bluuebunny/crossref_metadata_2025 huggingface dataset:
Oceanographic, topographic, and sediment interactions in deep water acoustic propagation. Part I. Sediment effects on water column propagation patterns
Authors: Carman Jessie C.
Published: October 2005

Effects of properties of a fluid sediment layer on low-frequency, long-range deep water acoustic propagation are studied numerically using a parabolic approximation to the Helmholtz equation. Representative Slope and Sargasso water mass sound-speed profiles are used in the water column; below the water, a uniform flow sediment layer is imposed having constant density, attenuation, and sound-speed discontinuity at the interface, and linear sound-speed gradient over the specified sediment depth. Two major propagation regimes are found which display qualitatively different forms of sensitivity to sediment model parameters: one regime in which sound refracting within the water column dominates long-range propagation patterns, and another in which bottom-glancing propagation paths remain important for mid to long ranges. Importance of such paths depends on low-frequency interference patterns and the angular distribution of sound striking the sediment. The dependence of the water-sediment Rayleigh reflection coefficient on sediment properties and the importance of bottom-reflected sound in the second regime renders such propagation patterns critically sensitive to properties of the sediment.
Oceanographic, topographic, and sediment interactions in deep water acoustic propagation. Part II. Gulf Stream simulations
Authors: Carman Jessie C. , Robinson Allan R.
Published: October 2005

Interacting low-frequency acoustic propagation effects of range-dependent oceanographic sound-speed profiles and range varying topography, with a fluid sediment layer, are modeled in the Gulf Stream region using a parabolic approximation to the Helmholtz equation. Oceanographic frontal effects, monotonically upsloping and downsloping topographic effects are identified in propagation between reciprocally chosen points on either side of the Gulf Stream at frequencies of 25, 50, and 100 Hz. For propagation from Slope to Sargasso water, surface shadow zone formation is documented, and ensonification of the shadow zone due to low-frequency diffraction. In propagation from Sargasso to Slope water, increased surface ensonification results. Topographic effects include truncation/reflection of deep propagation paths for upsloping topography, and increased depth for water column refraction for downsloping topography. Frequency and source depth-dependent oceanographic and topographic interaction effects are documented for two major propagation regimes: one containing primarily water-column refracting patterns, and one in which bottom-glancing propagation paths dominate sound fields for mid to long ranges.
Relating Arctic ambient noise to thermally induced fracturing of the ice pack
Authors: Lewis James K.
Published: October 2005

Thermally induced stresses within pack ice floes are simulated using a viscoelastic model that accounts for the time variation of the atmospheric forcing parameters and the temporal and spatial variations of snow cover. To relate the model-predicted stresses to the observed 500 Hz under-ice noise variations, a fracturing paradigm was developed. The fracturing paradigm includes factors related to ice tensile strength given its salinity and temperature and stress relief as a result of fracturing. A fracture count time history was produced using the thermal stress model and the fracturing paradigm for the fall of 1988 in the eastern Arctic Ocean. The results were compared with the observed 500-Hz noise. The fracture count shows increases for 11 of 13 under-ice noise episodes. Most of the observed under-ice noise episodes were of the type identified in previous studies; i.e., those associated with nightly cooling. In addition, this study identifies under-ice noise episodes related to longer-term occurrences associated with sustained cooling over several days after the passage of a cold front.
Doubly rotated SAW quartz cuts with low sensitivity to stress and temperature effects exhibiting a power flow angle close to zero
Authors: Ballandras S. , Bigler E.
Published: October 2005

Three doubly rotated quartz cuts for surface acoustic wave (SAW) devices have been theoretically found exhibiting a very low sensitivity to radial in-plane stresses and to statical temperature effects and also presenting a very small power flow angle. Such a conjunction of these phenomena offers new perspectives in the design of very high stability SAW resonators.
On the statistical characteristics of log-compressed Rayleigh signals: Theoretical formulation and experimental results
Authors: Kaplan Dmitry , Ma Qinglin
Published: October 2005

This paper addresses the effects of nonlinear log compression on the amplitude of the backscattered signals. The changes in the statistical characteristics of signals were examined and correlated with the compression parameters. An analytical formulation was developed for the probability density function (PDF) of log-compressed amplitude signals. To obtain the theoretical PDF, a Rayleigh distributed signal is subjected to a scaled log compression of the form n1 ln(x)+n2. Such transformation is common in medical ultrasound image formation as it allows independent control over the dynamic range and gain of the displayed image. The resulting Fisher–Tippett PDF and its statistical parameters are derived and compared with the empirically measured statistics of ultrasound images of scattering phantoms. The comparisons reveal a great degree of similarity between theoretical PDF and the histogram of the image, even though the goodness-of-fit tests indicate statistical mismatch from theoretical model due to factors such as nonideal log compression transfer, noise, envelope smoothing, etc.
Stability curves for a thermoacoustic prime mover
Authors: Atchley Anthony A. , Kuo Fan-ming
Published: October 2005

