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Journal of the Acoustical Society of America

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Jun 1989

Volume 85, Issue 6, pp. 2255-2702

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Transient ultrasonic waves in a viscoelastic plate: Theory

Richard L. Weaver, Wolfgang Sachse, and Lin Niu

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2255-2261 (1989); (7 pages) | Cited 5 times

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The nearfield response of a thick viscoelastic plate at epicenter, off‐epicenter, and on the same side of the plate to a point step load acting normal to the surface is discussed. The integral expressions resulting from Fourier and Hankel transforms of the governing equations are evaluated by two procedures. An asymptotic evaluation of the frequency‐domain response is presented for high frequencies corresponding to ray arrivals. A numerical double inverse transform procedure is developed for obtaining exact time‐domain waveforms.
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43.20.Bi Mathematical theory of wave propagation
43.35.Mr Acoustics of viscoelastic materials

Transient ultrasonic waves in a viscoelastic plate: Applications to materials characterization

Richard L. Weaver, Wolfgang Sachse, and Lin Niu

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2262-2267 (1989); (6 pages) | Cited 1 time

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The ray arrival behavior of an ultrasonic signal propagated through a thick viscoelastic plate is analyzed to determine the material dispersion and attenuation. Signal processing algorithms are developed and demonstrated with synthetic and real signals obtained in elastic and viscoelastic materials. Recovery of material properties is found to proceed reliably except for the case of attenuation recovery from real signals, where there were difficulties related to the use of a finite aperture receiver.
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43.20.Bi Mathematical theory of wave propagation
43.35.Mr Acoustics of viscoelastic materials
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Leaky Lamb waves in an anisotropic plate. I: An exact solution and experiments

Vinay Dayal and Vikram K. Kinra

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2268-2276 (1989); (9 pages) | Cited 6 times

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The propagation of leaky Lamb waves in a plate consisting of a general balanced symmetric composite material is considered. The problem has been examined both analytically as well as experimentally. An exact solution for the dispersion equation was obtained. Numerical results for complex‐valued wavenumber were obtained for an isotropic material (aluminum) and a (0/903)s graphite/epoxy laminate. Excellent agreement for the isotropic case and a satisfactory agreement for the anisotropic case between the theory and experiment were observed.
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43.20.Fn Scattering of acoustic waves
43.35.Pt Surface waves in solids and liquids

Effects of two‐dimensional topographies using the discrete wavenumber‐boundary integral equation method in P–SV cases

Stéphane Gaffet and Michel Bouchon

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2277-2283 (1989); (7 pages) | Cited 1 time

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The effect of topography on surface motion is studied in the case of incident P and SV waves and in presence of an explosive source. The discrete wavenumber‐boundary integral equation method is formulated for this case and is applied to the problem of diffraction of an elastic wave field by a ridge‐shaped topography. The amplitude of the scattered field, which mostly consists of surface P waves and Rayleigh waves, is strongly dependent on the steepness of the topography. The generation of surface waves by an explosion located in the vicinity of the ridge topography is studied and an increase in Rayleigh wave amplitude and a broadening of the Rayleigh pulse when the explosion occurs within the ridge is found.
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43.20.Fn Scattering of acoustic waves
43.35.Pt Surface waves in solids and liquids
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors

On the existence of the Rayleigh wave dipole resonance

Roger H. Hackman and Gary S. Sammelmann

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2284-2289 (1989); (6 pages)

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The acoustic scattering resonances of a solid elastic sphere are thoroughly analyzed in the low‐ka frequency region. No evidence is found to support the existence of the recently reported (1,1) Rayleigh wave dipole resonance.
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43.20.Fn Scattering of acoustic waves
43.20.Px Transient radiation and scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

A paraxial theory for the propagation of ultrasonic beams in anisotropic solids

Byron P. Newberry and R. Bruce Thompson

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2290-2300 (1989); (11 pages) | Cited 8 times

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The necessity of nondestructively inspecting cast steels, weldments, composites, and other inherently anisotropic materials has stimulated considerable interest in wave propagation in anisotropic media. Here, the problem of an ultrasonic beam traveling in an anisotropic medium is formulated in terms of an angular spectrum of plane waves. Through the use of small angle approximations, the integral representation is reduced to a summation of Gauss–Hermite eigensolutions. The anisotropic effects of beam skew and excess beam divergence enter into the solution through parameters that are simply interpreted in terms of the slowness surface. Both time harmonic and pulsed solutions are discussed. Formulas are also presented for transmission of a beam through a curved interface between two media. Examples are given illustrating how this method may be applied to predicting beam patterns during ultrasonic inspections.
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43.20.Fn Scattering of acoustic waves
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Scattering from multiple gratings of compliant tubes in a viscoelastic layer

