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Apr 1991

Volume 89, Issue 4B, pp. 1851-2015

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back to top Session 2EA: Engineering Acoustics: Transducers and Arrays
Contributed Papers
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High‐power test of a barrel stave flextensional transducer (A)

Mark B. Moffett and William L. Clay, Jr.

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1858-1858 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Barrel stave flextensional transducers are potentially useful as compact, low‐frequency, high‐power projectors. An equivalent circuit model that includes a higher‐mode, extensional compliance is used to estimate the maximum radiated power. Because the mechanical quality factor, Q, is low (on the order of 3 or 4), the source level of such a projector is limited by the maximum electric field that the piezoelectric ring stack driver can safely handle without depolarization or significant dielectric losses (about 400 kV/m for Navy type III lead zirconate titanate). A barrel stave flextensional projector 18 cm long and 9 cm in diameter with a mass of 4.1 kg in air was tested to 200 psig (1.4 MPa) in the pressure vessel at NUSC's Dodge Pond Field Station. A source level of 194.7 dB//1 μPa‐m was obtained at 1.56 kHz for an applied rms voltage of 5 kV. The projector figure‐of‐merit was about 14 W/kg‐kHz‐Q, and this number would be expected to apply to a larger, lower‐frequency projector of commensurate dimensions.
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Applications of very high‐energy density electrostrictive ceramics for underwater projectors (A)

A. P. Ritter, S. M. Pilgrim, P. Kuhn, S. R. Winzer, and J. Sewell

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1858-1858 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Performance of Navy sonar transducers is limited by the inherent energy density of the driver material—especially for those size‐constrained applications that require very high source levels and/or very low frequencies. Ultimately, the maximum sound‐pressure level will be limited by the amount of power that can be generated from the ceramic driver at its maximum engineering limit of 10–15 V/mil (∼0.5 MV/m). Incremental improvements in transducer performance may be possible through design refinements, however, revolutionary large‐scale improvements require new approaches to overcome the basic PZT material limitations. Electrostrictive ceramic materials, such as the PMN‐based compositions being developed at Martin Marietta Laboratories, have energy density values an order of magnitude higher than Navy PZT's and therefore could significantly improve transducer performance (i.e., maximum attainable source level) if substituted for PZT in conventional transducer designs. Transducer model calculations for comparable PZT‐ and PMN‐driven transducers show ∼ 10‐dB gain in the transmitting voltage response for the PMN transducer. These model predictions have been verified by experimental data obtained under a joint Martin Marietta/Navy materials development program.
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Using piezoelectric film and ultrasound resonance to measure the elastic moduli of spherical ceramic particles (A)

P. S. Spoor, M. J. McKenna, J. D. Maynard, and John R. Hellmann

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1858-1858 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The search for alternate sources of energy has prompted interest in small ceramic beads, called “proppants,” which were developed as a means of “propping” open cracks during the hydraulic fracturing of bedrock in the vicinity of oil wells; recently, they have been considered as possible thermal transfer media for use in solar receivers [J. R. Hellmann et al., “Evaluation of Spherical Ceramic Particles for Solar Thermal Transfer Media,” SAND86‐0981, Sandia National Laboratories, January 1987]. To monitor the effects of repeated thermal stresses on the proppants, one would like to have a reliable measure of their elastic constants; however, their spherical shape and small size (≃ 500 μm) make conventional techniques, such as pulse‐echo, inapplicable. Using a special piezoelectric film transducer and a small‐sample resonance technique [J. D. Maynard, J. Acoust. Soc. Am. Suppl. 1 85, S20 (1989)], the authors have been able to determine the elastic constants and their variation as a function of heat treatment. [Work supported by the Office of Naval Research and NSF Grant DMR 9000549.]
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Optimally formulated high efficient planar projector arrays (A)

P. M. Joseph and P. R. Saseendran Pillai

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1858-1859 (1991); (2 pages)