The purpose of this paper is to investigate the stability curves of the fundamental and second modes in a helium filled prime mover. The predicted and measured stability limits are in reasonable agreement for both modes at most mean pressures. There is, however, evidence that the stability of one mode is affected by the presence of the other. It is also observed that one mode can suppress the other. Measurements are also reported on a prime mover modified to selectively inhibit the fundamental mode. Results indicate that the reduced fundamental amplitude allows the stability curve for the second mode to extend into the regions where the fundamental mode previously dominated. This produces a region where both modes are simultaneously excited. Analysis of the waveforms show that the resulting oscillations are quasiperiodic.
Measured 1/f noise in the membrane motion of condenser microphones
Authors: Zuckerwar Allan J. , Ngo Kim Chi Thi
Published: October 2005

An acoustic isolation vessel described previously [K. C. T. Ngo and A. J. Zuckerwar, J. Acoust. Soc. Am. 93, 2974–2980 (1993)] has been employed to investigate the background noise in condenser microphones over the frequency range from 2 Hz to 25.6 kHz. Measurements were conducted on five B&K condenser microphones ranging from 1/8 in. to 1 in. diameter and representing both pressure and free field types. The experimental evidence reveals the existence of a purely mechanical 1/f noise component in the membrane motion of condenser microphones. The level of significance for the tested microphones, based on the t statistic, ranges from 0.985 to 0.999. It is found that the membrane 1/f coefficient correlates very well with the air layer resistance RA, which is responsible for the membrane damping. The theoretical implications of the existence of 1/f noise in the damped motion of vibrating systems are discussed.
Diffraction of flexural waves at structural joints
Authors: Guo Y. P.
Published: October 2005

This paper discusses flexural wave diffraction at structural joints that connect elastic plates. Transmission and reflection of flexural waves at the joints, as well as their conversion into other types of waves including compressional waves in the plates and sound waves in the surrounding fluid, are examined for various forms of attachments. It is shown that transmission of flexural waves across a structural joint is usually insignificant except for frequencies close to and above the plate coincidence frequency. However, it is found that bending motions may be transmitted through a joint into a structure to energize large amplitude vibrations in the internal structure. It is also shown that acoustic radiation from the wave/joint interactions may occur not only because of direct diffraction of flexural waves at the joints, but also as a result of conversion from nonradiating flexural waves to compressional waves. These waves have supersonic phase speed and may become very efficient radiators if coupled to the fluid; it is shown that the energy level involved in these waves may be much higher than that in the acoustic field due to direct diffraction.
Wavelet transform analysis of transient wave propagation in a dispersive medium
Authors: Önsay Taner , Haddow Alan G.
Published: October 2005

The wavelet transform is applied to the analysis of transient waves propagating in a dispersive medium. Experimental techniques are employed to measure the transient flexural vibrations of an impact excited uniform beam. The similarity in the fundamental characteristics of the analysis tool and the physical phenomena are exploited during the decomposition of the measured signals. The wavelet transform of the acceleration response resulted in a time-scale representation which provided a clear exposition of the time evolution of the spectral components during the dispersion process. The relation between the wavelet transform and the group properties of the dispersed waveform are emphasized. In the applications to finite systems, the efficacy of the wavelet transform is demonstrated by analyzing complex transient wave-interference patterns which evolve over wide spectral ranges. An interesting periodic pulse reformation phenomena is uncovered on a uniform beam with free boundaries. Following the dispersion and the multiple reflections of the bending waves, the original impulsive waveform is found to be reconstituted periodically in time. Based on the physical examples, the advantages and shortcomings of the wavelet transform are discussed.
Prefiltering for improved correlation detection of bandlimited transient signals
Authors: Pflug Lisa A. , Ioup George E. , Ioup Juliette W. , Field Robert L.
Published: October 2005

Prefiltering, or limiting the passband of a received signal, can be used to improve ordinary correlation threshold detector performance for an unknown source model. For the known source model, the cross-correlation detector is equivalent to matched filtering, and intrinsically contains prefiltering. Prefiltering also improves higher-order correlation threshold detector performance, but often with more advantage than seen in the ordinary correlation detector. This is true for both the unknown and known source models. Geometric interpretations are given to provide insight into the origin of potential higher-order advantage. Eight energy signals, each with three different Fourier magnitude-based filters, are used to test the cross-correlation, bicorrelation, and tricorrelation detectors by Monte Carlo simulation and hypothesis testing. Significant signal-to-noise ratio (SNR) gains are evident for both the known and unknown source models with the tricorrelation exhibiting the largest gains. The tricorrelation detector has superior performance versus the cross-correlation detector for all the eight test signals in the unknown source case, and was superior for seven of the eight test signals in the known source case. For the narrow pulse test signal, a probability of detection of 0.5 at probability of false alarm 0.001 was achieved at a power SNR −23.57 dB in the known source model, and at SNR −20.28 dB in the unknown source model. Some other test signals have lower SNRs in the unknown source model. Higher-order detectors can be limited to have equivalent information to that of the ordinary correlation detector. An example illustrating this case is given.
An ultrasonic method for monitoring tongue shape and the position of a fixed point on the tongue surface
Authors: Kaburagi Tokihiko , Honda Masaaki
Published: October 2005

