A simple thermal wave method for the evaluation of the polarization state of embedded piezoceramics

In this work, we demonstrate that the thermal wave method is a promising approach for non-destructive evaluation of polarization state of embedded piezoelectrics in integrated sensor–actuator modules. The embedded piezoceramics are subjected to periodic heating by a square wave-modulated laser array through the top layers. A transient thermal analysis was performed using the finite element modeling package ANSYS. The ANSYS simulation reveals the presence of a transient heating-up period before reaching steady state. Inside the PZT piezoceramics, the thermal excitation becomes nearly sinusoidal and shifted in phase as known for harmonic excitation. At low modulation frequencies, the pyroelectric response of the embedded Pb(Zr,Ti)O3 plates 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 single thermal relaxation time enabling an estimation of the thermal conductance at the interfaces of the embedded piezoelectric.