bluuebunny/crossref_metadata_2025 huggingface dataset:
Describing small-scale structure in random media using pulse-echo ultrasound
Authors: Insana Michael F. , Wagner Robert F. , Brown David G. , Hall Timothy J.
Published: October 2005

A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J. J. Faran, J. Acoust. Soc. Am. 23, 405–418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed.
Ultrasonic texture and stress measurements in anisotropic polycrystalline aggregates
Authors: Delsanto P. P. , Mignogna R. B. , Clark A. V.
Published: October 2005

A perturbative treatment of ultrasonic Rayleigh wave propagation is applied to investigate the case of an initally deformed metal plate, assumed to be homogeneous and to consist of an orthotropic disribution of cubic crystallites. Time-of-flight measurement techniques are proposed for the determination of both stress and texture. An analysis of these experimental results and a comparison with results of both ultrasonic bulk waves and neutron diffraction techniques confirm the reliability of this method. The special case of residual stresses is discussed in detail. Measurements of residual stresses with this technique agree with the results of strain gage measurements.
Pitch identification and discrimination for complex tones with many harmonics
Authors: Houtsma A. J. M. , Smurzynski J.
Published: October 2005

Four experiments are reported that deal with pitch perception of harmonic complex tones containing up to 11 successive harmonics. In particular, the question is raised whether the pitch percept of the missing fundamental is mediated only by low-order resolvable harmonics, or whether it can also be conveyed by high-order harmonics that the cochlea fails to resolve. Melodic interval identification performance was found to remain significantly above chance level even if the range of harmonics extended from the 20th to the 30th. Just-noticeable differences (jnd) in the pitch of the missing fundamental were found to increase with increasing harmonic order, but to level off when all harmonics are above the 12th. These results are consistent with the notion of the existence of two distinct neural pitch mechanisms in the auditory system, but are, in principle, also compatible with a single central-spectrum mechanism that uses the interspike interval histograms of auditory-nerve fibers as inputs.
Vibrotactile intensity discrimination measured by three methods
Authors: Gescheider George A. , Bolanowski Stanley J. , Verrillo Ronald T. , Arpajian Dean J. , Ryan Timothy F.
Published: October 2005

The difference threshold for the detection of changes in vibration amplitude was measured as a function of the intensity and frequency of stimuli delivered through a 2.9-cm2 contactor to the thenar eminence. Stimuli were either 25- or 250-Hz sinusoids, narrow-band noise centered at 250 Hz, or wideband noise. Thresholds were measured by two-interval, forced-choice tracking under three methods of stimulus presentation. In the gated-pedestal method, subjects had to judge which of two 700-ms bursts of vibration separated by 1000 ms was more intense. In the continuous-pedestal method, subjects had to detect a 700-ms increment in the amplitude of an ongoing pedestal of vibration. In the two-burst–continuous-pedestal method with 1500-ms pedestals, the subject had to detect which of two successively presented pedestals contained a 500-ms amplitude increment. Thresholds were consistently lower for detecting increments in the amplitude of a continuous pedestal of vibration than for detecting amplitude differences between briefly presented successive pedestals or amplitude increments in successive pedestals. A ‘‘near miss’’ to Weber’s law was found both for sinusoidal and for noise stimuli. The difference threshold was not affected by stimulus frequency condition.
A simple low-frequency acoustic technique for remote measurement of the temporal ocean wave spectrum
Authors: Lataitis R. J. , Crawford G. B. , Clifford S. F.
Published: October 2005

A theory is presented that describes a method for using low-frequency sound (≲150 Hz) to measure the waveheight variance and the nondirectional temporal waveheight spectrum of a random rough surface such as the sea surface. The technique requires a vertically pointing broadbeam acoustic source and a colocated broadbeam receiver which records the amplitude and phase fluctuations of the backscattered field. When the rms surface waveheight is much smaller than the acoustic wavelength, the temporal spectrum of the amplitude and phase fluctuations can be directly related to the nondirectional temporal surface waveheight spectrum. The theory predicts that the temporal waveheight spectrum out to frequencies of roughly 0.5 Hz can be retrieved.
Modeling of compliant tube underwater reflectors
Authors: Audoly Christian , Dumery Guy
Published: October 2005

A theoretical method for determination of multiple scattering of an acoustical wave by a grating of elastic obstacles is presented. The main advantages of the method are: The same formulation works for finite arbitrary gratings as well as for infinite plane gratings; and the calculation of the properties of the whole grating is decoupled from the calculation of the scattering properties of the individual components set in free field. Some results on compliant tube gratings (plane gratings and a parabolic reflector) are shown and compared to experiments.
Analysis of the scattering of a plane acoustic wave by a periodic elastic structure using the finite element method: Application to compliant tube gratings
Authors: Hennion A. C. , Bossut R. , Decarpigny J. N. , Audoly C.
Published: October 2005

