Ultrasonic Bibliography Page 3 - Selected Articles.
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).
THE CAVITATION BUBBLE
[image from University of Washington, Applied Physics Laboratory (Lawrence Crum, Ph.D.)
- bubble diameter approximately 1mm]
ULTRASONICS
AL-4 AMPLITUDE MEASUREMENT Aug 99
{This is a DRAFT, only; please substitute reprint PVI-2 for AP-0}
1. GENERAL - The difference between the terms "intensity"
and "power" in probe sonication has been discussed in detail in
Applications Primer AP-0, normally appended hereto, q. v. Power
is measured in watts. It is the energy required to drive the
radiating surface of a given horn, at a specified amplitude of
vibration, the excursion or stroke, against a specified load, at the
fixed resonant frequency of the device to generate cavitation in a
liquid. Intensity is a measure of the energy available per unit
volume of liquid and is directly related to amplitude. It is the
intensity of cavitation that determines the effectivity of sonication
in disrupting cells, accelerating physical and chemical reactions,
degassing, mixing "immiscible" liquids, shearing DNA, disaggregating
shale, and so forth, not the total power applied to the system.
Intensity is directly related to the amplitude of the radiating face
of the tip or horn. It is amplitude that must be provided,
maintained, and monitored. Any truly satisfactory ultrasonic
liquid processor or cell disruptor must provide controlled amplitude
under all varying load conditions within specifications.
1.1 Since the amplification factor of the horn is fixed by its
geometry (refer to AP-0), the measurements can be taken from any
surface perpendicular to the longitudinal centerline. Thus,
measurements can be taken outside a sealed pressure vessel, even by
direct contact, without breaching the vessel.
2. MEASUREMENT MEANS - Amplitude can be measured by
various methods which are mechanical, optical, electrostrictive
(piezoelectric or magnetostrictive), ultrasonic, etc., both directly
and indirectly.
3. MECHANICAL MEANS - An accurate, simple, and
historically least expensive means to measure tip amplitude is by
direct mechanical contact. A suitably calibrated dial indicator
can read amplitude directly from the radiating face.
[Illustration © S. Berliner, III - 1999]
3.1 Originally, the dial indicator was mounted alongside the
horn on a fairly rigid bracket which also held an axle for a lever
projecting under the radiating face. The tip and lever were
under the liquid surface and the indicator above. This
complexity was occasioned by the inability of early ultrasonic
disruptors/processors to maintain amplitude unloaded. With
accurate constant smplitude control, these measurements can now be
made in air, with the horn or tip unloaded. This technique is
shown in Figure 1. The dial indicator method can be used quite
effectively on large horns at moderately high amplitudes within the
operating range of a dial indicator. However, the smaller the
bulk of the horn and the diameter of the radiating face, the more the
dial indicator gearing loads the resonant device and affects the
output. In addition, too much amplitude may destroy the dial
indicator bearings and gears. However, for those who wish to use
this technique, the dial indicator is best nulled while the ultrasonic
device is operating and the reading taken when the device is turned
off. This will minimize erratic readings made while trying to
null the indicator; it will prove amazing how sensitive even the most
rigid indicator mounting will be. For this reason, it is
absolutely critical for good results that the convertor (transducer
housing) and the dial indicator be rigidly secured to a common, rigid
mechanical ground. A 3" (76mm) or heavier drill press column and
base, readily available from machine tool vendors, with very heavy
clamps for the convertor and indicator, is recommended. If the
mountings are not heavy, rigid, and secure, readings will drift.
3.2 If the rear surface of the horn projects beyond the front
driver and convertor case diameter sufficiently to provide axial
access for the dial indicator tip, a reading can be made directly from
the top of the rear surface with the indicator upright. The horn
amplification factor must be known accurately and verified.
Merely taking the ratio of the square of the body and tip diameters
may not be sufficently accurate for this method.
3.3 The amplitude read is that of rest-to-peak or single
amplitude, which must be doubled if comparing to the parameter
normally specified, peak-to-peak or double amplitude. The horn
tip merely pushes the indicator tip down and the inertia of the
indicator gearing prevents it from returning under spring pressure;
the net effect is that the indicator "floats" at the maximum excursion
of the horn/tip face.
4. OPTICAL MEANS - Direct and accurate measurement of
radiating face amplitude can also be made without in any way affecting
the action of the ultrasonic device or the resultant process by
optical means. Direct observation by microscope, indirect observation
by electronically-amplified and computer-analysed image processors,
interferometer measurements, and other means are available.
Optical measurements may be taken both with the tip vibrating in air
under no load or under clear or translucent liquid in a transparent
vessel. It is even possible to "see" inside an opaque suspension.
[Illustration © S. Berliner, III - 1999]
4.1 A simple, inexpensive field microscope with a calibrated
reticle is the least expensive method of optical amplitude
determination, as shown in Figure 2. Since the magnitude of
vibration at the radiating face is usually in the order of 1 to 250 µm
(micrometers) and the microscope axis is at right angles to the axis
of the convertor/horn, errors due to parallax or refraction through
the liquid/glass interface are negligible. The convertor should
be set up in a rigid stand with the horn hanging free beneath it.
