Index of content:
Volume 58, Issue 5, November 1975
58(1975); http://dx.doi.org/10.1121/1.380780View Description Hide Description
Use of the liquid surface as a detector of ultrasonic energy dates back to 1935. Its use as a detector in acoustical holography began early in 1964. The dynamic response of the liquid surface permits real‐time viewing of the image at frame rates of more than 100 per second. Color translation has been demonstrated but is not currently being used in practical systems. Images of soft tissue structures in the hand, arm, and in excised organs show much interesting and useful detail including tendons, muscles, tendon attachments to the skeletal structure, veins, and arteries.
Subject Classification: 10.60; 35.65.
58(1975); http://dx.doi.org/10.1121/1.380756View Description Hide Description
In this paper, we study the problem of obtaining the velocity of the wave propagation in an inhomogeneous medium from the reflection coefficient (given for all frequencies) for a one‐dimensional wave equation. Following the work of Kay and Moses, we reduce the problem to that of determining a ’’potential’’ for a Schrödinger‐type equation. However, in our work this ’’potential’’ depends quadratically on the wavenumber, and this dependence changes the structure of the spectral function and integral equations of the inverse problem. In the first part of the paper, we assume that the wave velocity c (x) has the same value at x=+∞ and at x=−∞. Then we relax this condition on c (x) and consider the cases where c (+∞) is different from c (−∞), but both quantities have well‐defined values. For certain types of velocities, we obtain the reflection coefficient analytically. We then use these reflection coefficients to get approximate solutions to the inverse problem. Finally, we present an example of a heterogeneous medium which is transparent for all frequencies of the incident wave.
Subject Classification: 20.30, 20.35, 20.15.
58(1975); http://dx.doi.org/10.1121/1.380781View Description Hide Description
A theoretical model that predicts difference frequency pressure within the interaction region of a parametric array is presented. Linear and nonlinear attenuation are neglected, and it is assumed that the primary signals are spherically spreading throughout the interaction region. It is shown that with these assumptions the three‐dimensional scattering integral can be reduced to a single integral if the primary pressure fields are axially symmetric. Analyses of the error introduced by assuming the primary fields are spherically spreading and by neglecting linear attenuation are presented. Theoretical results compare favorably to p’revious experimental results. The results indicate that diffraction effects are more important than attenuation when the observation point is within the interaction region and when primary signal level reduction is due more to spherical spreading than attenuation.
Subject Classification: 25.35; 20.30, 20.15.
58(1975); http://dx.doi.org/10.1121/1.380782View Description Hide Description
Acoustic volume reverberation was observed in the open ocean at a frequency of 330 kHz and a depth of approximately 20 m. The instantaneous scattering volumes were small, ranging in size from 0.2 to 0.9 m3. The reverberation was observed primarily as an incoherent return from multiple scatterers (probably greater than 10/m3) but there were also discrete echoes of duration equal to that of the transmitted tone burst, 1 msec. The backscattering strength of the water calculated from the incoherent reverberation was independent of the time of day and varied from about −86 dB relative to 1 m−1 down to −96 dB and is surmised to be due to phytoplankton. The discrete echoes were more numerous at night than during the day and were produced by scatterers most of whose target strengths were on the order of −94 to −86 dB, approximately what would be expected of the small zooplankters such as copepods which were present.
Subject Classification: 30.40, 30.30.
58(1975); http://dx.doi.org/10.1121/1.380783View Description Hide Description
A new technique, i.e., the variational method, is introduced to solve the problem of nonlinear oscillation of a spherical gas bubble in liquid. The method is simple in concept and straight‐forward in application. In a sinusoidal pressure field, it is shown that besides the fundamental response, harmonic oscillations of the bubble of order 2 and 3, and subharmonic responses of order 1/2 and 1/3 can also be generated. For illustration, the subharmonic response of order 1/2 is analyzed in detail. The amplitude and phase responses as well as the threshold pressures are explicitly exhibited for one branch of the solution. The existence of another complementary branch of solution is also indicated. Stability of the solution is finally discussed also from the variational approach.