A two-dimensional mathematical model has been developed to analyze the scattering of plane acoustic waves from an infinite, uniform, plane grating of compliant tubes. It relies upon the finite element method and uses the atila code [J. N. Decarpigny et al., J. Acoust. Soc. Am. 78, 1499 (1985)]. To do this, only the unit cell of the periodic structure, including a small part of the surrounding fluid domain, has to be meshed, thanks to the Bloch–Floquet theorem, and the effects of the remaining fluid domain are accounted for by matching the pressure field in the finite element mesh with simple plane wave expansions of the ingoing and outgoing waves. This paper describes results obtained for the scattering of a plane wave from different tube gratings, including internal losses, at oblique incidence. Comparing finite element results to analytical or experimental results allows for the validation of the model. Then, various compliant tube gratings are considered to demonstrate the efficiency and versatility of this approach. Finally, the generalization to doubly periodic gratings is emphasized.
Reciprocity theorems for acoustic wave fields in fluid/solid configurations
Authors: de Hoop Adrianus T.
Published: October 2005

The time Laplace-transform domain convolution-type reciprocity relation for acoustic waves in a fluid/solid configuration is derived. Arbitrary inhomogeneity, anisotropy, and loss mechanisms are taken into account. Reciprocity between transmitting and receiving transducers located in either the fluid or the solid parts of the configuration is established. It is shown how the reciprocity relation leads to the source-type wave field integral representations for direct source problems and to the integral-equation formulation of inverse source, and direct and inverse scattering problems through the associated contrast source representations. Since neither a fluid inclusion in a solid nor a solid inclusion in a fluid leads to a regular perturbation problem in the integral-equation formulation, the embedding must be adapted to the location of the contrast sources as far as the type of medium (fluid or solid) is concerned. Applications to acoustic emission and to acoustic imaging and profile inversion are briefly indicated.
Manifestly reciprocal scattering amplitudes for rough interface scattering
Authors: Berman David H. , Dacol Dalcio K.
Published: October 2005

A new exact expression for scattering amplitudes for rough interface scattering is presented. This expression is shown to hold for a variety of boundary conditions; Dirichlet, Neumann, impedance, fluid–fluid, and fluid–solid. The expression is shown to be a convenient starting point for deriving approximations that also respect reciprocity. Examples include a small-slope approximation, a reciprocal phase-perturbation approximation, and a reciprocal smoothing approximation.
The effect of an elastic basement in the interpretation of bottom loss data
Authors: Chapman N. R. , Bannister R. W. , Falconer R. K. H.
Published: October 2005

A bottom loss simulator has been developed to model low-frequency bottom loss measurements obtained at sites in the SW Pacific around New Zealand. The data for frequencies below 100 Hz have been grouped into two types according to the bottom environment. The first type is characteristic of continental margins where the bottom is composed of turbidite layers, and the second type is characteristic of deep-water basins where the bottom is silt–clay material overlying the ocean basement. The bottom loss simulator consists of a simple geoacoustic profile, composed of a thin-layer fluid sediment overlying an elastic basement, and a ray propagation model. Simulations were carried out with the model to study the effect of various types of solid substrates, including relatively low-speed consolidated sediment material and high-speed basalt. The model provides good agreement with both types of bottom loss data, using archival values from seismic and geological sources for the model parameters. The work demonstrates the importance of including shear-wave propagation in the substrate in modeling the bottom interaction in deep-water environments.
Effects of electrical polarization on inner hair cell receptor potentials
Authors: Dallos Peter , Cheatham Mary Ann
Published: October 2005

Ac and dc receptor potential components in response to tone-burst stimuli were measured from inner hair cells in the third cochlear turn of the guinea pig. Comparisons were sought between conditions when constant polarizing current was injected into the cell through the recording electrode and when there was no extrinsic current. Hyperpolarization of the cell increased all responses, while depolarization decreased them. The input–output functions were vertically translated by current injection.The extent of translation was a function of current level. In addition, the amount of current-induced change was frequency dependent. Largest changes were seen at low frequencies and the current-induced change tended toward a constant high-frequency asymptote between 1–2 kHz. Changes in the dc response component were considerably in excess of those for the fundamental ac response. The frequency-dependent effects are quantified with the aid of a hair cell circuit model [P. Dallos, Hear. Res. 14, 281–291 (1984)]. It is assumed that the quantity altered by polarizing current (actually by the transmembrane voltage) is the resistance of the cell’s basolateral membrane.
Neural responses to auditory temporal patterns
Authors: Robin Donald A. , Abbas Paul J. , Hug Linda N.
Published: October 2005

