Page 322 - Mechanics of Microelectromechanical Systems

5. Static response of MEMS 309

Figure 5.43 Maximum axial displacement of a fixed-free microbar as a function of the
extension load according to: (a) large-deformation theory; (b) small-deformation theory

The two plots of Fig. 5.43 show the tip displacements according to the
large-deformation theory – Fig. 5.43 (a) – and the small-deformation theory –
Fig. 5.43 (b) –, both in terms of the applied force. It can be noticed that the
predictions of the small-displacement theory are always higher than the ones
of the large-displacement theory –up to more than twice for large axial forces.
Many MEMS do deform by means of beam-like structures, and there are
situations where such members are subject to large deformations.

Figure 5.44 Cantilever with tip force producing large deformations

Figure 5.44 shows a microcantilever that is subject to large deformations
under the action of a tip force F. It can be seen that, unlike in the small-
displacement theory – where it is assumed that the projection of the bent