bluuebunny/crossref_metadata_2025 huggingface dataset:
The acoustical waveguide
Authors: Coppens Alan B. , Atchley Anthony A. , Moore Eric W.
Published: October 2005

Fundamental concepts of normal mode propagation in bounded media can be studied simply and practically in a water-filled rectangular waveguide with pressure-release boundaries. Use of broadband source and receiver allows generation and study of well-formed gated sine-wave pulses. The source is designed to excite the lowest (1,1) normal mode of the system and suppress excitation of the next few higher modes. This provides a useful frequency range for studying the behavior of the lowest mode both above and below its cutoff frequency. The cutoff frequency can be estimated by a number of techniques; this relates cutoff to several different phenomena associated with the propagation. Tone burst operation allows study of the rise time of the propagating tone burst and thereby the group speed of the carrier frequency. With an appropriate absorber at the far end of the waveguide, cw transmissions are almost purely traveling waves so that the phase speed of the input frequency can be determined. The apparatus is simple to construct and the electronics are not exotic. This experiment is a direct descendant of one that originated in the graduate lab of the physics department at Brown University approximately 35 years ago.
Linearized least-squares data analysis
Authors: Garrett S. L.
Published: October 2005

One of the most attractive features of many acoustic teaching laboratory experiments is their ability to produce high-quality (precision) data. This affords the possibility of also using the results of these laboratory exercises to teach advanced techniques for data analysis that exploit the ubiquity of least-squares data analysis routines which are now included in most hand-held calculators and all personal computer plotting packages. This talk will concentrate on the transformation of general two-parameter nonlinear equations into linear forms suitable for least-squares-fitting techniques. This transformation technique will be demonstrated to (i) extract the effective moving mass of the spring to correct the simple ω=(k/m)1/2 expression for the simple harmonic oscillator; (ii) extract the distance from the end of the pendulum string to the pendulum bob center-of-mass in the simple pendulum experiment; (iii) extract the location of the acoustic center of a projector from measurement of the free-field pressure versus separation; and (iv) extract the cutoff frequency and thermodynamic sound speed from the phase speed versus frequency measurement in a water-filled, pressure-released waveguide.
Laboratory experiments on the interaction of an air jet with a Helmholtz resonator
Authors: Cottingham James P.
Published: October 2005

The interaction of an air jet with a resonator is fundamental to the operation of several musical instruments and a significant topic in musical acoustics courses. Recent studies of a Helmholtz resonator excited by an air jet have explored the dependence of the frequency and amplitude of the Helmholtz mode on jet speed and other parameters. [R. Khosropour and P. Millet, J. Acoust. Soc. Am. 88, 1211–1221 (1990); J. P. Cottingham etal., J. Acoust. Soc. Am. 92, 2380 (1992)]. It has been observed that domains of jet speed, for which a single-frequency Helmholtz mode occurs, are separated by narrow transition regions. Investigation of this phenomenon, which is audible as well as measurable, has been adapted as a set of laboratory exercises for use in musical acoustics courses. Using a homemade air jet with the laboratory compressed air supply, students are able to study the internal sound field of a jet-excited resonator with a small tie clip microphone. Investigation of a significant nonlinear phenomenon is thus possible with simple equipment.
MultiSensory Sound Lab for Educational and therapeutic applications
Authors: Lederman Norman , Fisher Kimberly V.
Published: October 2005

The MultiSensory Sound Lab electronically processes sound signals from microphones, musical instruments/recordings, electronic stethoscopes, and other sources and directs them to loudspeakers, a vibrating floor, and various large visual technologies that display the frequency, spectral, intensity, and time aspects of the signal. Originally developed for use with deaf children, the lab provides visual and tactile information about sound that is useful in a wide range of applications ranging from instruction in acoustics and physics of sound, to speech and music therapy for normally hearing, as well as, hearing-impaired students. Example clinical and educational applications will be presented. Data from pre- and post-testing show that sound lab activities result in significant concept learning and skill acquisition. User surveys shows that the sound lab eases teaching tasks and motivates students. Note: this presentation will serve as introduction to the MultiSensory Sound Lab tours that will be conducted at the University of Colorado. [Project supported by the U.S. Department of Education.]
What physical acoustics can tell us about fluids
Authors: Beyer Robert T.
Published: October 2005

Traditionally, one has used physical data on fluids to study the propagation of sound in them. However, the opposite is also possible: To use the study of the propagation of sound in a fluid to determine some of its physical properties and its behavior. This was perhaps done for the first time by Einstein (for propagation in gases) in 1920. Today, physical acoustics can be used to gain information about phase transitions in liquid crystals, to study the behavior of mixtures of liquids, and of particles or bubbles in liquids, and in other ways. A review is given of these processes and the ways in which physical acoustics contributes to our knowledge of them.
Thermophysical properties of alternative refrigerants from acoustical measurements
Authors: Moldover Michael R.
Published: October 2005

