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Journal of the Acoustical Society of America

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Dec 1983

Volume 74, Issue 6, pp. 1673-1934

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Rapid solutions to the transient response of piezoelectric elements by z‐transform techniques

Richard E. Challis and John A. Harrison

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1673-1680 (1983); (8 pages)

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Calculation of the transient response of piezoelectric elements by analytical means is only possible for a small range of exciting functions for which simple Laplace transforms exist. Calculation tends to be tedious due to the large number of terms which must be evaluated. A method is presented by which the Laplace transformed three‐port model of a piezoelectric element is approximated by a discrete time system by application of the z‐transform. A recurrent time domain solution is developed and this is applied in the manner of a digital filter to a variety of exciting functions. The method has the advantage that the response to any real input can be evaluated and it is thus of considerable use in the testing of piezoelectric elements or the measurement of their physical properties in transient tests. Experimental results are presented which show that the technique is reliable and accurate.
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43.38.Ar Transducing principles, materials, and structures: general
43.38.Fx Piezoelectric and ferroelectric transducers
43.20.Px Transient radiation and scattering
43.20.Bi Mathematical theory of wave propagation

Effects of static and dynamic stress on the piezoelectric and dielectric properties of PVF2

Steven W. Meeks and Robert Y. Ting

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1681-1686 (1983); (6 pages) | Cited 1 time

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The effects of hydrostatic pressure and pressure cycling on the piezoelectric properties of polyvinylidene fluoride (PVF2) have been experimentally investigated by using an acoustic reciprocity technique. The hydrostatic piezoelectric constants and the relative dielectric constant were measured as a function of pressure and pressure cycling for both voided and nonvoided PVF2 samples. The dynamic response of these materials to high‐amplitude pressure pulses having a rise time of 1–3 ms was also determined. The results showed that the microvoid structures in PVF2 improve the material’s piezoelectric properties but at the same time increase its pressure dependence and introduce a hysteresis effect with changing hydrostatic pressure. Nonvoided PVF2 films were also shown to have a good dynamic response to pressure pulses and, therefore, are promising for applications such as underwater shock sensors.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
77.65.-j Piezoelectricity and electromechanical effects
77.22.Ch Permittivity (dielectric function)

Integration of spectral and temporal cues in discrimination of nonspeech sounds: A psychoacoustic analysis

Blas Espinoza‐Varas

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1687-1694 (1983); (8 pages)

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This study presents a psychoacoustic analysis of the integration of spectral and temporal cues in the discrimination of simple nonspeech sounds. The experimental task was a same–different discrimination between a standard and a comparison pair of tones. Each pair consists of two 80‐ms, 1500‐Hz tone bursts separated by a 60‐ms interval. The just‐discriminable (d′=2.0) increment in duration Δt, of one of the bursts was measured as a function of increments in the frequency Δf, of the other burst. A trade off between the values of Δt and Δf required to perform at d′=2.0 was observed, which suggests that listeners integrate the evidence from the two dimensions. Integration occurred with both sub‐ and supra‐threshold values of Δt or Δf, regardless of the order in which the cues were presented. The performance associated to the integration of cues was found to be determined by the discriminability of Δt plus that of Δf, and thus, it is within the psychophysical limits of auditory processing. To a first approximation the results agreed with the prediction of orthogonal vector summation of evidence stemming from signal detection theory. It is proposed that the ability to integrate spectral and temporal cues is in the repertoire of auditory processing capabilities. This integration does not appear to depend on perceiving sounds as members of phonetic classes.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency
43.66.Lj Perceptual effects of sound
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Additivity of forward masking

Donna L. Neff and Walt Jesteadt

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1695-1701 (1983); (7 pages) | Cited 4 times

