Design and processing of multi-layered flextensional piezoelectric actuators

Piezoelectric actuators are unique to other actuator systems due to their fast response time (∼10-4 s) and displacement accuracy on the order of a nanometer. Piezoelectric strain is obtained with the application of an electric field. Useful applications include adaptive optical systems and active vibration dampening. One type of piezoelectric actuator is the flextensional device, which requires a gradient in electromechanical properties to create a bending moment through non-uniform lateral stresses. The simplest flextensional device, called the unimorph, is a piezoelectric bonded to a metal plate. The bond between piezoelectric and metal is subjected to stresses that can lead to lifetime limitations. Fabrication requires cutting, polishing, and bonding, which does not facilitate miniaturization and curved shell structures. The monomorph and RAINBOW are modifications of the unimorph that seek to improve upon these drawbacks.; The monomorph is comprised of one plate of normally insulating piezoelectric that is made semiconductive with a dopant. With an applied field, a non-uniform electric-field distribution arises due to the semiconductor-electrode interface. Removal of the difficult tasks of surface preparation and bonding are processing advantages that better enable component miniaturization. RAINBOW removes potential interface problems of bonding dissimilar materials together by creating a metal-ceramic layer within the piezoelectric ceramic by chemically reducing the oxygen content. The processing methods of the monomorph and RAINBOW are limited since they can only create one functional gradient. Our work sought to create a modification of the unimorph with the capability for miniaturization while maintaining the positive attributes of the previously mentioned technologies.; Called PrinDrex, named for the collaborative effort between Princeton and Drexel Universities, we construct functional gradients by layering different ceramic-polymer tapes in an appropriate order. We construct 'custom-made' actuators by layering ceramics with different piezoelectric constants and electrical properties. After sintering this fully ceramic laminate only requires electrode application and poling to function. No post-sintering steps are required, which better enables the fabrication of large and small devices. PrinDrex is capable of generating displacements and forces equivalent to the best commercially available flextensional devices. We characterized with electron microscopy and modeled and predicted actuator performance with finite element analysis.