Online Publication Date: 14 Aug 2005

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Closely packed multi‐element transducer arrays are extensively used in underwater applications for achieving better directionality and longer transmission range. With the current tendency of extending their operation toward lower frequency and particularly near resonance, the acoustic interaction among the elements grows stronger and in turn will degrade the predicted transmitting characteristics. This troublesome effect is much alleviated in uniform planar arrays by restructuring it with the optimal interelement spacing at which the interaction force is minimum [P.M. Joseph and P. R. Saseendran Pillai, Acoust. Lett. 12 (11), 190—193 (1989)]. It has been seen from the results of computation that a further reduction in interaction can be achieved by incorporating the nonuniform array concept. A simple method for predicting the optimum configuration of element locations that reduce the interaction to a lower level, without altering the aperture dimension, is proposed in this paper. Here, the element locations are dispersed in accordance with Gaussian distributed random numbers by keeping the optimum spacing as the mean. Even though a large standard deviation value will greatly reduce interaction, a reasonable value is chosen, as large deviations produce deteriorated beams. This optimally formulated array does not exhibit any grating lobes nor does its radiation pattern differ much from the conventional λ/2 spaced and restructured arrays.
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The generation of sound by a dipole moving near the edge of a half‐plane (A)

Gerrit Schouten

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The shape and the spatial amplitude distribution of the sound pulse generated by the passage of a dipole (or ring vortex) near the sharp edge of a half‐plane are computed and presented in plots. Instead of using a low‐frequency approximation to the Green's function a direct approach to the potential of a moving dipole in a branched space is used together with an image dipole. In a compressible medium (with a finite velocity of sound) the wave is physically present. In the limit of an incompressible medium the wavelength becomes infinite and the wave degenerates into a time history of the pressure variation. The incompressible pressures agree with those obtained from direct differentiations of the classical results of Sommerfeld [Proc. London Math. Soc. 30, 121–163 (1897)]. The wave results are in conflict with some results presented in the literature [T. Kambe et al., J. Fluid Mech. 155, 77–103 (1985)] obtained with a low‐frequency approach.
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Characterization of anisotropy in wood composites (A)

V. Bucur

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The aim of this report is to study the anisotropic behavior of wood composites using the ultrasonic velocity method and acoustic emission method. Velocities of ultrasonic longitudinal and transversal waves were used for the estimation of five elastic constants. Complementary, stimulated acoustic emission, induced by breaking 0.5‐ram pencil lead on the surface of the specimen, was employed to measure five parameters of the acoustic emission signal (duration, counts number, energy, amplitude, and rise time). The anisotropy was estimated as the ratio of velocities, of acoustic invariants, and acoustic emission parameters.
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Flow noise induced in large arrays via the flexure of the support (A)

B. Dubus and R. E. Montgomery

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The noise induced by the turbulent boundary layer in sonar arrays is usually split into a direct path where the fluctuating pressures directly excite the hydrophones after traveling through an elastomer layer backed by a rigid surface, and the indirect path where the excitation of the support by the turbulent boundary layer induces the noise in the array. To describe this last phenomena, the force‐modal transform method [M. C. Junger and D. Feit, Sound, Structures, and Their Interaction (MIT Press, Cambridge, MA)] has been extended to describe the flexure of a submerged multilayered plate and the wave‐number spectrum of the noise sensed by the array. Several configurations are analyzed showing the effect of the stiffness and the damping of the support and of the distribution of the hydrophones. From these results, some solutions to reduce the noise level are proposed. [Work partially supported by Direction des Recherches Etudes et Techniques, Paris.]
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Wave propagation in a viscoelastic medium with a high concentration of pores (A)

Y. Ma, V. K. Varadan, V. V. Varadan, and C. Audoly

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Wave propagation in a viscoelastic and porous medium, whose properties are temperature and frequency dependent, was investigated. The propagation characteristics of compressional waves in such a medium cannot be predicted using single scattering models when the porosity of the medium is considerable. Different from a previous study [Y. Ms, V. K. Varadan, and V. V. Varadan, ASME J. Heat Transfer 112, 402–407 (1990)], which was for electromagnetic waves, this investigation provided another proof of enhanced attenuation due to dependent scattering for the acoustic case. Most importantly, this is a problem of an elastic wave propagation in a lossy host medium with lossless scatterers which has seldom been considered. Numerical results of phase velocity as well as of attenuation of such a medium for different temperatures and different frequencies are presented. Differences in results between single and multiple scattering when the porosity is increased are also shown. Numerical results considering multiple scattering compare favorably with those from the experimental work which was done independently by G.E.R.D.S.M. in France. [Work supported by CEEAM.]
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Computation of sound radiation from an arbitrary body with mixed boundary conditions using program CHIEF (A)

