The word "threshold" is used in several ways in regard to cavitation; we refer here to the most critical of these, that which affects the initiation, the onset, of cavitation.  As noted earlier, "Cavitation requires some discontinuity in the liquid, such as gas bubbles or dust motes, about which the bubble forms.  A theoretically pure liquid would require impractically high power levels to initiate cavitation."  This "initiator" could also be a sharp edge or projection on the radiating surface or even on an adjacent surface.  Normally, this is only of theoretical interest to one processing liquids with ultrasonics; however, with the wider availablity of probes and tanks with variable output power, especially those that are infinitely adjustable from no, or virtually no, amplitude, this now becomes a matter of practical importance.  On such machines, it is necessary to observe (visually or by the sizzling sound) the point at which full bubbling occurs; one must bring the amplitude up above that point, the threshold of cavitation, in order to process or clean.  Once beyond that point, the amplitude can be reduced somewhat without dropping out of cavitation.

The initiation of cavitation requires a situation where adjacent molecules of liquid are less tightly bonded bcause of the presence of a discontinuity (bubble, speck, point, or edge).   The threshold of cavitation is highly variable, being affected by the degree to which the liquid may have been previously degassed, by the temperature, pressure, and viscosity of the liquid, the types of discontinuities extant, and other parameters.  It is not the provenance of this short work to discuss the physics of the phenomenon, only to being it to your attention.

The ability of a transducer and generator (power supply) to operate at such low energy levels is a function of their design and the manufacturer of the equipment should be consulted before running the equipment at low output power levels unless such use is specifically allowed by the instructions given.

There are three most common methods to dissolve tablets, coupons, or other samples.  In all cases, care must be taken to avoid igniting or inhaling solvents.

Ultrasonic Cleaners - The simplest and often cheapest method is to use a laboratory ultrasonic cleaner (bath).  The sample could be placed directly in the tank but then the entire contebts of the tank must be removed and replaced for each sample; instead, each sample can be placed in a beaker or a well of a multi-well tray and then floated or held in the bath such that energy passes through the bottom of the beaker or well into the sample.  The drawback is that intensity is generally fairly low and repeatability is poor.

Ultrasonic Cup Horn - A more intense variation of the bath system is to use a Cup Horn, a bath driven by the convertor of a probe-type processor.  Intensity is fairly high and repeatability good but requires careful attention to physical placemnet of sample vessel.

Ultrasonic Processor - The most intense method, in which an active probe tip is inserted into the sample vessel. Intensity is extremely high and repeatabilioty excellent but the tip must be cleaned between samples (it can clean itself).

Among the many parameter variables to be considered are the vessel (thickness, configuration, material, and quality), liquid condition (surfactant coupler, temperature, depth, degassing, impurities, etc.); sample conditions (configuration and condition in vessel, particle size, density, solubility, etc.), cleaner bath (output frequency, amplitude, regulation, power capability, temperature variations, line voltage and frequency fluctuations, etc.); and so on and on.

Foaming and Aerosoling   (10 Oct 04)

Ultrasonic Propulsion (Propulsive Force) - Moving Material.   (10 Oct 04)

It will be interesting to follow the progress of this investigation.

However, at the 37th Annual Technical Symposium of the Ultrasonic Industry Association, on 07 Apr 2008, no less than Ken Suslick, who certainly knows his cavitation bubble, said he'd found no evidence of any fusion products.  Hmmm.   (11 Apr 08)

The primary references are (from Science's Website, "The report by R. P. Taleyarkhan et al. of observations of tritium decay and neutron emissions associated with the collapse of tiny bubbles in deuterated acetone and the possibility that those observations may have arisen from fusion reactions within the imploding bubbles"; the research article by Taleyarkhan et al., and three associated commentaries, a perspective by F. D. Becchetti describing the research and its significance; a news article by Charles Seife on some of the controversy stoked by the paper, and an editorial by Science's Editor in Chief, Donald Kennedy, on why Science decided that 'publication is the best option'.":

R. P. Taleyarkhan et al., Evidence for Nuclear Emissions During Acoustic Cavitation, Science 295, 1868 (2002) (in Research Articles)

F. Becchetti, Evidence for Nuclear Reactions in Imploding Bubbles, Science 295, 1850 (2002) (in Perspectives)

C. Seife, "Bubble Fusion" Paper Generates a Tempest in a Beaker, Science 295, 1808 (2002) (in News of the Week)

D. Kennedy, To Publish or Not to Publish, Science 295, 1793 (2002) (in Editorials)

I should be pleased to assist in this matter but probably do not have the credentials to be taken seriously (the fallout of not having taken advanced degrees).

Boosters (booster horns) are additional stages of mechanical amplification inserted between the front driver of a convertor (see Equipment and Terminology on main page) and the output horn:

(17 Oct 2003 image by and © 2003 S. Berliner, III - all rights reserved)

Boosters are available at various positive and negative gain factors, commonly from 3:1 to 0.5:1.  A booster is, in effect, simply another horn inserted ahead of a regular horn to give the output tip (radiating face) greater amplitude:

(17 Oct 2003 image by and © 2003 S. Berliner, III - all rights reserved)

(17 Oct 2003 image by and © 2003 S. Berliner, III - all rights reserved)

Quick Links to Major Ultrasonic Probe Manufacturers

Miniature probe machines (even battery-operated) are available from:   (15 Oct 05)

In addition to these processors, similar equipment is used for ULTRASONIC DRILLING and MILLING and the manufacturer of such equipment as a standard product line is:

Please note that a far-more detailed explanation of ultrasonic processing, as well as other technical literature, is available at no charge to consultation clients.  However, as what I believe to be a public service, I shall be adding more of my monographs on ultrasonics on this site; watch for them in the index.