S. Berliner, III's berliner-ultrasonics.org Ultrasonics Page 4a keywords = " ultrasonic ultrasound cavitat ultraschall sonde ultrasonique sonotrode acoustic sonic sound wave ultra liquid processing Ultrasonic Industry Association UIA bubble shock wave clean immersi vapor degreas weld join bond sew seal solder insert stak drill grind machin cut extru form spin sonochemi react accelerat pollut abat toxi waste treat beneficiat remediat particl dispers disrupt homogeniz emulsif dissol degas foam defoam sparg phaco phaeco lithotript liposuct prophyla history Narda microwave fusion propulsi fluid filtration home.att.net "
Updated:  02 Jun 2015; 14:30  ET
    [Created 10 Oct 2002;
original AT&T Worldnet Website begun 30 May 1996.]

Update info on the top on ALL pages for your convenience.
URL http://berliner-ultrasonics.org/uson-4a.html
(formerly http://home.att.net/~Berliner-Ultrasonics/uson-4a.html 
moved to this domain on 06 Mar 2010)

S. Berliner, III
Consultant in Ultrasonic Processing
"changing materials with high-intensity sound"


also see
Keywords (Applications) Index

[consultation is on a fee basis]

Specializing in brainstorming and devil's disciplery for new products and
reverse engineering and product improvement for existing products.


Technical and Historical Writer, Oral Historian
Popularizer of Science and Technology  

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Ultrasonics Page 4a


PLEASE NOTE:  If some internal links refuse to work,
please click on Back and scroll down.

Ultrasonics Index

On the main Ultrasonics Page:
    Applications List.
    Probe-type Ultrasonic Processing Equipment.
    Quick Links to Major Ultrasonic Probe Manufacturers (moved to this page 10 Jul 2002).
    Brain Storming - bright ideas, pipe dreams, pie-in-the-sky?

On Ultrasonics Page A
        (A Layperson's Explanation of a Complex Letterhead).

On Ultrasonics Page 1:
    (A Non-Technical Explanation of "Cold Boiling"
        moved from the preceding page 12 Feb 00).
    TUBULAR HORNS (Radial Radiators).
    CARE of TIPS (Radiating Faces).

On Ultrasonics Page 1A:
    Free Bubbling.
    Bubble Entrapment.
    Foaming and Aerosoling - moved 28 May 02 to this Page 4.
    Call for Contributions for Book.

On Ultrasonics Page 2:
    More on Cavitation.
            SINTERING, SLIPS].

On Ultrasonics Page 3:
    Keywords (Applications) Index.
    What's New?

On Ultrasonics Page 4:
    Foaming and Aerosoling - moved 28 May 02 from Page 1A
        and moved again on 10 Oct 04 to this Page 4a.
    Ultrasonic Propulsion (Propulsive Force) - Moving Material - moved on 10 Oct 04 to this Page 4a.
    Ultrasonic Fountains - Atomization, Nebulization, Humidification,
        Misting, Particle Creation and Sizing - moved on 10 Oct 04 to this Page 4a.
    Ultrasonics and Nuclear Fusion.
    Boosters (Booster Horns).
    Quick Links to Major Ultrasonic Probe Manufacturers (moved to this page 10 Jul 2002).

On Ultrasonics Page 4a (this page):
    Blanketing.   new.gif (09 Jul 08)
    Foaming and Aerosoling - moved 28 May 02 from Page 1A and again on 10 Oct 04 from Page 4.
    Ultrasonic Propulsion (Propulsive Force) - Moving Material - moved on 10 Oct 04 from Page 4.
    Ultrasonic Fountains - Atomization, Nebulization, Humidification,
        Misting, Particle Creation and Sizing - moved on 10 Oct 04 from Page 4.
    More about Probe-type Ultrasonic Processing Equipment.
        Resonant Bodies (Bells) (materials for horns).
        Cooling Samples.

