bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverberant transfer functions and cepstrum dereverberation
Authors: Tohyama Mikio , Lyon Richard H. , Koike Tsunehiko
Published: October 2005

Inverse filtering for transfer functions (TFs) in a reverberant space is an important issue in sound and vibration control. ‘‘Robust’’ inverse filtering procedures are needed for the TF variations. The TF can be thought of as a stochastic process on the frequency axis due to random occurrences of poles and zeros. This paper describes the pole-zero statistics of the TFs, and shows that the trend of TF phase is predictable. However, inverse filtering for source waveform recovery is still a problem because of the nonminimum-phase property of the TF and the local variability of the TF phase. Blind dereverberation is proposed without the TFs by ‘‘minimum-phase cepstrum windowing’’ for pulselike source waveform recovery. A reverberant response to the source signal is composed of the minimum-phase and all-pass components. The minimum-phase components of the source waveform can be recovered from the minimum-phase cepstrum of the response. This recovery process is less sensitive to the observation location and the changes of the TFs.
On the convergence behavior of the exterior acoustic modes of structures
Authors: Curry Noelle , Cunefare Kenneth A.
Published: October 2005

The use of a modal-style approach for the analysis of the exterior radiation characteristics of structures has recently received increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator. These acoustic modes are found through an eigenfunction or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. One advantage of this acoustic modal approach is that the total radiated power can be found by simply summing the contributions from individual acoustic modes, since they are completely decoupled. It is shown that the accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation operator. The most efficient acoustic modes are least sensitive to increasing degrees of freedom. The least efficient acoustic modes are most sensitive to changes in degrees of freedom. Further, it is shown that this convergence behavior of the acoustic modes can be related to the familiar convergence behavior of structural modes, through the Rayleigh quotient.
An algorithm for synthesis of low-peak-factor periodic functions
Authors: Hargrove Logan E.
Published: October 2005

Peak factor (PF) is the ratio of the range to the rms value of a periodic function. A low PF is desirable in applications such as radar, sonar, communications techniques, and the design of test signals. The PF of a frequency-modulated (fm) periodic function is low because the peak-to-peak amplitude remains fixed and the rms value changes very little for all values of the modulation index. But in some applications an ‘‘fm-like’’ function is undesirable, and for many applications a low PF periodic function consisting of a specified number of equal-amplitude and harmonically related frequency components is sought. Here, results from an algorithm that uses phases of some spectral components of a frequency-modulated sinusoid to construct low PF functions with M harmonically related and equal-amplitude components are presented for the range 1≤M≤101. These functions are less fm-like than frequency-truncated fm functions. [Work performed in the ONR Scientific Officer Research Program.]
Acoustic response of a torsional shear wave transducer in a viscoelastic medium
Authors: Walden Alan K. , Howarth Thomas R. , Ma Yushieh
Published: October 2005

Based on a previous design of a low-frequency, torsional shear wave transducer [A. K. Walden and T. R. Howarth, J. Acoust. Soc. Am. 91, 2463 (1992)], an analytical model is proposed to predict the radiated acoustic field. The stress and displacement fields produced by the S-wave source are analyzed with the appropriate boundary conditions. Then the continuity condition of the field (elastic wave equation) is employed to investigate the propagating subfields in the surrounding elastic/viscoelastic medium. The transducer studied is a cylindrical-type torsional vibrator. Therefore, it generates both horizontal and vertical radiation patterns. Computed, as well as measured results, of the acoustic response are presented for various couplings of different viscoelastic media with both the bimorph and torsional shear wave transducer designs. These results are useful for an optimal shear wave transducer design in the applications of ocean geoacoustics.
Coherence measurements of deep-ocean seismoacoustic noise and signals
Authors: Bibee L. Dale , Becklehimer Jeffrey L.
Published: October 2005

In April 1992, an array of six ocean bottom seismometer/hydrophone instruments was deployed on the seafloor in 3800-m-deep water. The instrument site was approximately 300 km west of San Diego, California and was within a few miles of the location of a smaller aperture array used in an experiment conducted in 1987. Initial calculations of the spatial coherence between vertical component seismometer recordings of ambient noise show remarkable similarities to data collected in the earlier experiment. The ratio of vertical to horizontal particle motion at the seafloor during ambient noise recording periods also is consistent with the earlier observations. The combination of coherence structure and particle motion ratios derived from the earlier experiment is used to infer that the ambient noise field at the site is dominated by seismic interface waves. With the new data set, this hypothesis is tested by examining: (1) the behavior of spatial coherence over a larger aperture (∼400 m) array, (2) the spatial coherence of the near-bottom pressure field and horizontal particle motion field, (3) the ratios of particle motion to near-bottom pressure, and (4) the particle motion ratios and spatial coherence of signals from near sea-surface and on-bottom explosive shots. [Work funded by ONR and ONT.]
The depth dependence of seismic background noise within the sea floor
Authors: Dorman Leroy M. , Schreiner Anthony E.
Published: October 2005

