Page 267 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

MECHANICAL SENSORS 247

detect low-energy microwave signals with a suitable design of the loop. The signal can
then be used, for example, to generate a SAW in a piezoelectric material for a wireless
mechanical sensor or simply to sense the electrical signal and pass it onto a decoder
(Figure 8.18).
As the microstrip can be made of aluminum, it is compatible with standard microtech-
nology and can be deposited along with the aluminum interconnects. However, the
microantenna can also be used as a transmitter, in which case it is acting as a radiation
microactuator.
The use of microantennae in SAW-IDT microsensors is described in Chapter 13 and
again in the concept of a smart electronic tongue in Chapter 15.
The way in which a machine interfaces with a person is important and is likely to
be a key issue in the future when microsensors and MEMS devices become smaller and
more autonomous. Therefore, the integrated microwave antenna may prove to be a very
useful tool in which a human operator can communicate with and remotely control a
small MEMS structure implanted in some inaccessible environment, such as inside the
human body!

8.4 MECHANICAL SENSORS

8.4.1 Overview

Mechanical microsensors are, perhaps, the most important class of microsensor because
of both the large variety of different mechanical measurands and their successful appli-
cation in mass markets, such as the automotive industry. Table 8.4 lists some 50 or so of
the numerous possible mechanical measurands and covers not only static and kinematic
parameters, such as displacement, velocity, and acceleration, but also physical properties
of materials, such as density, hardness, and viscosity.
Figure 8.19 shows a classification scheme for mechanical microsensors together with
an example of a device type.

Table 8.4 List of mechanical measurands. Adapted from Gardner (1994)

Acceleration Flow rate (mass) Momentum Sound level
Acoustic energy Flow rate (volumetric) Orientation Stiffness
Altitude Force (simple) Path length Tension
Angle Force (complex) Pitch Thickness
Angular velocity Frequency Position Torque
Angular acceleration Friction Pressure Touch
Compliance Hardness Proximity Velocity
Deflection Impulse Reynolds number Vibration
Deformation Inclination Roll Viscosity
Density Kinetic energy Rotation Volume
Diameter Length Roughness Wavelength
Displacement Level Shape Yaw
Elasticity Mass Shock Young's modulus