bluuebunny/crossref_metadata_2025 huggingface dataset:
Matching borehole modes for slowness estimation using constrained optimization
Authors: Ekstrom M. P. , Randall C. J.
Published: July 2002

Propagating modes often appear in borehole acoustical measurements, providing information about the surrounding formation. A dipole source, for example, excites borehole flexural waves, whose low-frequency slowness asymptote is the formation shear slowness. However, because the flexural mode may be highly dispersive, and its spectral amplitude is small in the low-frequency regime, the shear slowness is difficult to estimate. Monopole sources excite Stoneley waves whose slowness is dispersive and a complex function of formation properties, likewise making formation slowness estimation problematical. Theoretical modal dispersion characteristics may be predicted over a prescribed frequency range by finding the poles of a simplified analytical borehole reponse function [Kurkjian, Geophysics 50, 852–866 (1985)]. This model is used to estimate formation parameters based on nonlinear optimization. A new spectral estimator (frequency-wave number) is first used to estimate the slowness dispersion for a measured array dataset [M. P. Ekstrom and C. J. Randall, J. Acoust. Soc. Am. 98, 2867 (1995)]. The parameters of an analytical model are then iteratively adjusted via a nonlinear optimization algorithm to minimize the error between model and estimated slownesses. Optimizer performance depends on the error function construct, constraints imposed, and variational knowledge of the forward model. Results of using monopole and dipole field data sets will be shown.
The dynamic response of complex structures using hybrid methods
Authors: Halliday Peter J. , Grosh Karl
Published: July 2002

Within many complex structures, there are regions which easily lend themselves to closed-form analytic solutions. A hybrid analytic-numeric formulation for the time harmonic structural vibration response of such structures is presented. The seamless inclusion of analytic solutions into the Galerkin finite element method is accomplished by using transition elements which couple the tractions between analytic and numeric solution regions. The main advantage of this formulation is to increase the overall efficiency of a model by eliminating regions of the structure from the computational domain. In this way, the total number of degrees-of-freedom will be reduced, which in turn reduces memory requirements and computational time. This allows for the analysis of higher frequency or more complex problems. One application is the study of systems comprised of structural members which are coupled at nonidealized joints. Using a discretization of the equations of elasticity for a joint, its response may be represented to a desired level of accuracy. This elasticity model is coupled to the reduced beam or shell theory producing an efficient model of the complete structure. The effect of the joint and the level of modeling detail for prediction of the time harmonic response are studied.
Three-dimensional noise-field directionality estimation from towed line-array data
Authors: Wagstaff Ronald A. , Newcomb J.
Published: July 2002

The ideal measurement tool to measure the three-dimensional arrival structure of the noise field is a high-resolution volumetric array sonar system. Unfortunately, such a system is not generally available. However, towed horizontal line arrays are available and can be used, even though they are far from ideal. The beam patterns of a line array are conically symmetric about the axis of the array. When the axis of a horizontal line array is tilted slightly from the horizontal, the vertical character of the beam cones can be used to discriminate between various vertical arrival angles. By combining this character with measurements made on several different towed array headings, an estimate of the three-dimensional directionality of the noise field can be obtained. An algorithm that uses such a technique on single and multiline towed array data to generate an estimate of the three-dimensional directionality of the noise field is described herein. Some results using measured data from a recent noise measurement exercise using a single-towed line array are presented and discussed. [Work supported by ONR and NRL.]
Active sonar coherence measurements of underwater scatterers and channels using a cross correlation process
Authors: Kisenwether James , Ricker Dennis
Published: July 2002

The concept of coherence is fundamental and quite important in all fields dealing with fluctuating quantities. A new method for measuring coherence based on the cross correlations of the tones of a multi-component waveform has been developed. The correlation terms which comprise the measure are samples of the time-frequency correlation functions (TFCF) of scatterers and channels. The measure has been used to characterize the time-frequency spread associated with scatterers and channels and represents the signal coherence. This paper will provide a review of scattering function representations and aggregate coherence measures as derived from a correlation matrix. The new coherence measure termed correlation mass will be defined. It will be shown that this measure can be decomposed into correlated components resulting from interaction with a scatterer and a channel. In other words the composite correlation is obtained by sampling the product of the scatterer and channel TFCF’s. Data from in-water experiments and digital sonar simulations will be presented which validates the linear systems model of the composite scattering process.
Source localization at very long ranges in the presence of large-scale spatial variability
Authors: Gresham Lisa C. , Nolte Loren W.
Published: July 2002

