bluuebunny/crossref_metadata_2025 huggingface dataset:
Inversion for material, geometrical, positional, and radial speed parameters of a spherical target in a waveguide.
Authors: Fawcett John A.
Published: October 2009

In this paper, a moving spherical target in a Pekeris waveguide is considered. The classification of a target from its free space echo has been previously studied by many authors. In a waveguide, the received echo results from the coherent interference of the various multipaths incident upon and scattered from the target. When the position of the target in the waveguide is imprecisely known, the echo classification problem is more difficult. In addition, if the target is moving with an unknown radial speed, this further complicates the problem. In this paper, we consider a single omnidirectional transmitter and a single receiver and investigate the estimation of the material, geometrical, positional, and dynamical parameters of the sphere from the received echo. We use a simple simulated annealing approach to investigate the parameter estimation. We also consider various two-dimensional cost-function surfaces to illustrate the uncertainties in the parameter values.
Backscattering and synthetic aperature sonar imaging of partially exposed acoustically penetrable polymer cylinders.
Authors: Marston Timothy M. , Marston Philip L.
Published: October 2009

The scattering by a partially exposed circular cylinder parallel to a flat surface can have a complicated dependence on the amount of exposure h and the grazing angle. Even in the case of high-frequency scattering by a rigid cylinder, geometric analysis must be extended to eliminate abrupt jumps caused by transitions in the number of rays [K. Baik and P. L. Marston, IEEE J. Ocean. Eng. 33, 386–396 (2008)]. The present investigation concerns transitions in the ray contributions as a function of h for the more complicated case of a penetrable plastic cylinder lowered through a free surface. In this case it is helpful to observe the impulse response as a function of h and the time t. The slopes of trajectories in the (t, h) plane are useful for classifying the scattering mechanisms and the number of reflections from the adjacent flat interface. Some mechanisms (including transmission and refraction through the cylinder) fade with a decreasing h due to a loss of aperture. The evolution of SAS images can also be explained in this way. The investigation is also important for understanding backscattering by cylinders partially covered by sediment. [Work supported by ONR.]
Enhanced coupling to target modes from vertical acoustic pressure gradients caused by proximity to an interface and grazing incidence.
Authors: Espana Aubrey L. , La Follett Jon R. , Marston Timothy M. , Marston Philip L.
Published: October 2009

In prior research, it was demonstrated that for end-on illumination of a small horizontal aluminum cylinder, an elastic mode was preferentially excited with evanescent wave illumination in comparison to the case of a propagating wave [Espana et al., J. Acoust. Soc. Am. 125, 2732 (2009)]. A free-field finite element method simulation revealed that associated with this mode there was a rocking motion at the end of the cylinder. The evanescent wave coupled strongly because of its transverse dependence (along the vertical coordinate) on the excitation. Another way to generate transversely dependent excitation is to place the cylinder parallel to a flat reflecting surface and illuminate it with a propagating wave at grazing incidence. This enhancement of the coupling was demonstrated by placing the cylinder adjacent to a free surface and monitoring the end-on backscattering as a function of the position relative to the interface. The coupling to this mode depends on how the horizontal cylinder is positioned vertically. The response of this mode is also enhanced with the cylinder’s axis below the surface near a pressure minimum of the approximately horizontal Lloyd mirror pattern. [Research supported by ONR.]
Acoustic beams with modulated helicity and a simple helicity-selective acoustic reciever.
Authors: Marston Timothy M. , Marston Philip L.
Published: October 2009

Acoustic helicoidal beams have an azimuthal phase gradient and an axial null in amplitude. The sign and magnitude of the azimuthal phase gradient determine the helicity and topological charge of the beam. Beams with a unit-magnitude topological charge have been generated with a four-quadrant sectored array, adjacent quadrants being driven with a 90 deg phase offset [B. T. Hefner and P. L. Marston, J. Acoust. Soc. Am. 106, 3313–3316 (1999)]. The scattering by symmetric targets placed on the axis of such beams preserves the helicity and the axial null [P. L. Marston, J. Acoust. Soc. Am. 124, 2905–2910 (2008); F. G. Mitri, Ann. Phys. 323, 2840–2850 (2008)]. The present work shows how to rapidly alter (or modulate) the helicity with an appropriately timed reversal of the excitation of a single pair of opposite quadrants. A simple four-element helicity-selective detector (using appropriately offset elements) was also demonstrated. These beams may be useful for digital acoustic communication and they have a modulated axial angular momentum flux. They should also generate a modulated acoustic torque on targets. [Work partially supported by ONR.]
Propagation of low-frequency guided waves in three-dimensional submerged heterogeneous pipes.
Authors: Bingham Jill P. , Calvo David C.
Published: October 2009

