Ultrasonic transducers built in the first after the war for application in the wash were piezoelectric with natural quartz elements. These transducers, however, were very weak, fragile and unsuitable to withstand the high powers needed to achieve good results.
In the 1960s manufacturers then adopted magnetostriction using iron-nickel lamellar packs with various shapes and balance-brazing systems. Of course, the ferrous materials did not have the performance of the piezoelectric quartz, but being robust you could go up with the powers.
The disadvantage of this type of transducer was the very low carrying frequency due to high noise, as the ferrous materials can not stretch and shrink to the quartz speed, which instead of nature has the property to oscillate at very high frequencies.
It was overshadowed by noise with lead-insulating and anti-mist on the plates. In addition, much of the power delivered by the generator is dispersed in heat by Joule effect. Finally, magnetism was induced on the washed parts, counterproductive for the removal of metallic dust on the surfaces.
Piezoelectric ultrasonic transducers
It comes to the 1980’s when the ceramic industry manages to produce special piezoelectric transducer elements using metal oxides very suitable for the purpose (titanate and zirconate lead and barium).
PZT elements have been found to be very suitable for the ultrasonic cleaning industry
- No problem even at high temperatures in washing liquids.
- High mechanical strength without molecular friction and therefore no heat generation.
- It is possible to model transducers in various shapes and sizes: disks, rings, plates, tubes, for each particular application.
- Extremely easy to fix on walls or bottom of tanks.
- No magnetism induced on the pieces to be treated.
Piezoelectric transducers have the mechanical strength of the ferrous materials used for magnetostrification if not higher, so they have been immediately adopted by all the manufacturers of the ultrasonic sector.
Nowadays transducer ultrasonic piezoelectric devices hold 95% of the market.
An interesting field of application of ultrasonic transducers is the dissolution of gases in liquids (water or solvents).
In fact, the solubility of the gases in the liquids is determined by Enrico’s law, according to which the amount of gas dissolved in a liquid is proportional to its partial pressure. Therefore, the reduction in pressure caused by ultrasound action results in a lower gas solubility.