Deciphering the scattering code contained in the resonance echoes from fluid-filled cavities in solids.

From the echoes of elastic waves incident on inclusions in solids, one may extract certain resonance features. These "spectral lines" and their widths form a code identifying the material composition of the inclusion in a way that resembles spectroscopy. This idea finds applications in geophysics, materials science, and any field dealing with materials containing inclusions.