bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave scattering using a hybrid MMP–FE technique
Authors: Imhof Matthias G.
Published: October 2005

Among the methods amendable to solve acoustic or elastic scattering problems are the finite elements method (FEM) and multiple multipole (MMP) expansions [M. G. Imhof, J. Acoust. Soc. Am. 97, 754–763 (1995)]. Among the difficulties the FEM encounters are long calculation times, large memory requirements, and the need for absorbing boundary conditions. On the other hand, the FEM is perfectly suited for heterogeneous media because it automatically accounts for changes in material properties. In contrast, the computational cost of MMP expansions is independent of the source–receiver geometry. An unbounded domain poses no difficulty since the expansion functions account automatically for the radiation condition. MMP expansions often converge with very few terms and therefore reduce the computational effort. Unfortunately, expansion functions for heterogeneous media are difficult to find. Scattering problems with heterogeneous scatterers embedded in a homogeneous background are difficult (FEM) or impossible (MMP) to solve with either of these techniques alone. Therefore, the MMP expansions are coupled with the FE method. For a cylindrical scattering problem, the resulting solution is compared to the analytical one. Results for multiple inhomogeneous scatterers embedded in a homogeneous media are presented.
Acoustic imaging of thin films or interfaces
Authors: Harris John G. , Wickham Gerry
Published: October 2005

The imaging of thin solid films or interfaces by a confocal arrangement of ultrasonic transducers is modeled in both a two-dimensional and a three-dimensional context. In the first model, an antiplane shear, focused beam is directed across an interface comprised of an array of cylinders, with contrasting material properties. Its periodicity is destroyed by removing cylinders arbitrarily. In the second, a thin solid film, having quite general mechanical properties, is immersed in a fluid and scanned by a three-dimensional acoustic beam. This last work is only partially completed. An approximate integral representation of wave fields scattered by these thin regions of heterogeneity in terms of a Green’s function for the host media, and the stress and momentum polarizations averaged through the thickness of the film or interface is the starting point. The stress polarization measures the change in elastic properties and the momentum polarization that in inertial properties, both changes being with respect to the properties of the host media. The scattered waves are calculated by formulating and solving integral equations. Those received are estimated using a measurement model that mimics the receiving transducer. [Supported by the NSF, MSS 91-14547.]
Time reversal of ultrasonic waves in solids: Theory and experiments
Authors: Draeger Carsten , Cassereau Didier , Fink Mathias
Published: October 2005

In previous works, the capacity of time-reversal mirrors (TRM) has been presented to optimize ultrasonic focusing on a pointlike source. However, the evaluation of the focusing quality has so far been limited to fluid media. In this paper, the first theoretical approach is presented to determine the capacity of the TRM to focus on a point situated in a homogeneous isotropic solid. P and S waves emitted by a pointlike source in the solid yield the generation of transmitted pressure waves in a fluid that limits the solid via a plane boundary. A TRM placed in the fluid behind the interface measures both incoming wavefronts and is hence able to reverse them one by one. The reversed pressure fields backpropagate to the interface, resulting in P and S waves in the solid. It is shown that, in spite of the losses at the interface, both kinds of waves focus at the location of the initial source. Numerical simulations are carried out, showing that the time reversal is more favorable using the S waves than the P waves, in terms of the width of the focal spot as well as in terms of displacement amplitude. The results are compared with experiments carried out with a laser source working in the ablation regime.
Detailed observation of the complete fracture process of brittle carbon foam
Authors: Krysac L. C. , Maynard J. D.
Published: October 2005

Using wideband transducers, we have observed the acoustic signals produced by individual bond breaking events during the fracture of open cell brittle carbon. The complete fracture process, beginning with intermittent precursor bursts of small numbers of bonds breaking, and ending with the final rupturing catastrophic event, has been recorded with 20-MHz pinducers and a 400-Megasample/s digital oscilloscope. The statistics of the precursors, etc., including the force applied at any time during the fracture process, have been acquired, related to the acoustic record, and compared with the predictions of the random fuse model for the fracture of brittle material. The role of dynamics and stress waves affecting the fracture of real materials, which is not accounted for in the random fuse model, will be discussed.
Phase-insensitive homomorphic image processing for speckle reduction
Authors: Chen Yan , Broschat Shira L. , Flynn Patrick J.
Published: October 2005

Speckle appears in all conventional ultrasound images and is caused by the use of a coherent transducer. Speckle is an undesirable property as it can mask small but perhaps diagnostically significant features. Speckle noise can be reduced using a phase-insensitive imaging technique to cancel the linear phase relationship between elements. However, with current devices this is hard to achieve because of the large memory and high sampling rate requirements for the 64 or more multiple channels used. To address the problems above, a hybrid method is introduced that combines the phase-insensitive technique with a phase-sensitive speckle reduction method. Several phase-correlated subimages (2 or 4) are formed using classical imaging techniques. Then nonlinear homomorphic processing is applied to destroy the phase relationship between these images. The homomorphic, phase-insensitive, and hybrid nonlinear processing method is developed and examined in this paper. Experiments with synthetic and real ultrasound imagery show that the proposed method improves the signal-to-noise ratio in both lesion and cyst areas and preserves edge clarity. [Work supported by NSF.]
A new approach to compute the resultant pressure of linear array
Authors: Assaad Jamal , Bruneel Christian , Looten Isabelle
Published: October 2005

