Large band gaps in elastic phononic crystals with air inclusions

We find that a large absolute band gap can be created by inserting air inclusions in a two-component elastic phononic crystal with small density contrast and filling fraction. The positions of the insertion are chosen to suppress the shear potential energy of the first optical band and lower their frequencies. This is demonstrated in a two-dimensional system consisting of aluminum cylinders in a triangular lattice with a filling fraction of 0.145 embedded in an epoxy host. Both the band structure and the transmission calculations show that the insertion of air cylinders in the earlier system is capable of creating a large elastic band gap with gap/midgap ratio Deltaomega/omega(c)=0.53. Such a system makes the realization of a light and effective sonic insulator possible. (C) 2003 American Institute of Physics.