Expansions of reflected-transmitted signals to estimate the slow wave strength in fluid-saturated porous layers

A method for estimating the strength of the slow wave in the modes propagating in porous layers is presented. It is based upon expansions on transition terms which are linear combinations of the reflection and transmission coefficients. Suitable forms of these coefficients are needed and it is shown how they can be obtained. Both open pore and sealed pore boundary conditions are investigated. It is shown that the zeroth-order and the first-order terms of the expansions suffice to describe accurately the modes and to estimate the strength of the slow wave. Approximations of the absorption coefficient by the porous layer can be deduced. Angles of incidence above and below the critical angle of the shear wave are considered. Comparisons between theory and experiments for the two types of boundary conditions are presented at normal incidence for the transition terms. (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3463816]