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The piezoelectric actuator is a form of micro-control electro-mechanical system. It relies on the piezoelectric effect with some crystals such that, when an electrical field is applied to the crystal, it creates mechanical stress in its structural lattice which can be translated into movement at a micrometer or nanometer scale. Types of actuators can range from heavy industrial systems that are powered by pneumatic or hydraulic force down to small piezoelectric actuators, which have a very limited but precisely-controlled range of movement. A typical piezoelectric actuator will generate longitudinal movement when electrical force is applied to the unit of a shaft or other mechanical linkage with a displacement range of around 4 to 17 microns (0.0002 to 0.0007 inches). This type of actuator system is often incorporated into a strain gauge also known as an extensometer, which is used to measure very fine levels of contraction and expansion in materials and surfaces.
There are three general types of piezoelectric actuator designs or movement schemes that determine the unique range of piezoelectric actuator parts that make up the mechanical movement of the device. These are cylindrical, bimorph, and unimorph, or multilayer actuators, and each also has a mode designation that is dependent on the type of piezoelectric coefficient for mechanical stress that is induced. A multilayer 33-mode actuator is designed to generate movement along the path of the applied electric field, whereas a cylindrical 31-mode actuator exhibits movement perpendicular to the electric force. A 15-mode actuator utilizes shear strain in the crystal for diagonal force, but they are not as common as other types of piezoelectric actuator, as shear strain is a more complex crystal reaction that is difficult to control and for which to manufacture systems.
The purpose for which a piezoelectric actuator is used is usually based on the fact that is can have a mechanical response to electrical force in a fraction-of-a-second time frame, as well as not generate significant electromagnetic interference in its operation. This includes common use for the components in tunable lasers and various adaptive optics sensors, as well as micro-level control of valves where the flow rate of fuel is critical for the amount of thrust generated, such as in fuel injection systems and avionics controls. The piezoelectric actuator also has many uses in the field of medicine where it is built into micro-pumps for procedures such as dialysis and automated drug dispensers or droplet dispensers. Research arenas also depend on the piezoelectric actuator, such as where it is an essential component of the atomic force microscope (AFM) in the field of nanotechnology.
Other advanced fields of research that utilize the piezoelectric actuator include precision machining, astronomy controls for telescopes, biotechnology research, as well as semiconductor engineering and integrated circuit manufacturing. Some of these fields require a piezoelectric actuator that can control movement ranges down to the level of 2 microns (0.0001 inches) in a time period of less than 0.001 seconds. The piezoelectric actuator is an optimal device for such applications as well because it has several unique characteristics including very low power consumption, it generates no magnetic fields, and it can operate at cryogenic temperatures. Probably the greatest useful feature of the device, however, is that it is a solid-state device that requires no gears or bearings, so that it can be repeatedly operated up to billions of times without showing evidence of performance degradation.
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