Fast acoustic modes guided by multilayered solid structures

Layered waveguides are shown to support the propagation of non-radiating acoustic modes with the velocity exceeding that of both the quasitransverse bulk waves in the external solid medium, where the waveguide is immersed. An analytical criterion has been derived for the existence of these fast waves in a three-layered waveguide. Numerical computations have been performed for a number of structures. According to our computations, monolayered waveguides can also support the propagation of fast modes under particular conditions.