Evaluation of the pyroelectric response of embedded piezoelectrics by means of a Nyquist plot

In this work, we evaluate the pyroelectric response of PZT plates and rods embedded in epoxy resin, low temperature cofired ceramics and polyamide by measuring the pyroelectric current spectrum originated by temperature oscillations generated by illuminating the sample surface with a square-wave-modulated laser beam. Transfer functions H(iω) describing amplitude attenuation and phase lag at each modulation frequency were analyzed by means of a Nyquist plot. Changes in pyroelectric current amplitude and phase produced by small periodic perturbations around the equilibrium are related to thermal losses governing the return of the system to the equilibrium. This allows evaluating the thermal contact of PZT with the embedding material.