We numerically investigate the propagation of low-frequency guided waves in a fluid-filled elastic pipe submerged in a liquid. In a vacuum, axisymmetric modes travel through the pipe wall. When filled with a fluid of low sound speed, the pipe system can develop modes that are mainly supported by the interior fluid. As mode cut-offs are approached, an increasing amount of energy penetrates the surrounding fluid. In order to determine these cut-off frequencies, we have numerically obtained dispersion curves for the guided pipe modes from the characteristic equations for thick- or thin-walled layered systems in cylindrical coordinates. As a complement to the separation of variable method, we also compute group speed curves from the propagation of interior source pulses through the medium using the time-domain elastodynamic finite-integration technique (EFIT). A time-frequency analysis of the received signals at select probe locations reveals the group speed structure. We also compute the stability of the modes in the presence of heterogeneous contents such as gas or solid particulates using direct simulation with the EFIT code. Finally, we consider propagation through three-dimensional structures such as valves.
A new mixed optimization algorithm for array pattern synthesis.
Authors: Yingmin Wang , Hua Qi , Yanli Yu
Published: October 2009

A numerical pattern synthesis algorithm based on adaptive notched noise and genetic optimization procedure is presented. For a given array, this technique allows one to attain a set of weight coefficients that shape the array with designed main beam in given directions and lower sidelobes. The algorithm may search for optimization attainable patterns for the specific elements if the desired pattern cannot be found. The new algorithm combines adaptive array principle with genetic technique and a mixed two-step optimization approach is formulated. The first step is based on adaptive theory and the elements of the given array are supposed as the elements of an adaptive array. The desired direction of the main beam is chosen to be the steering direction and sidelobes are controlled by assigning a number of interfering noise throughout the so-called sidelobe area. An initial weight coefficient or pattern is obtained after several iterations. Then an energy function based on the difference between desired pattern and the initial pattern is introduced. A simple genetic algorithm is used to minimize the energy function. The effectiveness of the algorithm is demonstrated on an example of a double-circular array.
Predicting acoustic performance in reconfigurable classrooms.
Authors: Roy Kenneth P. , Good Kenneth W.
Published: October 2009

Both laboratory component tests and field system evaluations were conducted to screen architectural designs relative to sound quality performance within a classroom, and noise intrusion between classrooms. Recognized standards such as ANSI S12.60 for Acoustics in Schools and other rating systems such as LEED for Schools and CHPS provide guidance on performance/design needs for K-12 schools. But what about postsecondary schools and especially those designed with reconfigurable architectural elements such as relocatable walls and raised floor system—can these be made to work? Initial results from this ongoing research will be discussed, including wall performance, ceiling/plenum effects, and sound system effects.
Classroom reinvented, a quantum leap in classroom design.
Authors: Good Kenneth
Published: October 2009

How do you design an environment to maximize your impact on a child’s development when you are limited to just an hour or two a week? Traditional academic education or biblical instruction, the environment is critical to success in reaching children and youth. This case study will explore the acoustical performance and design strategies that went into LCBC’s new and nontraditional building for children and students.
Working towards an enforceable standard for classroom acoustics.
Authors: Thibault Lois
Published: October 2009

The US Access Board has proposed to reference ANSI/ASA S12.60-2002 (R-2009) in the 2012 International Building Code (IBC), which will provide for local enforcement. If this proposal is adopted, the Board will then update its 2004 ADA-ABA Accessibility Guidelines to harmonize with the IBC. This paper will review the history of classroom acoustics initiatives, including the standard, and update attendees on the current process. Other classroom acoustics activity will be highlighted, particularly sustainability and green design proposals, and the 2010 re-authorization activities under the Individuals with Disabilities Education Act.
Integrating acoustical issues in the design of high-performance schools.
Authors: Siebein Gary W. , Jones Chris , Lilkendey Robert M. , Paek Hyun , Skelton Reece
Published: October 2009

ANSI 12.60 presents acoustical performance criteria for interior finishes to control reverberation inside classrooms, provide sound isolating wall and floor/ceiling assemblies between rooms, and limit noise from building equipment to allow perception and understanding of human voices within educational occupancies by young listeners with normal hearing and some degrees of hearing impairments. In practice, many schools are built that develop in an uneasy way trying to meet or sometimes to avoid meeting ANSI criteria because of perceived difficulties and expense in achieving the required results. A method to integrate acoustical design principles with the basic architectural design scheme of a school that can be implemented early in the design process was developed so acoustical performance can be simply implemented in school projects. This paper presents a core set of acoustical planning principles that can be implemented early in the design process so that ANSI criteria for room finishes, sound isolation, and building equipment noise can be met as the design progresses.
The estimation of geoacoustic parameters via low frequencies (50–100 Hz) for selected Shallow Water 06 test data.
Authors: Tolstoy A. , Jiang Yong-Min
Published: October 2009

