On the boundary conditions for acoustic waves at a solid–solid or fluid–solid interface

The boundary conditions at a solid–solid interface are analyzed in the transition from a solid–solid interface to a liquid–solid interface. This transition is mathematically performed by means of a limit process, that is, by letting the Lame shear coefficient of one medium tend to zero. The behavior of the reflection coefficient for transverse waves in the transition can be derived from the boundary conditions. In particular, a linear shear‐velocity dependence of its magnitude has been found. As a consequence, the magnitudes of the other reflection and transmission coefficients are also linear. Numerical calculations of the coefficients have been performed. The results confirm the theoretical analysis and point out some critical angles where the linear trend does not occur.