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.