bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of probability modeling and Bayesian inversion to passive sonar signal processing. I. Concepts and formulation
Authors: Pitre Richard , Davis Nolan R.
Published: October 2005

This work considers the benefits of, and methods for the application of probability modeling to passive sonar signal processing. The equal-likelihood probability modeling approach systematically accounts for the combination of data, a priori information, propagation models, array models, and linear and nonlinear models for sources, noise, and environmental descriptors. In Part I, model-consistent, nonstationary, non-Gaussian, equal-likelihood probability models are defined. An optimal nonstationary space-time beamformer and maximum a posteriori probability parameter estimation are derived from equal-likelihood distributions based on autocovariance models employed in conventional matched field processing. Combining information in different frequency bands is seen as an application of a natural data fusion property of stationary Gaussian probability modeling. Part II presents simulation results for the ocean acoustic source localization problem for a shallow water ocean environment under low signal-to-noise conditions. These simulations demonstrate the time evolution of the a posteriori distribution for increased data integration time for single and multiple sources, and illustrate data fusion over a range of frequencies and multiple sensors.
Energy branching of a subsonic flexural wave on a plate at an air–water interface. I. Observation of the wave field near the interface and near the plate
Authors: Matula Thomas J. , Marston Philip L.
Published: October 2005

The radiation of subsonic flexural plate waves due to a discontinuity in fluid loading is experimentally investigated. A tone burst of flexural waves propagates down a plate, the lower section of which is submerged in water. Measurements indicate that there occurs a branching of energy as the flexural wave passes through the air–water interface, with little reflected energy. A portion of the transmitted energy continues along the plate as a subsonic flexural wave with an associated acoustic evanescent wave. A second acoustic wave (which is termed transition radiation) originates at or near where the plate crosses the interface, and propagates in water to the far field. In the near field of the interface there exists an interference between the two acoustic waves in water that results in a series of pressure nulls. The pressure nulls are associated with a π phase change in the wave field and are indicators of wavefront dislocations. A numerical computation of the wave field in an unbounded fluid due to a line-moment excitation of a plate has similar features as the null pattern observed but differs in certain details.
Synthesized wave packet basis for monostatic scattering from a randomly ribbed, finite cylindrical shell
Authors: Hughes David H. , Gaumond Charles F. , Dragonette Louis R. , Houston Brian H.
Published: October 2005

Wave packets are synthesized from scattering highlights in the signal Wigner distribution of the monostatic form function of a randomly ribbed, cylindrical shell in water. It is argued that they, like the acoustic rays derived from partial wave series representations of form functions for canonical geometries, form an approximate basis for the monostatic scattering from this more complex structure. It is shown that, despite the presence of a small amount of structural disorder in the rib spacings, rib excitations such as Bloch waves and Bragg reflections still occur and are significant contributions to the form function.
Dispersion characteristics of sound waves in a tunnel with an array of Helmholtz resonators
Authors: Sugimoto N. , Horioka T.
Published: October 2005

This paper examines dispersion characteristics of sound waves propagating in a tunnel with an array of Helmholtz resonators connected axially. Assuming plane waves over the tunnel’s cross section except a thin boundary layer, weakly dissipative effects due to the wall friction and the thermoviscous diffusivity of sound are taken into account. Sound propagation in such a spatially periodic structure may be termed ‘‘acoustic Bloch waves.’’ The dispersion relation derived exhibits peculiar characteristics marked by emergence of ‘‘stopping bands’’ in the frequency domain. The stopping bands inhibit selectively propagation of sound waves even if no dissipative effects are taken into account, and enhance the damping pronouncedly even in a dissipative case. The stopping bands result from the resonance with the resonators as side branches and also from the Bragg reflection by their periodic arrangements. In the ‘‘passing bands’’ outside of the stopping bands, the sound waves exhibit dispersion, though subjected intrinsically not only to the weak damping due to the dissipative effects but also to the weak dispersion due to the wall friction. Taking a plausible example, the dispersion relation and the Bloch wave functions for the pressure are displayed. Finally the validity of the continuum approximation for distribution of the Helmholtz resonators is discussed in terms of the dispersion relations.
Information paths and the determination of state relations from displacement velocity measurements of elastic rods
Authors: Kadish Abraham
Published: October 2005

New methods are developed for determining the nonlinear compressional state relation between stress and strain for one-dimensional elastic materials from measurements of displacement velocity. An iterative procedure is proposed when the early displacement velocities are provided at both ends of the sample. This procedure is rapidly convergent and simple to implement in the weakly nonlinear regime. Noniterative procedures are developed for displacement velocity data provided at an end and a location in the interior of the sample or for displacement velocity data provided at an end and at a fixed laboratory coordinate.
The relationship between local- and global-scale scattering functions for fractal surfaces under a separation of scales hypothesis
Authors: Goff John A.
Published: October 2005

