Tag Archives: cavitation

Multiple Frequencies Maximize Ultrasonic Effectiveness

In our last blog we explored a fundamental phenomenon related to ultrasonic cleaning: frequency.  We arrived at the observation that lower frequencies produce relatively larger and higher energy cavitation bubbles, and higher frequencies produce smaller bubbles that are able to penetrate into smaller areas.  We saw that the most common frequency compromise between scrubbing power and cleaning penetration is found at 40khz.

However, while this is certainly one good takeaway from the study of frequency in ultrasonic cleaning applications, UPC wanted to come up with a solution that worked well to incorporate multiple frequencies into the cleaning process, to better take advantage of the different ways in which the different frequencies work.  The result is our Vibra-Bar®technology that reliably produces multiple frequencies simultaneously (Simultaneous Multi-frequency®).  While the advantages of such an arrangement may be apparent, the technique for the creation of these frequencies is less readily so.

The typical shape of a vibrating membrane to produce sound waves is a circle – think drum heads, and audio speakers.  The advantage of a round shape is that it produces a more uniform signal dispersion to minimize distortion.  However, for cleaning purposes (that are out of range of the human ear), distortion is actually desired because it is the very presence of multiple resonant frequencies that is advantageous.  The rectangular shape of our Vibra-Bar® and its structural design allows Simultaneous Multi-frequency® resonance even though only one (40khz) is supplied to the piezoelectric stacks.  This happens because of the complex resonant properties of a three dimensional rectangle shape, when driven by two separate piezoelectric stacks.

The technology behind UPC’s flagship product is certainly complex, but the results are clear: faster operation, deeper cleaning, less erosion, higher reliability, and wider range of cleaning capability.  At UPC, we’re continually pursuing new and innovative ways to help our customers get the most out of this technology, and our Vibra-Bar® design providing Simultaneous Multi-frequency® is just a manifestation of that pursuit.

Ultrasonic Cleaning: Frequency ranges and Applications

Now that you have read information on the UPC website, and our previous Blogs, you likely have a good feel for the basics about the technology behind precision ultrasonic cleaning.  There are many different aspects of the cleaning process that are application-specific and technically complicated, but for the purposes of this blog, let’s explore just one important aspect: frequency. High-frequency sound waves introduced into liquid to create cavitation, effectively scrub contaminants from the targeted parts in a cleaning tank.

A Closer Look at Cavitation

There are many technical papers written on the subject of cavitation, including some with respect to minimizing the adverse effects of cavitation in relation to propeller design.  Yet, at UPC, rather than finding ways to circumvent the adverse phenomenon, as those in the marine industry seek to do, we’re seeking to take advantage of cavitation by manipulating the amplitude and frequency of sound waves to make it work in useful ways, to promote precision ultrasonic cleaning.

Characteristics of the phenomenon of cavitation change as a result of the frequency at which the rarefaction and compression of the wave occurs.  The key concern is the size of the bubbles created – the lower the frequency, the larger the pressure waves. The larger the pressure waves, the larger the bubbles.  Larger bubbles create greater energy, and so bubble diameter size and ultrasonic frequency is an inverse relationship; the ultrasonic energy produced by cavitation (scrubbing) increases as frequency decreases.

One related point to consider is that while larger bubbles have higher energy output, they have less potential for cleaning penetration in small cracks, crevasses and blinds because of their size.  The frequency that is most often used as the ideal compromise between power and penetration for ultrasonic cleaning is 40kHz, which creates a cavitation bubble with a diameter of approximately 1 micron.  For industrial applications involving heavy mechanical equipment such as cleaning engine blocks, radiators, dies, and other metals where the finish isn’t a critical consideration, 25khz is often used – a lower frequency, a more powerful cleaning technique, but potentially destructive if used in the wrong parts cleaning applications.  Accordingly, for more delicate operations, such as precision optics, hard drive parts, and the like, 68kHz is another common frequency.  On the higher end of the spectrum, 170kHz is occasionally employed, often for pharmaceutical products, medical implants, and titanium components.

In our next blog, we will explore some other techniques that we employ (and have patented) for optimal application of much of the information we have covered here.  Be sure to check back here for our next blog – and in the interim, tweet @ultrasonicpower or visit our website to get in touch, – we would love to hear from you.