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Journal of the Acoustical Society of America

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Dec 1977

Volume 62, Issue S1, pp. S1-S102

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back to top Session Z. Engineering Acoustics IV: Detection and Materials
Contributed Papers
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A 1‐MHz linear phased array ultrasound system for imaging the major intracranial arteries (A)

R. W. Barnes and W. A. Riley

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S56-S56 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A linear phased array ultrasound system has been constructed to image the major intracranial arteries from the superior surface of the cranium. The transducer array consists of 20 elements, 1.54 mm wide and 15 mm long, with an interelement spacing of 0.19 mm. Ten elements are excited for each transmit pulse and excitation pulses are phased for nominal transmit focus of 7 cm. On the receive side, echo signals from each element are logarithmically compressed and dynamically focussed by variable delay lines to within ±25 ns of an ideal phase coherent system at the input to a summing amplifier. The transmit/receive response results in a −6 dB beamwidth of about 6 mm at a depth of 7 cm. A two‐dimensional image is formed by sequencing consecutive ten elements along the array. The major intracranial arteries imaged include the internal carotids in the intradural pertion of the siphon, the middle cerebrals as they travel laterally from the internal carotid arteries, the basilar artery, the posterior cerebral arteries as they follow the lateral aspect of the midbrain, and the perical‐losal artery as it travels posteriorly along the superior surface of the corpus callosum. It is our interest to interface this linear phased array system with an on‐line digital moving target indicator system to produce a two‐dimensional image of only the intracranial arteries. [Work supported by NINCDS grant NS‐06655.]
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Optimization of magnetically coupled drive of the ear (A)

John A. Mooney and George Moushegian

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The ear level hearing aid represents the ultimate in basic hearing aid configuration. This paper presents a feasible electromagnetic drive approach that virtually eliminates acoustic feedback problems of ear level aids as well as providing precise low distortion performance heretofore unavailable in a miniature aid. New magnetic materials of the platinum‐cobalt and rare earth cobalt class make possible the realization of the goal of 100 dB re 0 dB = 0.0002 dyn/cm2 sensation level for 1 mW input as needed for low battery drain. These acoustic levels are measured via frequency following potentials (FFP) as well as by the microphonic cochlear potentials recorded at the round window. Suggested additional features are covered as well as the culminating role of electret microphones, lithium batteries, and modern IC fabrication techniques to make possible a programmable aid of unprecedented quality. [Supported by NIH grant.]
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Effects of temperature on the aging rate of piezoelectric polymer (A)

J. M. Powers

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Results of aging measurements at 20°C, 57°C, and 66°C are presented for commercially available piezoelectric polymer (28‐μm thick, poled polyvinylidene fluoride). The g31 (electric field/stress) and d31 (charge density/stress) piezoelectric constants were measured by a static dead weight tension test. The relative dielectric constant Kmath was obtained from a 1‐kHz capacitance measurement. At room temperature (20°C), aging rates of 10%/time decade for g31, 15%/time decade for d31, and 7%/time decade for Kmath were obtained over a 100‐day period from date of poling. Values of g31 and Kmath were measured (at room temperature) for samples held at 57°C and 66°C for 100 days starting at 400 days from poling. For the 57°C case, g31 values at 401, 410, and 500 days showed a 3%, 10%, and 16% decrease over the 400‐day value. The 66°C case showed decreases of 16%, 19%, and 21% in g31 over the same time period. No change in Kmath was observed for either of these cases. [Work supported by R. R. Smith, Code 302, Naval Ocean Systems Center, San Diego, CA.]
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Effect of fillers on acoustic properties of silicone rubber at ultrasonic frequencies (A)

R. D.\ Corsaro and J. Klunder

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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We have had a recurring need for molded articles (wave guides) and thin anechoic coatings, composed of rubbers with well defined and continuously variable acoustic properties. To fill this need, we have measured the dependence of various acoustic properties (sound speed, density, absorption) on the amount and type of filler added to RTV 602 silicone rubber. Both high impedance (ferric oxide, lead) and low impedance (glass and backlite microballons) modifiers were added, in two and three component mixes. A diluent (toluene) was found, which had no observed effect on the acoustic properties of the resulting rubber. Acoustic measurements were made using thick (molded) slabs, as well as thin (sprayed) coatings. In the latter cases, sound speed and absorption is evaluated using the measured frequency dependence of the coating's impedance. In all cases, we find that density and sound speed is well described using ideal mixture theory, providing the geometry of the microballons is taken into account. Absorption is described by simple phenomenological equations, and compared with theoretical predictions.
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Experimental study of the effects of water repellent treatment on the acoustic properties of Kevlar (A)

C. D. Smith and T. L. Parrot

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The effects of water repellant treatment of the acoustic properties of a bulk absorber have been investigated. The bulk absorber consisted of a synthetic fibrous material (Kevlar 29, style 1270) manufactured by DuPont. The propagation constant, γ, and the characteristic impedance Zc were measured over the frequency range 0.5 to 3.5 kHz. The measurements were conducted before and after a controlled application of water repellent treatment (“Zepel” DA‐24M), also manufactured by DuPont. A comparison of test results indicated changes in both γ and Zc. These changes in γ and Zc generally increased with frequency. At the highest test frequency, the attenuation constant (real part of γ) and phase constant (imaginary part of γ) decreased by about 8% and 10%, respectively, when the treatment was applied. Corresponding changes in the real and imaginary parts of Zc at the test frequency of 3.5 kHz were about 6% and 25%, respectively.
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Experimental determination of acoustic properties using a two‐microphone random‐excitation technique (A)

