Characterization and modeling of local electromechanical response in stress-biased piezoelectric actuators

Numerous investigators have explored the factors that contribute to the high electromechanical performance of stress-biased actuators with particular attention being given to the importance of the extrinsic (domain wall translation) response mechanism. Based on the variation in lateral stress through the thickness of the piezoelectric layer within these devices, it has been suggested that the piezoelectric coefficient varies as a function of position within the layer, though no direct evidence has been previously presented. In this study, the results of Moire interferometry investigations of local strains within these devices are reviewed. The technique permits effective depth-profiling of local deformations at reasonably high (0.25 /spl mu/m) resolution. A least squares regression analysis approach was used in conjunction with classical laminate theory and free edge effects to fit this experimental data to depth-dependent piezoelectric response. As expected, higher d-coefficients were predicted for the upper free surface of the device compared to the interface with the stainless steel substrate. The predicted values were in general agreement with expectation and are further considered from the perspective of recent reports in the literature regarding multi-axial loading effects on the electromechanical properties of lead zirconate titanate-based piezoelectric ceramics.