In this paper, a new calculation scheme is proposed to compute the nearfield and the farfield directivity pattern of such arrays including interactions and without assumptions concerning the displacement field of the transducer radiating surface. For this purpose, using the finite element method (FEM), the farfield directivity pattern of a part of the array (2Q +1 transducers) is computed using dipolar dampers and a previous described extrapolation algorithm [Assaad etal., J. Acoust. Soc. Am. 94, 562–573 (1993)]. This part consists of an active elementary transducer (electrically driven) mounted between 2Q passives (electrically grounded) neighboring transducers. Then, the radiation field of a finite phased and focused array (N elements) can be obtained by summing up the farfield directivity patterns of the 2Q + 1 transducer sets weighted by the classical term used to take account of the geometrical and electrical phase shifts.
Response of a focused transducer facing a rigid reflector
Authors: Manley Martin , Hsu Nelson
Published: October 2005

The diffraction correction factor for a transducer first acting as a transmitter and then receiving the signal reflected off a rigid plane is useful in determining the system transfer function of a pulse-echo system. The determination of the diffraction correction factor is well understood for flat disk transducers, but is more complex for focused transducers. Recently, a method was derived [Chen etal., ‘‘Acoustic coupling from a focused transducer to a flat plate and back to the transducer,’’ J. Acoust. Soc. Am. 95, 3049–3054 (1994)] for approximating the diffraction correction factor of a cylindrically focused transducer for the case when the rigid plane is close to the focal plane of the transducer. In this work, results are presented for cases when the rigid plane is not close to the focal plane of the reflector.
Implosion sound
Authors: Yen Nai-chyuan
Published: October 2005

An open end axisymmetrical cavity is used to study the generation of implosion sound. The cross section of the cavity’s profile has a shape which will distort the wave front of a plane shock wave converging it into a single point. Hence, a spherical collapsing phenomenon can be approximately achieved when a shock wave propagates into the opening of this finite size artificial cavity. Through the shock and shock interference mechanism, a strong impulse therefore is generated at the focal point caused by the pressure difference between the inside and outside of the cavity. This highly localized impulse then is radiated out from the opening of the cavity as a sound projector. A prototype model of 0.5 ℓ size has been constructed and tested in the laboratory. The preliminary experimental results indicated that this device can reach a peak sound pressure level of 146 dB//20 μPa in air and 185 dB//30 μPa in water, with an ambient pressure of 1 atmosphere (1 bar). The 50% pulse width is about 20 and 30 μs for air and water, respectively. Analysis and application of this type of sound projector will be discussed.
Systematic measurements of duct end corrections in the Greenspan viscometer
Authors: Gillis Keith A. , Moldover Michael R. , Mehl James B.
Published: October 2005

A Greenspan viscometer is a Helmholtz resonator that has been optimized for viscosity measurements in gases. It consists of two chambers connected by a duct. The model, design considerations, and performance of such a device have been described elsewhere [Gillis etal., ‘‘Acoustic Greenspan viscometer for gases,’’ submitted to Rev. Sci. Instrum.]. The model represented the effects of nonuniform flow near the ends of the duct as a complex acoustic impedance Zend, based on the numerical calculations by Mehl [J. Acoust. Soc. Am. 97, 3327 (1995) and unpublished calculations]. In this work, the ‘‘end corrections’’ were measured in a Greenspan viscometer with interchangeable ducts and a detector located in each chamber. This new design enabled a series of viscosity measurements to be performed with the same chambers and transducers, and with three different duct lengths and two duct diameters. The consistency between the experiments and the model will be presented. [Work supported by the Office of Naval Research.]
Sound velocity measurements of thin sheet materials at high temperatures
Authors: Matsuda Youichi , Nakano Hidetoshi , Shin Shoichirou , Nagai Satoshi
Published: October 2005

Longitudinal sound velocities of thin sheet materials were determined between room temperature and 1000 °C. The velocities were calculated from sample thickness and round trip echo times. A micrometer or an ellipsometer was used for thickness measurement. A single optical pulse was extracted from a passively mode-locked Nd:YAG laser by using an optical switch. The optical pulse has 30-ps pulse duration and 10-mJ output energy, which is focused on the sample surface to generate ultrasound. Ultrasound is detected with a Michelson interferometer having a frequency response up to 1 GHz. Since this system has no contact with the sample, it is suitable for acoustic measurements at high temperatures. Sound velocities of 304 stainless-steel sheets were measured at various temperatures in the range from RT to 1000 °C. It was shown that round trip echo time could be measured to an accuracy of 3% for the sample of 20 μm thickness. Furthermore, several kinds of ceramic thin sheets were also examined.
Networks for piezoceramic resonators
Authors: Ballato Arthur , Ballato John
Published: October 2005