On Ultrasonics Page 5:
    Ultrasonic Whistles (Nozzles, Atomizers, Nebulizers).

On the Ultrasonic Cleaning Page:
    ULTRASONIC CLEANING {in process}.
        Immersible Transducers.
        What's New?

    ULTRASONICS GLOSSARY {in process}.

    Ultrasonic Bibliography Page 1 - Reference Books on Acoustics,
        Vibration, and Sound.
    Ultrasonic Bibliography Page 2 - Sonochemistry.
    Ultrasonic Bibliography Page 3 - Selected Articles.

You are invited to visit the ULTRASONIC INDUSTRY ASSOCIATION home page.

CALL FOR CONTRIBUTIONS:  I am writing a book on "High-Intensity Ultrasonic Technology and Applications", on the practical application of power (high intensity) ultrasonics, the use of ultrasonic energy to change materials.  Contributions are welcome (see below).


Larry Crum's Cavitation Bubble

[image from University of Washington, Applied Physics Laboratory (Lawrence Crum, Ph.D.)
- bubble diameter approximately 1mm]



"Blanketing" is a limiting phenomenon in the cavitation field in which the density of the bubble cloud is so great that no further cavitation can take place when additional energy is introduced (analgous to the phenomenon at the temperature of thermal boiling, above which no further change of state occurs ("blanketing" is a term coined by Berliner).  The "blanketing threshold" is that intensity of cavitation at which the blanketing phenomenon occurs; for practical purposes, the blanketing threshold may be considered a relative term based on the efficiency of conversion from increased radiated energy to increased cavitation ("blanketing threshold" is also a term coined by Berliner).

Ultrasonic Blanketing
(18 Mar 2002 image by and © 2008 S. Berliner, III - all rights reserved)

The bubble cloud, a cloud of cavitation bubbles which hovers in front of an activated radiating surface, is strongest when the liquid has been degassed first; in a cleaning tank, this entails running the tank for a few minutes until dissolved and suspended air and other gases are driven out by cavitation.  Not doing so allows energy to be dissipated in the degassing phenomenon and not to be available for the cleaning process.  However, in disruption and allied high-intensity probe procedures, degassing is virtually instantaneous and can be ignored in most applications; nevertheless, the possibility of blanketing must be kept in mind should problems occur at extremes of amplitude and intensity.

Note also that the horn or microtip might well break from over-extension when blanketing occurs at very high amplitude since the tip "unloads" when the resistence of the liquid is replaced by the lack of resistance of the gas or resultant foam (see below).

Foaming and Aerosoling

    (expanded from Page 1A and moved on 10 Oct 04 from Page 4.)

When a foam is generated in a lab sample, it interposes bubbles between the radiating surface and the body of the liquid to be treated or in which treatment is to occur.  This is somewhat akin to "blanketing" but is the result of gas bubbles, not cavitation bubbles interfering with free radiation of acoustic energy into the bath.  It is a self-limiting process.

Once a foam has been created, especially in viscous liquids, it becomes necessary to stop sonication and degas the liquid.  In some cases, at low viscosity, bubbles may rise against gravity and escape through the liquid surface.  If, however, they persist in the bath, short bursts of energy (pulsing), with long rest times between, may be sufficient to break the foam.  A fine mist of the parent liquid can be sprayed against the foam to break it; ultrasonic nozzles excel at this.  In extreme cases, centrifuging and/or vacuum must be applied or the sample may even have to be discarded.

Similarly, on the reverse stroke, molecules of liquid adhering to the surface of a vibrating object may be dragged above the interface (liquid surface) and released, or even ultrasonically nebulized and driven off ballistically, into the atmosphere ("aerosoling").  Obviously, this could pose a significant risk if the liquid is toxic or contains biohazards.  Various techniques beyond the scope of this monograph are available to minimize aerosoling or prevent the escape of the aerosol.