An ultrasonic method is presented that combines B-mode ultrasonic imaging with pulsed-transmission ultrasound to image the lateral contour of the tongue and to detect the position of an ultrasonic sensor placed on the tongue surface in the same plane. Measurement accuracy was investigated with respect to the distance between the ultrasonic transducer and the sensor, and with respect to the tilt and lateral displacement of the sensor. An experiment measured movements of the tongue during continuous speech.
On coordinate systems and the representation of articulatory movements
Authors: Westbury John R.
Published: October 2005

Hypothetical examples are used to demonstrate how certain quantitative characterizations of kinematic events can be affected by the placement and orientation of reference axes against which measurements are made. The variation in coordinate systems among a representative sample of recent publications describing speech movements and postures is summarized, and a standard, easily defined coordinate system for future descriptions is proposed. Interpretative benefits associated with the proposed representational standard are noted.
The effects of age and sex on speech intonation and duration for matched statements and questions in French
Authors: Ryalls John , Le Dorze Guylaine , Lever Nathalie , Ouellet Lisa , Larfeuil Céline
Published: October 2005

Intonation characteristics (mean F0, standard deviation of F0, and F0 difference) and speaker rate (duration) were assessed in 40 matched statement–question pairs produced by 40 normal adult speakers of Canadian French, similar to Eady and Cooper [J. Acoust. Soc. Am. 80, 402–415 (1986)] for American English. Subgroups were also compared by both sex (male versus female) and age (younger versus older subjects). Results revealed a greater difference in fundamental frequency between statement–question pairs than reported by Eady and Cooper, as well as a previously unreported interaction between sentence duration and sentence type. There were also age-related differences in both intonation and rate.
Radiation from cylindrical shells driven by on-surface forces
Authors: Guo Y. P.
Published: October 2005

Asymptotic analysis is used to study sound radiation from cylindrical shells driven by on-surface forces. The far-field sound is analyzed in terms of radiations from helical waves in the shell excited by the forces, which are shear and compressional waves in frequency domains well below the coincidence frequency of the shell plating where thin shell theory is applicable. These shell-borne waves are shown to be crucial contributors to the far-field radiation; they dominate the frequency dependence of the radiated field, because they carry with them features of the elastic waves such as resonances, their radiation covers a wide spatial domain, unaffected by the shadowing effects of the shell, and they may overwhelm in amplitude the direct radiation from the forces in some directions, the latter following a direct fluid-borne propagation path from the driving forces to the far field. It is found that tangential forces on the shell cause more acoustic radiation than normal forces, because the former excite radiating shell waves more easily than the latter.
Slot depth resolution in vibration signature monitoring of beams using frequency shift
Authors: Man XiuTing C. , McClure Lawrence M. , Wang Zhijing , Finch Robert D. , Robin Pierre Y. , Jansen Ben H.
Published: October 2005

A major issue in defect detection by vibration monitoring is the resolution of defect size. To investigate this issue, a simple structure, namely, a beam, was used. A fixture was designed for experimental testing on beams with several classic end conditions. By allowing for the variation of moment of inertia of a slotted beam, a theoretical model was developed that fits the experimental data closely. It is shown how the relationship between slot size and frequency shift can be used to resolve the question of the minimum detectable crack size. It is concluded that slots of the size of critical cracks should be detectable with commercial frequency counters. Finally, the practicalities that might prevent cracks of such size from being detected are discussed. In the present experiment, the minimum slot depth detected was found to be 10% of the beam depth under the particular conditions of our experiment.
Experimental performance of high-resolution array processing algorithms in a towed sonar array environment
Authors: Gao Shi-Wei , Griffiths J. W. R.
Published: October 2005

In this paper the performance of some typical high-resolution sensor array processing algorithms is investigated using real towed sonar array data. Particular attention is focused on the robustness of the algorithms to gain and phase mismatches between different sensors and the associated receiving channels. A method is also proposed to deal with the gain mismatches. The results provide some new insight into the behavior of the algorithms in real sonar environment.
Visual detection efficiency in ultrasonic imaging: A framework for objective assessment of image quality
Authors: Insana Michael F. , Hall Timothy J.
Published: October 2005

Experimental methods for estimating detection efficiencies of human and computational observers viewing low-contrast circular targets in acoustic noise are described. Sonographic images were simulated with signal and noise properties specified exactly. These images were presented to observers in two-alternative forced-choice (2AFC) experiments. Relative to the ideal observer of these images, i.e., the prewhitening matched filter, human observers were 60% efficient for detecting targets over a broad range of target energies and for both target polarities. Studies were limited to situations where target diameters were much larger than the correlation length of the noise. In that case, observers unable to decorrelate the noise showed no reduction in detectability as predicted by theory. For example, the efficiency of one computational observer, a nonprewhitening matched filter, was nearly ideal. Its response was proportional to that of the average human observer, which suggests a role for computational observers in image evaluation.
The transverse Doppler spectrum for focused transducers with rectangular apertures
Authors: Newhouse V. L. , Faure Philippe , Cathignol Dominique , Chapelon Jean-Yves
Published: October 2005

