Viscothermal wave propagation, including acousto-elastic interaction

Abstract

Standard wave equation models neglect the effects of viscosity and thermal conductivity on acoustic wave propagation. For wave propagation in narrow tubes or thin layers, like in MEMS devices, this might not be accurate. This presentation outlines models that take the effects of inertia, viscosity, thermal conductivity and compressibility into account. Three classes of models are described and characterized based on the use of dimensionless parameters. The most important parameter is the shear wave number, an unsteady Reynolds number that indicates the ratio between inertial and viscous effects. It is shown that for most applications the low reduced frequency model is sufficient and the most efficient. The wave propagation models are coupled to the structural models to capture the acousto-elastic interaction. For simple geometries, analytical solutions can be found for these coupled analysis cases. For more complex geometries, a finite element model was developed, based on the low reduced frequency model, in which viscothermal acoustic finite elements are coupled to structural elements. Examples of applications are presented.