Effects of electrodes and protective layers on the electromechanical characteristics of piezoelectric stack actuators

Piezoelectric stack actuators are a type of excellent smart devices that can activate large power and displacement outputs due to their unique stack configuration and have been widely used in linear vibrators for various engineering applications. For the fabricated piezoelectric stack actuator, it usually consists of multiple thin piezoelectric wafers, multiple electrodes, and two protective layers. All the piezoelectric wafers are connected electrically in parallel through the electrodes and are protected by two protective layers at the two ends. However, in most of the theoretical models, the active piezoelectric portion is mainly considered, while the electrodes and protective layers are usually neglected to simplify the complicated problem, which results in an inaccurate prediction of the electromechanical characteristics. In our previously published work, the exact theoretical models of the piezoelectric stack energy harvester and sensor with the electrodes and the protective layers included have been established successfully to evaluate the electromechanical performance of these two types of devices, and their validity has verified by the experimental results. However, the exact theoretical model of the piezoelectric stack actuators has not been established, and the effects of the electrodes and the protective layers on the electromechanical characteristics of the actuator are not fully understood. In this article, the exact theoretical model of piezoelectric stack actuator was derived based on our previous work, and the effects of these two factors on the electromechanical characteristics were investigated. Comparisons with the results in the earlier literatures and the experimental results were presented to validate the model. Furthermore, two kinds of typical working states, including clamped-free (C-F) and free-free (F-F), were discussed. The results showed that neglecting the electrodes and the protective layers will greatly affect the accuracy of the prediction model, thus providing some valuable guidelines in designing the piezoelectric stack actuators.