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Principles of Microelectromechanical Systems by Ki Bang Lee

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CHAPTER 8

PIEZOELECTRIC AND THERMAL ACTUATORS

In previous chapters we described the principles for micro- and nanosystems: the statics and dynamics of flexible and rigid elements, fluid dynamics, and electromagnetics. Since MEMS are systems in which mechanical and electrical components are combined for specific purposes (e.g., actuating mechanical components, and sensing physical quantities), the mechanical and electrical behavior of the combined components must be investigated to design actuators and sensors and to conduct further research on MEMS. In MEMS, most actuators used for actuating mechanical components are also used for sensing physical quantities. We describe piezoelectric and thermal actuators in this chapter, and electrostatic and electromagnetic actuators are covered in Chapter 9.

8.1 COMPOSITE BEAMS

In Chapters 3 and 4 we described the static and dynamic behavior of beams made of uniform material. In some MEMS, composite elements, which are made of more than one material, are also used (e.g., bimetals actuated by temperature change and piezoelectric cantilever beams driven by an electric field). To analyze actuators using composite beams, we must find relations between the driving forces (e.g., the temperature for bimetals) and the responses (e.g., deflection). Let us begin by considering the straight composite beam shown in Fig. 8.1a, which consists of two different materials of different Young’s moduli, E1 and E2, and whose cross section is symmetric about the ...

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