Further results are reported of a study of seafloor noise using an array of ocean-bottom seismometers in a sediment pond in deep water off the California coast. Earlier (Schreiner and Dorman, 1990) measurements were presented of coherence between elements of the array that contained interelement spacings in the 8–156 m range and it was shown that they represented the fundamental and first three overtones of seismic surface and interface waves. Here, the ratios of power spectra (horizontal to vertical component) in the 0.500–10 Hz frequency band were used to refine the estimates of the interface wave mode excitation that were made earlier using the interelement coherences. There is a simple frequency dependence in the mode excitation functions. The fundamental mode dominated below 0.65 Hz and is succeeded by the first three overtones in order as the frequency increases. The other transition frequencies are 0.95 and 6.5 Hz. From these excitation functions, the depth dependence of background noise was synthesized, using the vertical wave functions from the known shear velocity structure. For some depths in the 0.8–10 Hz frequency range, the amplitude of vertical component noise is up to 29 dB greater than at the surface, due to the prominence of higher mode interface waves in this band. Varying degrees of noise suppression are obtained outside this band. The noise suppression (or enhancement) is strongly dependent on the relative mode excitation. At frequencies where the fundamental mode dominates there will be noise reduction downhole while at frequencies where the overtones are prominent, there will be noise enhancement at some depths. For horizontal-component noise there is noise suppression with depth at all frequencies. [Work supported by ONR and ONT.]
Environmental noise in the parabolic equation
Authors: Rees C. David
Published: October 2005

It is desirable to develop a theoretically rigorous, numerically efficient technique for treating the problem of oceanic noise fields generated by extended environmental noise sources (ocean wave fields, rainfall, icefields, seismicity, etc.) in general environments. The tensor Green’s function technique originally developed by Kuperman and Ingenito [W. A. Kuperman and F. Ingenito, J. Acoust. Soc. Am. 67, 1988–1996 (1980)] for a range-independent (normal mode) environment provides a guide to developing a rigorous formalism using the parabolic equation (PE) approach for range-dependent environments. The theory and technique developed is described and numerical results are shown. Intrinsic difficulties arising from the PE forward-only assumption are pointed out and techniques to overcome this problem are presented. [Work supported by NRaD-Independent Research.]
The effect of transient signal vertical directionality on hydrophone array performance
Authors: Becklehimer Jeffrey L. , Bibee L. Dale
Published: October 2005

Signals from explosive sources were measured by a near-bottom vertical array of hydrophones during an experiment conducted by the Naval Research Laboratory. Using a beamformer, estimates of the source energy spectrum were made with the array steered toward the direct-path arrival; estimates of the directional noise energy spectrum are made using the same look angle. Signal-to-noise (SNR) estimates were then computed for various ranges and steering angles. As expected, the SNR decreases rapidly at longer ranges and lower grazing angles. This decrease is due in part to lower signal levels, but is dominated by large increases in the ambient noise field for grazing angles less than the critical angle of the water–sediment reflection. The SNR for a vertical acoustic dipole formed by differencing two elements of the array also is computed. Despite the decreased response of the dipole beam at low grazing angles, the SNR remained unexpectedly high at longer range and exceeded that of the beam-steered array. As grazing angle decreased, bottom loss also decreased resulting in a large amount of signal energy in higher-angle, water-column multiples. These energetic signals fall into the broad dipole beam pattern, but are excluded from the beam-steered array. These results imply that to maximize SNR for the vertical array, the total vertical arrival structure of the signal (and of the noise) must be considered in choosing beamforming coefficients. [Work funded by ONT.]
Acoustic measurements of suspended sediments in the laboratory and at sea
Authors: Thorne Peter D. , Waters Kendall R. , Manley Clayton , Brimelow Jason
Published: October 2005

The application of acoustics for measuring suspended sediment transport processes potentially offers the opportunity for examining suspensions with a spatial and temporal resolution sufficient to probe turbulent and within wave sediment mechanisms. This should provide a significant advance in the understanding of the coupling between the fluid dynamics and the sediment response. Although acoustic backscattering devices have been employed by sedimentologists for over a decade to investigate marine suspensions, it is only relatively recently that a theoretical framework for interpreting the interaction of sound with marine suspensions has become available. In the present work a comparison is made between laboratory measurements of the backscattering and attenuation from a suspension and recent developments based on incoherent first-order multiple scattering. This analysis is also applied to acoustic data collected in an estuarine environment over sandwaves under turbulent tidal conditions. Acoustic estimates of the suspended concentration have been calculated and compared with independent tranditional measurements of the suspended concentration. The two observations of suspended sediments are shown to be in good agreement and this has provided confidence for calculating high spatial and temporal resolution estimates of suspended load. The latter display a highly variable concentration field and the relationship between this variability and turbulent structures is speculated upon. [Work supported by ARL:UT, NOARL, and MAFF UK.] a)On leave from the Proudman Oceanographic Laboratory, Merseyside L43 7RA, UK.
Attenuation spectroscopy of suspended sediment suspensions
Authors: Schaafsma A. S.
Published: October 2005

