Ultrasonic Absorption and Velocity in Water Containing Algae in Suspension

A study is made of the ultrasonic absorption and velocity of longitudinal waves in water containing suspended algae in order to determine the effect of biological suspensions on sound propagation. The ratio α/f² is found to be independent of frequency and is linearly dependent on algae concentration. These results indicate that scattering is not a mechanism for absorption and also shows that there is negligible interaction between particles. It was also found that the excess loss due to algae had the same temperature dependence as the shear viscosity. However the magnitude of the excess absorption calculated from the shear viscosity is insufficient to account for the total loss. Assuming that the structural viscosity of the liquid is increased by either the presence of the suspended material modifying the structural viscosity of the pure liquid, or by a structural viscosity associated directly with the cell, it is found that the increase in structural viscosity is 44 times the increase in shear viscosity for a given increase in concentration.