Indications of Material Character from the Behavior of Diffuse Ultrasonic Fields
While concert and lecture halls have long been studied for their reverberant sound field behaviors, similar studies have begun only recently in solid bodies. Modern instrumentation is allowing the study of incoherent spectral ultrasonic energy densities in solids as they evolve in time and space. In principle this evolution can provide many indications of volume averaged material properties. These include measures of absorption (equivalent to viscoelastic moduli or other sources of internal friction), of mean free path (equivalent to attenuation due to scattering from material inhomogeneities) and of spectral densities of normal modes. It is particularly worth noting that absorption can be measured at low levels and high accuracies far beyond the sensitivities and capabilities of conventional techniques. Furthermore, attenuation as quantified by mean free paths is measurable in a high attenuation domain not otherwise accessible. The concepts, problems and potential of the technique are reviewed and a few laboratory examples presented.
KeywordsPower Spectral Density Internal Friction Diffuse Field Ultrasonic Attenuation Diffuse Wave
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