The insitu measurement of the size distribution and the concentration of suspended sediment, by means of the technique of acoustic attenuation spectroscopy in the frequency range of 1–100 MHz, is discussed. Results of laboratory experiments in well-defined conditions are presented to illustrate the possibilities to develop a general analysis method, for apriori unknown particle size distributions. For spherical scatterers, a satisfactory phyiscal interpretation of the attenuation spectra can be given [A. E. Hay and A. S. Schaafsma, J. Acoust. Soc. Am. 85, 1124–1138 (1989)]. For nonspherical scatterers, e.g., sediment particles, one possible approach is a purely empirical one, which, however, involves the need of extensive calibrations [A. S. Schaafsma, in UltrasonicsInternational 89, ConferenceProceedings (Butterworth, London, 1989), pp. 388–393]. Nevertheless, the results indicate that a size resolution of about a factor of 2 can be obtained, for average sediment sizes in the range of 5–500 μm. As a further development along these lines, it is shown that a semi-empirical method for irregularly shaped (sediment) particles, involving less extensive calibrations, gives promising (preliminary) results.
Coastal benthic boundary layer special research program
Authors: Richardson Michael D.
Published: October 2005

A five-year special research program (SRP) was established at the Naval Research Laboratory, which addresses the physical characterization and modeling of marine benthic boundary layer processes and the subsequent impact of these processes on seafloor properties that affect mine countermeasures operations. Recommendations of four workshops held to set scientific priorities for the SRP can be summarized in the following statement: ‘‘Sediment structure provides the common perspective required to unravel relationships among sediment physical, acoustic, electrical, and mechanical properties; quantify the effects of environmental processes on sediment properties; and predict sediment behavior under acoustic, electrical, and mechanical stress.’’ In this presentation, SRP program origins, workshop recommendations, and current SRP direction will be discussed. The first attempt to integrate modeling, hypothesis testing, and field experimentation aspects of the program will be presented.
Complex trace analysis of DTAGS data recorded at the Blake Escarpment face
Authors: Sarwar Abu K. M. , Rowe Mary M. , Gettrust Joseph F.
Published: October 2005

Lateral inhomogeneity of the subsurface beyond the vertical/near vertical face of the Blake Escarpments is investigated using data acquired in 1989 by the Navy Research Laboratory’s (NRL’s) Deep Towed Acoustics/Geophysics System (DTAGS). These data are ideal for the application of Hilbert transform-based analysis to characterize the face and the shallow interior at the Blake Escarpment. This study presents local characterization of lateral inhomogeneity in terms of reflection strength, instantaneous phase, and instantaneous frequency. Those attributes are studied using both constant offset sections and individual shot gathers, and reveal interesting geological features and their related Fresnel effects. [Work supported by the Office of Naval Technology.]
Small scale lateral variability of geoacoustic properties of the upper 40 m of the seafloor
Authors: Lindwall Dennis A. , Gettrust Joseph F.
Published: October 2005

The spectral response versus grazing angle of the seafloor sediment for several kilometers of deep towed, multichannel seismic reflection data from Atlantic seafloor near the Blake outer ridge shows variations of as much as 15 to 20 dB in bottom loss over distances of less than 50 m. A video of this spectrum versus offset (SVO) data, which explicitly shows the lateral variations as the DTAGS instrument is towed along just above the seafloor, is presented. A few regions of anomalously high shear wave velocities also are identified in these observations. These data demonstrate that a seemingly smooth seafloor can be a rough, frequency-dependent scattering surface. [This work is supported by the Office of Naval Technology.]
Remote sensing of seafloor geoacoustic properties using SH and Love waves
Authors: Stoll Robert D. , Bautista Edgar
Published: October 2005

A new source is described for generating SH and Love waves in marine sediments immediately beneath the seafloor. The source, which generates torsional pulses over a small circular area of the seabottom by utilizing the energy stored in a rotating flywheel, and an array of geophones are both deployed on the seafloor. In theory, in a laterally homogeneous medium, this type of source should produce a radially symmetric wave field composed only of horizontally polarized shear waves (SH waves) and the resulting Love modes caused by vertical inhomogeneity. However, in reality, some of the energy may be converted to p-wave and SV-wave motion for a variety of different reasons (e.g., imperfect coupling with the seafloor, anisotropy and lateral inhomogeneity). Since most marine sediments exhibit a strong gradient in shear-wave velocity near the seafloor, it is possible to use the dispersion of the resulting Love waves as a basis for inversion to obtain a geoacoustic model of the bottom. Data from shallow water experiments in New York harbor are presented and a sediment model derived by constrained, least-squares inversion is described. Some results from experiments on land are also presented and the potential for use on the ice sheet is discussed. [Work supported by ONR, Code 11250A.]
Human newborns show a ‘‘perceptual magnet effect’’ for native language and non-native language prototypes
Authors: Walton Gail , Socotch Tina
Published: October 2005

