Spatial and Temporal Absorption in a Viscous Medium.

The relation between spatial and temporal absorption for acoustic waves in a viscous medium is discussed by considering the problem of a viscous-liquid filled tube with a piston at one end and a reflecting termination. The solution of the problem is found in terms of traveling waves from image sources, and standing waves in a tube. The phase velocity and attenuation of the steady-state terms for both solutions are the same. The transient part of the standing wave solution gives rise to the usually plotted velocity and temporal attenuation; it is shown that these do not have the same meaning as in the spatial absorption case, since they depend upon the allowed wave numbers of the system, that is, upon the geometry and boundary condition. [ABSTRACT FROM AUTHOR]