On Propagation of Discontinuity Waves in Thermo-Piezoelectric Bodies

With regard to a body composed of a linear thermo-piezoelectric medium, referred to a natural configuration, we consider processes for it constituted by small displacements, thermal deviations and small electric fields superposed to the natural state. We show that any discontinuity surface of order r 1 for the above processes is characteristic for the linear thermo-piezoelectric partial differential equations. We show that discontinuity surfaces of order 0 generally are not characteristic; hence the conditions are written which characterize the discontinuity surfaces of order 0 that are characteristic