Kuhl demonstrated that adults and 6-month-old human infants showed a ‘‘perceptual magnet effect’’ for vowel prototypes. Kuhl etal. also showed that Swedish infants do not show a magnet effect for phoneme categories that are not present in their native language. This study demonstrated that the ‘‘perceptual magnet effect’’ was also present in human newborns. Newborns of English- and Spanish-speaking mothers were presented phoneme exemplars around the prototypes /i/ and /ℑ/, and also around non-prototypical /i/ and /ℑ/. Neonates of Spanish-speaking mothers demonstrated the magnet effect for the prototype /i/, a speech sound present in their native language, and also for the prototype /ℑ/, a sound not present in their native language. The results suggest that newborns enter the world with "platonic forms" for phoneme categories that are influenced by subsequent linguistic experience.
Perceptual representation in spoken word recognition: Evidence from CVCC and CCVC stimuli
Authors: Gagnon Deborah A.
Published: October 2005

The representation used to recognize spoken words was investigated using natural CVCC and CCVC word and nonword stimuli in a primed lexical decision task. In this task, subjects decided whether the second item in a prime-target pair was a word or nonword, as quickly and accurately as possible. Five prime-target relations were devised: identity (/pats/–/pats/), break cluster (spat/–/pats/), change vowel (/p ts/–/pats/), change both (/st p/–/pats/), and control (/grin/–/pats/). The pattern of mean RTs and accuracy across these five relation types provides insight into issues such as the nature of the representation underlying spoken words (possibilities include the abstract phoneme, position-specific phoneme, triphone, and syllable) and the cohesiveness of consonantal clusters (will a cluster act as a cohesive unit or as separate phonemes?). Furthermore, enough data were collected to partition the RTs into fast, medium, and slow ranges. It was reasoned that the pattern of results in the slow range would reflect a post-lexical representation while the results from the fast range would reflect the prelexical level of representation that is used in recognizing spoken words. [Work supported by NIDCD Grant No. DC00219 to SUNY at Buffalo.]
Perception of ethnic identity: The role of F0
Authors: Yeni-Komshian Grace H. , Hawkins Francine Dove
Published: October 2005

This study was conducted to examine the perceptual consequences of specific modifications in the F0 of speech samples. To this end, isolated /ae/ vowels from two black and two white speakers were synthesized at nine F0s, creating a continuum ranging from an F0 of 93 Hz to an F0 of 147 Hz. These synthesized speech stimuli were judged for ethnicity by 180 listeners. The listeners were divided equally by ethnicity, gender, and site of residence. The results showed that, for all speakers, as the F0 of the speech sample decreased, the number of ‘‘black’’ responses increased significantly; conversely, as the F0 increased, the number of ‘‘black’’ responses decreased. These findings indicate that modifications in the F0 of speech produce a significant and predictable shift in ethnic identification responses. Listener variables, such as ethnicity, gender, and site of residence, did not show consistent effects. The results also showed that the effect of F0 modifications, although statistically significant, was not of equal magnitude across speakers. These findings may be used to argue that mental stereotypes of the way different ethnic groups should sound, rather than physiological differences in their vocal tracts, serve as the basis for perceived differences in ethnicity. [Work supported by NICHD Contract No. N01-HD-5-2910.]
Using auditory models to enhance telephone speech for the hearing impaired
Authors: Terry Mark , Mortz Margaret
Published: October 2005

Previously the effectiveness of frequency shaping and compression achieved via manipulation of the short-term spectrum of telephone speech for mild-to-moderate hearing impaired individuals was presented [Terry etal., J. Acoust. Soc. Am. 88, S169 (1990)]. This paper compares this technique with two analysis/resynthesis techniques designed to enhance the consonant parts of speech. In one system a time-domain auditory model (similar to the model proposed Goldstein [Hear. Res. 49, 39–60 (1990)] was used to analyze the speech. A set of consonant identifying features was then used to drive the resynthesis of the speech from the periodicity spectrum. In the other system the speech was resynthesized from LPC coefficients obtained via LPC analysis of the telephone speech signal. Again a set of consonant identifying features derived from LPC analysis was used to drive the resynthesis. The consonant-enhanced telephone band speech was presented to subjects with sensori-neural hearing loss. A consonant-confusion analysis will be presented comparing and evaluating both analysis/resynthesis techniques with a frequency shaping technique based on the subjects audiogram. [Work supported by US West.]
Experimental verification of the theory for sound propagation in a wedge with a shear supporting bottom
Authors: Glegg Stewart A. L. , Deane Grant B.
Published: October 2005

