“…First, in Section 6, the main feature is that the damping is concentrated and, therefore, the limit problem is a wave equation with boundary feedback boundary condition; in particular, the damping acts only on the boundary in the limit. In such a situation the type of approximating problems we consider, appear naturally in control theory/stabilization of waves, see [15,44,59,47,48], or in homogenization of vibration problems with inclusions near the boundary, see [51,28,29,17] and references therein. On the other hand, the limit problem appears in the boundary control theory, see [40,41,39,67,50,19] and references therein.…”