Volume 65, Issue S1, June 1979
Index of content:
- PROGRAM OF THE 97TH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA 50TH ANNIVERSARY CELEBRATION
- Session B. Engineering Acoutics I: Transducers and Arrays
- Contributed Papers
65(1979); http://dx.doi.org/10.1121/1.2017192View Description Hide Description
Fiber optichydrophones offer potentially significant improvements in sensitivity, versatility, ruggedness, and reliability over conventional transducers. Calculations based on the assumption that a fiber optichydrophone is quantum noise limited show promise for an excellent signal to noise ratio. However, in practice other noisesources, arising from the inherent sensitivity of a fiber to vibration and nonacoustic pressures, may dominate and prevent a fiber optic sensorsystem from operating at its quantum limit. Estimates of vibration sensitivity for a raw fiber indicate an equivalent self‐noise about 100 dB above this limit at 1 g. Transduction of nonacoustic pressures within structures containing optical elements will take place. Because this will occur over an extended aperture, this contribution to self‐noise will be smaller than that of a point sensor.Noise mechanisms due to undesirable mechanical interactions between the fibers and the nonacoustic pressure fields (e.g., the generation of free waves within the fiber) may be important. Similarly, the acoustic sensitivity of a fiber optictransducer may depend on the details of its construction and incorporation into a structure. Certain well designed configurations are expected to yield enhanced signal sensitivity and signal to noise ratio.
65(1979); http://dx.doi.org/10.1121/1.2017193View Description Hide Description
Amplitude shading techniques are used in arrays to achieve reduced sidelobe levels with reasonably small major lobe width. Most papers on shading consider arrays without restriction of amplitude and location of the shading function to discrete choices. For some arrays such as resonant sonar arrays, it is desirable to achieve the amplitude shading by series‐parallel combinations of discrete elements of the array. Such an arrangement forces a relationship between the width and amplitude of discrete zones. This problem is illustrated in the design of a linear array of 24 elements for which the sidelobe level must be less than −20 dB. One discrete shading configuration had −21.9 dB sidelobe level. The best choice of series‐parallel combinations achieved a narrower beamwidth and a −25.7 dB sidelobe level. [Work supported by Naval Sea Systems Command.]
65(1979); http://dx.doi.org/10.1121/1.2017194View Description Hide Description
A low frequency transducer in the form of an “octagonal ring,” 10 in. in diameter and 6 in. high, driven by 16 rare earth Terfenol D (Tb0.3Dy0.7Fe2) rods, has been developed. In the design, eight curved magnesium pistons couple the small magnetostrictive rods to the water medium. The transducerresonates in a circumferential expansion mode at 750 Hz with a mechanical Q of 2.4 and an effective electromechanical coupling coefficient of 0,4. Measurements were made using both continuous and pulsed bias methods. Results are also presented for a smaller “square ring” rare earth transducer. [Work supported by NOSC.]
65(1979); http://dx.doi.org/10.1121/1.2017195View Description Hide Description
The barrel‐stave projector comprises several concave metal staves joining two cylindrical head pieces which are driven axially by a stack of piezoelectricceramic. This radiating system has been analyzed using an axially symmetric finite element model. The metal staves are modelled as an anisotropic material having normal axial and radial stiffness but low hoop stiffness. The performance of an experimental unit, 12 cm long and 7.6 cm in diameter, which resonates near 1500 Hz, is compared with predictions of the finite element model. Additional computer modelling has been carried out with an anisotropiccarbon fiber composite replacing the metal staves.
65(1979); http://dx.doi.org/10.1121/1.2017235View Description Hide Description
Each installation of an electroacoustic aid to ship navigation has a unique requirement of sound pressure levels over geographical areas. To meet these requirements horn arrays. special horns, and baffles are required. Design is greatly aided by being able to predict the performances of horn‐horn driver combinations. A design method and measurement technique are reported here that characterize a horn by its driving point impedance at the throat, its transfer function of SPL at one meter to‐throat pressure, and its directivity characteristics. The driver is characterized by its electroacoustic two‐port parameters. Examples will be given where the electrical potential and power requirements can be predicted from the far field acoustical requirements. [This work was sponsored by the OceanEngineering Division of the U.S. Coast Guard.]
65(1979); http://dx.doi.org/10.1121/1.2017236View Description Hide Description
Known analytical solutions of the sound fields around some elementary sources have been combined in numerical models for the purpose of calculating the directivity of three‐dimensional arrays of such elementary sources. The elementary sources considered are the monopole, the baffled piston, and the oscillating cap in a solid sphere. Results based on the analytical models have been compared with directivity measurements taken on a 12‐sided polyhedron with single and multiple loudspeakers mounted on its surface. Good correspondence was found between calculated and measured directivities for loudspeaker diameters less than the acoustic wave‐length. The oscillating cap in solid sphere proved to be the most useful elementary source model for calculating directivity over a wide frequency range. Implications to the design of isotropic arrays are discussed.