Large-scale spatial variability in the ocean environment results in uncertain sound-speed variations on the order of 10–15 m/s, a potentially significant factor in many ocean acoustic applications. The effect of this variability on source localization performance at a range of one megameter is investigated. The optimum uncertain field processor (OUFP) [A. M. Richardson and L. W. Nolte, J. Acoust. Soc. Am. 89, 2280–2284 (1991)], in its narrow-band and wideband forms, is introduced as an alternate and superior processor to the traditional Bartlett processor for this application. The Bartlett processor, which assumes the environmental parameters to be the average values, essentially ignores the large-scale spatial fluctuations. Optimally incorporating a priori information about the environmental and source parameters, as does the OUFP, makes this processor robust to uncertainty in these parameters and provides an upper bound on localization performance. Measures such as a posteriori distributions of source location, the probability of correct localization, and the standard deviation of range estimation error reveal that the spatial variability has a significant degrading effect on localization performance, the magnitude of which is dependent on the source frequency. Results are discussed for 25- and 75-Hz sources as well as their coherent and random combinations. [Research supported by ONR (Ocean Acoustics).]
Analytical and experimental comparison of azimuth/range/depth bias errors in MFP source localization using vertical and tilted arrays
Authors: D’Spain Gerald L. , Hodgkiss William S. , Murray James J. , Schey Phil W. , Booth Newell O.
Published: July 2002

During a recent shallow-water (200-m) experiment west of San Diego, two 120-m aperture hydrophone arrays were deployed from the R/P FLIP. One array was oriented in the vertical direction, while the second was deployed at a 45-deg tilt. A set of 13 tones, from 49 to 388 Hz, were transmitted from a 60-m-deep towed source traveling cross slope over a 6- km track. At CPA, the source was at endfire to the horizontal aperture of the tilted array. The data from both arrays were used to perform matched- field processing (MFP) for source localization in range and depth using replica vectors generated from a range-independent environmental model. In addition, the data from the tilted array were used to simultaneously localize the source in azimuth. The range and depth MFP biases of the two arrays agree quite well with one another and with analytical predictions from previous work. Here, those results are extended to successfully predict the offset bias in the MFP azimuth results, which reaches a maximum of 20 deg at endfire. [Work supported by ONR, Code 321(US).]
Matched-field processing of multi-tone acoustic signals in shallow water with a horizontal line array
Authors: Schey Phil , Booth Newell O. , Dorrance Gary , Aburto Al , Hodgkiss William S.
Published: July 2002

Matched-field processing results are presented which compare the resolution (in range, depth, and azimuth) and peak-to-sidelobe ratios obtained using a bottom-mounted horizontal line array and a tilted vertical line array. The arrays were deployed in the May 1996 shallow water evaluation cell experiment (SWellEx-96) carried out west of Point Loma in 200-m water of complex bathymetry. Results are presented for a towed source transmitting signals between 49 and 388 Hz at ranges between 0.7 and 6 km and at bearings between broadside and endfire. [Work sponsored by Office of Naval Research, Code 321(US).]
Acoustic field reconstruction using optical interferometry
Authors: Mattei Christophe , Adler Laszlo
Published: July 2002

Acousto-optical measurements inside transparent media is a well-known noninvasive method for acoustic field probing. The laser interferometric detection technique provides a noncontact, local, and quantitative measurement of pressure or dilatation fields in transparent media [X. Jia, Ch. Mattei, and G. Quentin, J. Appl. Phys. 77, 5528–5537 (1995)]. The optical phase shift of a probe beam passing through an ultrasonic beam is detected using a Mach–Zender interferometer and is related to the amplitude and phase of the pressure field. Since the optical phase shift integrates the pressure field over the optical beam pathlength, this technique assumes a constant acoustic field along the laser beam path. In order to obtain a complete mapping of the acoustic field, as required in many applications, e.g., transducer characterization, we propose the use of tomographic techniques associated with the interferometric detection which permits a reconstruction of the acoustic field in the acoustic beam cross section from a set of projection data. The time variation of the pressure field in a cross section as well as the amplitude and phase spectra can be displayed. The mapping of the near pressure field (1 mm) of an ultrasonic transducer is achieved using this technique and other examples of field characterization are presented. a)Permanent address: G.P.S., Univ. Paris 7, CNRS Ura No. 17, 2 place Jussieu, 75251 Paris Cedex 05, France.
Ultrasonic enhancement of fiber-optic biosensors
Authors: Zhou Chonghua , Pivarnik Philip , Rand A. Garth , Letcher Stephen
Published: July 2002

An enhanced fluorescent fiber-optic biosensor system using ultrasonic concentration of particles and cells has been developed and applied in the detection of Salmonella typhimurium. A biosensor test chamber also serves as an ultrasonic standing-wave cell that allows microspheres or cells to be concentrated in parallel layers or in a column along the axis of the cell. A fiber probe along the axis of the cell delivers laser excitation to fluorescent dye molecules and collects the fluorescent signal. In a ‘‘sandwich’’ assay, the dye molecules are bonded to Salmonella antibodies that, in turn, attach themselves to Salmonella cells that have been captured by unlabeled antibodies that have been immobilized on the surface of polystyrene microspheres. This entire structure can be manipulated acoustically. The most effective procedure is a uniform stratification of the complexes in a plane-wave field followed by a concentration along the axis of the cell by a Gaussian-profile field. The increase in the fluorescent signal, which can be an order of magnitude, indicates the presence of Salmonella. [Work supported by USDA/NRICGP and by the URI Partnership for Sensors and Surface Technology.]
Practical considerations in methods of rating room noise
Authors: Goodfriend Lewis S. , Alexander Martin
Published: July 2002

