Piezoelectricity
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[edit] What is Piezoelectricity anyway??
[edit] Denotation
Piezoelectricity -(n)
(pE-A-zO-lek-'tri-s(i)tE)
The generation of electricity or of electric polarity in dielectric crystals subjected to mechanical stress, or the generation of stress in such crystals subjected to an applied voltage.
[edit] Derivation of the Word
The word piezoelectricity is derived from the Greek word piezein meaning to press or to squeeze.
[edit] Conotation
Piezoelectricity or the piezoelectric effect can be defined as a relationship between mechanical strain and voltage across the crystals' surfaces. When the crystals are compressed or pulled, if the crystal is piezoelectric, it will build up alternate charges on opposite faces, thus acting like a capacitor with an applied voltage. A current, called piezoelectricity, can then be generated between the faces of the crystal. It is this stress that causes the crystal to resonate at precise frequencies (depending on the size and cut of the crystal).
The molecules inside piezoelectric materials cause the piezoelectric effect to occur. Some of the molecules inside the materials are permanently polarized, some are positively charged and some are negative. When an electric field is applied to them, the polarized molecules align themselves with the electric field, resulting in dipoles within the crystaline structure of the material, which causes the piezoelectric effect.
http://www.mse.cornell.edu/courses/engri111/images/piezo-2.gif
The Piezoelectric Effect
[edit] How does piezoelectricity relate to my daily life...AT ALL??
[edit] Quartz
Piezoelectric crystals are more common in our daily lives than one might think. The tiny little words inscribed on the face of a watch entitled quartrz, signify that the watch contains piezoelectric crystals which release the precise frequencies (almost exactly one second apart), thus keeping the time. Quartz is a piezoelectric material, meaning that it generates an electrical charge when mechanical pressure is applied. Quartz crystals will also vibrate due to voltage from an outside source, such as a batteries in watches. During the 1920's, it was scientist W.G. Cady who recognized that due to their elastic qualities, mechanical strength and durability, quartz crystals could be used to fabricate very stable resonators. Cady also discovered that the crystals could be cut in specific ways that would create resonators of almost any frequency. Quartz crystals were first used as a time standard by Warren Marrison, who invented the first quartz clock in 1927. Juergen Staudte invented a method for mass-producing quartz crystals for watches in the early 1970s.
[edit] More Piezoelectric Materials
Piezoelectric crystals are not just used in quartz watches and in primitive sonar devices. There are many uses of piezoelectric crystals that have been invented since the time of the discovery of piezoelectric crystals in the early 1900's. Piezoelectric technology can be found in a range of items used today: high-voltage sources, actuators, sensors, frequency standards, and transducers. More familiarly, piezelectricity can be found in many facets of our daily life. In the spark ignition, tire pressure, safety alarms and sound systems of our automobiles. In ink jet printers, keyboards, and disk drives in our computers. In telephone ringers, speakers, humidifying atomizers, smoke detectors and gas ignitions in our houses. In welding, machines and flaw detection in our factories. In fetal heart monitors, blood flow diagnoses, insulin pumps and ultrasonic surgery in our hospitals. And last but not least in our sonar and ignition fuses for our military.More Piezoelectric technology The posibilities of uses for piezoelectric technology seem endless. The need for power and oscillation voltage can be so easily gained from piezoelectric materials, and can create power much more easily than using coils and capacitors.
[edit] A Brief History of Piezoelectricity
[edit] Pierre and Jacques Curie
http://nobelprize.org/physics/laureates/1903/pierre-curie.gif Pierre Curie
http://www.tau.ac.il/~phchlab/experiments/QCM/Piezoelectric_History_files/image002.jpg Jacques Curie
Two masterful scientists by their mid-twenties, Pierre and Jacques Curie discovered the basic principles of piezoelectricity. The brothers discovered piezoelectricity when Pierre was just 21, and Jacques 24. Together they discovered that when pressure is applied to crystals, they generate an electric voltage. Similarly, they reciprocate this notion when placed in electric field, the crystals became compressed. Once the brothers recognized the similarity between these two phenomena, Pierre was able to develop ideas about the vital role of symmetry within the laws of physics. The Curie brothers then invented the piezoelectric quartz electrometer, which was able to measure small electric currents. In the latter part of the 19th century the Curie brothers began to realize experimental connections between the macroscopic piezoelectric phenomena and crystallographic structure. Their experiments concluded that the measurement of surface changes were subjected to stress. The Curie brothers discovered the mutually exclusive correspondence between the electrical effects of temperature change, and the mechanical stress that was placed on a given crystal.
Pierre Curie went on to discover Polonium and Radium with a woman by the name of Marie Sklodowska, later to change her name to the more familiar Marie Curie, after they married. Along with Marie's help, they were also among the first to discover the nuclear energy emmited by Radium, and the affects of nuclear energy (experments and discoveries of which they were not credited). Marie, Jacques and Pierre's work with radioactivity led to the creation of the piezoelectric electrometer. In 1903, Pierre and Marie Curie recieved the Nobel Prize in Physics for the discoveries in radiation phonomena. Shortly after this immense honor, Pierre Curie died tragically in April of 1906 in a traffic accident in Paris.
