PIEZOELECTRIC PHENOMENA

From Big Medical Encyclopedia

PIEZOELECTRIC PHENOMENA — emergence of potential difference (polarization) on the surface of substance-dielectric under the influence of the mechanical tension, or deformations (direct piezoelectric effect), or emergence of mechanical deformations under the influence of electric field (the converse piezoelectric effect). Item I. arise in dielectrics with the arranged arrangement of atoms or molecules. A so-called ferroelectric material concerns to them (a segnetova salt, barium titanate, etc.). It is known the St. 1500 substances having piezoelectric properties.

Receiving ultrasound in supersonic generators, and also a design of various devices which found broad application in medical practice is based on piezoelectric effect (see. Pyezografiya , Hearing aids , Ultrasound ).

P.'s nature I. consists in relative displacement of atoms in a crystal cell and deformation of electron shells, and in substances of an organic origin (a bone tissue, sinews, etc.) — in preferential orientation of molecular electric dipoles (see. Polarization ).

The size of the electric moment of polarization (R) is characterized by area density of electric charges and quantitatively described by expression:

P = σα + ε 0 nE,

where σ — mechanical tension, α — coefficient of piezoelectric deformation, E — electric field strength, ε 0 — dielectric permeability, n — a dielectric susceptibility of material.

Item I. are inherent to a bone tissue, sinews, skin and muscles. It is established that P. I. are connected with the structural organization biol, fabrics: mechanical tension → emergence of electric charges → laying of collagenic fibrilla → management of activity of cells → structural changes in a bone.

Assume that P. I. are important for life activity of fabrics. In particular, the hypothesis of the mechanism of formation of a bone is offered, on a cut growth of a bone tissue is regulated by the piezoelectric effect depending on distribution of mechanical tension. V. F. Chepel (1977) explains origins of electric charges (the mechanism of piezoelectric polarization) in collagenic fibers with turn of dipoles of peptide sites of a molecule of collagen under the influence of mechanical tension. Connect the mechanism of healing of changes with piezoelectric effect. In experiences on rabbits and dogs it was shown that the osteanagenesis in the place of a change is accelerated under the influence of the negative electrode implanted in the place of a change; in the field of a positive electrode the rassasyvaniye of a bone tissue takes place.


Bibliography: Zheludev I. S. Physics of crystal dielectrics, M., 1968; Kittel Ch. Introduction to solid state physics, the lane with English, page 509, M., 1978; M e z about and At. Piezoelectric crystals and their use in ultrasonics, the lane with English, M., 1952; H e p e l V. F. Issledovaniye of piezoelectricity of a bone at influence by ultrasound, Biophysics, century 5, page 936, 1977; Sham os M. a. Lavine L. S. Piezoelectricity as and fundamental property of biological tissues, Nature (Lond.), v. 213, p. 267, 1967.

V. V. Lavrentyev.

Яндекс.Метрика