It is shown analytically that, for focused transducers whose apertures have axes of symmetry, the Doppler spectrum shape is related to that of the aperture in a simple way. Specifically it is found that, for line flow through the focus, parallel to an aperture axis of symmetry, the Doppler amplitude spectrum has the shape of the aperture on either side of the axis of symmetry convolved with itself. The analysis is exact in the limit in which the wave fronts in the focal region are planar, i.e., when the transducer diameter to focal length ratio is sufficiently large. The theory is applied to the case of focused rectangular aperture transducers. For these the predicted spectral shape is that of a triangle, whose width is proportional to the product of the flow velocity, with the length of the side of the rectangle parallel to the flow. For flows with velocity components parallel to both sides of the rectangle, the Doppler spectrum is found to be the convolution of the spectra produced by each velocity component. A numerical calculation that does not make the limiting assumptions of the analysis predicts bandwidths within 10% of the analysis for transducer diameter-to-focal length ratios equal to or larger than 0.2. Experimental bandwidths for a thread phantom rotated about the beam axis of a focused strip agree with the numerical model to within 25%.
Gerbil brain-stem auditory-evoked responses to maximum length sequences
Authors: Burkard R.
Published: October 2005

This study evaluated the feasibility of obtaining brain-stem auditory-evoked responses (BAERs) to trains of clicks with average rates of up to 500 clicks per second in the gerbil, in order to evaluate BAER behavior at rates higher than those possible in conventional averaging, and to evaluate whether these higher rates allow obtaining BAERs more efficiently. Gerbils were anesthetized with Nembutal, and normothermia was maintained with a homeothermic blanket system. Pseudorandom pulse trains, called maximum length sequences (MLSs), were generated by an Ariel DSP-16 board housed in an IBM-AT. Electrical activity was recorded with Grass needle electrodes placed subdermally. This activity was amplified and filtered by a Nicolet Compact Four, and digitized by the A/D of the Ariel DSP-16. Clicks were presented at levels of 50, 60, 70, 80, and 90 dB pSPL. Conventional BAERs were obtained at a rate of 30 Hz. MLS BAERs were obtained by presenting MLS pulse trains which were comprised of 64 pulses. Following collection of the response to MLS pulse trains, the MLS BAER was obtained by cross correlating the response with a recovery sequence. The minimum time between pulses is called the minimum pulse interval (MPI). MLS BAERs were obtained for MPIs of 6, 4, 2, and 1 ms. BAERs were obtained in ten young adult gerbils for all rate by click-level conditions. BAERs were observed in all animals for all click levels and rates. Generally, with increasing click level there were decreases in peak latencies and increases in peak amplitudes. With increasing rate (decreasing MPI), there were increases in peak latencies, increases in the i–iv interval, and decreases in peak amplitudes. Computations suggested the the most efficient rate (i.e., the rate producing a constant signal-to-noise ratio response in the least amount of time) is not necessarily the fastest rate, but depends on the BAER peak and click level.
Conventional and cross-correlation brain-stem auditory-evoked responses in the white leghorn chick: Rate manipulations
Authors: Burkard Robert , Jones Sherri , Jones Timothy
Published: October 2005

Rate-dependent changes in the chick brain-stem auditory evoked response (BAER) using conventional averaging and a cross-correlation technique were investigated. Five 15- to 19-day-old white leghorn chicks were anesthetized with Chloropent. In each chick, the left ear was acoustically stimulated. Electrical pulses of 0.1-ms duration were shaped, attenuated, and passed through a current driver to an Etymotic ER-2 which was sealed in the ear canal. Electrical activity from stainless-steel electrodes was amplified, filtered (300–3000 Hz) and digitized at 20 kHz. Click levels included 70 and 90 dB peSPL. In each animal, conventional BAERs were obtained at rates ranging from 5 to 90 Hz. BAERs were also obtained using a cross-correlation technique involving pseudorandom pulse sequences called maximum length sequences (MLSs). The minimum time between pulses, called the minimum pulse interval (MPI), ranged from 0.5 to 6 ms. Two BAERs were obtained for each condition. Dependent variables included the latency and amplitude of the cochlear microphonic (CM), wave 2 and wave 3. BAERs were observed in all chicks, for all level by rate combinations for both conventional and MLS BAERs. There was no effect of click level or rate on the latency of the CM. The latency of waves 2 and 3 increased with decreasing click level and increasing rate. CM amplitude decreased with decreasing click level, but was not influenced by click rate for the 70 dB peSPL condition. For the 90 dB peSPL click, CM amplitude was uninfluenced by click rate for conventional averaging. For MLS BAERs, CM amplitude was similar to conventional averaging for longer MPIs. At MPIs below 2 ms, CM amplitude increased with decreasing MPI. The amplitude of waves 2 and 3 decreased with decreasing click level and increasing click rate.
Single neurons in the frog inferior colliculus exhibit direction-dependent frequency selectivity to isointensity tone bursts
Authors: Xu Jinghua , Gooler David M. , Feng Albert S.
Published: October 2005