Laboratory experiments have been carried out to investigate underwater sound propagation over a sloping bottom that can support shear. The sound field was measured in both the across slope and down slope direction for many different frequencies and bottom slopes. The experimental results have been compared with the source image theory for sound propagation in a penetrable wedge [G. B. Deane, J. Acoust. Soc. Am. 91, 2390 (A) (1992)] and have shown very good agreement for both down slope and across slope propagation. In particular the effect of shear waves on across slope propagation has been demonstrated both theoretically and experimentally. Further the effect of a sediment layer has been successfully incorporated into the source image theory for comparison with the experimental measurements at low frequencies. One of the problems with laboratory scale measurements of underwater sound propagation is the determination of the bottom parameters with sufficient accuracy for acoustic calculations. In this case the model of the sea floor consisted of a sediment layer (modeled experimentally by epoxy) over a hard basement made of concrete requiring 11 variables to describe the geo-acoustic features of the bottom. These were obtained by inverting measurements of the acoustic field in water of constant depth over the same model. The results are therefore geo-acoustically calibrated. [Work supported by ONR.]
Masking level differences for tones and speech in elderly listeners with relatively normal audiograms
Authors: Poth E. A. , Grose J. H.
Published: October 2005

Masking level differences (MLDs) were measured for both tones and speech in a group of elderly listeners with normal, or near-normal, audiometric sensitivity. The tonal MLD was obtained for the detection of a 500-Hz tone masked by a 100-Hz wide band of noise centered at 500 Hz. The speech MLD was obtained for the recognition of spondaic words masked by speech-shaped noise. For both types of stimuli, the MLDs measured in the elderly listeners were significantly smaller than those measured in a control group of normal-hearing young listeners. This reduction was primarily due to an elevation of the NoSπ thresholds in the elderly group. The results support the hypothesis that a reduced binaural advantage may contribute to the difficulty of understanding speech in noise reported by the elderly listeners. Furthermore, the use of listeners with normal, or near-normal, audiometric sensitivity suggests that factors other than peripheral sensitivity loss may play a role in speech understanding in noisy listening conditions. [Research supported by NIDCD and the Andrus Foundation.]
Minimum audible angles for synthesized localization cues presented over headphones
Authors: McKinley Richard L. , Ericson Mark , Perrot David , Gilkey Robert , Brungart Douglas , Wightman Frederic
Published: October 2005

Several methods can be used to synthetically generate auditory localization cues over headphones. Very little traditional auditory performance data have been presented for these types of synthesizers. The data were collected using stimuli similar to those used by Mills [J. Acoust. Soc. Am. 30, 237–246 (1958)]: 500-Hz tone, 1 s on, 1 s off, 1 s on, 70-ms ramps for on period, and 500 ms off after response before the next stimulus was presented. The paradigm used was the two-source two-interval experiment described by Hartmann and Rakerd [J. Acoust. Soc. Am. 85, 2031–2041 (1985)]. The minimum audible angle (MAA) was measured at seven locations in the horizontal plane for synthetic stimuli presented over headphones. MAA data will be presented for 10 normal hearing subjects for each of the seven locations. The MAA data using headphones will be compared with free-field MAA data from the literature and with mean localization error data using headphones.
On the measurement of source separation
Authors: Wakefield Gregory H. , Runkle Paul R.
Published: October 2005

It has been conjectured that certain acoustic cues present in a complex waveform are used by the auditory system to decompose that waveform into a set of auditory sources. The disparity between the perceived source(s) and the physical sources in such phenomena as stereophony suggests that there is not necessarily a one-to-one correspondence between the acoustic composition of signals and the perceptual decomposition of the combined signal into auditory sources. In an earlier paper [Wakefield and Runkle, Issues in Advanced Hearing Aid Research Conference (May 1992)], a method was proposed for measuring the strength of such cues adaptively, however, the hypothesis that the measuring technique itself was responsible for the results could not be rejected. In the present paper, an alternative measuring tool is introduced that is capable of independently suppressing and enhancing different spectral regions, unlike the original tool. Results are presented concerning the salience of co-modulation, harmonicity, onset and offset cues, and amplitude spectrum with respect to auditory sources using the new tool. A recognition paradigm is integrated into the proposed method to help validate the results. [Work supported by grants from the NIH NIDCD and from Ford Motor Company.]
Discrimination of short speech-like formant transitions
Authors: van Wieringen Astrid , Pols Louis C. W.
Published: October 2005

In a series of experiments frequency and duration discrimination thresholds of short, linear rising or falling, speech-like transitions were determined by means of same/different paired comparison tasks. Difference limens of single formant transitions varying in frequency extent at a constant duration (experiment 1), decreased with increase of transition duration. They were, on average, 70, 63, and 57 Hz for 20, 30, and 50 ms, respectively. However, when transition duration varied at a constant frequency extent (experiment 2), difference limens were, on average, 2.7, 4.5, and 4.9 ms for standard transitions of 20, 30, and 50 ms, respectively. In both experiments, thresholds between rising and falling transitions, determined in two frequency regions, and between transitions with either higher or lower rates of frequency change than the standard transition, were comparable. The extent to which the first formant transition and the steady-state interfere with discrimination of the second formant transition is studied further with single and combined formants, bounded by plateaus (experiment 3). The data suggest that, although transition rate is varied, different psychoacoustical cues are extracted by the auditory mechanism.
Contribution of bottom-refracted sound to oceanic sound propagation
Authors: Arvelo J. I. , Yuan J. R. , Bao X. L. , Überall H.
Published: October 2005