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Masked thresholds for a 1000‐Hz sinusoidal signal were measured as a function of masker level in both forward and simultaneous masking for two types of maskers: a 1000‐Hz sinusoid and a narrowband noise, 60‐Hz wide, centered at 1000 Hz. In forward masking, the noise masker produced much steeper growth‐of‐masking functions than the sinusoid. Presenting a contralateral broadband noise ‘‘cue’’ with the forward masker dramatically reduced the slope of masking for the noise masker but did not influence results for the sinusoidal masker. The noise remained the more effective masker. The amount of masking produced by combinations of equally effective narrowband‐noise and sinusoidal maskers was compared to that produced by each masker individually with and without the contralateral cue. No additional masking beyond that predicted by energy summation was measured for forward masking. Additional masking beyond energy‐sum predictions was measured for analogous conditions in simultaneous masking. Comparisons of results obtained with and without the contralateral cue suggest that signal thresholds in the presence of narrowband‐noise forward maskers can reflect nonperipheral auditory processes.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Frequency discrimination and signal detection in band‐reject noise

David S. Emmerich, William S. Brown, Deborah A. Fantini, and Nicholas C. Navarro

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1702-1708 (1983); (7 pages) | Cited 1 time

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An experiment was conducted in order to compare the importance of information from frequency regions remote from the nominal signal frequencies for frequency discrimination and signal detection. In both tasks, signals were presented within the ‘‘notch’’ of band‐reject noise, and different notch widths were employed. The results indicate that information is integrated over a wider range in frequency discrimination than in signal detection. Further, experiments in which a noise floor was present as well as band‐reject noise, indicate that disrupting the information from regions remote from the nominal signal frequencies impairs frequency discrimination even in the absence of any significant impairment of signal detection performance.
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43.66.Fe Discrimination: intensity and frequency
43.66.Dc Masking
43.66.Lj Perceptual effects of sound

Discrimination of envelope frequency

Søren Buus

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1709-1715 (1983); (7 pages) | Cited 2 times

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Discrimination of envelope frequency was measured as the just noticeable increase in envelope frequency of monotic, 60‐dB two‐tone complexes at geometric center frequencies (CFs) of 500, 1000, 2000, and 4000 Hz. (The envelope frequency is equal to the frequency separation ΔF, between the two components.) At a given CF the jnds were approximately constant up to a critical envelope frequency between 10% and 20% of the CF, roughly equivalent to the critical band, beyond which they increased to a maximum at about 40% of the CF. Below the critical envelope frequency, the jnd increased with CF. Measurements at 40 dB SPL with and without masking of the aural distortion products showed that the influence of aural distortion is minimal. Additional measurements showed that at narrow frequency separations, discrimination was better for monotic two‐tone complexes than for pure tones, three‐tone complexes, and dichotic two‐tone complexes. The results indicate that envelope frequency may serve as a cue for discrimination up to a frequency between 30% and 40% of the CF, although its effectiveness at high enevelope frequencies is severely diminished by the auditory filter. A comparison with other data on envelope frequency discrimination indicates that the jnds’ dependence on the envelope frequency may depend on how the slope of the temporal envelope varies with envelope frequency.
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43.66.Fe Discrimination: intensity and frequency
43.66.Ba Models and theories of auditory processes

Simulation of auditory analysis of pitch: An elaboration on the DWS pitch meter

Michael T. M. Scheffers

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1716-1725 (1983); (10 pages) | Cited 6 times

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A model was developed for estimating the pitch of complex sounds that are partially masked by background sound. Our ultimate aim is to obtain a model that can separate two simultaneous sounds on the basis of the harmonic structure of at least one of the sounds. The MDWS model is an extension of the Duifhuis, Willems, and Sluyter pitch meter (DWS) [J. Acoust. Soc. Am. 71 1568–1580 (1982)] which is a practical implementation of Goldstein’s optimum processor theory of pitch perception [J. Acoust. Soc. Am. 54, 1496–1516 (1973)]. The main modifications incorporated in MDWS consist of a more faithful modeling of auditory frequency analysis and of an alteration to the criterion used to decide which fundamental best fits a set of resolved components. Effects of the latter modification were investigated in a comparison between model estimates of the pitch of inharmonic complex signals and results obtained for humans. Furthermore, the accuracy of model estimates of the pitch of periodic signals (among which were synthesized vowel sounds), partially masked by noise, was compared with the just noticeable difference of fundamental frequency of these sounds for human observers. The results of these two tests show that the model estimates come close to human perception.
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43.66.Hg Pitch
43.66.Ba Models and theories of auditory processes