Since 1955, the NC curves have been used with considerable success to specify and rate room sound quality. Although newer rating schemes have appeared, and in several areas supplanted the NC curves, many practitioners still use and prefer the old scheme. The newer RC and NC-B rating techniques exhibit one aspect which makes them both problematic in practical use. They both attempt to include in one rating number a further ‘‘quality’’ factor of the sound. While it is simple to establish the goal that room noise should meet a specific RC (or NC or NC-B) value, with a specific curve shape (neither ‘‘rumbly’’ or ‘‘hissy’’), it may be more difficult to evaluate whether a space meets the criteria. If the goal is to provide a background sound level of RC-40, or NC-B 40, does a room which is RC-35R meet the criteria, or fail it? Is an NC-B 30R better or worse than an NC-B 40? These questions are faced by the practitioner on a regular basis, and is one of the factors which makes the NC scheme more acceptable. When the room noise is ‘‘rumbly’’ or ‘‘hissy,’’ or when it is modulated or cyclic, or contains pure tones, a statement can be made to indicate this. The practitioner must first be able to specify the measurable physical quantities without ambiguity. Where there are sound quality factors present, they may indicate that an otherwise acceptable spectrum is unacceptable. Detailed background material is included along with examples, including those from the literature. [See NOISE-CON Proceedings for full paper.]
Time-dependent radiation and scattering from elastic plates
Authors: Feit David , Carroll Gerard P.
Published: July 2002

The far-field time-dependent radiation pattern for an elastic plate excited by a transient point or line load is calculated. Comparisons are made between results calculated by both Timoshenko-Mindlin and classical plate theories. Such results have been obtained by others, but by viewing the results as a function of time and in a polar angle plane, one is better able to visualize and describe how the directional beam patterns are generated. The supersonic waves generated by the transient excitation give rise to a radiated field appearing as a precursor (with respect to the time of arrival of the sound emanating from the drive point) in a direction perpendicular to a Mach cone. The cone angle is determined from the ratio of the sound speed in the fluid to that of the flexural wave traveling with a velocity characteristic of the frequency at which the transient force spectrum has a peak. In those cases where an inhomogeneity, such as a dynamic system is attached to the plate, the time-dependent scattering pattern, in response to an ensonifying pulse, allows one to image and estimate the parameters of the scatterer.
High-frequency backscattering enhancements for thick truncated cylindrical shells in water at oblique incidence
Authors: Morse Scot F. , Marston Philip L. , Kaduchak Gregory
Published: July 2002

Various authors have shown that the backscattering by a finite thin cylindrical shell at oblique incidence is enhanced when resonance conditions are met for the propagation of a leaky wave on the shell [see, e.g., M. L. Rumerman, J. Acoust. Soc. Am. 93, 55–65 (1993)]. To explore the backscattering enhancements relevant to high-frequency detection, impulse response measurements were carried out for slender thick cylindrical shells using a broad bandwidth PVDF sheet source, for tilt angles ranging from broadside to end-on incidence. These measurements reveal large backscattering enhancements beyond the shear wave cutoff angle, which extend to near end-on incidence in the coincidence frequency region. A simple approximation for the phase velocities of several surface waves is used to identify the underlying mechanisms. A broad enhancement feature is shown to result from the axial propagation of the supersonic a0 leaky Lamb wave. The associated meridional ray radiates a backward directed wavefront having a vanishing Gaussian curvature. Also observable are what appear to be resonance loci associated with the helical propagation of the subsonic a0−. [Work sponsored in part by the Office of Naval Research and by the ARL:UT Independent Research and Development Program.]
Statistical change detection using nonlinear models
Authors: Parker Gene
Published: July 2002

An important objective in monitoring mechanical and other systems is the detection of changes in the underlying dynamics governing system behavior. Statistical change detection (SCD), or change-point detection, can play a crucial role in the early detection of small changes in mechanical systems. The primary challenge is to detect changes manifest in very small deviations in the statistical behavior of the observations. Statistical change detection algorithms act as novelty detectors, obviating the need to collect examples of all possible fault signature patterns for the purpose of training pattern classifiers. With respect to SCD, the use of nonlinear models can provide useful benefits. In particular, detector performance may be enhanced through the use of more appropriate model structures, such as when processing nonlinear and/or non-Gaussian data. Second-order statistics are, in general, adequate when data being fitted are Gaussian. When data are non-Gaussian, or represent the output of a nonlinear process, higher-order statistics (HOS) (e.g., bispectrum, trispectrum, etc.) may be more useful in characterizing a process. An attractive aspect of the SCD approach is its ready extensibility to include higher-order statistical moments, where necessary, to exploit additional information in the data. Since HOS are polynomial functions of the observed data, polynomial neural networks are well suited for the implementation of signal detectors based on HOS. In this paper, the performance benefits arising from the use of nonlinear models in SCD algorithms are considered. [See NOISE-CON Proceedings for full paper.]
Matched-field source tracking with SWELLEX-1 data
Authors: Tantum Stacy L. , Nolte Loren W. , Krolik Jeffrey L.
Published: July 2002