This work will demonstrate the geoacoustic inversion “success” on data of using only one or two low frequencies, multiple ranges, and multiple realizations for geoacoustic inversion of actual SW06 data. The data used are the same as those processed by Jiang and Chapman and involves three ranges (1, 3, and 5 km) and multi-tonal continuous wave data collected on a 16 phone vertical array. Multiple realizations of the data were used where each reduced the non-uniqueness a bit. The multiple ranges and frequencies also reduced the non-uniqueness of the suggested solutions. However, there still remains a significant number (hundreds) of possible “solutions,” (values of ctop, cbot, hsed, and chsp) for which MFP<0.9 (including those suggested by Jiang and Chapman). The use of higher frequencies requires refinement of more parameters (such as the ocean sound-speed profile, source depth and range, water depth, and phone locations) but would not necessarily improve estimates of such bottom parameters as chsp and hsed. Thus, non-uniqueness of bottom parameters is an issue which may well exist for all inversion approaches.
Measurements of sound speed in bubbly liquids under high-pressure conditions.
Authors: Greene Chad A. , Wilson Preston S.
Published: October 2009

Methane hydrates occur naturally on the ocean bottom and in the upper layers of sediment on continental shelves. Seismic surveying could be used to locate methane hydrates; however, their low-frequency acoustic properties are not well-known. In addition, these properties can vary dramatically depending on whether the methane is in a gas or solid phase. As a step toward better understanding the three-phase case of gassy sediments in water, the two-phase case of methane gas bubbles in water was investigated. Wood’s equation is often used to model sound propagation in bubbly liquids and has been widely verified by experiments at atmospheric pressure. However, there is little information in the literature verifying the validity of Wood’s equation at high pressures. Low-frequency (0.5–10-kHz), resonator-based sound speed measurements were obtained for air bubbles in water and methane bubbles in water under pressures ranging from 1 to 10 atm at room temperature. The results are presented and compared to the predictions of Wood’s equation. [Work sponsored by ONR.]
A brief history of the discovery of the low frequency sound absorption mechanism in seawater and its pH dependence.
Authors: Browning David G. , Simmons Vernon P. , Thorp William H.
Published: October 2009

In the 1960s tests with a new surface ship sonar indicated that low-frequency (less than 10 000 Hz) propagation loss was greater than predicted by the existing MgSO4 absorption model. Propagation measurements in the SOFAR channel showed that the anomalous absorption was up to ten times greater than predicted and could be fitted by a 1-kHz relaxation. This was not without controversy at the time, but interest in this fundamental parameter spurred a major measurement effort by the U.S. Navy Underwater Sound Laboratory and other laboratories in the US, Canada, New Zealand, Europe, and Australia, resulting in at-sea measurements from Hudson Bay to the Tasman Sea. Yeager and Fisher conducted laboratory t-jump measurements that identified a boron based low-frequency relaxation mechanism in seawater. Simmons and Fisher followed with resonant sphere measurements to quantify the resulting acoustic absorption. A compilation of the at-sea results showed, somewhat surprisingly, a correlation with pH: the lower the pH, the lower the absorption. Mellen quantified the pH dependence by extensive laboratory resonator measurements. These results were confirmed by measurements conducted in China. The possible application of acoustically monitoring ocean pH was first suggested by Browning and Mellen in 1990.
Long-term trends in ambient noise levels.
Authors: Frisk George V.
Published: October 2009

This paper addresses the subject of long-term trends in ambient noise levels, a topic of great interest to both the scientific community and the general public. This attention stems primarily from concerns over the effects of apparently increasing sound levels on marine mammals. A growing, though limited, body of literature suggests that low-frequency noise levels increased approximately 15 dB during the period 1950–2000, an amount that corresponds to about 3 dB/decade. One hypothesis states that this increase is predominantly anthropogenic in nature and can be attributed to increased commercial shipping activity, which, in turn, can be linked to global economic growth. As a result, a direct correlation may be drawn between ambient noise levels and the behavior of the global economy. This special session addresses an additional consequence of global economic activity, namely, increased ocean acidification leading to decreased absorption and therefore to increases in ambient noise levels associated with distant shipping. This paper also suggests topics of considerable interest for future research including (1) the relative contributions of commercial shipping activity versus ocean acidification to ambient noise levels and (2) the effect of the current economic downturn on noise levels. [Work supported by ONR.]
The design of quarter-wavelength impedance matching layers for cylindrical transducers.
Authors: Heyden Douglas R. , Wilson Preston S. , Crawford Richard H.
Published: October 2009

Impedance matching layers are commonly used in piezoelectric underwater acoustic projectors. The layer maximizes transmitted power from the ceramic into the water and also increases the bandwidth of the projector. For the design of cylindrical transducers, it is common in practice to utilize the familiar plane wave formulation of the quarter-wavelength impedance matching layer as a starting point for the design of the cylindrical layer. Material properties and thickness are then modified by trial and error, heuristic, or empirical methods to optimize the design. This practice is undertaken because, apparently, the quarter-wavelength impedance matching layer formulation is not readily available in the acoustics literature for the cylindrical coordinate system. To address this deficiency, the reflection and transmission coefficients for the cylindrical three-medium problem were derived. No general zero-reflection, perfect transmission condition was found, but the equations can be used to find the material properties and layer thickness required to maximize transmission at a given frequency. The results of the derivation are shown and used in the design of a layered cylindrical piezoelectric transducer.
Time reversal focusing for pipeline structural health monitoring.
Authors: Harley Joel , O’Donoughue Nicholas , Moura José M.F. , Jin Yuanwei
Published: October 2009