The relationship between the cross‐correlation coefficient of two‐channel acoustic signals and sound image quality

Kohichi Kurozumi and Kengo Ohgushi

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1726-1733 (1983); (8 pages) | Cited 4 times

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In order to investigate sound image quality, white and bandlimited noises with various cross‐correlation coefficients are reproduced from two loudspeakers placed in anechoic or echoic chambers. Subjects are asked to make similarity judgments and some subjective evaluations of pairs of the noises. The experimental data are analyzed by Kruskal’s multidimensional scaling (MDS) program. The analysis of the experimental data shows the following: (1) sound image quality depends mostly on the width and the distance of the sound image, (2) the width of the sound image depends on the absolute value of the cross‐correlation coefficient, (3) the distance of the sound image depends on the cross‐correlation coefficient itself, (4) with respect to physical and psychological factors governing sound image quality, there is no fundamental difference between anechoic and echoic chambers.
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43.66.Pn Binaural hearing
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.60.-c Acoustic signal processing

A comparison between basilar membrane and inner hair cell receptor potential input–output functions in the guinea pig cochlea

R. Patuzzi and P. M. Sellick

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1734-1741 (1983); (8 pages) | Cited 9 times

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Intracellular recordings were made from inner hair cells and basilar membrane motion was measured at a similar place, but in different preparations, in the first turn of the guinea pig cochlea. Potential recordings were made using glass microelectrodes and mechanical measurements were made using the Mössbauer technique. Intensity functions of DC receptor potential and basilar membrane velocity in animals with good and poor thresholds are presented. In animals with good thresholds, stimuli at and above the characteristic frequency produce similarly compressive input–output functions for both inner hair cell receptor potentials and basilar membrane motion. However, for frequencies lower than the characteristic frequency, receptor potential input–output functions obtained from animals in good and poor condition show saturation at high stimulus intensities at which basilar membrane motion is linear. This discrepancy is believed to be due to a nonlinear inner hair cell transduction mechanism. We propose that nonlinearity observed in receptor potential input–output functions is a consequence of the simple cascading of a frequency‐dependent nonlinear mechanical input and a frequency‐independent nonlinear transduction process.
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43.64.Kc Cochlear mechanics
43.64.Ld Physiology of hair cells
43.64.Tk Physiology of sound generation and detection by animals

Effects of acoustic trauma on the cochlear potentials

Donald P. Gans

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1742-1746 (1983); (5 pages)

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The cochlear microphonic, summating potential, and action potential were recorded from all three turns of the gerbil cochlea prior to and following a 1‐h exposure to a high‐intensity pure tone. Results proved that the depression in the cochlear microphonic was greater when recorded from the upper two turns of the cochlea. The losses for the summating potential were not dependent on recording location. Although the cochlear microphonic and to some extent, the negative summating potential, reflected locally generated activity from the hair cells, the positive summating potential appeared to be dependent on distant electrical activity.
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43.64.Nf Cochlear electrophysiology
43.64.Tk Physiology of sound generation and detection by animals

Frequency information in the auditory brainstem response evoked by tonal transients

Thomas M. Helfer and George M. Gerken

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1747-1751 (1983); (5 pages)