Subject Classification: 30.60, 30.75.
58(1975); http://dx.doi.org/10.1121/1.380754View Description Hide Description
In a previous paper, the authors developed a formulation for mathematically modeling the scattering of plane acoustic waves by an elastic body, and results were presented for the scattering of normally incident plane waves from a disk. In this paper, results are presented for scattering of obliquely incident plane waves from the same disk. Total scattering cross sections are calculated as functions of frequency and incident angle. For an incident wave angle of 60°, the calculated displacement distributions on the disk are decomposed into the disk’s free vibrational eigenmodes at selected frequencies. The scattering patterns of total pressure and of scattered pressure and contour plots of the nearfield pressure distributions are also presented for frequencies of interest.
Subject Classification: 30.35, 30.40, 30.30.
58(1975); http://dx.doi.org/10.1121/1.380755View Description Hide Description
Various surface wave modes may exist on solid elastic cylinders imbedded in a fluid. They fall into two classes, having velocities close to either the wave speed in the fluid (Stoneley‐ and Franz‐type modes), or to the bulk wave speeds in the solid (Rayleigh‐ and Whispering Gallery‐type modes). Using analytic and numerical methods, we present here a discussion of the modes of the first class, as well as of the Rayleigh mode. In the limit of infinite cylinder radius, the wavenumbers of the Rayleigh and Stoneley modes tend towards those of the Rayleigh and Stoneley waves on a flat elastic half‐space, while the Franz‐mode wavenumbers tend towards the wavenumber of sound in the ambient fluid. The sheet structure of the elasticsurface waves is discussed in an appendix.
Subject Classification: 35.54; 40.26;30.50;20.35.
58(1975); http://dx.doi.org/10.1121/1.380758View Description Hide Description
The problem of the generation of sound from an intensity‐modulated laser is generalized to include the effect of spherical spreading of the propagating laser beam. It is shown that divergence of the laser beam reduces the sound generated perpendicular to the axis of the laser beam and increases the beam width of the sound wave.
Subject Classification: 35.65.
58(1975); http://dx.doi.org/10.1121/1.380759View Description Hide Description
Fundamental construction and some experimental results of incoherent ultrasonic imaging systems are presented. A means for the generation of incoherent ultrasonic fields, a proper scanning method of receivers for the detection of coherence functions, and methods of signal processing for the reconstruction of images from the detected coherence functions are proposed and their properties are discussed theoretically. A concrete system based on these discussions is constructed. The experimental results show the usefulness of the proposed system, though the experiments are carried out only for one‐dimensional objects. Moreover, as an example for showing the special feature of the system, it is applied to imaging in a turbulent medium. The effectiveness of the method is illustrated by comparing the result with that of a holographicimaging system.
Subject Classification: 35.65; 60.30.
58(1975); http://dx.doi.org/10.1121/1.380760View Description Hide Description
In this paper the unidirectional wave propagation in a rod made of viscoelastic material of the Maxwell type is considered. The rod is subjected to nonuniform temperature gradients and its mechanical properties are assumed to be temperature‐dependent. A perturbation technique incorporated with the usual Laplace transform method is employed to obtain the analytical solution in series form. The strong temperature‐history effect on the attenuation of the wavefront is demonstrated in simple examples for the case where a stress discontinuity due to constant velocity impact propagates along the rod.
Subject Classification: 40.22; 35.50.
58(1975); http://dx.doi.org/10.1121/1.380761View Description Hide Description
When a towed array of hydrophones is significantly nonlinear due to bending, ordinary linear array beamforming gives a biased estimate of the true source bearing. By processing the array as a sequence of smaller aperture subarrays and then computing the mean of the subarray bearings, the variation due to bending is reduced and a reasonably precise estimate is obtained if the average bending angle with respect to the nominal axis is small. The median and mean subarray bearings are analyzed for a theoreticalstatistical model and are tested using artificial data for various sinusoidal array geometries.