Ronald P. Radlinski

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2301-2310 (1989); (10 pages) | Cited 2 times

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Previous studies of scattering from multiple gratings of resonant compliant tubes in water determined that noncompliant, antisymmetric structural modes excited by evanescent waves severely degraded the reflectivity of closely packed gratings. Also, low‐frequency performance was diminished by transmission resonances due to the spring–mass–spring configuration of the two compliant gratings separated by a fluid mass. In this paper, encapsulating a single grating in a layer of elastomer whose shear properties are well below its rubber–glass transition region is shown to only reduce the maximum insertion loss. For two gratings, both the transmission resonances and the evanescent wave excitations are mitigated by encapsulation in a rubberlike material. Insertion loss performance with an encapsulant whose shear properties are in the rubber–glass transition region occurs at reduced bandwidths and shifted frequency responses. The mathematical model for gratings in fluid is extended to include the viscoelastic layer and calculations from this model are compared with experiments.
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43.20.Fn Scattering of acoustic waves
43.20.Tb Interaction of vibrating structures with surrounding medium
43.35.Mr Acoustics of viscoelastic materials

Dispersion relations of plate modes in anisotropic polycrystalline sheets

M. Hirao and H. Fukuoka

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2311-2315 (1989); (5 pages)

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The presence of texture can explain the anisotropy of ultrasonic propagation velocities in polycrystalline materials. This paper derives dispersion relations with which the phase velocities can be calculated for plate modes guided along an arbitrary direction in the plane of an orthorhombic sheet. The effect of texture is brought into the analysis through the crystallites’ orientation distribution coefficients (ODCs). The dispersion relations are split into two parts, one for the P–SV motion and the other for the SH motion. The result for the symmetric P–SV motion approaches the angular variation in the velocity of the lowest (S0) mode with decreasing frequency. The anisotropy in Rayleigh surface wave velocity is also derived as a solution in the high‐frequency limit. These limiting solutions are useful for the nondestructive characterization of texture from ultrasonic velocity measurements.
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43.20.Hq Velocity and attenuation of acoustic waves
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Acoustical higher‐order mode scattering matrix of circular nonuniform lossy tubes without flow

Herbert Hudde

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2316-2330 (1989); (15 pages) | Cited 2 times

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In this paper, the acoustical behavior of circular ducts with nonuniform area functions is considered in terms of a corresponding scattering matrix. The elements of the scattering matrix denote the portions of reflected and transmitted waves of the mode order k when a wave of mode order n is incident. This way, the approach is able to treat wave modes of arbitrary order. When the tube under consideration consists of sections of constant cross‐sectional area, the method of calculation can be applied directly. Otherwise, the (continuous) area function has to be approximated by a corresponding step function; i.e., the tube is modeled by a certain number of contiguous sections (stepped duct approximation). In contrast to other publications, the area function is not restricted to be slowly varying along the tube axis. Losses as well as liners are simply taken into account by altering propagation constants and wave impedances, correspondingly. After derivation of the numerical algorithm, some examples of nonuniform ducts are investigated. The results are compared to some low‐frequency solutions. The accuracy of numerical results depends on some parameters occurring in the algorithm presented. The influence of different parameters on the resulting accuracy is investigated. Finally, the theory is verified by a measurement.
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43.20.Mv Waveguides, wave propagation in tubes and ducts

Nonlinearly generated spectral components in the nearfield of a directive sound source

Tomoo Kamakura, Naoaki Hamada, Kenich Aoki, and Yoshiro Kumamoto

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2331-2337 (1989); (7 pages) | Cited 4 times

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Nonlinear propagation of sound waves generated by a directive ultrasound source in air is discussed theoretically and experimentally. The circular source of 21 cm in radius consists of 1410 small PZT bimorph transducers, whose resonance frequency is 28 kHz. For a single‐frequency wave excitation, sound pressures of the fundamental, second, and third harmonics are measured and are compared with the numerical results using a method of Aanonsen et al. [J. Acoust. Soc. Am. 75, 749–768 (1984)]. Extending their initial condition to the case of a two‐frequency wave excitation, propagation curves and beam patterns of the difference frequency sound are obtained and compared with the measured data. All observations quantitatively agree very well with the numerical calculation. Nonlinear attenuation of spectral components by increasing the source pressure is clearly confirmed.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Ed Effect of nonlinearity on velocity and attenuation

Intermodulation and generation of elastic and piezoelectric waves in anisotropic solids

Naoum Daher and Gérard A. Maugin

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2338-2345 (1989); (8 pages)

