bluuebunny/crossref_metadata_2025 huggingface dataset:
An adaptive time delay estimation with direct computation formula
Authors: Chern Shiunn-Jang , Lin Shyh-Neng
Published: October 2005

The problem of estimating and tracking time delay between signals received at two spatially separated sensors is essential in varied fields. For example, in the sonar system, the information of time delay can be used to localize the radiating source. In real-time processing, an adaptive time delay estimation (TDE) method with desired performance and less computational time is preferred. In this short paper, a simple and efficient method is suggested for TDE. This is done by employing a direct formula coupled with the adaptive LMS TDE algorithm. The advantage of the presented method, in terms of the accuracy as well as execution time, over the conventional lookup table method and interpolation formula method is shown in both the stationary and nonstationary time delay environments. Moreover, the capability of estimating time delay in an environment with multipath propagations is investigated.
Application of the short-time Fourier transform and the Wigner–Ville distribution to the acoustic localization of aircraft
Authors: Ferguson Brian G. , Quinn Barry G.
Published: October 2005

The dominant feature in the acoustic spectrum of a propeller-driven aircraft is the spectral line corresponding to the propeller blade rate that is equal to the product of the propeller shaft rotation rate and the number of blades on the propeller. The frequency of this line, when measured by a stationary observer on the ground, changes with time due to the acoustical Doppler effect. In this paper, the short-time Fourier transform and the Wigner–Ville distribution are used to estimate the propeller blade rate at short time intervals for a turbo-prop aircraft flying at a constant altitude and speed over an acoustic sensor located just above ground level. The temporal variation in the observed blade rate is then used to estimate the speed and altitude of the aircraft, together with the source (or rest) frequency of the blade rate. Finally, the estimated values for these parameters are compared with the actual values recorded onboard the aircraft during each of the eighteen transits formed by pairing each element of a set of speeds: 150, 200, and 250 kn, with each element of a set of aircraft altitudes: 250, 500, 750, 1000, 1250, and 1500 ft.
Bispectral analysis of underwater acoustic data
Authors: Richardson A. M. , Hodgkiss W. S.
Published: October 2005

Estimates of the power spectral density have been found to be very useful in a variety of signal processing applications over the last several decades. Higher-order spectra contain information not present in the power spectrum and recently, estimates of higher-order spectra have been shown to be useful in certain signal processing problems. In particular, estimates of the bispectrum and bicoherence have been found useful in detecting non-Gaussianity and nonlinearity in system identification, and in detecting transient signals. This paper is concerned with the estimation of the bispectrum and bicoherence of underwater acoustic signals. Some of the properties of the bispectrum and bicoherence are introduced and described. Estimates of bispectra of actual data taken from a freely drifting Swallow float and also from an element of a moored acoustic array are presented and discussed. In the results portion of the paper, three particular properties of bispectrum estimation are focused on. It is demonstrated how the bispectrum estimate can be used to detect non-Gaussianity, nonlinearity, and harmonic coupling. The detection of harmonic coupling is shown to be a useful property of the particular bispectrum estimation algorithm employed here.
Wave-number–frequency (k-ω) analysis using an eigenvalue decomposition technique
Authors: Salisbury John I.
Published: October 2005

Noise source localization is of great interest and has been studied for many years. The information is used to detect and track objects in the ocean environment and to locate and identify position of radiating noise sources on objects for noise diagnostic efforts. In many cases the sonar system utilizes a line array having equally spaced sensors. Wave-number–frequency (k-ω) plots are used to analyze the data recorded by line arrays to detect the present of noise generators, either acoustically radiating targets located in the ocean environment or nonacoustical energy generated by the array itself. In this paper a hybrid technique (ED-FFT) is presented that uses an eigen decomposition (ED) technique in the spacial dimension and a fast Fourier transform (FFT) in the time domain. This combination generates k-ω plots having better spatial resolution than is currently possible using the conventional technique (FFT-FFT) has the added advantage of being able to separate the various noise generators and to eliminate any unwanted sources. In addition, it does not have the adverse effect of being signal-to-noise (SNR) dependent. Other techniques [autoregressive (AR) AR-AR, AR-FFT] have been investigated in order to improve the resolution of the k-ω plots [J. Acoust. Soc. Am. 87, 1603–1611 (1990); 90, 3155–3160 (1991)] and have been shown to be SNR dependent.