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The auditory brainstem response (ABR) is a composite of potentials generated by neural activity stemming from several regions of the cochlea. A derivation technique is described for reducing the contributions to the ABR that arise from frequencies outside of the frequency band of interest. The technique treats averaged waveforms in an algebraic manner and uses a method of successive substitutions to obtain a derived waveform. The recorded and derived ABR waveforms were analyzed with respect to changes of latency and morphology. The behavior of the waveform components of the derived regional responses was in accord with the data of other studies in which narrow‐band responses were derived from waveforms produced by high‐pass masking of click stimuli. Frequency information was thus extracted from the ABR without the simultaneous presence of other stimuli as in masking‐based derivations. The method of successive substitutions used with brief transient stimuli of different frequencies appears to yield derived ABRs that reflect activity from different cochlear regions.
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43.64.Ri Evoked responses to sounds
43.66.Lj Perceptual effects of sound

A stochastic analysis for cross‐spectral density method of measuring acoustic intensity

Gopal P. Mathur

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1752-1756 (1983); (5 pages)

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A stochastic analysis for the cross‐spectral density method of measuring acoustic intensity is presented. The analysis is based on the theory of linear mean‐square estimation as applied to stochastic processes and its generality is preserved through the use of some concepts from the theory of multidimensional stochastic processes. A general theoretical expression, in terms of spatial‐correlation and cross‐spectral density functions between two closely spaced microphones, is obtained for estimating acoustic intensity. The stochastic analysis presented in this paper highlights the effects of incorporating finite difference approximations. It is also shown that how the present cross‐spectral density formula can be reduced to an exact expression for the specific case of plane‐wave sound field.
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43.60.Gk Space-time signal processing, other than matched field processing
43.58.Dj Sound velocity

The reduction of blast noise with aqueous foam

Richard Raspet and S. K. Griffiths

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1757-1763 (1983); (7 pages)

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Experiments were performed to investigate the potential of water‐based foams to reduce the farfield noise levels produced by demolitions activity. Measurements of the noise reductions in flat‐weighted sound exposure level (FSEL), C‐weighted sound exposure level (CSEL), and peak level were made for a variety of charge masses, foam depths, and foam densities (250:1 and 30:1 expansion ratio foams). Scaling laws were developed to relate the foam depth, foam density, and charge mass to noise reductions. These laws provide consistent results for reductions in the peak level, FSEL and CSEL up to a dimensionless foam depth of 2.5. A two part model for the mechanisms of sound level reductions by foam is suggested.
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43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.28.Mw Shock and blast waves, sonic boom

Noise monitoring in the vicinity of general aviation airports

Paul D. Schomer

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1764-1772 (1983); (9 pages)

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In order to examine issues related to noise monitoring in the vicinity of moderate‐sized airports, monitoring was performed for 5 months at three sites in the vicinity of the Decatur, Illinois Municipal Airport. The study issues included (1) comparison of predicted and measured day/night average sound levels (DNL), (2) comparison of individual aircraft levels with prediction, (3) temporal sampling requirements for monitoring, and (4) validation that the measured noise is aircraft noise and not other community noise. The measured DNL and the computer predictions compare quite favorably, and most individual aircraft levels compare favorably with data in the FAA computer models. In terms of temporal sampling requirements, it appears that one can use a strategy of choosing four random weeks throughout the year (one from each quarter) to achieve a +2 to −3‐dB tolerance. It was not possible to differentiate ‘‘airport’’ noise from other ‘‘community’’ noise. The results show that it may be better (and far less complex) to choose quiet sites where the airport noise predominates and measure only the total daily DNL values.
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43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.50.Ba Noisiness: rating methods and criteria

A survey of community attitudes towards noise near a general aviation airport

Paul D. Schomer

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1773-1781 (1983); (9 pages) | Cited 2 times

