U.S. patent application number 11/658356 was filed with the patent office on 2008-03-27 for plasma nozzle array for providing uniform scalable microwave plasma generation.
This patent application is currently assigned to AMARANTE TECHNOLOGIES, INC.. Invention is credited to Jay Joongsoo Kim, Sang Hun Lee.
Application Number | 20080073202 11/658356 |
Document ID | / |
Family ID | 35197707 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080073202 |
Kind Code |
A1 |
Lee; Sang Hun ; et
al. |
March 27, 2008 |
Plasma Nozzle Array for Providing Uniform Scalable Microwave Plasma
Generation
Abstract
The present invention provides microwave plasma nozzle array
systems (10, 70, 230, and 310) and methods for configuring
microwave plasma nozzle arrays (37, 99, and 337). The microwaves
are transmitted to a microwave cavity (323) in a specific manner
and form an interference pattern (66) that includes high-energy
regions (69) within the microwave cavity (32). The high-energy
regions (69) are controlled by the phases and the wavelengths of
the microwaves. A plurality of nozzle elements (36) is provided in
the array (37). Each of the nozzle elements (36) has a portion
(116) partially disposed in the microwave cavity (32) and receives
a gas for passing therethrough. The nozzle elements (36) receive
microwave energy from one of the high-energy regions (69). Each of
the nozzle elements (36) includes a rod-shaped conductor (114)
having a tip (117) that focuses on the microwaves and a plasma (38)
is then generated using the received gas.
Inventors: |
Lee; Sang Hun; (San Ramon,
CA) ; Kim; Jay Joongsoo; (Los Altos, CA) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
AMARANTE TECHNOLOGIES, INC.
3550 Scott Boulevard, Bldg. 16
Santa Clara
CA
95054
Noritsu Koki Co., Ltd.
579-1, Umehara
Wakayama-shi
640-8550
|
Family ID: |
35197707 |
Appl. No.: |
11/658356 |
Filed: |
July 21, 2005 |
PCT Filed: |
July 21, 2005 |
PCT NO: |
PCT/US05/26280 |
371 Date: |
January 22, 2007 |
Current U.S.
Class: |
204/164 ;
422/186.29 |
Current CPC
Class: |
H01J 37/32192 20130101;
H05H 1/46 20130101; H05H 2001/4622 20130101; A61L 2/14
20130101 |
Class at
Publication: |
204/164 ;
422/186.29 |
International
Class: |
H05H 1/46 20060101
H05H001/46; H01J 37/32 20060101 H01J037/32 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2004 |
US |
10/902435 |
Claims
1. A method for configuring a microwave plasma nozzle array,
comprising the steps of: directing microwaves into a microwave
cavity in opposing directions such that the microwaves interfere
and form a standing microwave pattern that is stationary within the
microwave cavity; adjusting a phase of at least one of the
microwaves to control high-energy regions generated by the standing
microwave pattern; and disposing a nozzle array at least partially
in the microwave cavity so that one or more nozzle elements of the
nozzle array are configured to receive microwave energy from a
corresponding one of the high-energy regions.
2. A method as defined in claim 1, wherein said step of directing
microwaves includes the steps of: transmitting microwaves to the
microwave cavity; and reflecting microwaves using a sliding short
circuit operatively connected to the microwave cavity.
3. A method as defined in claim 1, wherein said step of directing
microwaves includes the step of: transmitting microwaves generated
by two microwave power heads to the microwave cavity.
4. A method for configuring a microwave plasma nozzle array,
comprising the steps of: directing a first pair of microwaves into
a microwave cavity in opposing directions along a first axis;
directing a second pair of microwaves into the microwave cavity in
opposing directions along a second axis, the first axis being
normal to the second axis such that the first and the second pairs
of microwaves interfere and form high-energy regions that are
stationary within the microwave cavity; adjusting a phase of at
least one of the microwaves to control the high-energy regions; and
disposing a nozzle array at least partially in the microwave cavity
so that one or more nozzle elements of the nozzle array are
configured to receive microwave energy from a corresponding one of
the high-energy regions.
5. A method as defined in claim 4, wherein said step of directing
the first pair of microwaves includes the steps of: transmitting
microwaves to the microwave cavity; and reflecting microwaves using
a sliding short circuit operatively connected the microwave
cavity.
6. A method as defined in claim 4, wherein said step of directing
the first pair of microwaves includes the step of: transmitting
microwaves generated by two microwave power heads to the microwave
cavity.
7. A method as defined in claim 4, further comprising the steps of:
generating the microwaves by a microwave power head; and providing
a power splitter connected to the microwave power head.
8. A method as defined in claim 4, wherein said step of adjusting a
phase of at least one of the microwaves includes adjusting phases
of the first pair of microwaves.
9. A method as defined in claim 4, wherein said step of adjusting a
phase of at least one of the microwaves includes adjusting phases
of the second pair of microwaves.
10. A method as defined in claim 4, wherein said step of adjusting
a phase of at least one of the microwaves includes adjusting phases
of both the first pair and the second pair of microwaves.
11. A microwave plasma nozzle array unit, comprising: a microwave
cavity; and an array of nozzles, each of said nozzles including: a
gas flow tube adapted to direct a gas flow therethrough and having
an inlet portion and an outlet portion; and a rod-shaped conductor
axially disposed in said gas flow tube, said rod-shaped conductor
having a portion disposed in said microwave cavity to receive
microwaves and a tip positioned adjacent said outlet portion.
12. A microwave plasma nozzle array unit as defined in claim 11,
wherein each of said nozzles further includes: a vortex guide
disposed between said rod-shaped conductor and said gas flow tube,
said vortex guide having at least one passage for imparting a
helical shaped flow direction around said rod-shaped conductor to a
gas passing along said at least one passage.
13. A microwave plasma nozzle array unit as defined in claim 12,
wherein said microwave cavity includes a wall, said wall of said
microwave cavity forming a portion of a gas flow passage
operatively connected to the inlet portion of said gas flow
tube.
14. A microwave plasma nozzle array unit as defined in claim 11,
wherein each of said nozzles further includes: a shield disposed
adjacent to a portion of said gas flow tube for reducing a
microwave power loss through said gas flow tube, said shield being
made of a conducting material.
15. A microwave plasma nozzle array unit as defined in claim 11,
wherein each of said nozzles further includes: a grounded shield
disposed on an exterior surface of said gas flow tube for reducing
a microwave power loss through said gas flow tube, said grounded
shield having a hole for receiving the gas flow therethrough.
16. A microwave plasma nozzle array unit as defined in claim 15,
wherein each of said nozzles further includes: a position holder
disposed between said rod-shaped conductor and said grounded shield
for securely holding said rod-shaped conductor relative to said
grounded shield.
17. A microwave plasma nozzle array unit as defined in claim 11,
wherein said gas flow tube is made of quartz.
18. A microwave plasma nozzle array unit as defined in claim 11,
wherein each of said nozzles further includes a pair of magnets
disposed adjacent to said gas flow tube, said pair of magnets
having a shape approximating a portion of a cylinder.
19. A microwave plasma nozzle array unit as defined in claim 11,
wherein each of said nozzles further includes: an anode disposed
adjacent to a portion of said gas flow tube; and a cathode disposed
adjacent to another portion of said gas flow tube.
20. A microwave plasma nozzle array unit as defined in claim 11,
wherein said microwave cavity includes: a microwave inlet; and a
sliding short circuit configured to reflect microwaves transmitted
through said microwave inlet.
21. A microwave plasma nozzle array unit as defined in claim 11,
wherein said microwave cavity includes: two microwave inlets
disposed in opposite sides of said microwave cavity.
22. A microwave plasma nozzle array unit as defined in claim 11,
wherein said microwave cavity includes: two microwave inlets
disposed in sides of said microwave cavity which are non-nal to
each other; and two sliding short circuits configured to reflect
microwaves received by said inlets.
23. A microwave plasma nozzle array unit as defined in claim 11,
wherein said microwave cavity includes: a first pair of microwave
inlets disposed in opposite sides of said microwave cavity along a
first axis; a second pair of microwave inlets disposed in opposite
sides of said microwave cavity along a second axis, the second axis
being substantially normal to the first axis.
24. A microwave plasma nozzle array unit as defined in claim 11,
wherein said microwave cavity is configured to generate a plurality
of stationary high-energy regions using microwaves directed thereto
and wherein said portion of said rod-shaped conductor is disposed
within the space occupied by said stationary high-energy
regions.
25. A microwave plasma system, comprising: a microwave source; a
pair of isolators operatively connected to said microwave source; a
microwave cavity having a pair of inlets; a pair of waveguides,
each of said waveguides being operatively connected to a
corresponding one of said isolators and to a corresponding one of
said inlets of said microwave cavity; and a pair of non-rotating
phase shifters, each of said non-rotating phase shifters being
operatively connected to a corresponding one of said waveguides and
to a corresponding one of said isolators; and an array of nozzles,
each of said nozzles including: a gas flow tube adapted to direct a
gas flow therethrough and having an inlet portion and an outlet
portion; and a rod-shaped conductor axially disposed in said gas
flow tube, said rod-shaped conductor having a portion disposed in
said microwave cavity to receive microwaves and a tip positioned
adjacent said outlet portion.
26. A microwave plasma system as defined in claim 25, wherein each
of said nozzles further includes: a vortex guide disposed between
said rod-shaped conductor and said gas flow tube, said vortex guide
having at least one passage for imparting a helical shaped flow
direction around said rod-shaped conductor to a gas passing along
said at least one passage.
27. A microwave plasma system as defined in claim 26, wherein said
microwave cavity includes a wall, said wall of said microwave
cavity forming a portion of a gas flow passage operatively
connected to the inlet portion of said gas flow tube.
28. A microwave plasma system as defined in claim 25, wherein each
of said nozzles further includes: a shield disposed adjacent to a
portion of said gas flow tube for reducing a microwave power loss
through said gas flow tube, said shield being made of a conducting
material.
29. A microwave plasma system as defined in claim 25, wherein each
of said nozzles further includes: a grounded shield disposed on an
exterior surface of said gas flow tube for reducing a microwave
power loss through said gas flow tube, said grounded shield having
a hole for receiving the gas flow therethrough.
30. A microwave plasma system as defined in claim 29, wherein each
of said nozzles further includes: a position holder disposed
between said rod-shaped conductor and said grounded shield for
securely holding said rod-shaped conductor relative to said
grounded shield.
31. A microwave plasma system as defined in claim 25, wherein said
gas flow tube is made of quartz.
32. A microwave plasma system as defined in claim 25, wherein each
of said nozzles further includes a pair of magnets disposed
adjacent to said gas flow tube, said pair of magnets having a shape
approximating a portion of a cylinder.
33. A microwave plasma system as defined in claim 25, wherein each
of said nozzles further includes: an anode disposed adjacent to a
portion of said gas flow tube; and a cathode disposed adjacent to
another portion of said gas flow tube.
34. A microwave plasma system as defined in claim 25, wherein said
microwave cavity is configured to generate a plurality of
stationary high-energy regions using microwaves directed thereto
and wherein said portion of said rod-shaped conductor is disposed
within the space occupied by said stationary high-energy
regions.
35. A microwave plasma system as defined in claim 25, wherein each
of said isolators includes: a circulator operatively connected to
at least one of said waveguides; and a dummy load operatively
connected to said circulator.
36. A microwave plasma system as defined in claim 25, further
comprising: a pair of tuners, each of said tuners being operatively
connected to a corresponding one of said waveguides and said
microwave cavity.
37. A microwave plasma system as defined in claim 25, further
comprising: a pair of circulators, each of said circulators being
operatively connected to a corresponding one of said waveguides and
configured to direct microwaves to a corresponding one of said
non-rotating phase shifters.
38. A microwave plasma system as defined in claim 25, further
comprising: a pair of couplers, each of said couplers being
operatively connected to a corresponding one of said waveguides and
a power meter for measuring microwave fluxes.
39. A microwave plasma system as defined in claim 25, wherein said
microwave source includes a pair of microwave power heads, each of
said microwave power heads being operatively connected to a
corresponding one of said isolators.
40. A microwave plasma system as defined in claim 25, wherein said
microwave source includes: a microwave power head for generating
microwaves; and a power splitter for receiving, bisecting and
directing the microwaves to said isolators.
41. A microwave plasma system, comprising: a microwave source; an
isolator operatively connected to said microwave source; a
microwave cavity having an inlet; a waveguide operatively connected
to said isolator and to said inlet of said microwave cavity; a
non-rotating phase shifter operatively connected to said waveguide
and said isolator; a circulator operatively connected to said
waveguide and configured to direct microwaves to said non-rotating
phase shifter; a sliding short circuit operatively connected to
said microwave cavity; and an array of nozzles, each of said
nozzles including: a gas flow tube adapted to direct a gas flow
therethrough and having an inlet portion and an outlet portion; and
a rod-shaped conductor axially disposed in said gas flow tube, said
rod-shaped conductor having a portion disposed in said microwave
cavity to receive microwaves and a tip positioned adjacent said
outlet portion.
42. A microwave plasma system as defined in claim 41, wherein each
of said nozzles further includes: a vortex guide disposed between
said rod-shaped conductor and said gas flow tube, said vortex guide
having at least one passage for imparting a helical shaped flow
direction around said rod-shaped conductor to a gas passing along
said at least one passage.
43. A microwave plasma system as defined in claim 42, wherein said
microwave cavity includes a wall, said wall of said microwave
cavity forming a portion of a gas flow passage operatively
connected to the inlet portion of said gas flow tube.
44. A microwave plasma system as defined in claim 41, wherein each
of said nozzles further includes: a shield disposed adjacent to a
portion of said gas flow tube for reducing a microwave power loss
through said gas flow tube, said shield being made of a conducting
material.
45. A microwave plasma system as defined in claim 41, wherein each
of said nozzles further includes: a grounded shield disposed on an
exterior surface of said gas flow tube for reducing a microwave
power loss through said gas flow tube, said grounded shield having
a hole for receiving the gas flow therethrough.
46. A microwave plasma system as defined in claim 45, wherein each
of said nozzles further includes: a position holder disposed
between said rod-shaped conductor and said grounded shield for
securely holding said rod-shaped conductor relative to said
grounded shield.
47. A microwave plasma system as defined in claim 41, wherein said
gas flow tube is made of quartz.
48. A microwave plasma system as defined in claim 41, wherein each
of said nozzles further includes a pair of magnets disposed
adjacent to said gas flow tube, said pair of magnets having a shape
approximating a portion of a cylinder.
49. A microwave plasma system as defined in claim 41, wherein each
of said nozzles further includes: an anode disposed adjacent to a
portion of said gas flow tube; and a cathode disposed adjacent to
another portion of said gas flow tube.
50. A microwave plasma system as defined in claim 41, wherein said
microwave cavity is configured to generate a plurality of
stationary high-energy regions using microwaves directed thereto
and wherein said portion of said rod-shaped conductor is disposed
within the space occupied by said stationary high-energy
regions.
51. A microwave plasma system as defined in claim 41, wherein said
isolator includes: a circulator operatively connected to said
waveguide; and a dummy load operatively connected to said
circulator.
52. A microwave plasma system as defined in claim 41, further
comprising: a tuner operatively connected to said waveguide and
said microwave cavity.
53. A microwave plasma system as defined in claim 41, further
comprising: a coupler operatively connected to said waveguide and a
power meter for measuring microwave fluxes.
54. A microwave plasma system, comprising: a microwave source; a
pair of isolators operatively connected to said microwave source; a
microwave cavity having a pair of inlets; a pair of waveguides,
each of said waveguides being operatively connected to a
corresponding one of said isolators and to a corresponding one of
said inlets of said microwave cavity; a pair of non-rotating phase
shifters, each of said non-rotating phase shifters being
operatively connected to a corresponding one of said waveguides and
to a corresponding one of said isolators; a pair of sliding short
circuits, each of said sliding short circuits being operatively
connected to said microwave cavity; and an array of nozzles, each
of said nozzles including: a gas flow tube adapted to direct a gas
flow therethrough and having an inlet portion and an outlet
portion; and a rod-shaped conductor axially disposed in said gas
flow tube, said rod-shaped conductor having a portion disposed in
said microwave cavity to receive microwaves and a tip positioned
adjacent said outlet portion.
55. A microwave plasma system as defined in claim 54, wherein each
of said nozzles further includes: a vortex guide disposed between
said rod-shaped conductor and said gas flow tube, said vortex guide
having at least one passage for imparting a helical shaped flow
direction around said rod-shaped conductor to a gas passing along
said at least one passage.
56. A microwave plasma system as defined in claim 55, wherein said
microwave cavity includes a wall, said wall of said microwave
cavity forming a portion of a gas flow passage operatively
connected to the inlet portion of said gas flow tube.
57. A microwave plasma system as defined in claim 54, wherein each
of said nozzles further includes: a shield disposed adjacent to a
portion of said gas flow tube for reducing a microwave power loss
through said gas flow tube, said shield being made of a conducting
material.
58. A microwave plasma system as defined in claim 54, wherein each
of said nozzles further includes: a grounded shield disposed on an
exterior surface of said gas flow tube for reducing a microwave
power loss through said gas flow tube, said grounded shield having
a hole for receiving the gas flow therethrough.
59. A microwave plasma system as defined in claim 58, wherein each
of said nozzles further includes: a position holder disposed
between said rod-shaped conductor and said grounded shield for
securely holding said rod-shaped conductor relative to said
grounded shield.
60. A microwave plasma system as defined in claim 54, wherein said
gas flow tube is made of quartz.
61. A microwave plasma system as defined in claim 54, wherein each
of said nozzles further includes a pair of magnets disposed
adjacent to said gas flow tube, said pair of magnets having a shape
approximating a portion of a cylinder.
62. A microwave plasma system as defined in claim 54, wherein each
of said nozzles further includes: an anode disposed adjacent to a
portion of said gas flow tube; and a cathode disposed adjacent to
another portion of said gas flow tube.
63. A microwave plasma system as defined in claim 54, wherein said
microwave cavity is configured to generate a plurality of
stationary high-energy regions using microwaves directed thereto
and wherein said portion of said rod-shaped conductor is disposed
within the space occupied by said stationary high-energy
regions.
64. A microwave plasma system as defined in claim 54, wherein each
of said isolators includes: a circulator operatively connected to
at least one of said waveguides; and a dummy load operatively
connected to said circulator.
65. A microwave plasma system as defined in claim 54, further
comprising: a pair of tuners, each of said tuners being operatively
connected to a corresponding one of said waveguides and said
microwave cavity.
66. A microwave plasma system as defined in claim 54, further
comprising: a pair of couplers, each of said couplers being
operatively connected to a corresponding one of said waveguides and
a power meter for measuring microwave fluxes.
67. A microwave plasma system as defined in claim 54, further
comprising: a pair of circulators, each of said circulators being
operatively connected to a corresponding one of said waveguides and
configured to direct microwaves to a corresponding one of said
non-rotating phase shifters.
68. A microwave plasma system, comprising: a microwave source; a
microwave cavity having four inlets; four waveguides, each of said
waveguides being operatively connected to a corresponding one of
said inlets of said microwave cavity and said microwave source;
four non-rotating phase shifters, each of said non-rotating phase
shifters being operatively connected to a corresponding one of said
waveguides and said microwave source; four circulators, each of
said circulators being operatively connected to a corresponding one
of said waveguides and configured to direct microwaves generated by
said microwave source to at least one of said non-rotating phase
shifters; and an array of nozzles, each of said nozzles including:
a gas flow tube adapted to direct a gas flow therethrough and
having an inlet portion and an outlet portion; and a rod-shaped
conductor axially disposed in said gas flow tube, said rod-shaped
conductor having a portion disposed in said microwave cavity to
receive microwaves and a tip positioned adjacent said outlet
portion.
69. A microwave plasma system as defined in claim 68, wherein each
of said nozzles further includes: a vortex guide disposed between
said rod-shaped conductor and said gas flow tube, said vortex guide
having at least one passage for imparting a helical shaped flow
direction around said rod-shaped conductor to a gas passing along
said at least one passage.
70. A microwave plasma system as defined in claim 69, wherein said
microwave cavity includes a wall, said wall of said microwave
cavity forming a portion of a gas flow passage operatively
connected to the inlet portion of said gas flow tube.
71. A microwave plasma system as defined in claim 68, wherein each
of said nozzles further includes: a shield disposed adjacent to a
portion of said gas flow tube for reducing a microwave power loss
through said gas flow tube, said shield being made of a conducting
material.
72. A microwave plasma system as defined in claim 68, wherein each
of said nozzles further includes: a grounded shield disposed on an
exterior surface of said gas flow tube for reducing a microwave
power loss through said gas flow tube, said grounded shield having
a hole for receiving the gas flow therethrough.
73. A microwave plasma system as defined in claim 72, wherein each
of said nozzles further includes: a position holder disposed
between said rod-shaped conductor and said grounded shield for
securely holding said rod-shaped conductor relative to said
grounded shield.
74. A microwave plasma system as defined in claim 68, wherein said
gas flow tube is made of quartz.
75. A microwave plasma system as defined in claim 68, wherein each
of said nozzles further includes a pair of magnets disposed
adjacent to said gas flow tube, said pair of magnets having a shape
approximating a portion of a cylinder.
76. A microwave plasma system as defined in claim 68, wherein each
of said nozzles further includes: an anode disposed adjacent to a
portion of said gas flow tube; and a cathode disposed adjacent to
another portion of said gas flow tube.
77. A microwave plasma system as defined in claim 68, wherein said
microwave cavity is configured to generate a plurality of
stationary high-energy regions using microwaves directed thereto
and wherein said portion of said rod-shaped conductor is disposed
within the space occupied by said stationary high-energy
regions.
78. A microwave plasma system as defined in claim 68, wherein said
microwave source includes: four microwave power heads; and four
isolators, each of said isolators being operatively connected to a
corresponding one of said microwave power heads and to at least one
of said waveguides, each of said isolators including: a circulator
operatively connected to said waveguide; and a dummy load
operatively connected to said circulator.
79. A microwave plasma system as defined in claim 68, wherein said
microwave source includes: two microwave power heads; two
isolators, each of said isolators being connected to a
corresponding one of said microwave power heads, each of said
isolators including: a circulator operatively connected to said
waveguide; and a dummy load operatively connected to said
circulator; and two power splitters, each of said power splitters
being operatively connected to a corresponding one of said
isolators, each of said power splitters being configured for
receiving, bisecting and directing the microwaves to a
corresponding two of said waveguides.
80. A microwave plasma system as defined in claim 68, wherein said
microwave source includes: a microwave power head; an isolator
operatively connected to said microwave power head, said isolator
including: a circulator operatively connected to said waveguide;
and a dummy load operatively connected to said circulator; and a
power splitter connected to said isolator, said power splitter
being configured to receive, split and direct the microwaves to a
corresponding one of said waveguides.
81. A microwave plasma system as defined in claim 68, further
comprising: four tuners, each of said tuners being operatively
connected to a corresponding one of said waveguides and said
microwave cavity.
82. A microwave plasma system as defined in claim 68, further
comprising: four couplers, each of said couplers being operatively
connected to a corresponding one of said waveguides and a power
meter for measuring microwave fluxes.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to a concurrently filed PCT
application Ser. No. ______, filed on Jul. 21, 2005, entitled
"SYSTEM AND METHOD FOR CONTROLLING A POWER DISTRIBUTION WITHIN A
MICROWAVE CAVITY" which is hereby incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to plasma generating systems,
and more particularly to microwave plasma systems having plasma
nozzle arrays.
[0004] 2. Discussion of the Related Art
[0005] In recent years, the progress on producing plasma has been
increasing. Typically, plasma consists of positive charged ions,
neutral species and electrons. In general, plasmas may be
subdivided into two categories: thermal equilibrium and thermal
non-equilibrium plasmas. Thermal equilibrium implies that the
temperature of all species including positive charged ions, neutral
species, and electrons, is the same.
[0006] Plasmas may also be classified into local thermal
equilibrium (LTE) and non-LTE plasmas, where this subdivision is
typically related to the pressure of the plasmas. The term "local
thermal equilibrium (LTE)" refers to a thermodynamic state where
the temperatures of all of the plasma species are the same in the
localized areas in the plasma.
[0007] A high plasma pressure induces a large number of collisions
per unit time interval in the plasma, leading to sufficient energy
exchange between the species comprising the plasma, and this leads
to an equal temperature for the plasma species. A low plasma
pressure, on the other hand, may yield one or more temperatures for
the plasma species due to insufficient collisions between the
species of the plasma.
[0008] In non-LTE, or simply non-thermal plasmas, the temperature
of the ions and the neutral species is usually less than
100.degree. C., while the temperature of electrons can be up to
several tens of thousand degrees in Celsius. Therefore, non-LTE
plasma may serve as highly reactive tools for powerful and also
gentle applications without consuming a large amount of energy.
This "hot coolness" allows a variety of processing possibilities
and economic opportunities for various applications. Powerful
applications include metal deposition systems and plasma cutters,
and gentle applications include plasma surface cleaning systems and
plasma displays.
[0009] One of these applications is plasma sterilization, which
uses plasma to destroy microbial life, including highly resistant
bacterial endospores. Sterilization is a critical step in ensuring
the safety of medical and dental devices, materials, and fabrics
for final use. Existing sterilization methods used in hospitals and
industries include autoclaving, ethylene oxide gas (EtO), dry heat,
and irradiation by gamma rays or electron beams. These technologies
have a number of problems that must be dealt with and overcome and
these include issues such as thermal sensitivity and destruction by
heat, the formation of toxic byproducts, the high cost of
operation, and the inefficiencies in the overall cycle duration.
Consequently, healthcare agencies and industries have long needed a
sterilizing technique that could function near room temperature and
with much shorter times without inducing structural damage to a
wide range of medical materials including various heat sensitive
electronic components and equipment.
[0010] Atmospheric pressure plasmas for sterilization, as in the
case of material processing, offer a number of distinct advantages
to users. Its compact packaging makes it easily configurable, it
eliminates the need for highly priced vacuum chambers and pumping
systems, it can be installed in a variety of environments without
additional facilitation needs, and its operating costs and
maintenance requirements are minimal. In fact, the fundamental
importance of atmospheric plasma sterilization lies in its ability
to sterilize heat-sensitive objects, simple-to-use, and faster
turnaround cycle. Atmospheric plasma sterilization may be achieved
by the direct effect of reactive neutrals, including atomic oxygen
and hydroxyl radicals, and plasma generated UV light, all of which
can attack and inflict damage to bacteria cell membranes. Thus,
there is a need for devices that can generate atmospheric pressure
plasma as an effective and low-cost sterilization source.
[0011] One of the key factors that affect the efficiency of
atmospheric plasma sterilization systems, as in the case of other
plasma generating systems, is scalability of plasmas generated by
the systems. There are several microwave nozzle based atmospheric
pressure plasma systems widely used in the industrial and
educational institutions around the world. The most of these
designs are single nozzle based and they lack large volume
scalability required for sterilization of medical devices
applications. Also, such plasma systems generate high temperature
plasma, which is not suitable for sterilization applications.
[0012] One solution to provide uniform plasma uses a nozzle array
coupled to a microwave cavity. One of the challenging problems of
such a system is controlling the microwave distribution within the
microwave cavity so that the microwave energy (or, equivalently
microwave) is localized at intended regions (hereinafter, referred
to as "high-energy regions") that are stationary within the cavity.
In such systems, plasma uniformity and scalability may be obtained
by coupling nozzles to the controlled high-energy spots, which also
enhances the operational efficiency of the system.
[0013] Most of the conventional systems having a microwave cavity
are designed to provide a uniform microwave energy distribution in
the microwave cavity. For example, Gerling, "WAVEGUIDE COMPONENTS
AND CONFIGURATIONS FOR OPTIMAL PERFORMANCE IN MICROWAVE HEATING
SYSTEMS," published on www.2450mhz.com by Gerling Applied
Engineering Inc. in 2000, teaches a system having two rotating
phase shifters. In this system, the two rotating phase shifters
generate high-energy regions that continuously move within the
microwave cavity to insure a uniform heating distribution within
the microwave cavity.
[0014] In contrast to such conventional systems, a plasma
generating system that has a plasma nozzle array should be able to
deterministically control the microwave in its microwave cavity and
generate high-energy regions coupled to the nozzle array. Thus,
there is a strong need for plasma generating systems that can
deterministically generate and control high-energy regions within
the microwave cavity and have plasma nozzle arrays disposed so as
to receive microwave energy from the high-energy regions.
SUMMARY OF THE INVENTION
[0015] The present invention provides various systems that have
microwave plasma nozzle arrays and methods for configuring the
plasma nozzle arrays.
[0016] According to one aspect of the present invention, a method
for configuring a microwave plasma nozzle array includes steps of:
directing microwaves into a microwave cavity in opposing directions
such that the microwaves interfere and form a standing microwave
pattern that is stationary within the microwave cavity; adjusting a
phase of at least one of the microwaves to control high-energy
regions generated by the standing microwave pattern; and disposing
a nozzle array at least partially in the microwave cavity so that
one or more nozzle elements of the nozzle array are configured to
receive microwave energy from a corresponding one of the
high-energy regions.
