A method and apparatus for enhancing and shaping acoustical levitation forces in a single-axis acoustic resonance system wherein specially shaped drivers and reflectors are utilized to enhance to levitation force and better contain fluid substance by means of field shaping is described

Berge, L. H.

Johnson, J. L.

Oran, W. A.

Reiss, D. A.

English

NASA Technical Reports Server

Oraw et all. 
[54] METHOD AND APPARATUS FOR SHAPING 
AND ENHANCING ACOUSTICAL 
LEVITATION FORCES 
[75] Inventors: William A. Oran, Huntsville; LeRoy 
H. Berpe, Athens; Donald A. Weiss; 
Jerry E. Johnson, both of Huntsville, 
all of Ala. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 57,466 
[22] Filed: Jul. 13, 1979 
[51] Int. Cl.3 .............................................. P16C 32/06) 
[52] U.S. C1. ......................................... 73/505; 308/10 
[58] Field of Search ................... 73/504, 505; 74/5 R, 
269/20; 308/10 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,164,022 1/1965 Ensley .................................... 73/505 
3,882,732 5/1975 Fletcher et al. ....................... 73/505 
OTHER PUBLICATIONS 
“An Electromagnetic Sound Generator for Producing 
Hntense High Frequency Sound”, by St. Clair, Review 
of Scientific Instr., May 1941, (pp. 250-256). 
Primoty Examiner-James J. Gill 
Attorney, Agent, or Firm-J. H. B’eumer; J. R. Manning; 
L. D. Wofford, Jr. 
[571 ABSTRACT 
A method and apparatus for enhancing and shaping 
acoustical levitation forces in a single-axis acoustic reso- 
nance system wherein specially shaped drivers and 
reflectors are utilized to enhance the levitation force 
and better contain fluid substances by means of field 
shaping. 
13 Claims, 5 Drawing Figures 
--A 
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https://ntrs.nasa.gov/search.jsp?R=19810007252 2020-03-21T09:08:11+00:00Z
Aug. 26, 1986) B 
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ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
BACKGROUND OF THE lNVENTION 
This invention relates to an apparatus and method for 
suspending and positioning objects by the use of acous- 
tical energy. In many instances, the study of materials 
and material processes and the determination of their 
properties can be more readily accomplished when the 
specimens under study are maintained out of contact 
with the walls of containers and solid supports. A levi- 
tated specimen of a material may be advantageously 
heated in a levitation furnace or by a spot heating de- 
vice such as a laser. 
Heretofore, apparatus has been proposed for suspend- 
ing objects in zero gravity such as disclosed in U.S. Pat. 
No. 3,882,732 wherein three dynamic speaker devices 
are oriented along the three major axis of a chamber and 
are driven so as to provide a spherical nodal position at 
the intersection wherein an object may be suspended. 
Another prior device commonly referred to as a St. 
Clair device has been utilized wherein a solid cylindri- 
cal vibrating element having a planar face is driven in an 
ultrasonic generator and a planar reflector is positioned 
in such a manner above the vibrator element that a 
standing wave field between the vibrating element and 
reflector is set up whereby a small object may be sus- 
pended in mid-air supported only by the radiation pres- 
sure. However, the leviation force produced by such a 
device is limited having application mainly to lighter 
materials. 
SUMMARY OF THE INYENTION 
It has been found according to the invention that 
apparatus for levitating an object can be had wherein 
the levitation force is enhanced and shaped by provid- 
ing a curved surface in the surface of one or both of the 
driver and reflector elements. 
A method for increasing and shaping the levitation 
force in an acoustic resonance system includes machin- 
ing one or both ofa driver and reflector element so as to 
have a concavely curved surface and spacing the ele- 
ment depending on the curvature. It has been found by 
providing a spherically curved surface, the levitation 
force is increased and shaped enabling the support of 
heavier materials. 
Accordingly, an important object of the present in- 
vention is to provide apparatus for enhancing the levita- 
tion force in an acoustic resonance system by which an 
object may be levitated. 
Yet another important object of the present invention 
is to provide an acoustic resonance system in which an 
object is suspended in a gaseous medium wherein the 
pressure wave pattern may be advantageously shaped. 
Yet another important object of the present invention 
is the provision of a method for increasing and shaping 
the levitation force in an acoustic resonance system 
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whereby heavier elements and more difficult liquid 
specimens may be 1 evitated. 
BRIEF DESCRIPTION OF THE DRAWING 
The constructed designed to carry out the invention 
will be hereinafter described, together with other fea- 
tures thereof. 
The invention will be more readily understood from 
a reading of the following speci.fication and by refer- 
ence to the accompanying drawing forming a part 
hereof, wherein an example of the invention is shown 
and wherein: 
FIG. B is a diagrammatic isometric view illustrating 
apparatus for enhancing and shaping the levitation 
forces in an acoustic resonance system according to the 
invention; 
FIG. BQ is a sectional view illustrating a concave 
curved surface of an acoustical driver and reflector 
according to the invention; 
FIG. 2 is a plan view of a spherically curved surface 
of a driver and reflector surface according to the inven- 