Acoustic resonance techniques have been developed at NIST to make accurate (±0.01%) speed-of-sound measurements in gases a routine matter. These techniques have been applied to many environmentally acceptable candidate replacement refrigerants. The data were used to deduce ideal-gas heat capacities and virial coefficients. These results are an important component of the computer package REFPROP that is being used by designers of refrigeration equipment. NIST is actively involved in developing acoustic methods for determining the viscosity and thermal conductivity of gases. NIST is also extending these measurement techniques to corrosive gases and to gases at high temperatures.
Attenuated leaky Rayleigh waves
Authors: Qi Quan
Published: October 2005

The attenuation of leaky Rayleigh waves due to viscous damping in a boundary layer at the interface of an elastic solid half-space and a fluid half-space is studied by matched asymptotic method. Viscosity of the fluid is considered unimportant except in a thin boundary layer at the interface. By keeping the leading order effect, shown by the inverse of square root of a Reynolds number based on the shear velocity of the solid substrate, a new characteristic equation is obtained. One of the numerically obtained solutions gives the leaky Rayleigh wave speed and the attenuation coefficient due to both radiation into fluid and viscous damping of the boundary layer. It is shown that the viscous attenuation in the boundary layer may be as important as that due to radiation into the fluid half-space for some fluid–substrate combinations. These results may be used to improve our interpretation of experimental results of acoustic signature of materials. Extension of the analysis to a fluid layer instead of a half-space will be discussed. [Work supported by the Hunt Fellowship.]
Reduction of backscatter coefficient from pulse-echo measurements: A new formulation
Authors: Chen Xucai , Mottley Jack G. , Schwarz Karl Q. , Parker Kevin J.
Published: October 2005

A new formulation for the reduction of the absolute backscatter coefficient from pulse-echo measurements is presented. Using this formulation, the diffraction correction is straightforward. This correction is a weak function of frequency, rather than the frequency squared dependence proposed by earlier investigators. A much simpler calibration method is proposed. Initial experimental evidence using a focused transducer and polystyrene spheres as scatters is presented. The proposed formulation and polystyrene spheres are sufficiently simple as to be utilized in many laboratories, enabling cross checking and consistency between sites. [Work supported by NIH and NSF.]
Acoustic coupling from a focused transducer to a flat plate and back to the transducer
Authors: Chen Xucai , Schwarz Karl Q. , Parker Kevin J.
Published: October 2005

An exact solution for the acoustic coupling function from a focused transducer to a flat plate and back to the transducer (the diffraction correction function) is provided. This function is useful for the system calibration where is pulse-echo system or transmit–receive system is used. Numerical results will be presented for the case where the reference plate is placed near the focal plane of the transducer. The solution for a flat disk transducer is obtained as a limiting case. [Work supported by NIH and NSF.]
Acoustics laboratory experiments for all levels
Authors: Rossing Thomas D.
Published: October 2005

Acoustics is a subject that is best learned by incorporating hands-on experience in the laboratory; this applies to students majoring in music as well as in physics or engineering. The author’s laboratory manual, AcousticsLaboratoryExperiments, describes 52 experiments at several levels of sophistication. Some are intended for students with no previous experience in a physics laboratory, some for advanced undergraduates, and some for graduate students beginning their study of acoustics. Some experiments can be performed on more than one level. Several experiments will be described and demonstrated.
Laboratory experiments in the acoustics course at the U. S. Naval Academy
Authors: Elder S. A. , Korman M. S.
Published: October 2005

For about 25 years the Physics Department has offered an acoustics course as a senior elective for physics and electrical engineering majors, based on the text by Kinsler, Frey, Coppens, and Sanders. A 2-h laboratory is provided each week. The aim of the lab is to illustrate the theory by teaching basic experimental measurement techniques. The specialties include a modal analysis system (B&K) to study, for example, the vibration of guitars, Pyrex flasks, and student-made ‘‘musical’’ triangular steel plates. Students study the directivity of speaker arrays, musical instruments, and psychoacoustic effects in a 200-Hz–20-kHz anechoic chamber. IBM PC and Mac II work stations provide instruction in hardware interfacing, signal processing, spreadsheets (for data analysis), as well as specialized techniques of FFTs and digital filtering. Work stations have a midi-interface for sound and music synthesis. Ultrasonics and underwater acoustics experiments often involve electroacoustics. Projects include measuring the effects of interference, diffraction, reverberation, and classification of material properties. In addition, each student participates in a major project, usually in a small group. Recently the class performed an acoustical evaluation of the new Bob Hope Theater of the Performing Arts on the USNA campus.
Acoustic characterization of chemically altered cortical bone
Authors: Broz Jerry J. , Simske Steven J. , Greenberg Alan R.
Published: October 2005

