The piezoelectric effect is produced in an object if it exhibits this physical phenomenon: an elongation corresponds to a voltage variation on the two opposite faces, e.g. the measured voltage on the poles increases proportionally to the elongation. Otherwise, a shrinkage corresponds to a proportional decrease in voltage until it becomes negative.
This phenomenon was discovered in 1880 by Jacques and Pierre Curie brothers on some crystalline minerals, such as, for example, quartz, and Greek “”piezein”” was called PIEZOELETTRICO. There were many applications of this effect, but the one most concerned with is the transformation of electric energy into mechanical vibration. In fact, by generating a sinusoidal voltage at the poles of the PZT elements, i.e. continuously varying from positive to negative and vice versa, the elements are stretched and narrowed at very high frequencies (33,000 Hz in the case of the case).
As already mentioned in another chapter, in the sector ns. of the washing are very high, and this was only possible with the development of very special ceramic materials obtained by the formation of fine powders of metal oxides, generally titanium or zirconium with lead or barium (PbTiO2 -PbZrO3-BaTiO3) in well-coded proportions and then heated to mix evenly.
All of this is mixed with organic binder and placed in melds with different shapes to obtain the various models: disks, rings, plates, tubes, etc. The material is heated for a determined time during which the powders sinter and assume a very compact structure. Finally, the cooled pieces are mechanically machined to obtain the desired precise dimensions and ultimately the electrodes are applied to the faces (usually silver applied with vacuum metallization).
At this point there is a product that at the temperature above the point of Curie has a simple crystalline structure with cubic symmetry and dipoles without any electric charge, while just below the point of Curie the structure assumes a tetragonal or rhomboidal symmetry and the dipoles have an electric charge..
At this point, the dipoles loaded, but randomly arranged in the reticular structure, must be oriented in the same direction (polarized) in order to obtain the maximum piezoelectric effect. Then the material is heated up just below the Curie point and simultaneously subjected to a strong electric field whereby the dipoles are oriented in the same direction. When the electric field is removed most of the dipoles retain the orientation assumed, i.e. the material keeps the polarization i.e. the piezoelectric effect at maximum efficiency.
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