Two-dimensional model for acoustic absorption of viscoelastic coating containing cylindrical holes

A two-dimensional analytic model based on linear viscoelastic Kelvin-Voigt model has been established for analyzing the reflection and absorption from a coating containing periodic cylindrical holes at normal incidence. Approximating the unit of coating as hollow viscoelastic cylindrical shell, an eigen equation of the axisymmetric waves is derived. Using the boundary conditions of the front and back boundaries the expressions of resonance frequencies and reflection coefficients of coating are given. The anechoic performance at low frequencies and rigid backing has been calculated by derived formulae. The calculated results show that (1) The larger the material losses, the larger is the absorption coefficient. But the frequencies of peaks of absorption coefficient are nearly inrariable. (2) The thicker the coating, the lower is the frequencies of peaks of absorption coefficient. (3) The smaller the porosity, the higher are the frequencies of peaks of absorption coefficient and the larger is the peak of absorption coefficient.