Lecture
Piezoelectric effect (from the Greek. Piézō ( πιέζω ) - I press, I compress) - the effect of the occurrence of dielectric polarization under the action of mechanical stresses ( direct piezoelectric effect ). There is also a reverse piezoelectric effect - the occurrence of mechanical deformations under the action of an electric field.
With the direct piezoelectric effect, the deformation of the piezoelectric sample leads to the appearance of an electrical voltage between the surfaces of the deformable solid, while with the inverse piezoelectric effect, applying a voltage to the body causes its deformation.
The direct effect was discovered by the brothers Jacques and Pierre Curie in 1880 [1] . The opposite effect was predicted in 1881 by Lippmann on the basis of thermodynamic considerations. In the same year, experimentally discovered by the Curie brothers.
Piezoelectric substances always have both direct and inverse piezoelectric effect. It is not necessary that the substance be a single crystal, the effect is also observed in polycrystalline substances pre-polarized by a strong electric field during crystallization, or during a phase transition at the Curie temperature point during cooling for ferroelectrics (for example, ceramic piezoelectric materials based on lead zirconate-titanate) imposed external electric field.
The total energy imparted to the piezoelectric element by an external mechanical force is equal to the sum of the energy of elastic deformation and the energy of charge of the capacity of the piezoelectric element. Due to the reversibility of the piezoelectric effect, a piezoelectric reaction occurs: the electrical voltage generated due to the direct piezoelectric effect (as a result of the inverse piezoelectric effect) creates mechanical stresses and deformations that counteract external forces. This is manifested in the increase in stiffness of the piezoelectric element. If the electric voltage arising due to the piezoelectric effect is excluded, for example, by shorting the electrodes of the piezoelectric element, then the reverse piezoelectric action will not be observed and the rigidity of the piezoelectric element will decrease [2] .
Studies of the piezoelectric effect showed that it is explained by the property of the unit cell of the structure of the material. Since the unit cell is the smallest symmetric unit of material, by repeating it repeatedly you can get a microscopic crystal. A necessary prerequisite for the appearance of the piezoelectric effect is the absence of a center of symmetry in the unit cell [3] .
Direct piezoelectric effect is used:
Reverse piezoelectric effect is used:
Direct and reverse effect are simultaneously used:
Some minerals of rocks have a piezoelectric property due to the fact that the electrical axes of these minerals are not randomly located, but are mainly oriented in one direction, therefore, the same ends of the electrical axes (“pluses” or “minuses”) are grouped together. This scientific discovery was made at the Institute of Physics of the Earth by Soviet scientists M. P. Volarovich and E. I. Parkhomenko and entered into the State Register of Discoveries of the USSR under number 57 with a priority of 1954. Based on this discovery, a piezoelectric method of geological exploration of quartz, pegmatite was developed and crystal veins, which are accompanied by gold, tungsten, tin, fluorite and other minerals [5] .
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Electrostatics
Terms: Electrostatics