Evaluation of the polarization state of integrated piezoelectric modules using the thermal wave method

In this work, we demonstrate that the thermal wave method is a promising approach for nondestructive evaluation of the polarization state of embedded piezoelectrics in integrated sensor-actuator modules. Embedded Pb(Zr,Ti)O3 (PZT) plates and fibres are subjected to periodic heating by a square wave-modulated laser array through the corresponding top layers. At low modulation frequencies, the pyroelectric response of PZT is governed by thermal losses to the embedding layers. Here, the sample behavior can be described by a harmonically heated piezoelectric plate exhibiting heat losses to the environment characterized by a continuous distribution of relaxation times. A transient thermal analysis was performed using the finite element modeling package ANSYS. Modulation frequencies for particu lar penetration depth were determined for die-casted piezoelectric modules. The average pyroelectric coefficient of piezofiber composites was measured and their thermal diffusivity was estimated by means of the frequency dependence of the pyroelectric coefficient.