Page 184 - MEMS Mechanical Sensors

CHAPTER 8
Inertial Sensors

8.1 Introduction

Micromachined inertial sensors are a very versatile group of sensors with applica-
tions in many areas. They measure either linear acceleration (along one or several
axes) or angular motion about one or several axes. The former is usually referred to
as an accelerometer, the latter as a gyroscope. Until recently, medium to high per-
formance inertial sensors were restricted to applications in which the cost of these
sensors was not of crucial concern, such as military and aerospace systems. The
dawn of micromachining has generated the possibility of producing precision iner-
tial sensors at a price that allows their usage in cost-sensitive consumer applications.
A variety of such applications already exists, mainly in the automotive industry for
safety systems such as airbag release, seat belt control, active suspension, and trac-
tion control. Inertial sensors are used for military applications such as inertial guid-
ance and smart ammunition. Medical applications include patient monitoring, for
example, for Parkinson’s disease. Many products, however, are currently in their
early design and commercialization stage, and only one’s imagination limits the
range of applications. A few examples are:

• Antijitter platform stabilization for video cameras;
• Virtual reality applications with head-mounted displays and data gloves;
• GPS backup systems;
• Shock-monitoring during the shipment of sensitive goods;
• Novel computer input devices;
• Electronic toys.

Clearly, micromachined sensors are a highly enabling technology with a huge
commercial potential. The requirements for many of the above applications are that
these sensors be cheap, can fit into a small volume, and their power consumption
must be suitable for battery-operated devices. Micromachined devices can fulfill
these requirements since they can be batch-fabricated and they benefit from similar
advantages as standard integrated circuits.
Tables 8.1 and 8.2 give an overview of some existing and future applications for
accelerometers and gyroscopes, respectively. Typical values for required band-
width, resolution, and dynamic range are quoted (these are provided for approxi-
mate guidance only).
As can be seen from the tables, the typical performance requirements for each
application are considerably different. This implies that it is highly unlikely that

173