A ‘‘separation of scales hypothesis’’ is an important component of both composite roughness and facet scattering theories applied to fractal (i.e., realistic) surfaces. It asserts that a scattering surface is separated by the acoustic wavelength into two scale regimes; features larger than the acoustically defined ‘‘separation scale’’ act to reflect rays specularly, whereas features smaller than the separation scale act to scatter acoustic energy diffusely. This paper explores the consequences of this hypothesis by formulating the relationship between an arbitrary local-scale scattering strength function, describing the diffuse component of scattering relative to a local-scale slope, and three global-scale scattering strength functions, which describe scattering over the entire surface relative to the horizontal. These include: mean and rms scattering strength, and grain ratio scattering strength (the ratio of scattering strength from two principal directions of an anisotropic surface). Each provides an important independent constraint on the relationship between local- and global-scale scattering properties: (1) Mean global-scale scattering strength is essentially a more diffuse version of local-scale scattering strength; (2) rms global-scale scattering strength exhibits great sensitivity at low grazing angles to the local-scale scattering strength model; and (3) grain ratio scattering strength is sensitive to the functional form of local-scale scattering strength, especially at low grazing angles. Examples demonstrate that sinusoidal local-scale scattering produces sinusoidal global-scale scattering, whereas Lambertian local-scale scattering does not result in Lambertian global-scale scattering.
Backscattering from a suspension in the near field of a piston transducer
Authors: Downing Andrew , Thorne Peter D. , Vincent Christopher E.
Published: October 2005

The problem of acoustic backscattering from suspended particulates in the near field of a piston source is examined. A monostatic configuration is used, with the transducer acting as a transceiver. Predictions for the range dependence of the backscatter signal are calculated, and formulated into a nondimensional general form. To compare predictions with observations, a series of laboratory experiments, using a number of transducers insonifying varying homogeneous suspensions, has been conducted. To first order the outcome shows good agreement between prediction and observation.
The influence of the modal properties of a stiff layer embedded in a solid medium on the field generated in the layer by a finite-sized transducer
Authors: Lowe M. J. S. , Cawley P.
Published: October 2005

This paper is the second of a pair which compare the modal properties of a stiff layer embedded in a solid medium with the minima of the reflection coefficient. In the first paper [J. Acoust. Soc. Am. 97, 1625–1637 (1995)] the modal properties and the plane-wave reflection coefficient are compared. In this paper a finite width incident beam is modeled and the reflected field is studied, the spatially realistic simulation enabling the comparisons to address the issues which will arise in practical measurements of reflection coefficient minima. The finite beam reflection minima can be caused both by minima of the plane-wave reflection coefficient and by interference of the leaking field produced by a propagating mode with the specular reflection. In systems in which there is a large acoustic impedance contrast between the layer and the surrounding medium, these phenomena occur under practically the same conditions. However, when the surrounding medium is similar to the layer, major changes in the reflection behavior are seen. Predictions are presented for single interfaces and embedded layers, assuming both fluid and solid embedding media. For a single interface it is shown that the reflection coefficient minima correlate directly to the modal properties since plane-wave reflection coefficient minima do not occur. For an embedded layer whose properties are similar to those of the embedding medium, the plane-wave reflection coefficient minima dominate the response and the (strongly leaking) modes of the layer are only excited very weakly by the incident beam.
Moments and angular spectrum for rough surface scattering at grazing incidence
Authors: Spivack Mark
Published: October 2005

This paper considers the statistics of a plane wave scattered at low grazing angles from a one-dimensional rough surface, when the interaction with the surface is mainly in the forward direction. The mean intensity and autocorrelation of the scattered field and the corresponding angular spectrum, to second order in surface height is found. The diffuse component of the spectrum vanishes with the square of the grazing angle, while the specular part approaches unity linearly. The higher moments of the field at the mean surface are also obtained. It is shown that to first order in the grazing angle the moments of the scattered field change only by a phase factor with distance into the medium, so that in the small angle limit the moments in the medium can be derived from those at the surface. The results depend explicitly upon the autocorrelation function of the surface and its first derivative.
Multiple multipole expansions for acoustic scattering
Authors: Imhof Matthias G.
Published: October 2005

