Abstract

Acoustic waves are the physical manifestation of mechanical vibrations traveling through a medium. These wave propagations can be described with physical attributes, such as phase, wavelength, amplitude, and velocity. The velocity of an acoustic wave can be determined by two material properties of the propagation medium: the bulk modulus and the density. Specifically, the squared phase velocity of an acoustic wave equals the bulk modulus multiplied by the inverse of the density. For all natural medium, positive bulk modulus and density are observed. The recent development of acoustic metamaterials demonstrate media that exhibit either a negative bulk modulus, a negative density, or both negative bulk modulus and negative density. As the fundamental physics of these metamaterials become better understood, researchers are beginning to develop applications of these materials.