In the deep ocean, sound from an underwater source is channeled in the SOFAR channel to form a long series of convergence zones. These may be influenced by bottom reflections when the propagation occurs down a sloping ocean floor. Experiments [W. M. Carey, J. Acoust. Soc. Am. 79, 49 (1986)] show important residual intensities (∼10 dB excess) between convergence zones whose origin could not be conclusively explained by downslope conversion, but could have been due to ‘‘refraction’’ (bottom penetration). Earlier pulse return experiments by Christensen etal. [J. Acoust. Soc. Am. 57, 421 (1975)] conclusively established the presence of bottom penetration effects in the presence of upward-refracting sound-speed gradients in ocean-floor sediments from a flat, deep (4000-m) ocean floor. In the present model calculation, carried out for the Christiansen deep-water case by using normal-mode and fast-field models, the influence of a shear-supporting, upward-refracting ocean floor on oceanic sound propagation, including the long-range presence of inter-convergence zone residual sound fields caused by bottom penetration is demonstrated. [Work supported by the ONT.]
Piezoelectric electronically focused shock wave generator
Authors: Nachef Sylvain , Cathignol Dominique , Birer Alain
Published: October 2005

Recently, shock wave generators (electrohydraulic, electromagnetic, or piezoelectric) have become of common use for the treatment of renal calculi and gallstones. In all these generators, the focal zone is fixed. This is a major drawback since it is well known that the stones move according to the respiratory cycle. Consequently, the shock waves are not always well focused on the stone, which results in an increase of the duration of the treatment and the development of lesions in the neighboring tissues. To resolve this problem, a piezoelectric electronically focused shock wave generator has been designed. Measurements of the sound field produced in water by the first prototype of this novel generation of extracorporal lithotripters are presented, which clearly demonstrate the advantages of this type of focusing.
A systematic experimental investigation of a highly intense pressure field generated by a plane circular transducer
Authors: Nachef Sylvain , Cathignol Dominique , Tjo/tta Jacqueline Naze
Published: October 2005

This work is part of a study of highly intense sound beams with application to medical therapy in mind. A systematic experimental investigation of a sound beam propagated into water from a plane circular transducer was for the first time, it is believed, performed for a large range of cw excitation levels. The fundamental frequency was 1 MHz and the on-source pressure ranged from 0.8 to 24 bar (shock formation distance to Rayleigh distance ratio ranging from 1.8 to 0.06). The pressure amplitude distributions of the five first harmonic components, along and across the acoustic axis, are presented and discussed. New nonlinear effects are uncovered: a nonlinear self-defocusing of the beam and an alteration of the near-field structure of the harmonic components.
Theoretical model for the unimorph flexural disk transducer
Authors: Warren Daniel M. , Lafleur L. Dwynn , Shields F. Douglas
Published: October 2005

The unimorph is a very popular piezoelectric transducer used in consumer products ranging from musical greeting cards to smoke alarms. Recently unimorphs have been used to construct low-frequency hydrophone projectors [D. M. Warren etal., J. Acoust. Soc. Am. 91, 2325 (A) (1992)]. Despite their popularity, no mathematical analysis adequately addresses this unique transducer. The unimorph is a bilaminate disk−one layer piezoelectric, the other metal. The metal layer has a larger radius than the piezoelectric and the thicknesses of the layers are not necessarily equal. Theoretical treatments of other flexural disk transducers, like the bimorph disk, assume layers of the same material [E. G. Thurston, J. Acoust. Soc. Am. 24, 656 (1952)], elasticity controlled by a single layer [T. D. Sullivan and J. M. Powers, J. Acoust. Soc. Am. 63, 1396 (1978)], or effective elastic constants to be measured experimentally [S. Hanish, NRL Rep. 5259 (1959)]. Furthermore, all assume equal radii. The current theory offers a more suitable treatment of a simply supported unimorph operating against a vacuum. Calculations of the surface velocity profile are compared to laser Doppler measurements. [Work supported by ONR.]
A low-frequency one-sided flextensional transducer
Authors: Boucher Didier
Published: October 2005

In this paper, a one-sided flextensional projector, which has been designed and constructed, is presented. Roughly, it looks like a class IV flextensional transducer but with only a partial aluminum shell defining the radiating part. Inside the shell, longitudinal piezoelectric stacks are tightly inserted, with regular spacing, parallel to the shell pseudo-major axis. Steel inserts are fixed at both ends of these stacks and conventional tie rods are used for prestressing. A steel housing situated behind the shell as well as top and bottom caps ensure watertightness. Under an electrical drive, the stacks undergo a longitudinal vibration that is transmitted to the shell and converted into flexural motion with a larger mechanical displacement. Nevertheless, despite the similarities, the operating mode of this projector is very different from the conventional flextensional operating principle. Such an original behavior has been obtained by a careful design of the transducer. A trial-and-error procedure has been carried out with a numerical analysis tool to optimize the main electromechanical parts. Fairly accurate comparisons with experimental results have been obtained for the transmitting voltage response as well as for directivity patterns. It is confirmed that this one-sided flextensional transducer is directive, leading to a front-to-back ratio equal to about 10 dB in the frequency range of interest. Close-packed arrays can be easily realized with the one-sided flextensional transducer type. Some new array designs are discussed and illustrated with theoretical results.
Image derived second-order differential microphones
Authors: West J. E. , Elko G. W. , Kubil R. A. , McAteer J. P.
Published: October 2005

