Thermodynamic theory for wave guides

Abstract

The mechanical waves of an earthquake travelling in the crust of the Earth show that the material is not perfectly elastic. To study the propagation in a viscoelastic material needs a model, the parameters of which which can be fitted to the measurements. To survey the possible choices, we assume the thermodynamic theory of viscoelasticity. To get experience in the thermodynamic theory of wave propagation, the electromagnetic waves in a wave guide have been studied. The most simple model based on the hypothesis of local equilibrium turned out to be oversimplified, while extended thermodynamics and Gyarmati's wave approach of thermodynamics gave equivalent results, which can be simplified to the usual model of a wave guide without losses. Introducing several kinds of dynamic degrees of freedom, a hierarchy of models for wave guides with losses has been obtained.