Sets of regularly repeating auditory stimuli elicit unique perceptions; listeners are able to identify specific temporal patterns. Some temporal patterns are unambiguous (only one pattern can be perceived), while others are ambiguous (numerous patterns can be detected). While the psychophysical properties of such percepts have been well studied, little is known about the underlying neurological bases of temporal pattern perception. In this experiment, the role of adaptation in temporal pattern perception is examined by studying neural responses in four cats to a temporal pattern that is perceptually unambiguous and one that is perceptually ambiguous. Measurements were made of the whole-nerve action potential, the auditory brain-stem response, and potentials from the surface of the primary auditory cortex. The adaptation patterns corresponded with the perceptual organization of temporal patterns in humans at all levels of the nervous system studied.
The combination of interaural time and intensity in the lateralization of high-frequency complex signals
Authors: Hafter Ervin R. , Dye Raymond H. , Wenzel Elizabeth M. , Knecht Kitty
Published: October 2005

In an effort to examine the rules by which information arising from interaural differences of time (IDT) and interaural differences of intensity (IDI) is combined, d′ ’s were measured for trains of high-frequency clicks (4000 Hz, bandpass) possessing various combinations of IDT and IDI. The number of clicks was either 1 or 8, with the interclick interval either 2 or 10 ms. A 2-IFC task was employed in which the paired values of IDT and IDI favored one side during one interval and the other side during the other interval. Data obtained with the combined cues are compared to those obtained with IDTs or IDIs alone in order to determine the degree to which processing of the two cues is done independently. Results suggest that lateralization with such stimuli is based on the sum of the temporal and intensive differences and not on independent evaluations of their separate presences.
Minimum audible angle thresholds for sources varying in both elevation and azimuth
Authors: Perrott David R. , Saberi Kourosh
Published: October 2005

Minimum audible angle (MAA) thresholds were obtained for four subjects in a two-alternative, forced-choice, three up/one down, adaptive paradigm as a function of the orientation of the array of sources. With sources distributed on the horizontal plane, the mean MAA threshold was 0.97°. With the sources distributed on the vertical plane (array rotated 90°), the mean MAA threshold was 3.65°. Performance in both conditions was well in line with previous experiments of this type. Tests were also conducted with sources distributed on oblique planes. As the array was rotated from 10°–60° from the horizontal plane, relatively little change in the MAA threshold was observed; the mean MAA thresholds ranged from 0.78° to 1.06°. Only when the array was nearly vertical (80°) was there any appreciable loss in spatial resolution; the MAA threshold had increased to 1.8°. The relevance of these results to research on auditory localization under natural listening conditions, especially in the presence of head movements, is also discussed.
Asymptotic solution to the crack-opening displacement integral equations for the scattering of plane waves by cracks: I. The symmetric problem
Authors: Gautesen A. K.
Published: October 2005

The scattering of a symmetric pair of plane waves by a crack in an isotropic, homogeneous, linearly elastic solid is considered. For high frequency, an asymptotic solution to the integral equation for the normal crack-opening displacement (COD) is found. The elliptical and penny-shaped cracks are considered in some detail. For the penny-shaped crack, excellent agreement with numerical results is found as well as agreement with other asymptotic results.
Nonlinear propagation in an ocean acoustic waveguide
Authors: Ambrosiano John J. , Plante Daniel R. , McDonald B. Edward , Kuperman W. A.
Published: October 2005

The nonlinear progressive wave equation (NPE) is used to investigate propagation of acoustic pulses in a shallow ocean waveguide. The nonlinearity is shown to affect transmission and reflection at a fluid–fluid interface. It is shown that one effect of the nonlinearity is to reduce the critical angle for total internal reflection from that of the linear case. When loss versus range for a simple isovelocity waveguide is compared with linear normal mode and parabolic equation calculations, the nonlinear result shows increased transmission loss as long as the wave amplitude is significant (an expected result of shock processes), and increased bottom penetration. Nonlinear aging of the waveform alters the excitation of linear modes in the farfield.
Tone generation by aeroacoustic sources in pipes with flow
Authors: Shakkottai P. , Kwack E. Y. , Back L. H.
Published: October 2005

Sound production by axisymmetric ring cavities in internal flow has been investigated experimentally. These ring sources generate sound when the acoustic motion in the cavity is in resonance in one of many possible modes. Experimental results agree with predictions of a model eddy-driven oscillator. It is observed that the standing waves produced by reflections from regions upstream and downstream of the source are adjusted by the source such that the source is at a pressure antinode at the condition of maximum sound emission.
Wide-angle parabolic equation solutions to two range-dependent benchmark problems
Authors: Thomson David J.
Published: October 2005

Numerical solutions are presented to two benchmark problems involving acoustic propagation in range-dependent media. The two problems deal with: (1) upslope propagation in a wedge-shaped channel with a penetrable bottom, and (2) propagation in a plane-parallel waveguide with a range-varying sound-speed profile. The solutions are based on a pair of wide-angle, variable-density, parabolic equations, one of which is solved using a finite-difference algorithm while the other is solved using a split-step algorithm.
Benchmark calculations for higher-order parabolic equations
Authors: Collins Michael D.
Published: October 2005