The effects of sound direction on frequency selectivity of inferior colliculus (IC) neurons were investigated by measuring the neuron’s isointensity frequency responses (FRs) to tone bursts emanating from a free-field loudspeaker at several sound levels. The loudspeaker was rotated across the frontal field at 0° elevation through 180° of azimuth (from contralateral 90° or C90° to ipsilateral 90° or I90°). At each frequency, to assess the magnitude of response change with sound direction, the mean spike count obtained at an azimuth was compared to that at C90°. The FR of most IC neurons (75/83 or 90%) was direction dependent. For most of these neurons, bandwidths of FRs were narrower when sounds originated from ipsilateral azimuths. Remarkably, with a change in sound azimuth, some segments of these FRs showed very distinct changes in shape, while other portions of the same FRs remained essentially unchanged. These narrow-band changes associated with restricted portions of the FR, were also exhibited by neurons with direction-dependent frequency-threshold characteristics (Gooler et al., 1993). Additionally, the most frequent direction-dependent change in the FRs occurred in a narrow frequency band around the units’ best excitatory frequency.
Profile analysis and comodulation detection differences using narrow bands of noise and their relation to comodulation masking release
Authors: Fantini Deborah A. , Moore Brian C. J.
Published: October 2005

Experiment 1 examined the ability to compare relative level across frequency (profile analysis) for stimuli that were dynamically varying over time. The task was to detect an increment in level of a narrow band of noise (the target) in the presence or absence (reference condition) of four flanking bands (FBs). The envelopes of the FBs were either the same as that of the target (correlated condition), independent of that of the target but the same as each other (co-uncorrelated condition), or all independent (all-uncorrelated condition). The overall level of the stimuli was either fixed or randomly varied from one stimulus to the next. The results showed that subjects can make effective use of spectral-shape cues even for stimuli whose amplitudes vary markedly over time. In the correlated condition, the threshold for detecting an increment in the level of the target band was decreased (relative to the reference condition) both when the overall level was fixed and when it was varied randomly from stimulus to stimulus. In the uncorrelated conditions, the FBs did not lead to better performance when the overall level was fixed; rather they produced a small interference effect. When the overall level was randomized, the presence of uncorrelated FBs produced thresholds that decreased with increasing bandwidth and, for a bandwidth of 64 Hz, produced an improvement in performance (relative to the reference condition) that was almost as large as that produced by the correlated FBs. It seems that the more rapid fluctuations in the wider bands of noise were smoothed by the auditory system, enabling information about the long-term spectral shape to be extracted effectively. Experiment 2 used similar stimuli, but the task was to detect the target, rather than to discriminate its level. Detection thresholds in the presence of FBs were lowest in the co-uncorrelated condition, higher in the correlated condition, and highest in the all-uncorrelated condition. Thus the presence of correlated FBs improved discrimination thresholds in the profile analysis task, but impaired performance in the detection task. Reasons for the discrepancy between the effects of correlated FBs in the two tasks are discussed in the context of the cues available to the listener.
Effect of masker level on overshoot in running- and frozen-noise maskers
Authors: von Klitzing Regine , Kohlrausch Armin
Published: October 2005

Masked thresholds were measured with running- and frozen-noise maskers. The 5-kHz signal was 2 ms in duration. The masker was low-pass noise (20 Hz–10 kHz); its total duration was 300 ms. The overall level of the masker was 30, 50, or 70 dB SPL. The onset of the signal was delayed by 0, 3, 8, 18, 198, or 278 ms relative to the onset of the masker. In all frozen-noise measurements, the signal was added to the same fine structure of the noise. Overshoot in frozen noise was measured for two starting phases of the signal that led to a 10-dB difference for large signal-onset delays. In all three configurations (running noise and frozen noise with two different signal phases) masker level had a similar influence on overshoot. At the intermediate masker level (50 dB SPL), a significant amount of overshoot (up to 15 dB) was observed in all three conditions. At the low and the high masker levels, overshoot was very much reduced, and even became negative in most conditions for the 30-dB-SPL masker. For the 50-dB frozen-noise masker, the total variation of thresholds with signal phase was 8 to 11 dB for long signal-onset delays, but only 3 to 6 dB for short delays. For the low- and high-level maskers, where only a small overshoot was observed, the threshold variation with phase for a signal at masker onset was the same as that for the long-delay condition. An explanation for the variation of signal detectability with masker level is proposed that refers explicitly to the compressive input–output characteristic of the basilar membrane at intermediate levels.
Modulation detection and discrimination with three-component signals
Authors: Edwards Brent W. , Viemeister Neal F.
Published: October 2005