The paper presents a new approach to solve multiple scattering of acoustic waves in two dimensions. Traditionally wave fields are expanded into an orthogonal set of basis functions. Often these functions build a multipole. Unfortunately, these multipoles converge rather slowly for complex geometries. The new approach enhances convergence by including multiple multipoles into each region, allowing irregularities of the boundary to be resolved locally. The wave fields are expanded into a set of nonorthogonal basis functions. The incident wave field and the fields induces by the scatterers are matched in the least-square sense by evaluating the boundary conditions at discrete matching points along the domain boundaries. Due to the nonorthogonal expansions we choose more matching points than actually needed resulting in an overdetermined system which is solved in the least-squares sense. This allows an estimate of how well the expansion converges and can help to tune the scheme to enhance accuracy or reduce runtime. The idea of the multiple multipole can be extended by using more complicated basis functions which are closer to the solution sought. The resulting algorithm is a very general tool to solve relatively large and complex two-dimensional scattering problems.
Diffraction by plane screens
Authors: Tran Van Nhieu Michel
Published: October 2005

A new approach is proposed to address the problem of the diffraction of a spherical incident wave by soft or hard plane screens of arbitrary shape at high frequencies. The theoretical formalism is based upon the matched asymptotic expansions method and the analysis is restricted to single diffraction at the edge of the screen. It is shown that the inner solution which is valid near the edge can be approximated by the solution of the diffraction by a half-plane while far from the edge, the outer solution may be built up as the sum of two components: One is the physical optics solution and the other is the sum of two edge integral solutions. These last solutions are an extension of the solution which has been used to describe the acoustics of the slender bodies and their calculations are considerably simplified when the incident angle is perpendicular to the edge. It is proved that the present results are asymptotically equivalent to the geometrical theory of diffraction and the physical theory of diffraction when single diffraction is taken into account. Some other applications are also given to support the present formalism.
Low-frequency acoustic behavior of highly porous, layered, flexible, fine fiber materials
Authors: Lambert Robert F.
Published: October 2005

This paper is concerned with predicting the acoustic behavior of highly porous, layered, flexible, fine fiber materials at low frequencies. A theoretical model of fiber behavior is developed that consists of two independent modes of vibration that exhibit resonance at zero frequency and a finite frequency. This model also incorporates a fiber parameter g that governs the fraction of fibers that can resonate which is now hypothesized to be frequency dependent and was found to range between a comparatively low value g0 near zero frequency and a high value g∞ at higher frequencies. These asymptotic values and the location of the transition region were found empirically. There is good agreement between this model and experiments designed to measure the effective resistivity φe and the effective density ρe of the fluid in the pores of the fibers over a wide range of frequencies.
Modeling space-time domain acoustic wave fields in media with attenuation: The symbolic manipulation approach
Authors: Verweij Martin D.
Published: October 2005

A method is presented for the determination of the space-time domain acoustic wave field, and in particular the space-time domain Green’s function, in homogeneous, isotropic, lossy equivalent fluid media that represent solids with a complicated viscoelastic behavior. The loss properties of the equivalent fluids are modeled with the aid of arbitrarily intricate compliance memory functions and, eventually, inertia memory functions. The presented integral transformation-type method consists of three steps. First, a temporal Laplace transformation and a horizontal spatial Fourier transformation are performed. Due to the application of the temporal Laplace transformation, causality of the acoustic wave field is automatically dealt with. Second, the resulting transform domain problem is solved using a convergent Neumann series solution. Analytical expressions for the terms of this Neumann series solution are obtained by means of a recurrence scheme that can ideally be evaluated with the aid of symbolic manipulation. Third, the transformation back to the space-time domain is performed analytically using the Cagniard–De Hoop method. No numerically imposed limitation of the bandwidth of the wave field quantities or the Green’s function shows up. In principle, the method offers the possibility of generating space-time domain results, both for the acoustic wave field and the Green’s function, for any time instant with any desired degree of accuracy. After deriving the general theory, numerical results for several lossy equivalent fluids with an almost constant-Q behavior, as shown by many types of rock, are presented.
Experimental observation of acoustic resonances in square cross section rods
Authors: de Billy M.
Published: October 2005

It is well known that an acoustic wavetrain scattered from an axisymmetric elastic target presents a distortion at resonant frequencies. This property is used to experimentally characterize the acoustic reradiation from a square cross section bar of infinite length, excited at resonance frequencies by acoustic waves traveling perpendicularly to the axis of the sample. An analysis of the angular variations of the acoustic pressure measured in the free reemission section of the detected signal reveals structures whose shape depends on the parameter Fd (frequency times the width of the rod) for a given material. It is verified that plate mode types are excited and that they can be characterized by their behavior in directions perpendicular to the direction of the incident beam. Additional resonances have been also observed at low frequencies. These unexpected modes were attributed to the excitation of ‘‘cross-sectional modes of vibration.’’
Resonance angular diagrams observed from anisotropic cylinders submitted to an acoustic excitation
Authors: de Billy M.
Published: October 2005