In this paper, the robust eigen decomposition technique has been utilized to generate high spatial resolution k-ω plots. The hybrid technique (ED-FFT) is implemented by taking a one-dimensional fast Fourier transform (FFT) on the sampled time series data and using these results to obtain a frequency-dependent cross spectral density matrix (CSD). Eigen decomposition is applied to this CSD matrix to obtain the eigenvalues and eigenvectors. An FFT is applied to the eigenvectors and modified according to the eigenvalues. The eigenvalues are arranged in descending order, the first being the largest and corresponds to the largest source. If only random noise is present, the eigenvalues will be equal and small. Each eigenvector represents an independent source, [IEEE J. Ocean Eng. OE-9(1) (1984)] therefore each source can be examined separately. This technique does not require any a priori knowledge of the number of sources as does techniques such as MUSIC [Trans. IEEE Antennas Propag. AP-34(3) (1986)] since it is not necessary to predetermine the signal and nonsignal subspace or the AR model order. Comparisons of the spacial resolution are made between the conventional method (FFT-FFT) and the hybrid (ED-FFT) for various target bearing angles using simulated data. The advantages of being able to isolate a particular noise generator is demonstrated.
Wideband processing of acoustic signals using wavelet transforms. Part I. Theory
Authors: Weiss L. G. , Young R. K. , Sibul L. H.
Published: October 2005

Wideband processing of acoustic signals is described and applied to the problem of source localization in an environment with multiple sensors and sources. To localize sources, the wideband correlation receiver output is expressed as an affine convolution equation. This expression for the wideband correlation receiver output is then deconvolved to obtain a minimum mean-square estimate of the wideband spreading function (also called the density function or the source distribution function). This deconvolved estimate is first derived for the case of one sensor actively imaging the environment. An estimate is then derived for the case of three or more passive sensors. This wideband processing removes many of the narrow-band restrictions and allows for significant motion between the sources and sensors. The underlying tool used is the wavelet transform.
Sexual differences in the tympanic frequency responses of the American bullfrog (Rana catesbeiana)
Authors: Hetherington Thomas E.
Published: October 2005

Adult male and female American bullfrogs (Rana catesbeiana) have sexually dimorphic middle ears. The most conspicuous feature is the relatively large tympanum of adult males. The acoustic responsiveness of the tympana of adult male and female bullfrogs was studied with a laser vibrometer. Clear sex-related differences in middle ear frequency responses were observed between the sexes. The middle ear of adult males was generally more sensitive, but, more significantly, it showed a distinct peak in sensitivity at very low frequencies around 200 Hz that was entirely lacking in the female middle ear. The male middle ear therefore is especially responsive to the distinct low-frequency peak in the male mating call centered around 200–300 Hz. The enlarged middle ear of male bullfrogs therefore may have evolved as a result of selective pressure to improve detection of the mating vocalizations of other males. Female bullfrogs lack tympanic sensitivity to the low-frequency peak in the male mating call, and presumably respond more to the higher frequency components of call.
Insertion loss measurement of panels by time delay spectrometry
Authors: Papanikolaou George , Trochidis Athanasios , Kalliris George
Published: October 2005

This paper describes a new method for measuring the insertion loss of panels or partitions based on time delay spectrometry (TDS). Using a TEF 12 analyzer the insertion loss of single leaf steel panels were measured. The results are shown to be in reasonable agreement with existing measurements giving confidence to the use of the method for design purposes. Based on several measurements, the performance and the limitations of the method proposed are analyzed and discussed.
A method for finding an exact solution of the homogeneous equations of motion of a viscously damped discrete system
Authors: Wei Li-Ding , Lee Wei
Published: October 2005

The objective of this Letter is to present a method for the study of the free vibration of a generally damped discrete system. The technique, developed from the force response of the undamped system, reduces the original eigenvalue problem with eigensolution within the complex domain to a common real-eigenvalue problem. Without the use of the 2n-dimensional state vector and no iteration required, this method is efficient and effective for system dynamic analysis.
Perception of prominence in speech intonation induced by rising and falling pitch movements
Authors: Hermes Dik J. , Rump H. H.
Published: October 2005

The object of this study was to investigate whether subjects are able to compare the prominence caused by different types of accent-lending pitch movements and, if so, whether some pitch movements lend more prominence to a syllable than others. These experiments were carried out with the utterance /ma’mama/, with the second syllable accented by either a rise, a fall, or a rise–fall. Subjects adjusted the variable excursion size of a comparison stimulus to the fixed excursion size of a test stimulus in such a way that the accented syllable in test and comparison stimuli had equal prominence. The rise–fall was only presented in one ‘‘standard’’ position, while the fall and the rise were tested for five different temporal positions in the syllable. Subjects were found to be quite capable of equating the prominence of syllables accented by the following types of pitch movement: the rise–fall in standard position, the rise starting before the vowel onset, and the fall whatever its temporal position in the syllable. When lending equal prominence, the early starting rise and the rise–fall had equal excursion sizes. The fall, however, appeared to lend more prominence to a syllable than the rise or the rise–fall of equal excursion size, independent of its position in the syllable. This difference between the fall on the one hand and the rise and the rise–fall on the other increased with increasing declination of the pitch contour. A model is presented which can explain these phenomena quantitatively.
Further studies of a maximum-likelihood yes–no procedure
Authors: Gu Xiang , Green David M.
Published: October 2005

