A study is made to determine the frequency and concentration dependence of the ultrasonic absorption in aqueous suspensions of (1) scenedesmus and diatoms, two forms of algae, and (2) artemia (brine shrimp) eggs. The measurements were made over a frequency range of 125 kc/sec to 55 Mc/sec. The excess absorption caused by scenedesmus is found to be linearly dependent on concentration and has a value of α/f2=7×10 16 m−1 sec2 for the highest concentration measured, 0.72 g/liter of water. The excess absorption caused by diatoms is also linearly dependent on concentration and has a value of 25×10−15 m−1 sec2 for 290 g/liter of water, the highest concentration measured. For both scenedesmus and diatoms, it is concluded that the normal concentration of these forms of algae found in large bodies of water causes negligible absorption compared to the absorption of the water itself. The major portion of the excess attenuation due to the shrimp eggs in the kilocycle region is attributed to a scattering mechanism. Application of a theory for elastic scattering in this wavelength region (ka<1) gave good agreement with experimental results. A phase-velocity investigation of a resonance phenomenon at 7 Mc/sec revealed a characteristic velocity dispersion.
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Watson et al. (1963) studied this question.