Traditional piezoelectric actuators have been a mainstay in numerous applications such as precision positioning systems, sonar and medical ultrasound imaging. More recently, new types of piezoelectric actuators have been developed, including transverse mode actuators such as THUNDER and flexible actuators like Micro-fiber composites (MFC). Yet, many aspects of these actuators are still not well understood and have not been adequately modeled. We will present some Finite Element models that represent the manufacturing process of THUNDER actuators as well as their response to DC electric fields and compare the model to experimental results. In addition, we will present experimental results of THUNDER response to AC fields at or near the fundamental resonance frequency. We will compare the results to a nonlinear theory originally developed for piezodriven cantilevers for atomic force microscopes (AFM). Finally, we will briefly mention an aeronautical application of MFC actuators.