Sonic Band Structure in Fluids with Periodic Density Variations

In direct analogy to the electronic band structure found in semiconductors andthe photonic bands for light in a medium with a periodic dielectric constant, a periodic density variation in a fluid can give rise to sonic frequency passbands and band gaps. Hence, a fluid medium can be constructed that prohibits ound propagation at certain frequencies while allowing practically free propagation at others. The effect of a sonic band medium on a monopole acoustic source is discussed in a simple one-dimensional model. In particular, the complete quenching ofradiated power is seen for a harmonic radiator at a frequency that corresponds to a band gap--in analogy with a similar effect that is predicted for the atomic emission ofelectromagnetic waves in a photonic band structure. The ability to construct a medium that selectively prohibits sound propagation a d emission i a certain range of frequencies, while allowing transmission and enhanced radiation rates at others, could have interesting practical applications.