Experimental study of directed band gaps of 2D phononic crystal consisting of steel cylinders in water with square lattice

Based on the ultrasonic immersion transmission technique,the directed band gaps of two-dimensional(2D) phononic crystal consists of a square array of steel cylinders in water were measured experimentally along the Γ-X and Γ-M directions of first irreducible Brillouin zone.The relations of layers and first band gaps stability can be analyzed in detail.This is better advantage of design for finite-sized 2D phononic crystal or acoustic devices.An excellent agreement between the frequency range of overlapping transmission spectra of acoustic waves and complete band gap of 2D phononic crystal for theoretical predict with plane wave expansion method is observe.