Page 168 - Mechanical design of microresonators _ modeling and applications

0-07-145538-8_CH04_167_08/30/05

Source: Mechanical Design of Microresonators

Chapter
4

Microbridges: Lumped-Parameter

Modeling and Design

4.1 Introduction
This chapter will analyze microbridges, which are fixed-fixed members,
as shown in Fig. 4.1. Constructively, a microbridge might be identical
to a microcantilever (or a microhinge), except for the end boundary con-
ditions, although specific designs can be utilized for either category.
Bridges are mainly implemented in micro- and nanosensing and
radio-frequency (RF) applications. Fabrication advances that permit
size reduction of bridge resonators in the nanometer realm substan-
tially improve the performance of devices that are designed to capture
the effects of extraneous mass attachment. Attogram (10 í15 g) quan-
tities deposited on chemically prepared mechanical nanooscillators can
be detected through shifts in the resonant frequencies. Simple doubly
clamped beams and paddle bridges have been utilized to monitor
1
2,3
various processes of mass addition by Ilic et al. Sekaric et al., or Evoy
4
et al. among others. Such nanodevices perform with sensitivities in the
10 í19 g/Hz domain and are capable of sensing deposition of substances
at the cellular level. More details on mass addition detection by means
of micro- and nanoresonators are given in Chap. 6.
5
One of the smallest NEMS oscillators reported, by Husain et al., is
a nanowire only 1.3 Ím long and 43 nm in diameter with a resonant
frequency of more than 100 MHz. Microbridge resonators have also
been researched from other angles to address topics such as elec-
6
tromechanical frequency tuning by Syms, mechanical optimization for

167
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.