[0017] According to another aspect of the present invention, a
method for configuring a microwave plasma nozzle array includes
steps of: directing a first pair of microwaves into a microwave
cavity in opposing directions along a first axis; directing a
second pair of microwaves into the microwave cavity in opposing
directions along a second axis, the first axis being normal to the
second axis such that the first and the second pairs of microwaves
interfere and form high-energy regions that are stationary within
the microwave cavity; adjusting a phase of at least one of the
microwaves to control the high-energy regions; and disposing a
nozzle array at least partially in the microwave cavity so that one
or more nozzle elements of the nozzle array are configured to
receive microwave energy from a corresponding one of the
high-energy regions.
[0018] According to still another aspect of the present invention,
a microwave plasma nozzle array unit includes: a microwave cavity;
and an array of nozzles, each of the nozzles including: a gas flow
tube adapted to direct a flow of gas therethrough and having an
inlet portion and an outlet portion; a rod-shaped conductor axially
disposed in the gas flow tube, the rod-shaped conductor having a
portion disposed in the microwave cavity to receive microwaves and
a tip positioned adjacent the outlet portion.
[0019] According to yet another aspect of the present invention, a
microwave plasma system includes: a microwave source; a pair of
isolators operatively connected to the microwave source; a
microwave cavity having a pair of inlets; a pair of waveguides,
each of the waveguides being operatively connected to at least one
of the isolators and to at least one of the inlets of the microwave
cavity; a pair of non-rotating phase shifters, each of the
non-rotating phase shifters being operatively connected to at least
one of the waveguides and to at least one of the isolators; and an
array of nozzles, each of the nozzles of the array including: a gas
flow tube adapted to direct a flow of gas therethrough and having
an inlet portion and an outlet portion; a rod-shaped conductor
being axially disposed in the gas flow tube, the rod-shaped
conductor having a portion disposed in the microwave cavity to
receive microwaves and a tip positioned adjacent the outlet
portion.
[0020] According to another aspect of the present invention, a
microwave plasma system includes: a microwave source; an isolator
operatively connected to the microwave source; a microwave cavity
having an inlet; a waveguide operatively connected to the isolator
and to the inlet of the microwave cavity; a non-rotating phase
shifter operatively connected to the waveguide and the isolator; a
circulator operatively connected to the waveguide and being
configured to direct microwaves to the non-rotating phase shifter;
a sliding short circuit operatively connected to the microwave
cavity; and an array of nozzles, each of the nozzles of the array
including: a gas flow tube adapted to direct a flow of gas
therethrough and having an inlet portion and an outlet portion; a
rod-shaped conductor being axially disposed in the gas flow tube,
the rod-shaped conductor having a portion disposed in the microwave
cavity to receive microwaves and a tip positioned adjacent the
outlet portion.
[0021] According to another aspect of the present invention, a
microwave plasma system includes: a microwave source; a pair of
isolators operatively connected to the microwave source; a
microwave cavity having a pair of inlets; a pair of waveguides,
each of said waveguides being operatively connected to a
corresponding one of said isolators and to a corresponding one of
said inlets of the microwave cavity; a pair of non-rotating phase
shifters, each of said non-rotating phase shifters being
operatively connected to a corresponding one of said waveguides and
to a corresponding one of said isolators; a pair of sliding short
circuits, each of said sliding short circuits being operatively
connected to said microwave cavity; and an array of nozzles, each
of the nozzles of the array including: a gas flow tube adapted to
direct a flow of gas therethrough and having an inlet portion and
an outlet portion; a rod-shaped conductor being axially disposed in
the gas flow tube, the rod-shaped conductor having a portion
disposed in the microwave cavity to receive microwaves and a tip
positioned adjacent the outlet portion.
[0022] According to another aspect of the present invention, a
microwave plasma system, comprising: a microwave source; a
microwave cavity having four inlets; four waveguides, each of the
waveguides being operatively connected to at least one of the
inlets of the microwave cavity and the microwave source; four
non-rotating phase shifters, each of the non-rotating phase
shifters being operatively connected to at least one of the
waveguides and the microwave source; four circulators, each of the
circulators being operatively connected to at least one of the
waveguides and being configured to direct microwaves generated by
the microwave source to at least one of the non-rotating phase
shifters; and an array of nozzles, each of the nozzles of the array
including: a gas flow tube adapted to direct a flow of gas
therethrough and having an inlet portion and an outlet portion; and
a rod-shaped conductor being axially disposed in the gas flow tube,
the rod-shaped conductor having a portion disposed in the microwave
cavity to receive microwaves and a tip positioned adjacent the
outlet portion.
[0023] These and other advantages and features of the invention
will become apparent to those persons skilled in the art upon
reading the details of the invention as more fully described
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic diagram of a system having a plasma
nozzle array in accordance with one embodiment of the present
invention.
[0025] FIG. 2A schematically illustrates the interference of two
microwaves within the microwave cavity of the system shown in FIG.
1, where the microwaves travel in opposing directions.
[0026] FIG. 2B schematically shows a distribution of high-energy
regions within the microwave cavity for the system shown in FIG.
1.
[0027] FIG. 3 is a schematic diagram of a system having a plasma
nozzle array in accordance with another embodiment of the present
invention.
[0028] FIG. 4A shows a top view of the microwave cavity and plasma
nozzle array shown in FIG. 1.
[0029] FIG. 4B shows a cross-sectional view of the microwave cavity
and nozzle depicted in FIG. 4A taken along the line IV-IV.
[0030] FIG. 4C shows a cross-sectional view of an alternative
embodiment of the microwave cavity and nozzle array depicted in
FIG. 4B.
[0031] FIG. 4D shows a cross-sectional view of another alternative
embodiment of the microwave cavity and nozzle array depicted in
FIG. 4B.
[0032] FIG. 5A shows a top view of an alternative embodiment of the
plasma nozzle array shown in FIG. 4A.
[0033] FIG. 5B shows a cross-sectional view of the microwave cavity
and nozzle array depicted in FIG. 5A taken along the line
IV'-IV'.
[0034] FIG. 5C shows a cross-sectional view of an alternative
embodiment of the microwave cavity and nozzle array depicted in
FIG. 5B.
[0035] FIG. 5D shows a cross-sectional view of another alternative
embodiment of the microwave cavity and nozzle array depicted in
FIG. 5B.
[0036] FIGS. 6A-6F show cross-sectional views of alternative
embodiments of the microwave plasma nozzle depicted in FIG. 4C,
illustrating additional components for enhancing nozzle
efficiency.
[0037] FIG. 7 is a schematic diagram of a system having a plasma
nozzle array in accordance with another embodiment of the present
invention.
[0038] FIG. 8 shows an interference pattern of high-energy regions
found within the microwave cavity of the system shown in FIG. 7,
illustrating one arrangement of the nozzle array in the high-energy
regions.
[0039] FIG. 9 is a schematic diagram of a microwave cavity and
waveguides for generating high-energy regions in a two-dimensional
array form in accordance with still another embodiment of the
present invention.
[0040] FIG. 10 shows an alternative interference pattern of
high-energy regions found within the microwave cavity of the
systems shown in FIGS. 7 and 9, illustrating an alternative
arrangement of the nozzle array in the high-energy regions.
[0041] FIG. 11 is a schematic diagram of a system having a plasma
nozzle array in accordance with yet another embodiment of the
present invention.