Benchmark solutions generated with parabolic equation (PE) models are presented for range-dependent underwater acoustic propagation problems involving both penetrable and perfectly reflecting ocean bottoms. The solution of the wide-angle PE of Claerbout [J. F. Claerbout, Fundamentals of Geophysical Data Processing (McGraw-Hill, New York, 1976), pp. 206–207] agrees with the outgoing coupled-mode solution for the problems involving penetrable bottoms. The solution of the higher-order PE of Bamberger et al. [Bamberger et al., ‘‘Higher Order Paraxial Wave Equation Approximations in Heterogeneous Media,’’ SIAM J. Appl. Math. 48, 129–154 (1988)], which is a generalization of Claerbout’s PE, agrees with the outgoing coupled-mode solution for problems involving large variations in sound speed and propagation nearly orthogonal to the preferred direction. The computer code FEPE was used to generate the benchmark solutions and was found to run several times faster than the IFDPE computer code due to a tridiagonal system solver in FEPE that is optimized for range-dependent problems.
Numerical simulation of intensity fluctuations caused by wind gusts
Authors: Robertson J. S.
Published: October 2005

Many mechanisms can be responsible for fluctuations of sound intensity and phase through the atmosphere over the Earth’s surface. In this Letter, the effect of wind gusts on received intensity at short range is examined. Using a parabolic approximation, relative intensity for a continuous wave (cw) omnidirectional source is calculated using the effective sound-speed profiles obtained from meteorological data. Two characteristic scale thicknesses are used to model the wind gust profiles. The thinner layer thickness can result in temporal intensity fluctuations as high as 10 dB at a range of 100 m. It is emphasized that these fluctuations are refractive and deterministic. In an actual experiment, these fluctuations would be detected along with additional variations caused by wind noise turbulent scattering.
Reply to comments by S. W. Autrey [J. Acoust. Soc. Am. 8
7, 1355–1356 (1990)]
Authors: Carey William M.
Published: October 2005

In this Letter, the author replies to comments made by S. W. Autrey [J. Acoust. Soc. Am. 87, 1355–1356 (1990)]. [AIP]
Intermodulation distortion in the cochlea as shown by offset action potential (AP) masking curves
Authors: Schmiedt Richard A.
Published: October 2005

In their recent article ‘‘Offset AP masker tuning curve and the FFT of the stimulus’’ [J. Acoust. Soc. Am. 84, 1354–1362 (1988)], Henry and Lewis demonstrated that the tuning curve obtained by the simultaneous masking of the whole nerve action potential (AP) could have two tips when the AP is generated at the offset of the envelope of a high-level probe. The primary tip falls below the probe frequency, whereas the secondary tip falls above the probe frequency. Curves obtained for the onset response with either forward or simultaneous masking did not show the secondary peak, nor did curves obtained for the offset response with forward masking. Henry and Lewis discussed various reasons for the secondary tip, but came to no conclusion as to the underlying mechanisms. Here, it is reasoned that the secondary tip of the offset curve can be simply explained by the generation within the cochlea of intermodulation distortion (IMD), which acts as a forward masker to the offset response. The IMD is dominated by the cubic component (2f1−f2) and arises from the interaction of the probe tone and the simultaneous masker. Finally, it is reasoned that the lower sideband of the frequency splatter present at probe offset is the primary stimulus for the evoked neural response under probe offset conditions. Thus the offset curve will always have a primary tip that is lower in frequency than that of the respective onset curve. These hypotheses are supported by single-fiber data.
Comment on ‘‘Thermal noise in a fiber optic sensor’’ [J. Acoust. Soc. Am. 8
4, 471–475 (1988)]
Authors: Mermelstein Marc D.
Published: October 2005

The phase noise associated with thermal strain fluctuations in strain-sensitive fiber optic interferometric sensors is calculated from the fluctuation–dissipation theorem and is presented in a general format that is applicable to a variety of sensors. This analysis was first utilized by this author to determine the thermal noise floor of a fiber optic magnetometer.
An approximate elastic f-k Green’s function within WKBJ (high-frequency) approximation
Authors: Cao Di , Beydown Wafik B.
Published: October 2005

