surveys, boat-based studies and acoustical censusing was carried out to search for blue whales in the Rottnest trench, west of Perth. Historical records indicated a Western Australian population of blue whales, while a preliminary boat survey in 1994 suggested a Rottnest trench aggregation. This was confirmed in 2000, with 17 blue whales sighted. Of 5000 acoustic records almost all contained blue whale calling, some having up to nine distinct callers. Although of a different format, the calls had a similar character to those described from other populations. A call was composed of three signals, each respectively 44–45 s, 20–23 s and 20–25 s in length, separated by 5–10 s and 23 s with the sequence repeated every 78 s. Each component was dominated by constant or slowly up-sweeping amplitude-modulated tones over 18–26 Hz, with harmonics evident up to 100 Hz and a secondary pulsed source of frequency 65–66 Hz present. Components had different source levels. Several other baleen whale calls were also common. The low frequency (<100 Hz) sea noise spectra made over 33.5 days off Rottnest was dominated by whale calling.
An improved contour extractor for bottlenose dolphin whistles
Authors: Suzuki Ryuji , Buck John R.
Published: February 2014

The time-frequency contours of bottlenose dolphin (Tursiops truncatus) whistles are commonly extracted features for the classification and comparison of these signals. We have previously developed a method to extract the whistles’ fundamental frequency contours [J. Acoust. Soc. Am. 108, 2635 (2000)] by sequentially tracking the contour. These contours are often extracted from recorded rather than real-time signals, which allows us to read ahead or access the ‘‘future’’ signal. This talk extends our previous work to propose a technique to estimate the fundamental frequency at each time from the ‘‘future’’ values of the recorded signal in addition to the past and present signals. This technique is similar to the Kalman smoother except that the states are probability densities, and it uses a probabilistic state transition model with a Bayesian projection to produce the maximum a posteriori probability estimate of the frequency contour based on all recorded data, not just the present and past signal. Experimental evaluation indicates that this method greatly improves the reliability of contour extraction from noisy signals, with considerable resistance to strong harmonics, some dropouts and echolocation clicks, when compared to our previous technique. A huge improvement is achieved from the technique proposed by Buck and Tyack [J. Acoust. Soc. Am. 94, 2497–2506 (1993)].
WARBLE: A high resolution approach to subbottom geoacoustic inversion
Authors: Holland Charles W. , Osler John
Published: February 2014

Subbottom geoacoustic information supports a broad range of activities serving military, scientific, and commercial needs. Since direct sampling (i.e., coring) of the seabed is costly and time-consuming, numerous acoustic inverse methods have been developed. One of the most serious weaknesses, which is suffered by all the inversion methods, is a uniqueness problem, wherein multiple solutions fit the data equally well. An associated problem is that some methods have no means to determine the number of sediment layers in the solution space. Our WARBLE (wide-angle reflection and bottom loss experiment) method addresses these problems by conducting the inversion in both the space-time and the space-frequency domains in order to maximize the amount of independent data. The space-time data provide the number of important layers as well as the layer thicknesses, and interval sound speeds. The space-frequency domain data provide sound velocity, density, and attenuation for each layer. High-resolution results can be obtained with this method, resulting in layer thickness of order several tens of centimeters. Penetration depends upon sediment type and water depth but is typically 50–150 m. The inversion method will be illustrated with several shallow-water measurement/inversion results, including comparisons with core data.
Techniques for estimating sediment properties from chirp sonar data
Authors: Schock Steven G.
Published: February 2014

The chirp sonar is a towed wideband FM reflection profiler developed to collect normal incidence reflection data suitable for sediment property inversions; the sonar also generates detailed reflection profiles of the seabed. The chirp sonar system transmits FM pulses with high time-bandwidth products to attain high pulse energy; consequently, the acoustic data have a high signal-to-ambient-noise ratio after correlation processing. The vertical resolution of the images is about 1 cm when transducer bandwidth is approximately 40 kHz. Data processing methods have been developed to automatically map the locations of sediment layer interfaces, and to estimate compressional wave attenuation, acoustic impedance, and compressional wave velocity of sediment layers using normal incidence FM reflection data. The height of sand ripples and the phase dispersion of compressional waves can also be measured from the acoustic imagery. Field data collected by other investigators during the High Frequency Acoustics DRI experiments off Fort Walton Beach were used to verify the acoustic property estimates. Comparisons show that chirp sonar estimates of acoustic properties agree with direct measurements of the properties based on in situ acoustic probe data and sediment core data collected by investigators from Naval Research Laboratory, Stennis Space Center, and APL, Washington State.
Seismo-acoustic inversion using artificial neural networks optimized with a genetic algorithm—direct inversion
Authors: Ruppel Timothy
Published: February 2014

Traditional inversion methods search the parameter space for a minimum in the difference between the observed acoustic field and that predicted by a forward acoustic model. While this method is well established and has exhibited excellent results, it requires that many time-consuming forward model runs be performed for each prediction. This paper will describe an inversion technique (direct inversion) which uses genetic algorithms to train a neural network before any observations are made. In essence, an inverse acoustic model is generated whose inputs are the acoustic field values and whose outputs are the environmental parameters of interest. This allows for rapid inversion calculations at the time of observation if sufficient time has been allowed for training. Some results inverting simulated and experimental acoustic signals will be given. [Work supported by ONR.]