Absolute thresholds were estimated for pure tones of 500, 1000, and 2000 Hz using both a maximum-likelihood yes–no procedure and a traditional three-down one-up forced-choice adaptive procedure. Threshold estimates obtained with the two procedures were highly correlated. In the maximum-likelihood yes–no procedure, the false-alarm probability was poorly estimated. A simple change in that procedure produced less-biased estimates of the false-alarm rate. In a second experiment, the influence of the false-alarm rate on the threshold estimates was investigated. The listeners’ absolute thresholds were estimated when they adopted either a liberal or conservative criterion for detecting the signals. Data were collected using both a constant-stimulus yes–no procedure and a maximum-likelihood yes–no procedure. Threshold estimates are 5 to 6 dB higher for the low than for the high false-alarm rates. Psychometric functions based on a stimulus-power model provided the best fit to the data obtained with the constant-stimulus method. This stimulus-power model was used to produce the assumed psychometric function in the maximum-likelihood yes–no procedure. Computer simulations were conducted to determine how threshold estimates were affected by the listener’s inattention or by mismatches between the slope parameter of the listener’s psychometric function and that assumed in the maximum-likelihood procedure.
Path-averaged turbulent dissipation measurements using high-frequency acoustical scintillation analysis
Authors: Di Iorio Daniela , Farmer David M.
Published: October 2005

The path-averaged turbulent kinetic energy dissipation (per unit mass) is estimated in a shallow tidal channel using acoustical scintillation analysis. The tidal current ensures that fully developed turbulence prevails. In order to make measurements of the turbulence parameters, a high-frequency (67-kHz) acoustic propagation experiment was conducted. Our acoustic data is compared to the weak scattering theory of Tatarski assuming a Kolmogorov turbulence model and compared with available oceanographic data. Analysis of log-amplitude, phase, and phase-difference spectra shows close agreement with the theory. Comparison of the acoustic data with direct measurement of temperature and salinity fluctuations using in situ sensors allows evaluation of the contribution of turbulent velocity fluctuations to the scintillation signal. The results show that turbulent velocity fluctuations are the dominant (∼95%) component of the observed acoustic scintillation, leading to estimates of the path-averaged turbulent energy dissipation, which rises and falls with the tidal current (ε∼10−7–10−5 m2s−3). A confirmation of the validity of the weak scattering theory together with the Kolmogorov turbulence model in this environment is given within the context of the scattering strength–refractive index variance parameters (Γ,X).
An approximate solution to sound radiation from slender bodies
Authors: Tran Van Nhieu Michel
Published: October 2005

Approximate analytical expressions are proposed to calculate the sound pressure radiated from axisymmetric slender bodies. The spatial Fourier spectrum of the velocity surface distribution may be continuous but is specified to be of limited bandwidth with the highest wave number smaller or in the order of the inverse of the body length. The source strength distribution of the integral solution is determined from an asymptotic expansion of the solution with respect to the slenderness ratio near the body surface. The radiated pressure has a wave representation and is expressed in terms of the helical wave components of the Fourier transform of the surface velocity. The formalism is valid at low and medium frequencies where the acoustic wavelength is larger or in the order of the radius of the body. It is shown that most results of previous works can be reproduced in a systematic way from the derived formulas for the radiated pressure.
Acoustic propagation through anisotropic, surface-layer turbulence
Authors: Wilson D. Keith , Thomson Dennis W.
Published: October 2005

The effects of atmospheric wind and temperature fluctuations on acoustic signal variability is discussed, with emphasis on the effects of large-scale turbulence (motions having size larger than or comparable to the integral length scale). Such large-scale turbulence is anisotropic, is generated by both shear and buoyancy instabilities, and has structure that depends strongly on the meteorological conditions as well as the distance from the ground. Previous research in the atmospheric sciences literature regarding length scales and anisotropy is reviewed and incorporated into an acoustic propagation model. The model is based on a multiply scaled, six-termed, sound-speed correlation function. A second, simpler model, based on fluctuating curvature of the vertical wind profile, is also proposed. Both models are compared with experimental measurements of amplitude and travel-time fluctuations obtained during the Rock Springs Tomography Experiment, which involved concurrent monitoring of acoustic fluctuations and atmospheric turbulence statistics. An important conclusion is that large-scale turbulence is a significant cause of acoustic signal fluctuations, particularly in the signal phase.
Nonlinearly unstable waves dominated by entropy mode
Authors: Yoon W. S. , Chung T. J.
Published: October 2005

This paper is concerned with instability of flow fields which are dominated by the entropy mode with the presence of usual acoustic and vortical modes. These combined modes lead to nonlinear unstable waves which may occur in automobile, aircraft, or rocket engines. In this study instability in a side-burning rocket is investigated. It is shown that the energy growth rate parameters increase with an increase of the energy growth factor. The energy growth rate parameters for turbulent flows are larger than those for laminar flows. It is further shown that unstable wave motions for the high-temperature side-burning rocket are dictated mostly by the entropy mode, somewhat by the vortical mode, and least by the acoustic mode.
Fluid effects on velocity and attenuation in sandstones
Authors: Gist Grant A.
Published: October 2005

