Acoustic metamaterials of sonic crystals

Acoustic wave exhibits inherently different characters when propagating in sonic band-gap materials. We address negative refractions of acoustic wave both experimentally and theoretically in two dimensional sonic crystals constructed with steel rods embedded in air. With lattice symmetry and artificial ldquoatomsrdquo designing, refraction of acoustic wave in the crystals could be manipulated from positive to negative and from defocusing to focusing with sonic crystal plates. Analogous to enhanced transmission of optical wave, enhanced acoustic wave transmission through narrow slit smaller than wavelength has been established as well, which is modeled as the coupling of surface waves and cavity mode in the slits. These abnormal behaviors show that sonic crystal is emerging as a kind of acoustic metamaterials.