Dynamic Behavior of Particulate Viscoelastic Composites for Sound Absorption

摘要

We have developed a general frequency-dependent theory for the effective material properties (i.e., sound speed, attenuation, bulk, dilatational and shear moduli, etc.) of viscoelastic (i.e., sound absorbing) substances which contain ensembles of gas-filled cavities--assumed spherical for this analysis--of various concentrations and size distributions. The method accounts for the frequency dependence of the effective properties in a fundamental way based on the first principles of Mechanics, that permits the study of resonance effects present in all the spectra of all the effective properties we have determined. The method accounts for the primary interactions of the incident wave with all the cavities, although for the concentration levels considered here, re-scattering and multiple interaction between the various cavities have an effect of secondary magnitude. Our method accounts for the presence of any arbitrary level of dilatational and/or shear viscous absorption in the matrix (the fluid inclusions are assumed lossless) in a fundamental way emerging from basic viscoelastic continuum models such as Kelvin-Voight's. Numerous calculations have been generated at various absorption levels and for cases where the cavities are either all of the same uniform size or when they follow some simple size distribution function.