Ultrasonic velocity and attenuation measurements in sandstones with a variety of saturating fluids are compared with the predictions of Biot’s theory of porous media acoustics. Velocity data show systematic deviations from Biot theory as a function of pore fluid viscosity. Ultrasonic attenuation is much larger than the Biot prediction and for several sandstones is nearly constant for a three decade variation in viscosity. This behavior contrasts with synthetic porous media such as sintered glass beads, where Biot theory provides accurate predictions of velocity and attenuation. A sandstone was modified by curing a residual saturation of epoxy in the pore space, filling small pores and microcracks. This altered rock has a significantly reduced attenuation, demonstrating the dominance of small pores in controlling ultrasonic attenuation. Discrepancies between Biot theory and ultrasonic measurements are due to complex pore shapes in sandstones that are not present in simpler synthetic porous media such as sintered glass beads. Two non-Biot viscous attenuation mechanisms are needed: local flow in microcracks along grain contacts, and attenuation from pore-wall surface roughness. The combination of these mechanisms with Biot theory can explain ultrasonic measurements on sandstones. A model calculation of attenuation for a pore wall with surface roughness shows a significant increase in attenuation compared to the smooth wall calculation of Biot theory. This attenuation enhancement explains the absence of a Biot slow wave in fluid saturated rocks, and the observed correlation between ultrasonic attenuation and clay content in sandstones. When extended to the lower frequencies of geophysical field measurements, attenuation from all viscous dissipation mechanisms is negligible. This implies that ultrasonic attenuation measurements of sandstones provide no useful information about seismic attenuation in fluid-filled rocks in the earth, and mechanisms other than viscous dissipation must be invoked to describe the attenuation in geophysical field measurements.
Comments on ‘‘Patterns of expressive timing in performances of a Beethoven minuet by nineteen famous pianists’’ [J. Acoust. Soc. Am. 88, 622–641 (1990)]
Authors: Clynes Manfred
Published: October 2005

The Beethoven pulse forms microstructure through a combined time and amplitude warp, thought to be meaningful and desirable for performing his works. In an attempted search Repp [J. Acoust. Soc. Am. 88, 622–649 (1990)] measured only time aspects of the pulse, but not those of amplitude, analyzing performances by 19 famous pianists of Beethoven’s Minuet Op. 31, No. 3. The Beethoven pulse appeared clearly on level 2—the level on which observation was possible. Structural properties could not in any known way account for the numerical proportions observed. A computer performance supplied to Repp by the author, prepared for a different experiment, should not have been compared directly by subjects with the pianists’ performances. It only had partial microstructure, and lacked other expressive factors that could have readily been incorporated. The Beethoven pulse should appear in salient, but not necessarily in all sections of the piece. In this instance the Beethoven pulse was appropriately found in the minuet (but not in the trio).
Commentary and numerical examples on ‘‘Effects of propagation on the operation of a synthetic aperture sonar’’ [J. Acoust. Soc. Am. 82, 1403–1408 (1987)]
Authors: Rolt Kenneth D. , Schmidt Henrik , Rolt George H.
Published: October 2005

This paper comments on ‘‘Effects of propagation on the operation of a synthetic aperture sonar’’ by J. H. Tarng and C. C. Yang [J. Acoust. Soc. Am. 82, 1403–1408 (1987)]. Shortcomings in those analyses are identified and corrections and a discussion are provided. This is accomplished through the application of standard synthetic aperture analysis methods common to both radar and sonar, combined with a ray tracing algorithm that models the ocean having an arbitrary sound-speed profile.
Exact analytic expressions of Green’s functions for wave propagation in certain types of range-dependent inhomogeneous media
Authors: Li Y. L.
Published: October 2005

Some exact analytic expressions of Green’s functions are obtained for wave propagation in range-dependent inhomogeneous media where the refractive index profile can be a function of radial or horizontal distance. These solutions are obtained by starting with a onefold integral representation for the solution that was derived from the path integral. The study is extended to the cases involving either a soft or hard boundary. These solutions are particularly useful for testing the validity of approximate or numerical solutions for wave propagation through range-dependent media, and for construction of more general solutions for problems with boundaries, through the use of integral equation techniques.
A computationally efficient method for the calculation of the transient field of acoustic radiators
Authors: Lee Chankil , Benkeser Paul J.
Published: October 2005

A computationally efficient approach to the calculation of the transient field of an acoustic radiator was developed. With this approach, a planar or curved source, radiating either continuous or pulsed waves, is divided into a finite number of shifted and/or rotated versions of an incremental source such that the Fraunhofer approximation holds at each field point. The acoustic field from the incremental source is given by a 2-D spatial Fourier transform. The diffraction transfer function of the entire source can be expressed as a sum of Fraunhofer diffraction pattern of the incremental sources with the appropriate coordinate transformations for the particular geometry of the radiator. For a given spectrum of radiator velocity, the transient field can be computed directly in the frequency domain using the diffraction transfer function. To determine the accuracy of the proposed approach, the impulse response was derived using the inverse Fourier transform for commonly used radiator geometries. The results obtained agree well with published data obtained using the impulse response approach. While the approach does not lead to a general or exact solution, its computational efficiency and accuracy compares favorably to those of the point source method and the impulse response approach for many useful cases.
Radiated sound energy of a fluid-loaded cylinder as a function of force time duration and multiple pulse time spacing
Authors: Kruger Daniel H. , Mann J. Adin
Published: October 2005