[0042] FIG. 12 shows a cross-sectional view of the microwave cavity
and the nozzle array depicted in FIG. 11 taken along a direction
normal to the z-axis.
[0043] FIG. 13 is an exploded perspective view of the nozzle shown
in FIG. 12.
[0044] FIGS. 14A-14I show cross-sectional views of alternative
embodiments of the rod-shaped conductor depicted in FIG. 13.
[0045] FIG. 15 shows a flowchart illustrating exemplary steps for
coupling a microwave nozzle array in accordance with at least one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] The following detailed description is of the best currently
contemplated modes of carrying out the invention. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention,
since the scope of the invention is best defined by the appended
claims.
[0047] It must be noted that, as used herein and in the appended
claims, the singular forms "a", "and", and "the" include plural
referents unless the context clearly dictates otherwise. Thus, for
example, reference to "a nozzle" includes one or more nozzles and
equivalents thereof known to those skilled in the art, and so
forth.
[0048] As mentioned previously, conventional microwave plasma
systems generate a uniform power distribution within a microwave
cavity by controlling phase differences between two microwaves
transmitted to the microwave cavity. Unlike existing systems, the
present invention provides methods and systems for controlling the
phases of the microwaves so that they can generate stationary
high-energy regions within microwave cavities. Also methods for
configuring a plasma nozzle array so as to use power from the
high-energy regions are disclosed.
[0049] FIG. 1 is a schematic diagram of a system 10 having a plasma
nozzle array in accordance with one embodiment of the present
invention. As illustrated, the system 10 comprises: a microwave
source 13 having a microwave power head 12 that generates
microwaves and a power splitter 14 having two outlets that split
the microwaves generated by the microwave power head 12; a pair of
isolators 17a and 17b configured to dissipate retrogressing
microwaves that travel toward the microwave power head 12, each
isolator including a dummy load 18a and 18b for dissipating the
retrogressing microwaves and a circulator 16 for diverting the
retrogressing microwaves to the corresponding dummy load 18a and
18b; a pair of non-rotating phase shifters 24a and 24b for shifting
the phases of the microwaves; a pair of circulators 22a and 22b for
directing microwaves from the power splitter 14 to the non-rotating
phase shifters 24a and 24b, respectively; waveguides 20a and 20b
for transmitting microwaves; and a microwave cavity 32. In an
alternative embodiment, the system 10 may further comprise:
couplers 26a and 26b connected to power meters 28a and 28b for
measuring microwave fluxes; and tuners 30a and 30b for matching
impedance of microwaves. Typically, the microwave power head 12
includes a microwave generator and a power supply, which are not
shown in FIG. 1 for simplicity. In another alternative embodiment,
an isolator may be located between the microwave power head 12 and
the two-outlet power splitter 14, thereby replacing the pair of
isolators 17a and 17b.
[0050] A nozzle array 37 comprising one or more nozzles 36 is
connected to the microwave cavity 32 and generate plasma plumes 38a
to 38n from a gas provided from a gas tank 34 through a mass flow
control (MFC) valve 35. Several embodiments of the nozzles 36 and
the microwave cavity 32 that may be used for the system 10 are
discussed in a copending PCT Application entitled "Microwave Plasma
Nozzle with Enhanced Plume Stability and Heating Efficiency," filed
on Jul. 5, 2005, which is hereby incorporated by reference in its
entirety.
[0051] The microwaves 40a and 40b transmitted from the power
splitter 14 travel in opposing directions along an x-axis within
the microwave cavity 32 and yield an interference pattern, as shown
in FIG. 2A. FIG. 2A shows a plot 50 of microwaves 52a and 52b that
interfere with each other to yield a standing microwave 54 within
the microwave cavity 32. The abscissa and ordinate of the plot 50
represent the direction of microwave propagations and amplitude of
microwaves, respectively. Since the intensity of the standing
microwave 54 is proportional to the square of amplitude, the
standing microwave 54 has peak locations 64 for each cycle where
the amplitude reaches its maximum amplitude 58. (For simplicity,
hereinafter, the amplitude refers to the absolute value of the
amplitude.)
[0052] High-energy regions 69 may refer to the locations where the
amplitude of the standing microwave 54 exceeds a threshold 60 that
may be set by a user. As will be explained in connection with FIGS.
5A and 10, more than one nozzle may be located along x-direction in
each high-energy region 69. In such cases, the width 62 of the
high-energy regions 69 may be determined considering the dimension
of the nozzles, spacing between two neighboring nozzles and the
value of the maximum amplitude 58. For example, the user may set
the threshold 60 to 75% of the maximum amplitude 58 to provide
microwave energy for the entire nozzles in the high-energy regions
69.
[0053] Peak locations 64 and maximum amplitudes 58 of the peaks as
well as a width 62 of the high-energy regions 69 may be controlled
by the non-rotating phase shifters 24a and 24b, while a pitch 56 is
determined by the wavelength of the microwaves 52a and 52b. If the
phase difference between the microwaves 52a and 52b decreases, the
maximum amplitude 58 and the width 62 of the high-energy regions 69
increase. If the phases of two microwaves 52a and 52b are shifted
in one direction along the x-axis, the peak locations 64 may shift
in that direction.
[0054] FIG. 2B shows a distribution 66 of the high-energy regions
69 within the microwave cavity 32 viewed in a direction normal to
the x-z plane. As shown in FIG. 2B, the high-energy regions 69 are
generated by interference of the microwaves 52a and 52b propagating
in the directions 68a and 68b, respectively, within the microwave
cavity 32. As the microwaves 52a and 52b may be one-dimensional
waves, each of the high-energy regions 69 may be in a rectangular
strip shape and spaced by half of the pitch 56. In FIGS. 2A and 2B,
the microwave cavity is assumed to be a rectangular parallelepiped
for the purpose of illustration. However, it should be apparent to
those of ordinary skill in the art that the microwave cavity can
have any other shape without deviating from the present
invention.
[0055] In an alternative embodiment, microwave source 13 may be
replaced by two separate microwave power heads and two isolators
attached thereto, respectively, where each microwave power head may
transmit a microwave to the microwave cavity 32. In this
embodiment, two microwaves 52a and 52b may have different
wavelengths and amplitudes. However, by applying the same principle
set forth above, the non-rotating phase shifters 24a and 24b can be
used to control the peak locations 64 and the maximum amplitude 58
as well as the width 62 of high-energy regions 69.
[0056] FIG. 3 is a schematic diagram of a system 70 for
deterministically generating high-energy regions within a microwave
cavity in accordance with another embodiment of the present
invention. As illustrated, the system 70 may include a microwave
power head 72 for generating microwaves; an isolator 74 having a
dummy load 76 configured to dissipate the retrogressing microwaves
that propagate toward the microwave power head 72 and a circulator
78 for diverting the retrogressing microwave to a dummy load 76; a
non-rotating phase shifter 82 for controlling a microwave phase; a
circulator 80; a microwave cavity 92; a waveguide 90 for
transmitting microwaves from the microwave power head 72 to the
microwave cavity 92; and a sliding short circuit 94 for controlling
the phase of the reflected microwaves. In an alternative
embodiment, the system 70 may further include a coupler 86
connected to power meters 84 for measuring microwave fluxes; and a
tuner 88 for matching the impedance of the microwaves. In another
alternative embodiment, the sliding short circuit 94 may be
replaced by a wall, where the dimensions of the microwave cavity 92
along the microwave propagation is a multiple of half a wavelength
of the microwaves. A nozzle array 99 comprising nozzles 98 may be
connected to the microwave cavity 92 and generate plasma plumes 100
from a gas provided from a gas tank 96. The specific details of the
nozzles 98 will be discussed below.
