885095938

THURSDAY AFTERNOON, 2 MAY 1991

CARROLL, 1:00 TO 5:00 P M.

Session 7PA

Physical Acoustics: Propagation and Radiation

Victor Sparrow, Chair

Graduate Program in Acoustics, Pennsylmnia State Uniuersity.    157 Hammond Building, Uniuersity Park,

Pennsyluania 16802

Contributed Papers

1:00

7PA1. Reflection and transmission of spherical waves incident on a concentric spherical interface. David T. Blackstock (Appl. Rcs. Lab. and Mech. Eng. Dept., The Univ. of Te.xas at Austin, Austin, TX 78713-8029) and Christopher L. Morfey (The Univ. ofTexas at Austin, Austin, TX 78713-8029 and Univ. of Southampton, Southampton, Hampshire S09 5NH, England)

The traditional analysis of sound reflection and transmission at an interface between Iwo losslcss fluids is for piane waves and a piane interface. Considered here is reflection and transmission of a spherical wave at a concentric spherical interface, either concave or convex. The pressure reflection (R) and transmission (T) coefficients are found to be complex; the coefficients for a convex interface are complex conju-gates of those for a concave interface. Among the (somewhat surpris-ing) results are these. First, although at high frequency the expressions for R and Tare the same as for piane waves, at Iow frequency /? — — 1 regardless of the value of the ratio p₂c₂/p,c, (provided p₂^p,). Second, perfect transmission rcquires both p₂=pi and c₂=c,, not just p₂c₂=p,c,. Third, if the source is a monopole and the interface radius a—0, the sound power transmitted into the second medium is that expected for a single fluid; the same is not truć, howcvcr, if the source is a dipole. [Work supportetl by ONR, NASA, and Southampton Uni-versity.)

1:15

7PA2. Effect of dispersion on a piane ultrasonic pulse. Christopher L. Morfey" (Inst. of Sound and Vibration Rcs., Univ. of Southampton, Southampton S09 5NH, U.K.)

Propagation through typical biologicai media involves dispersion as well as attcnuation. sińce the attenuation coefłicicnt varies with fre-quency morę slowly than /^: in the ultrasonic rangę. Dispersion effects are explored for piane pulses in a homogeneous medium. The smoothing of an initially steplike pulse as it propagates through different attenuat-ing media is illustrated numerically. Pulse waveforms are compared with and without allowance for dispersion, using a family of model a{J) curves. The associated dispersion in each case is obtained from the Kramers-Kronig relations, which ensure that the propagation transfer function iscausal. ^a,On leave 1990-91 at PennsyWania State Univ._t Ctr. for Acoust. and Vib. and Univ. of Texas at Austin, Appl. Res. Lab., Austin. TX 78713-8029.

1:30

7PA3. Measuring the frequency-dependent ultrasonic attenuation of liquids with a pulse transmission method. Peng Jiang and Robert E. Apfcl (Dept. of Mech. Eng., Yale Univ., P.O. Box 2159, New Haven, CT 06520)

1971 J. Acoust. Soc Am., Vol. 89, No. 4, Pt. 2, ApriI 1991

To measure the ultrasonic attenuation of a lossy liquid or liquid mixture, an experiment setup using a pulse transmission method has been developed. The setup consisls of a focused transmitting transducer, a measurement celi, which is used to hołd the liquid, a PVDF receiver, a preamplifier, and a digital scope. It has several advantages ovcr other methods usually employed in attenuation measurement. Compared with or = 0.109y¹ measured by ultrasonic interferometer [G. S. Verma, J. Chem. Phys. 18, 1352-1354 (1950)], the attenuation of olive oil is found to be fitted by either a = 0.103/^{2 0,1} or a = 0.111/ ⁾⁵ⁱ, where a is the attenuation in dB/cm and / the frequency in MHz. The error sources in the method are analyzed both theoretically and experimen-tally. The attenuation of some liquids and liquid mixtures is given. The potential use of the setup in industry and medicine is discussed. (Work supported by the National Institutes of Health through Grant No. 5ROICA39374]

l.*45

7PA4. Acoustic Bloch wave energy transport and group velocity. Charles E. Bradley and David T. Blackstock (Appl. Res. Lab., The Univ. of Texas at Austin, P.O. Box 8029, Austin, TX 78713-8029)

The relationship between the steady-state ratę of energy transport and the group velocity is investigatcd for acoustic Bloch waves in a periodic waveguide. A lime-average energy flux relation is derived and used to find the energy transport velocity for an arbitrary periodic waveguide. An apparent disparity between the energy transport velocity and the power delivery is discussed. The group vclocity is derivcd using a Bloch wave generalization of the usual Fourier transform method and is shown to be equal to the ratę of energy transport. The integral transform method works well for the boundary salue problem as the associated Bloch wave transform is relatively straightforward. The initiaJ value problem, however, involves the inoerse Bloch wave transform, the problems associated with which are discussed. (Work supported by the Office of Naval Research.]

2:00

7PA5. Surface roughness induced attenuation of ultrasonic waves transmitted through a liquid-solid interface at oblique incidence. Peter B. Nagy (The Ohio State Univ._f 190 W. !9th Ave., Columbus, OH 43210)

Scattering of ultrasonic waves at a randomly rough liquid-solid in-terfacc has been studied for a long time and continues to be of consid-erable interest. Most previous efforts were directed at studying the dif-fuse reflection from rough surfaces while much less is known about the

121st Meeting: Acoustical Society of America 1971