The wave equation can be solved exactly in simple media, and approximately in smoothly varying media. The hypothesis of a smooth medium corresponds in fact to a Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) approximation to the Green’s function [K. Aki and P. G. Richards, Quantitative Seismology, Theory and Methods (Freeman, San Francisco, 1980); C. H. Chapman and J. A. Orcutt, Rev. Geophys. 23, 105–163 (1985)]. Within the WKBJ approximation, a two-dimensional elastic Green’s function is analytically formulated in the frequency and wavenumber (f-k) domain. It is derived for a unidirectional force acting upon a one-dimensional (vertically) heterogeneous, isotropic, unbounded medium. Depth-dependent medium parameters are assumed to vary slowly as compared to the seismic wavelength (high-frequency approximation), the acquisition geometry (sources/receivers) being two-dimensional. The approximate Green’s function is found via elastic potentials, and simulates the farfield behavior of direct P and S body waves. Theoretical comparisons with other known analytical solutions and numerical examples compared to finite differences are given to validate both amplitude and phase variations of this Green’s function.
Nonlinear viscoelastic effects on the harmonic generation of a finite-amplitude acoustic wave
Authors: Milliken William J. , Kersulis Antonia , Powell Robert L.
Published: October 2005

The effect of fluid viscoelasticity on the second-harmonic wave generated by a planar acoustic wave is considered. It is shown that the growth, decay, wavenumber, phase, and amplitude of the second-harmonic wave are all modified by fluid viscoelasticity. The effect on the amplitude, the most readily measured property, is discussed in detail. It is found that viscoelasticity in the form of frequency thinning causes a shift in the maximum of the second-harmonic amplitude to distances further from the acoustic source. Finite linear and nonlinear viscoelasticity are found to cause both harmonic suppression and harmonic enhancement, depending on the properties of the fluid and the dimensionless frequency of oscillation. The harmonic suppression predicted here may be associated with changes in the noise spectrum of cavitation that have been observed for dilute polymer solutions.
Dispersion analysis of acoustic velocities in rocks
Authors: Wang Zhijing , Nur Amos
Published: October 2005

Acoustic velocity dispersions in three rocks saturated with water, normal decane (n-decane), and a heavy oil (in petroleum engineering, heavy oil is referred to as crude oil with viscosity higher than 0.5 Pa s), respectively, are calculated in this paper. The results show that the apparent velocity dispersion in light fluid (low-viscosity)-saturated rocks is relatively small, usually less than 3% to 5%, whereas that in the same rocks saturated with heavy oil is much larger. Such apparent velocity dispersion can be well explained by the ‘‘local flow’’ mechanism, which relates dispersion to the viscosity of the pore fluid, the pore geometry of the rock, and the effective pressure and temperature. The Biot velocity dispersion calculated using the Gassmann equation and the Biot high-frequency limit of the velocities in the rocks is very small, typically less than 2%. Such Biot dispersion can be explained in terms of the Biot theory, which relates dispersion to the viscosity of the pore fluid and the permeability of the rock in a way that is just opposite to the local flow mechanism. According to either the local flow mechanism or the Biot theory, the temperature dependence of the compressional wave velocities in heavy-oil-saturated rocks in the seismic frequency band should be no less than that observed in the laboratory at 0.8-MHz frequency, which means that the laboratory results can be applied to the field as a basis for seismic monitoring of thermal floods.
Diffraction tomography of strongly scattering infinite cylindrical objects of arbitrary cross-sectional shape
Authors: Jegannathan S. , Ramamurthi Bhaskar
Published: October 2005

A new method for imaging an infinite cylindrical object with arbitrary cross-sectional shape, without any small-perturbation approximations, is proposed. In this method, the well-known integral equation equivalent to the inhomogeneous Helmholtz wave equation is discretized. The discretized equation expresses the scattered pressure field at any point in terms of the samples of the product of the unknown object function and the unknown pressure field present inside the object. Based on this relation, simultaneous equations are set up, relating these samples to the samples of the pressure field measured outside the object. By requiring the measurement points to lie on circles around the object, these equations are solved efficiently using the fast Fourier transform (FFT). From the product samples thus obtained, the samples of the unknown object function are extracted by means of a second set of FFT calculations. Details of illustrative computer simulations for the case of an elliptic cylinder are described.
Signal processing of ideal echoes resonantly scattered by underwater structures
Authors: McDaid Edward , Gaunaurd Guillermo C.
Published: October 2005

A study is presented of the scattering of sound waves that results when penetrable underwater obstacles of various types are insonified by various incident transient signals. The targets are elastic shells, although the case of a rigid sphere was also studied for comparison. The deformation of the shell is described both exactly, by means of the three-dimensional equations of elasticity, and approximately, by means of Donnell’s shell theory. The goal is to identify significant signal processing parameters that are useful at the source, the target, and the receiver, to properly and quantitatively estimate the nature of the backscattered echoes from submerged structures. These parameters play an important role in the ultimate goal of active target identification. The methodology presented has similarities to that most commonly used for impenetrable targets (i.e., perfect conductors)—in the radar literature. The analysis is first introduced here for targets away from boundaries, and in noiseless media. It is believed that the type of echo received from a sonar target should be known, before such return is distorted and corrupted by the environment. As presented here, this idealized situation is well suited to later account for the presence of noise in the medium, as well as for the proximity to environmental boundaries. The methodology already takes advantage of the machinery of statistical communication theory (viz., matched filters, ambiguity and correlation functions, etc.) to extract desired signals from signals mixed with undesirable noises. The work is naturally divided into descriptions and characteristics of: (a) the incident pulses, (b) the elastic targets themselves, and (c) the backscattered returns. The various quantities are illustrated at all stages with many computed displays.
On the prediction of propeller tone sound levels and gradients in an airplane cabin
Authors: Pope Larry D.
Published: October 2005

