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transmitted component that plays a very important role in ultrasonic nondestructive evaluation of materiał properties. A comprehensive ex-perimental study has been conducted to measure the surface roughness induced attenuation of ultrasonic waves transmitted through liquid-solid interfaces at obliąue incidence. Sand and shot-blasted aluminum samples with 5- to 50-//m rms roughness were used to determine the frequency spectrum of the transmitted beam between 2 and 20 MHz. A simple first-order ph&se perturbation technique [Nagy and Adler, J. Acoust. Soc. Am. 82, 193 (1987)] was extended for oblique incidence to derive approximate analytical formulas for the frcqucncy and angular dependence of the surface roughness induced attenuation of the coher-ently transmitted field. Good agreement was found between these analytical predictions and the mcasured experimental data. Further im-provements are cxpected from cornparing the data to morę sophisticated theoretical techniques adapted to the case under consideration. [Work supported by NSF under contract ECD-9008272.]

2:15

7PA6. On the liquid-wedge technique to generate Scholte-Stoneley waves. F. Luppe (LAUE, U.R.A. CNRS 1373, Universitć du Havre, Place R. Schuman, 76610 Lc Havre Cedex, France), J. Doucet, and M. de Billy (GPS, Universite Paris 7, France)

The liquid-wedge technique is described in the case of the generation of a Scholte-Stoneley wave on a water-aluminum interface with the use of an alcohol wedge. Tłie exact conditions under which the desired Scholte-Stoneley wave is actually generated are reviewed. In particular, spccial attention has to bc given to the selection of the incidence anglc given by the Snell-Descartes laws, the relative position of the transducer with respect to the wedge, and the hydrostatic condition relating the alcohol height to the one of water, which ensures a good coupling. Measurements are presented, and the damping of a 2-MHz Scholte-Stoneley wave propagating over a 400-mm distancc on a water-aluminum interface is invcstigated and compared to theoretical calcu-lations. Results of a theoretical study, done by L. Sebbag, of the reflection coefficient of an either homogeneous or cvanesccnt piane wave on an alcohol-aluminum-water interface are aLso presented. Thcy con-firm the actual generation of the Scholte-Stoneley wave at the water-aluminum interface. [This work has been done at Paris 7 Uoiversity and supported by French D.R.ET.]

2:30

7PA7. Acoustic scattering from porous aggregates. Kavitha Cłiandra and Charles Thompson ' (Dept. of Elec. Eng., Lab. for Advanced Computation, Univ. of Lowell, Lowell, MA 01854)

The interaction of acoustic waves in a two-phase biological medium characterized by randomly oriented porous aggregates is examined by direct solution of the integral equation representing the scattered and propagating field. The Bom senes is shown to converge in the limit as the compressibility variation is of order zero. However, pathological conditions exhibit a high degree of porosity requiring Solutions to be carried out in the high compressibility limit. This results in a divergence of the perturbation series. By considering the Bom series in an asymp-totic sense, we obtain Solutions by applying the optimal truncation rule and in extreme cases by an analytic continuation beyond the region of convergence by the method of Pade approximants. The present problem is of interest, in that angular measurements of the scattered field around the sample provides estimates of the characteristic porę sizes of the biological sample examined.

2:45

7PA8. Determination of transient acoustic wave fields in continuously layercd media using the modified Cagniard method. Martin D. Vcrwcij and Adrianus T. de Hoop (Lab. of Electromag. Res., Dept. of Elec. Eng., Delft Univ. ofTechnol., P.O. Box 5031, 2600 GA Delft, The Netherlands)

A combination of the Neumann series solution and the modified Cagniard method is used to derive a theoretically exact space-time do-main solution for the 3-D acoustic wave propagation problem in continuously layered media. In view of the application of a time lepiące transformation with a real positive transform parameter, the conver-gencc of the iterative Neumann scheme for an arbitrary continuously layered configuration is guaranteed, both in the transform domain and in the space-time domain. The iterates, which represent successively reflected waves, are transformed back to the space-time domain using the modified Cagniard method. Using this method, continuously layered configurations with relatively large horizontal source/recciver distances lead to an unconventional type of integration contour. In contrast to the standard angular wave number/frequency domain analysis, difficultics due to “tuming rays” can be avoided. The inverse transformation procedurę is demonstrated for the direct wave and the wave due to single partial reflections. Numerical results for these wave constituents are presented.

3:00-3:15

Break

3:15

7PA9. Statistical description of ray diffusion in random inhomogeneous media. Alexander I. Saichev and Yevgeny G. Shchemelev (Dept. of Radiophysics, Nizhnj Novgorod State Univ., Gagarin 22, Nizhnj Novgorod 60332, USSR)

The ray approach is often used when coordinates and incoming angles for waves, propagating through smooth inhomogencities, are an-alyzed. The probability density for coordinates and angles of rays with

1972 J. Acoust. Soc. Am., Vol. 89, No. 4, Pt. 2, April 1991 fixed ray lenglhs is determined by a diffusion equation. But if the solution of the diffusion equation is known it is impossible to give an answer about statistical properties of the incoming angle fluctuations at the point of reception. The cause of this is that the length of rays received at the fixed point is not known. This problem is especially important when the smali angle approach is violated. The probability density determination for ray length and incoming angles in the fixed point is needed here. The derivation of this probability density is suggested for determination of the statistical properties of the rays in the receiving piane.

121st Meeting: Acoustical Society of America 1972