5-Piezoelectric materials:
5.1-Introduction: (abstract):
Is the charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity
means electricity resulting from pressure. The piezoelectric effect is understood as the linear electromechanical interaction
between the mechanical and the electrical state in crystalline materials.
The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal
generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect (the
internal generation of a mechanical strain resulting from an applied electrical field).
Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages,
electronic frequency generation, microbalances, and ultrafine focusing of optical assemblies. It is also the basis of a number of
scientific instrumental techniques with atomic resolution, the scanning probe microscopes such as STM, AFM, MTA, SNOM,
etc., and everyday uses such as acting as the ignition source for cigarette lighters and push-start propane barbecues.
Gautschi, G (2002). Piezoelectric Sensorics: Force, Strain, Pressure, Acceleration and Acoustic Emission Sensors, Materials and
Amplifiers.. Springer.
5.2-Discovery and early research
The pyroelectric effect, by which a material generates an electric potential in response to a temperature change,
was studied by Carl Linnaeus and Franz Aepinus in the mid-18th century.
Drawing on this knowledge, both René Just Haüy and Antoine César
Becquerel posited a relationship between mechanical stress and electric
charge.
The first demonstration of the direct piezoelectric effect was in 1880 by the brothers
Pierre Curie and Jacques Curie. They combined their knowledge of pyroelectricity
with their understanding of the underlying crystal structures that gave rise to
pyroelectricity to predict crystal behavior, and demonstrated the effect using
crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt (sodium
potassium tartrate tetrahydrate). Quartz and Rochelle salt exhibited the most
piezoelectricity.
For the next few decades, piezoelectricity remained something of a laboratory curiosity. More work was done to explore and
define the crystal structures that exhibited piezoelectricity.
Lippman, G. (1881). "Principe de la conservation de l'électricité" (in French). Annales de chimie et de physique 24: 145.
5.3-Mechanism:
The nature of the piezoelectric effect is closely related to the occurrence of electric dipole moments in solids. The latter
may either be induced for ions on crystal lattice sites with asymmetric charge surroundings (as in BaTiO3 and PZTs) or may
directly be carried by molecular groups (as in cane sugar).
Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but
can be aligned using the process of poling (not the same as magnetic poling), a process by which a strong electric field is
applied across the material, usually at elevated temperatures. Not all piezoelectric materials can be poled.
Of decisive importance for the piezoelectric effect is the change of polarization P when applying a mechanical stress. This
might either be caused by a re-configuration of the dipole-inducing surrounding or by re-orientation of molecular dipole
moments under the influence of the external stress. Piezoelectricity may then manifest in a variation of the polarization
strength, its direction or both, with the details depending on:
1. the orientation of P within the crystal,
2. crystal symmetry and
3. the applied mechanical stress. The change in P appears as a variation of surface charge density upon the crystal faces.
S. Trolier-McKinstry (2008). "Chapter3: Crystal Chemistry of Piezoelectric Materials". In A. Safari, E.K. Akdo˘gan. Piezoelectric
and Acoustic Materials for Transducer Applications. New York: Springer. ISBN 9780387765389.
5.4-These are some videos about the piezoelectric effect:
http://www.youtube.com/watch?v=Xuw9frP1GNo&feature=endscreen&NR=1
http://www.youtube.com/watch?v=RCOBA3Yfm1k&feature=endscreen&NR=1
5.5-Examples of some piezoelectric materials:
Naturally occurring crystals
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Berlinite (AlPO4), a rare phosphate mineral that is structurally identical to quartz.
Sucrose (table sugar).
Quartz.
Rochelle salt.
Topaz.
Tourmaline-group minerals.
Quartz
Topaz
Sucrose
5.6-Applications:
5.6.1-Surgery:
A recent application of piezoelectric ultrasound sources is piezoelectric surgery, also known as piezosurgery.
