Phase Transition and Acoustic Localization in Arrays of Air-Bubbles in   Water
  Wave localization is a ubiquitous phenomenon. It refers to situations that transmitted waves in scattering media are trapped in space and remain confined in the vicinity of the initial site until dissipated. Here we report a phase transition from acoustically extended to localized states in arrays of identical air-filled bubbles in water. It is shown that the acoustic localization in such media is coincident with the complete band gap of a lattice arrangement of the air-bubbles. When the localization or the band gap occurs, a peculiar collective behavior of the bubbles appears. 
Zhen Ye and Haoran Hsu