Large acoustic band gaps created by rotating square rods in two-dimensional periodic composites

Effects of orientations of square rods on the acoustic band gaps in two-dimensional periodic arrays of rigid solid rods embedded in air are studied. The acoustic band gaps will be opened and enlarged greatly by increasing the rotation angle. For any filling fraction F, the maximum acoustic band gaps appear at the same rotation angle θ = 45° for the cases of F⩽0.50, otherwise they will appear at different limit values θ_c and the largest band gap is achieved at a filling fraction of about F = 0.85. This gap-tuning effect will be stronger with increase in filling fraction. This tuning mechanism of band gap suggests a new way to design band gaps of two-dimensional phononic crystals.