A Sonic Crystal

A sonic crystal is to sound waves in air what a photonic crystal is to light waves or a semiconductor is to electrons-it permits the passage of waves at some energies but not others. Scientists in Spain (contact Francisco Meseguer Rico, fmese@fis.upv.es, 349-6387-9841; Jose Sanchez Dehesa, jsdehesa@upvnet.upv.es) are the first to use a sonic crystal, an arrangement made of aluminum rods (see figure), as an acoustic lens for focusing sound waves at audible frequencies. They also create thereby an interferometer which, like its lightwave counterpart, causes two wavetrains of soundwaves to interfere with each other in a characteristic pattern. (Cervera et al., Physical Review Letters, 14 January 2002.)