Piezoelectric effect

The creation of electrical voltage piezoelectric. The amplitude of the disk oscillations is increased for clarity.

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.

History [ ]

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.

Physics Phenomenon [ ]

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] .

Not to be confused with other phenomena [ ]

• Piezo effect should not be confused with electrostriction. In contrast to electrostriction, the direct piezoelectric effect is observed only in crystals without a center of symmetry. Although there is no center of symmetry in the class of 432 cubic systems, piezoelectricity in it is also impossible. Consequently, the piezoelectric effect can be observed in dielectric crystals belonging only to one of the 20 classes of point groups.

• The piezoelectric effect should not be confused with the piezoresistive effect (English) Russian. .

Using the piezoelectric effect in the technique of [ ]

Direct piezoelectric effect is used:

• in piezogenerators of various types of electric power:
  • in piezo lighters, to obtain high voltage on the discharger from finger movement;
  • in the contact piezoelectric fuse (for example, to RPG-7 shots);
• in sensors:
  • as a sensitive element (the greater the force, the higher the voltage at the contacts), for example, in load sensors, pressure sensors for liquids and gases;
  • as a sensitive element in microphones, hydrophones, pick-up heads of electrophones, receiving elements of sonars;

Reverse piezoelectric effect is used:

• in acoustic emitters:
  • in piezo-ceramic sound emitters (effective at high frequencies and have small dimensions; for example, they are embedded in musical cards, various sirens used in various home appliances, from watches to kitchen appliances);
  • in ultrasonic radiators for humidifiers, ultrasonic hydrotreatment (in particular, ultrasonic washing machines and industrial ultrasonic baths);
  • in sonar emitters;
• in systems of mechanical movements (activators):
  • in systems of ultra-precise positioning, for example, in a needle positioning system in a scanning tunneling microscope or in a positioner for moving a hard disk head ^[4] ;
  • in adaptive optics, for bending the reflecting surface of a deformable mirror.
• in piezoelectric engines;
• for ink supply in inkjet printers.

Direct and reverse effect are simultaneously used:

• in quartz resonators used as a frequency standard;
• in piezotransformers to change the high frequency voltage.
• in devices on the effect of surface acoustic waves:
  • in ultrasonic delay lines of electronic equipment;
  • in sensors on surface acoustic waves.

Piezoelectric properties of rocks [ ]

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] .

See also [ ]

• Piezoelectric
• Piezoelectricity
• Electrostriction
• Villari effect