Guided wave technologies have become popular tools for nondestructive testing due to their potential to travel long distances. Unfortunately, analyzing data from guided waves is often difficult because of the numerous multimodal and dispersive effects that distort signals in solid media. Time reversal has been shown to be robust against these unwanted and adverse effects. Time reversal techniques are commonly used to focus ultrasonic waves across a medium and have been used to perform nondestructive testing using pulse-echo techniques. This paper investigates the use of time reversal processing techniques to compensate for multimodal and dispersive effects in a low-power structural health monitoring system for pipelines. Time reversal methods are demonstrated as a pitch-catch operation between two transducer arrays to illuminate changes caused by damage on a pipe. It is then shown and discussed how differences in the location and severity of damage affect the signals recorded at the receiving transducer array and how these results can be interpreted to measure those changes. The results are demonstrated experimentally and then compared with equivalent finite element simulations. [National Energy Technology Laboratory (NETL) is the funding source for this effort with Cost Share being provided by Carnegie Mellon University (CMU). CMU is funded under a Subcontract Agreement with Concurrent Technologies Corporation. N.O. is supported by a National Defense Science and Engineering Graduate Fellowship.]
A planar acoustic array for voice collection.
Authors: Gonski David J. , Tran-Luu Duong , Tenney Stephen
Published: October 2009

A planar 7×7 acoustic array of microphones spaced 1 in. apart has been developed and tested. This array is intended for the collection of human speech. A simple analog electronic summation of the 49 microphone signals is carried out to form a preferential collection area in front of the array. We have conducted an analysis of the directional performance of the array to model its directivity. Two configurations of the array were tested. An array was populated with omnidirectional hearing aide microphones, and a second array was configured with cardioid microphones. Performance of each of these arrays was measured in an anechoic chamber and compared with the theoretical performance. To improve the front to back rejection a sound-absorbing pad was placed on the backside of the array. Two versions of the pad were characterized in the anechoic chamber, both were found to be effective. The array was packaged into a plastic box with open cell foam on the front for wind noise suppression and the sound-absorbing pad on the back for improved front to back rejection. Detailed acoustic and electronic design characteristics are presented.
On the radiation and wave propagation of sound within horns.
Authors: Tengelsen Daniel , Villamizar Vianey , Anderson Brian E. , Leishman Timothy W.
Published: October 2009

The horns used in loudspeaker systems are well known for their ability to increase radiation efficiency and control directivity. Because of the horn’s ubiquitous nature, significant research efforts have been undertaken to explore both its directional and frequency response characteristics. The following research reported in this presentation incorporates several numerical methods (including finite difference and boundary element analysis) to better understand the nature of wave propagation through horns and the effects that geometrical and configurational changes have in better controlling directivity and improving frequency response.
On the acoustic impedance of a sealed loudspeaker enclosure.
Authors: Leishman Timothy W. , Chen Xi
Published: October 2009

The acoustic impedance of a sealed loudspeaker enclosure is often oversimplified in loudspeaker models, which typically include only rough acoustical characteristics of the enclosed air volume and absorptive fill materials when no driver is present. The acoustical effects produced by sound transmission through and around the rear driver elements (e.g., the frame, magnet, voice-coil former, spider, pole-piece vent, etc.) may also be important for certain loudspeakers and applications. This presentation explores these effects through a discussion of enhanced modeling possibilities and the introduction of measurement techniques that may be used to assess the acoustic impedance of a loudspeaker enclosure when the driver is in place. The impedance more closely represents that actually seen by the rear portion of the driver diaphragm.
Acoustical curiosities of an American reed organ.
Authors: Muir Thomas G.
Published: October 2009

Free reed organs of the 19th and early 20th centuries have long provided interesting pursuits involving their acquisition, restoration, history and musicology, as well as performance, and for some—acoustical studies of the instruments. There is a preservation society with a journal, and the literature includes a treatise, books, and learned articles. Some acoustical curiosities of one such instrument are described, including stop types, reed spectra, waveforms, loudness, and intonation.
Physics of water crotales.
Authors: Worland Randy
Published: October 2009

Contemporary composers writing for percussion often incorporate unconventional playing techniques with the use of traditional instruments. Among these extended techniques is the lowering of gongs and crotales into water as they are being struck, resulting in a unique glissando effect that involves changes in both pitch and timbre. The orchestral crotale has a relatively simple geometry and overtone structure, making it an appropriate starting point for the study of this performance technique. Building on previously published work on the physics of crotales [B. M. Deutsch, C. L. Ramirez, and T. R. Moore, J. Acoust. Soc. Am. 116, 2427–2433 (2004)], an experimental investigation of the overtone frequencies and frequency ratios of a crotale as a function of water depth is presented. Mode images created using electronic speckle-pattern interferometry are also shown.
The auger shell whistle.
Authors: Zietlow Daniel , Moore Thomas
Published: October 2009

