Propagation and reflection of harmonic waves in a plane acoustic layer with non-homogeneous flexible walls

A plane acoustic layer bounded by elastic membranes, one of which has an insert with different material properties, is considered. The propagation and reflection of harmonic waves in such a layer is studied. The source of vibrations is an incident mode, coming from infinity. The solution in three regions (before the insert, under the insert, after the insert) is sought as modal expansion. The numerical results for the reflected power coefficient are presented.