Transfer functions measured by near-field acoustical holography (NAH) are used to simulate the sound radiated by a point-driven, fluid-loaded, cylindrical shell with spherical end caps in the time domain for a variety of force inputs. This paper represents a continuation of work described in an earlier paper [J. Acoust. Soc. Am. 90, 1656–1664 (1991)]. Radiated sound energy from the shell as a function of force time duration and time separation between multiple pulses in a force is studied. A single pulse consists of a single frequency cosine wave that is Gaussian windowed. A multiple pulse consists of several equally time spaced single pulses. As the time duration of force pulses or spacing between force pulses is varied, the fraction of input mechanical energy which is radiated as sound to the far field varies greatly. For example, as the time separation varies between two pulses in a single force time history, the fraction of sound energy radiated to the far field varied from one third to three halves of the sound energy radiated if the force time history were a single pulse. A frequency domain model is used to explain the variation. Since input mechanical energy is either absorbed by the shell or radiated as sound, the results show that it is possible to force more energy to be mechanically damped in the shell by adding a second pulse to the force, reducing the amount radiated as sound. These properties are noticed when results are observed in the time domain while also considering the frequency domain model.
Response to ‘‘Comments on ‘Evaluating a speech-reception threshold model for hearing impaired listeners’ ’’ [J. Acoust. Soc. Am. 96, 586–587 (1994)]
Authors: Humes Larry E. , Lee Lidia W.
Published: October 2005

In his commentary on our recent evaluation [L. W. Lee and L. E. Humes, J. Acoust. Soc. Am. 93, 2879–2885 (1993)] of Plomp’s speech-reception threshold (SRT) model, Plomp [J. Acoust. Soc. Am. 96, 586–587 (1994)] attempts to make three points: (1) that our results were invalid due to the use of a restricted set of spondaic words as stimuli; (2) that our results, as well as those of Smoorenburg [J. Acoust. Soc. Am. 91, 421–437 (1992)] which we cited as supporting our results, were entirely consistent with his SRT model; and (3) that the articulation index (AI) model provided a poorer explanation of these data than his model. Each of these points are discussed in this letter.
Nature of the sound sources in low-speed jet impingement—Further considerations
Authors: Powell Alan
Published: October 2005

Extending the paper ‘‘Nature of the sound sources in low-speed jet impingement’’ [A. Powell, J. Acoust. Soc. Am. 90, 3326–3331 (1991)], it is first pointed out that the directionality of far-field radiation of the postulated dominant lateral quadrupoles with one pair of the four maxima randomly oriented in the plane of the plate, i.e., about the normal to the plate (the direction of the other maxima), differs somewhat from that of the individual quadrupoles. Further comparison is now made with experiments by Sutherland and Brown [Tech. Rep. AFFDL-TR-71-180, Wright–Patterson Air force Base, OH (1972)] in which flow resonance occurred, in which the deep minima at close to the theoretical angle were observed. Recent correlation measurements by Shen and Meecham [J. Acoust. Soc. Am. 94, 1415–1424 (1993)] for turbulent (nonresonant) impingement noise display deeper minima than do simple intensity measurements, at close to the theoretical 48°. The substantial agreement with experiment appears to validate the type of dominant quadrupole postulated in the theory, and therefore use of both the ‘‘reflection argument’’ [A. Powell, J. Acoust. Soc. Am. 32, 982–990 (1960)] and the ‘‘three-sound-pressures theorem’’ [A. Powell, J. Acoust. Soc. Am. 34, 902–906 (1962)], for such a flow. The latter has implications for certain other flows, e.g., free turbulent jets.
Searching for the second harmonic
Authors: Holt R. Glynn
Published: October 2005

To mathematically model the oscillations of a spherical bubble, either the time-dependent volume V(t) or the radius R(t) can be used as the dependent variable. A recent exchange between the advocates of the volume approach [E. A. Zabolotskaya, J. Acoust. Soc. Am. 94, 2448 (1993)] and the radius approach [J. Wu and G. Du, J. Acoust. Soc. Am. 94, 2446 (1993)] concerns an apparent discrepancy in the predicted nonlinear acoustic emissions from a bubble subject to a time-periodic external pressure field. This Letter attempts to resolve the discrepancy via an examination of the arguments offered by both sides. In addition, some general comments on nonlinear harmonic and subharmonic emissions from acoustically forced bubble oscillations are presented.
A constrained iterative multiple operator deconvolution technique
Authors: Sacha John R. , Johnson Blane L.
Published: October 2005