65(1979); http://dx.doi.org/10.1121/1.2017237View Description Hide Description
An inexpensive source of repetitive sound pulses was built using automotive ignition parts. Using the pulse source and an oscilloscope (having delayed sweep, storage capabilities and spectrum analyzer), it has been possible to perform experiments which are useful in demonstrating a variety of acoustical phenomena. Among the phenomena that can be shown are visualization of direct and reflected pulses, change in pressure amplitude with distance, location of echo sources, insertion loss of acoustical materials (including a piece of paper), frequency response and directivity of microphones, and estimation of temperature fluctuations over a 1.8 m path. Other uses of the pulse source might include in situmeasurements of reflectivity of surfaces, measurement of changes in reflectivity with angle, acoustical modeling, and measurement of transmission around barriers of different shapes.
- Session C. Physical Acoustics I: Bioacoustics
65(1979); http://dx.doi.org/10.1121/1.2017238View Description Hide Description
A Canada wide survey of the diagnostic,therapeutic, and surgical applications of ultrasound in medicine was conducted in the Fall of 1977. A total of 4154 questionnaires were sent to 1341 hospitals, 1887 chiropractors, 300 physiotherapists, and 726 sports medicine clinics. 62% of the questionnaires were returned, 40% of these completed. The comprehensive questionnaire provides information on the type of equipment used, the operator qualifications, the patient exposure, the number of patients treated, and adverse effects. Statistics of the results of the survey will be presented. The survey is believed to be the most detailed study undertaken to date of the use of ultrasound in medicine, and the results will be of interest to all ultrasound regulatory bodies and physicians working in the field.
An approach to modeling the relationship between ultrasonic propagation properties and constituent properties of mammalian tissues65(1979); http://dx.doi.org/10.1121/1.2017239View Description Hide Description
Literature values for ultrasonic attenuation,absorption, and velocity in several tissues, including brain, heart, kidney, liver, tendon, fat, and blood at frequencies of 1, 3 and 5 MHz, along with the percent constituency of each tissue (by weight) were used to develope an algorithm relating the acoustical propagation properties of a tissue to it's biological properties. Such an algorithm is hoped to provide the biological content of a tissue sample (e.g., % collagen content, % protein content, etc.…), given the ultrasonic propagation properties within that tissue. A first order model, assuming a linear relationship between constituency and acoustical properties, employs a least squares solution to a system of linear equations. This solution is a set of attenuation coefficients one, for each of the constituents considered. Results show that such a model works for only a limited number of highly structured tissues. A modified first order approach examines scattering (defined as attenuation minus absorption) as a function of collagen content alone. Here it is suggested that, as a function of frequency over the 0.5–7MHz range, the magnitude of scattering increases, but the dependency of scattering on collagen content is decreasing. [This work was supported in part by grants from NIH and FDA.]
65(1979); http://dx.doi.org/10.1121/1.2017287View Description Hide Description
The velocity of sound has been determined for excised human and canine arterial tissues using a time delay spectroscopy technique. Frequency was swept from 0 to 10 MHz with data being taken in the range from 2 to 10 MHz. The velocity was determined using a comparison of the time delay for the received signal between a water path and sample tissue of measured thickness. The velocity was measured as a function of temperature and tissuepathology. Normal tissue is nondispersive and the velocity of sound increases monotonically with increasing temperature from a mean value of 1587 m/s (standard deviation, S.D., 12 m/s) at 25°C to 1609 m/s (S.D., 8 m/s) at 37°C. For fatty lesions the velocity of sound is also nondispersive and for a given temperature increases with increasing attenuation associated with the fatty deposits. In calcified lesions larger than the ultrasound beam area the time delays can vary greatly with frequency and are indicative of multipath effects caused by structure of the precipitated calcium. [Support by the National Research Council and NIH contract N01‐HV‐729301.]
65(1979); http://dx.doi.org/10.1121/1.2017288View Description Hide Description
Ultrasonic characterization, using digital techniques, is being applied to clinical data gathered in examination of the eye and orbit. Digital rf echo signals are obtained from structures situated within a 7.5 × 20 mm region of the eye. A dedicated minicomputer system is employed to select specific portions of these records for analysis. Using a simple instruction set, a variety of analysis techniques can be chosen to characterize specific types of structures. For example, small ocular tumors are examined with spectrum analysis techniques to delineate surface features, internal scatteringcharacteristics, and shadowing of posterior scatterers such as orbital fat elements. The use of analysis procedures is guided by the display of reconstructed, gray‐scale B‐scans. Computational results are presented in a variety of display formats (including color‐coded and isometric modes) to facilitate recognition of fundamental tissue features. Data are catalogued for continuing evaluation of tissue characteristics that are useful for diagnostic purposes and for refinement of mathematical modeling based on histological preparations resulting from surgery. [Work supported by the NIH.]