Theoretical and computational methods are presented that will permit a basic prediction of the spatial variation of sound-pressure level in an airplane cabin arising from propeller excitation of fuselage sidewall structure. Analytical results focus on the calculation of the axial variation (or gradient) of the average mean-square pressure in cross section for the case of a trimmed cabin of uniform cross-sectional area terminating fore and aft in reflecting (and absorbing) partitions (i.e., bulkheads). Sample numerical predictions and qualitative comparisons with some available measurement data are presented.
Frame junction vibration transmission with a modified frame deformation model
Authors: Moore James A.
Published: October 2005

A previous paper dealt with vibration transmission through junctions of connected frame members where the allowed frame deformations included bending, torsion, and longitudinal motions [J. A. Moore, J. Acoust. Soc. Am. 88, 2766–2776 (1990)]. In helicopter and aircraft structures the skin panels can constitute a high impedance connection along the length of the frames that effectively prohibits in-plane motion at the elevation of the skin panels. This has the effect of coupling in-plane bending and torsional motions within the frame. This paper discusses the transmission behavior through frame junctions that accounts for the in-plane constraint in idealized form by assuming that the attached skin panels completely prohibit in-plane motion in the frames. Also, transverse shear deformation is accounted for in describing the relatively deep web frame constructions common in aircraft structures. Longitudinal motion in the frames is not included in the model. Transmission coefficient predictions again show the importance of out-of-plane bending deformation to the transmission of vibratory energy in an aircraft structure. Comparisons are shown with measured vibration transmission data along the framing in the overhead of a helicopter airframe, with good agreement. The frame junction description has been implemented within a general purpose statistical energy analysis (SEA) computer code in modeling the entire airframe structure including skin panels.
Nonlinear piezoelectric d constants determined from extensional mode resonators
Authors: Kittinger E. , Tichý J.
Published: October 2005

The material frame theory of the electroelastic effect of piezoelectric extensional mode resonators is reformulated so that the nonlinear piezoelectric constants dKλμ are the only third-order constants involved. In this form, it is applied to quartz, resulting in an independent determination of d122, d124, d134, and of the linear combinations (d144−2d113) and (d111−2d315). Results are in good agreement with values calculated from third-order stiffnesses and nonlinear piezoelectric e constants obtained by different experimental techniques.
A general formulation for the sound radiation from rectangular, baffled plates with arbitrary boundary conditions
Authors: Berry Alain , Guyader Jean-Louis , Nicolas Jean
Published: October 2005

The radiation of sound from a baffled, rectangular plate with edges elastically restrained against deflection and rotation is analyzed. The elastic constants along the contour can be varied to reproduce simply supported, clamped, free, or guided edges as limiting cases. The formulation is based on a variational method for the vibration of the plate, and assumes no fluid loading of the structure. The elastic boundary conditions appear in the Hamiltonian of the plate through a dynamic contribution, which is expressed in terms of nondimensional edge parameters. The extremalization of the Hamiltonian is achieved using a Rayleigh–Ritz method, and both the free vibrations and the forced vibrations of the plate are presented. The radiation of sound from the plate is analyzed in the far field, and is calculated from one-dimensional Fourier transforms. Numerical results are presented for the radiation efficiency of modes of simply supported, clamped, free, and guided plates. The values found agree well with predictions of Wallace in the simply supported case, and of Gomperts in the guided case. It is found that a low deflection stiffness at the edges decreases the radiation efficiency of the elastic modes in a spectacular manner. The radiation efficiency of the rigid modes of the plate is derived analytically in low frequencies. It is seen that, when rigid motion of the plate is permitted, it is responsible for almost all the acoustical power radiated. The new case of a plate which is locally clamped along its four edges is also presented.
Vibrational relaxation in SiF4 using a computer-controlled ultrasonic interferometer
Authors: Jacobs Bradley , Cerami Richard , Olson John R. , Amme R. C.
Published: October 2005

A variable-path ultrasonic interferometer has been modified to permit automatic data collection and analysis utilizing an Apple IIe microcomputer and an ADC interface board possessing a crystal-controlled clock for precision data sampling. The micrometer screw is driven by a synchronous motor also controlled by the interface board. The system allows rapid sampling and recording of the crystal driving voltage for each resonant node in the gas column, thereby reducing running time and improving overall accuracy and sensitivity. For SiF4, the (single) vibrational relaxation time was found to be (2.20±0.14)×10−8 s at a temperature of 304 K and 1 atm of pressure.
Full wave-field simulation of the autocorrelation of a low-frequency broadband signal in an ocean with a layered sediment bottom
Authors: Ebbeson Gordon R.
Published: October 2005

