Page 205 - Mechanics of Microelectromechanical Systems

192 Chapter 4

Figure 4.11 Bent beam versus straight bar in terms of bloc force as a function of inclination
angle and length

Figure 4.12 Bent beam versus straight bar in terms of bloc force as a function of leg’s width

2.3 Two-Beam Thermal Actuator

A two-beam thermal actuator is sketched in Fig. 4.13 (a) consisting of
two parallel beams of dissimilar lengths and a connecting rigid link. When
the longer beam is heated‚ its free thermal expansion is prevented by the rigid
connecting link as well as by its own fixed end.
The resulting deformed shape‚ which is sketched in Fig. 4.13 (b)‚ is
produced by bending of both the thermally-active (long) beam and the
passive (short) one. The geometric parameters defining this actuator system
are given in Fig. 4.14. The result of prevented thermal expansion can be
modeled by a force which is applied parallel to the heated beam at its end‚
and which is given in Eq. (4.2). As mentioned previously‚ the free
displacement and the bloc force fully defined the performance of a thermally-
driven fixed-free bar.