tion; 
FIG. 3 is a plan view illustrating an alternate form of 
a curved elliptical driver and refl'ector surface accord- 
ing to the invention; and 
FIG. 4 is a plan view of a field shaping ring according 
to the invention. 
DESCRIPTION OF A PREFERRED 
EMBODIMENT 
The drawing illustrates apparatus and a method for 
enhancing and shaping an acoustical levitation field in 
an acoustic resonance system of the type wherein an 
ultrasonic transducer generates a high-frequency radia- 
tion field in which a specimen of material is levitated in 
a gaseous medium. The apparatus includes an acoustical 
driver element A and a concavely curved surface 
formed at one end of the driver element. An acoustical 
reflector I3 is spaced above the driver element. A con- 
40 cavely curved reflector surface is formed at one end of 
the reflector element disposed opposing the concavely 
curved surface of driving element A. The acoustical 
driver element is operably connected to the ultrasonic 
transducer for generating a high-frequency radiation 
45 pressure field whereby an increased levitation force is 
produced between the curved surfaces of the driver and 
reflector elements. 
The driver element A is formed as a solid cylindrical 
element of any suitable material such as aluminum hav- 
50 ing a concavely curved surface I@ Formed at the free 
end thereof. The driving element is coupled with a 
magnetic driving device 12 and together form an ultra- 
sonic transducer which may be driven by a conven- 
tional amplifier circuit. The ultrasonic transducer may 
55 be any suitable device such as a magnetostrictive system 
or a St. Clair device. The schematic illustration of the 
device in FIG. B illustrates the acoustic system in the 
form of a basic St. Clair device which operates in a 
gaseous environment such as air. The conventional flat 
60 surface of the device has been replaced by a specially 
curved surface in accordance with the invention formed 
by any suitable means such as machining. Details of a 
conventional St. Clair device magi be had by reference 
to an article entitled "An Electromagnetic Sound Gen- 
65 erator For Producing Intense High Frequency Sound" 
by H. W. St. Clair appearing in the May, 1941 issue of 
Review of Scientific Instruments, pages 250 through 256. 
The reflector element B includes a cylindrical element 
4,213,921 
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such as aluminum having a concavely curved surface driver and reflector elements a distance approximately 
114 formed in one end thereof which faces and opposes equal to the radius of curvature of the elements, or the 
the concave surface BO of the driving element. The smaller curvature if different. The system may then be 
reflector element B may be secured and affixed by any tuned to its resonant frequency. 
suitable means at 16 in a properly spaced position di- 5 It has been fourld utilizing curved surfaces in an 
rectly above the driver element A. acoustical resonance system according to the invention 
It has been found according to the invention that that the increased levitation forces produced therein are 
when the surfaces of the driver and reflector are curved capable of levitating platinum which has a density more 
concavely a standing Pressure wave Pattern is created than five ( 5 )  times that of iron oxide which is about the 
which has an enhanced levitation force along the axis 10 heaviest object that can be levitated in an acoustic reso- 
88. While the drawing illustrates both surfaces PO and 84 nance system utilizing a conventional St. clair device 
of the respective driver and reflector elements as being having planar driving and reflector surfaces. 
curved, it has been found that other combinations of Thus, it can be Seen that an advantageous apparatus 
curved surfaces also produce an enhanced levitation and method can be had according to the invention 
force and that only one of the surfaces of either the 15 wherein the levitation force of an acoustic 
advantageous results. When the opposing surfaces of 
driver or reflector &ments may be curved producing system may be greatly enhanced and shaped whereby 
both elements A. and B are curved,-ihe 1e;itation force 
may be increased by an approximate factor of 6. When 
only one of the driver or reflector surfaces is specially 
curved, it has been found that the levitation force is 
increased approximately by a factor of 2. It has also 
been found that if the reflector surface is provided with 
a greater radius of curvature than the driver element, 
more stability in the resulting radiation pressure field 
can be had. 
In one example, a reflector element B was utilized 
with a concavely curved surface 114 having a 4 inch 
radius of curvature and driver element A was provided 
with a spherically curved surface BO having a 2 inch 
radius of curvature. It has further been found that the 
best results are achieved by spacing the respective op- 
posed surfaces of driver element A and reflector ele- 
ment B by a distance approximately equal to the small- 
est radius of curvature. Thus, in the above example, the 
desired spacing would be a distance of 2 inches. 
Field shaping means for shaping the standing pressure 
wave field may be provided in the form of a washer 
element 26) having a solid ring portion 22 and a circular 
central aperture 24. With the shaping disk 20 carried 
intermediate the driver and reflector elements as illus- 
trated in FIG. 1, pressure wave patterns may be focused 
or shaped within the central aperture 24 so as to pro- 
duce an enhanced levitation force at a levitation node 