[0057] In FIG. 3, an inset diagram 102 illustrates the propagation
of microwaves transmitted from the microwave power head 72 to the
microwave cavity 92. The transmitted microwaves are reflected from
the sliding short circuit 94, as indicated by an arrow 104, and
they interfere with the incoming microwaves to generate standing
microwaves within the microwave cavity 92. The sliding short
circuit 94 can control the phase of the reflected microwaves and,
if it is used in conjunction with a non-rotating phase shifter 82,
control the locations and the maximum amplitude of the standing
waves as well as the width of high-energy regions that are similar
to the high-energy regions 69 shown in FIG. 2B.
[0058] FIG. 4A is a top view of the plasma nozzle array 37 shown in
FIG. 1, illustrating the nozzles 36 located within the high-energy
regions 69 established within the microwave cavity 32 by microwaves
traveling in opposing directions 68a and 68b. As illustrated, the
nozzle array shown at 37 is described as a two-dimensional array.
However, it should be apparent to those of ordinary skill that
other arrangements of nozzles may be used. For example, the nozzle
array 37 may have only a one-dimensional array of the nozzles 36
arranged in either the z-direction or the x-direction. It is noted
that a nozzle array 99 in FIG. 3 may have the same arrangement as
shown in FIG. 4A.
[0059] FIG. 4B shows a cross-sectional diagram 110 of the microwave
cavity and nozzle array depicted in FIG. 4A taken along the
direction IV-IV. As illustrated, the microwave cavity 32 includes a
wall 111 that forms a gas flow channel 112 for admitting a gas from
the gas tank 34; and a cavity 113 for receiving microwaves
transmitted from the microwave source 13 and generating the
high-energy regions 69. Each nozzle 36 may include a gas flow tube
120 connected to the cavity wall 111 to receive a gas through the
gas flow channel 112; a rod-shaped conductor 114 having a portion
116 for collecting microwaves from the high-energy regions 69 in
the cavity 113; and a vortex guide 118 disposed between the
rod-shaped conductor 114 and the gas flow tube 120. The vortex
guide 118 has at least one opening 119 for producing a helical
swirl flow path around the rod-shaped conductor 114. The microwaves
received by the rod-shaped conductor portion 116 are focused on its
tapered tip 117 to generate the plasma plumes 38 using the gas. The
gas flow tube 120 may be made of a material that is substantially
transparent to microwaves. For example, the gas flow tube 120 may
be made of a dielectric material, such as quartz.
[0060] The width 62 of the high-energy regions 69 may be optimized
by controlling the non-rotating phase shifters 24a and 24b. In
general, a smaller width of high-energy regions 69 may yield a
higher operational efficiency of the nozzles 36. However,
considering the potential variation of the high-energy regions 69
during operation of the system 10, the width 62 of the high-energy
regions 69 may be slightly larger than the diameter of the
rod-shaped conductor 114.
[0061] FIG. 4C is a cross-sectional diagram of an alternative
embodiment 122 of the microwave cavity and nozzle array depicted in
FIG. 4B. As illustrated, a nozzle 128 has similar components as
those shown in FIG. 4B. FIG. 4C includes a gas flow tube 134
sealingly connected to a wall 126 to a receive a gas through a gas
flow channel 127; a rod-shaped conductor 130 for collecting
microwaves from the high-energy regions 69 in a cavity 133; and a
vortex guide 132. The gas flow tube 134 may be made of any material
that is substantially transparent to microwaves (i.e., microwaves
can pass through the gas flow tube 134 with very low loss of
energy) and, as a consequence, the gas flowing through the gas flow
tube 134 may be pre-heated within the cavity 133 prior to reaching
the region of the tapered tip of the rod-shaped conductor 130.
[0062] FIG. 4D shows a cross-sectional view of another alternative
embodiment 140 of the microwave cavity and nozzle array depicted in
FIG. 4A. As illustrated, nozzles 144 have components similar to
their counterparts in FIG. 4B: a gas flow tube 148 sealingly
connected to a wall 143 of a microwave cavity 142 to receive a gas;
a rod-shaped conductor 152 for collecting microwaves from the
high-energy regions 69; and a vortex guide 146. The microwave
cavity 142 may form a gas flow channel connected to the gas tank
34. The rod-shaped conductor 152 may be similar to the conductor
114 illustrated in FIG. 4B where the portion 116 of the rod-shaped
conductor 114 is inserted into the cavity 113 to receive
microwaves. Then, the received microwaves travel along the surface
thereof and are focused on the tapered tip.
[0063] A mentioned previously, the width 62 (FIG. 2) of the
high-energy regions 69 may be optimized by controlling the
non-rotating phase shifters 24a and 24b. In general, a smaller
width of high-energy regions 69 may yield a higher operational
efficiency of the nozzles 36. For this reason, in FIGS. 4A-4D, the
width 62 of the high-energy regions 69 may be slightly larger than
the diameter of the rod-shaped conductor 114. In these
applications, the interval between two neighboring nozzles in
x-direction may be half wavelength of the microwaves traveling in
opposing directions 68a and 68b. However, in some applications, the
interval of half-wavelength may introduce fluctuations in plasma
characteristics along the x-direction and, as a consequence, a
smaller interval between nozzles may be required. FIGS. 5A-5D
illustrate nozzle arrays having various intervals between two
neighboring nozzles in x-direction.
[0064] FIG. 5A is a top view of an alternative embodiment 37' of
the plasma nozzle array shown in FIG. 4A, illustrating nozzles 36'
located within high-energy regions 69' that are established by
microwaves traveling in opposing directions 68a' and 68b'. As
depicted, the width 62' of the high-energy region 69' may be large
enough to accommodate one or more nozzles 36' in x-direction, even
though the pitch 54' is equal to the wavelength of the microwaves.
The width 62' may be controlled by varying the phase difference
between the microwaves 68a' and 68b' as described in connection
with FIG. 2A. It is noted that a nozzle array 99 in FIG. 3 may have
the same arrangement as shown in FIG. 5A.
[0065] FIGS. 5B-5D are cross-sectional views of various embodiments
of the microwave cavity and nozzle array in FIG. 5A taken along the
line IV'-IV'. As illustrated, the three embodiments shown at 110'
(FIG. 5B), 122' (FIG. 5C) and 140' (FIG. 5D) are similar to their
counterparts shown at 110, 122 and 140, respectively, with the
difference that the width 62' may be large enough to accommodate
more than one nozzle in x-direction.
[0066] Each nozzle depicted in FIGS. 4B-4D and 5B-5D includes a
rod-shaped conductor that has a portion inserted into the cavity to
receive microwaves. Then, the received microwaves travel along the
surface thereof and are focused on the tapered tip. Since a portion
of the traveling microwaves may be lost through the gas flow tube,
a shielding mechanism may be used to enhance the efficiency of the
nozzles, which are illustrated in FIGS. 6A-6B.