Equivalent circuits for characterizing piezoelectric resonators have been used for many years, and in a wide variety of applications. The future will see applications extended through the UHF band for ferroelectric ceramic thin-film resonant microstructures, e.g., for cellular radios. Such applications will require material and processing uniformity far greater than is currently achieved, and means for their verification. Piezoceramics occupy a difficult position, however, when it is required to obtain precise material parameters from broadband electrical measurements. This situation arises because of their particular attributes: high coupling and moderate loss. Highly accurate lumped equivalent networks for these frequencies have been developed for both canonical cases of thickness- and lateral-field excitation. Measurements on these circuits permit the extraction of the complex dielectric, piezoelectric, and elastic parameters of the ceramic material. This paper discusses both traditional and modern electrical network descriptions of piezoelectric resonators; and also treats how they are modified by the conditions of excitation and inclusion of loss mechanisms.
Four-pole parameters of a duct with low Mach number flow
Authors: Zhenlin Ji , Jiazheng Sha
Published: October 2005

The relationship between the four-pole parameters of a duct with and without low Mach number flow is established. A transformation of the variable is used to enable the sound propagation problem with low Mach number flow to be reformulated as the solution of an ordinary Helmholtz equation for the transformed variable. Thereby, the expression for the four-pole parameters of a duct with flow is derived which can be determined by evaluation of the four-pole parameters for the case of the stationary medium. The results show there is a noticeable variation in the four-pole parameters, but there is not any variation in the transmission loss with mean flow.
Broadband acoustic scattering from a ribbed shell
Authors: Houston Brian H. , Bucaro J. A. , Photiadis Douglas M.
Published: October 2005

Monostatic acoustic scattering measurements have been made on a large aspect ratio (L/D=6.2) ribbed cylindrical shell over the frequency range 0.8<ω/ωr<12 (where ωr is the ring frequency for the shell). The ribs are arranged in a near periodic array with small random deviations in the rib locations of magnitude da/a=0.05. The physical processes that give rise to peaks in the scattering cross section are discussed and the ability of various theoretical models to predict the locations of the highlights is examined. The measurements provide further confirmation that the principle sources of scattering for typical ribbed shells in this frequency range are specular reflection, phase matching to fast membrane waves, phase matching to flexural Bloch waves, and Bragg scattering from the ribs. They also reveal that the scattered spectrum of the flexural Bloch waves can be more complicated than originally thought.
Elastic constants and crystal orientation of individual grains of polycrystalline solids from scanning acoustic microscopy
Authors: Sathish Shamachary , Mendik Michael , Cantrell John H. , Yost William T.
Published: October 2005

The angular dependence of the surface acoustic wave velocity has been measured on an individual grain of aluminum alloy 2519 using a continuous-wave scanning acoustic microscope equipped with a cylindrical lens. The elastic constants and crystal orientation of the grain have been determined simultaneously using a two step nonlinear least-squares fitting of the data. This is the first time that simultaneous measurements of these properties have been reported using scanning acoustic microscopy. The C11 elastic constant is determined to be (113±5) GPa, C12 is (61±3) GPa, and C44 is (29±2) GPa. These values are within 5% of those reported for pure aluminum. The average Young’s modulus for the grain is calculated from the elastic constants to be (74.5±3.0) GPa and is in agreement with the value 74.4 GPa reported for static load measurements of bulk Al 2519 material. The surface plane orientation of the grain is determined to be (210)±4° and is in agreement with an independent determination using x-ray Laue backreflection measurements.
The New Jersey shelf shallow water random media propagation experiment
Authors: Orr Marshall H. , Lynch James F.
Published: October 2005

The range-dependent properties of a variety of pulsed acoustic signals (200–1000 Hz) propagating in a shallow water waveguide (New Jersey shelf, July–Aug. 1995) randomized by internal waves, bottom heterogeneity and surface roughness have been measured during a 27-day interinstitutional experiment. A 40-km acoustic propagation path located along the NSF Ocean Drilling Program seismic line 1003 was instrumented with moored acoustic sources, three moored acoustic vertical line arrays; eight moored thermistor strings; two moored ADCPs; and two surface gravity wave spectrum buoys. The ocean surface was imaged with ship, P-3 aircraft and ERS-1 radars. The water volume was imaged with high-frequency acoustic systems. Water properties were also measured with shipborne ADCP and CTD sensors. Acoustic sources and receiving arrays were positioned with DGPS and acoustic navigation systems. Timing was maintained with Rubidium clocks. The theoretical/experimental rationale for this experiment will be outlined. The anticipated effects of internal wave- and seafloor-induced randomness on the range-dependent properties of the acoustic signals will be summarized. Preliminary results of the measurements will be presented. [Work supported by ONR.]
Amplitude fluctuation effects in acoustic scattering due to shallow water internal waves
Authors: Fu Lei , Lynch James F.
Published: October 2005

Amplitude fluctuation effects in acoustic scattering due to shallow water internal waves are examined using both adiabatic and coupled normal mode theory. The discussion is restricted to linear (nonsoliton) internal waves with a Garrett–Munk spectrum in this work. Coherent and incoherent effects, adiabatic versus coupled scattering, and the range, frequency, and internal wave amplitude sensitivity of the scattering will be discussed. Directions for future work will be discussed.
Separation of turbulence velocity and temperature sound-speed variability with reciprocal transmission
Authors: Farmer David M. , Di Iorio Daniela
Published: October 2005

Acoustical scintillation results from the combined contribution of scalar (i.e., temperature and salinity) and vector (velocity) fluctuations. Reciprocal transmission allows us to separate these components. In a turbulent flow, in which the measured scales lie within the vertical subrange, the velocity fluctuations can be used to derive the rate of turbulent kinetic energy dissipation. Reciprocal transmission measurements at 67 kHz were recently acquired as part of the U.S. Office of Naval Research ‘‘Moderate to High Frequency’’ research program. The results are interpreted in terms of the effective refractive index structure parameter and compared both with the independent shear probe measurements of Lueck (personal communication) and the recent theoretical analysis of Ostachev [Waves Random Media 4, 403–428 (1994)].
The nonlinear interaction of two plane waves in a viscous medium
Authors: Jiang Zhong-Yue , Greenleaf James F.
Published: October 2005

Earlier studies [P. J. Westervelt, J. Acoust. Soc. Am. 29, 199–203, 934–935 (1957)] of the mutual nonlinear interaction of two plane waves of sound with each other are extended to include the viscous effect. The viscous effect is considered both from the equations of motion and the equation of state of the medium. An analytical solution to the lowest order scattering process is obtained if the viscous effect of second order and higher can be neglected. In fact, it is shown that the scattered density ρs of two interacting plane waves having the frequencies ω1 and ω2, respectively, satisfies the following equation: ⧠2vρs=⧠2v{c0−2E12+[(2cosθ +B/A)/2ω1ω2 (1−cosθ)]∇2W12 +[DB(c20ω1ω2)−1 / 4A ×(1−cosθ)2]∇2(∂W12/∂t)+[DB(3+cosθ)/2Ac40 (1−cosθ)](∂V12/∂t)}, where E12, V12, and W12 are, respectively, the total, potential, and special defined energy densities, D is the sound diffusivity, B and A are nonlinearity parameters, θ is the intersecting angle, and ⧠2v is a modified d’Alembertian operator. [Work supported by CA43920 NIH.]
Influence of phase between original frequencies on the nonlinear generation of new harmonics. Examples of application from nonlinear acoustics
Authors: Hedberg Claes M.
Published: October 2005

It is assumed that the solution to a problem is given in the form of a complex multiple Fourier series infinite in each of the original frequencies. In this paper a simple theorem shows that the absolute values of the individual frequency coefficients in the series are independent of the phase relation between the original frequencies. But the coefficients division into real and imaginary parts is phase dependent. When the relation between the frequencies and original phase is not an irrational number, there exists in the sum several coefficients giving the same frequency, and hence the total amplitude for a specific frequency depends on the phase. An example of application is shown resulting from nonlinear acoustics where, e.g., the importance of original phase for parametric arrays can be estimated. [Work supported by TFR, Sweden.]
Acoustic reciprocity-type and energy conservation theorems for flow-structure problems
Authors: Godin Oleg A.
Published: October 2005

Recently the reciprocity principle was proved for acoustic fields in motionless fluid/solid structures [A. N. Norris and D. A. Rebinsky, J. Acoust. Soc. Am. 94, 1714–1715 (1993)] and a flow reversal theorem (FRT) was established for sound and acoustic-gravity waves in 3-D inhomogeneous, moving fluids [O. A. Godin, J. Acoust. Soc. Am. 97, 3396(A) (1995)]. The FRT is counterpart of the reciprocity principle when ambient flow is present. The theorem states symmetry of some field quantity with respect to interchange of the source and receiver positions and the simultaneous reversal of flow. An FRT will be presented which generalizes results of the above-mentioned works to include waves in flow/solid structures of arbitrary geometry. Parameters of the medium are allowed to be spatially inhomogeneous but time independent. Wave propagation and ambient flow are considered as adiabatic thermodynamic processes. It is assumed the prestresses in the solids due to ambient flow are small. Conservation of a quasienergy for the wave is established and its relation to known acoustic energy corollaries as well as to the FRT is discussed. Some possible applications of the general theorems will be considered. [Work supported by NRC.] a)On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.
Computation of transient Green’s functions through plane interfaces
Authors: Draeger Carsten , Cassereau Didier
Published: October 2005

