Ultrasonic Transducers Technique

In the first post-war period, natural quartz elements were used for ultrasonic cleaning systems. These types of transducers, derived from SONAR applications, immediately proved to be too weak and unsuitable to support the high power levels required for cleaning.

Then, in the 1960s, research focused on the study and application of magnetostriction. Iron-nickel lamellar packs were used, in various forms, which became brazed on stainless steel. Ferrous materials did not have the performance of piezoelectric quartzes, but as they were robust, it was possible to increase power.

Unfortunately, the magnetostrictive transducers proved to be incapable of operating at a very low frequency. This meant they produced very high noise levels since ferrous materials can not lengthen and shorten at the frequency of quartz, which instead has the natural property of oscillating at very high frequencies, much higher than the frequencies which can be heard by humans.

Manufacturers were therefore forced to resort to lead and sound-deadening insulation on sheet metal. On the other hand, much of the power delivered by the generator is dispersed in heat by the Joule effect and therefore has a low yield. Lastly, and even more serious, the cleaned parts became magnetised, a phenomenon which was counterproductive to the removal of metallic particulate from the surfaces.

With the arrival of the 1980s, the ceramics industry was able to produce special piezoelectric transducer elements using metal oxides which were highly suitable for the purpose (lead zirconate-titanate and barium).

The PZT elements have proven to be perfectly suitable for the ultrasonic cleaning sector

• Operation at very high frequencies to decrease noise levels.
• No problems, even at high cleaning liquid temperatures.
• High mechanical resistance without molecular friction, meaning no heat is generated.
• The ability to model transducers in various shapes and dimensions: discs, rings, plates and tubes for any specific application.
• Easy to mount on a wall or the bottom of the tank.
• No magnetism induced on parts to be treated.

Piezoelectric transducers have the same, if not higher, mechanical resistance as the ferrous materials used for magnetostriction, so they were immediately adopted by all the manufacturers in the ultrasonic cleaning sector.

cleaning sector.
Today, piezoelectric ultrasonic transducers hold a 95% share of the marketplace.

An interesting field of application for ultrasonic transducers is the degassing of liquids (water or solvents).

In fact, the solubility of gases in liquids is determined by Henry’s law which states that the amount of dissolved gas is proportional to its partial pressure in the gas phase. Therefore the decrease in pressure due to ultrasonic effects results in a decrease in the solubility of the gas.

A new trend is spreading throughout the food industry:
the reduced use of heat treatments for the purpose of preserving all the nutritional and organoleptic characteristics of food products

The conservation of foods is based on methods and techniques whose purpose is to slow down or stop their natural process of alteration, keeping their microbial load under control or destroying it

Food conservation techniques, whatever method is used, have the common objective of creating an environment which is unfavourable to the life, development and activities of microorganisms.

Sonication, which has the same principle for use as ultrasound, is among these technical innovations.