In an attempt to study the processing of amplitude and frequency modulation (AM and FM), detection and discrimination tasks using mixed modulation (MM) signals were performed. Modulation detection thresholds were obtained for three-component signals that span the parameter space between AM and quasi-FM. A single-cue modulation detection model predicts the thresholds with reasonable accuracy. If one assumes that the AM and FM components are extracted separately, thresholds are also well predicted if the d′ of the MM signals is equal to the sum of the separate d′s of the AM and FM components (two-cue summation model). This could arise from common internal noise that puts the AM and FM information along a single decision axis. A modulation discrimination task was then examined in which the subjects discriminate between signals with both different modulation depths and different modulation types. The single-cue model predicts performance well. In order for the two-cue model to predict the results, the AM and FM cues must be combined into a single statistic before a decision can be made; the listener cannot process the cues separately.
Vibrotactile temporal masking: Effects of multiple maskers
Authors: Weisenberger Janet M.
Published: October 2005

Previous investigations of temporal masking effects in vibrotactile detection tasks have generally produced results suggesting considerable similarities in stimulus processing between the tactile system and the auditory system. Auditory presentation of combinations of maskers (e.g., two forward maskers) has yielded masking effects in excess of the level of masking predicted by a simple intensity sum of each masker’s individual effect. This ‘‘additional masking’’ has led to predictions of compressive nonlinearities in auditory stimulus processing. In the present study, two experiments were conducted to investigate further temporal masking phenomena for the tactile system. In the first experiment vibrotactile temporal masking functions for single forward and backward maskers were generated to examine trade-offs among values of masker duration, masking intensity, and interstimulus interval to maintain constant detectability of a target. Results suggested that stimuli in very close temporal proximity to the target might follow somewhat different trading equations from those farther removed. Overall, results were consistent with previous findings of temporal integration in the tactile system, and support the notion of an energy integrating mechanism. In the second experiment, pairs of maskers were presented to determine whether additional masking effects occurred in vibrotactile detection. In contrast to findings for auditory presentation, in which all masker configurations generated additional masking, the tactile results showed substantial amounts of additional masking only for pairs of backward maskers. Several possible explanations for this result are evaluated, and results are discussed in terms of similarities and dissimilarities in auditory and tactile temporal processing.
Propagation of vertical shock waves in the atmosphere
Authors: Besset Christophe , Blanc Elisabeth
Published: October 2005

Modeling the propagation of shock waves is a major problem for studies of wave propagation in the atmosphere because of the exponential amplification of the wave amplitude during the vertical propagation. The waves generated by pulse sources at the ground can have shock wave characteristics upon reaching the upper layers of the atmosphere. This paper proposes a new computation method based on studies of shock propagation in ray tubes for laboratory experiments and attempts to adapt this method to atmospheric propagation. This nonlinear approach shows reflections from the stratospheric temperature increase that were not predicted by the linear acoustic theory for the same atmospheric model. The nonlinear computations also predicts focusing of the rays at mesospheric altitudes.
Stop bands for elastic waves in periodic composite materials
Authors: Economou E. N. , Sigalas M.
Published: October 2005

The frequency ω versus wave vector k of elastic waves propagating in periodic binary composites consisting of solid inclusions placed periodically in a host matrix was calculated. Attention was focused on the possibility of stop bands (spectral gaps) for all directions of propagation in such composites. It was found that gold or lead inclusions of about 10% volume fraction in a Si or Be matrix give rise to stop bands.
Spherical wave functions and tensor Green’s functions in transversely isotropic saturated poroelastic media
Authors: Ren Wei
Published: October 2005

This paper is an outgrowth of the method of angular spectrum expansions studied recently in electromagnetics. A spherical wave function theory for bounded homogeneous transversely isotropic saturated poroelastic media (TISPM) is developed. Series forms, integral representations, and addition theorems of the spherical wave functions of the first, second, third, and fourth kind for homogeneous TISPM are presented. Weyl’s method of deriving the scalar Green’s functions in isotropic media is generalized so as to study tensor Green’s functions in TISPM. The series representations of Green’s functions are of the form of separation variables. These representations are well suited to imposing the boundary conditions in dealing with fields and waves in spherically layered TISPM.
Elastic waves in homogeneous and layered transversely isotropic media: Plane waves and Gaussian wave packets. A general approach
Authors: Spies M.
Published: October 2005

