Acoustic band structures in two-dimensional phononic crystals consisting of periodic square arrays of stainless-steel cylinders in water

The present study aims to investigate experimentally and theoretically the acoustic band structures in two-dimensional phononic crystals (PCs) consisting of periodic square arrays of stainlesssteel solid cylinders with diameters of 1.0 mm in water. Two types of PCs with different lattice constants (a), 1.5 and 3.0 mm, were assembled to investigate the influence of structural parameters on their band gaps. The dispersion relations were calculated along the ΓX direction of the first Brillouin zone by using the finite element method. The experimental and the theoretical transmission coefficients were obtained for 2, 4, 6, 8, and 10 layers of cylinders along the ΓX direction. The first band gap of the PC with a = 1.5 mm was found around a frequency of 0.5 MHz while that of the PC with a = 3.0 mm was found around 0.25 MHz. Relatively wide band gaps were observed in the PC with a = 1.5 mm compared to that with a = 3.0 mm. The combination of the two different PCs in tandem with different structural parameters was demonstrated to lead to a superposition of their individual band gaps.