We report on investigations of a musical instrument made from the shell Terebra Turritella, or auger shell. To our knowledge, this instrument has been developed only recently. The instrument is played from the large end using an edge tone, and a diatonic scale is achievable merely by drilling five tone holes in a straight line down the length of the spiral shell. It is surprising that a naturally occurring cavity can produce a diatonic scale, and implies that there is something special about the shape of the auger shell. However, experimental and theoretical investigations reveal that the auger shell does not actually have such a resonance structure.
Why using complex stimuli for acoustical measurements may be necessary to get physically relevant analysis results.
Authors: Millot Laurent
Published: October 2009

Classical methods for measurements and analysis in Musical Acoustics (and also Acoustics) rely on Fourier transforms, linear excitation superposition assumption, and monochromatic excitation or noise equivalents. It is shown that classical methods using measurements at a single point (input impedance measurement, for instance) may not be physically relevant. Indeed, only a time sampling and related time Fourier transforms are performed while physical phenomena are spatio-temporal. Even if one considers a monochromatic forward traveling wave excitation, the use of the dispersion relation is not valid in spatio-temporal or spatio-frequency parameter space. It is shown that measurements need to be performed using also a spatial mapping to be physically relevant which implies at least Fourier bi-transforms (plane case). Then, it may be more simple and physically relevant to perform measurements with the whole complex excitation and use a frequency subband analysis tool, with a perceptive frequency subband mapping. Such a tool is described and it is shown that is permits the real-time switch between listening of partial to total resynthesis for any studied measurement signal, providing great surprises for the physical relevant subband(s) and the perceptive relevant ones. Audio performance will be given.
Historical aspects of the Khokhlov–Zabolotskaya equation and its generalizations.
Authors: Rudenko Oleg V. , Khokhlova Vera A. , Hamilton Mark F.
Published: October 2009

Derivation of the Khokhlov–Zabolotskaya (KZ) equation provided a new approach to describing the combined effects of nonlinear propagation and diffraction in sound beams. In this paper, historical aspects of the KZ equation and its generalizations are presented. The interest in nonlinear acoustic beams of Academician Khokhlov and his colleagues at Moscow State University was inspired in the 1960s by emerging developments in laser physics and the corresponding models of nonlinear optical beams. The two cases, acoustical and optical, represent two limiting cases of nonlinear beams in weakly and strongly dispersive media, respectively, which required different theoretical approaches. The KZ equation and analogous nonlinear evolution equations of nonlinear wave physics are reviewed. It is illustrated how theoretical studies combined with numerical modeling resulted in predictions of new physical phenomena in nonlinear acoustic beams. Concurrently, newer applications of nonlinear acoustics such as parametric arrays, sonic booms, and medical acoustics stimulated the derivation of generalized KZ-type equations together with analytical and numerical methods to solve them. Modern applications and corresponding generalized KZ-type models that include effects such as frequency-dependent absorption, weak dispersion, scalar and vectorial inhomogeneities of the propagation medium, different orders of nonlinearity, and more accurate description of diffraction are presented.
Variations of the nonlinear equation for diffracting beams in fluids to study different modes of propagation in elastic media.
Authors: Zabolotskaya Evgenia A.
Published: October 2009

Four variations of the equation for nonlinear acoustic beam propagation derived originally for a fluid will be reviewed. These variations describe finite amplitude beam propagation in isotropic elastic solids and in crystals, influence of diffraction on nonlinear Rayleigh waves, and nonlinear shear wave beams. The distinguishing features of each case will be discussed. The equation for nonlinear longitudinal wave beams in isotropic solids is based on nonlinear theory of elasticity and is close to the original equation for fluids. The equation for sound beams in crystals takes into account that the direction of energy propagation does not coincide with the direction normal to wavefronts. Nevertheless, the general form of the equation is similar to that of the original equation for fluids. Distinguishing features of Rayleigh waves are that they are two-dimensional and their nonlinearity is nonlocal. Because of the nonlocal nonlinearity, the evolution equation for this case was derived in the frequency domain using Hamiltonian formalism. The equation for nonlinear shear wave beams was derived in the cubic approximation in terms of particle displacement and it accounts for any polarization. Solutions of these evolution equations will be presented to illustrate phenomena specific to each case.
Group analysis of the Khokhlov–Zabolotskaya type equations.
Authors: Sapozhnikov Oleg A.
Published: October 2009