Air Entrapment
(18 Mar 2002 image by and © 2008 S. Berliner, III - all rights reserved)

There is, however, far more to this subject and its commercial applications than merely working with laboratory samples.  Historically, a major effort to suppress foam, especially in beer and ale, was carried out in the 1950s and 1960s but little evidence remains.

As noted above, foam may be broken by applying ultrasonic energy from below the gas-liquid interface but another technique exists which is drawing more and more attention in which acoustical energy is driven through a gas onto the surface of the foam, much as in the '50s and '60s, but with far more effective devices.

Based largely on the work of Prof. Juan A. Gallego-Juárez, Research Professor of the Higher Council for Scientific Research (CSIC), and working at the Instituto de Acústica, Serrano, 144, 28006 Madrid, Spain, this technique utilizes large diameter "plate radiators" which are, in effect, oversized radiating faces driven by relatively "standard" horns.  A graphic representation of such a device is shown:

Plate Radiator
Plate Radiator
[Image by and © 2002 S. Berliner, III - all rights reserved.]

Where this device differs from previous equipment is in that it has a very high "aspect ratio", the diameter of the radiating face is quite large in proportion to its thickness and the diameter of the driving horn.  Dr. Gallegos's own personal development, this device represents a break-through in design of large-diameter radiators and permits efficent transfer of acoustic radiation from a radiating surface, througn a gas, to a work surface (in this case, the gas bubbles that form the foam).  Part of the success of this radiator, whereby it has a high service life without fracturing, lies in the novel multi-step design of the reverse side of the plate.

The radiator drives acoustic vibrations through the gas (air) into the foam bubbles, which are stressed beyond their elastic limit and break (pop), thus exposing the next layer of foam bubbles; the process is quite efficient and rapid:

Ultrasonic Defoaming
Ultrasonic Defoaming
[Image by and © 2002 S. Berliner, III - all rights reserved.]

The substance of foam bubbles, consisting only of a thin skin of the parent liquid around a core of gas, simply runs back into the parent liquid once the skin bursts.

Ultrasonic Propulsion (Propulsive Force)

Moving Material
    (moved on 10 Oct 04 from Page 4)

{14 Aug 2002 - preliminary}

A phenomenon of ultrasonic radiation that is little-used and little-known is that of ultrasonic propulsion.  As discussed elsewhere, when a high-intensity ultrasonic probe is energized, vibration is imparted to the gas in which it stands or the liquid in which it is immersed.  Because energy leaves the horn (in the form of acoustic vibration), a physical reaction takes place such that material is pushed away from the radiating surface.

This phenomenon can most easily be seen by placing a horn tip just above a liquid and observing the waves that occur on the surface of the liquid; however, this may well cause the formation of standing waves.  To visualize the propulsive force, simply turn the horn system at a slight angle and you will see the liquid being pushed away from the tip; increasing the angle will increase the propulsive effect until at over 45° there is more lateral motion than vertical motion:

Ultrasonic Propulsion
(14 Aug 2002 image by and © S. Berliner, III 2002 - all rights reserved)

Taking this a step further, particulates in a gas can be moved away from the radiating surface, which leads directly to the next phenomenon, Ultrasonic Fountains (Atomization, Nebulization, Humidification, Misting, Particle Creation and Sizing):

Ultrasonic Propulsion
(14 Aug 2002 image by and © S. Berliner, III 2002 - all rights reserved)

Ultrasonic Fountains

Atomization, Nebulization, Humidification,
Misting, Particle Creation and Sizing

(moved on 10 Oct 04 from Page 4)

{09 Jul 2002 - preliminary}

A phenomenon of cavitation that is commonly-used by, but little-known to, the general public is the ultrasonic fountain.

When cavitation is induced in a film of liquid, or at least near the surface of a body of liquid, the bubbles bursting at or very near the gas-liquid interface cause fine droplets to be driven off to some distance:

Ultrasonic Fountain
(09 Jul 2002 image by and © S. Berliner, III 2002 - all rights reserved)

This projection of these droplets can be used for the formation of fine mists which, in turn, can be used for humidification and cooling and, in practice, is the basis for the prolific and inexpensive ultrasonic humidifiers in common use.