W. Thompson, Jr. and C. M. Siders

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The computer program CHIEF has been modified to allow the computation of sound radiation from an arbitrary‐shaped body where the normal velocity is prescribed on only part of the surface of the body while a locally reacting complex impedance is assumed to cover the remainder of the surface. This impedance can range in value from zero (pressure‐release boundary condition) to essentially infinity (rigid boundary condition). Different values of impedance are allowable on different portions of the same surface. Some results of computations of far‐field directivity patterns and the radiation impedance loading on simple‐shaped radiators with the mixed boundary conditions are presented. [Work sponsored by ONT.]
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Finite element model for a planar fiber optic hydrophone (A)

Paul J. Zoccola and Paul C. Shang

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1859 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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A finite element model has been developed for estimating the acoustic sensitivity of a planar fiber optic hydrophone. The sensor consists of a single‐mode fiber surrounded by a thin layer of silicon and a hytrel jacket. This strand is coiled and embedded in an elastomer layer. The model will allow use of nonisotropic materials also; these materials are less suitable for analytical modeling. The finite element model uses linear solid elements and uses symmetry about two or three planes, depending on the configuration. Because the sensor is designed for low‐frequency measurements, hydrostatic pressure loading is used. Sensitivity is calculated using the strain on the fiber. The results are compared to closed form solutions for cylindrical configurations and to experimental results. They show that for most practical purposes, sensitivity is mostly controlled by the volume of the elastomer surrounding the fiber.
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Theoretical study of a fiberacoustic waveguide with continuous variation of the radial acoustic velocity (A)

A. G. Yin, V. K. Varadan, and V. V. Varadan

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1859-1860 (1991); (2 pages)

Online Publication Date: 14 Aug 2005

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In this paper, a geometrical acoustics method has been presented to describe acoustic wave propagation in a fiberacoustic waveguide in which the acoustic velocity varies continuously in the radial direction. Based on the acoustic wave equation, a WKBJ approximate method has been used to analyze the propagation and cutoff characteristics of guided acoustic modes in this waveguide. It is believed that this acoustic fiber can transmit acoustic and optical signals at the same time when the refractive index of the core material is greater than that of the cladding material and the acoustic velocity of the core material is less than that of the cladding material. Furthermore, this type of acoustic fiber is suitable because of low loss and hence long distance transmission paths.
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A unified reciprocity method for two basic types of vibration calibrators (A)

Li‐Feng Ge

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1860-1860 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Two basic types of vibration calibrators, i.e., electrodynamic‐type and piezoelectric‐type standard vibration generators, can be described by a uniform dynamic model and equivalent circuit [L.‐F. Ge, J. Acoust. Soc. Am. 86, 210–214 (1989)]. The calibration factor of both types, which is defined as a ratio of the mechanical output (velocity or acceleration) to the electrical input (current or voltage), viz., the transmitting current or voltage response, is given and formularized by a uniform equation: Ti  =  (CZ + D)−1(m s−1/A) or Te  =  (AZ + B)−1(m s−1/V), where Z is the mechanical lead impedance and A, B, C, and D are the reciprocity network parameters of the calibrator. The former is suitable for an electrodynamic‐type calibrator, because the thrust of the shaker depends on input current on the basis of the Faraday′s law; the latter is suitable for a piezoelectric‐type calibrator, since the voltage change leads to motion of the table according to the piezoelectric effect. Measurements performed on piezoelectric calibrators have obtained accurate calibration results at high‐frequency range; experiments on a commercial electrodynamic shaker at 1 kHz have also shown that the method is attractive.
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