Finite element modeling analysis of photostrictive materials use in optical actuator for microdevices

Photostrictive materials are ferrodielectric ceramics that have a photostrictive effect. Photostriction is a phenomenon in which strain is induced in the sample by incident light. In principle, this effect arises from a superposition of the photovoltaic effect, i.e. the generation of large voltage from the irradiation of light, and the converse-piezoelectric effect, i.e. expansion or contraction under the voltage applied. When non-centrosymmetric materials, such as ferroelectric single crystals or polarized ferroelectric ceramics, are uniformly illuminated, a high voltage, considerably exceeding the band gap energy, is generated. Along with this photovoltage, mechanical strain is also induced due to the converse piezoelectric effect. Photostrictive materials are (Pb, La)(Zr, Ti) O₃ ceramics doped with WO₃, called PLZT, exhibit large photostriction under uniform illumination of high-energy light. Traditional transducing actuators such as shape memory alloys and electroceramics (piezoelectric and electrostrictive) have been used for active structural vibration control. But the main drawback of these traditional actuators is that they require hard-wired connections to transmit the control signals. As a result, due to the existence of external electromagnetic fields, the metallic signal wires introduce electrical noise into the control signals. On the other hand photostrictive materials offer the potential for actuators with many advantages over conventional electromechanical actuators, such as noncontact actuation, remote control, and immune from electric/magnetic disturbances. They have potential use in numerous MEMS devices where actuation of microbeams is a common phenomenon. The objective of this project is to develop and analyze a finite element model to study the feasibility of photostrictively-driven actuators for excitation of microdevices. Much work has been done toward developing microdevices which are capacitively driven or piezoelectrically driven. The author has developed a computational method useful for design of systems incorporating thin film photostrictive actuators. The element has been implemented in an inhouse finite element code. The effect of different parameters such as actuator thickness, incident light intensity and convective heat transfer coefficient in the actuation of beam using the thin film photostrictive actuators has been investigated. In this current work, derived finite element for static analysis of photostrictive thin films has been used to investigate the application of photostrictive actuators for different structure and various boundary conditions of microbeams with various actuator location and length. A successful conclusion of these tasks will affirm the potential of the technology for use in actual microdevices.