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A study of nonlinear waves of small amplitude is presented in elastic and electroelastic media through an asymptotic iterative procedure known as ‘‘Poincaré’s expansion.’’ The controversy surrounding the nonlinear elastic solution derived by use of different approaches is resolved and the resulting expressions are compared to recent experimental verifications. After the reconciliation of the various theoretical and experimental results, the new version of Poincaré’s method is extended to electroelastic anisotropic solids. Analytical, as well as numerical, evaluations concerning the relative velocity change due to electroelastic nonlinearities are presented.
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43.25.Dc Nonlinear acoustics of solids

The generation of sound by the convection of inhomogeneities through space‐varying flows, by analogy with the scattering of acoustic and evanescent waves

Alan Powell

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2346-2353 (1989); (8 pages)

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It is pointed out that the scattering theory of Rayleigh for sound waves interacting with inhomogeneities of a stationary medium can also be applied to evanescent waves. By considering the fluid to be moving and the wave system stationary and caused by a fixed wavy wall, the problem of the sound generated by inhomogeneities of a fluid carried through a supersonic or subsonic space‐varying flow field past the wall can then be addressed. As in that scattering theory, the inhomogeneities must be small in extent compared to the scale of the pressure gradient of the basic flow and also of the resultant sound: This is the low‐frequency approximation (which excludes application of the theory to shockwaves). It is found that inhomogeneities in density and compressibility of the gas (i.e., of the gas constant) both result in sound power that varies as the sixth power of the speed in all the cases of supersonic and subsonic flow, and when the interaction takes place far from, or close to, the wall or body, except that, at supersonic speed, interactions close to the body result in the sound power due to density fluctuations varying with only the fourth power of the Mach number and that due to the gas constant (compressibility) at subsonic speeds varying as the eighth power. In all cases, the sound power depends acutely on the shortness of the length characterizing the pressure gradients in the flow; specifically, it varies inversely as the sixth power of the characteristic length. It is pointed out that, in most engineering applications, the effects of density inhomogeneities are likely to overwhelm those due to variations in the compressibility of the gas, and interactions in the subsonic case must be close to the body to be significant, due to the very rapid decay of the pressure field away from the body.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Nm Aerodynamic and jet noise
43.25.Vt Intense sound sources
43.28.Py Interaction of fluid motion and sound, Doppler effect, and sound in flow ducts

Environmental mismatch in shallow‐water matched‐field processing: Geoacoustic parameter variability

C. Feuillade, D. R. Del Balzo, and Mary M. Rowe

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2354-2364 (1989); (11 pages) | Cited 6 times

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The effects of variations in geoacoustic environmental parameters on the performance of a matched‐field localization processor in shallow water were investigated. The SUPERSNAP propagation model was used to generate a reference acoustic pressure field and to simulate an ‘‘experimentally detected’’ field due to an acoustic ‘‘source.’’ These were then correlated using a maximum‐likelihood estimator for selected degrees of mismatch of environmental parameters. It was found that small perturbations in a downward‐refracting summer water sound‐speed profile of ±1σ (i.e., ±1 standard deviation) from average measured values caused severe degradation in localization performance, with predictions of source range and depth becoming highly unstable. However, similar perturbations of an almost isospeed winter profile caused comparatively little degradation. Similarly, perturbations in the sediment sound‐speed profile of up to ±1σ from average measured values were possible while still giving stable and reliable estimates of source location. The processor also appeared to be relatively insensitive to mismatch of sediment density and attenuation. The source was correctly localized even when the density and attenuation deviated by significantly more than ±1σ from average measured values.
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43.30.Bp Normal mode propagation of sound in water
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Gk Space-time signal processing, other than matched field processing

Flexural resonances in obliquely insonified solid elastic spheroids

M. F. Werby and G. C. Gaunaurd

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2365-2371 (1989); (7 pages)

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Form functions ‖ f∞‖ from submerged solid elastic spheroids generated by an obliquely incident plane wave contain a variety of resonance features. Predictions are presented for these form functions obtained by means of the T‐matrix method in the frequency band: 2≤kL/2≤24, as the aspect ratio (L/D) varies in the interval: 1.5≤L/D≤5, and the oblique incidence is kept at an angle of 45° with the axis of the spheroid. The lowest of the observed resonances starts to appear at kL/2 values that are approximately inversely proportional to the aspect ratio of the spheroid, a fact which is the converse of that for Rayleigh resonances. To determine the nature of these resonances, the spheroid is assumed to be a free–free Timoshenko beam of (constant) circular cross section and the same L/D as the spheroid, excited into reradiation by the obliquely incident wave. The resonances obtained by this simple Timoshenko‐beam model, and those obtained by the T‐matrix method agree quite closely at all aspect ratios. The comparison also verified the trend toward lower resonances as L/D increases. Therefore, this study shows that these are flexural (bending) resonances caused by the transverse oscillations of the spheroid as a free–free beam when it is excited by the obliquely incident wave.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.20.Fn Scattering of acoustic waves

