טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentElka Eyal
SubjectThe Electromechanical Response of Multi-Layered
Piezoelectric Structures
DepartmentDepartment of Mechanical Engineering
Supervisors Professor David Elata
Professor Haim Abramovich


Abstract

In recent years new technologies enable the deposition and integration of advanced piezoelectric thin films into MEMS devices. Piezoelectric microstructures have become a building block in MEMS and have many applications. The electromechanical response of piezoelectric structures is complex as it involves a mechanical response, an electrostatic response, and a mutual coupling between the mechanical and electrical domains.

In this work, the constitutive equations of multi-layered piezoelectric structures are derived in an original form that provides new insight. In this form, the electromechanical coupling is presented as an additional stiffness matrix.  This matrix is a true property of the piezoelectric structure and is independent of specific mechanical boundary conditions that may apply to the structure. A novel model of the electromechanical response of such structures is presented.  This model accounts for the 3D kinematics of the structure deformation. Specifically, the new model emphasizes the double curvature induced by the internal moment that characterizes piezoelectric structures. Solution of example problems using the new model shows excellent agreement with 3D finite element simulations.  These solutions are also compared with the results of previous model approximations presented in literature. The inaccuracies associated with these previous models are discussed and it is shown the 2D approximations are deficient. Moreover, it is clearly shown that in contrast to prevalent conviction, the 2D approximations of plane strain and plane stress are not bounds of the exact 3D response.

Deflections of a piezoelectric micro structure were measured and demonstrate the potential of achieving large deflections using piezoelectric actuation. Various optimizations of the structure deflection are considered, and a method for additional deflection enhancement of already optimal structures is proposed.