[edit] More History of Piezoelectricity
Through a few more decades of research, the knowledge and extent of piezoelectricity skyrocketed. At the end of the 19th century and into the early 20th century, European scientists developed the original ideas of piezoelectricity further, discovering more and more properties of the phenomena. It was discovered that the crystals exhibiting the piezoelectric effect (a release of electricity from applied stress), were also exhibiting a converse piezoelectric effect (stress in response to the applied electric field). This property was mathematically subtracted from the thermodynamic principles discovered by a scientist by the name of Lippmann in 1881. This discovery lead scientists to gain more quantitative proof of the reversability of the electro-elasto-mechanical deformations in piezoelectric crystals.
The first useful developments in piezoelectric devices was the use of sonar in World War I. In the early 1900's in France, scientist Paul Langevin developed these ultrasonic detectors, or sonars. The sonars were a transducer. This transducer was made from thin pieces of quartz that were glued between two steel plates, and an attached hydrophone in order to detect the returning echo. By applying pressure on the quartz from the steel plates, a high-frequency chirp was emitted, thus giving us the ability to calculate distance based on the time it takes for the sound to return. This technology was very similar to echolocation (used by bats to determine distances. The usefulness and success of the sonar led to more scientists trying to find even more uses for piezoelectricity.
http://photos-273.facebook.com/ip005/v31/2/62/1380960008/n1380960008_30001273_8951.jpg Piezoelectric Sonar
[edit] Piezoelectric Materials
The criterion for piezoelectric materials are very simple. The material must have the ability to produce voltage output in repsonse to stress, and the ability to produce strain output in response to applied voltage. Some examples of piezoelectric materials are quartz, barium Titanate(BaTiO3), Lead Niobate(PbNb2O6, Lead Zirconate Titanate(PbZr.52Ti0.48O3), Polyvinylidene Flouride(CH2CF2, Strontium Titanate(SrTiO3),Sodium Tungstate(NaxWO3), Potassium Niobate(KNbO3), Berlinite(AlPO4) and Gallium Orthophosphate (GaPO4).
http://photos-274.facebook.com/ip005/v31/2/62/1380960008/n1380960008_30001274_7140.jpg
Traditional Structure of Piezoelectric Materials
[edit] Piezoelectric vs. Electret
The only problem with the ambiguity and simplicity in the definition of piezoelectric materials, is that they are often mistaken for materials which exhibit electret behavoirs. Materials that are labeled as electrets are usually polymers such as rubber, wool, hair and wood fibers, which are clearly not crystaline materials like piezoelectric materials are. The difference between piezoelectric materials and electret materials is that the orientation of polarization is not limited in electrets, whereas in piezoelectric materials, is it limited. Electrets are also very similar to permanent magnets, because of their usual polarization, with one side being positive, and the other being negative. What makes electrets unique, is that they are not limited to this dipole polarization, they can also be electrically charged. It is the similarity between the properties of piezoelectric matierals and electrets that sometimes causes confusion between the two.
[edit] Bone??
A very interesting point about piezoelectricity, is that it is not limited to any type of crytal. For example, bone exhibits piezoelectric properties, because of the apatite crystals present in bones. Some scientists have thought that the piezoelectric qualities of bone are the reason that bones respond to stress and why growth can be stimulated by electric fields. Bones are constantly changing and regrowing as a result of everyday stresses. Throughout a persons life, bones change shape and density, from the release of calcium to repair the bones' micro-damages. From the bones ability to repair itself, more in parts of high stress, and less in parts of low stress, it allows for hypothesis that this rebuilding quality is a direct result of the bones' piezoelectric qualities, which create calcium from electric potentials created from bones being under stress.
[edit] A Mathematical Approach
Piezoelectricity can be mathematically described in an equation, using variables (T) defining the material's stress, (S) for the material's strain, (D) for the material's charge-density displacement, and (E) for the interaction of electric fields surrounding the piezoelectric material.
http://www.efunda.com/materials/piezo/piezo_math/equations/constitutive_d.gif
This equation is one of four different arrangements of the piezoelectric constitutive law, which governs piezoelectric activities. The remainder of these equations can be found by clicking the following link for more piezoelectric equations
The overall piezoelectric equation is a compilation of many different equations. The derivation stems from the equations governing the variables that make up piezoelectricity. The beginnings of the piezoelectric equation start from the mechanical aspect of piezoelectricity:
http://www.efunda.com/materials/piezo/piezo_math/equations/hookes_law.gif
This equation is simply Strain = Compilance x Stress.
Since piezoelectric crystals are also affected by electricity, an electric component must be added to the equation:
http://www.efunda.com/materials/piezo/piezo_math/equations/constitutive_dielectric.gif
This equation explains that Charge Density = Permetivity x Electric Field.
Thus, from the assimilation of the two equations results in this constitutive equation: http://www.efunda.com/materials/piezo/piezo_math/equations/constitutive_d.gif This equation is necessary when analyzing piezoelectricity, because it incorporates the mechanical and the electric aspects that make up piezoelectricity. There is no other way to describe piezoelectricity without using an equation that incorporates both the electric aspects and the mechanical aspects. Piezoelectricity is a very mathematically complex concept, because it involves aspects of more than one type of measurement.
[edit] References and Resources
1. Image of Jacques Curie
2. Image of Pierre Curie
3. Mathematics in Piezoelectricity
4. Definition of Piezoelectricity
5. Uses of Piezoelectricity
6. Image of Piezoelectric Effect
7. Piezoelectric Materials
8. Scientific Standards for Piezoelectric Materials
9. History of Curie Brothers
10. More History of the Curie Brothers
11. Extremely Thorough Look At Piezoelectricity
12. Image of Piezoelectric Structure
