Elastic wave band gaps for three-dimensional phononic crystals with two structural units

We investigated the absolute elastic wave band gaps in three-dimensional systems consisting of steel inclusions embedded in plastic matrix. Numerical results show that the configurations formed by inserting an additional steel object (either a sphere of different size or a cube) into each unit cell of a simple cubic structure with spherical steel inclusions, exhibit larger absolute elastic wave band gaps compared with the original simple cubic structure. However, for simple cubic structures originally consisting of steel cubes embedded in plastic matrix, it shows inserting additional cubes results in smaller band gaps