A novel combination of microscopic evaluation techniques is utilized to evaluate localized compositional and material properties of bovine femoral cortical bone. Cortical bone sections were selectively demineralized by timed immersion in supersaturated (ethylenedinitrilo)-tetraacetic acid. Optical microscopy of the sections indicated that a collagen layer of varying thickness surrounded a core of mineralized tissue. The treated sections were characterized with a scanning acoustic microscope (SAM) using a 50-MHz transducer. Based on the acoustic signals reflected from both the surface of the collagen layer and the mineralized tissue layer below, the sonic wave velocities and elastic stiffnesses of the mineralized tissue and collagen were 3.65±0.12 km/s and 1.49±0.06 km/s and 27.2±2.5 GPa and 2.95±0.26 GPa, respectively [Broz etal., 12th South. Biomed. Conf., Tulane Univ. (1993)]. Following the acoustic evaluation, microhardness and elemental composition maps were obtained for the sections using a diamond pyramid indenter and a Jeol JXA-8600 Superprobe, respectively. The size and location of the demineralized regions as determined by the microhardness testing and wave dispersive analysis were in good agreement with the acoustic micrograph data. The combination of acoustic, chemical, and mechanical microscopic techniques provides important insights into the site-specific phasic properties of cortical bone.
Design of ultrasonic scattering experiments for tissue characterization
Authors: Mast T. Douglas , Waag Robert C.
Published: October 2005

Measurements of differential scattering cross section as a function of angle and frequency make possible the separation of compressibility effects from density effects. From these measurements, one can obtain the power spectrum of compressibility variations, the power spectrum of density variations, and the cross spectrum of compressibility and density variations. Measurements of these spectra has potential use for tissue characterization on scales corresponding to the wavelengths employed. Here, concepts are presented that make possible optimal design of experiments to measure ultrasonic scattering as a function of angle and frequency. Conditions are given for emitter and detector beam patterns and time gates that yield measurement system-independent scattering data. A method is presented for minimization of the effects of statistical fluctuations in the scattering estimates by solution of an overdetermined set of equations. The limitations of such measurements are also treated. As an example, an experiment currently being designed is discussed; the goal of this experiment is to measure differential scattering cross section with greater spatial resolution than has been achieved to date.
Limitations introduced by material attenuation in pulse-echo systems employing nondiffracting x waves
Authors: Fatemi Mostafa
Published: October 2005

Ultrasonic nondiffracting beams are of interest for use in pulse-echo systems because they have long depth of field and small beamwidth. Recently, a new class of nondiffracting beams, termed the x waves, has been discovered and its properties in lossless media have been reported. In some pulse-echo applications, however, propagation media are dissipative. It can be shown that x waves diffract in such media, i.e., the beam spreads and its amplitude decays with distance. In order to limit beam spread within a reasonable range, attenuation of the media must be taken into account while designing the transducer and the excitation signal. Also, amplitude decay of the echoes must be compensated for at the receiver by using a proper time gain compensation curve. In this paper, conditions for designing an x wave pulse-echo system for use in dissipative media are described. Given the attenuation coefficient and maximum allowable beamwidth, proper values for transducer parameters, such as diameter, axicon angle, beam concentration parameter in lossless media, and the bandwidth of the interrogating pulse are discussed and determined. Also, variations of the beamwidth are investigated. It is shown that for wideband x waves, the beam spreads linearly with depth. Furthermore, analytical expressions for the time gain compensation curve are obtained. In contrast to the conventional exponential gain function, the gain function for the wideband x wave approaches a linear function of time.
Prediction of potential disturbance of baleen whales by low-frequency acoustic transients
Authors: Malme Charles I.
Published: October 2005

High-energy, low-frequency sound sources are useful tools for geophysical surveying, submarine detection, and long distance acoustic tomography. These sources produce impulsive, narrow-band and swept-tonal signals at high levels in the oceanic environment. This study was made to estimate the received level-time duration characteristics of acoustic transients that can potentially influence baleen whale behavior, the species of particular concern. Findings of acoustic disturbance studies show that continuous sound levels ≥120 dB re: 1 μPa produces ≥50% avoidance by gray and bowhead whales. However, for impulsive airgun sounds of duration ≤0.5 s, effective pulse levels 30 to 50 dB higher are required to produce 50% avoidance for the same species. Little information is available on whale response to intermediate sound durations representative of some sonar and tomography source operations. Consequently, the literature on human response to acoustic transients was examined for response prediction methodologies suitable for application to whale acoustic response. Similarities were found that support the application of a modified equivalent level (Leq) metric. The exposure level–time duration characteristics obtained from this analysis are preliminary estimates. The predictions should be tested using data obtained in the oceanic environment using representative sources, signals, and whales. [Work supported by the U.S. Navy.]
Response of steel beams with elastically restrained end conditions with and without cracks
Authors: Pandya Shail R. , Wang Zhijing , Finch Robert D. , Jansen Ben H.
Published: October 2005