Solutions to the equation of motion are derived for transversely isotropic media such as fiber composites, ideally fiber-textured austenitic steels, or extruded metal-matrix composites. The approach is most general in that the orientation of the materials’ axis of rotational symmetry is arbitrary. Thus the results obtained using a coordinate-free representation are particularly convenient in view of layered structures, where for the materials of interest the fiber axis is perpendicular to the surface normal, but variable in orientation. Plane elastic waves are characterized by the corresponding wave vectors, making especially possible a quantitative evaluation of the deviation of wave propagation direction and energy flux, which is characteristic for anisotropic materials. Reflection and refraction of plane waves at an interface between two arbitrarily oriented transversely isotropic media is examined yielding an algorithm that provides the respective reflection and transmission coefficients. The propagation of elastic waves of finite spatial and temporal extent is modeled using the concept of Gaussian wave packets. The relations given in the literature for general anisotropic media are specialized to the homogeneous and layered transversely isotropic cases. Numerical evaluation of the analytical results is included.
Generalized basic equations for bending motions of piezoelectric bars formulated from Hamilton’s principle
Authors: Tanaka Haruo
Published: October 2005

For the bending motion of piezoelectric bars, the basic equations have generally been formulated from Hamilton’s principle. Using these equations, the bending motions of bars can be analyzed more easily, and the equivalent circuits for the bending vibrators of the bars also can be derived more systematically.
Impulse-response method to predict echo responses from targets of complex geometry. Part II. Computer implementation and experimental validation
Authors: Lhémery Alain , Raillon Raphaële
Published: October 2005

A theoretical model has been proposed for the complete solution of the problem of the radiation of transient ultrasonic pulses, their scattering by targets of complex shape and arbitrary acoustic impedance, and their reception [A. Lhémery, ‘‘Impulse-response method to predict echo responses from targets of complex geometry. Part I: Theory,’’ J. Acoust. Soc. Am. 90, 2799–2807 (1991)]. Here, its computer implementation and its experimental validation are considered. First, the theoretical formulation is derived in a discrete form and an algorithm is explicitly given to allow its computer implementation. Precautions to be taken to ensure good precision of numerical results are discussed in detail. Then, predicted waveforms are compared with existing measurements (scattering by planar targets) and new measurements (scattering by nonplanar targets). The model is shown accurately to predict measured echoes, both qualitatively and quantitatively. However, some discrepancies are observed and explained as resulting from the lack of precision in the Kirchhoff-like approximation made in the model’s derivation.
A high-frequency approximation of sound propagation in a stratified moving atmosphere above a porous ground surface
Authors: Li Kai Ming
Published: October 2005

This paper examines the sound propagation in a moving stratified atmosphere above a porous ground surface. A generalized expression is derived for the sound field above a porous half-space and the existence of an asymptotic behavior is demonstrated. The leading term of the solution is not only consistent with ray theory but mathematically rigorous. The analysis starts from the fundamental hydrodynamic equations of pressure and particle velocity, etc., and the assumption that the atmosphere is vertically stratified. These hydrodynamic equations are reduced to a one-dimensional Helmholtz equation by applying the Fourier transform method. The solution for the simplified Helmholtz equation is approximated in the high-frequency limit and then the sound pressure is represented by a Fourier integral. The method of stationary phase is used to evaluate the Fourier integral in order to give an asymptotic expression for the sound pressure. It should be emphasized that the Weyl–Van der Pol formula has been generalized to give the field due to a point source in a moving stratified medium above an extended reaction boundary. The total sound field is derived as the sum of three components: a direct contribution from the source, a geometrically reflected component, and a ground wave term, respectively. The ground wave gives a significant contribution to the total sound field especially at low frequencies and at the ground effect dip.
Oceanographic–topographic interactions in acoustic propagation in the Iceland–Faeroes front region
Authors: Carman Jessie C. , Robinson Allan R.
Published: October 2005

Effects of oceanographic variation with distance on long-range, low-frequency acoustic propagation in the Iceland–Faeroes front region of the ocean are considered in the presence of realistic topographic variations. A numerical model using a parabolic approximation to the Helmholtz equation, a fluid sediment parametrization and variable topography, is used to calculate acoustic propagation. Oceanographic sound-speed fields output from the Harvard Open Ocean Model, supplemented by climatology in deep regions, provide input sound-speed profiles. Two different propagation transects are considered, both running from shallow to deep water across a developing eddy and across the front. Source depths near the surface, middle, and bottom of the shallow starting profile are studied. Some cases of near invariance to oceanographic changes are found, as are other cases of locally large oceanographic effects (≳30 dB).
Bubble production by capillary-gravity waves
Authors: Kolaini Ali R. , Crum Lawrence A. , Roy Ronald A.
Published: October 2005

