Slow group velocity propagation of sound via defect coupling in a one-dimensional acoustic band gap array

Abstract

A simple experimental system is presented in which the group velocity of acoustic wave packets traveling in an air-filled waveguide can be slowed to values much smaller than the speed of sound in air. The experiment is an acoustic analog of the much-studied optical phenomenon of slow light propagation. Slow (or even stopped) light propagation has been observed in atomic vapors in the vicinity of strong dispersion, typically associated with electromagnetically induced transparency. In the acoustic experiment described here, strong dispersion is produced by the introduction of a defect in an otherwise perfectly periodic one-dimensional acoustic band gap array. The defect produces a narrow transmission band within the forbidden acoustic band gap region resulting in strong dispersion. By tuning the carrier frequency of the acoustic wave packet to the peak transmission of the defect, the group velocity can be slowed to 0.24vs, where vs is the speed of sound in air. These results are shown to be consistent with theoretical calculations.