26. 
The concave surfaces 10 and 12 may be advanta- 
geously shaped other than spherically. For example, an 
extension of the invention would be to utilize an ellipti- 
cal shaped surface IOU, curved concavely, to obtain 
multiple off/axis levitation nodes in the standing wave 
pattern. The use of multiple off/axis levitation nodes 
would have application to liquid coalescence. In such 
an application, the shaping disk means 20 or similar ring 
elements, screens, and other passive or secondary re- 
flectors may be utilized at different points about the axis 
to achieve a stable liquid configuration and to fine tune 
the acoustic field. Another application for plural nodes 
in a horizontal plane would be in heat of mixing experi- 
ments for phase diagram calculations. Two different 
liquids or materials can be suspended at two different 
levitation nodes and heated. The material may be 
brought together, such as by tuning at an offhesonance 
frequency, and the heat of mixing determined. 
The enhancement and shaping of levitational forces 
according to the iilvention can be carried out by ma- 
chining the planar surface of a St. Clair acoustic driver, 
machining a spherically curved surface in the planar 
face of a conventional reflector element and spacing the 
much heavier objects may be suspended and liquid 
substances better contained. 
While a preferred embodiment of the invention has 
2o been described using specific terms, such description is 
for illustrative purposes only, and it is to be understood 
that changes and variations may be made without de- 
parting from the spirit or scope of the following claims. 
What is claimed is: 
1. Apparatus for enhancing and shaping acoustical 
levitation forces in an acoustic resonance system in 
which a specimen of material may be suspended in a 
fluid medium, said apparatus comprising: 
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3o an acoustical driver element; 
a concavely curved surface formed at an end of said 
driver element; 
an acoustical reflector element spaced above said 
driver element; 
a concavely curved reflector surface formed at an 
end of said reflector element faced opposing said 
concavely curved surface of said driving. element; 
and 
drive means operatively connected to said acoustical 
driver element for generating a high frequency 
radiation pressure field in which an enhanced, 
shaped levitation force is produced between said 
curved surfaces of said driver and reflector ele- 
ments; 
whereby heavier materials and liquid substances may 
be levitated and better contained. 
2. The apparatus of claim 1 wherein said concave 
driver and reflector surfaces are spherical. 
3. The apparatus of claim 4 wherein said concave 
50 driver and reflector surfaces are elliptical. 
4. The apparatus of claim B wherein said concavely 
curved surface of said reflector element has a greater 
curvature than that of said driver element. 
5. The apparatus of claim 4 wherein the spacing be- 
55 tween said driver and reflector elements is at least ap- 
proximately equal to the radius of curvature of said 
concavely curved driver element surface. 
4. The apparatus of claim 1 including shaping means 
disposed intermediate said driver and reflector elements 
60 for shaping the pressure wave pattern in the acoustical 
field. 
7. Acoustical levitation apparatus for levitating a 
specimen of a material in a gaseous media comprising: 
an acoustical driver element; 
an acoustical reflector element spaced above said 
driver element in an opposing manner; 
means operatively connected to said driver element 
for generating a high-frequency radiation field so 
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6 
as to produce a levitation force between said driver 
and reflector elements; and 
a concavely curved surface formed at an end of one 
of said vibrating or reflecting elements whereby an 
enhancing levitation force is produced. 
8. The apparatus of claim 7 wherein the spacing be- 
tween said vibrating and reflecting element is at least 
approximately equal to the radius of curvature of said 
is produced by said pressure field intermediate said 
driver and reflector elements, said method comprising 
the steps of forming an outwardly concaved curve sur- 
face in the surface of one of said driver and reflector 
5 surfaces and spacing said reflector element a predeter- 
mined distance above said driver element as a function 
of the curvature of said surface. 
11. The method of claim 10 including forming a con- 
concavely curved surface. cavely curved surface in both end surfaces of said 
disposed intermediate said driving and reflecting ele- 12. The method of claim 11 wherein said driver ele- 
ments for shaping the pressure wave pattern in the ment surface is provided with a smaller curvature than 
acoustical field. said refiector surface. 
PO. A method for enhancing and shaping levitation 13. The method of claim 12 including spacing said 
force in an acoustical resonance system of the type 15 driver and reflector elements a distance approximately 
having an ultrasonic transducer having a driver element equal to the smaller radius of curvature of said curved 
for generating a high-frequency standing wave pressure surfaces. 
9. The apparatus of claim 7 including shaping means 10 driver and reflector elements. 
field and a reflector element whereby a levitation force * C a s * *  
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Method and apparatus for shaping and enhancing acoustical levitation forces

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