65(1979); http://dx.doi.org/10.1121/1.2017289View Description Hide Description
Fresh mammalian tendon threads (diameter ≃110 μm) were examined using the scanning laser acoustic microscope (Sonomicroscope 100 R , Sonoscan, Inc., Bensonville, IL) at 100 MHz to make quantitative ultrasonic velocity and impedance measurements. Tendon is high in collagen (about 30% wet weight, 50%–90% dry weight), a structural protein which is believed to be important in the ultrasonic visualization of tissues.Ultrasonic velocitymeasurements are made by measuring a shift in the phase front of the sound as it propagates through the tissue as compared with the surrounding medium. Ultrasonic impedance measurements are made by comparing the acoustic contrast of the specimen with respect to that of the surrounding medium. The use of different media provides the opportunity to match velocity and impedance of the medium with that of the collagen threads thus yielding quantitative values of these ultrasonic characterization parameters. The use of different media also allows examination of the possibility that the medium itself is affecting the collagen thread. Two reference media at various concentrations were used, viz., aqueous solutions of sodium chloride or glycerine. Initial results using the different media indicate that the velocity of tendon is similar to that of pure glycerine (velocity ≃ 1926 m/s). This is almost 30% greater than the ultrasonic velocity of soft tissues. An impedance match has not been obtained using the reference media of the present study. This result suggests that the collagen thread may not be homogeneous with respect to its ultrasonic properties. This result when considered with the high velocity of the tendon, indicate that there is a marked difference in the ultrasonic characteristics of this tissue and other biological tissue. [This work was supported in part by grants from NIH and a Biomedical Research grant from University of Illinois, Urbana‐Champaign.]
Effect of phase cancellation artifact on frequency dependence of ultrasonic attenuation measurements65(1979); http://dx.doi.org/10.1121/1.2017290View Description Hide Description
It is well known that the ultrasonic attenuation coefficient of mammalian tissues, in the low megahertz frequency range, varies approximately linearly with frequency for all measurement methods (recent work has shown that the absorption coefficient of these tissues also varies nearly linearly with frequency). However, the magnitude of the measuredattenuation may vary by as much as a factor of three with the measurement technique. In particular it has been shown that measurements with phase sensitive receivers, which are subject to phase cancellation due to an inhomogeneous velocity distribution within the tissue yield higher values than methods utilizing phase insensitive receivers. The frequency dependence of the phase cancellation artifact depends upon the frequency range examined, the range of velocity inhomogeneity, the sample thickness and the receiver aperture.
Nonlinear acoustic behavior in focused ultrasonic fields: Propagation in water and biological tissue65(1979); http://dx.doi.org/10.1121/1.2017291View Description Hide Description
Nonlinear acoustic behavior in the form of harmonic generation is observed within the focal region of a focused ultrasonic field in degassed distilled water as well as in biological tissue. The observations were made using a miniature hydrophone probe whose frequency response has been characterized. The phenomena was also observed in nonlinear absorption measurements in biological tissues using the transient thermoelectric technique. Harmonic generation appears to be of significance at spatial peak intensities greater than about 60 W/cm2 in the media studied here. While harmonic generation itself appears to be confined to the focal region of the beam, the harmonics are seen to propagate well beyond the focus. The implications of this phenomena with respect to the application of high‐intensity ultrasonic fields used in medicine and biology are discussed. [Work supported by NINCDS and NIH.]
65(1979); http://dx.doi.org/10.1121/1.2017342View Description Hide Description
On day 8 of pregnancy we exposed pregnant Swiss Webster CFW mice to continuous ultrasound at 2 MHz, 0.5(± 10%) W/cm2 spatial average intensity [in the vacant water bath (37°C)] for 60, 100, 140, and 180 s. Estimated intensity at the uterus was 0.45(±20%) W/ cm2. By comparison with sham treated controls we found the ultrasound had no effect on the survival of neonatal mice through day 25 of age (84 to 108 neonates per group). This result may be compared with Curto's (1976) report [K. A. Curto, Ultrasound in Medicine 2, 535‐6 (1976)] of 13% to 26.7% reduction in neonatal survival after exposure of CFI mice on day 13 of pregnancy to 1 MHz, 0.125 to 0.5(±20%) W/cm2 spatial average intensity [in the vacant saline bath (30°C)] for 180 s. Curto sought enhancement of exposure and her conditions could have resulted in intensities at the uterus as great as 1.0(±20%) W/cm2. We conclude that the expression of this end‐point at (0.5 W/cm2, 180 s) as cited in summaries is at least questionable and is possibly dependent on other conditions of exposure. [Research supported by NIH grant ♯GM 22684.]