There are two major approaches to the problem of signal deconvolution: Direct methods attempt to explicitly form an inverse operator, while iterative methods rely on successive approximations. In general, direct methods are computationally efficient. Iterative methods enjoy advantages in terms of ill-conditioning and flexibility; in particular, they are easily modified to incorporate constraints that force the solution to exhibit features known a priori. It has previously been shown that the classical direct least squares and regularized least-squares inverse operator methods are equivalent in the limit to corresponding iterative solution methods. In some cases, multiple blurring operators can be used to convert instances of ill-posed problems into ones that are well-posed. A new iterative restoration that corresponds to the direct inversion solution associated with multiple operators is formulated here. This method has the advantages of the constrained iterative routines as well as the advantages associated with multiple operator direct inverse deconvolution. Examples are presented to illustrate that combining a constrained iterative technique with multiple operators can yield a restoration superior to that of a single operator constrained iterative estimate alone or that of a multiple operator direct inverse estimate alone.
A water-filled cylindrical wave-number calibration array
Authors: Luker L. Dwight , Van Buren Arnie L. , Rogers Peter H.
Published: October 2005

This paper describes an investigation of a prototype cylindrical wave-number calibrator (CWC). The CWC is a water-filled device designed to generate nonacoustic-wave-number pressure fields propagating axially in the water within the calibrator. It can therefore be used to simulate the effects of flow noise on a device placed in the water. Insight into the design of the CWC is obtained from an analysis of an infinitely long, liquid-filled, cylindrical chamber with an axially-symmetric, normal-velocity distribution on the wall of the chamber. Additional insight is provided by a study of the propagation speed in the fluid inside an infinite-length elastic tube surrounded by another fluid. A finite-length CWC is then investigated with several computer models of the CWC using the CHIEF acoustic-radiation program and the ATILA finite element program. These models are integrated into a computer program that uses the electroacoustic transfer matrix for the system to compute electrical drives designed to produce the desired nonacoustic-wave-number fields within the CWC. A prototype CWC with 40 independently driven bands was constructed from a piezoelectric-PVDF tube. The pressure fields within the CWC resulting from drives computed using measured and modeled transfer matrices were measured and compared with predicted fields. The results show that relatively uniform nonacoustic-wave-number pressure fields can be created within the CWC. The results are considerably better using measured transfer matrices rather than matrices determined using the models.
Wavefront amplitude distribution in the female breast
Authors: Zhu Qing , Steinberg Bernard D.
Published: October 2005

Ultrasound measurements of a large population of wavefronts transmitted through female breasts at 3 and 4 MHz show that the wavefront amplitude distribution is close to Rayleigh. This finding is consistent with a fully developed scatter field, implying that the scatter energy removed from the coherent incident beam dominates the wavefront. The wavefront received from an inhomogeneous medium is the superposition of an incident wave plus a scattered wave. If the scattered field is weak, the received field is dominated by the incident field and the wavefront amplitude distribution is Rician. If the scattered field is strong, the received field is primarily the scattered field and the wavefront amplitude distribution is Rayleigh. If, in addition to scattering, refraction between bodies of different refractive indexes occurs, the total net effect on the wavefront amplitude distribution is the same as for strong scattering. This is what we have observed in the highly refractive female breast. This result has implications for the design of high lateral-resolution echo scanners that will incorporate adaptive phase deaberration algorithms. The published algorithms were developed for weak scattering and therefore may not be powerful enough. Alternatives have to be found to deaberrate the severe wavefront distortion in the breast.
Axisymmetric free vibrations of piezolectric finite cylindrical bone
Authors: Paul H. S. , Natarajan K.
Published: October 2005

Axisymmetric vibrations in a finite piezoelectric circular solid cylinder of class 6 or 6 mm is considered. A series solution is derived and the natural frequencies are found for the vibration of the solid cylinder with traction-free and electric potential-free surfaces. The series solution converges rapidly with few terms. The numerical results are carried out for the piezoelectric bone (class 6) and PZT4 (class 6 mm). The modes of vibrations are calculated for various half-height to radius ratios and plotted graphically. The stresses and electric potential distribution over the entire cylinder are also presented graphically.
Flexural waves in a disk soon after impact
Authors: El−Raheb Michael
Published: October 2005

Some aspects of linear flexural wave propagation in a disk soon after impact by a projectile of finite mass are studied. Approximate expressions for speed of wavefront, impedance at the footprint, and bending stress produced by impact are derived based on the inertial evolution of the cone of influence. Deceleration of the projectile is also derived. All approximations agree with results from a modal analysis adopting Mindlin’s plate equations.
Masked detection thresholds and temporal integration for noise band signals
Authors: Formby C. , Heinz M. G. , Luna C. E. , Shaheen M. K.
Published: October 2005