It was demonstrated that, at resonance frequencies, isotropic cylinders normally insonified by an acoustic wavetrain point out reemission angular diagrams characterized by a regular pattern whose structure depends on the frequency of excitation. In this paper the reemission pattern associated to anisotropic cylindrical samples is investigated. The experimental results achieved on a stainless-steel cylinder demonstrate that the resonances of the Rayleigh series are not affected by the anisotropy of the sample whereas the diagrams which correspond to the Whispering Gallery waves are different than those observed with isotropic cylinders.
Thermoviscous effects on transient and steady-state sound beams using nonlinear progressive wave equation models
Authors: Too Gee Pinn James , Lee Shyi Tsong
Published: October 2005

Earlier NPE (nonlinear progressive wave equation) models were developed without considering dissipative effects of the media. In the present study, the thermoviscous dissipation term is derived and added to the NPE models. According to types of waves and coordinates under consideration, four formulations of dissipative versions of NPE are developed. Cylindrical and spherical versions of NPE which are suitable for describing propagation of sound beams are used to study the dissipative effects on a tone burst. The dissipative NPE version gives excellent agreement with experiment data by Moffett et al. [J. Acoust. Soc. Am. 47, 1473–1474 (1970); 49, 339–343 (1971)] and Lockwood et al. [J. Acoust. Soc. Am. 53, 1148–1153 (1973)]. Also, the dissipative NPE version can describe phenomena of self-demodulation. In addition, it is concluded that the number of wavelengths that are needed in an initial tone burst in order to obtain steady-state parts in the waveform is affected by the locations under consideration and the dissipation value.
Evolution equations for nonlinear Rayleigh waves
Authors: Hamilton M. F. , Il’insky Yu. A. , Zabolotskaya E. A.
Published: October 2005

Evolution equations are derived for nonlinear Rayleigh waves on the surface of an isotropic solid. Two evolution equations are derived, one in terms of the real horizontal displacement component, and the other in terms of a complex displacement variable. The equations are derived from the theoretical model developed by Zabolotskaya [J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. To simplify the present analysis, not all nonlinear terms are included. However, the simplified model is shown to provide a good approximation of the nonlinear effects predicted by the complete model. Moreover, the present analysis can be extended to include the remaining nonlinear terms. Numerical solutions obtained by solving the complex evolution equation in the time domain are compared with frequency domain calculations.
Acoustic energy quantities and radiation force in higher approximation
Authors: Beissner K. , Makarov S. N.
Published: October 2005

Extending the familiar linear acoustics treatment, the acoustic energy density, the acoustic energy flux density (acoustic intensity), and the acoustic radiation stress tensor in a three-dimensional acoustic field in a lossless and nondispersive fluid are calculated up to any order of approximation. The formulas obtained are used to discuss the question of the validity limitations of the familiar second-order result for the relation between radiation pressure and intensity. This question is important in connection with the widespread use of the radiation force method for ultrasonic power measurements. An answer is given by calculating the third- and fourth-order expressions for the specific case of a plane-progressive wave impinging on a perfect absorber. The result is that in the whole amplitude range covered by current ultrasonic medical equipment (therapeutic and diagnostic), the third- and fourth-order correction to the second-order formula is less than 1% and can thus be neglected.
Time-domain modeling of pulsed finite-amplitude sound beams
Authors: Lee Yang-Sub , Hamilton Mark F.
Published: October 2005

A time-domain algorithm that solves the Khokhlov–Zabolotskaya–Kuznetsov (KZK) nonlinear parabolic wave equation is described. The algorithm models the propagation of pulsed finite amplitude sound beams radiated from axisymmetric sources in homogeneous, thermoviscous fluids. Numerical results are presented for waveform distortion and shock formation in directive beams radiated by pulsed circular pistons. Waveforms are calculated through the shock region and out to far-field locations where they are dominated by the nonlinearly generated low-frequency components. Effects of pulse duration, frequency modulation, and noise are examined. Methods for including relaxation and focusing are described.
Wave collation visual speech display: Design and evaluation
Authors: Mitchell Philip A. , Easton Randolph D.
Published: October 2005