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This paper describes a community attitudinal noise survey performed in the vicinity of the Decatur, Illinois Airport. Two hundred thiry‐one respondents were drawn from four distinct noise zones in populated areas near the airport. The day/night average sound levels (DNL) ranged from 44–66 dB. The area is otherwise quiet, residential with large (l/2 acre) lots. The primary analysis arrayed the percent of respondents highly annoyed versus DNL. Good agreement was found between the results of this survey and the general relation developed by Schultz from surveys worldwide, primarily in the vicinity of large commercial airports and highways. In addition, reasonable comparisons were found between respondent estimates of the number of aircraft operations and actual traffic counts. It was also found that respondents who were highly annoyed by aircraft noise were three to four times as likely to be highly annoyed by some other noise than were other respondents.
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43.50.Qp Effects of noise on man and society
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.50.Sr Community noise, noise zoning, by-laws, and legislation

Experimental investigation on the effect of some temporal factors of nonsteady noise on annoyance

Kozo Hiramatsu, Koichi Takagi, and Takeo Yamamoto

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1782-1793 (1983); (12 pages) | Cited 1 time

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The effects of some temporal factors of nonsteady noise on annoyance was investigated by means of six experiments. The factors are rising speed, fluctuation speed, fluctuation frequency, and fluctuation deviation. The results show that the ratio of annoyance and the rising speed are in linear relation in log–log coordinates and the annoyance increase with the increase of rising speed from 25 to 1000 dB/s corresponds to the increase of sound pressure level of 2.6 dB. The fluctuation speed, the fluctuation frequency, and the fluctuation deviation have little effect on annoyance provided the equivalent sound level (Leq) is constant. The validity of some rating scales of fluctuating noise is discussed on the basis of the present experimental results.
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43.50.Qp Effects of noise on man and society
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Use of ‘‘corner microphones’’ for sound power measurements in a reverberation chamber

Thomas W. Bartel, Simone L. Yaniv, and Daniel R. Flynn

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1794-1800 (1983); (7 pages)

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A comparison was made between acoustic measurements conducted with microphones mounted in the trihedral corners of the 425‐m3 NBS reverberation chamber and similar measurements using microphones located in the room interior, away from the room boundaries. Measurements of broadband and discrete‐frequency sound pressure and of reverberation time were included. It was found that for frequency bands below the 200‐Hz 1/3‐octave band, the difference in sound pressure level between the corner and interior locations was, in general, more than 9 dB. In addition, the variations in the broadband steady‐state sound pressure level and in the reverberation time were much less among the corners than among the interior locations for frequencies below 100 Hz. It is concluded that for the lower frequency bands, use of the corner locations may reduce systematic errors associated with the interference patterns and provide greater measurement precision because of the lower spatial variance.
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43.50.Yw Instrumentation and techniques for noise measurement and analysis
43.50.Cb Noise spectra, determination of sound power
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response

New ultrasonic resonator method using optical diffraction for liquids

P.‐K. Choi, Y. Naito, and K. Takagi

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1801-1804 (1983); (4 pages)

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A new resonator method has been developed for measuring ultrasonic absorption in liquids in the frequency range 0.3–10 MHz. This method utilizes Raman–Nath light diffraction to detect a resonance spectrum of standing waves in a cylindrical cavity. Comparison with the spectrum obtained by conventional resonator method demonstrates that distortion of plane‐wave peaks by higher modes can be avoided with the present method. The use of a concave reflector is found to reduce a cavity loss considerably, enabling us to measure absorption down to a few hundred kHz. Results for water obtained using three types of reflectors with curvature radius 100–400 mm are shown.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Dispersion of extensional waves in fluid‐saturated porous cylinders at ultrasonic frequencies

James G. Berryman

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1805-1812 (1983); (8 pages) | Cited 7 times

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Ultrasonic dispersion of extensional waves in fluid‐saturated porous cylinders is studied by analyzing generalized Pochhammer equations derived using Biot’s theory. Cases with open‐pore surface and closed‐pore surface boundary conditions are considered. For both cases, the dispersion of the fast extensional wave does not differ much qualitatively from the dispersion expected for extensional waves in isotropic elastic cylinders. A slow extensional wave propagates in the case with a closed‐pore surface but not in the case with an open‐pore surface. The propagating slow wave has very weak dispersion and its speed is always lower than, but close to, the bulk slow wave speed.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
62.30.+d Mechanical and elastic waves; vibrations
43.20.Bi Mathematical theory of wave propagation

