An acoustic levitation system is provided for acoustically levitating an object by applying a single frequency from a transducer into a resonant chamber surrounding the object. The chamber includes a stabilizer location along its height, where the side walls of the chamber are angled so they converge in an upward direction. When an acoustic standing wave pattern is applied between the top and bottom of the chamber, a levitation surface within the stabilizer does not lie on a horizontal plane, but instead is curved with a lowermost portion near the vertical axis of the chamber. As a result, an acoustically levitated object is urged by gravity towards the lowermost location on the levitation surface, so the object is kept away from the side walls of the chamber

Allen, J. L.

Barmatz, M. B.

Granett, D.

English

NASA Technical Reports Server

United States Patent 1193 [ i l l  Patent Number: 4,520,656 
Barmatz et al. 1451 Date of Patent: Jun. 4,1985 
[54] GRAVITY ENHANCED ACOUSTIC 
[75] Inventors: Martin B. Barmatz, Glendale; James 
L. Allen, LaCrescenta; Dan Granett, 
Los Angeles, all of Calif. 
represented by the Adminstrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
LEVITATION METHOD AND APPARATUS 
[73] Assignee: The United States of America as 
[21] Appl. No.: 559,988 
[22] Filed: Dec. 9, 1983 
[51] Int. Cl.3 ............................................. GlOK 10/00 
[52] US. C1. ...................................................... 73/505 
[58] Field of Search .......................................... 73/505 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,882,732 5/1975 Fletcher et al. ...................... 73/505 
4,218,921 8/1980 Oran et al. ... 73/505 
Primary Examiner-Stewart J. Levy 
Assistant Examiner-John E. Chapman, Jr. 
Attorney, Agent, or Firm-Paul F. McCaul; John R. 
Manning; Thomas H. Jones 
1571 ABSTRACT 
An acoustic levitation system is provided for acousti- 
cally levitating an object, by applying a single fre- 
quency from a transducer into a resonant chamber sur- 
rounding the object. The chamber includes a stabilizer 
location (29, FIG. 2) along its height, where the side 
walls of the chammber are angled so they converge in 
an upward direction. When an acoustic standing wave 
pattern is applied between the top and bottom of the 
chamber, a levitation surface (28) within the stabilizer 
does not lie on a horizontal plane, but instead is curved 
with a lowermost portion (31) near the vertical axis of 
the chamber. As a result, an acoustically levitated ob- 
ject (30) is urged by gravity towards the lowerrnost 
location (31) on the levitation surface, so the object is 
kept away from the side walls of the chamber. 
8 Claims, 8 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19850021381 2020-03-22T19:29:30+00:00Z
U.S. Patent 
FIG. I 
PRIOR ART 
C 
H 4  
FIG.3 
30 
5-J 
G 
68$' 52 FIG4 
+88 
Jun. 4,1985 4,520,656 
FI G.2 
32 /d.es;x 
/ I '  
22 
FlG.5 w -  
\\\\?73 
L 75 
70 
74 
. 
I 
I 
71 77 
82 
FlG.7 
4,520,656 
1 2 
the curved levitation surface to hold the obj 
from the walls of the chamber. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
5 be best understood from the following description when 
read in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
FIG. is a sectional view of a prior art levitation 
system. 
FIG. 2 is a sectional side view of a levitation system 
constructed in accordance with one embodiment of the 
present invention. 
An object can be acoustically levitated within a FIG. 3 is a partial sectional view taken on the line 
chamber having a vertical axis, flat top and bottom 15 3-3 ofFIG. 2. 
walls, and a uniform cross-section along its height. Lev- FIG. 4 is a sectional view of a levitation system con- 
itation is accomplished by applying acoustic energy structed in accordance with another embodiment of the 
resonant to the height of the chamber, SO the object is invention. 
levitated near an acoustic levitation surface, which is at FIG. 5 is a sectional view of a levitation system con- 
an acoustic potential minimum of the standing wave 20 structed in accordance with another embodiment of the 
pattern. Such a levitation surface will lie in a horizontal invention. 
plane (corresponding to a pressure node). As a result, FIG. 6 is a sectional view of a levitation system con- 
the position of the object is not localized, but has an structed in accordance with another embodiment of the 
equal probability of being situated at any position on the invention. 
surface, including the walls of the chamber. Since a 25 FIG. 7 is a sectional view of a levitation system con- 
major purpose of acoustic levitation is to avoid the structed in accordance with another embodiment of the 
direct contact of a levitated object with a solid support, invention. 