If either the process is inclined so that gravity has a vector at right angles to the axis of motion of the radiating face, or a gas stream is applied perpendicular to that axis, droplets will act ballistically and fall away dependent on their size.  In this way, fine particulates can be produced, such as from molten metals or super-saturated solutions of precipitates, and they can be sorted or characterized by their ballistic trajectories.

    See also Ultrasonic Whistles (Nozzles, Atomizers, Nebulizers).

I should note here that two of the oldest and least-cost-effective applications of high-intensity ultrasonic (cavitation) atomization/nebulization are the ULTRASONIC OIL BURNER and the ULTRASONIC CARBURETOR.  While both of these applications were eminently successful, technically, they have always failed commercially (to date) because the equipment required has been too costly, and has required too much maintenance, compared to simple mechanical devices used in home and commercial oil burners and in automotive carburetion.

    {Refs. (just for examples - there are many of each):

U. S. Patent #5,671,701, "Apparatus and method for enhancing the efficiency of liquid-fuel-burning systems", and
U. S. Patent #4,337,896, "Ultrasonic fuel atomizer".}

[Oil burners and carburetors are such perennial "better mousetraps" that I used to start my lectures to new engineers and salespeople by warning them NOT to get suckered into spending any time on such schemes as they were almost guaranteed to be approached by would-be Edisons for just such earth-shaking "inventions"-cum-"discoveries"!  That does not mean that no one can ever come up with a workable system, but I do notice that when I mention money (as in my getting paid to work on such schemes), the geniuses (genii?) instantly evaporate!]

More about Probe-type Ultrasonic Processing Equipment.

    (continued from the main Ultrasonics Page, Probe-type Ultrasonic Processing Equipment.)

Horn Terminology
Horn Terminology

Horn Types
Horn Types

STEP HORNS provide maximum amplification (high gain) with high stress at the step and are used primarily in liquid processing.  EXPONENTIAL HORNS provide moderate gain with moderate stress.  CATENOIDAL HORNS provide low gain with low stress and are used primarily in joining.

[Note also that horns are commonly called "tools" in joining (welding, bonding, etc.) applications.]

For a brilliant (literally and figuratively) dissertation on horn design, see Don Culp's Krell Engineering site, replete with horn performance (FEA) animations.

Cup Horns

Cup Horns
(Click on picture for a larger image)

CUP HORNS are high-intensity baths used in ultrasonic liquid processing to prevent cross-contamination of samples and tips, in which the sample is placed in a test tube or small beaker placed in a transmission liquid in the cup and irradiated through the base and walls of the vessel.

Boosters (Booster Horns) are sometimes used to enhance output amplitude.

Frequency - one problem that frequently (yes - I wrote that!) arises is the question of what frequency is best for a particular operation.  As noted elsewhere, higher frequencies result in smaller bubble size, penetrating further into crevices or inter-granular spaces but with lower shock-front intensity, while lower frequencies give bigger bubble sizes with higher shock-front intensity ("more bang for the buck") but less penetration.  In addition, frequencies lower than 20KHz are readily audible and can cause personal discomfort.  When an experimenter is unsure of which equipment to obtain, the obvious answer is to get a multi-frequency device; the problem with that idea is that there aren't any such on the market.  Bear in mind that the probe (horn/tool) is a resonant body (i.e.: it rings like a bell) and so has only one primary resonant frequency (usually ~20KHz or ~40KHz); while it is possible to design units (and I have had them made) to force vibration at higher and lower harmonics, such as 10KHz or 80KHz, coping with mechanical impedance in the probe prevents such machines from being economically viable.