The wave collation display is a pitch-synchronous, time-domain visual speech display. Collation processing maps the speech waveform into a planar array, condensing the waveform and making speech information, including pitch contour and formant transitions, salient. Evaluation included both analytic evaluation and training. Analytic evaluation was based on a perceptual sorting task using untrained subjects. Subjects sorted printed speech display tokens by visual similarity in a match-to-exemplar design. Stimuli included vowels, with single speaker, multiple speakers, and multiple phonemic contexts, and voiceless consonants. Results for untrained subjects ranged from 73% correct (consonants) and 71% correct (vowels) for single speaker tokens to 46% correct (multiple speaker vowels). For comparison, analytic evaluation using spectrograms was also performed for vowels with single and multiple speakers. Overall results were statistically equivalent to the collation display, with 76% correct (single speaker vowels) and 44% correct (multiple speakers). In the training component, four subjects were trained on collation display sorting tasks as above; after mastering these tasks, generalization to novel stimuli was tested. The tasks were mastered in a few hours, and generalization to novel tokens from a familiar speaker was nearly perfect; generalization to unfamiliar speakers was imperfect.
Laser-induced piezoexcitation of plane shear bulk acoustic pulses
Authors: Telenkov S. A. , Gusev V. E. , Avanesyan S. M.
Published: October 2005

Laser-induced piezoexcitation of bulk transverse acoustic waves in high-resistance CdS1−xSex crystals has been investigated. These experiments confirm the possibility of generating plane shear acoustic pulses, propagating normally to the irradiated surface. These observations demonstrate the possibility of achieving the optoacoustic imaging of the electric field distribution in piezosemiconductor-based microelectronic circuits.
New formulas for predicting the accuracy of acoustical measurements made in noisy environments using the averaged m-sequence correlation technique
Authors: Bleakley Chris , Scaife Ronan
Published: October 2005

The averaged m-sequence correlation technique has been established as a means of measuring linear system responses under high noise conditions. This Letter examines the theoretical basis for the technique and derives an analytical formula for the expected error in the estimated system response under noisy conditions at the system input and/or output. The formula shows close agreement with previously published experimental results [W. Zuomin and W. T. Chu, J. Acoust. Soc. Am. 94, 1409–1414 (1993)] and with newly derived simulation results.
Further comments on proportional duration and proportional variance as factors in auditory pattern discrimination
Authors: Lutfi Robert A.
Published: October 2005

This brief comment, in response to the letter by Gary Kidd [J. Acoust. Soc. Am. 97, xxx (1995)], asserts that two recent accounts of the discrimination of variable tone patterns are more similar than they are different—the real difference being that only one (the CoRE model) develops a shared premise into an explicit prediction for d′. Advantages of the CoRE model are more accurate predictions for the effects of proportional duration, and the ability to make explicit predictions for the effects of other important variables and their interaction.
A direct boundary element method for acoustic radiation and scattering from mixed regular and thin bodies
Authors: Wu T. W.
Published: October 2005

In this paper, the direct boundary element method is applied to acoustic radiation and scattering from mixed regular and thin bodies. A typical application problem involves a regular body with thin fins either attached to or in the neighborhood of the body. It is shown that the mixed-body integral formulation requires interactions between the conventional Helmholtz integral equation and the hypersingular thin-body integral equation. If at least one regular body is involved in a mixed-body environment, the direct integral formulation possesses the well-known nonuniqueness difficulty. This nonuniqueness difficulty is overcome by either the CHIEF method or the Burton and Miller method. Since both the thin-body integral equation and the Burton and Miller equation contain a hypersingular integral, a regularized form recently derived by Krishnasamy et al. [ASME J. Appl. Mech. 57, 404–414 (1990)] is adopted in this paper. Numerical results show excellent agreement with a multidomain boundary element solution and a point-source solution.
Modal superposition in the time domain: Theory and experimental results
Authors: Boone Marinus M. , Janssen Gilles , van Overbeek Michiel
Published: October 2005

Time domain expressions of the modal superposition are derived. It is shown that modal superposition in the time domain is a valuable tool to describe the stationary and nonstationary behavior of acoustic systems, especially in active noise control applications. The mathematical expressions show physical insight in the fundamental differences between stationary and decaying sound fields. Simulations and measurements based on the time domain expressions have been carried out for the special case of a lightly damped rectangular cavity. These simulations and measurements show a good agreement.
Phase and energy velocities of cylindrically crested guided waves
Authors: Ditri John J.
Published: October 2005

The excitation and propagation of axisymmetric, cylindrically crested, azimuthally polarized elastic waves in a homogeneous isotropic plate is analyzed. As is well known, the frequency spectrum of the azimuthally polarized waves is identical to the analogous (straight crested) horizontal shear (SH) modes. It is shown, however, that the phase and energy velocity dispersion curves of the azimuthally polarized waves can differ significantly from their SH mode analogs. In addition, it is shown that both the phase and energy velocity dispersion curves of the azimuthally polarized waves are functions of radial position. Finally, it is demonstrated analytically that at observation distances large in comparison to the ‘‘far-field wavelength’’ the phase velocity curves of the azimuthally polarized waves converge to the corresponding SH curves and that the energy velocity curves of the cylindrically crested azimuthally polarized waves converge to the group velocity dispersion curves of the SH modes. The convergence is, in both cases, nonuniform with frequency and is shown to depend on the ratio of observation distance to the far-field wavelength of the mode.
Acoustic calibration in shallow water using sparse data
Authors: Rouseff Daniel , Siderius Martin , Fox Warren L. J. , Porter Robert P.
Published: October 2005

Conventional numerical techniques for calculating acoustic propagation may produce unsatisfactory results if there is insufficient information about the medium. These difficulties are exaggerated in highly variable shallow-water locales. In the proposed approach, sparse environmental measurements are supplemented by making a limited number of direct acoustic measurements. The combined data set can in principle be used to calibrate in-water systems. In this paper, acoustic calibration is demonstrated for the field extrapolation problem where the objective is to predict propagation over an extended regime. Two alternative versions of the extrapolation algorithm are first postulated and then verified analytically for the special case of adiabatic propagation. The method is then tested numerically using archival sound-speed and bathymetric data for a strongly range-dependent site. The individual and cumulative effects on down slope propagation from variations in bathymetry, imperfect knowledge of the sediment, and variability in the water column are quantified.
Dynamic analysis of space-based inflated beam structures
Authors: Main John A. , Carlin Robert A. , Garcia Ephrahim , Peterson Steven W. , Strauss Alvin M.
Published: October 2005

This paper examines the dynamic behaviors of inflated beam aerospace structures. The principal foci of this investigation are the determination of the damping mechanisms active in structures constructed from inflated cylindrical beams, development of a practical modeling method for complex structures, and an examination of the difficulties in predicting on-orbit dynamic behavior from ground tests. A Euler–Bernoulli model of the inflated beam is used to determine distributed damping coefficients from modal tests. The results show that the viscous damping in the inflated beam is independent of beam pressure, but that the pressurization stress levels in the beam fabric affect the strain-rate damping. The Euler–Bernoulli inflated beam model is used in conjunction with a conventional finite element package to model the dynamic behavior of a complex inflated beam structure, a 1.7-m-diam inflated dish antenna mockup. The model accurately predicts the lower natural frequencies of the dish structure. A comparison of modal tests of inflated beam structures performed both in the near weightlessness of the NASA KC-135 low gravity simulator aircraft and in a ground laboratory demonstrates that gravity level can have a dramatic effect on system damping.
A generalized model for predicting the sound transmission properties of generally orthotropic plates with arbitrary boundary conditions
Authors: Woodcock Roland , Nicolas Jean
Published: October 2005

Sound transmission is of significant concern in practical situations, such as building noise insulation or quietening of mechanical products. If the medium- and high-frequency response are well mastered, it is not the case in the low-frequency range where some discrepancies between experiments and theory remain sometimes unexplained. In view of these limitations, the scope of this work is to develop a generalized model which focuses on aspects particularly important in the low-frequency range, namely (1) the finite size of the panel, (2) the orthotropy properties, and (3) the boundary conditions. A variational approach is adopted. The Hamilton functional is built starting with the general tensor relationships between stresses and strains for a generally orthotropic plate. The extremalization is performed using the Rayleigh–Ritz method in conjunction with a nonorthogonal polynomial basis in order to deal with general boundary conditions. The excitation is an acoustic plane wave of any incidence and the radiated field is calculated with an impedance matrix including the cross coupling terms. The different vibroacoustic indicators are the quadratic velocity of the plate, its radiation efficiency, and the transmission loss. The importance of including the intermodal interaction is clearly pointed out. It produces narrow peaks of transmission loss well above the classical mass law. The effect of the dimensions of the panels is shown rigorously and suggests that experimental results should be given in narrow-band if one wants to get usable data. The model also allows, probably for the first time, the effect of the boundary conditions to be fully analyzed. Interestingly enough, the free-free case gives a much bigger transmission loss in the low-frequency range which gives an insight, when possible, for improving the transmission loss.
An application of systolic spatial processing technique in adaptive beamforming
Authors: Chang Shun-Hsyung , Huang Chen-June
Published: October 2005

The adaptive beamformer applied in underwater acoustics, radar, or sonar, etc. must be able to achieve real-time signal processing and to overcome a variety of adverse environmental factors, such as coherent interference and pointing error, which often result in serious degradation of the array performance. Coherent interference is generally caused by multipath transmission or active jammer. On the other hand, pointing error is caused by an error in target signal direction estimation. Along with the advancement of very large-scale integration technologies, some of the common algorithms of signal processing are now implemented in highly pipelined and regular systolic arrays. This paper, adopting a QR systolic array as the computational engine and using the generalized sidelobe canceller (GSC) adaptive beamformer as the underlying architecture featuring a simple hard preprocessor, advances the systolic spatial processing technique (SSPT) to suppress effectively coherent interference and to improve the influence caused by pointing error. SSPT converges speedily and needs only a limited amount of sampling data to achieve adaptive processing. The computer simulations prove that the performance of SSPT is satisfactory.
An optimum computer-generated pulse signal suitable for the measurement of very long impulse responses
Authors: Suzuki Yôiti , Asano Futoshi , Kim Hack-Yoon , Sone Toshio
Published: October 2005

Transfer functions of acoustic systems often exhibit wide dynamic ranges and very long impulse responses. A ‘‘time-stretched’’ pulse as proposed by Aoshima (ATSP), though originally given in a very specific form seems to be one of the most promising signals to measure transfer functions with characteristics of acoustic system mentioned as above. In this paper, this pulse (ATSP) is first generalized and then optimized for the measurement of long impulse responses. This optimized ATSP (OATSP) has an almost ideal characteristic to measure impulse responses shorter than its specific length N. Moreover, it is newly shown in this paper that OATSP has also a good characteristic to measure impulse responses longer than N. Discussion is presented on how to design OATSP suitable for a specific situation of measurement by analyzing errors, when the pulse is used to measure impulse responses longer than N.
Force threshold for hearing by direct bone conduction
Authors: Carlsson Peder , Håkansson Bo , Ringdahl Anders
Published: October 2005

The bone-anchored hearing aid is connected, by means of a skin-penetrating bayonet coupling, to an implanted titanium fixture. Hence, direct bone conduction (dbc) excitation is used. Since no international standard of audiometric zero for dbc force threshold exists, it is of general interest to determine the dbc force threshold for normal hearing subjects. Two different methods have previously been applied to estimate the relation between bone conduction (bc) and dbc thresholds. One preliminary problem was to make a measurement of the output-force level of dbc transducers, which is equivalent to the situation in situ. A skull simulator, TU-1000, has been designed for measuring the output-force level of dbc transducers. The skull simulator does, in an adequate way, reflect the mechanical point impedance of the human skull. This opportunity to determine equivalent dbc force thresholds has motivated the present study in which a linear relation between the dbc force threshold and the bc force threshold was estimated. The estimate found in the present study conforms fairly well with the two previously found estimates. It is suggested that the estimate found in the present study be used as the reference equivalent threshold force level for dbc.
Contralateral and ipsilateral suppression of the 2f1−f 2 distortion product in human subjects
Authors: Williams Deirdre M. , Brown Ann M.
Published: October 2005

The amplitude of the 2f1−f2 distortion product was measured under four conditions in human subjects: during simple two-tone stimulation, during stimulation with a third, pure tone in the ipsilateral ear, during contralateral stimulation with broadband noise, and with combined ipsilateral third tone and contralateral noise. The amount of ipsilateral suppression produced varied with suppressor frequency but was maximum close to the f2 primary frequency as previously demonstrated using similar stimulus parameters [A. M. Brown and D. T. Kemp, Hear. Res. 13, 29–37 (1984); F. P. Harris, R. Probst, and L. Xu, ibid. 64, 133–141 (1992)]. Contralateral stimulation also suppressed the level of distortion. During ipsilateral suppression combined with contralateral stimulation, the amount of ipsilateral suppression of the distortion product was reduced. This interaction may indicate a common mechanism for ipsilateral and contralateral suppression. The decrease in ipsilateral suppression under contralateral stimulation was most pronounced at the peak of the ipsilateral suppression tuning curves and this produced some broadening of the function. In the majority of ipsilateral suppression curves, the peak ipsilateral suppression frequency was observed to shift upwards during contralateral stimulation. These results suggest that contralateral stimulation alters the frequency-selective properties of the cochlear response.
Intensity discrimination under forward and backward masking: Role of referential coding
Authors: Plack Christopher J. , Carlyon Robert P. , Viemeister Neal F.
Published: October 2005

The present experiments investigated the hypothesis that listeners can code intensity by reference to proximal stimuli in order to improve intensity discrimination performance in conditions of nonsimultaneous masking. The experiments used 30-ms tone bursts as the masker, pedestal, and ‘‘proximal burst.’’ The masker level was 80 dB, the pedestal level was 50 dB. In the first experiment the silent interval between the masker and the pedestal was varied. Surprisingly, in both forward and backward masking situations, the Weber fraction decreased as the silent interval was decreased from 100 to 12.5 ms. This is consistent with the referential coding hypothesis: At short intervals performance improves because the level of the pedestal is coded by reference to the proximal masker. In a further set of experiments, the silent interval was 100 ms and an additional proximal burst was presented either 12.5 ms before or 12.5 ms after the pedestal. The proximal burst produced a substantial decrease in the Weber fraction, but only when it was close in frequency to the pedestal, and with a higher intensity. The results are consistent with the auditory system having the ability to produce a robust intensity measure by reference to proximal signals. These findings also provide further evidence that the mid-level elevation in forward masking is not solely the result of processes operating at the level of the auditory nerve.
Voice simulation with a body-cover model of the vocal folds
Authors: Story Brad H. , Titze Ingo R.
Published: October 2005

