J. Adach et al., ULTRASONIC PROPAGATION, SCATTERING, AND DEFOCUSING IN SUSPENSIONS, The Journal of the Acoustical Society of America, 93(6), 1993, pp. 3208-3219
Fine resolution narrow-band pressure amplitude distribution measuremen
ts have been performed using a hydrophone in the field of a weakly foc
used bowl transducer radiating into castor oil and 1 % and 2 % by volu
me suspensions of 320-mum polystyrene beads in castor oil over the fre
quency range 1.0 to 2.5 MHz at 20-degrees-C. The axial distributions p
ermitted determination of the excess attenuation due to scattering in
the suspensions as a function of frequency. The frequency range includ
ed a resonance. The excess attenuation measured was compared with the
theoretical predictions of Waterman and Truell [J. Math. Phys. 2, 512-
537 (1961)] and good agreement was obtained. The values of the excess
attenuation obtained were used to predict axial pressure amplitude dis
tributions in the suspension. Although the excess attenuation was dete
rmined from far-field measurements, the agreement between the predicte
d axial distributions and those measured experimentally extended well
into the near field. Lateral distributions were measured at seven freq
uencies at the position of the geometrical center of curvature of the
source and at the position of the true focus in the 1% suspension. Com
parison with similar scans in castor oil alone revealed no detectable
defocusing due to the presence of the scatterers.