The optimal approach to tracking a moving source in an uncertain environment is one which incorporates a priori knowledge about both the continuity of the propagation environment and the nature of the source movement. The optimum uncertain field tracking algorithm (OUFTA) [S. L. Tantum and L. W. Nolte, ‘‘Tracking and localizing a moving source in an uncertain shallow water environment,’’ J. Acoust. Soc. Am. (submitted)] extends the optimum uncertain field processor (OUFP) [A. M. Richardson and L. W. Nolte, J. Acoust. Soc. Am. 89, 2280–2284 (1991)] to include modeling of the source motion as a Markov process. This differs from the suboptimal approach which performs a series of independent source localizations and then combines the results to estimate the path taken by the source. The performance of the OUFTA and the suboptimal approach is evaluated using the SWELLEX-1 data collected off the San Diego coast. Results using the SWELLEX-1 data are also presented which show how this optimal philosophy can be used to guide the modification of some popular beamformers, such as the minimum variance adaptive beamformer with environmental perturbation constraints (MV-EPC) [J. L. Krolik, J. Acoust. Soc. Am. 92, 1408–1419 (1992)], to incorporate source motion. [Work supported by ONR.]
Speech intelligibility in rooms
Authors: van der Werff Johan
Published: July 2002

Speech is a method of communication between two or more minds. The actual forming and understanding of the message are in the physiological domain. The transmission of the speech by sound waves is in the physical domain. Only the latter can be controlled by means of acoustical engineering. The relevant processes in the physiological domain can be contained in the term ‘‘proficiency of speaker and listener.’’ The relevant processes in the physical domain can be contained in the term ‘‘information loss.’’ This paper will deal with: (a) the underlying factors of information loss and assessing them by measurement and calculation as accurately as possible; (b) the means and limitations of quantifying the information loss: ALcons, STI, etc.; (c) for the calculation of the information loss, an adaption of the ‘‘classic’’ Peutz equation, suitable for data generated by contemporary computer programs, will be given; (d) the accuracy of the data, with some examples like comparison of results from word lists, STI measurement and ALcons calculation; (e) results in extreme situations like a large, closed sports stadium with a 9-reverberation time and a tunnel with a length of 1 k; (f) design considerations for sound systems regarding the proficiency of speaker and listener. [See NOISE-CON Proceedings for full paper.]
Some comparison of C50 with other speech-intelligibility predictors
Authors: Marshall L. Gerald
Published: July 2002

STI (including the abbreviated version, RASTI), %Alcons and the 50-ms early-to-late sound energy ratio (C50) are well known as predictors of speech intelligibility. Among these, C50 is the least used both as a design equation and for room-acoustic and sound-system measurements, and its performance as a predictor of intelligibility is probably the least well validated. To better understand the performance of C50, data from miscellaneous sources are examined with respect to: (1) correlations between the predictors; and (2) their ability to predict actual intelligibility from measurements and from calculations using statistical-behavior formulas. Relationships are shown between calculated values, between calculated and measured values, and between measured values for the three predictors.
Calculated pulse widths and spectra of sonoluminescing nitrogen and argon bubbles
Authors: Moss William C. , Clarke Douglas B. , Young David A.
Published: July 2002

By modeling the hot compressed gas in a sonoluminescing bubble as a thermally conducting plasma it is shown that the measured picosecond pulse widths are due to electron conduction and the rapidly changing opacity of the plasma at the onset of ionization. The model shows that these mechanisms are also responsible for the absence of an ‘‘afterglow’’ subsequent to the sonoluminescent flash, as the hot bubble expands and cools. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains only argon, in agreement with a recent theoretical analysis. [This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]
Detection and discrimination of amplitude modulation
Authors: Sheft Stanley , Yost William A.
Published: July 2002

Amplitude-modulated stimuli have been used in psychophysical experiments to address a variety of issues including intensity discrimination, frequency and temporal resolution, and roughness perception. Thresholds for detecting amplitude modulation (AM) and discriminating a change in AM rate or depth are the basis for much of this work. Early work emphasized the role of the peripheral excitation pattern in AM detection. More recent studies have often concentrated on the temporal aspects of modulation coding. With sinusoidal AM, the change in detection threshold as a function of modulation rate is commonly interpreted as a temporal modulation transfer function (TFTF) and has been used to assess temporal resolution. Stimulus parameters that affect the TMTF include carrier spectrum, level, and gating characteristics. The effects of these parameters and implications for AM processing will be reviewed. This current work measures the ability to discriminate a change in either modulator phase or envelope regularity as a function of AM rate. Irregular AM was generated with frequency modulation of a sinusoidal envelope modulator. Results from these experiments will be discussed in terms of auditory processing of modulation as characterized by the TMTF. [Work suported by NIH.]
Coding of amplitude modulation in the central auditory system
Authors: Schreiner C. E. , Bedenbaugh P. , Cheung S. , Bonham B. , Taha S. , Nagarajan S.
Published: July 2002

