Negative refractions of acoustic waves in a two-dimensional (2D) sonic crystal were studied both experimentally and theoretically. By calculating the acoustic band structure and equifrequency surfaces, we theoretically analyzed the acoustic single-beam negative refraction in the first band operating in the ultrasonic regime. A 2D square sonic crystal was constructed with $2.0\text{−}\mathrm{mm}\text{−}\mathrm{diam}$ steel cylinders arranged as square arrays of $2.5\mathrm{mm}$ lattice constant. A scanning transmission measurement of spatial distribution was carried out to establish the acoustic refraction of a single Gaussian beam. It was demonstrated that the negative refraction is strongly dependent on both frequencies and incident angles, which shows great potential in acoustic devices.

• Received 19 July 2004

DOI:https://doi.org/10.1103/PhysRevB.72.033108