Masked detection thresholds were measured at a center frequency of 2500 Hz for a range of noise signal bandwidths (W=62 to 6000 Hz) and durations (T=10 to 480 ms) approximating that found acoustically in speech. The signals were presented in an uncorrelated 480-ms, 6000-Hz-wide masker. The masker was presented: (1) at a constant spectrum level (53 dB SPL/Hz) or (2) with the overall level varied randomly over a 50-dB range from interval to interval of a trial. Performance was disrupted in the random-level masker only for the condition where the signal and uncorrelated masker were gated on and off simultaneously and were matched spectrally. Time constants (τ) estimated from temporal integration functions fit to the masked detection threshold data were related inversely to W for W broader than the critical bandwidth. Sensitivity to the noise signals was evaluated in the context of an optimum-detection model (Green, 1960). The results did not follow the prediction of a constant bandwidth-duration (WT) product, but may be understood in terms of cues available to the listener from the relative combination of signal and masker parameters. At least three cues for detection were identified in these experiments: (1) a relative timing cue, (2) a spectral shape cue, and (3) a traditional energy cue compared across observation intervals. The relative timing cue and spectral shape cue together contributed as much as a 10- to 12-dB advantage relative to detection based on the traditional energy cue alone. A new multi-cue detection model for predicting the masked detection thresholds was derived. Predictions from the new model were highly correlated (r=0.95) with the empirically measured masked detection thresholds.
The detection of differences in the depth of frequency modulation
Authors: Plack Christopher J. , Carlyon Robert P.
Published: October 2005

Thresholds were measured for the detection of differences in the depth of 5-Hz frequency modulation (FM). In the first experiment, listeners detected differences between sequentially presented sinusoidal carriers. The Weber fractions for FM depth decreased from about 0.5 to about 0.3 as the baseline depth was increased from 2.5% to 20%, and were slightly higher for a carrier frequency of 0.5 kHz compared to carrier frequencies of 1, 2, and 4 kHz. In the second experiment, complex carriers were used consisting of consecutive harmonics of 125- and 250-Hz fundamentals (f0’s), bandpass filtered between 1375 and 1875 Hz. Performance was worse with these stimuli than with the sinusoidal carriers: The Weber fractions for the 250-Hz f0 ranged from about 0.4 to about 2.0 across listeners, and were roughly invariant with baseline depth. The Weber fractions for the 125-Hz f0 showed a steady decrease from about 3.2 to about 0.6 as the baseline depth was increased from 2.5% to 20%, so that threshold corresponded, approximately, to a constant increase in FM depth, independent of baseline depth. The absolute detectability of the FM may have been a limiting factor for the lower two baseline depths at this f0. In the final experiment, psychometric functions were measured for the detection of simultaneous across-frequency differences in FM depth. Three conditions were tested; in the first of these the two carriers to be compared were 666- and 1500-Hz pure tones. In the second condition the two carriers were complex tones, both with f0’s of 250 Hz, filtered between 125 and 625 Hz and between 1375 and 1875 Hz, respectively. The third condition was similar, except that the two (complex) carriers had different f0’s of 111 and 250 Hz. In the first and third conditions performance was extremely poor, even when the FM depths of the two carriers to be discriminated were 10% and 50%. Listeners did perform substantially better, however, on the second condition. The implications of these results for the idea that listeners use differences in FM depth to perceptually segregate concurrent sounds are discussed.
Development of temporal resolution in children as measured by the temporal modulation transfer function
Authors: Hall Joseph W. , Grose John H.
Published: October 2005

Temporal modulation transfer functions (TMTFs) were measured in listeners aged 4 years to adult in order to characterize the development of temporal resolution in children. Four age groups were tested, 4–5 years of age, 6–7 years of age, 9–10 years of age, and adult. Sensitivity to sinusoidal modulation of a noise carrier (a bandpass noise from 200–1200 Hz) was determined for modulation frequencies of 5, 20, 100, 150, and 200 Hz. The data from all listeners indicated decreasing sensitivity to modulation as a function of increasing frequency of modulation. Time constants were derived from the 3-dB down points of functions that were fitted to the data. No age effects were observed for the derived time constants. However, sensitivity to modulation was found to be reduced in the children 4–5 and 6–7 years of age, as compared to adults, and in the children 4–5 years of age as compared to children 9–10 years of age. The agreement of time constant across all age groups was interpreted as indicating that the peripheral encoding of the temporal envelope is probably adultlike in children aged 4 years and above; however, young children appear to be relatively inefficient in processing the information underlying modulation detection.
Temperature dependence of the electromechanical properties of 0–3 PbTiO3-polymer piezoelectric composite materials
Authors: Rittenmyer Kurt M.
Published: October 2005

The electromechanical properties of 0–3 ceramic–polymer composite piezoelectric materials manufactured by NTK Corporation in Japan have been measured as a function of temperature using several techniques. The elastic, dielectric, and piezoelectric constants were measured by fitting the complex admittance vs frequency spectrum to a model of a piezoelectric resonator near the electromechanical resonance [Xu et al., J. Wave Mater. Interact. 2, 105–181 (1987)]. These properties are shown to vary significantly with temperature as a result of the glass-transition region of the polymer phase. The theory of viscoelasticity in polymers discussed by Ferry (WLF theory), which explains the influence of the glass transition on the elastic properties of polymers, is used to describe the temperature dependence of the elastic and dielectric properties of the composite materials. The temperature dependence of the dielectric permittivity is shown to be similar in form to the temperature dependence of the elastic properties. For a material with larger filler particles, the temperature dependence corresponds exactly. For materials containing smaller particles, the magnitude of the time-temperature superposition shift parameters are not consistent for the different properties. The application of the time-temperature superposition principle for shifting experimental data to account for differences in measurement frequencies and temperatures is demonstrated. These measurements are compared with independent elastic property measurements and with results from thermal analysis. They are found to be consistent. Values for Poisson’s ratio are calculated using independent measurements of the elastic constants SE11 and CD33. The observed properties can be related to the structure of the composite material.
Coherent and incoherent scattering by oceanic bubbles
Authors: Sarkar K. , Prosperetti A.
Published: October 2005