This work studies the acoustical field generated by a point source after reflection or transmission by a plane interface. There are two classical approaches to calculate such transient Green’s functions, using either a Laplace or a Fourier transform over time. However, the second approach involves numerical integrations that are difficult to carry out because of singularities of the integrand. It is shown that it is possible to avoid this difficulty using an excitation in the form of a temporal Lorentz function of variable width, introducing several judicious variable changes and finally deforming the integration path in the complex plane. By developing the expression of the transmission/reflection coefficient into Taylor’s series around suitable points, it is even possible to carry out a piecewise integration analytically, therefore resulting in an approximate expression of the acoustical field as a function of space and time. Since this expression turns out to be in a closed form, it can be evaluated fast and even be manipulated later on.
Interaction of shear wave polarization and composite laminate layup: Experiment and modeling
Authors: Fischer Brent A. , Hsu David K.
Published: October 2005

The interaction of shear wave polarization and the fiber directions in a composite laminate makes shear waves a sensitive probe for evaluating ply orientation and sequence in a layup. The transmitted shear wave signal, with the transmitting and receiving transducers perpendicular to each other, can easily distinguish a [0/+45/90/−45]6 from a [0/+45/90/−45]3S, and detect an error in the form of a single misoriented ply: the 12th ply in [0/90/+45/−45]3S mistakenly placed at +45° instead of at −45°. Shear waves can therefore detect subtle but realistic layup anomalies in composite laminates. In this work, a model is developed for the propagation of shear waves through a laminate with arbitary ply orientation and sequence. Experimental results and model predictions are compared, and the model is used for identifying layup anomalies that are detectable with shear waves. Potential applications of this new method in nondestructive evaluation of composite laminates will be discussed. [Work supported by NSF I/U Center for NDE.]
Sound absorption height and width limits for polymer glass transitions
Authors: Hartmann Bruce , Lee Gilbert F. , Lee John D. , Fedderly Jeffry J.
Published: October 2005

At the glass transition of a polymer, the shear sound absorption per wavelength displays a relaxation covering many decades of frequency. Calculations were made of the peak height and half-width of this relaxation based on the Havriliak–Negami dispersion relation. These calculations are an extension of our earlier study of the complex modulus loss factor height and width [B. Hartmann, G. F. Lee, and J. D. Lee, J. Acoust. Soc. Am. 95, 226–233 (1994)]. It was found that height and width are not independent: A high peak has a narrow width while broadband absorption can only be achieved for low-peak heights. The calculation predicts that height times width is approximately constant, as expected for a relaxation for which the area under the curve is constant. These predictions are compared with published experimental data on various polymers, chiefly polyurethanes, and found to be in good agreement.
Dipole relaxation rates of mass-loaded spherical inclusions in elastic matrix materials
Authors: Scharnhorst Kurt P.
Published: October 2005

It is necessary to be aware of the rise times of dominant resonances when tone bursts or wide bandwidth pulses are used to test the acoustic response characteristics of materials containing resonant inclusions. In practice the monopole of a void and the dipole of a mass-loaded inclusion are the most important basic resonances. The dipole center of mass relaxation rate of a mass-loaded, rigid spherical inclusions in an elastic matrix material is analyzed. Inclusion to matrix mass density ratios ranging from one to eight and matrix shear stiffnesses ranging over more than an order of magnitude are considered. It is found that the rise time of center of mass oscillations is much longer than that of cavity oscillations in the case of heavily mass-loaded inclusions in rigid matrix materials. In soft materials, the reverse is true. In terms of the period of oscillation at resonance, the relaxation time of the rigid dipole is less than half a period long. This rate may be viewed as the lower bound on the relaxation rates of mass-loaded viscoelastic inclusions.
Borehole acoustic waveform decomposition and analysis via spectral estimation
Authors: Ekstrom Michael P. , Randall C. J.
Published: October 2005

The response of an acoustic logging tool in a fluid-filled borehole is quite complex, being composed of multiple interferring components. Each component has unique velocity dispersion and attenuation characteristics which are related to properties of the formation surrounding the borehole. Robust and accurate methods to decompose the borehole signals and to analyze the components have been the subjects of much interest. In this paper, a new hybrid spectral estimator is introduced to estimate the velocity dispersion and attenuation of space-time wave fields from borehole array sensor data. This high-resolution estimator is based on an eigensystem decomposition of a matrix pencil, and provides an enhanced statistical performance while avoiding the severe ill conditioning of the classical Prony’s method [Lang etal., Geophysics 52, 530–544 (1987)]. This improvement in spectral resolution allows the estimated wave-number-frequency spectrum to be decomposed into its constitutive parts for subsequent individual analysis and wave field reconstruction. These estimation and decomposition procedures are mechanized in a set of MATLAB routines, and will be first validated by processing model waveforms for a homogeneous formation, then demonstrated with a variety of both model and field-acquired data [C. J. Randall, J. Acoust. Soc. Am. 90, 1620–1631 (1991)].
Modeling backscatter from a shallow-water soliton: Relationship to the anomalous resonance effect observed in Yellow Sea data
Authors: Chin-Bing Stanley A. , King David B.
Published: October 2005