Khokhlov–Zabolotskaya (KZ) equation is the basic equation of the theory of acoustic beams propagating in quadratically nonlinear media. Being generalized for the case of a medium with general-type nonlinearity and expressed in dimensionless notation, it has the form [uz+P(u)uτ]τ=uxx+uyy, where u represents waveform, τ is retarded time, z is axial coordinate, x and y are lateral coordinates, and P(u) characterizes a nonlinear addition to the linear wave velocity: quadratic nonlinearity corresponds to P(u)=u, cubic one to P(u)=u2, etc. No general analytical solution has been obtained for this nonlinear KZ-type equation, so numerical methods or asymptotic approximations are usually employed. Additional powerful mathematical tool is Lie group analysis that enables to find general symmetries of differential equations. These symmetries help to generalize known analytical and numerical solutions, derive new solutions, and obtain conservation laws. Results of group analysis of KZ and KZK equations are discussed for various nonlinearities P(u). Examples of obtaining of new solutions and deriving of reduced equations are presented. It is also shown that the generalized KZ equation can be written in Euler–Lagrange form, which makes it possible to apply Nöther theorem and derive new conservation laws for nonlinear acoustic beams.
Acoustic dissipation and finite-amplitude sound propagation in two-phase porous media.
Authors: Pushkina N. I. , Osypik J. I. , Zhileikin Ya. M.
Published: October 2009

Acoustic spectroscopy is known to be an important tool for studying various media. In the presented work, specific features of acoustic dissipation in two-phase porous media are theoretically studied and the propagation of a finite-amplitude attenuating sound beam described by the KZK-type equation is analyzed numerically for the case of a marine sediment. The KZK-type equation has been derived from the classical Biot equations, and it contains a dissipative operator corresponding to the frequency correction function F(κ) in the Biot equations. In the present work, the properties of the correction function are studied and its well applicable representations are obtained. It is shown that the expansion of the correction function over κ2 converges at κ<5. An asymptotic expansion of this function is obtained at large κ values. For high frequencies, simple dependence of viscous attenuation and phase velocity on parameters of a medium, useful for diagnostics of these parameters, has been found. The propagation of a finite-amplitude acoustic beam in a dissipative marine sediment has been numerically analyzed which showed that intense acoustic beam propagation can be accompanied by considerable non-linear phenomena while diffraction only weakly affects the process.
Nonlinear pulsing schemes for diagnostic ultrasound.
Authors: Averkiou Michalakis
Published: October 2009

With the introduction of ultrasound contrast agents and the development of tissue harmonic imaging (THI), nonlinear acoustics has become a major research direction in diagnostic ultrasound. In THI an image is formed from the nonlinear components (due to nonlinear propagation) of the backscattered signal. Pulsing schemes have been invented to specifically detect the nonlinear components. These schemes are pulse inversion (PI), power modulation (PM), and their combinations (PMPI2, PMPI3, and PMPI4). The KZK equation is used to investigate these pulsing schemes in conditions that closely resemble ultrasound imaging in order to fully understand the properties of these schemes. Measurements of nonlinear propagation of such pulses were compared with the KZK predictions and were found in good agreement. Pulse inversion isolates the even harmonic components only and extracts the total amount of nonlinearity in those components. With pulsing schemes with different amplitudes (PM, PMPI2, and PMPI3), the differential nonlinearity between pulses is detected, with PMPI2 extracting the largest total amount. In addition, the schemes with amplitude modulation have a nonlinear fundamental component that suffers less than the higher harmonics from thermoviscous absorption and thus offers more signal in penetration limited cases.
Statistical solutions of the Khokhlov–Zabolotskaya–Kuznetsov equation for analyzing mechanisms of image quality enhancement in tissue harmonic imaging.
Authors: Yan Xiang , Hamilton Mark F.
Published: October 2009

Statistical solutions of the Khokhlov–Zabolotskaya–Kuznetsov equation were obtained to analyze mechanisms contributing to image quality enhancement in tissue harmonic imaging (THI). The focus is on suppression of image clutter due to phase aberration and reverberation. Tissue heterogeneity is modeled with a random phase screen characterized by its variance and spatial correlation length. Solutions for the mean intensities of the linear (fundamental mode) and second-harmonic fields were derived from a focused Gaussian beam that is transmitted through a phase screen located an arbitrary distance from the source. The random phase variations of the screen are assumed to be small and described by a Gaussian autocorrelation function. The solutions are validated by comparison with ensemble averages of direct numerical simulations. A benefit of the analytical approach is separation of the different contributions to deformation of the beam by the phase screen, and the statistical approach is convenient for quantifying the merits of THI. The degree to which THI reduces beam deformation is assessed using a measure based on signal-to-clutter ratios introduced previously for this purpose by C. E. Bradley [Proceedings of 17th International Symposium on Nonlinear Acoustics (AIP, New York, 2006)]. Statistical solutions will also be presented for backscattering. [Work supported by NIH DK070618.]
Nonlinear acoustical beam formation and beam profiles in fluids.
Authors: Pantea Cristian , Sinha Dipen N.
Published: October 2009