Second-order differential (SOD) toroidal and uniaxial microphones derived using a first-order differential (FOD) sensor and a reflecting plane are described. For a uniaxial implementation a dipole FOD sensor is positioned with its axis perpendicular to and suspended a few centimeters from a large acoustically reflecting surface. The resulting sensor image is phase reversed resulting in a transducer that is a linear quadrupole. The linear quadrupole can be described by two dimensions, the distance corresponding to the FOD sensor dipole distance and the distance from the reflecting plane. If the reflecting surface is large enough, or if the wall of an enclosure is used, the resulting microphone becomes a SOD axial microphone. The close match between the sensor and its image from a good acoustic reflector results in a uniaxial SOD microphone with a 3-dB beamwidth of 66°. The sensor will operate as a differential microphone at frequencies below 3 kHz for a 2.5-cm spacing between the sensor and reflecting surface. A wall-mounted toroid can be formed by using two FOD sensors at right angles to each other and with the axis of each sensor at 45° to the reflecting surface. Also, the spacing between sensors is twice the height of the sensors from the reflecting plane. Measurements show that these transducers can be realized with existing commercially available electret condenser dipole sensors.
Intensity-modulated fiber-optic microphone
Authors: Stec James P. , Buchholz Jeffrey C. , Gunseor Larry A. , McKinley Richard L. , McCavitt Angela R.
Published: October 2005

A fiber-optic microphone has been developed that can detect low acoustic sound pressure levels. The microphone is an extrinsic intensity-modulated fiber-optic level sensor. The optical mechanisms involved and the effect on performance of fiber placement with respect to the optical element will be discussed. Plots of frequency response, sensitivity, and a tape recording made using the microphone will be presented.
Ultrasonic flux imaging in anisotropic solids
Authors: Weaver Richard L. , Hauser Matt R. , Wolfe James P.
Published: October 2005

A new method is discussed for characterizing acoustic flux propagation in anisotropic media. The technique utilizes a pair of water-immersion focused acoustic transducers as a point source and point detector. Raster scanning of either the source or detector over a slab-like specimen of an anisotropic solid produces a transmission pattern that exhibits the anisotropies in acoustic flux previously known as ‘‘phonon focusing.’’ Unlike phonon focusing images, however, the pattern is modulated by ‘‘internal diffraction’’ fringes arising from interference between sheets on the acoustic wave surface. In addition to the diffraction effects, the images reveal interesting critical-cone structures associated with the water/solid interface. These images may be understood theoretically by taking into account the full anisotropy of the medium, the boundary conditions between the solid and the water, and the pressure fields produced by the immersion transducers. The theoretical predictions agree well with the experimental observations of UFI in silicon and a number of other materials, which include single-crystal metals, insulators, and semiconductors. As a new method, UFI holds promise for examining anisotropies in the vibrational properties, and, possibly, electron–phonon coupling in metals and superconductors. The principles and techniques may also have application in the nondestructive characterization of textured polycrystalline and composite materials. [Work supported by MRL Grant NSF DMR-89-20538 and by NSF MSS-91-14360.]
Wave propagation in stochastic fractals
Authors: Herrmann F. J.
Published: October 2005

Wave propagation in random media has become a subject of increasing interest for a wide range of different research areas. The reason for this is that most insonified media clearly reveal a highly irregular behavior that can be quantified. A stochastic fractal yields a random process that displays a behavior similar to observations from, e.g., well-log and seafloor topology measurements. Considerations of wave propagation in random media indicate that the leading behavior of the coherent part of the wave field (the signature) is predominantly determined by the spatial autocovariance function of the medium. Dispersion is always present and the question is how to account for this in a global way, i.e., without local information. For the 1-D situation it can be shown that the signature gradually converges to a limiting solution that is determined by the stochasticexpectation of the power spectrum of the medium contrasts. The required globaleffective medium representation can be found after combination of the wave propagation operator with the stochastic fractals. In this way information on the complexity of the medium can be transferred to the description of wave propagation and vica versa. During the presentation the theory will be illustrated by examples.
Auditory spectral resolution and the localization of clicks in the sagittal plane
Authors: Hartmann William Morris , Rakerd Brad
Published: October 2005

