Abstract :
Cavity modes for the single-cavity and the double-cavities in two-dimensional phononic crystal are studied by using a plane waves expansion supercell method. We show that the single-cavity behaves like an atom while the double-cavities behave like a molecule. Couplings of cavity modes with the waveguide modes are investigated for typical configurations. Suitably designed waveguides with introduced cavities might be used as acoustic filter in waveguide applications.