for reasons such as to avoid contamination of the object FIG. 8 is a perspective view of a levitation system 
when it is heated to a liquid temperature, means must be constructed in accordance with another embodiment of 
provided to keep the object away from the walls of the 30 the invention. 
chamber. One technique is to also establish acoustic 
standing wave patterns along one or two horizontal 
directions within the chamber. However, the need to 
apply such horizontal standing wave patterns or use 
other 
chamber, adds to the complexity of a levitation system. 
GRAVITY ENHANCED ACOUSTIC LEVITATION 
METHOD AND APPARATUS 
ORIGIN O F  THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
DESCRIPTION O F  THE PREFERRED 
EMBODIMENTS 
FIG. 1 illustrates a levitation system A of the prior art 
to position the object in the center of the 35 which includes walls forming a chamber B and a trans- 
ducer C which establishes an acoustic standing wave 
A levitation system which enabled the positioning of an 
object so that it not only did not move downwardly, but 
pattern 
at D. An Object E is 
the height Of the as represented 
near an acoustic levita- 
also so it did not sidewardly against the walls of 
the chamber, using a single frequency to form a single 
acoustic standing wave pattern within the chamber, 
would be of considerable value. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present 
invention, an acoustic levitation apparatus and method 
are described which enable a single acoustic frequency 
to be applied to a chamber to position an object within 
includes a chamber with side walls that form a stabilizer 
location at a position along the height of the chamber, 
where the side walls are angled so they converge in an 
upward direction. Means are Provided for applying 
acoustic energy to the chamber at a frequency which is 55 an object against a force such as gravity, but 
resonant to the height of the chamber to produce a 
standing wave pattern along the height of the chamber. 
An acoustic standing wave pattern is chosen which 
produces an acoustic levitation surface(s), to which FIG. 2 illustrates an acoustic levitation system of the 
objects are urged, at the height of the stabilizer location. 60 present invention 10 which includes walls 12 forming a 
The resulting acoustic levitation surface(s) is curved SO chamber 14 having a top and bottom 16, 18 and having 
that it has a lowest point spaced from the side walls of side walls 20. The side walls form a stabilizer portion 22 
the chamber. The object is urged towards the lowest along the height of the chamber, where the side walls of 
point by gravity or other downward force. Thus, the the chamber are angled so that they converge in an 
acoustic standing wave pattern supports the object 65 upward direction. When a transducer 24 is energized to 
against the force of gravity or other force urging it in a produce the standing wave pattern 26 which has an 
downward direction, while the gravity or other force acoustic levitation surface at 28 which is at the same 
also urges the object towards the lowermost position on height as a location 29 along the stabilizer portion 22, 
tion surface F resulting from the acoustic standing wave 
40 pattern. While the object is prevented from falling, it is 
cha 
lin 
the chamber along three dimensions. The apparatus 
wave patterns indicated at D and G. 
standing wave pattern can be used not only to 
position or levitate an object in perpendicular d 
such as along the two horizontal dimensions of a c 
her. 
accordance with the present invention, 
4.520,65 6 
3 
the levitation surface 28 does not lie in a horizontal 
plane, but instead is curved so that it is concave when 
viewed from the top of the chamber. 
Acoustic forces urge the levitated object 30 to lie on 
the levitation surface 28. However, gravity urges the 
object 30 toward the lowest point 31 along the levita- 
tion surface, which lies on or near the vertical axis 32 of 
the chamber. Thus, the force of gravity on an object 
lying on the curved levitation surface 28 automatically 
urges the object away from the walls of the chamber, so 
that no auxiliary standing wave pattern or the like is 
necessary to keep the object away from the wall of the 
chamber. 
The levitation surface 28 is curved because where it 
meets the side walls of the chamber the levitation sur- 
face extends perpendicular to the side walls. The 
greater the angle of convergence X at the stabilizer 
location 29 where the object is levitated, the greater the 
sideward force urging the object towards the center line 
32 of the chamber. It may be noted that in a rectangular 
chamber the levitation surface to which an object is 
acoustically urged, coincides with a pressure node of 