The vibration response of uniform and cracked beams with elastically restrained end conditions under impact excitation is being experimentally investigated. Preliminary work has revealed that the response obtained does not match that predicted theoretically for pinned–pinned end conditions. In practice, most beams have nonclassical end conditions as a certain amount of flexibility is unavoidable. Therefore a theory of vibration of beams with elastically restrained end conditions was applied. The results of this theory were in close agreement with the response obtained from beams mounted on elastic supports. An antiresonance for the pinned–pinned beam has been found for the fifth mode of vibration whose frequency matches the natural frequency of the supports. Cracks simulated by slots are currently being made at various locations along the length of the beam. The impact response of these slotted beams will also be reported and comparisons will be made between the theoretical and the experimental results. [Work supported by NSF Grant No. MSS-9024224.]
Noise attenuation provided by flexible shields for industrial equipment
Authors: Sizova Natalia V.
Published: October 2005

A general physical model and method for the calculation of the noise reduction provided by a flexible shield consisting of thin, rigid, narrow plates, joined together lengthwise into a chain is represented. The model selected is one plane containing a set of linear rectangular plates placed side-by-side, separated by narrow spaces. All plates are making flexural oscillation under the influence of evenly distributed noise pressure. The model is based on the determination of the sound pressure caused by sound radiation of a thin rectangular rigid plate in average frequency range (63–8000 Hz), in far field. The loss factor of the plates junction was determined experimentally and used for the calculation of the noise reduction. Some experimental data for the noise reduction provided by different designs (different number of the plates, material, thickness) were represented and compared to the calculated results. The method allows to determine the optimal parameters which are necessary to achieve maxima of the noise reduction. [Work supported by Scientific-Research, Institute of Printing Machinery, Moscow.]
Diagnosis of the Bjoerk–Shiley heart valve failure from acoustic signatures
Authors: Chondros Thomas
Published: October 2005

The replacement of human heart valves by mechanical ones was pioneered in the 1960s. Shiley, Inc., of Irvine, California, was one of the early manufacturers of such valves. The Bjoerk–Shiley 60 convexo-concave valve was introduced in 1967 and about 85 000 people received this valve until 1986, when it was withdrawn from the market. Analysis of sound emitted from the strut of the Bjoerk–Shiley 60o CC valve due to impact was used to monitor the propagation of the fatigue crack before it would lead to the failure of one or both legs of the outlet strut. Analytical and experimental results established that the range of the fundamental natural frequency is 2500 to 8000 Hz. It was found that previous experimental investigations were performed within a window of lower frequencies and they could not capture the transition of the natural frequency during the propagation of the fatigue crack, which would take several months. It was found that for crack depths above 50% of the diameter, the change in the natural frequency, thus the dominant component of the signal, was substantial and easily measurable. This may lead not only to diagnosis of the fracture at one end of the outlet strut but also to detection of the propagating crack long before it would lead to the partial or complete strut failure.
Acoustic diagnosis of the onset of strut fracture of the BS/CC prosthetic heart valve
Authors: Eberhardt Allen C. , Chassaing Charles E.
Published: October 2005

A replacement prosthetic heart valve functions in a corrosive environment in which it cannot readily be inspected or repaired. It must cycle repeatedly, at a rate of 40 million cycles per year, over a service life that may extend many years. The opening and closing sounds of Bjoerk–Shiley convexo-concave prosthetic heart valves are brief transients that are being studied for detection of incipient valve failure. The sounds are produced by the impact of the occluder disk with the metallic struts that retain it within an orifice ring. These sounds have been recorded invivo for two distinct conditions or classes, valves that are intact, and valves that exhibit an in-service failure of one of two legs of a strut which is critical to the function of the valve. The small size and rapid motion of the valve occluder disk produce a broadband acoustic transient that exhibits subtle changes as a valve strut proceeds toward failure. Features are detected, and a nonlinear expansion is used to develop a set of coefficients from the time and frequency domains to separate the two conditions. The recorded invivo data are used as the training set. The coefficients are then applied to invivo recordings as a method of detection of a progressive failure of the valve. Results of the expansion and of a parallel approach using neural nets are shown to be most effective for patients with normal heart rhythm.
Time response analysis of sound fields in rooms and the temperature condition of the air
Authors: Shimoda Hidemaro , Kashiwa Tatsuya , Yoshida Norinobu , Fukai Ichiro
Published: October 2005

Transient analysis in the time domain is very important to determine acoustical properties in rooms. In this paper, the transmission line network is used as a simulation code named Bergeron’s method [J. Acoust. Soc. Am. Suppl. 1 84, S64 (1988)]. Time responses in the rectangular scale model excited with pure tones were compared to analytical results. In the study, the medium condition as a temperature of the air turned out to be very sensitive to simulated time responses in sound fields in rooms. Even though it is known that the sound speed varies with a change in the temperature of the air, the standard sound speed corresponding to the standard temperature of the air, such as 15 °C in ordinary sound field simulations, is often used. Analytical time responses, however, as compared with experimental responses in the model, were found to be very different from each other in about 1% change of the sound speed.
Responses of humpback whales to playback of natural and artificial sounds in Hawaii
Authors: Frankel Adam S. , Herman Louis M.
Published: October 2005