The coding of temporal information, as reflected in the response to amplitude-modulated signals, changes dramatically between the auditory midbrain and the auditory cortex. Most neurons in the inferior colliculus are tuned to specific AM rates between ten and several hundred Hertz. This tuning is expressed either in their capacity to phaselock their response to the AM rate or by their overall response magnitude. In the primary auditory cortex, this capacity is largely reduced to AM rates below 20 Hz. Other cortical fields show even lower AM limiting rates and usually only one field (the anterior field in the cat, and the posterior field in New World monkeys) shows a slightly higher following capacity. The consequences of this overall reduction in repetition coding capacity for the representation of temporal properties of complex signals, such as fundamental frequency or details of the temporal envelope, are profound. A second property of the temporal coding in the midbrain, its systematic distribution along the isofrequency-axis of the nucleus, is also diminished or absent at the cortical level. Potential origins of this transformation in temporal coding and consequences for the perception of temporal information will be discussed. [Work supported by NIH R01-02660.]
Modeling auditory processing of amplitude modulation
Authors: Dau Torsten
Published: July 2002

A popular model of the processing of amplitude modulation (AM) [Viemeister, J. Acoust. Soc. Am. 66, 1364–1380 (1979)] consists of a bandpass filter, a rectifying nonlinearity, a low-pass filter, and a decision device. The low-pass filtering (or integration) stage was intended to simulate the temporal resolution limit by attenuating rapid changes in the envelope of the signal. Fleischer [Acustica 47, 155–163 (1981)] developed a model describing the influence of the inherent fluctuations within a noise carrier on the detectability of added modulation. The modulation spectrum was weighted by a certain factor which also essentially represented a low-pass characteristic. In a recent modeling approach [Dau et al., submitted to J. Acoust. Soc. Am. (1997)], a modulation filterbank replaced the low-pass filter, to analyze the envelope fluctuations of the stimuli in each peripheral auditory filter. The inclusion of a modulation filterbank was motivated by results from several studies on modulation masking which provided evidence for frequency selectivity in the modulation-frequency domain. In addition, the role of peripheral filtering for the processing of amplitude modulation, the envelope statistics, and the spectral distribution of modulation power in the modulation spectrum are discussed.
Quantitative verification of laser-modulated phase-stepping digital shearography for monofrequency vibration measurement
Authors: Bard Benjamin A. , Wu Shudong , Tittmann Bernhard R.
Published: July 2002

An offspring of holographic and shearing interferometry, digital shearography is a full-field, optical technique. Its full-field nature allows examination of approximately a one square foot area, requiring no scanning. In its usual implementation for vibration studies, time-averaged speckle correlation fringes are formed. While sufficient for observing mode shapes, these fringe patterns carry several disadvantages when quantitative interpretation is attempted. Digital shearography, combined with stroboscopic laser illumination and optical phase stepping, overcomes these limitations. The differential displacement field during monofrequency vibration is calculated independently at each point, and is no longer dependent upon fringe interpretation. The system, a new combination of several well-established techniques, has not been validated in either the optics or acoustics literature. The goal of the current work is to verify the technique via side-by-side measurements made with shearography and laser vibrometry. A simple cantilever beam is vibrated at several resonance and antiresonance frequencies and examined by both methods. Analysis techniques for comparing velocity output of the vibrometer to differential displacement output from shearography will be discussed. Agreement between the two systems is excellent, demonstrating the potential usefulness of this new method. [Work supported by the Penn State University Applied Research Lab.]
A new trigonometric functions set for predicting plate bending, using the hierarchical finite element method
Authors: Beslin Olivier , Nicolas Jean
Published: July 2002

This communication proposes a new hierarchical functions set to predict flexural motion of platelike structures in the medium-frequency range. This functions set is built from trigonometric functions instead of polynomials as classically encountered in the literature. It is shown that such a trigonometric set presents all the advantages of a classical hierarchical polynomials set and additional ones which are of interest if very high-order functions are desired to be used. It is stated that this new trigonometric set can be used at very high orders, up to 2048, without taking care of computer roundoff errors, while the polynomials set fails at order 46 because of the limited numerical dynamic of computers. This trigonometric set can be easily implemented on a computer. It does not require quadruple precision precomputed arrays. Only a very low number (which do not depend on the function order) of basic operations is needed when calling such functions. Moreover, it is shown that this trigonometric set presents a better convergence rate than polynomials when predicting high-order natural flexural modes of rectangular plates with any boundary conditions.
Convergence analysis of p-version FEM on vibration problem
Authors: Cote Andre F. , Charron Francois , Atalla Noureddine
Published: July 2002