In a sagittal plane localization experiment, listeners (N=8) were required to localize a train of eight clicks that originated from a source that was either directly in front, overhead, or behind. Click trains were made from 25-μs pulses, separated by 110 ms, and were presented in an anechoic room. The principal experimental parameter was the peak level of the clicks: 68, 74, 80, 86, 92, or 98 dB SPL. All listeners except one showed a leveldisadvantage: The localization error rate increased with increasing level, on the average by a factor of 10 over the range of levels. It was conjectured that the level disadvantage arises from a failure of the auditory system to resolve details of the spectral shaping caused by pinna, head, and upper torso in the case of a high-level pulse. Resolving these details is necessary for localization in the sagittal plane. This conjecture was tested in headphone experiments on filtered click discrimination. Many instances of level disadvantage were found, but none so strong or consistent as the original localization effect. [Work supported by the NIDCD, DC00181.]
Experiments involving auditory localization over headphones using synthesized cues
Authors: Ericson Mark A. , McKinley Richard L.
Published: October 2005

An auditory localization cue synthesizer has been developed that can electronically encode directional information on various auditory signals and present the sounds over headphones. Performance of the synthesizer has been evaluated in several laboratory studies to validate its reproduction of free-field cues and its potential for various applications. Data were collected for localization in noise, binaural intelligibility level difference, and target acquisition experiments. Subjects were able to localize sounds in spectrally similar noise at low (−10 to −20 dB) signal-to-noise ratios. A 3- to 6-dB release from masking was observed in various single talker and competing message experiments. Directional audio information facilitated visual target acquisition under high visual workload conditions. A comparison between these data and free-field localization data indicates that the synthesizer is capable of reproducing the free-field cues necessary to localize sounds over headphones. The technology for generating localization cues over headphones has shown beneficial effects in these applications without additional training by the listeners.
Absorption of ultrasonic waves in air at high frequencies (10–20 MHz)
Authors: Bond Leonard J. , Chiang Chih-Hung , Fortunko Christopher M.
Published: October 2005

A high power and sensitive gated radio-frequency (rf) measurement system has been used to determine the absorption of compressional waves in air, in the frequency range from 10–20 MHz. The measured absorption, between 80 and 90 kPa and at room temperature (15 °C to 25 °C), has been found to be in good agreement with that predicted, by extrapolation, from low-frequency (below 1 MHz) data for the combination of the classical and rotational loss effects. The measured data fit a classical-plus-rotational absorption loss coefficient (αcr) for a 20 °C value of 1.83×10−11 Np/m. Above 500 kHz at normal atmospheric pressures, this coefficient becomes dominant, and the effects of variation in humidity are insignificant. The bounds for the parameter domain for this relationship to be valid are now pressures between 80 and 90 kPa, temperatures between 15 °C and 25 °C, and frequency/pressure combinations up to 200 Hz Pa−1. The velocity of ultrasound in air in the frequency range from 10–18 MHz has also been measured and is in good agreement with that predicted from theory. For example, at 83.3 kPa (625.5 mm Hg) and 24.4 °C, the measured velocity is 347.6±1 m/s at 10 MHz and that calculated, including the effect of humidity, is 346.4 m/s. Normalized velocity and attenuation data plotted against Knudsen numbers and a rarefaction parameter are in good agreement with those obtained at reduced pressure and lower frequencies.
A new method for a realistic treatment of the sea bottom in the parabolic approximation
Authors: Papadakis John S. , Taroudakis Michael I. , Papadakis Panagiotis J. , Mayfield Betty
Published: October 2005

A new method for realistic treatment of the bottom in the parabolic approximation in underwater acoustics is presented. The method utilizes a finite difference scheme for the numerical implementation of the parabolic equation and the boundary condition is introduced to the problem in the form of an impedance condition. The impedance condition for the fluid half-space bottom can be implemented analytically, while total numerical implementation is necessary for a general type bottom. A characteristic type of bottoms that can be handled by this method is the homogeneous elastic half-space. The reliability of the method is confirmed by examples where the results obtained by the method are compared with well-known results of reference problems.
Forward scattering from fetch-limited and swell-contaminated sea surfaces
Authors: Novarini Jorge C. , Keiffer Richard S. , Caruthers Jerald W.
Published: October 2005

By using a Helmholtz–Kirchhoff (HK) approach described in a previous paper [J. Acoust. Soc. Am. 91, 831–822 (1992)], the forward scattering from nonfully developed sea surfaces is examined and the full three-dimensional scattering problem is addressed. Two types of departures from the limiting case of the fully developed sea are considered: fetch-limited seas and the more general case of seas that are time-evolving and swell-contaminated. Estimates of several statistical parameters of the forward scattered field are calculated for these surfaces as ensemble averages and are compared to those obtained for fully developed seas due to the same wind speed. Results are obtained for frequencies from 0.2 to 2 kHz, for moderate angles of incidence and moderate wind speeds. It is found that the fetch strongly affects the coherence and strength of the forward scattered field at and near the specular direction. In this frequency range, discrepancies in excess of 11 dB with respect to the fully developed case are predicted. For swell-contaminated surfaces, the scattering coefficient and the coherence are strongly influenced by the relative contributions of sea and swell to the total roughness and directional characteristics of the surface. Swell-contaminated sea surfaces having the same total roughness but different sea-swell compositions are shown to result in significantly different scattering patterns.