A substantial amount of research on acoustic scattering by underwater bubbles is based on the theory of incoherent scattering. More recent work, devoted to much denser bubble assemblies, has instead used effective-media formulations that presuppose coherent effects. Here the mutual relationship between the two approaches is elucidated. It is shown that, underlying the incoherent results, is a WKB approximate solution of the effective equations. As an application, the scattering by tenuous subsurface bubble layers and acoustical bubble counting techniques are examined. Significant differences with previous results are found.
A method for determination of elastic constants of a unidirectional lamina from ultrasonic bulk velocity measurements on [0/90] cross-ply composites
Authors: Chu Y. C. , Rokhlin S. I.
Published: October 2005

In this paper we introduce an inversion method to determine elastic moduli of a unidirectional lamina from ultrasonic time-delay measurements on [0/90] cross-ply composites. A lamina is a single ply (layer) of unidirectional fibers in a multiply composite plate. This method is based on a geometrical acoustic model relating the lamina properties with time-delay data for a [0/90] cross-ply composite. Interference due to multiple reflections within the laminate is assumed to be negligible. It is shown via numerical simulation that the reconstructed lamina moduli are highly accurate for composites with transversely isotropic laminae even for data containing large random scatter. For composites with orthotropic laminae, the method gives a very close approximation to the true lamina properties with reasonable accuracy. Experimental time-delay measurements in [0/90]2s cross-ply metal matrix composites (SiC/Ti–15V–3Al–3Cr–3Sn) are made in different incident planes. To avoid the effect of wave interaction within the laminate, we used the first arrival of the ultrasonic signal for time-delay measurements. From the [0/90]2s composite measurements, the elastic moduli of the lamina are determined and compared to those of a thin unidirectional composite panel measured independently by ultrasonic plate modes. The agreement between the two independent measurements is good. Utilization of measurements in the 45° plane in [0/90] composites for determination of lamina moduli is also discussed.
Experimental study of inhomogeneous wave reflection from a solid–air periodically rough boundary using leaky Rayleigh waves
Authors: Huang W. , Briers R. , Rokhlin S. I. , Leroy O.
Published: October 2005

In this paper a leaky Rayleigh wave is used as a source generating an exponentially decaying (along the wave front) inhomogeneous wave in a fluid. The inhomogeneity of the leaked wave beam profile is measured experimentally and compared with that predicted from the theoretically calculated imaginary part of the leaky Rayleigh wave number. The excited inhomogeneous wave is incident normally upon an aluminum sample with a rough back surface. The rough surface is isolated by a gap from the immersing liquid. The reflection of this wave from a solid–air boundary of periodic sawtooth profile is studied. The frequency spectrum of the wave reflected from such an aluminum–air rough surface is measured and a sharp dip in the spectrum is observed which can be attributed to the excitation of a Rayleigh wave along the rough surface. Good agreement is obtained between experimental data and inhomogeneous plane wave theory.
Generalization of the split-step Padé solution
Authors: Collins Michael D.
Published: October 2005

The split-step Padé solution [J. Acoust. Soc. Am. 93, 1736–1742 (1993)] is generalized to simultaneously permit arbitrarily large range steps (in range-independent regions) and dense sampling in range. Although the range step size is limited by the rate of range dependence, range steps of many wavelengths are possible for many range-dependent ocean acoustics problems. At each range point in a dense grid, the acoustic pressure is defined over depth in terms of a linear combination of solutions of tridiagonal systems. On a multiprocessor computer, each of the tridiagonal systems is solved on a different processor, and the acoustic field can be generated throughout a large range-independent region in the time required by standard finite-difference solutions to take one range step. The generalized split-step Padé solution is also applicable to elastic media.
Spectral and modal representations of the Doppler-shifted field in ocean waveguides
Authors: Schmidt Henrik , Kuperman W. A.
Published: October 2005

A simple spectral representation is derived for the Doppler-shifted field in general stratified waveguides, including those with elastic bottoms and ice covers. By transforming the field representation for a moving, finite bandwidth source into the moving receiver’s frame of reference, a spectral integral representation is obtained for the dynamic transfer functions, which may then be transformed into time domain responses by standard Fourier synthesis. The spectral representation of the Doppler-shifted field is more general than earlier modal formulations since it is not based on any assumptions concerning the invariance of mode shapes, and it properly accounts for modal cutoff effects. However, it will be demonstrated that its approximate modal expansion is consistent with earlier modal formulations. The spectral formulation has been implemented in an existing wave-number integration code, and applied to illustrate the fundamental physics of the source/receiver dynamics in stratified waveguides. Examples include moving source/receivers in shallow water, and the acoustic emission produced by propagating ice fractures in the Arctic.