From low-frequency acoustic measurements carried out over the Tufts Abyssal Plain of the Northeast Pacific Ocean, it was found that the correlations between the multipath arrivals from a broadband source can be greatly affected by the bottom sediment. As an aid to explaining these effects, the pulse version of the safari full wave-field propagation model was modified to simulate the autocorrelation of the received signal. As with the original model, the bottom environment is input in the form of a geoacoustic profile. However, the inputs to the modified model also include the source level, realistic ambient noise and sea state conditions, noise due to distant shipping, and the self-noise levels of the receiving array. Simulations were carried out using the environment of the Tufts Abyssal Plain, including a geoacoustic profile that has been developed for the area. It was found from these simulations that the distortions observed in the measured correlograms can be predicted reliably.
Acoustic resonance spectroscopy for elastic spheroids of varying aspect ratios, and the level crossing phenomenon
Authors: Werby Michael F. , Castillo Jaime J. , Nagl Anton , Miller Russel D. , D’Archangelo James M. , Dickey Joseph W. , Überall Herbert
Published: October 2005

The ‘‘level crossing’’ phenomenon, which has been pointed out earlier [M. F. Werby et al., J. Acoust. Soc. Am. 84, 1425–1436 (1988)], is studied here for solid elastic spheroids of varying aspect ratios. Using a T-matrix code, the frequencies (both fundamentals and overtones) of the resonances are calculated as excited by an end-on incident plane wave. Aspect ratios of the tungsten carbide spheroids range from b/a=1 (sphere) to 4 in steps of 0.25. The resonance frequencies are presented in the form of an acoustic spectroscopic level scheme. They are expressed in units kb (b=semimajor axis) and correspond to resonating surface waves as they form standing waves around the meridional circumference. While for the resonating Rayleigh waves the resonance frequencies only rise gradually with increasing aspect ratio, those for the Whispering Gallery waves rise much more rapidly, and hence successively cross over the various overtones of the Rayleigh resonances. This phenomenon is explained on the basis of the different character of the dispersion curves (phase velocity versus frequency) for the Rayleigh and the Whispering Gallery waves, as calculated in an exact fashion for a tungsten carbide (WC) sphere and used locally on the spheroids.
Sea ice noise-generating processes
Authors: Pritchard Robert S.
Published: October 2005

An ambient noise model is presented for sound generated in compact ice by ridging, microcracking, and mixed layer shearing. The model describes sound intensity as the sum of these different processes and the sum of intensities propagated from all source locations. The source intensity changes as a function of time for each frequency and can depend on material parameters that affect behavior, such as ice thickness. The processes are identified by their driving forces. The large-scale stress state is related to the local stress in each ice floe, which, when small, can cause local cracking but does not contribute to large-scale deformations. If the stress level is large enough to cause ridging, rafting, and leading, then large-scale deformations occur. Independently of these large-scale deformations, the ice can move as a rigid body, which shears the mixed layer. Each of these processes is assumed to have its own spectral signature, and each is driven by a different environmental variable. Local cracking is driven by the stress. Ridging is driven by the stress and deformation. Mixed layer shearing is driven by the ice velocity relative to the current. Each driving force is converted to an energy dissipation to serve as a source level to the model. These variables provide the key to successfully modeling the different processes and to isolating them from one another and from other processes. Ambient noise measurements taken during the October 1988 CEAREX Drift Experiment were successfully simulated by the model. Day-to-day temporal variations in the 31.5-Hz noise intensity were reproduced by the mixed layer shearing, pressure ridging, and shear ridging models. Microcracking was apparently not active during this time period.
Sector-focused stability methods for robust source localization in matched-field processing
Authors: Frichter G. M. , Byrne C. L. , Feuillade C.
Published: October 2005

Capon’s maximum likelihood method (MLM) is being used increasingly for improved localization and high resolution of sources in matched-field processing (MFP) in a waveguide environment. When the noise component is dominated by modal noise (that is, noise due to excitation of the modal structure of the waveguide by distant sources of acoustic energy, e.g., wave action, distant shipping), the MLM can become unstable; when the number of modes (M) supported by the waveguide is considerably less than the number of sensors (N), a ‘‘reduced’’ MLM is available to stabilize the processing [Byrne et al., J. Acoust. Soc. Am. 87, 2493–2502 (1990)]. In this paper the sector-focused stability (SFS) methods of Byrne and Steele (Proc. IEEE., ICASSP 1987) are employed to treat the case of M nearly equal to N. Simulations, using a shallow-water range-independent environment, are presented to illustrate the increase in stability of SFS over MLM in the presence of phase errors on the sensors or more general mismatch.
Nonlinear energy exchange among harmonic modes and its applications to nonlinear imaging
Authors: Wu Jin-yuan , Shung K. Kirk
Published: October 2005