Subject Classification: 60.20; 30.82.
58(1975); http://dx.doi.org/10.1121/1.380762View Description Hide Description
In response to a tone burst, a pattern of activity is set up in the set of auditory nerve fibers. A simplified model is described in this paper that can represent this pattern both with respect to the number of nerve fibers involved and the detailed time course of the firings. The parameters of the model concerning frequency selectivity and latency are adapted from measurements with the so‐called reverse correlation technique. Further properties incorporated in the model are saturation for excitation over 40 dB above threshold and high sensitivity. When specific assumptions are made regarding the contribution of the firing of each nerve fiber to the whole‐nerve potential, the waveform of the action potential (AP) can be synthesized from the model. The theory gives a quantitative account of the dependence of the AP latency upon stimulus intensity. Two main contributing factors are frequency selectivity and latency distribution of nerve fibers. Experimental AP amplitudes show a more complex course as a function of stimulus intensity than the theory predicts. Several possible improvements of the method are discussed. Since AP recordings are often used for diagnostic purposes, a separate section of the paper is dedicated to the connection between the properties of auditory nerve fibers and of the whole‐nerve AP in abnormal ears.
Subject Classification: 65.42, 65.35.
58(1975); http://dx.doi.org/10.1121/1.380763View Description Hide Description
A detailed study was made of the amplitude and phase characteristics of auditory distortion product 2f 1−f 2 in the neighborhood of an amplitude minimum. For f 2=1.0, 1.2, and 1.4 kHz, f 1 was varied from 0.68⋅f 2 to 0.88⋅f 2, and the (equal) intensity of the two primary tones was varied from 50 to 70 dB SPL. For the one subject investigated, the ampltiude of the 2f 1−f 2 distortion product exhibited a single minimum in the portion of the f 1/f 2 versus intensity plane explored. The value of f 1/f 2 at the minimum was 0.8 and was roughly constant for various frequencies of f 2. The primary‐tone amplitude at the minimum decreased with increasing f 2 from 60 dB SPL at 1 kHz to less than 50 dB SPL at 1.4 kHz. The 2f 1−f 2 phase in the neighborhood of the null was complicated. It changed abruptly at the minimum, it changed more rapidly with f 1/f 2 at primary‐tone intensities below the null than above, and it changed slowly with primary‐tone intensity at f 1/f 2 ratios both below and above the null. Therefore, a complete circuit around the null in the f 1/f 2 versus intensity plane resulted in a change of 2f 1−f 2 phase of 360°.
Subject Classification: 65.56.
58(1975); http://dx.doi.org/10.1121/1.380764View Description Hide Description
Observers in a 2IFC detection task were instructed to listen for ’’primary’’ tones with one of two frequencies, in the presence of a broad‐band background noise. On a small proportion of trials, probe tones of other frequencies were presented instead, following the procedure of Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 (1968)]. The function relating percent correct to signal frequency may be interpreted as an average internal filter characteristic. All six observers responded correctly on 70%–90% of trials on which primary signals were presented; performance on probe trials was poorer, falling to chance for probe frequencies sufficiently above the higher primary, sufficiently below the lower primary, and for some probes between the two primaries. The widths of the listening bands around the primaries were found to be similar to the widths estimated from one‐primary control conditions. Examination of the sequential data suggests that, while the pattern of sensitivity changes from trial to trial, a model postulating a single filter shifting from one primary to the other is not adequate. Other models of uncertain‐frequency detection are discussed.
Subject Classification: 65.35, 65.75, 65.58.
58(1975); http://dx.doi.org/10.1121/1.380765View Description Hide Description
Backward recognition masking refers to the interference of a second sound on recognition of another sound presented earlier in time. Previous experiments have demonstrated backward recognition masking in an absolute judgment task. In those experiments, all of the experimental conditions were varied randomly within a test session. In the first experiment reported here, backward‐masking functions generated between blocks of trials were compared to those determined within an experimental session. The results showed backward masking using both experimental procedures. The next two experiments evaluate backward‐masking effects in a two‐interval forced‐choice task and a successive‐comparison task. Backward masking was observed in both experiments. The final experiment showed that selectively attending to the ear of the test tone presentation does not attenuate the backward‐masking effects of a second tone presented to the opposite ear.
