Piezoelectric phenomena

The piezoelectric crystals are patterned with two excitation electrodes (electronic surface films) on their opposite sides. Due to the converse piezoelectricity phenomenon, when -> alternating voltage is applied to the attached electrodes mechanical oscillations occur within the crystal lattice. These oscillations are stable only at the natural resonant frequency of the crystal. 

The observations and researches of rock fracture electromagnetic radiation (EME) were carried out earlier in China and the former Soviet Union. In 1953 Guevara Pavlovic, Pal Mainbranch(° experimentally recorded and studied granite, gneiss and quartz piezoelectric phenomenon and the light... 

Bent-core liquid crystal elastomers have shown to exhibit large values of flexoelectricity as many as three orders of magnitude larger than liquid crystal elastomers containing rod-shaped molecules [44]. These high responses are attributed to a piezoelectric phenomenon. Liquid crystal elastomers combine elasticity and flexibility inherent to rubbers and the optical and electrical properties of liquid crystals, and are promising materials for applications such as electrooptics, flexible electronics, and actuator technologies for biomedical applications. 

The piezoelectric phenomenon could be described as one of the substantial discoveries of the 19th century. The term piezo is derived from the Greek word piezein, meaning pressure (Kholkin et al., 2008). Piezoelectricity is electricity produced due to pressure exerted on a piezoelectric material. 

The piezoelectric response investigation also provides direct evidence that significant inelastic deformation and defect generation can occur well within the elastic range as determined by the Hugoniot elastic limit. In quartz, the Hugoniot elastic limit is 6 GPa, but there is clear evidence for strong nonideal mechanical and electrical effects between 2.5 and 6 GPa. The unusual dielectric breakdown phenomenon that occurs at 800 MPa under certain... 

In this chapter studies of physical effects within the elastic deformation range were extended into stress regions where there are substantial contributions to physical processes from both elastic and inelastic deformation. Those studies include the piezoelectric responses of the piezoelectric crystals, quartz and lithium niobate, similar work on the piezoelectric polymer PVDF, ferroelectric solids, and ferromagnetic alloys which exhibit second- and first-order phase transformations. The resistance of metals has been investigated along with the distinctive shock phenomenon, shock-induced polarization. 

Piezoelectricity is also a natural by occurring phenomenon in the human body. Studies have shown... 

These two anciently served as a means of ignition. They still can. Although the sparking of flint and steel is strictly a mechanical phenomenon, any subsequent fires will not be. Other forms of silica still serve as igniters to this day, via the piezoelectric effect. 

In situations where absorption of the incident radiation by the transducing gas is troublesome a piezoelectric transducer (made from barium titanate, for example) can be attached to the sample (or sample cuvette in the case of liquids) to detect the thermal wave generated in the sample by the modulated light (8,9). The low frequency, critically damped thermal wave bends the sample and transducer thus producing the piezoelectric response. The piezoelectric transducer will also respond to a sound wave in the solid or liquid but only efficiently at a resonant frequency of the transducer typically of the order of 10 to 100 KHz (see Figure 4). Thus neither in the case of microphonic nor piezoelectric detection is the PA effect strictly an acoustic phenomenon but rather a thermal diffusion phenomenon, and the term "photoacoustic" is a now well established misnomer. 

Electrostriction. As distinct from inverse piezoelectric effect, electrostriction is a phenomenon in which the strain and the electrical field inducing the strain are related by Sy = where My are electrostriction coefficients. Several relaxor... 

When a polymer film is deformed sinusoidally with time with an angular frequency to, an open-circuit voltage or a short-circuit current of the same frequency is observed across the electrodes on both surfaces of the film. This phenomenon is called the piezoelectricity of the film. The deformation is usually the elongational vibration along an axis in the film plane and sometimes the bending vibration. 

When the film is short-circuited and heated to high temperatures at which the molecules attain a sufficiently high mobility, a current is observed in the external circuit. This phenomenon is called pyroelectric effect, thermally stimulated current, or, when the film has been polarized by a static field prior to measurement, depolarization current. The conventional definition of pyroelectricity is the temperature dependence of spontaneous polarization Ps, and the pyroelectric constant is defined as dPJdd (6 = temperature). In this review, however, the term will be used in a broader definition than usual. The pyroelectric current results from the motion of true charge and/or polarization charge in the film. Since the piezoelectricity of a polymer film is in some cases caused by these charges, the relation between piezoelectricity and pyroelectricity is an important clue to the origin of piezoelectricity. 

The piezoelectric effect has been shown to exhibit a relaxational nature and the complex piezoeletric constant is a function of frequency and temperature. In Group (A), the relaxation is ascribed to either the nature of the crystallite itself or the viscoelasticity of the amorphous phase in which the crystallites are embedded. In the former case, the piezoelectric relaxation is a cross-coupling phenomenon of dielectric relaxation and mechanical relaxation of the crystallite. In the latter, on the other hand, the relaxation is governed by the mechanical relaxation of the amorphous phase. 

PIEZOELECTRICITY. Electric energy created by application of pressure to ceramics of plastics. Devices utilizing this phenomenon are gas flame igniters, ultrasonic welding tools, and sonar navigation aids. 

In a piezoelectric crystal an applied stress ajk produces an electric polarization P so that Pt = dijkajk. Prove that a crystal with a center of symmetry cannot exhibit the phenomenon of piezoelectricity. 

The Curie brothers were drawn to the subject of piezoelectricity because of their familiarity with a phenomenon known for many centuries, that of pyroelectricity. Pyroelectricity refers to the tendency of certain materials to generate an electric current when they are heated. The phenomenon was first described in 314 b.c.e. by the Greek philosopher Theophrastus (ca. 370-ca. 285 b.c.e.), who observed the effect with the mineral tourmaline. Little research was done on pyroelectricity until the early 1800s, when the effect was rediscovered and studied in detail by the Scottish physicist Sir David Brewster (1781-1868). Then in 1878, William Thomson, Lord Kelvin (1824-1907), offered an explanation of the atomic changes that take place when pyroelectric effects occur. These developments in the understanding of pyroelectricity led the Curie brothers to study the possibility of producing electricity from crystals by physical means other than heating. 

Converse piezoelectricity is a specific kind of a more general phenomenon known as electrostriction. Electrostriction is the deformation of a material exposed to an electrical field. Nearly all dielectrics... 

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