Nonlinear acoustical beam formation in fluids is investigated in several different configurations: (i) collinear mixing due to simultaneous excitation of a single transducer by two different high frequency signals, (ii) non-collinear mixing due to excitation from two separate transducers, (iii) nonlinear de-modulation of an amplitude modulated fixed frequency, and (iv) nonlinear mixing due to excitation of a single transducer by a fixed frequency and a chirped frequency signal. In all cases, the difference frequency acoustic beam generated by nonlinear mixing in the fluid is investigated. In contrast to using solids as the nonlinear medium, fluids have the advantage that the beam can be scanned in all directions allowing the determination of three-dimensional beam profile. The experiments were performed mainly in water and Fluorinert FC43. In the collinear measurement configuration, where the nonlinear down-converted beam is produced from a single transducer, the experimental results are compared with the predictions from the KZK equation. Electronics and transducer nonlinearity and the role of transducer “effective diameter” will also be discussed.
Infants’ vowel discrimination in modulated and unmodulated noise.
Authors: Werner Lynne A.
Published: October 2009

Adults detect and discriminate masked sounds better in temporally modulated maskers than in unmodulated maskers. It is not known whether the same is true of infants. In this study, 7–9-month-olds learned to respond when a repeated vowel changed from /a/ to /i/ or from /i/ to /a/ in speech spectrum noise. Discrimination was assessed using an observer-based procedure. In one condition the noise was unmodulated. In the other, the noise was modulated with the envelope of single talker speech. The level of the noise was 60-dB SPL. For infants in group 1, the level of the vowel in both conditions was set so that d′=1 was achieved in the unmodulated noise; discrimination in modulated noise was the second condition tested. For infants in group 2, the level of the vowel was fixed at the average level used to test the infants in group 1; discrimination in modulated noise was tested first. In both groups, d′ in the modulated noise condition averaged only 0.5. Thus, infants were unable to take advantage of masker modulation to improve speech discrimination. Their speech discrimination was poorer in modulated than in unmodulated noise. [Work supported by NIH R01 DC00396 and P30 DC04661.]
Efficient coding of correlated complex acoustic dimensions through active listening.
Authors: Stilp Christian E. , Rogers Timothy T. , Kluender Keith R.
Published: October 2009

Efficient coding extracts and exploits redundancy to optimize information processing in sensorineural systems. Stilp et al. [J. Acoust. Soc. Am. 124, 2496 (2008)] reported evidence for rapid and efficient adaptation to correlation among complex acoustic attributes. In the study, following passive exposure to highly correlated stimulus features, discriminability of sound pairs violating the correlation is temporarily lost before subsequent recovery via active testing with stimuli whose features were poorly correlated. The present study examines listeners’ ability to extract and exploit correlation between stimulus attributes exclusively through active testing. Listeners discriminated stimuli (AXB) for which two complex, independent dimensions, attack/decay (AD) and spectral shape (SS), were highly correlated (r2=0.96). In the first testing block of 128 trials, discrimination of sound pairs respecting the correlation is superior to sound pairs violating the correlation. Only through successive testing blocks, listeners discover variance orthogonal to the otherwise perfect correlation between AD and SS, and discrimination recovers to baseline levels. Listener performance will be discussed within the context of maximum likelihood and connectionist models. [Work supported by NIDCD.]
Speech transformation: Increasing intelligibility and changing speakers.
Authors: Kain Alexander
Published: October 2009

Speech transformation changes an aspect of speech without changing its message, typically using a process of analysis, feature modification, and synthesis. The feature modification step can consist of a (trainable) mapping function or a hybridization of several feature sets for the purposes of perceptual experimentation. First, speech transformation approaches are presented that aim to increase the intelligibility of speech. One approach is used in the context of increasing the intelligibility of conversationally spoken speech for hearing-impaired listeners. Another approach aims to increase the intelligibility of speaking-impaired individuals by the general population. Second, transformation approaches are presented which aim to change a source speaker’s speech (natural or TTS-generated) to sound as if a specific target speaker had spoken it (also known as voice transformation).
Quasi-articulatory synthesis as a tool for basic science and education.
Authors: Hanson Helen M.
Published: October 2009

HLsyn is a quasi-articulatory speech synthesis system based on Klatt’s formant synthesis model [D. K. Klatt and L. C. Klatt, J. Acoust. Soc. Am. 87, 820–857 (1990)]. The elements of a circuit model of the vocal tract are derived from cross-sectional areas of constrictions and subglottal pressure. Solution of the circuit results in pressure drops across constrictions, which in turn lead to source characteristics (both periodic and noise). The circuit model imposes constraints on the relations between the pressures and flows in the circuit, resulting in more natural variation in the amplitudes of two simultaneous sources, e.g., a periodic source and a noise source. While the virtues of HLsyn as a speech synthesis system have often been sung [e.g., Hanson and Stevens, J. Acoust. Soc. Am. 112, 1158–1182 (2002)], HLsyn has other uses that may go unnoticed. Using HLsyn to explore or simulate the production of certain sounds often leads to insights about how speech is produced. That is, this synthesizer can be used to explore the basic science of speech production and perception. Likewise, HLsyn as a tool in basic speech science courses brings equations and circuits to life for students. Examples of insights gained through HLsyn will be described. [Work supported by NIH.]
Advances in simulation of sentence-level speech production with kinematic models of the vocal tract and vocal folds.
Authors: Story Brad H.
Published: October 2009