the standing wave pattern which is where the acoustic 
pressure is a minimum. However, there are other sys- 
tems where the levitation surface does not coincide 
with the location of pressure nodes. Accordingly, the 
term “levitation surface” is used to describe the location 
(position of the acoustic potential minimum) to which 
the object is urged by acoustic forces. It is also noted 
that the object typically lies below the acoustic surface, 
at a location where the upward acoustic forces equal 
the downward gravity forces. It also should be noted 
that when the system is used in an outer space environ- 
ment where there is zero gravity, other forces such as 
the force of centrifugal motion or electostatic or mag- 
netic forces may be used in place of gravity and the 
“downward” direction is a direction in which the object 
is urged by such nonacoustic forces. 
In the system 10 of FIG. 2, the transducer 24 is driven 
by electrical signals generated by a variable frequency 
generator 36. The precise frequency output of the gen- 
erator 36 is controlled by a control 38 which is con- 
nected to an acoustic pressure sensor 40 that senses the 
pressure at the top of the chamber. The control 38 ad- 
justs the frequency of the acoustic energy to maintain it 
substantially at a resonant frequency. In some applica- 
tions, the object 30 must be heated to a molten tempera- 
ture, which can be accomplished by the use of heating 
coils 42 located near the stabilizer location 29. An actu- 
ator 44 can move the bottom wall up and down to vary 
the height of the chamber so the resonant frequency 
does not have to vary within a very wide range. This 
adjustable height chamber is necessary when fixed fre- 
quency transducers are used. The object 30 can be 
placed on a holder 46 which is inserted into the cham- 
ber, so acoustic pressure lifts the object off the holder 
and up towards the levitation surface 28. 
The chamber 14 can have a variety of shapes. FIG. 3 
shows the particular chamber 14 as having a circular 
cross-section as taken along the vertical axis 32, but the 
chamber could be constructed with a square or rectan- 
gular cross-section as shown at 50. 
FIG. 4 shows another system 52 which includes a 
stabilizer 54 spaced from both the top 56 and bottom 58 
of a chamber 60. The bottom wall 58 is the upper sur- 
face of a transducer 62. The stabilizer 54 is located, and 
the transducer 62 is driven at a resonant frequency, to 
4 
produce a levitation surface 64 at which the object 30 is 
levitated. 
The upper portion of the chamber is situated within a 
furnace 66. The position of the stabilizer section may be 
5 varied along the height of the chamber by a motor 68. 
After a sample has been processed at high temperature 
it can be moved out of the furnace area by simulta- 
neously lowering the stabilizer region and changing the 
frequency to different resonant frequencies to maintain 
FIG. 5 illustrates another system 70 wherein the walls 
of the chamber are vertical along most of the height of 
the chamber, but have a smaller cross-sectional area at 
the upper end of the chamber than at the lower end. 
The transition region 72 forms a stabilizer portion at 
which a levitation surface 74 is curved so it is concave 
in an upward facing direction. The transducer 73 is 
coupled to the top 75 of the chamber, where there is the 
smaller cross-sectional area, to produce maximum 
The bottom wall of the chamber includes a trap door 
71 that can be opened by an actuator 77 to allow the 
object to fall through. When the object or sample is 
finished being processed in a furnace formed by the 
25 walls of the chamber 72 which includes heating coils 
(not shown), the sample can be dropped out of the bot- 
tom of the chamber into a coolant (not shown) by simul- 
taneously turning off the sound signal and opening the 
FIG. 6 shows a similar system 76, wherein the transi- 
tion region which forms the stabilizer portion 78, is 
continually curved rather than cone shaped. 
FIG. 7 shows another system 80 wherein the cham- 
35 ber 82 has side walls that are angled from the vertical 
axis 84 along the entire height of the chamber. It should 
be noted that the greater the portion of the chamber 
which is angled from the horizontal, the greater the 
deviation of the resonant frequency from a frequency 
40 which is resonant to a chamber having flat horizontal 
upper and lower walls and a uniform cross-section 
throughout its entire height, as in the case of the cham- 
ber shown in FIG. 1. 
FIG. 8 shows another system 86 of rectangular cross- 
45 section along its vertical axis 88, and with the walls of 
the chamber curved so they converge in an upward 
direction but at varying angles. The concave curvature 
