De-ageing of 1-3 piezocomposites by thermal cycling and degradation due to encapsulation

The effect of thermal cycling on certain dielectric, piezoelectric and mechanical properties of 1–3 piezocomposites is studied. In each cycle, the samples are heated to 100° C for 6 hrs and allowed to cool naturally to room temperature. Electrical admittance spectra are recorded after each cycle and the material parameters are estimated by non-linear regression analysis. The material parameters of the 1–3 piezocomposite, namely, K ^s ₃₃ , k _t , c ^D ₃₃ , tan δ, e ₃₃ , d ₃₃ and C ^E ₃₃ are found to vary initially for low number of thermal cycles and tend towards constant values as the number of cycles is increased. This suggests that the piezocomposite materials undergo de-ageing with thermal cycling. Prolonged heating of 1–3 piezocomposites at 70°C severely degrades their characteristics and results in catastrophic failure at 100°C. During the process of encapsulation, curing of Polyurethane at temperature of about 70°C for extended periods is found to adversely affect the characteristics of 1–3 piezocomposite transducers. These studies give insight into the limiting factors that can prevent degradation in performance of 1–3 piezocomposite transducers under certain situations where they are subjected to thermal cycling and prolonged exposure to high temperatures during operation.