Nonlinear energy exchange and redistribution among the harmonic modes have been investigated. A problem with the pre-bias boundary condition, which means that in addition to the fundamental harmonic, nonzero higher harmonics with adjustable amplitudes and phases are also applied to the input simultaneously, has been considered. The results show that the pre-bias technique that is proposed in this paper may offer a better means for detecting the nonlinear properties of the medium. The feasibility of the approach was validated by computer simulation and experimental results.
Wave equation solution by a coupled mode multiple reflection series method
Authors: Pai D. M.
Published: October 2005

In inhomogeneous media, wave equations are nonseparable and numerical techniques are usually employed. This paper presents an efficient and stable eigenmode solution method. The medium is divided into thin layers and the solution within each layer is expanded in terms of modes. The method differs from the usual eigenmode methods in that mode couplings are achieved through an iterative one-way wave multiple reflection series, which requires only matrix-vector multiplications. The solution is computationally simple, has physical interpretation, and remains stable with respect to evanescent waves.
Reflection and transmission of compressional waves by a stratification with discontinuities in density and/or sound speed
Authors: Lekner John
Published: October 2005

Formulas are derived for the reflection and transmission amplitudes due to a stratification with discontinuities in density ρ or sound speed c, or both. The formulas are exact in the case of a uniform layer (ρ and c constant within the stratification), and accurate down to surprisingly low frequencies for nonuniform layers. At very low frequencies these formulas ultimately fail, but there a long-wave theory is available. An additional limitation on the applicability of the theory given here is that it fails at classical turning points: Thus total reflection and tunneling are excluded. Comparison with an exactly solvable stratification model is made, from zero frequency up.
Scattering from slender bodies in a homogeneous waveguide
Authors: Tran-Van-Nhieu Michel
Published: October 2005

A formalism based on the matched asymptotic method is developed for the scattering from slender bodies, in a homogeneous fluid layer overlying a rigid bottom. The scattered field is represented at the scale of the body length, by a continuous distribution along the body axis of elementary solutions that are the acoustic pressure generated in the waveguide by spherical harmonic singularities; their densities and the expression of the scattered far field are determined by using their image sources and their mode representations. Asymptotic expressions are obtained for the first two terms of the expansion of the scattered pressure, corresponding to the impulse and the rescattering contributions due to the first two reflections of the rays on the surface of the body in the multiple scattering mechanism.
Phased-array beam scanning as a possible aid to horizontal localization in horseshoe bats
Authors: Hartley David J.
Published: October 2005

It has recently been shown that oscillating ear movements in horseshoe bats (genus Rhinolophus) are necessary for localization of targets in the vertical dimension. Target elevation thus seems to be calculated from changes in interaural intensity ratios caused by ear movements during echo reception. This letter suggests that, if the radiated beam were spatially oscillated in a similar manner, target azimuth could be deduced from the corresponding oscillation in echo intensity. The potential for rapid phased-array beam steering exists in horseshoe bats because they emit their echolocation pulses through the nostrils.
On modeling convective turbulence
Authors: Mellen Robert H.
Published: October 2005

Models of convective turbulence are based largely on measurements of space/frequency correlation of fluctuations along the longitudinal and transverse axes. The wave number/frequency spectrum is then derived from an analytic model by Fourier transformation. In the exponential model, separation in the axial variables yields irregular results because the isoamplitude contours of the Fourier window are rhombic. Regular results are achieved with the smoother elliptic window. Relative effects of these two models are considered.
Spectral and duration properties of front vowels as cues to final stop-consonant voicing
Authors: Fischer Rebecca M. , Ohde Ralph N.
Published: October 2005

The perception of voicing in final velar stop consonants was investigated by systematically varying vowel duration, change in offset frequency of the final first formant (F1) transition, and rate of frequency change in the final F1 transition for several vowel contexts. Consonant–vowel–consonant (CVC) continua were synthesized for each of three vowels, [i,I,æ], which represent a range of relatively low to relatively high-F1 steady-state values. Subjects responded to the stimuli under both an open- and closed-response condition. Results of the study show that both vowel duration and F1 offset properties influence perception of final consonant voicing, with the salience of the F1 offset property higher for vowels with high-F1 steady-state frequencies than low-F1 steady-state frequencies, and the opposite occurring for the vowel duration property. When F1 onset and offset frequencies were controlled, rate of the F1 transition change had inconsistent and minimal effects on perception of final consonant voicing. Thus the findings suggest that it is the termination value of the F1 offset transition rather than rate and/or duration of frequency change, which cues voicing in final velar stop consonants during the transition period preceding closure.