Global Positioning System Reference
In-Depth Information
FIGURE 8.2.
A MEMS chip. Low power, small size, and low cost have led to many and
varied applications of MEMS technology, including acceleration and rotation sensors
in navigation instruments.
Photo by Maggie Bartlett.
from those of mechanical gyrocompasses and ring laser gyros. MEMS
devices work by converting the mechanical movement of (small) parts
within the device into an electrical signal using the piezoelectric proper-
ties of the MEMS components or else their electrical capacitance. In the
first case, we are exploiting a characteristic of some crystals (both natural
crystals such as quartz and man-made crystals) to generate an electric
charge when mechanically stressed. In the second case, the capacitance
of two small blocks of substrate material depends upon their physical
separation, and this separation changes when the substrate is accelerated
or rotated.
MEMS thus consist of a small mechanical sensor and a microprocessor
that monitors, processes, and outputs an electronic signal indicating the
existing levels of torque or acceleration. Currently, MEMS devices are not
as accurate as macroscopic measuring instruments, but they already have
many applications. MEMS gyros are employed in some automobiles to
sense yaw: if a threshold is exceeded, stability control mechanisms kick in.
MEMS accelerometers (accelerometers that measure linear acceleration)
are used in electronic games controllers, airbag deployment, inkjet print-