Computer simulations have confirmed that large amplitude shallow-water internal waves (solitons) can effect transmission loss. Zhou etal. [J. Acoust. Soc. Am. 82, 287–292 (1987)] first hypothesized that solitons caused the anomalous transmission loss observed in acoustic data taken in the Yellow Sea. Others [Chin-Bing etal., Math. Model. Sci. Comput. 4, (1994); King etal., Theoret. Comput. Acoust. 2, 793–807 (1994)] confirmed via computer simulations that interactions of acoustic energy with shallow-water solitons resulted in coupling between the lower-order propagation modes and the very lossy, higher-order modes. Furthermore, a single soliton packet could transfer sufficient acoustic energy from lower-order modes to higher-order bottom-attenuated modes to produce the anomalous transmission loss effects observed in the Zhou data. Recently this simulation study has been extended to include a wave-number analysis of the backscattered field from the soliton. Examples of the backscattered field from the soliton will be presented that include the frequency interval where the forward-field acoustic mode conversion (and corresponding anomalous transmission loss) occur. [Work supported by ONR/NRL and by a Federal High Performance Computing DoD grant.]
Modeling of high-frequency pulse propagation in the Yellow Sea with internal wave and rough boundary scattering
Authors: Tang X. , Tappert F. D. , DeFerrari H. A.
Published: October 2005

The broadband UMPE ocean acoustic model is used to simulate high-frequency (3 kHz) pulse propagation in the Yellow Sea. Internal waves are known to be active in the summer, and are modeled with a broad spectrum of excitation. Due to the existence of a strong thermocline in the upper part of the water column, the signal at a distant (5 km) receiver exhibits a characteristic multipath structure according to the geometric configuration of source and receiver—whether above and/or below the thermocline. When internal wave fluctuations are introduced, the simulated waveforms are altered and agree better with the experimental observation made in the summer of 1993 [R. Zhang, J. Acoust. Soc. Am. 97, 3368(A) (1995)]. Both rough surface and rough water–sediment interface scattering are included in the model in the belief that their effects cannot, in general, be separated from the volume scattering by internal waves. A 10-h time history of repeated pulse transmissions simulated in accordance with the recorded ocean temperature fluctuation is computed and displayed, and illustates the temporal instability of shallow-water propagation. [Work supported by ONR.]
Applications of the Foldy–Wouthuysen transformation to acoustic modeling using the parabolic equation method
Authors: Orris Gregory J. , Wurmser Daniel
Published: October 2005

The application of the Foldy–Wouthuysen transformation on the Helmholtz equation has been previously demonstrated [J. Acoust. Soc. Am. 96, 3343 (A) (1994)]. The result provides an asymptotic expansion for correction terms to the parabolic equation (PE). These terms include contributions from the coupling of the forward propagating and backward propagating solutions to the Helmholtz equation, caused by propagation through range-dependent media. The new correction terms have been found to depend on the curvature of the local index of refraction and can be calculated from available environmental parameters. A finite element PE (FEPE) has been modified to include these new correction terms. This new PE is used to model propagation of an acoustic field through an ocean with fluctuating sound-speed profiles caused by internal waves and other range-dependent oceanographic properties. The effects of these new terms and the circumstances under which they are expected to be most important are discussed, with special emphasis placed on global-scale propagation.
Some factors influencing comodulation masking release and across-channel masking
Authors: Hicks Michelle L. , Bacon Sid P.
Published: October 2005

The purpose of this study was to determine whether comodulation masking release (CMR) and across-channel masking (ACM) are by-products of a similar across-channel mechanism. This was addressed by examining how the two are affected by stimulus manipulations expected to influence their magnitude. Subjects were required to detect a 1000-Hz signal in the presence of a masker that consisted of a 1000-Hz (on-frequency) component alone or that component and up to six flanking components (500, 600, 700, 1300, 1400, and 1500 Hz). The on-frequency and flanking components typically were sinusoidally amplitude modulated at 10 Hz, although not necessarily in phase with one another. In experiment 1, the amount of CMR and ACM was highly influenced by whether the signal consisted of one or three 50-ms tone bursts; in fact, ACM was only observed when the signal was a train of three 50-ms tone bursts. In experiments 2 and 3, CMR tended to increase as the modulation depth or the number of flanking components increased, whereas ACM was relatively unaffected by these manipulations. In addition, ACM was observed under dichotic situations, whereas CMR was not. Taken together, the results suggest that ACM and CMR may be mediated by different mechanisms.
The perception of frequency peaks and troughs in wide frequency modulations. III. Complex carriers
Authors: Demany Laurent , Clément Sylvain
Published: October 2005