65(1979); http://dx.doi.org/10.1121/1.2017343View Description Hide Description
An experimental program, utilizing over 50 rabbits, evaluated the use of focused ultrasound to cause accelerated resorption of vitreous membranes. Membranes were formed in the vitreous of the anesthetized rabbit eye by injection of 0.1 ml of platelet‐rich plasma. Membranes formed in the vitreous produced sequelae similar to those produced by membranes seen clinically. Membranes were insonified with multiple, 5‐s duration exposures of focused ultrasound at 9.8 MHz. Insonified membranes resorbed at a significantly accelerated rate when compared to uninsonified membranes (controls and shams). Pulsed insonification at 10 Hz pulse repetition rate was found to be most effective. Careful positioning of the focused beam on the membrane enhanced effectiveness of low intensities and reduced unwanted effects on adjacent normal tissue structures. [Work supported by the NIH.]
65(1979); http://dx.doi.org/10.1121/1.2017344View Description Hide Description
Heated human erythrocytes gradually lose their form‐maintaining structure as the temperature is increased to 49°C and behave in many respects as a viscous liquid. We have discovered that heated erythrocytes that are stressed by shear forces in liquid flow develop periodic disturbances along their length that are wavelike in appearance. We have developed a technique for heating and stressing these cells that is novel, simple, and quantitatively precise. We have applied this technique to heated human erythrocytes and have caused them to be drawn out into long thin cylinders that show wave development similar to that observed in liquid jets. From an analysis of the instability development in liquid jets as applied to the erythrocyte system we can obtain more precise values for the membrane surface tension than previously reported by other techniques. [Work partially supported by Office of Naval Research.]
- Session D. Speech Communication I: Vowels and Voicing
65(1979); http://dx.doi.org/10.1121/1.2017345View Description Hide Description
In order to shed light on a specific theory of peripheral auditory representation (drawn from work by Zwicker and recently formalized by Schroeder, Atal, and Hall) we have used data on how listeners match two‐formant vowels to four‐formant stimuli. We report on two experiments designed to test the hypothesis that such listeners determined their favored F 2′ according to a distance measure (adapted from Plomp) formulated in terms of such auditory representations. This theorymodels the auditory transformation of the acoustic signal as a conversion of the power spectrum into a sones/Bark representation by computing critical‐band densities and applying a (basilar membrane‐like) frequency smearing function. The computed pseudoauditory vowel distance measure was found to correlate very highly with the listeners judgments of vowel‐quality distance obtained from the two experiments described, which involved the comparison of numerous vowel pairs from reported F 2′ data. The results suggest that a model of peripheral auditory representation is available which would be useful as a building block in any theory of speech perception.
65(1979); http://dx.doi.org/10.1121/1.2017397View Description Hide Description
It is a well‐known fact that the categorical judgment on a stimulus is generally influenced by the context, but systematic studies on quantitative aspects of the context effect are rather few. The present study investigated the influence of the relative positions of the target and context stimuli both on the stimulus continuum and on the time axis. The influence of stimulus attributes was also investigated using pure tones, complex tones with a formant structure, and synthetic vowel sounds. The results indicated the existence of a gradual transition from assimilation to contrast in almost all cases studied, the contrastive effect becoming more intense with increased stimulus complexity in nonspeech stimuli and most intense in speech stimuli. An interpretation of the results is presented on the basis of a model for the process of categorical judgment. [Work supported by Grant‐in‐Aid for Scientific Research from the Ministry of Education.]
65(1979); http://dx.doi.org/10.1121/1.2017398View Description Hide Description
The objective of the preliminary research to be described is to quantify the psychophysical similarity of vowel‐like stimuli that differ in certain spectral and waveform characteristics. To that end, the vowel /æ/has been synthesized by adding together sinusoidal harmonics of the appropriate frequencies, amplitudes, and phases. Changes to these parameters and to fundamental frequency are made on a period‐by‐period basis. The resulting synthetic waveform is essentially indistinguishable from that produced by a conventional cascade formantsynthesizer, but the present synthesis technique permits the experimenter to manipulate certain spectral and temporal details more easily. A set of 65 different vowels acoustically similar to /æ/have been synthesized by manipulating formant frequencies, formant bandwidths, spectral tilt, phase relations among harmonics, and filtering passband/stopband. Subjects are asked to estimate the psychophysical distance between each stimulus and a reference vowel in a 380‐trial randomized test. Results will be discussed in terms of various theories of vowel perception. [Research supported in part by an NIH grant.]