Sonic band‐gap materials as acoustical components

Sonic band‐gap (SBG) crystals can be made by periodic distributions of scatterers. In particular, it was found that two‐dimensional (2D) arrays of rigid cylinders in air do have acoustic band gaps that could be of application in acoustic devices related to control and filtering of sound. Here, it is pointed out that this type of SBG crystal can be used as custom‐made acoustical components in the linear region well below the gap. This idea is supported by the fact that sound velocities in these materials are smaller than that of air. Also, it was previously measured that their transmittance is high; i.e., they exhibit low reflectance [J. V. Sanchez‐Perez et al., Phys. Rev. Lett. 80, 1208–1212 (1998)]. Both features guarantee the practicality of sonic crystal lenses and other optical components. Finally, 2D SBG crystals based on triangular and square arrays are classified as acoustically uniaxial or biaxial. [Work supported by CICyT of Spain.]