The p-version FEM has proven to be very efficient for static problem. An analysis of the possibilities of this method on vibration problem is presented. The method is first explained and compared with the classic h-version FEM. Then, convergence indicators are defined and a convergence analysis is performed. To follow the performance on diverse situations, three types of plates are used as test problems: a rectangular plate, an L plate, and a stiffened plate. It is shown that the p-version outperforms the classic h-version by an average factor of 5 (the number of converged eigenvalues, for the same number of DOF, is five times greater). [Work supported by NSERC and FCAR.]
Extracting modal wave numbers from data collected in range-dependent environments
Authors: Kessel Ronald T.
Published: July 2002

Properties of the seafloor can be determined from the horizontal wave numbers of the normal modes of sound propagation. The wave numbers can be extracted from the harmonic sound field measured in range-independent media using a single hydrophone, by applying a Hankel transform to compute the wave-number spectrum from the field when either the source or hydrophone (not both) are towed [S. D. Rajan et al., J. Acoust. Soc. Am. 82, 998–1017 (1987), for example]. In range-dependent environments, the wave numbers vary owing to changes in bathymetry and geoacoustics, and this smears the wave-number spectrum, making the extraction of individual modes uncertain, if not impossible. This is particularly true for high-order modes which, penetrating more deeply into the sediment layers, provide more information about the sediments than low-order modes. A wave-number demodulation technique is derived from an adiabatic mode model whereby range-dependent wave numbers can be extracted from a considerably smeared spectrum. This not only extends the wave-number-based measure of seafloor properties to weakly range-dependent environments, but it provides a method for localizing a moving source in range-dependent shallow waters, simply by matching wave-number tracks in time with bathymetry maps.
America’s need for standards and guidelines to ensure satisfactory classroom acoustics
Authors: Lubman David
Published: July 2002

Architectural guidelines and standards for classroom acoustics are needed for the general population, as well as for special groupings such as hearing- and learning-disabled students, non-native listeners and talkers, and teachers with mild-to-severe hearing handicaps. Without specific guidelines, economic considerations or ignorance may tempt architects and school boards to use ‘‘standard commercial practices’’ for classroom construction such as ‘‘Noise Criteria’’ (NC) classifications. Proposed NC-40 ratings are unacceptable for many people in special groupings. An NC-40 classroom is sub-optimum for serious learning situations, even for the general population of children and adults. Needed acoustical guidelines can ensure adequately low noise and reverberation so that the speech-to-noise ratio and speech-to-reverberation ratio allow satisfactory communication and learning. Acoustical guidelines are also needed in connection with the growing use of classroom amplification to ensure that amplified speech is not used inappropriately, such as in reverberation-limited conditions or where inadequate sound isolation between adjacent classrooms produces distracting crosstalk. Guidelines can be developed with the cooperation of acousticians, architects, audiologists, school building officials, and government. Some of the costs for higher acoustical standards will be returned indirectly. Quiet classrooms may be a good investment for America.
Can noise levels at school gymnasia cause a hearing loss: A case study of a physical education teacher
Authors: Jiang Tao
Published: July 2002

There is mounting evidence that noise is widespread at schools. Poor acoustic conditions affect speech and academic performance. Noise can be detrimental to teachers. Recent research has found noise at schools can become a hazard to the hearing. Unacceptable noises at gymnasia have been documented. Nevertheless, cases are rare that teachers are at risk of noise-induced hearing loss (NIHL). Presented is a case study of a physical education (PE) teacher diagnosed with NIHL. The audiologic evaluation indicates a bilateral sensorineural hearing loss characterized by a typical noise notch. To rule out presbycusis, the ISO 1999 standard is utilized. Consequently, medical and audiological evaluations have confirmed his NIHL. To investigate its cause, a noise study was conducted in the gymnasium. The noise levels ranged between 72 and 119 dBA during classes. Dosimetry recorded LAeq 8h 90.8 dB(A) with the peak at 125 dB. The calculated dose exceeded the safety limit by 300%. Furthermore, to determine in situ noise levels of blowing whistles used by PE teachers, a real-ear analysis was performed using a probe microphone. The whistle noise reached 130 dB at the tympanic membrane. In conclusion, the teacher has developed a NIHL caused by hazardous noises associated with his teaching work. [See NOISE-CON Proceedings for full paper.]
Nonlinear interactions of acoustic, vorticity, and entropy modes, with applications to computational aero- and hydro-acoustics
Authors: Grace Sheryl M. , Pierce Allan D.
Published: July 2002

The paper deals with fluid dynamical disturbances governed by the full nonlinear set of equations for a compressible fluid with viscosity and thermal conductivity included with arbitrary Prandtl number. The field governed by these equations is regarded as being a set of five functions of space and time, these functions being the three fluid velocity components, the pressure, and the entropy. A projection operator formalism is defined which uniquely separates the five-component field at any instant into three component fields, labeled for convenience as acoustic, vorticity, and entropy modes. The equations coupling these can be developed to any order of nonlinearity, but the superposition principle applies regardless of order. Lighthill’s formulation of sound generated by flow falls easily out of the formulation without any intrinsic arbitrariness. Applications to computational aero-acoustics are discussed, with some numerical results for the case of sound generated by two adjacent line vortices.
The development of self focused pulses of nonlinear second sound in helium II from delayed edge waves
Authors: Krysac L. C. , Maynard J. D.
Published: July 2002

