Absorption of Supersonic Waves in Water and in Aqueous Suspensions

Abstract

The absorption of supersonic waves in both water and in an aqueous suspension of lycopodium spores was measured at seven different frequencies ranging from 990 kilocycles to 2500 kilocycles in approximately equal steps. A piezoelectric quartz plate was used in each case as a sound source and was driven by an electron-coupled oscillator and two-stage amplifier capable of yielding 100 watts. The radiation pressure of the sound waves against a cone suspended in the field was measured directly with a chainomatic balance. The differences in the absorption coefficients found for lycopodium suspension and for water were compared with the classical theoretical expectation as derived by Sewell. These differences approach more nearly the theoretical value as the frequency increases. This may be due to the relative nonrigidity of the spores at lower frequency-a situation which would violate the theoretical boundary conditions.