A simple, low-dimensional model of the body-cover vocal-fold structure is proposed as a research tool to study both normal and pathological vocal-fold vibration. It maintains the simplicity of a two-mass model but allows for physiologically relevant adjustments and separate vibration of the body and the cover. The classic two-mass model of the vocal folds [K. Ishizaka and J. L. Flanagan, Bell Syst. Tech. J. 51, 1233–1268 (1972)] has been extended to a three-mass model in order to more realistically represent the body-cover vocal-fold structure [M. Hirano, Folia Phoniar. 26, 89–94 (1974)]. The model consists of two ‘‘cover’’ masses coupled laterally to a ‘‘body’’ mass by nonlinear springs and viscous damping elements. The body mass, which represents muscle tissue, is further coupled laterally to a rigid wall (assumed to represent the thyroid cartilage) by a nonlinear spring and a damping element. The two cover springs are intended to represent the elastic properties of the epithelium and the lamina propria while the body spring simulates the tension produced by contraction of the thyroarytenoid muscle. Thus contractions of the cricothyroid and thyroarytenoid muscles are incorporated in the values used for the stiffness parameters of the body and cover springs. Additionally, the two cover masses are coupled to each other through a linear spring which can represent vertical mucosal wave propagation. Simulations show reasonable similarity to observed vocal-fold motion, measured vertical phase difference, and mucosal wave velocity, as well as experimentally obtained intraglottal pressure.
Classification of background noises for hearing-aid applications
Authors: Kates James M.
Published: October 2005

A background-noise classification procedure is being developed for hearing-aid applications, wherein the hearing-aid response would be adjusted in response to changes in the noise environment. The classification procedure is based on measuring four signal features giving the fluctuations of the signal envelope and the mean frequency and low- and high-frequency slopes of the average spectrum. A more complicated procedure, based on determining the envelope modulation spectra in auditory critical bands, was also investigated and was found to offer no advantages over the simpler procedure. The accuracy of the classification procedure was determined for eleven everyday background noises under optimal conditions where the training and test noise sequences were different portions of the same short noise recording. A cluster analysis was used to determine the similarities among the feature vectors for the noises, and when the noises are grouped into a reduced number of clusters the noise-classification accuracy using the four features exceeds 90%.
Modeling the glottal volume-velocity waveform for three voice types
Authors: Childers D. G. , Ahn Chieteuk
Published: October 2005

The purpose of this study was to model features of the glottal volume-velocity waveform for three voice types: modal voice, vocal fry, and breathy voice. The study analyzed data measured from two sustained vowels and one sentence uttered by nine adult, male subjects who represented examples of the three voice types. The primary analysis procedure was glottal inverse filtering, which estimated the glottal volume-velocity waveform. The estimated glottal volume-velocity waveform was then fit to an LF model waveform. Four parameters of the LF model were adjusted to minimize the mean-squared error between the estimated glottal waveform and the LF model waveform. Statistical averages and standard deviations of the four parameters of the LF glottal waveform model were calculated using the data for each voice type. The four LF model parameters characterize important low-frequency features of the glottal waveform, namely, the glottal pulse width, pulse skewness, abruptness of closure of the glottal pulse, and the spectral tilt of the glottal pulse. Statistical analysis included ANOVA and multiple linear regression analysis. The ANOVA results demonstrated that there was a difference in three of the four LF model parameters for the three voice types. The linear regression analysis between the four LF model parameters and a formal rating by a listening test of the quality of the three voice types was used to determine the most significant LF model parameters for each voice type. A simple rule was devised for synthesizing the three voice types with a formant synthesizer using the LF glottal waveform model. Listener evaluations of the synthesized speech tended to confirm the results determined by the analysis procedures.
An approximate integral method for calculating the diffracted component from multiple two-dimensional objects
Authors: Nightingale T. R. T.
Published: October 2005

A method for determining the diffracted or scattered components due to the interaction of a wave with multiple two-dimensional objects is given. The method presented uses approximate boundary conditions to simplify the numerically cumbersome set of integral equations associated with nonapproximate analytic solutions of the Helmholtz integral. The approximate boundary conditions, defined here, are shown to decouple the N by N set of simultaneous equations. The approximate boundary conditions are used to calculate the insertion loss for various sizes of two-dimensional objects. The predictions are compared to measured results and limitations are discussed.