The plane waves in pyroelectric medium

The propagation of waves in an infinite pyroelectric medium is studied in this paper. The governing equations for the pyroelectrics are written in the compact algebraic form. Four characteristic wave velocities are found, three being analogous to those of elastic waves and the fourth wave, which is predominantly a temperature disturbance, corresponding to the heat pulse known as the second sound. From computing example for BiTiO₃ it is found that all the velocities and attenuation coefficients are related to the wave normal and the material constants. The effect of the electric properties on the wave propagation is considered, which indicates that the temperature wave is not sensitive to pyroelectricity and piezoelectricity in the discussed case. The effects of the terms containing relaxation time on the attenuation are researched in detail in one-dimensional case, where 11 cases are discussed. It is found that larger relaxation time affects the wave more; the electric relaxation could be ignored in real situation, while the elastic relaxation and heat inertia are considerable; the heat inertia term can amplify the mechanical wave and its role is opposite to the elastic and pyroelectric damping terms.