Page 299 - Mechanics of Microelectromechanical Systems

286 Chapter 5
whereas the similar motion of the microdevice of Fig. 5.19 (b) is:

Similarly, the linear motion of the proof mass of Fig. 5.19 (b) about an in-
plane direction x is:

Example 5.11
Compare the sensitivities of the two microaccelerometers shown in Fig.
5.19 (a) and (b) by considering they have identical proof masses and flexure
hinges.

Solution:
The sensitivity of an accelerometer can be defined as the ratio of
displacement to the (inertial) force, namely:

By way of Eqs. (5.56) and (5.57) it follows that the sensitivities of the two
microaccelerometers relate as:

which indicates that the three-flexure microaccelerometer is approximately
33% more sensitive than its four-flexure counterpart.

5. DISPLACEMENT-AMPLIFICATION
MICRODEVICES

This section discusses lever-based and sagittal displacement-
amplification microdevices by analyzing their performance criteria, the most
important being the displacement amplification ratio.

5.1 Lever-based Displacement-Amplification Microdevices

Displacement-amplification microdevices are designed based on the
principle illustrated in Fig. 5.20. The actuation force F works against the
torsional spring of stiffness and produces the rotation angle which is,
according to the moment balance, equal to: