.................................................................................................
Piezoelectric Effect
Piezoelectric Effect is the ability of certain
materials to generate an electric charge in response to applied mechanical
stress.
The word Piezoelectric is derived from the Greek
piezein, which means to squeeze or press, and piezo, which is Greek for “push.”
One of the unique characteristics of the
piezoelectric effect is that it is reversible, meaning that materials
exhibiting the direct piezoelectric effect (the generation of electricity when
stress is applied) also exhibit the converse piezoelectric effect (the
generation of stress when an electric field is applied).
When piezoelectric material is placed under
mechanical stress, a shifting of the positive and negative charge centers in
the material takes place, which then results in an external electrical field.
When reversed, an outer electrical field either
stretches or compresses the piezoelectric material.
The piezoelectric effect is very useful within
many applications that involve the production and detection of sound,
generation of high voltages, electronic frequency generation, microbalances,
and ultra fine focusing of optical assemblies.
It is also the basis of a number of scientific
instrumental techniques with atomic resolution, such as scanning probe
microscopes (STM, AFM, etc).
The piezoelectric effect also has its use in
more mundane applications as well, such as acting as the ignition source for
cigarette lighters.
The History of the Piezoelectric Effect
The direct piezoelectric effect was first seen
in 1880, and was initiated by the brothers Pierre and Jacques Curie.
By combining their knowledge of pyroelectricity
with their understanding of crystal structures and behavior, the Curie brothers
demonstrated the first piezoelectric effect by using crystals of tourmaline,
quartz, topaz, cane sugar, and Rochelle salt.
Their initial demonstration showed that quartz
and Rochelle salt exhibited the most piezoelectricity ability at the time.
Over the next few decades, piezoelectricity
remained in the laboratory, something to be experimented on as more work was
undertaken to explore the great potential of the piezoelectric effect.
The breakout of World War I marked the
introduction of the first practical application for piezoelectric devices,
which was the sonar device.
This initial use of piezoelectricity in sonar
created intense international developmental interest in piezoelectric devices.
Over the next few decades, new piezoelectric
materials and new applications for those materials were explored and developed.
During World War II, research groups in the US,
Russia and Japan discovered a new class of man-made materials, called
ferroelectrics, which exhibited piezoelectric constants many times higher than
natural piezoelectric materials.
Although quartz crystals were the first
commercially exploited piezoelectric material and still used in sonar detection
applications, scientists kept searching for higher performance materials.
This intense research resulted in the
development of barium titanate and lead zirconate titanate, two materials that
had very specific properties suitable for particular applications.
Piezoelectric Materials
There are many materials, both natural and
man-made, that exhibit a range of piezoelectric effects.
Some naturally piezoelectric occurring materials
include Berlinite (structurally identical to quartz), cane sugar, quartz,
Rochelle salt, topaz, tourmaline, and bone (dry bone exhibits some
piezoelectric properties due to the apatite crystals, and the piezoelectric
effect is generally thought to act as a biological force sensor).
An example of man-made piezoelectric materials
includes barium titanate and lead zirconate titanate.
In recent years, due to the growing
environmental concern regarding toxicity in lead-containing devices and the
RoHS directive followed within the European Union, there has been a push to
develop lead free piezoelectric materials.
To date, this initiative to develop new
lead-free piezoelectric materials has resulted in a variety of new
piezoelectric materials which are more environmentally safe.
Applications Best Suited for the Piezoelectric Effect
Due to the intrinsic characteristics of
piezoelectric materials, there are numerous applications
that benefit from their use:
that benefit from their use:
High Voltage and Power Sources
An example of applications in this area is the
electric cigarette lighter, where pressing a button causes a spring-loaded
hammer to hit a piezoelectric crystal, thereby producing a sufficiently high
voltage that electric current flows across a small spark gap, heating and
igniting the gas.
Most types of gas burners and ranges have a
built-in piezo based injection systems.
Sensors
The principle of operation of a piezoelectric
sensor is that a physical dimension, transformed into a force, acts on two
opposing faces of the sensing element.
The detection of pressure variations in the form
of sound is the most common sensor application, which is seen in piezoelectric
microphones and piezoelectric pickups for electrically amplified guitars.
Piezoelectric sensors in particular are used
with high frequency sound in ultrasonic transducers for medical imaging and
industrial nondestructive testing.
Piezoelectric Motors
Because very high voltages correspond to only
tiny changes in the width of the crystal, this crystal width can be manipulated
with better-than-micrometer precision, making piezo crystals an important tool
for positioning objects with extreme accuracy, making them perfect for use in
motors, such as the various motor series offered by Nanomotion.
Regarding piezoelectric motors, the
piezoelectric element receives an electrical pulse, and then applies
directional force to an opposing ceramic plate, causing it to move in the
desired direction.
Motion is generated when the piezoelectric
element moves against a static platform (such as ceramic strips).
The characteristics of piezoelectric materials
provided the perfect technology upon which Nanomotion developed our various
lines of unique piezoelectric motors.
Using patented piezoelectric technology,
Nanomotion has designed various series of motors ranging in size from a single
element (providing 0.4Kg of force) to an eight element motor (providing 3.2Kg
of force).
Nanomotion motors are capable of driving both
linear and rotary stages, and have a wide dynamic range of speed, from several
microns per second to 250mm/sec and can easily mount to traditional low
friction stages or other devices.
The operating characteristics of Nanomotion’s
motors provide inherent braking and the ability to eliminate servo dither when
in a static position.
No comments:
Post a Comment