Piezosurgery is a minimally invasive technique that aims to cut a target tissue with little damage to neighboring
tissues. For example, Hoigne et al.Reported its use in hand surgery for the cutting of bone, using frequencies in the
range 25–29 kHz, causing microvibrations of 60–210 μm. It has the ability to cut mineralized tissue without cutting
neurovascular tissue and other soft tissue, thereby maintaining a blood-free operating area, better visibility and
greater precision.
Manbachi, A. and Cobbold R.S.C. (November 2011). "Development and Application of Piezoelectric Materials for
Ultrasound Generation and Detection". Ultrasound 19 (4): 187–196. doi:10.1258/ult.2011.011027.
5.6.2-Infertility treatment:
In people with previous total fertilization failure, piezoelectric activation of oocytes together with intracytoplasmic
sperm injection (ICSI) seems to improve fertilization outcome.
Baltaci V, Ayvaz OU, Unsal E, et al. (May 2009). "The effectiveness of intracytoplasmic sperm injection combined
with piezoelectric stimulation in infertile couples with total fertilization failure". Fertil. Steril. 94 (3): 900–4.
doi:10.1016/j.fertnstert.2009.03.107. PMID 19464000.
5.6.3-Reduction of vibrations and noise
Different teams of researchers have been investigating ways to reduce vibrations in materials by attaching piezo
elements to the material. When the material is bent by a vibration in one direction, the vibration-reduction system
responds to the bend and sends electric power to the piezo element to bend in the other direction. Future applications
of this technology are expected in cars and houses to reduce noise.
In a demonstration at the Material Vision Fair in Frankfurt in November 2005, a team from TU Darmstadt in
Germany showed several panels that were hit with a rubber mallet, and the panel with the piezo element immediately
stopped swinging.
Piezoelectric ceramic fiber technology is being used as an electronic damping system on some HEAD tennis rackets.
"Isn’t it amazing how one smart idea, one chip and an intelligent material has changed the world of tennis?". HEAD. Retrieved
2008-02-27.
5.6.4-Frequency standard
The piezo-electrical properties of quartz are useful as standard of frequency.
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Quartz clocks employ a crystal oscillator made from a quartz crystal that uses a combination of both direct
and converse piezoelectricity to generate a regularly timed series of electrical pulses that is used to mark time.
The quartz crystal (like any elastic material) has a precisely defined natural frequency (caused by its shape
and size) at which it prefers to oscillate, and this is used to stabilize the frequency of a periodic voltage
applied to the crystal.
The same principle is critical in all radio transmitters and receivers, and in computers where it creates a clock
pulse. Both of these usually use a frequency multiplier to reach gigahertz ranges.
5.6.5-Piezoelectric motors
A slip-stick actuator.
Types of piezoelectric motor include:
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The traveling-wave motor used for auto-focus in reflex cameras
Inchworm motors for linear motion
Rectangular four-quadrant motors with high power density (2.5 watt/cm3)
and speed ranging from 10 nm/s to 800 mm/s.
 Stepping piezo motor, using stick-slip effect.
All these motors, except the stepping stick-slip motor work on the same
principle. Driven by dual orthogonal vibration modes with a phase difference of
90°, the contact point between two surfaces vibrates in an elliptical path,
producing a frictional force between the surfaces. Usually, one surface is fixed causing the other to move. In most
piezoelectric motors the piezoelectric crystal is excited by a sine wave signal at the resonant frequency of the motor.
Using the resonance effect, a much lower voltage can be used to produce a high vibration amplitude.
Stick-slip motor works using the inertia of a mass and the friction of a clamp. Such motors can be very small. Some
are used for camera sensor displacement, allowing anti shake function.
Many other applications such as:
5.6.6-Actuators
5.6.7-High voltage and power sources
5.6.8-Sensors
Ana gayeb kolo mn el Wikipedia
http://en.wikipedia.org/wiki/Piezoelectric_material
This page was last modified on 16 February 2012 at 20:08.
Abdallah ismail Mohamed bayomy
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