Resonant Bodies (Bells) - talking about frequency (preceding), the materials used for resonant bodies have to conduct sound well; they are, as noted elsewhere on these pages, "bell" metals and the horns themselves are longitudinal "bells".  If one holds a horn (or Microtip or extender) at the "sweet spot", the nodal point, and strikes it with a hard object, it will ring just like a bell.  In fact, if not damped, in fact, not only will it ring purely and sweetly for a very long while before the sound attenuates but such ringing can be used as a rough test for a cracked horn , which will not ring true.  In order to ring, the material must have the same acoustic properties as any bell and the best bell metals follow the same series as for electrical conductivity:  "SCAG" - i.e., Silver, Copper, Aluminum, and Gold.  Close behind these metals are Iron and Titanium.  'Way down the scale comes Stainless Steel, which is very "lossy" (a poor conductor).

Clearly, the least "lossy" materials, the best conductors, leave a lot to be desired.  Silver is soft and malleable, expensive, and very reactive.  Copper is also soft, expensive, and reactive, as well as being poisonous.  Aluminum, while relatively inexpensive, is soft and reactive.  Finally, Gold, while non-reactive, is soft and a wee bit expensive.  Iron, while an excellent bell metal, is VERY reactive (rust, anyone?).  Two good metals are Nickel and Monel, a nickel alloy, both of which are expensive and hard.  Other than being "lossy", Stainless Steel offers a lot; moderate cost, strong, machineable, inert, and readily available; in sheet form, as the diaphragm between the transducer and the liquid in ultrasonic cleaning tanks, it serves quite well.  However, it just does not ring well and so is not a good choice for horns.  Well, that leaves us with Titanium - also moderately priced, as strong as steel, machineable, inert, and readily available, almost as light as aluminum, AND an excellent bell metal.

Thus, Titanium has long been the material of choice for horns, Microtrips, and extenders.

Cooling Samples - one problem that also plagues researchers is that the energy imparted to liquid samples rapidly translates into heat, raising the temperature of the sample and degrading the components.  The most obvious solution (another pun?) is to reduce the intensity of sonication, often quite unacceptable; another is to place the sample vessel (test tube, beaker, etc.) in a cooling bath.  If the rate of temperature rise exceeds the rate of heat transfer through the vessel walls, increasing the surface area of the vessel can give better energy dissipation.  That can be rather hard to do with very small samples, so, in the earliest days of the technique, Dr. Theodore Rosett designed the ROSETT COOLING CELL:

Rosett Cooling Cell
(05 Aug 2006 image by and © S. Berliner, III 2006 - all rights reserved)

This vessel, available in several sizes, has three tubulations at the lower end which divert the flow of the sample through arms that greatly increase the available surface area for cooling.  An improvement to the cell developed by the author (SB,III) ca. 1976-77 was to add a cusp at the juncture of the arms to improve flow diversion, amplifying the propulsive force generated by the vibrating tip (see above). 

Rosett Cooling Cell Cusp
(02 Jun 2015 image by and © S. Berliner, III 2015 - all rights reserved) added.gif (02 Jun 2015)

Although primarily intended for use with MICROTIPs, the larger sizes are appropriate for use with ½" (12.7mm) and ¾" (19.1mm) horns.

As with any glass vessel, avoid contact with the oscillating tip to prevent MICROTIP or vessel breakage.

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 main index.

You may wish to visit the main ULTRASONICS page, et seq., with more on ultrasonics, as well as the Ultrasonics Cleaning page and the Ultrasonics Glossary page {in process}.

Those persons interested in SONOCHEMISTRY might wish to look at the sonochemistry pages of:

Prof. Kenneth S. Suslick of the University of Illinois at Urbana-Champaign, and

Dr. Takahide Kimura at Shiga University in Japan.

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To tour the Ultrasonics pages in sequence, the arrows take you from the main Ultrasonics Page (with full index) to Pages A, 1, 1A, 2, 3, and 4, Glossary Page, Cleaning Page, and Bibliography Pages 1, 2, 3, and 4 (see Index, above).

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