Second sound entropy waves in helium II are considered as a scalar temperature field imposed on an underlying counterflow velocity vector field. This unusual viewpoint offers a conceptual explanation of the form of nonplanar pulses of second sound, as well as a tool for understanding, and perhaps solving, the evolution of nonlinear pulses of second sound. A simple model of two point sources will be used to show how the large and negative finite amplitude nonlinearity near the phase transition of helium II is responsible for some of the observed features of the recently observed self-focusing of second sound.
A generalized reverberation model
Authors: LePage Kevin
Published: July 2002

A model for bottom and subbottom scattering is proposed which estimates the short time average of the received level as a function of the processing bandwidth and the channel characteristics. The model also estimates the degrees of freedom available in the received level as a function of time. The model describes how the backscatter from individual modes decorrelates as a function of time and processing bandwidth. For narrow bandwidths, modes interrogate the same bottom patches at large time, giving structure to the expected received level. Narrow-band signals also interrogate more roughness correlation lengths, yielding lower expected fluctuations about the mean. Results from the model are compared to experimental observations and conclusions are drawn regarding the validity of the proposed approach.
An algorithm to count fatigue cycles in an arbitrary loading waveform
Authors: Kendig R. P.
Published: July 2002

The purpose of this investigation is to introduce a different algorithm for counting fatigue cycles due to an arbitrary acoustic or vibration excitation. The scope of this study is limited to a mathematical analysis with comparisons to several standard fatigue counting methods. The proposed algorithm, based on the Hilbert transform, processes a time history representing the loading condition to generate the number of cycle-counts with their corresponding amplitudes. The approach is general, is accurate within any desirable degree of accuracy, and is amenable to modern signal processing. The utility of the algorithm is demonstrated through comparisons to standard fatigue cycle-counting practices. [See NOISE-CON Proceedings for full paper.]
Application of resonance acoustic spectroscopy to nondestructive evaluation of clad rods
Authors: Honarvar F. , Sinclair A. N.
Published: July 2002

The application of resonance acoustic spectroscopy (RAS) for the purpose of nondestructive evaluation (NDE) of various properties of a clad rod is investigated in this paper. RAS is the study of the resonances of an elastic object, which are excited by an incident wave, for characterization of the material properties of the elastic object. The equations for the backscattered pressure field from an elastic/viscoelastic clad rod at both normal and oblique incident angles are derived. Numerical studies show how RAS can effectively help in monitoring the variations of the cladding thickness and cladding delamination. Experimental measurements, conducted on copper-clad aluminum rods, are found to be consistent with numerical results obtained from the mathematical model. It is demonstrated that there exists a potential for using RAS for NDE and on-line monitoring of various properties of clad rods.
Modeling of signal spreads in shallow water for one-way, two-way, and two-way time-reversed signals
Authors: Preston John R. , Gauss Roger C.
Published: July 2002

Shallow-water broadband propagation modeling and time-series simulation was done for representative ocean environments. Simulations of two-way temporal signal dispersion for both time-forward and time-reversed transmissions are presented. The modeling effort used the OASES and ORCA models to simulate acoustic conditions from horizontal line arrays and omnidirectional sources in the 30 to 600-Hz frequency region. Two-way predictions are presented and compared to data results for several representative cases. Some sets of signals were time reversed and back propagated through several perturbations of selected experimental conditions to quantify signal decorrelation effects due to the environment. Additionally, the effects of water depth on pulse shape and spread are demonstrated for two hypothetical shallow-water cases. Comparisons with one-way time series measured during the Celtic Duet sea trial conducted off the Southwest Approaches in July 1992 are discussed. Results for one-way modeling in one hypothetical case for a sandy bottom show pulse spreads gradually increasing up to 2 s as depth is varied from 50 to 350 m and ranges are increased out to 18 km. [Work supported by ONR and NAWC.]
The art of handbell ringing
Authors: Ebling-Thorne Kathleen
Published: July 2002

The history and art of handbell ringing will be discussed. Members of the Westminster Concert Bell Choir will demonstrate some of the techniques used in modern handbell choirs, such as martellato, plucking, thumb damping, and four-in-hand ringing, as well as techniques for special effects, such as echo and gyro.
Comparison of traffic noise levels from various bridge/soundwall configurations
Authors: Greene Michael
Published: July 2002