Transient response of an elastic spheroid—Surface waves and quasicylindrical modes

Kevin L. Williams, Gary S. Sammelmann, David H. Trivett, and Roger H. Hackman

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2372-2377 (1989); (6 pages) | Cited 3 times

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The low kL/2 transient response of an elastic spheroid to an acoustic wave incident along the axis of symmetry is analyzed. The emphasis is upon a direct theoretical and experimental determination of the group velocity of the lowest elastic mode of the spheroid. With these results, a critical examination is made of the consequences of two different physical pictures that have been proposed for the low kL/2 elastic response of such targets (the surface wave and ‘‘quasicylindrical’’ mode pictures). Large discrepancies are found between predictions of the group velocity based on the surface wave picture and both the T‐matrix analysis and the experimental results presented here. In contrast, the predictions of the quasicylindrical mode picture are found to be in excellent agreement with these results. It is concluded that, although the surface wave description is useful at high kL/2, the quasicylindrical mode picture provides a more meaningful description of resonance phenomena in the low‐to‐medium kL/2 region.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Fn Scattering of acoustic waves

Vertical spatial coherence of scattering from the Arctic ice canopy: Comparison of theory with experiment

Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2378-2382 (1989); (5 pages)

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The results of experiments to measure the vertical spatial coherence of the high‐frequency acoustic field scattered from the Arctic ice canopy are presented. The dependence of the coherence on measurement geometry is found to be in agreement with theoretical predictions based on the method of physical optics. In addition, analyses to isolate the effects of under‐ice roughness on the coherence yield results in accord with theoretical predictions.
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43.30.Hw Rough interface scattering
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Detection of oil‐derivative contamination of water surfaces by statistical analysis of scattered acoustical signals

Stanislaw J. Pogorzelski

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2383-2387 (1989); (5 pages)

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The statistical distribution of the amplitude of the acoustical signal scattered by a water surface undulated by an air stream was studied under laboratory conditions. The surface was covered with layers of oil substances of different physical properties. Statistical parameters of the distribution were determined as functions of the speed of the air stream and the thickness of the oil layer. Values of the obtained parameters differ from those expected for the scattering on the surface of clean water. Simultaneous analysis of all the statistical parameters could be a starting point for determining the weight fraction of the given substance and its thickness.
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43.30.Hw Rough interface scattering
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Impedance profile and overall attenuation estimation of layered sea bottoms from their normal incidence acoustic reflection response

P. Cobo‐Parra and C. Ranz‐Guerra

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2388-2393 (1989); (6 pages) | Cited 1 time

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Inversion of high‐frequency acoustic reflection data in low‐noise layered sea bottoms is presented. The assumed geoacoustic model includes attenuation effects. An overall attenuation coefficient of the whole sedimentary column is estimated by logarithmic regression on the spectral ratio of nonoverlapped replicas. The attenuation response is filtered out of the impulse response by the minimum square inversion of the sea bottom lossy transfer function, previously computed by deconvolving the input pulse from the reflection response. Applying this inversion scheme to a known artificial bottom, experimental values lying within a 7.4% range below the actual data are obtained.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Sensitivity of matched field processing to sound‐speed profile mismatch for vertical arrays in a deep water Pacific environment

A. Tolstoy

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2394-2404 (1989); (11 pages) | Cited 21 times

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In this paper, the sensitivity of matched field processing to sound‐speed profile mismatch will be examined (based upon archival profiles resulting in various degrees of mismatch). A 10‐Hz source is considered whose field is generated by a normal mode model and only the water‐borne energy is used, thereby eliminating issues relating to the estimation of bottom parameters. This paper will examine how array parameters, i.e., number of phones and array depth, affect range and depth localization for various degrees of mismatch. In particular, it will be seen where an array is most and least sensitive to sound‐speed mismatch as a function of depth from the surface and range from the source, and the degree to which range and depth resolution are possible under ideal, as well as under likely, mismatch conditions.
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43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.60.Gk Space-time signal processing, other than matched field processing

Optoacoustic observation of internal relaxation in liquid CS2

Charles H. Thompson, Stanley A. Cheyne, Henry E. Bass, and Richard Raspet

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2405-2409 (1989); (5 pages) | Cited 1 time

