An Introduction to Ultrasonic Transducers

A shoebox  immersion transducer.
A shoebox immersion transducer.

Most of our posts on ultrasonic cleaning describe the role of ultrasonic transducers in producing cavitation in the cleaning solution.  We thought it would be a good idea to provide a short tutorial on ultrasonic transducer design configurations.

What Transducers do:

Ultrasonic transducers turn electrical energy into mechanical energy measured in thousands of cycles per second (kHz).  Benchtop ultrasonic cleaners have transducers bonded to the outside of the bottom and/or sides of the cleaning tank and connected to the unit’s ultrasonic generator.  Mechanical energy passes through the tank material – typically stainless steel – to create cavitation bubbles that do the cleaning.  Here we’ll briefly describe the types available and variations on those types.

The Piezoelectric Transducer

The term is derived from the Greek piezo, meaning to squeeze or press and electron, standing for amber, which is ancient source of electrical charge.  As described in Wikipedia, piezoelectricity was discovered in 1880 by French physicists Jacques and Pierre Curie. A commonly used piezoelectric transducer is a “sandwich” of piezoelectric ceramic material separated by a metal cone and excited by an alternating voltage from the generator.  This causes the assembly to expand or contract, thus producing the sound waves.

This transducer design is prevalent for ultrasonic cleaners today because it readily accommodates the sweep mode essential for uniform distribution of cavitation action throughout the bath, and can accommodate a pulse mode delivering intermittent bursts of higher cleaning power.

A variation on piezoelectric design is called the Langevin bolt transducer.  They find application in areas where low ultrasonic frequencies are required such as 28 kHz although higher frequencies are available.  The Electrowave ultrasonic cleaners offered by Tovatech can be ordered with frequencies from 13 to 100 kHz.

The other basic provider of cavitation is the magnetostrictive transducer, which as the name implies operates on the magnetic principle.  A stack of magnetic (magnetostrictive) laminations has one end bonded to the tank surface.  A magnetic field is created by a coil of wire wrapped around the assembly.  Electrical current applied to the assembly causes the laminate to expand or contract to produce ultrasonic sound waves.

While both designs are reliable generators of ultrasonic cavitation, as noted above piezoelectric transducers, unlike magnetostrictive transducers, are better able to provide sweep and pulse frequencies to the ultrasonic cleaning solution.

Immersible Ultrasonic Transducers

Immersible transducers are immersed in the cleaning bath rather than mounted on the outside of the tank.  Immersion transducers find their widest application in large industrial-scale ultrasonic cleaning tanks. There are two typical configurations, the so-called ultrasonic shoebox transducer and the ultrasonic rod transducer.

The shoebox design has transducers mounted inside a hermetically sealed stainless steel “box” that is immersed in the cleaning solution and connected to a generator by wires.  The box can be attached to the tank, sit on the bottom or placed along the side(s).  These transducers operate the same as bonded external transducers.  A major selling point for the equipment is easy replacement.  This is particularly advantageous in large industrial ultrasonic cleaning systems.  That is because in the event of an equipment malfunction it is much more economical to replace the box rather than the entire cleaning unit. They can also be used in customer-supplied tanks.

An ultrasonic rod transducer system.
An ultrasonic rod transducer system.

Ultrasonic rod transducers are in the form of a rod that is immersed in the cleaning tank and radiates waves throughout the cleaning solution.  This configuration is especially advantageous for difficult-to-clean tasks such as cylinders or for removing heavy contaminant deposits.

Both shoebox and rod configurations are available in several commonly employed ultrasonic frequencies.

In conclusion, we hope this brief description of ultrasonic transducer systems proves useful.  If you’d like to learn more additional information is available online.  In the meantime please contact the ultrasonic cleaning professionals at Tovatech for recommendations that will help solve your cleaning challenges.

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More