Applications
A piezoelectric system can be constructed for virtually any
application for which any other type of electromechanical
transducer can be used. For any particular application, however,
limiting factors include the size, weight, and cost of the
system. Piezoceramic devices fit into four general categories:
generators, sensors, actuators, and transducers. Characteristics
of each group are briefly summarized here.
Generators
Piezoelectric ceramics can generate voltages sufficient to spark
across an electrode gap, and thus can be used as ignitors in
fuel lighters, gas stoves, welding equipment, and other such
apparatus. Piezoelectric ignition systems are small and simple
-- distinct advantages relative to alternative systems that
include permanent magnets or high voltage transformers and
capacitors.
Alternatively, the electrical energy generated by a
piezoelectric element can be stored. Techniques used to make
multilayer capacitors have been used to construct multilayer
piezoelectric generators. Such generators are excellent solid
state batteries for electronic circuits.
Sensors
A sensor converts a physical parameter, such as acceleration or
pressure, into an electrical signal. In some sensors the
physical parameter acts directly on the piezoelectric element;
in other devices an acoustical signal establishes vibrations in
the element and the vibrations are, in turn, converted into an
electrical signal. Often, the system provides a visual, audible,
or physical response to the input from the sensor -- automobile
seatbelts lock in response to a rapid deceleration, for example.
Actuators
A piezoelectric actuator converts an electrical signal into a
precisely controlled physical displacement, to finely adjust
precision machining tools, lenses, or mirrors. Piezoelectric
actuators also are used to control hydraulic valves, act as
small-volume pumps or special-purpose motors, and in other
applications. Piezoelectric motors are unaffected by energy
efficiency losses that limit the miniaturization of
electromagnetic motors, and have been constructed to sizes of
less than 1 cm3. A potentially important additional advantage to
piezoelectric motors is the absence of electromagnetic noise.
Alternatively, if physical displacement is prevented, an
actuator will develop a useable force.
Transducers
Piezoelectric transducers convert electrical energy into
vibrational mechanical energy, often sound or ultrasound, that
is used to perform a task.
Piezoelectric transducers that generate audible sounds afford
significant advantages, relative to alternative electromagnetic
devices -- they are compact, simple, and highly reliable, and
minimal energy can produce a high level of sound. These
characteristics are ideally matched to the needs of
battery-powered equipment.
Because the piezoelectric effect is reversible, a transducer
can both generate an ultrasound signal from electrical energy
and convert incoming sound into an electrical signal. Some
devices designed for measuring distances, flow rates, or fluid
levels incorporate a single piezoelectric transducer in the
signal sending and receiving roles, other designs incorporate
two transducers and separate these roles.
Piezoelectric transducers also are used to generate
ultrasonic vibrations for cleaning, atomizing liquids, drilling
or milling ceramics or other difficult materials, welding
plastics, medical diagnostics, or for other purposes.
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