A comparison of two techniques for measured iodine release as an indicator of acoustic cavitation

Victor Ciaravino and Morton W. Miller

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1813-1816 (1983); (4 pages)

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A spectrophotometric and a radioactive‐label technique were used to assess for acoustically induced iodine release from sodium iodide. For both techniques there was a dose‐dependent relationship between the percentage of iodine released and the ultrasound intensity (1 MHz, ISP to 30 W/cm2, continuous wave for 1 min). Iodine release decreased with increased atmospheric pressure or increased concentrations of the radical scavenger cysteamine, thus confirming that the release was related to cavitational processes.
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43.35.Ei Acoustic cavitation in liquids

Pulsed spectrophone measurements of vibrational energy transfer in CO2

Henry E. Bass and Hai‐Xing Yan

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1817-1825 (1983); (9 pages)

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A pulsed spectrophone has been developed to study vibrational energy transfer processes in gases. CO2 was chosen as the test gas to allow comparisons with other methods. The spectrophone proves to be a powerful tool to measure relaxation rates and study relaxation pathways when coupled with other measurement techniques. All the micro‐ and macroscopic processes which affect the spectrophone response must be considered simultaneously in order to interpret the measured temporal evolution of pressure following excitation. Formulas which include a generalized treatment of multilevel systems and important macroscopic processes are presented. The experimental data are represented in terms of characteristic times of the pressure waveform and amplitudes of pressure changes. At intermediate (20 Torr and above) pressures, collisional energy transfer rates and mechanisms have the greatest influence on computed waveforms. Spontaneous emission has an obvious effect on the zero pressure intercept of the characteristic times. Acoustic propagation and thermal conduction determine the rate at which the gas, once perturbed, returns to equilibrium; at intermediate and higher pressures, acoustic propagation is found to be most important. The assumed rates of energy transfer and the relaxation mechanisms are varied to give computed pressure waveforms which agree with the measured spectrophone response (characteristic times and amplitudes), and which are simultaneously consistent with measurements using other techniques. This process indicates that the path of energy transferred from CO2 (001) to CO2 (040) is consistent with all experimental observations.
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43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids
51.40.+p Acoustical properties
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Ocean flow measurements using acoustic scintillation

Steven F. Clifford and David M. Farmer

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1826-1832 (1983); (7 pages) | Cited 1 time

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A wave propagating in a medium having random fluctuations in refractive index will suffer phase and amplitude perturbations. In the receiving plane, a random interference pattern will appear and this so‐called scintillation pattern will vary in time for two reasons: (1) the decay of the refractive‐index fluctuations producing the amplitude perturbation (eddy decay) and (2) advection of the eddies by the flow. In the case where eddy lifetimes are long compared with the scintillation period, we can derive estimates of flow from a statistical analysis of the scintillation pattern. In this paper, we discuss the propagation theory and report measurements of oceanic flows by analysis of the acoustic scintillation pattern produced by the density fluctuations in the ocean. By mounting a 214‐kHz source and two receivers on opposite sides of a barge such that the axis of propagation is perpendicular to the direction of travel, we induce a known flow rate equal to the barge velocity. We compute the slope of the time‐lagged covariance function of the logarithm of the amplitude at the two detectors. The slope is proportional to the path‐averaged flow transverse to the propagation path. Simultaneous measurements with a current meter provide sea truth. We have shown that such a technique will measure flow velocity with reasonable accuracy. An interesting result of the measurements is the demonstration that sound speed fluctuations in the spatial window 15–30 cm satisfy the Kolmogorov spectral slope for an inertial subrange, at the shallow depth (2.1 m) of the observation.
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43.30.Bp Normal mode propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.60.Cg Statistical properties of signals and noise
92.10.Vz Underwater sound