A 100X field microscope with calibrated reticle is oriented
perdendicular to the axis of the con-vertor and horn such that the
reticle scale is vertical and the longitudinal (vertical) displacement
of the tip can be read directly through the calibrated eyepiece
(ocular lens). The microscope is focused on, and the measuring
scale is zeroed on, the horizontal image of the radiating face (or on
a horizontal scratch or mark on the side of the tip immediately
adjacent to the face) and the ultrasonic device activated. The
observer sees the edge (or mark) blur and, because of the speed of
oscillation, sees two distinct images at each end of the blur.
Since the horn is a resonant body, vibrating from rest, the images
seen are the peak amplitudes in the positive and negative mode; that
is, the viewer sees that point at which the face stops advancing up or
down and starts to return to rest. These images, then, are those of
maximum positive and negative excursion from rest. The distance
measured between these two images is the double amplitude, or
peak-to-peak excursion, of the radiating face.
4.2 The microscope image may be electronically amplified and
analysed by computerized image processors for greater accuracy and
automation.
4.3 As with the mechanical dial indicator method, it is
important that the microscope and convertor be rigidly mounted to a
common, rigid, mechanical ground. The drill press stand noted in
Para. 3.1 is useful.
[Note: It has been reported in using the optical method with
magnetostrictive transducers that a line voltage can be superimposed
over the driving voltage, especially under fluorescent light, possibly
resulting in a blurred image, but this problem does not seem to occur
with piezoelectric processors.]
5. OTHER NON-CONTACT MEANS - Magnetostrictive and
piezoelectric sensors have been used to determine amplitude.
One of the first methods was to embed a nickel or monel pin in the
back surface of a horn, parallel to the axis of the horn, and place a
sensing coil around it. As the pin was accelerated axially, it
changed the impedance of the coil. Piezoelectric wafers can be
placed in the stack (new piezoelectric polymer films just introduced
at this writing may find use in this manner) and send a signal
proportional to amplitude. Voltage feedback from the driving
crystals may also provide a proportional signal. Laser and
microwave interferometers and similar devices can be used to sense
high frequency displacement. X-ray or neutron sources might be
combined with interferometry to read amplitude with closed volumes.
Ultrasonic sensors may also be used, provided the frequency is such
that it does not interact with that of the device being measured.
6. EQUIPMENT - The 100-power field microscope with
calibrated reticle referenced in Paragraph 4.1 for optical measurement
of tip amplitude was imported from Japan by Southern Precision
Instruments under their Part Number 1837 and is {was?} available as
their Direct Measuring Microscope under Catalog No. N61,193 (on Page
21 in August 1, 1988, Catalog 18N7) from:
Edmund Scientific Co., 101 East Gloucester Pike, Barrington, NJ
08007
tel.: 609-547-6250 or -3488, FAX: 609-573-6295
The dial indicator referenced in Section 3 for direct mechanical measurement of tip amplitude was made in Japan by Mitutoyo as their Model No. 2109, 6 Jewels, Shockproof, rated at 0.001 - 1 mm or Model No. 2119, Jewelled, rated at 0.001 - 5 mm. The choice of range (1 to 40 mils or 1 to 200 mils) is best determined by the expected amplitude to be measured. The Model 2109 is desirable for greater accuracy at lower amplitudes; the Model 2119 is chosen for measuring higher amplitudes. A flat indicator tip was originally used; later both cupped (concave) and broad radius (convex) tips were tried, but flat tips seem best, overall. It is important to assure perpendicularity such that the horn or sample radiating face doesn't skitter off center. One source for the dial indicator is {was?}:
MSC Industrial Co., Long Island Division, 151 Sunnyside
Blvd., Plainview, NY 11803
tel.: 800-645-7270 or 516-349-7100; local: 800-645-7008 or
516-645-7270;
FAX: 800-255-5067; Telex: 221719 SIDTL UR
The metric system model numbers noted did not appear in MSC's
last-seen catalog; only English system indicators were listed.
Neither the specific microscope or indicators shown, nor their sources,
are critical. Equivalent or better equipment will serve.
7. For information regarding any specific processor/disruptor
and horn or tip, refer to the referenced primer or contact the author.
© S. Berliner, III 1999/1995/1993 (all rights reserved)
Free Bubbling
Elsewhere on this site, I use the term "Free Bubbling"; it is
not a term of art to my knowledge. By "Free Bubbling", I mean
the outgassing of air (or other gas) bubbles from the liquid in which
cavitation is to (takes/has taken) place, without the
application of ultrasonic energy. The difference between free
bubbling and cavitation bubbles can be easily and dramatically
demonstrated. Observe the bubble formation in the cavitation
field in an active tank or in front of the radiating surface of an
active, immersed sonicating probe. Then turn off the power.