In widely frequency-modulated (FM) sine tones, local frequency maxima are perceived more accurately than local frequency minima [L. Demany and K. I. McAnally, J. Acoust. Soc. Am. 96, 706–715 (1994); L. Demany and S. Clément, J. Acoust. Soc. Am. 97, 2454–2459 (1995)]. The aim of the present work was to determine if a similar perceptual asymmetry exists for nonsinusoidal FM carriers. Within each stimulus, the logarithm of instantaneous frequency followed one cycle of a (2.5- or 5-Hz) cosine function, starting at phase π in the ‘‘peak’’ condition and phase 0 in the ‘‘trough’’ condition. In each condition, subjects had to detect shifts in the frequency apex occurring at the temporal center of the stimuli. In experiment 1, the FM functions were imposed on complex tones consisting of a series of consecutive harmonics. Some of the stimuli were bandpass filtered in a 1-oct window with fixed edges. The measured thresholds were about four times lower in the peak condition than in the trough condition, which suggests that the asymmetry previously observed for ‘‘spectral’’ pitches also exists for ‘‘virtual’’ pitches. In experiment 2, the FM carriers were Shepard tones. With such carriers, the standard peak and trough stimuli could be made identical at both the apex and the end points. In spite of these local identities, the results were similar to those of experiment 1, which suggests that the perceptual asymmetry is not determined by local differences between the stimuli and is instead a genuine ‘‘motion’’ effect. In experiment 3, FM was imposed on the frequency of an amplitude modulation of high-pass noise; thus the modulated frequency could have only a temporal (and no place) representation in the auditory nerve. Performance was again better in the peak condition than in the trough condition for apexes near 120 Hz. However, a slight trend in the opposite direction was observed for apexes near 70 Hz.
Source localization in a partially known shallow-water channel
Authors: Naidu Prabhakar S. , Ganesan T.
Published: October 2005

The source localization in shallow water is beset with problems arising from the presence of a large number of correlated multipaths. Nevertheless, given a complete knowledge of the water channel it is definitely possible to localize a source. A complete knowledge of the channel, however, is rarely available under most practical conditions. A new approach is proposed wherein the bottom reflection coefficients are not required; hence the bottom conditions need not be known. Further, because of the use of signal subspace for localization, the proposed approach is robust against the background noise (−20 dB) and channel depth uncertainty (10λ). All these nice features of the proposed approach are possible only when the array size is large (≳40 sensors).
Doppler speed and range estimation using frequency and amplitude estimates
Authors: Quinn B. G.
Published: October 2005

A parametric form for the received ‘‘instantaneous frequency’’ of a pure tone is derived for the case of relative straight line motion between source and receiver. Ferguson and Quinn [J. Acoust. Soc. Am. 96, 821–827 (1994)] have recently described an algorithm which, given a sequence of high-accuracy frequency estimators, produces estimators of the closest distance between the source and receiver, the relative speed, the rest frequency, and the time at closest approach. In this paper, an improved algorithm which uses amplitude estimators as well is introduced, and the statistical behavior of the estimators derived. The technique is automatic and will work even if only a section of the Doppler track is available.
Acoustic imaging in turbulent media with the spatial bispectrum
Authors: Tague John A. , Cheng Yan Don
Published: October 2005

A new array processing system that performs high-resolution imaging in turbulent ocean media is introduced. It exploits information contained in higher-order spatial spectra and images to a resolution which is limited by the array aperture rather than the medium. Precise a priori knowledge of the turbulence’s spatial coherence structure is not needed. Furthermore, the signal processing is straightforward to implement, the system is self-calibrating, and the computational demands are reasonable. Initial tests of the imager have been conducted and several representative examples are presented. It is found that precise bispectrum estimates are required for good image quality. Since this requires large data sets, in essence this algorithm trades data requirements for resolution. In addition, the direction of arrival information, contained in phase terms that are processed with the bispectrum, is lost in the averaging process. Nevertheless, the system provides very good quality images, even in severe environments.
On the bandwidth of diffusors based upon the quadratic residue sequence
Authors: ten Kate Warner R. Th.
Published: October 2005

The lower and upper frequency boundary are discussed within which a diffusor based upon the quadratic residue sequence shows its typical operation. Using a qualitative model of the diffusor’s way of operation these limits are found to be related with the diffusor’s width and well width, respectively. Therefore, the prime number N on which the underlying quadratic residue sequence is constructed is an indicator for the bandwidth. The choice of the design frequency is discussed.
Balcony overhangs in concert auditoria
Authors: Barron M.
Published: October 2005

Measurements in seven concert halls with balconies have been analyzed to establish the acoustic effects of balcony overhangs. It was found that overhangs reduce the late sound more than the early and that local reflections from back walls and soffits in the overhung section of the hall help to maintain sound level. In general, the most significant subjective effect of overhangs is seen to be a reduction in the sense of reverberation. Design considerations and criteria for overhang design are considered but there appear to be no obvious solutions to the dilemma of reduced reverberance other than striving to maintain a large enough vertical angle of view for listeners of the main body of the hall.
Objective measures of listener envelopment
Authors: Bradley J. S. , Soulodre G. A.
Published: October 2005

