When I first started working with ultrasonic cleaning back in the early 1960’s “ultrasonic” meant 20kHz. That’s all there was! Some very early sonic cleaning equipment used by one of the major automotive manufacturers in the prior decade had operated at 10kHz using a motor/generator to develop the driving signal for some very crude transducers that were, literally, crafted from loudspeaker bodies. Although I never actually witnessed this equipment in operation, I was told that it was operated within a soundproof enclosure because of the intense noise that was generated within the audible frequency range.
Early, practical, ULTRAsonic cleaning equipment utilized a frequency of 20kHz. That’s all there was for two basic reasons. First, it was above the frequency range that can be heard by most people (which established the LOW end) and, second, it was within the range of frequencies attainable using the then available high power generator and transducer capability (which established the HIGH end). The earliest ultrasonic transducers used coil and magnet technology which, as a mechanical system, has limitations as operating frequency is increased.
In the decades of the 1960’s and 1970’s, piezoelectric technology was developed that opened the door to ultrasonic operation at higher frequencies. These devices, which convert electrical signals into mechanical output without the intermediary step of generating a magnetic field, although previously known, had not been up to the task of reliably powering an ultrasonic cleaning system. The availability of reliable, robust, piezoelectric transducers gave way to the growth of the ultrasonic marching band. Today’s ultrasonic marching band includes “instruments” that play a wide range of frequencies and have the ability to generate tonal qualities that were physically impossible for the instruments that were available in an earlier day.
Think of early sonic or ultrasonic instruments as the equivalent of a bass drum. It plays one and only one note. The only possible variation is in loudness as the drummer hits the drum with greater or less force. In the decades following the 1960’s, we added field drums. Field drums still sound a single but higher frequency note. In the 1990’s the band’s drum family was joined by the trombone which has the ability to change frequency within a given range. This gave way to “sweep” ultrasonic technology. With further passage of time the orchestra was enriched with wind and reed instruments which have the ability to play resonant notes at various frequencies. This, then, is “multi-frequency” technology. Today we are rounding out the ensemble with triangles and piccolos which represent “megasonic” and MULTImegasonic technology.
Just as a band made up of only a bass drum would be musically quite uninteresting, an ultrasonic cleaning system using only a single ultrasonic frequency and timbre has limitations in the cleaning world. The ultrasonic band now has the orchestration to accommodate and satisfy a wide range of “listeners.” Without direction and organization, however, even the most we-rounded musical ensemble provides little more than cacophony when all the instruments are played randomly. All that is needed to assure beautiful “music” is a good musical score a talented and experienced conductor. Learn more in future blogs.