Attenuation of Ultrasonic Waves in Suspensions of Viscoelastic Spheres

Abstract

The attenuation of ultrasonic waves for suspensions of polymethyl methacrylate particles (mean radius a =ca. 40µ) in ethyl alcohol, carbon tetrachloride and their mixtures are measured in the range of frequency 1–6 Mc/s. For k a >0.5 ( k =2π/wave length) the scattering and reflection losses are found to be predominant origins of the attenuation. But when k a approaches unity, the observed attenuation lies markedly below the prediction from Rayleigh's formula which is established under the condition of k a ≪1. For k a <0.5, the viscous loss predicted by Lamb and Urick and the loss due to the internal viscosity of suspended particles become appreciable. A simple theory for the latter loss is developed under some assumptions. The sum of the theoretical values of these three kinds of losses is in satisfactory agreement with the experimental one. In the frequency range where the internal loss predominates, the method employed in this research can be used to measure the volume viscosity of a solid material.