In the absence of whitecapping, other physical mechanisms may contribute to the generation of high-frequency ambient noise. It has been suggested [Longuet-Higgins, in NATO Advanced Research Workshop on Sound Generation Mechanisms at the Open Surface (NATO, Geneva, 1987)] that capillary waves, with surface profiles that are peaked downward in the troughs and are relatively flat at the crests, can inject acoustically active bubbles into the ocean, and thus contribute to the ambient noise background. It has been demonstrated in the laboratory that bubble injection can be generated at the trough of capillary-gravity, short-fetched waves by blowing air over water contained in a long, narrow tank. Simultaneous in situ acoustic and high-speed video monitoring of the capillary-gravity waves demonstrate that these waves can produce acoustically active bubbles. The generation of capillary waves depends principally upon the surface tension, which can be changed by adding surface-active agents to the water. The bubble production rate per unit area of these capillary-gravity waves was measured, as well as the dependence of this rate on wind speed, laboratory wind fetch, and surface tension. It was determined that an increase in water salinity and a reduction in surface tension increases the bubble production rate. The spectra of radiated frequencies ranges from 1 kHz to over 100 kHz with a broadband peak located around 4 kHz. The measured spectral densities were weakly related to wind speed. The wind-speed threshold value for bubble production was determined to be approximately 8.6 m/s (14.6 m/s at 10-m level) in fresh water and salt water, which decreased to 8.1 m/s (13.8 m/s at 10-m level) with a surface tension of 40.5 dyn/cm.
Delta operator technique to improve the Thomson–Haskell-method stability for propagation in multilayered anisotropic absorbing plates
Authors: Castaings Michel , Hosten Bernard
Published: October 2005

A modified version of the transfer-matrix method that models propagation of heterogeneous plane waves through immersed multilayered plates made of anisotropic absorbing layers is presented. Since this method suffers from numerical instabilities, the so-called delta matrix operator is applied. As for propagation through isotropic media, the case of propagation in the principal plane of anisotropic media requires us to define sixth-order delta matrices. This method eliminates numerical difficulties. The same technique is used for propagation out of the principal plane. Fifteenth-order delta matrices are necessary to get improved results. However, numerical problems persist with computational data corresponding to the usual experimental situations. Then, a modified version of the delta matrix operator is proposed. From the reflection and transmission coefficients expressions, both 15th- and 20th-order delta matrices are necessary to get reliable numerical results, whatever the computational data may be.
Focusing of fast transverse modes in (001) silicon at ultrasonic frequencies
Authors: Kim Kwang Yul , Every Arthur G. , Sachse Wolfgang
Published: October 2005

This paper presents observations of the focusing of fast transverse (FT) ultrasonic waves in a (001) oriented, disk-shaped silicon single crystal. These modes are almost perfectly shear horizontally (SH) polarized and were absent from earlier reported observations of focusing of ultrasonic waves based on axisymmetric excitation and sensing. In an experiment the FT modes are generated and detected at room temperature by two small [100] polarized PZT piezoelectric shear transducers. The source transducer is fixed on the bottom surface of the specimen and the detector scans the top surface in the [100] direction along lines that intersect the [010] axis at various distances from epicenter. The observed focusing pattern indicates a strong concentration of the FT mode flux in a narrow band about the (100) plane containing the source. Because of the specific way in which the monopolar source acts, the radiated acoustic flux pattern breaks the fourfold symmetry associated with cubic media. While it shows a strong concentration of FT flux toward the (100) plane, it suppresses FT modes propagating very near the (010) plane passing through the source. The spatial variation of the Fourier components of the detected signal at approximately 2, 6, and 8 MHz has been examined, and there is good accountability for this variation on the basis of the computed frequency domain elastodynamic Green’s function for silicon.
A new concept of a low-frequency underwater sound source
Authors: Donskoy Dimitri M. , Blue Joseph E.
Published: October 2005

A new concept of a low-frequency (<1000-Hz) underwater sound source has been developed and tested. The oscillation of a rigid body and a means for converting the dipole oscillation of the body to monopole radiation are used in this source. The source can be powered with electric or linear motors or hydrodynamic exciters that convert tow or flow to vibration. To prove the concept, a small version of the electric motor powered source has been built and successfully tested. To extend the bandwidth of the source, the variable resonance frequency and multiresonances of the device are discussed. A gas spring with a frequency-dependent stiffness is employed for the multifrequency resonant source design. The source promises to be reliable, inexpensive, highly efficient, and powerful.
Response of a fluid-loaded infinite plate subject to a line force excitation in mean flow
Authors: Zhu Jinshuo , Wu Sean F.
Published: October 2005

Asymptotic formulations are derived to estimate the dynamic response of a fluid-loaded infinite plate subject to a line force excitation in mean flow. Analysis shows that mean flow may have significant effects on the plate flexural waves when the excitation frequency is above the plate coincidence frequency, moderate effects around the coincidence frequency, and little effects below the coincidence frequency. This is because at high frequencies, most of plate vibration energy is converted to acoustic energy. Since mean flow can greatly modify the radiated acoustic pressure, the effect of mean flow on plate flexural vibration becomes obvious. At low frequencies, there is no sound radiation and most of plate vibration energy stays close to the surface. Consequently, the effect of mean flow on plate vibration is greatly reduced. The asymptotic behaviors of the branch cut integrals at large distances from the point of excitation are also investigated. It is shown that the leading terms of the branch cut integrals decay with distances along the plate surface. The presence of mean flow suppresses the amplitude of the disturbance propagating in the upstream direction, but enhances that of the disturbance propagating in the downstream direction. [Work supported by ONR.]