D. F. Ross and A. F. Seybert

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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An experimental technique is presented for the determination of normal acoustic properties in a tube, including the effect of mean flow. White noise is used to produce a randomly fluctuating sound field and two stationary, wall‐mounted microphones measure the sound pressure at arbitrary but known positions in the tube. Theory is developed, including the effect of mean flow, showing that the incident‐ and reflected‐wave spectra, and the phase angle between the incident and reflected waves, can be determined from measurement of the auto‐ and cross‐spectra of the two microphone signals. Expressions for the normal specific acoustic impedance and the reflection coefficient of the tube termination are developed for a random sound field in the tube. Three no‐flow test cases are evaluated using the two‐microphone random‐excitation technique. Comparison is made between results using the present method and approximate theory and results from the traditional standing wave method. In all cases agreement is very good. [Research conducted at Purdue University, Lafayette, IN.]
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Scattering of a sound wave from a grating of hollow elastic bars in a viscoelastic layer (A)

R. P. Radlinski and J. J. Libuha

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S57-S57 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The problem of the scattering of a normally incident plane sound wave by an infinite grating of hollow elastic bars in a viscoelastic layer between two fluid haft spaces is solved by the method of partial domains. The solution in the layer is formulated in terms of inhomogeneous plane dilatational and shear waves. The attenuation is found to be always normal to the plane of the grating. The evanescent waves in the viscoelastic medium necessarily cannot propagate parallel to the grating as is the case for an elasticlike or fluid medium. The dependence of the grating transmissivity on parameters of the individual bars and the complex‐valued, frequency dependent, material properties of the layer is analyzed quantitatively. By using measured viscoelastic material properties as input to the model, comparisons of predictions of transmissivity are made with experimental data. [Work supported by NAVSEA.]
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A parametric sonar performance calculator (A)

Thomas B. Pederson

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S58-S58 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Predicting the difference frequency source levels and beamwidths which will be developed by a given parametric sonar projector is a somewhat complicated procedure involving a number of calculations and the use of several curves or nomograms. We will introduce a slide calculator we have developed which will compute in a relatively straightforward manner these quantities for a parametric sonar operating in the unsaturated regime.
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Acoustic window model (A)

J. F. Kilpatrick, Jr.

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S58-S58 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A model was developed to predict the effect on the beam pattern of an array caused by the presence of a rigid, semi‐cylindrical acoustic window. Using the basic theory of Brekhovskikh and previously proven methods of loss measurement and prediction, [E. E. Mikeska and J. A. Behrens, J. Acoust. Soc. Am. 59, 1294–1298 (1976)] the amplitude and phase distortion of the window can be predicted as a function of angle of incidence and frequency. This information, coupled with the relative geometries of the window and array, can be used to determine the beam pattern of the array/window combination. Theoretical patterns were compared with measured data on a high resolution line array with excellent results.
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Acoustic/seismic vehicle locator (A)

George W. Brooks, Gwynn M. Reel, Norman P. Huffnagle, and Martin Marietta

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S58-S58 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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We are investigating an automatic range measuring/target classification method based on the relative velocity differences of airborne acoustic and seismic waves. The technique appears to be a promising way to measure target range to an accuracy commensurate with present target interdiction techniques. In brief, assumptions on the relative velocities and their variances appear to be sound: errors of ±20% do not materially degrade interdiction probabilities. C. F. Richter and others have determined that the relation between the three seismic waves (Prompt‐P, Shear‐S, and Rayleigh‐R) is virtually invariant for many media. One of the methods being investigated takes advantage of this invariance to measure range. A closed‐loop system using a 512‐element CCD serial analog delay as one element of a seismic/acoustic correlator shows promise as a viable method. Replacing the seismic/acoustic inputs by the P and R waves (polarized at right angles to each other and having wide velocity dispersion), this correlator would work as a single medium range system. Coupling this target range‐measuring method with a Martin Marietta‐developed target classification technique that also provides range measurement using Doppler and the amplitude increase function on the narrow‐band spectra of predetermined targets, target interdiction by this multipath method leads to a system that is very immune to countermeasures and natural events.
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Microphone coupler for noise source location (A)

James H. Botsford

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S58-S58 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Reducing noise generation requires determining where sound waves originate. Machinery connected to other structures can form a complex vibrating noise source that is difficult to analyze. Measuring sound levels close to surfaces suspected of radiating noise can help in finding sound sources. But results are sometimes inconclusive because of sound reflections from the surface, especially where standing waves exist. Using accelerometers to detect surface vibration overcomes the sound reflection problem but is a complicated and time‐consuming technique, requiring sophisticated equipment and calculations for definitive results. To overcome some of these difficulties, a flexible coupler was developed for the microphone of a sound level meter. The microphone fits into the throat of the flaring coupler and the mouth of the coupler is pressed against any surface suspected of radiating sound. The flexible mouth conforms even to curved surfaces and seals out extraneous noises. Sound radiated from the surface closing the coupler mouth is collected in the cavity, sensed by the microphone and indicated on the sound level meter. This useful device allows positive identification of vibrating surfaces responsible for sound generation.
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Parameter identification in nonclassical linear mechanical systems (A)

C. D. Michalopoulos and L. T. Wheeler

J. Acoust. Soc. Am. Volume 62, Issue S1, pp. S58-S58 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The identification problem for a system whose motion is governed by [A]{math(t)}+[B],{math(t)}+[C]{x(t)} = {f(t)}, where [A], [B], and [C] are not the classical inertia, damping and stiffness matrices, is studied. Specifically, the eigenvalues of the associated reduced system of equations are determined by processing in the frequency domain the response {x} to a random excitation {f}, whose power spectral density is assumed constant (or reasonably flat). This is accomplished through the minimization of a mean‐square error function involving the theoretical and measured power spectral densities of the response. It is shown that the level of the assumed white‐noise excitation need not be known. [Work supported by NASA.]
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