of the levitation surface 90, which can be appreciated in 
this figure, has its lowest position within the chamber. 
Thus, the invention provides acoustic levitation sys- 
tems for use in environments wherein a gravity or other 
force urges an object in a predetermined downward 
direction, which enables the levitation of an object so it 
is held against movement in all three dimensions, with 
55 the application of a single acoustic standing wave pat- 
tern within the chamber. The systems include walls 
forming a chamber having a top, bottom, and side walls, 
with the side walls including a stabilizer portion along 
which the side walls are angled from the vertical to 
60 converge in an upward direction. A means for estabiish- 
ing an acoustic wave pattern within the chamber, cre- 
ates an acoustic levitation surface at a stabilizer location 
along the height of the stabilizer portion. An object 
located near the levitation surface, can be supported 
65 near the levitation surface against the downward pull of 
gravity or other force, but also is urged towards a low- 
ermost location on the levitation surface which is 
spaced from the walls of the chamber. 
10 levitation of the sample. 
2o acoustic intensity at 74. 
3o trap door. In this way samples can be quickly cooled. 
50 
4,520,656 
5 6 
Although particular embodiments of the invention 
have been described and illustrated herein, it is recog- 
nized that modifications and variations may readily 
occur to those skilled in the art and consequently, it is 
intended that the claims be interpreted to cover such 
modifications and equivalents. 
said side walls form a stabilizer portion alon 
the side walls are angled to converge in an upward 
direction, said stabilizer location lying at a position 
on said stabilizer portion, said stabilizer portion 
being 'paced from both the top and bottom 
wall of said chamber and said side walls being 
vertical both above and below said stabilizer por- 
tion. 
What is claimed is: 
1. An acoustic levitation system for use in an environ- 5. The system described in claim 1 wherein: 
merit wherein a gravity Or Other force urges an Object in 10 said side walls are angled from the vertical along the 
entire height of the chamber. a predetermined downward direction, comprising: 
walls forming a chamber having a top wall, a bottom 
wall, and side walls, said side walls forming a stabi- 
lizer location at a position along the height of said 
chamber where said side walls are angled SO they 15 
converge in an upward direction; and 
means for applying acoustic energy to said chamber 
at a frequency which is resonant to the height of 
said chamber to produce a standing wave pattern 
along the height of the chamber, said frequency 20 
chosen so there is an acoustic levitation surface at 
the height of the stabilizer location. 
6.  The system described in claim 1 including: 
an object suspended at said acoustic levitation sur- 
7. The system described in claim 1 wherein: 
said top wall and bottom wall form opposite ends of 
said chamber; and 
said acoustic energy applying means includes a trans- 
ducer coupled to one end of said chamber, a vari- 
able frequency generator coupled to said trans- 
ducer to drive it, an acoustic pressure sensor cou- 
pled to an end of said chamber, and signal genera- 
tor means coupled to said generator and said sensor 
for varying the frequency of said generator to 
8. A method for acoustically levitating an object 
establishing said object within a chamber having a 
top wall, bottom wall, and side walls at the height 
said chamber wherein the side walls of the chamber 
are angled so they converge in an upward direc- 
tion; and 
establishing an acoustic standing wave pattern along 
the height of said chamber which produces an 
acoustic levitation surface at the height of said 
face. 
2. The system described in claim 1 wherein: 
said chamber has a height, as measured between its 
top wall and bottom wall, and said side walls ex- 
tend vertically along most of the height of said 
chamber. 
25 maintain said resonant frequency. 
comprising: 
3. The system described in claim 2 wherein: 
said chamber has an upper portion Of substantially 30 of a stabilizer portion formed by the side walls of 
constant cross-section, and a bottom portion of 
substantially constant cross-section, the cross-sec- 
tional area of the upper portion being less than that 
of the lower Portion, and said Chamber forms a 
transition region between said upper and lower 35 
portions, said stabilizer location being positioned at 
said transition region. stabilizer portion. * * * * *  4. The system described in claim 1 wherein: 
40 
45 
50 
55 
60 
65 


Gravity enhanced acoustic levitation method and apparatus

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server