Band gaps and localization in acoustic propagation in water with air cylinders

Multiple scattering of waves leads to many peculiar phenomena such as compl ete band gaps in periodic structures and wave localization in disordered me dia. Within a band gap, excitations are evanescent; when localized, they re main confined in space until dissipated. Here, we report acoustic band gap and localization in a two-dimensional system of air cylinders in water. Exa ct numerical calculations reveal the unexpected result that localization is independent of the precise location or organization of the scatterers. Loc alization occurs within a finite region of frequencies, coincident with the complete band gap for a periodic lattice of scatterers. Inside the gap or localization regime, a previously uninvestigated collective behavior of the cylinders appears. (C) 2000 American Institute of Physics. [S0003-6951(00) 05052-X].