Subject Classification: 65.22, 65.58, 65.75.
58(1975); http://dx.doi.org/10.1121/1.380766View Description Hide Description
Interaural attenuation was estimated for the guinea pig and the chinchilla by determining isopotential curves for the cochlear microphonic (CM) response produced by contralateral and by ipsilateral stimulation at frequencies from 300 Hz to 14.3 kHz. Intracochlear electrodes were used to record the CM from the basal turn. For ipsilateral stimulation, bulla‐sealed to bulla‐open sound pressure ratios showed effects similar to those reported by other investigators: 10–12‐dB loss for chinchilla and 20–22‐dB loss for the guinea pig for the bulla‐sealed condition. The variability of the sound pressuremeasures, considered across animals, was larger in chinchillas than in guinea pigs, and the variance was greatest at frequencies near those at which the external auditory canals and bulla cavities show resonant peaks. There appears to be additional low‐frequency resonances associated with contralateral stimulation for the closed bulla in the chinchilla, largest at 1.1 kHz for frequencies sampled in this report. The interaural attenuation for the chinchilla is largest at low frequencies and is at a minimum of about 34 dB for the open bulla, near 3.0 kHz; in the guinea pig, the minimum interaural attenuation occurs for the closed bulla, about 44 dB at 300 Hz.
Subject Classification: 65.42, 65.40, 65.75.
58(1975); http://dx.doi.org/10.1121/1.380757View Description Hide Description
A continuous wave of ultrasound through the larynx is used to determine the fundamental frequency of the vocal folds during normal speech. The variation of the ultrasound intensity transmitted between two matched transducers through the vocal fold level is recorded. The apparatus used for these recordings is described. Different transducer positions are investigated and, further, the transducer geometry is discussed.
Subject Classification: 70.20; 80.45.
58(1975); http://dx.doi.org/10.1121/1.380767View Description Hide Description
The behavior of an acoustic impedance formed by a capillary of annular cross section was investigated. The configuration used in previous work consisted of a cylindrical rod spaced concentrically within a cylindrical tube. Experimentally, this configuration was found to have an impedance magnitude which remained reasonably constant with frequency up to values for which the length of the capillary was comparable to the wavelength. This was checked numerically; computer calculations based on the relevant equations showed that for certain ranges of lengths and annulus thicknesses, the impedance magnitudes are reasonably constant over a useful frequency range. Graphs of impedance magnitudes and phases are displayed for representative values in these ranges.
Subject Classification: 75.40; 85.20; 75.35.
Comparison of cube‐textured and conventional nickel magnetostrictive ring transducers during low‐power linear drive58(1975); http://dx.doi.org/10.1121/1.380768View Description Hide Description
The magnetic and magnetostrictive properties of a scroll‐wound ring transducer made from cube‐on‐face‐textured nickel were measured and compared to the corresponding properties of a conventional Nickel 200 ring transducer. Both transducers were separately excited in air at low‐power linear drive levels with varying levels of bias induction, and their electrical input impedances were measured. Some in‐water measurements were also made on the two rings at nearly optimum values of bias induction. Nickel 200 exhibits larger μ T 33 and d 33 values at all induction levels, while the textured nickel shows larger k 33 and g 33 values. The data obtained can be used to choose the type of ring and bias induction level of operation which will best satisfy a given requirement.
Subject Classification: 85.46.
58(1975); http://dx.doi.org/10.1121/1.380769View Description Hide Description
The effect of changes in source position on the attenuation by a lined duct segment has been analyzed. The results show that variations in source position produce significant changes in the attenuation. This is the direct consequence of modifications in the model content of the exciting pressure field.
Subject Classification: 20.45, 20.35.