The cavitation bubbles will disappear instantly (within one half-cycle
of the frequency, far too quickly for you to be misled); any bubbles
which then remain and rise out of the bath are air or gas bubbles,
degassed from the liquid or created at an air/liquid/object interface.
Bubble Entrapment
These pages speak to degassing of liquids by active cavitation; they
have not, however, to date (29 Sep 99), dealt with the opposite
phenomenon, Bubble Entrapment. By this is meant the
forcing, by various mechanisms, of bubbles of ambient gas (usually
air) under the surface of the liquid being used in treating an object
or a liquid being treated. The degree to which this occurs is
directly proportional to the amplitude of vibration of the probe or
tank wall (or any vibrating object) at the object/gas/liquid interface
(visually somewhat akin to a triple point in metallurgy), as well as
inversely to the frequency.
Where a vibrating object breaks the gas/liquid interface, it can drag
molecules of gas adhering to its surface under the interface
(liquid surface) on the forward (downward) stroke and release them on
the reverse stroke. The further and faster the excursion of the
object, the greater the likelihood of entrapment. In extreme
cases, usually limited to probe sonication, although not impossible in
tank cleaning, this can result in foaming of the liquid and loss of
transmission of ultrasonic energy.
Foaming and Aerosoling
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
"blanketingblanketing" 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 balistically, 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.
More on this subject and its commercial applications will be found on
Ultrasonics page 4.
EXTENDERS (Extender Tips)
Horns are normally made of titanium or aluminum, both of which have a
half-wavelength of approximately 5"' at 20KHz. In order to reach
into narrow vessels or through necks of vessels or into process
streams and such, "extenders" (also called "extender tips") are
available from some probe manufacturers. Horns are normally a
half-wavelength long (~5") and extenders are usually made in "Half
Wave" and "Full Wave" length increments; they are usually
simple cylinders, solid or tapped for a tip. Solid extenders are
actually more than a wavelength increment; they have to be fitted to
tapped horns and so are longer than the wavelength increment by the
length of the regular replaceable tip in order to maintain resonance.
A Full Wave extender is represented graphically here:
Extender (Full Wave shown)
[Image by and © 2000 S. Berliner, III - all rights reserved.]
Call for Contributions
For the forthcoming book, "High-Intensity Ultrasonic Technology
and Applications", on the application of power (high intensity)
ultrasonics, the use of ultrasonic energy to change materials (intended
for Marcel Dekker's* "Mechanical Engineering Series", edited by
Profs. Lynn L. Faulkner and S. Bradford Menkes), I solicit input in
the following forms:
1. Corporate/Organizational/Personal History.
2. Significant Technical Breakthroughs.
3. Thumbnail Biographies of Leading Innovators.
4. Photographs of Major Representative Equipment, especially of
New and Unique Items.
5. Diagrams of Major Applications and Processes.
and, of course,
6. Permission to edit and reproduce the above for publication (with
the style in which appropriate credit is to be given).
7. Reprints of any articles published about equipment and applications.
8. Copies of any Patents which you feel cover(ed) outstanding
innovations in equipment and/or processes.
These are the gut items that will highlight, flesh out, and humanize
the otherwise dry facts of ultrasonic cleaning, welding, bonding,
joining, cutting, drilling, and the myriad other applications.
This will be a practical text, not so much "how-to" as "what has been
done, is being done, and can be done". I will need illustrations
of standard bonding and cleaning processes and special features.
If you wish those you use in your literature to be included in the
book, with appropriate credit to you or your firm (as appropriate), of
course, please forward copies.
Any illustrative material (photographs and diagrams) should be in
camera-ready form. Xerographic copies are not suitable.
Photographs should be glossy 4"x5" or 8"x10".
Naturally, no guarantee can be given that any material submitted will
be included but I want to give a balanced picture of the industry. I ask that you be selective; please don't just "dump" catalogs on me.
For this book and other work, I am seeking information about
Narda Ultrasonics Corporation, a firm
which pioneered high-intensity application of ultrasonic energy ca.
1946-1960, and was sold to Dynasonics Corporation of Minnesota
in 1965; however, some of the activities appear to have subsumed into
Narda Microwave Corporation, which was bought out by the
Loral Corporation, which, in turn, was acquired by Lockheed
Martin Corporation and so to L-3 Communications Corporation.
[* - Marcel Dekker has been aquired by Taylor & Francis and
this project assigned to CRC Press.]
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.
You may wish to visit the main ULTRASONICS page,
et seq., with more on ultrasonics, as well as the
Ultrasonic 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.
THUMBS UP!
THUMBS UP! - Support your local police, fire, and emergency personnel!
S. Berliner, III
To contact S. Berliner, III, please click here.
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, and 3, Glossary Page, Cleaning Page, and Bibliography Pages 1, 2, 3, and 4 (see Index, above).
© Copyright S. Berliner, III - 1999,
2001, 2002, 2007,
2008
- All rights reserved.
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