An object can be defined as “piezoelectric” if it shows the following physical phenomenon: any increase in width corresponds to a voltage variation on the two opposite faces of the object; for instance, the tension measured on the poles increases in parallel with length. Conversely, any size reduction corresponds to a parallel voltage decrease, until it becomes negative.
WAVE
This phenomenon was discovered in 1880 by the brothers Jacques and Pierre Curie on minerals such as quartz.. Among its many applications is the transformation (transduction) of electric energy into mechanical vibration: a sinusoidal wave is applied to the electrodes of PZT elements, this current constantly changes from positive to negative and vice versa, so that the size of the elements increases and decreases at very high frequencies (33.000 Hz in Moroni's plants).
As previously explained, ultrasonic cleaning needs very high frequencies and very special materials obtained with a combination of lead titanate and barium zirconate (PbTiO2 -PbZrO3-BaTiO3)
Such combination is mixed with organic material and moulded into different shapes: disks, rings, plates, tubes, etc. The mixture is then heated until the powders achieve a very compact structure. Finally the cool pieces are mechanically adjusted to the desired size, and electrodes are applied on their sides (generally silver applied with vacuum metallizing).
The product obtained has a simple crystalline structure with cubic symmetry and chargless dipoles above the Curie point, while just below the Curie point it has a tetrahedron symmetry with charged dipoles.
LAYOUT
In order to achieve the maximum piezoelectric eficacy, the charged dipoles must be polarized (i.e., they must be oriented in the same direction). The material is then heated up to just below the Curie point and at the same time is exposed to a strong electric field so that dipoles get oriented in the same direction. When the field is released, the majority of the dipoles keeps the direction they acquired; in other words, the, material keeps its polarization.