Humpback whales were exposed to the playback of humpback song, social sounds, Alaskan feeding call, artificially synthesized sounds, and blank tape control with a source level of 162 dB re: 1 μPA. Whales were observed and tracked from shore. A 20-min baseline observation preceded the 20-min sound presentation. The J-11 transducer was deployed at 7-m depth in water from 20 to 200-m deep. Acoustic velocity profiles conducted nearby indicated a uniform acoustic velocity field. The strongest reaction observed was the rapid approach response where whales changed course and approached the boat. The percentage of such responses varied with sound condition. Rapid approach responses were observed from whales up to a 1.5-km distance. Received levels can be approximated from the range between transducer and whale. The minimum received level that produced a strong reaction was probably between 100–115 dB, for 20 and 15 log R transmission loss models. These estimates could be improved as some playback experiments were recorded by a second vessel.
Vocalizations of blue and fin whales during a midocean ridge airgun experiment
Authors: McDonald Mark A. , Hildebrand John A. , Webb Spahr , Dorman LeRoy , Fox Christopher G.
Published: October 2005

Numerous seismic experiments are conducted each year in the deep oceans to study the nature of oceanic crust and to map the source of seismic signals associated with small earthquakes or volcanic activity. Whale vocalizations of the type associated with blue and fin whales are often recorded on the arrays of seafloor seismometers and hydrophones used for these experiments. These whale vocalizations are characterized from one such experiment conducted about 500-km offshore from Astoria, Oregon in August of 1990. The travel time differences and signal amplitudes from both direct and multipath arrivals across the seafloor seismometer array are used to locate the whales and predict the level of ship and airgun noise at the whale. Whale vocalizations were recorded during airgun operations and these vocalization patterns are compared to patterns recorded during times of relative quiet from the 12 days of data gathered in this experiment. Transient oceanic sound levels from transform fault earthquakes and seafloor volcanic activity are often louder than those produced by airguns.
Acoustics and synthesis of nasalization
Authors: Lin Qiguang , Flanagan James , Che ChiWei
Published: October 2005

In this paper acoustics and synthesis of nasalization is studied based on a comprehensive computer model of the vocal tract: TRACTTALK. TRACTTALK simulates the vocal-tract system in the frequency domain and derives the time-domain equivalent to produce sound output. It incorporates all important components of the system and decomposes the transfer function into its zero and pole parts. Such a decomposition enables one to accurately estimate poles and zeros of a nasalized sound. First, temporal trajectories of poles/zeros are examined as a function of the velopharyngeal opening, the presence of the nasal sinuses, and other articulatory parameters. This is in follow-up to previous work [Flanagan, AT&T Bell Labs. internal report (1983)]. The attempt is to systematically characterize the pole/zero pattern of nasalization for improving the performance of formant tracking and feature labeling algorithms. Secondly, synthesis of nasalization is described using TRACTTALK. Listening experiments are conducted to assess the relationships among perceived nasality, inclusion of the nasal sinuses, and the degree of the velopharyngeal opening. It is found, e.g., that inclusion of the nasal sinuses results in stronger perceived nasality. While the literature reports differing views on the role of sinuses in nasality, these results are consistent with the findings of Maeda [Proc. ICASSP 2, 911–914 (1982)]. Synthetic speech generated from the vocal-tract system will be demonstrated.
A diagnostic text-to-speech intelligibility test
Authors: Syrdal Ann K. , Sciacca Beki A.
Published: October 2005

A wider sampling of speech segments and contexts is required for adequately evaluating text-to-speech output than is typically used in standard intelligibility tests of human speech. The test developed expanded upon both the Diagnostic Rhyme Test (DRT) [W. D. Voiers, Speech Tech. (Jan/Feb.), 30–39 (1983)] and a TTS intelligibility test developed by van Santen [J. P. H. van Santen, Comp. Speech Lang. 7, 49–100 (1993)]. The featural system used to construct the test ensured that the most likely perceptual confusions were potential test items. One- and two-feature contrasts were tested in word-initial, word-medial, and word-final positions, in stressed and unstressed syllables. Vowel, consonant, and consonant cluster contrasts plus insertions and deletions were tested. Test items were presented in semantically anomalous sentences (e.g., ‘‘Happy mimes dance the book.’’) and were controlled for familiarity and verb transitivity. Testing was automated and conducted interactively with individual subjects who received no feedback on their performance. Results indicate the test was a useful diagnostic tool as well as evaluation technique.
Internal waves and matched-field processing
Authors: Jackson Darrell R. , Ewart Terry E.
Published: October 2005

The performance of matched-field processing is degraded due to randomness of the propagation medium. With a vertical array, this degradation takes the form of fragmentation and wandering of the peaks (mainlobe and sidelobes) in the range-depth ambiguity surface. The resulting errors in localization are characterized in terms of the rms processor output. Simulations and theory specialized to the cw Bartlett processor are used. First, the case of an ocean waveguide with a quadratic average sound-speed profile and vertically stationary sound-speed fluctuation statistics is examined. Next, approximations are introduced so that a relatively simple analytic model can be abstracted from the theory. This model is checked against Monte Carlo PE computations that avoid some of the simplifying approximations. The simple model contains scaling rules for processor performance as a function of frequency, array length, and medium vertical correlation length. In general, the effects of internal waves become more important as frequency increases, array length increases, medium correlation length decreases, and range increases. The processor is predicted to be most sensitive to internal-wave mismatch for sources that are in convergence zones. Finally, the analytical model is compared to Monte Carlo PE computations using oceanic realizations obtained from a realistic dynamic internal wave model.
The tomographic inverse beamforming (TIBF) solution—A new matched-field algorithm
Authors: Wilson James H.
Published: October 2005

