Characteristics of the localized modes in 2D phononic crystal with heterostructure point defect

A heterostructure point defect is constructed based on replacing one circular scatter cylinder with one square scatter cylinder in two-dimensional square arrays of circular aluminum cylinders embedded in an air host. Its localized mode characteristics have been studied by using the plane-wave expansion method in combination with a supercell technique and the sonic pressure distribution of the localized modes is also calculated. The results indicate that the localized modes of the heterostructure point defect appear in the gap. The position and number of the localized modes changes with the rotation and filling fraction of the heterostructure point defect. The pressure distribution of localized modes is decided by its position in the gap. The characteristics controlling the localized modes, based on changing the angle and size of the heterostructure point defect, are expected to have broad applications in directional sonic filters and narrow band sonic waveguides.