Normal mode filtering in shallow water

En‐Cen Lo, Ji‐Xun Zhou, and Er‐Chang Shang

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1833-1836 (1983); (4 pages) | Cited 4 times

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In the shallow water of the Yellow Sea, filtering of mode 1 and mode 2, by employing a vertical array of nine hydrophones, has been realized in the frequency range of 250–800 Hz with a near isovelocity condition. Eigenfunctions of the mode were calculated by two parameters (P, Q) to describe the characteristics of bottom reflection approximately at small grazing angles. The advantage of treating the bottom in terms of P and Q rather than using the familiar sound speed, density, and attenuation coefficient is that the bottom reflection loss due to the effect of bottom roughness can be incorporated. Results of mode filtering were quite favorable. Group delay measurement of mode 1 and mode 2 agrees well with theoretical values calculated by a fitting value of the bottom reflection phase shift parameter P. The parameter Q of the bottom reflection loss can be extracted from the amplitude ratio of mode 1 and mode 2. The extracted values of Q were near those of Q obtained by other approaches.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Augmented adiabatic mode theory for upslope propagation from a point source in variable‐depth shallow water overlying a fluid bottom

Allan D. Pierce

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1837-1847 (1983); (11 pages) | Cited 2 times

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A uniform asymptotic solution is presented for sound propagation from a constant frequency point source in shallow water whose depth H(r) decreases monotonically with cylindrical distance r. The water has constant sound speed c1 and density ρ1; the bottom fluid extends indefinitely in depth and has sound speed c2 and density ρ2, where c2>c1. The interface depth has constant value H0 up to range r0 and thereafter decreases linearly to zero. The solution appears as a sum of modal terms, each such mode eventually encountering a critical depth Hc(n) (at which modal phase velocity equals c2) at a critical range rc(n). A previously derived local solution for a modal term near its critical range is modified such that it automatically reduces to the adiabatic mode solution at nearer ranges and such that it is valid at arbitrary distances beyond the critical range. Bulk attenuation is incorporated into the model using an appropriate modal average over depth. Numerical results are compared with four parabolic equation computations supplied by Jensen. In these four cases only single mode propagation is considered and r0 is 0. The two theories agree well, with discrepancies typically less than 1 dB. Additional comparisons with parabolic equation computations (simultaneous propagation of three and two modes) presented by Jensen and Kuperman [J. Acoust. Soc. Am. 67, 1564–1566 (1980)] show comparable agreement, but for the higher modes there are marked discrepancies in the directions at which sound is beamed into the bottom fluid from regions encompassing those mode’s critical ranges. This is attributed to the progressive deterioration of the present theory with increasing mode number.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation

A wide‐angle split‐step algorithm for the parabolic equation

D. J. Thomson and N. R. Chapman

J. Acoust. Soc. Am. Volume 74, Issue 6, pp. 1848-1854 (1983); (7 pages) | Cited 25 times

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In this paper we describe a new wide‐angle parabolic equation based on an operator‐splitting that permits the use of a marching‐type Fourier transform solution method. The equation was first presented by Feit and Fleck [Appl. Opt. 17, 3990–3998 (1978)] for studying propagation within optical fibers. Existing computer codes which numerically solve the standard parabolic equation of ocean acoustics by the split‐step algorithm of Tappert and Hardin are easily modified to accommodate the wide‐angle capability of the new equation. In addition, since the new wide‐angle equation is less sensitive to the value of the reference wavenumber, the effects of phase errors are greatly reduced. The results of a simple error analysis indicate that improved accuracy can be achieved by the new wide‐angle equation for propagation conditions typical of deep ocean environments. This is supported by our numerical experience, a summary of which is presented in the paper. For test cases, where the variation of the acoustic index of refraction was large, the new wide‐angle equation gave results superior to those of the standard parabolic equation. Moreover, even for conditions which support long range, low‐angle propagation in the deep ocean, the predictions based on the new equation are a significant improvement over those obtained with the standard equation.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
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