The recent at-sea, real-time signal detection and tracking performance of the plane-wave solution to the inverse beam forming (IBF) integral equation (Wilson, 1983; Nuttall and Wilson, 1990) has shown significant (5 to 12 dB) gains compared to operational sonar systems and other adaptive processing methods. The Fourier integral method (FIM) (Nuttall and Wilson, 1990) was thought to be the ‘‘spikiest’’ solution to the IBF integral equation, that is also linear in the covariance matrix. A standard inverse technique (Backus and Gilbert, 1968) used in tomography has recently been applied to the IBF integral equation, and two new theoretical results have been obtained. First, the plane-wave solution, called the least-squares Wilson integral method (LSWIM), agrees with FIM only at the array design frequency, and is spikier or more ‘‘delta function like’’ than FIM below array design frequency. Second, the non-plane-wave or matched-field solution was obtained by allowing the measured data vector (covariance matrix) in the Backus–Gilbert inverse method to have two discrete indices instead of the usual one index. This work was performed during the analysis of Outpost SUNRISE data for the purpose of enhancing sonar detection and tracking performance, but has also a more general application in acoustical oceanography. [Work supported by AEAS.] a)On temporary leave from Neptune Sciences, Inc.
Track-before-detect matched-field processing
Authors: Baxley Paul A. , Williams Robert Bruce , Hodgkiss William H.
Published: October 2005

Matched-field processing (MFP) is well-suited for tracking applications because of its inherent source localization capability, as demonstrated by Wilmut etal. [J. Acoust. Soc. Am. 93, 2374 (A) (1993)]. If exact track determination is not an objective, improved detection at a low signal-to-noise ratio may be obtained using a simple track-before-detect technique that averages range-shifted MFP ambiguity-surface snapshots, with the range shift being determined by an assumed range rate. After searching through all candidate range rates, the signal function is approximately reconstructed in the average surface corresponding to the correct range rate. If peak-to-sidelobe relationships in the signal function vary little between snapshots, both the sidelobes and the main peak are maximized in the average surface for the correct range rate; otherwise, only the main peak is maximized. In either case, this maximization provides a detection clue along with an estimate of range rate. This detection enhancement at low signal-to-noise ratios is demonstrated via simulations for a 48-element full-water-column vertical array in a thickly sedimented shallow-water environment (500-m water depth) typical of the southeastern Mediterranean sea. A 50-Hz source moving at constant range rate and source depth was simulated using a normal mode program, while noise samples were obtained using a PE-based shipping noise model and the HITS II shipping distribution database.
Scattering function description of a shallow water channel
Authors: Cable Peter G.
Published: October 2005

The shallow water channel is considered as a random, time-varying linear filter. The sources of temporal variation of channel properties considered are source and receiver motion and the motion of the surface (that is, wind waves and swell). Using an energy flux description for acoustic propagation, after Smith, Weston, and Brekhovskikh, and employing Smith’s theory of coherence in multimode propagation, an explicit formulation of the scattering function for a shallow water channel has been obtained. The scattering function description seems suited to a mid or high frequency (5–20 kHz) description of the shallow water channel. The conditions necessary for the scattering function description, namely that the channel be wide-sense stationary with uncorrelated scatterers (WSSUS), are derived and discussed. Specific examples of the scattering function for different channels will be presented and discussed.
A comparison of three concert halls using impulse response spectrograms
Authors: Kleiner Mendel , Falk Patrik , Olsson Björn
Published: October 2005

Three concert halls, Symphony Hall (Boston), Concert Hall at Otis A. Singletary Center for the Arts (Univ. Kentucky, Lexington), and Konserthuset (Gothenburg, Sweden) have been investigated. The floor plans and sections of these halls are fundamentally different as are the scattering properties of the walls and ceilings of the halls. Impulse responses were recorded in a number of positions in each hall. These impulse responses were then analyzed using FFT and Wavelet spectrograms to study to what extent the obvious geometrical differences could be traced in the impulse responses. The spatial distribution of the sound in the halls was studied using a ‘‘running’’ short-time interaural cross-correlation technique based on the impulse responses recorded using a dummy-head. Results show that the wavelet spectrogram yields graphs which may be slightly easier to analyze than conventional FFT spectrograms. The expected differences due to geometry are visible in the spectrograms. The short-time interaural cross-correlation graphs add information which also agrees with expectations.
Text analysis for speech synthesis
Authors: Church Kenneth Ward
Published: October 2005