This paper reports the results of subjective studies to determine objective predictors of perceived listener envelopment in concert halls. Subjects, seated in an anechoic room, were exposed to simulated sound fields that were expected to have varied listener envelopment. As independent variables: the reverberation time, the early-to-late sound ratio, the overall sound level, and the angular distribution of the late-arriving sound levels were varied. All of these factors had statistically significant effects on perceived listener envelopment. The results indicate, however, that the angular distribution of the late arriving sound and the overall level would have the largest effects in real concert halls. Thus listener envelopment depends on having strong lateral reflections arriving at the listener 80 ms or more after the direct sound. Several objective measures correlated significantly with listener envelopment. However, a new measure, the late lateral sound level, as measured using a figure-of-eight microphone, was found to be both conceptually simple and a very good predictor of the perceived listener envelopment of the sound fields in this experiment.
Fuzzy logic for urban traffic noise prediction
Authors: Cammarata G. , Fichera A. , Graziani S. , Marletta L.
Published: October 2005

This paper addresses the problem of predicting acoustical noise. Acoustical noise and related quantities are considered in determining the relationships between noise and its causes. An innovative approach for the manipulation of traffic information is introduced: The fuzzy approach is used in order to obtain the relationship mentioned above. A set of data, collected during a measurement survey performed in a medium sized European town, is considered. The behavior of the fuzzy model is compared with the performance of the classical model, introduced in literature. The reported results show that the proposed fuzzy models contribute an improvement in the capacity to approximate real data.
Feedback control of sound radiation from a plate excited by a turbulent boundary layer
Authors: Thomas D. R. , Nelson P. A.
Published: October 2005

In this paper it is shown that the problem of applying active control to a simply supported plate excited by a turbulent boundary layer can be presented in a form which allows the application of optimal control theory. Linear regulator theory and stochastic linear regulator theory are briefly summarized. The approach taken follows that of Baumann et al. who show that the optimal control theory can be applied to structural acoustic problems if the sound power radiated by the structure is estimated from the vibration signal by means of a ‘‘radiation filter.’’ A modal model for the vibration of an elastic structure is presented and the state space realization of the model is given. It is shown that a simple Corcos model of the turbulent boundary layer excitation can be modeled by using a number of ‘‘excitation filters.’’ The state space realization of these filters can be combined with the state space model of a vibrating plate to give a model to which optimal control theory can be applied. In similar fashion the sound power radiated by the plate can be estimated by means of a radiation filter matrix. A detailed account of the calculation of such a radiation filter matrix is given. The state space forms of the excitation filters and radiation filter matrix can be combined with the state space model of the plate to give a system state space realization which can be used in the solution of a linear quadratic regulator problem. Optimal control analysis is then applied to the state equations and optimal reductions in the far-field radiated power are obtained for various arrangements of control forces. These results give insight into the possibilities for obtaining useful reductions in turbulent boundary layer induced noise in aircraft by the application of feedback control.
Two-dimensional wave propagation in cylindrical single-crystal solid–liquid bodies
Authors: Lu Yichi , Wadley Haydn N. G.
Published: October 2005

The significant difference in the ultrasonic velocity of liquid and solid semiconductors has led to an interest in ultrasonic characterization of anisotropic solid–liquid interfaces during semiconductor single-crystal growth. However, the large solid:liquid velocity ratio could result in potentially severe ray bending at the interface and so detailed ray path and wavefront analyses are needed both to design the sensing approach and to analyze its results. A ray tracing algorithm has been developed and used to analyze two-dimensional wave propagation on the transverse cross-sectional and the diametral planes of cylindrical single-crystal solid–liquid bodies. For a prescribed point source position and an initial ray angle, the refraction and reflection angles at an interface are determined using the Christoffel equation, Snell’s law, and the group velocity. The ray path between prescribed source and receiver positions is then determined using the shooting method. Wavefronts are obtained by connecting points on ray paths with the same traveling time. Ultrasonic time of flights are obtained by integrating the ultrasonic slowness along the ray path. Ray paths are indeed found to be severely bent, particularly at interfaces with crystal planes of greatest group velocity and largest interfacial curvature.

It indicates the need for precise ray path calculations if time-of-flight data are to be used for interface reconstruction. On the transverse plane, the simulated time-of-flight data identify simple strategies for determining the position and radius of the solid–liquid interface. Time-of-flight data obtained on the diametral plane with the source and receiver points having the same axial coordinate are found to easily identify the interfacial region. The curvature of convex interfaces can be directly determined from diametral plane data using the time of flight of doubly refracted ray paths or from the discontinuity in the time of flight for rays that propagate in the homogeneous solid and liquid regions adjacent to the interface. The convexity of concave interfaces can be determined from diametral plane time-of-flight measurements for the interface diffracted (i.e., creeping) ray provided the crystal orientation exhibits weak velocity anisotropy; for other orientations, additional measurements with unequal source/receiver axial coordinates are needed.
High-frequency propagation in shallow water. The rough waveguide problem
Authors: Uscinski B. J.
Published: October 2005

Acoustic propagation in shallow water is similar to that in a waveguide with randomly rough walls. The field in such a guide can be calculated as a sum of coupled modes. However, the approach breaks down for deep surface roughness when the number of modes becomes too large to handle. A method is presented, based on a set of coupled integral equations, that allows the field to be calculated in a guide when both surface and bottom can have deep modulations. The applicability to underwater acoustics is discussed and some examples given.