Noise levels at receptor locations of varying distances and heights above a lake in Geneva, Switzerland were calculated. The traffic noise levels were computed for two bridge heights and six receiver heights. In addition, traffic noise levels for six distances (15-, 30-, 125-, 250-, 500-, and 1000-m) from the receptor to the near edge of the roadway were computed for each of the two bridge heights and six receiver heights. Four separate soundwall design scenarios were analyzed: (1) no soundwalls (base case); (2) two edge-of-shoulder plus one center divider reflective soundwalls, each 1 m in height; (3) two edge-of-shoulder reflective soundwalls, each 2 m in height; and (4) two edge-of-shoulder absorptive soundwalls, each 2 m in height. Comparison of the results shows that for all receptor distances and heights, noise levels would be lower for the 30-m-high bridge than for the 10-m-high bridge. This effect tends to diminish with receiver distance, however. The results also show that there are calculable and audible noise effect differences among the various antinoise barriers considered. For all receptor distances and heights, the soundwall design providing the highest degree of mitigation would be soundwall design alternative (4).
An affordable, acoustically transparent, two-dimensional, high-resolution, acoustic imaging array
Authors: Benjamin Kim , Powers James , Nussbaum Fred , Stevens Gerald
Published: July 2002

The design, fabrication, and measured results for a prototype, two-dimensional, ultrasonic imaging array will be discussed. The active sensor consists of virtually three layers: (1) a piezoelectric 1-3 composite layer; (2) a flex-circuit component; and (3) a special z-axis conductive adhesive which joins them. The sensor construction utilizes electroplated, injection-molded, 1-3 piezoelectric composite as the active layer. Four acoustically thin, flex circuits provide the electrical connections required for addressing the 468 individual array elements. Of key importance to the fabrication process is the use of a composite, b-stage, adhesive film layer, which combines both conductive and nonconductive regions in a pattern-specific orientation within the plane comprising the bond line interface. The conductive regions of the adhesive film are registered with respect to the electroplated sections on both the flex circuit and the 1-3 piezoelectric composite substrate. The transducer array is a reciprocal device operable in both transmit and receive modes. Measured results will include individual element and array calibrations (i.e., transmit and receive responses, beam patterns, and relative phase). [Work supported by ONR 333, Kam Ng.]
High power piezoelectric characteristics and loss mechanisms of PMN-PT based ceramics
Authors: Chen YunHan , Kim Jin-Soo
Published: July 2002

Application of ultrasonic transducers for high-power piezoelectric devices such as motors and actuators has been vigorously studied in recent years. Those devices are usually driven at a rather high vibration level. However, it was shown that a drastic change in the electromechanical properties, as well as a great amount of heat generation, occurred above certain vibration velocity due to the large electrical and mechanical loss. In this research, lead magnesium niobium oxide-lead titanium (PMN-PT) based material were prepared and studied. The PMN-based ceramics is intriguing due to their extremely high electro-mechanical coupling factors. Combined with lead titanium and modified by some dopants, the mechanical quality can be much improved. The properties under high level driving and loss mechanisms of PMN-PT with different dopants will be reported in this paper. [Work supported by ONR.]
Dynamic performance of 1-3 type piezoelectric ceramic composites
Authors: Ma Yushieh
Published: July 2002

Expressions of the frequency-dependent displacement for the 1-3 type piezoelectric ceramic composite unit cell are derived using Navier’s equation in the cylindrical coordinates. It does not require an assumed form for the displacement field before the derivation. The formalism also covers that of the static cases. The thickness-drive vibration problem is analyzed under a uniaxial as well as a hydrostatic load. The frequency-dependent displacement, which is along the axis of the unit cell, depends on the aspect ratio, the relative content of both the discrete (ceramics) and continuous (matrix) phases, and also on the boundary conditions of both ends of the unit cell. In addition, Poisson’s ratio plays an important role on the dynamic response of the displacement. Numerical results are presented as normalized stress amplification parameters as a function of frequencies. The frequency-dependent hydrostatic piezoelectric constant and figure of merit are also computed, and they are depicted in figures under various configurations of the composites. From the computed resonance frequencies of the unit cell and the information provided, the 1-3 piezoelectric ceramic composites can be tailored to best suit for their medical and underwater applications over a wide frequency range.
Sound localization in noise in normal-hearing listeners
Authors: Lorenzi Christian , Gatehouse Stuart , Lever Catherine
Published: July 2002

The ability to localize a click train (100-Hz click rate, 300-ms duration, 70 dB SPL) was measured in the presence of a white noise masker, using an array of 11 speakers located in the horizontal plane at azimuth angles ranging from −90 to 90 deg. All clicks were low-pass filtered at 11 kHz. Clicks were low-pass filtered at 1.6 kHz in the low-pass condition and high-pass filtered at 1.6 kHz in the high-pass condition. Six signal-to-noise ratios (S/N) ranging from −9 to 18 dB (plus a silent condition) and three masker locations (−90-, 0-, and 90-deg azimuth) were tested. Results obtained with four normal-hearing listeners show that, in the broadband and high-pass conditions, localization performance is not affected by noise when S/N is greater than 0 dB. Below this value, performance degrades slowly when S/N decreases and when noise is presented straight ahead; performance degrades rapidly when S/N decreases and when noise is presented at the sides. The same pattern of results is observed in the low-pass condition when noise is presented straight ahead. When noise is presented at the side, performance measured with low-pass filtered clicks starts to worsen at higher S/N’s and reaches a lower level.