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Relaxation of liquid CS2 following absorption of a short pulse of 337‐nm UV radiation has been experimentally observed using an optoacoustic technique. A theoretical description of the optoacoustic signal based on a delta function response formulation that accounts for multiple relaxation has been developed and computational results compared to theory. Agreement requires adopting an energy transfer scheme that includes a relatively slow rate (11×106 s−1) between initial photon absorption and transfer to translation.
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43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Accurate depth‐independent determination of acoustic backscatter coefficients with focused transducers

Timothy J. Hall, Ernest L. Madsen, James A. Zagzebski, and Evan J. Boote

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2410-2416 (1989); (7 pages) | Cited 2 times

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The accuracy of a method of data reduction for determining acoustic backscatter coefficients was tested using focused transducers and narrow‐band pulses. Two phantoms with well‐defined scattering properties were the bases of the tests, one having low attenuation and one with tissue‐mimicking attenuation. The experimentally determined backscatter coefficients were found to be independent of transducer‐to‐scattering‐volume distance and to agree very well with theoretical values, typically within 10%.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Measurements with a thick conical piezoelectric transducer

D. A. Hutchins, L. F. Bresse, and S. B. Palmer

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2417-2422 (1989); (6 pages) | Cited 1 time

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Transducers have been designed and tested based on a piezoelectric element that is 25 mm thick and conical in cross section. These devices do not require any backing, have low levels of radial mode vibration, and present a small area of contact to the surface of a solid. Theory and experiment are compared, and reasonable results are obtained.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.38.Fx Piezoelectric and ferroelectric transducers

Dynamic response of cross‐ply laminated shallow shells according to a refined shear deformation theory

J. N. Reddy and A. A. Khdeir

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2423-2431 (1989); (9 pages)

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The dynamic response of cross‐ply laminated shallow shells is investigated using the third‐order shear deformation shell theory of Reddy [J. Appl. Mech. 41, 47 (1984)]. The theory accounts for cubic variation of the in‐plane displacements through the thickness and does not require shear correction coefficients. The state‐space approach is used to develop the analytical solutions of simply supported, cross‐ply shells using the classical, first‐order, and higher‐order theories. The use of the separation of variables technique for the higher‐order theory is also presented. Numerical results of the higher‐order theory for center deflection and normal stresses of spherical shells under various loadings are compared with those obtained using the classical and first‐order [or Sanders, Q. Appl. Math. 21, 21–36 (1963)] shell theories.
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43.40.At Experimental and theoretical studies of vibrating systems
43.40.Ey Vibrations of shells

Laminated piezopolymer plates for torsion and bending sensors and actuators

C.‐K. Lee and F. C. Moon

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2432-2439 (1989); (8 pages) | Cited 7 times

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A set of piezopolymer devices has been developed based on a composite laminate theory for piezoelectric polymer materials. By using different combinations of ply angles and electrode patterns, a piezopolymer/metal shim plate structure was built that exhibited both bending and torsion deformation under an applied electric field. A set of torsion‐beam sensor structures was also built that could distinguish between bending and torsion or between different vibration modes. These devices were based on a general theory of piezoelectric laminates. The experimental results agreed quite closely with the theoretical predictions. These integrated sensor–actuator devices may find application in the control of microactuators or may be used for modal control of larger continuous structures.
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43.40.Dx Vibrations of membranes and plates
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
43.38.Fx Piezoelectric and ferroelectric transducers

The scattering of sound from fluid‐loaded plates

Douglas M. Photiadis

J. Acoust. Soc. Am. Volume 85, Issue 6, pp. 2440-2451 (1989); (12 pages) | Cited 1 time

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The scattering of sound waves from a finite strip plate under conditions of heavy fluid loading is numerically simulated. Both baffled and unbaffled geometries are considered, and results for the nearfields and farfields are obtained. Under conditions of heavy fluid loading, scattering effects due to the plate elasticity are generally small unless the excitation frequency is close to a resonance frequency of the fluid–plate system. The general behavior of the fluid–plate system and the frequencies, radiation efficiencies, widths, and strengths of the resonances are determined. With these results, one can determine the relevance of such phenomena in a variety of applications. The reliability of predictions for the resonance parameters based on simple modeling techniques is evaluated. The results indicate that the frequencies and effective masses of the resonances can be reasonably approximated. However, the radiation efficiencies are difficult to estimate because of the effects of the strong fluid loading. In the unbaffled case, modeling techniques based on vacuum mode shapes tend to substantially underestimate the radiation efficiency; in the baffled case, such techniques tend to substantially overestimate the radiation efficiency.
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43.40.Dx Vibrations of membranes and plates
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
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