Speech simulation refers to a system in which computational models are used to simulate the physical processes of human sound production. These processes consist primarily of vocal fold vibration and acoustic wave propagation in the tracheal, nasal, vocal tract systems, and radiated acoustic output. Although simulations of various aspects of speech production are typically limited to short time scales, this presentation will focus on using kinematic models of the vocal folds and vocal tract shape to generate speech at the level of words and sentences. Specifically, the vibrating medial surface of the vocal folds is represented by a kinematic model which allows for direct time-dependent specification of fundamental frequency, amplitude of vibration, glottal geometry, and glottal symmetry. The vocal tract shape is also governed by a kinematic model, based on data collected with MRI and x-ray microbeam techniques, that allows for specification of time-dependent cross-sectional area changes in an acoustic waveguide. When these models are coupled, the result is an acoustically-interactive simulation of the sound production process from which pressures and airflows are generated. The components of the system will be presented and then used to demonstrate samples of simulated speech. [Work supported by NIH R01-DC04789.]
Time-frequency and position-wavenumber acoustic signal analysis.
Authors: Loughlin Patrick J.
Published: October 2009

The spectrogram, which is a plot of the spectral intensity of a signal over time, has been widely used in acoustic signal processing because many signals, such as speech, animal vocalizations, music, and the sonar backscatter from elastic objects, have frequencies that change over time, which convey important information about the signal or source from which it originated. Since the development of the spectrograph at Bell Laboratories in the 1940s, more modern methods for time-frequency analysis, such as the Choi–Williams and Zhao–Atlas–Marks distributions, have been developed, which overcome some of the limitations of the spectrogram and, in particular can show time-frequency detail in the signal that is obscured by the spectrogram. We will discuss these methods and the general area of time-frequency acoustic signal analysis with examples drawn from a variety of applications. A particular focus will be made on showing how time-frequency analysis, and also position-wavenumber analysis, can be used to formulate and gain physical insights into dispersive pulse propagation. We will also comment on and illustrate the use of wavelets for time-frequency analysis. [Work supported by ONR 321US.]
Gibbs sampling for modal arrival time and amplitude estimation from time-frequency representations of acoustic signals.
Authors: Michalopoulou Zoi-Heleni
Published: October 2009

A Gibbs sampling-maximum a posteriori approach is developed for modal arrival time and amplitude estimation from time-frequency representations of broadband acoustic signals propagating in underwater media. The goal is to obtain accurate estimates of arrival times of propagating modes and corresponding amplitudes, which can then be employed for source localization and geoacoustic inversion. The method provides uncertainty information on both modal arrival time and amplitude estimates, typically unavailable when traditional methods are used. Estimates and uncertainty are propagated through an inversion process, generating posterior probability distributions of source range and geoacoustic properties. [Work supported by ONR.]
Adaptive noise and interference removal from speech based on a modified short time Fourier transform.
Authors: Nelson Douglas J.
Published: October 2009

A simple linear adaptive method for removing noise and interference from speech is presented. The method is based on a linear time-frequency representation in which the short time Fourier transform (STFT) is concentrated (reassigned) in frequency. The concentration process results in a complex-valued surface in which speech components and narrowband AM/FM interference components are essentially time-varying spectral impulses. Unwanted components may be removed from the surface, and the clean signal with these components removed may be reconstructed as a linear time marginal, computed by integrating the surface with respect to frequency. This process is linear and results in a nearly distortion-free reconstructed signal. Moreover, unlike processes like methods such as spectral subtraction, the process requires no Fourier inversion. This process is computationally efficient since the STFT is implemented as a bank of recursive two tap filters.
Estimation of seismic interface wave dispersion in geoacoustic inversion.
Authors: Dong Hefeng , Liu Lanbo
Published: October 2009

Shear wave velocity variation as depth in underwater environment is closely related to dispersion of seismic interface waves traveling along the water/sediment boundary. An estimate of the dispersion of seismic interface waves can be obtained by time-frequency analysis. There are different methods for the time-frequency analysis to estimate dispersion of the interface waves. Phase velocity dispersion can be estimated by multi-sensor method, while group velocity dispersion can be estimated by single-sensor method. Multi-sensor method uses array data by knowing sensor-spacing, which gives the average estimate of the phase velocity within the ranges covered by the array. Single-sensor method uses one trace at a time by knowing the distance between source and the sensor, and gives the local group velocity estimate. In this paper, time-frequency analysis methods for both phase- and group-velocity estimations are presented. An experimental example for estimation of shear wave velocity variation as depth in the upper layers of the sediment is presented by inverting the estimated dispersion relations of seismic interface waves [Work supported by NFR under No. 186923/I30].