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FIGURE 20.16 MEMS comb actuator uses electrostatic actuation. (Courtesy of Sandia National Laboratories,
MEMS and Novel Si Science and Technology Department, SUMMIT Technologies, www.mems.sandia.com.)

Electrostatics—Electrical Field
Since electrical fields have lower energy density than magnetic fields, typical applications of electrical field
forces are limited to measurement devices and accelerating charge particles, where the required energy
density is small. Recently, with the proliferation of microfabrication technology, it is possible to apply
the small electrostatic forces to microelectromechanical actuators, such as comb actuators (see Fig. 20.16).
The advantage of electrostatic actuation is the higher switching rate and less energy loss as compared to
the electromagnetic actuation. However, the limitation in force, travel, and high operating voltage still
needs to be addressed. Electrostatic actuation is the main actuation for moving charged toner particles
in electrophotographic (xerographic) processes, e.g., laser printers.

Piezoelectric
Piezoelectric is the property of certain crystals that produces a voltage when subjected to mechanical
deformation, or undergoes mechanical deformation when subjected to a voltage. When a piezoelectric
material is under mechanical stress, it produces an asymmetric displacement in the crystal structure
and in the charge center of the affected crystal ions. The result is charge separation. An electric potential
proportional to the mechanical strain can be measured. This is called the direct piezoelectric effect.
Conversely, the material will have deformation without volume change when electric potential is
applied. This reciprocal piezoelectric effect can be used to produce mechanical actuation. There are two
categories of piezoelectric materials: sintered ceramics, such as lead-zirconate-titinate (PZT), and
polymers, such as polyvinylidence fluoride (PVDF). Piezoceramics have a larger force output and are
used more as actuators. PVDFs tend to generate larger deformation and are used more for sensor
applications.

©2002 CRC Press LLC