Video

MR.FRequenCY(www.myspace.com/freedomskey) and Etereys(www.myspace.com/phoenixserpent) demonstrating the piezoelectric effect. PIEZOELECTRIC EFFECT [piezoelectric effect] , voltage produced between surfaces of a solid dielectric (nonconducting substance) when a mechanical stress is applied to it. A small current may be produced as well. The effect, discovered by Pierre Curie in 1883, is exhibited by certain crystals, e.g., quartz and Rochelle salt, and ceramic materials. When a voltage is applied across certain surfaces of a solid that exhibits the piezoelectric effect, the solid undergoes a mechanical distortion. Piezoelectric materials are used in transducers , e.g., phonograph cartridges, microphones, and strain gauges, which produce an electrical output from a mechanical input, and in earphones and ultrasonic radiators, which produce a mechanical output from an electrical input. Piezoelectric solids typically resonate within narrowly defined frequency ranges; when suitably mounted they can be used in electric circuits as components of highly selective filters or as frequency-control devices for very stable oscillators. www.encyclopedia.com/doc/1E1-piezoele.html Quartz (which is a single-crystal form of SiO2) has been the material of choice for stable resonators since shortly after piezoelectric crystals were first used in oscillators - in 1918. Although many other materials have been explored, none has been found to be better than quartz. Quartz is the only material known that possesses the following combination of properties: 1) It is piezoelectric ("pressure electric"; piezein means "to press" in Greek). 2) Zero temperature coefficient resonators can be made when the plates are cut along the proper directions with respect to the crystallographic axes of quartz. 3) Of the zero temperature coefficient cuts, one, the SC-cut (see below), is "stress compensated." 4) It has low intrinsic losses (i.e., quartz resonators can have high Q's). 5) It is easy to process because it is hard but not brittle, and, under normal conditions, it has low solubility in everything except the fluoride etchants 6) It is abundant in nature. 7) It is easy to grow in large quantities, at low cost, and with relatively high purity and perfection. Of the man-grown single crystals, quartz, at more than 2000 tons per year (in 1991), is second only to silicon in quantity grown. The direct piezoelectric effect was discovered by the Curie brothers in 1880. They showed that when a weight was placed on a quartz crystal, charges appeared on the crystal surface; the magnitude of the charge was proportional to the weight. In 1881, the converse piezoelectric effect was illustrated; when a voltage was applied to the crystal, the crystal deformed due to the lattice strains caused by the effect. The strains reversed when the voltage was reversed. Of the 32 crystal classes, 20 exhibit the piezoelectric effect (but only a few of these are useful). Piezoelectric crystals lack a center of symmetry. When a force deforms the lattice, the centers of gravity of the positive and negative charges in the crystal can be separated so as to produce surface charges. The piezoelectric effect can provide a coupling between an electrical circuit and the mechanical properties of a crystal. Under the proper conditions, a "good" piezoelectric resonator can stabilize the frequency of an oscillator circuit. http://www.ieee-uffc.org/freqcontrol/quartz/vig/vigqrtz.htm