Page 78 - Mechanics of Microelectromechanical Systems

Chapter 2

MICROCANTILEVERS, MICROHINGES,
MICROBRIDGES

1. INTRODUCTION

This chapter studies the microcantilevers, the microhinges and the
microbridges, which are MEMS components that can operate either
individually – with no other accompanying structural component – or can be
incorporated into more complex configurations. Essentially, all three
components are designed to deform either in bending or torsion about a
sensitive axis, but in actuality they are also subject to other deformations
(called parasitic because they alter the intended functionality) such as those
produced by axial forces, shearing forces or bending moments about
directions other than the main sensitive axis. These microcomponents are
one-dimensional members with either fixed-free boundary conditions (such
as the microcantilevers and microhinges) or fixed-fixed boundary conditions
(such as the microbridges). In other words, the very same geometrical
configuration can function in either one of the three categories mentioned
here, subject to different boundary conditions and overall structure of a
specific mechanism. They can operate as sensors (the microcantilevers
particularly), actuators (both the microcantilevers and microbridges) or as
simple flexible joints in compliant microdevices (such as the case is with the
microhinges).
The three categories are defined here in terms of their relevant stiffnesses
and/or compliances according to the generic procedure outlined in the
previous chapter. Designs from each category are specifically analyzed and
discussed based on concrete and fully-solved examples. A section with
problems to be solved completes this chapter. Although the prefix micro
might seem redundant (and sometimes the structural dimensions can reduce
to the nanometer level, case where nano would work better), the micro
denomination will be kept here as in microcantilevers, microhinges and
microbridges, which is also the terminology used in the specialty literature.