Text analysis is a catch-all term for a range of tasks such as tokenizing the input text into words and sentences, assigning parts of speech identifying clitics, parsing phrasal verbs, identifying and expanding abbreviations, dates, fractions, and amounts of money, and so on. Text analysis is important for speech synthesis for two reasons. First, word pronunciation sometimes depends on usage: I can be a pronoun or a Roman numeral, wind can rhyme with ‘‘bind’’ of ‘‘binned,’’ Dr. can be ‘‘doctor’’ or ‘‘drive,’’ 2/3 can be ‘‘two thirds’’ or ‘‘February third,’’ or ‘‘two slash three.’’ A second, equally important reason for text analysis is that its results will be used to modulate the pitch, timing, and amplitude of the speech so as to present the text’s message clearly. For example, the function word ‘‘that’’ should be cliticized (reduced) in certain usages (e.g., as a subordinating conjunction: ‘‘It is a shame that [schwa] he is leaving’’) but not in other usages (e.g., ‘‘Did you see THAT [no schwa ]?’’). If a synthesizer could reliably make such distinctions, it might sound a little more like it knows what it is talking about (and that it cares).
Radiative transfer and multiple scattering of diffuse ultrasound in polycrystalline media
Authors: Turner Joseph A. , Weaver Richard L.
Published: October 2005

A model for the multiply scattered incoherent field in a continuous polycrystalline elastic medium is presented. Unlike a previous development based upon energy and flux conservation considerations [J. A. Turner and R. L. Weaver, J. Acoust. Soc. Am. 93, 2312 (A) (1993)] for a medium containing discrete random scatterers, the present model has been developed from the wave equation and first principles. Appropriate ensemble averaging of the wave equation leads to Dyson and Bethe–Salpeter equations that govern the mean Green’s function and the covariance of the Green’s function, respectively. These equations are expanded for weak heterogeneity and equations of radiative transfer are obtained. The result is valid for attenuations that are small compared to wave number: α/k≪1. Polarization effects are included, as before, through five elastodynamic Stokes parameters, one longitudinal and four shear. The theory is applied to a statistically homogeneous cubic polycrystalline half-space immersed in a fluid and illuminated by a plane wave. Results on the angular and temporal dependence of backscattered intensity are presented and compared with the predictions of a single-scattering theory. It is anticipated that this approach may be applicable to microstructural characterization through the study of the time, space, ultrasonic frequency, and angular dependence of multiply scattered ultrasound in elastic media. [Work supported by NSF.]
Guided waves in a fluid–solid bilayered plate
Authors: Yapura C. L. , Kinra V. K.
Published: October 2005

Consider a fluid–solid bilayer of infinite extent with the x3 axis perpendicular to the bilayer and the material axes coinciding with the x1, x2, and x3 axes. The fluid is assumed to be elastic (and isotropic) while the solid is assumed to be elastic and orthotropic (i.e., with nine independent elastic constants). Consider a plane wave propagating in the x1 direction with the particle motion confined to the x1-x3 plane and plane strain conditions in the x2 direction. There are six boundary conditions: zero normal and shear stresses at the traction-free boundaries, zero shear stress and continuity of normal displacements, and normal stresses at the interface. The dispersion equation is obtained by setting the determinant of the resulting six-by-six matrix to zero. Numerical results in the form of phase velocity, group velocity, and mode shapes are presented for the case of a water/graphite-epoxy bilayer. Several interesting features are observed and discussed. The physics underlying these phenomena has been explored by studying the mode shapes at (and in the vicinity of) the frequencies of interest. [Work supported by Texas Advanced Technology Program.]
Some structural acoustic features of multilayer composite plates
Authors: Kim M. , Hwang Y. F.
Published: October 2005

This paper discussed the propagation of free waves and the vibroacoustic response of a multilayer composite plate subjected to a point-force excitation. The dispersion characteristics for various modes of wave propagation as a function of geometrical configuration, elastic properties, and material loss factor are discussed. Acoustic radiation into water from a composite plate subjected to a point force acting on its dry (air) side has been evaluated. Numerical examples focus on a three-layer (elastic/viscoelastic/elastic) sandwich plate with a variety of different elastic/viscoelastic material properties (elastic constants, damping) and thicknesses. The advantages and disadvantages of a sandwich plate as compared to a homogeneous plate of equal flexural rigidity are also discussed. [Work supported by ONR.]
Optimization of acoustical treatments with respect to dynamic compliance and static deformation under load
Authors: Kerwin Edward M. , Martin Nathan C. , Zimmer Jeffrey A. , Doughty Jeffrey A.
Published: October 2005

This paper presents a method of organizing information on two important performance measures of an acoustical treatment or element whose dynamic compliance and total displacement under static loading are of concern. The method is simple but quite general, and allows one to select the optimum treatment from a set of candidates, or to modify and optimize a given candidate. The two normalized performance metrics are the unit-volume dynamic compliance q, and a unit thickness-deformation parameter V=ε/q, where ε is the static thickness strain under load. The optimization process utilizes these unit-volume parameters under the assumption that the required total dynamic compliance qtot will be specified, although its numerical value need not be known ahead of time. In this case it follows that V is always proportional to the total thickness and total deformation under load. In addition the V−q presentation has proven helpful in developing physical insight into the behavior of various compliant treatments. [Work supported by Office of Naval Research.]
Material tailoring of structures to achieve a minimum radiation efficiency
Authors: Naghshineh Koorosh , Koopmann Gary H. , Belegundu Ashok D.
Published: October 2005

A strategy is developed for designing structures that radiate sound inefficiently in light fluids. The problem is broken into two steps. First, given a frequency and overall geometry of the structure, a surface velocity distribution is found that produces a minimum radiation efficiency. This particular velocity distribution is referred to as the ‘‘weak radiator’’ velocity profile. A finite element adaptation of the integral wave equation is combined with the Lagrange multiplier theorem to obtain this surface velocity distribution. Second, a distribution of Young’s modulus and density distribution is found for the structure such that it exhibits the weak radiator velocity profile as one of its mode shapes. Extensive use of structural finite element modeling as well as linear programming techniques is made to find this distribution. The result is a weak radiator structure. When compared to a structure with uniform material properties, the weak radiator structural response is found to exhibit lower wave-number content in the supersonic region. The effect of modal overlap on the performance of the weak radiator structures is found to be negligible. The example of a simple beam radiating in a rigid baffle is used for the purpose of illustration.
Composite cylinder cross section tailoring for radiated noise reduction
Authors: Ratcliffe Colin P. , Crane Roger M. , Santiago Armando L.
Published: October 2005

This paper presents the results of an ongoing investigation into the reduction of transmitted noise for underwater cylindrical structures. A reduction in the radiated self-noise of cylindrical structures, compared with the conventionally utilized aluminum structures, was undertaken, investigating the use of composite materials with varying cross sections to meet the specified requirements. The cross sections investigated included several variations of a state-of-the-art triple skin construction, along with monolithic, constrained layer and a semi-debonded cross section. Cylinders have been fabricated and tested, comparing the dynamic vibration properties of the forced vibrations in air of the composite scaled cylinders to the baseline aluminum. The modal analysis determined mode shapes, natural frequencies, and damping loss factors. These were then tested in reverberant conditions under water to assess their acoustical performance. The in air and underwater tests were compared to identify similarities and differences between force excitation and acoustic excitation. The comparison showed where in air tests can be used as an aid to estimating underwater performance. The results also highlighted where in air tests are inadequate for predicting underwater behavior. The effect of the cross-sectional design for the tailoring of the acoustic signature will be discussed.
Exploratory materials development for towed array sensor systems
Authors: Capps Rodger N.
Published: October 2005

Extended towed array sensor systems are used for geophysical sensing and exploration in the petroleum industry, and for detection of submersible objects in naval applications. Many of the polymeric materials considered for use in towed array hoses either did not possess the necessary aging and weathering resistance; provided satisfactory self-noise performance at higher temperatures but were unacceptable in cold water; or experienced changes in self-noise through fill-fluid permeation and chemical reaction. There has been a need to develop and evaluate new classes of elastomers for use as hose wall materials. Array self-noise performance can also be improved through proper selection of polymers for use in vibration isolation modules for low-frequency towline excitation. Thermoplastic elastomers offer significant advantages over other types of elastomers in cost and ease of processing. Results are presented for both conventional elastomers and thermoplastics to show how these materials can be selected for the proper combination of Young’s modulus and internal loss, tensile properties, ozone and weather resistance, resistance to swelling and permeation by seawater and fill fluids, adhesion to reinforcing members, for fabrication and evaluation as acoustic modules. Use of thermoplastics for vibration isolation modules is also discussed. [Work supported by NAVSEA PM 0425.]
Development of a new rigid composite for high-frequency sonar window applications
Authors: Thompson C. M. , Ting R. Y. , Jenkins L. L. , Chiou C. C.
Published: October 2005

Successful operation of high-frequency sonar arrays requires an acoustic window that not only has a minimal interference with the acoustical signal but also is sufficiently rigid to protect the electronics from arctic ice penetration. Current designs of the window materials call for composite materials of epoxy containing either glass or Kevlar reinforcements. Those composites have unacceptably high insertion losses and beam pattern distortion. A new window material has therefore been developed based on a bromine-modified epoxy resin. The sound speed and the density of the composite were controlled by the bromine content and by using a soft microballon. The ‘‘Spectra’’ reinforcement fibers were used for meeting the strength requirement. Finite-element calculations shows that a three-layer structure of 1:3:2 Spectra/microballon/Spectra composite design should optimize the impact strength of the material while maintaining the acoustical performance. Samples of this new composite were fabricated and their mechanical properties evaluated, including the Izod impact strength. Insertion loss of test panels was measured in the USRD ATFI facility. The results of these tests will be presented for discussion. [Work sponsored by NAVSEA.]