[0067] FIG. 6A shows a cross-sectional view of a nozzle 160 which
is an alternative embodiment of the nozzle 36 shown in FIG. 4C. As
illustrated, the nozzle 160 includes: a rod-shaped conductor 162; a
gas flow tube 164; a vortex guide 166; and an inner shield 168 for
reducing microwave loss through the gas flow tube 164. The inner
shield 168 has a tubular shape and engages a recess formed along an
outer surface of the vortex guide 166. The inner shield 168 may
provide additional control of the helical swirl around the
rod-shaped conductor 162 and increase the plasma stability by
changing the gap between the gas flow tube 164 and the rod-shaped
conductor 162.
[0068] FIG. 6B is a cross-sectional view of another nozzle 170
which is another alternative embodiment of the nozzle 36 shown in
FIG. 4C. As illustrated, the nozzle 170 includes: a rod-shaped
conductor 172; a gas flow tube 174; a vortex guide 176; and a
grounded shield 178 for reducing microwave power loss through the
gas flow tube 174. The grounded shield 178 may cover a portion of
the gas flow tube 174 that is outside of the microwave cavity. Like
the inner shield 168, the grounded shield 178 may provide the
additional control of the helical swirl around the rod-shaped
conductor 172 and increase the plasma stability by changing the gap
between the gas flow tube 174 and the rod-shaped conductor 172.
[0069] As mentioned above, the main heating mechanism applied to
the nozzles shown in FIGS. 4B-4D and 5B-5D are the microwaves that
are focused and discharged adjacent the tapered tip of the
rod-shaped conductor, where the nozzles may produce non-LTE plasmas
for sterilization. In non-LTE plasmas, the temperature of ions and
neutral species may be less than 100.degree. C., while the
temperature of electrons can be up to several tens of thousand
degrees in Celsius. Thus, such plasmas are highly electronically
excited. To enhance the electronic temperature and increase the
nozzle efficiency, the nozzles may include additional mechanisms
that electronically excite the gas while the gas is within the gas
flow tube, as illustrated in FIGS. 6C-6F.
[0070] FIG. 6C is a cross-sectional view of a nozzle 180 which is
still another alternative embodiment of the nozzle 36 shown in FIG.
4C. As illustrated, the nozzle 180 includes: a rod-shaped conductor
182; a gas flow tube 184; a vortex guide 186; and a pair of outer
magnets 188 for electronic excitation of the swirling gas in the
gas flow tube 184. Each of the outer magnets 188 may have a
cylindrical shell having a semicircular cross section disposed
around the outer surface of the gas flow tube 184.
[0071] FIG. 6D shows a cross-sectional view of a nozzle 190 which
is yet another alternative embodiment of the nozzle 36 shown in
FIG. 4C. As illustrated, the nozzle 190 includes: a rod-shaped
conductor 192; a gas flow tube 194; a vortex guide 196; and a pair
of inner magnets 198, secured by the vortex guide 196 within the
gas flow tube 194, for electronic excitation of the helical swirl
in the gas flow tube 194. Each of the inner magnets 198 may have a
cylindrical shell having a semicircular cross section.
[0072] FIG. 6E shows a cross-sectional view of a nozzle 200 which
is a further alternative embodiment of the nozzle 36 shown in FIG.
4C. As illustrated, the nozzle 200 includes: a rod-shaped conductor
202; a gas flow tube 204; a vortex guide 206; a pair of outer
magnets 208; and an inner shield 210. Each of the outer magnets 208
may have a cylindrical shell having a semicircular cross section.
In an alternative embodiment, the inner shield 210 may have a
tubular shape.
[0073] FIG. 6F is a cross-sectional view of a nozzle 212 which is
another alternative embodiment of the nozzle 36 shown in FIG. 4C.
As illustrated, the nozzle 212 includes: a rod-shaped conductor
214; a gas flow tube 216; a vortex guide 218; an anode 220; and a
cathode 222. The anode 220 and the cathode 222, connected to an
electrical power source (not shown in FIG. 5F for simplicity), may
electronically excite the swirling gas in the gas flow tube
216.
[0074] As mentioned above, FIGS. 6A-6F show cross-sectional views
of various embodiments of the nozzle 36 shown in FIG. 4B. However,
it should be apparent to one of ordinary skill that the embodiments
shown in FIGS. 6A-6F can be applied to the nozzles shown in FIGS.
4C-4D and 5B-5D. Also, one skilled in the art will appreciate that
the descriptions in FIGS. 4A-6F may be equally applied to the
system 70 in FIG. 3.
[0075] Referring back to FIG. 2B, the nozzles 36 may be configured
within the high-energy regions 69 to maximize the use of microwave
energy within the microwave cavity 32. In general, operational
efficiency of the microwave cavity 32 may increase if the
high-energy regions 69 are confined only around the nozzles 36. As
the cross section of a typical nozzle is circular or rectangular
with an aspect ratio of a near unity, operational efficiency of the
microwave cavity may be maximized if the high-energy regions are
confined within rectangular regions in a 2-dimensional matrix form
as will be described in FIGS. 7-9.
[0076] FIG. 7 is a schematic diagram of a system shown at 230
having a plasma nozzle array in accordance with one embodiment of
the present invention. The components of the system shown at 230
are similar to their counterparts of FIG. 1, except that the
microwaves are traveling normal to each other in a microwave cavity
250. As illustrated, the system 230 includes: a microwave source
233 that has a microwave power head 232 and a power splitter 234
having two outlets; a pair of non-rotating phase shifters 244a and
244b; a pair of isolators 237a and 237b including a pair of
circulators 236a and 236b and a pair of dummy loads 238a and 238b;
a pair of circulators 242a and 242b; waveguides 240a and 240b; the
microwave cavity 250; one or more nozzles 256, preferably forming a
two-dimensional array; and a pair of sliding short circuits 254a
and 254b. Inset diagrams 260a and 260b represent microwaves
transmitted to the microwave cavity 250. The system 230 may further
include: a pair of couplers 246a and 246b; a pair of tuners 248a
and 248b; and a pair of power meters 247a and 247b connected to a
pair of couplers 246a and 246b, respectively. The gas tank 34 may
be connected to the microwave cavity 250 to provide a gas to the
nozzles 256 that are coupled to the microwave cavity 250. In an
alternative embodiment, an isolator may be located between the
microwave power head 232 and the power splitter 234, replacing the
isolators 237a and 237b.
[0077] FIG. 8 illustrates a distribution of high-energy regions
within the microwave cavity 250 viewed in a direction normal to a
plane defined by the propagation directions of two interfering
microwaves, wherein the two microwaves are shown by waveforms 260a
and 260b. As shown in FIG. 8, two microwaves, shown by the
waveforms 260a and 260b, and two reflected microwaves, shown by
waveforms 261a and 261b, generate high-energy regions 268 in a
two-dimensional array form, where intervals 264a and 264b
correspond to half-wavelengths of the microwaves 260a and 260b,
respectively. By the same principle as applied to the interference
pattern shown in FIG. 2B, the microwaves 260a and 261a, and the
microwaves 260b and 261b, generate two standing microwaves that
yield strip-shaped high-energy regions 262a and 262b, respectively.
Then, the standing microwaves may further interfere to generate
high-energy regions 268 in a matrix form as depicted in FIG. 8.
Locations and widths 266a and 266b of the high-energy regions 258
may be controlled by the non-rotating phase shifters 244a and 244b
and/or the sliding short circuits 254a and 254b. A portion of the
rod-shaped conductor of each nozzle 256 may be located within the
high-energy regions to collect the microwave energy, as illustrated
in FIG. 8.
[0078] In an alternative embodiment, two separate microwave power
heads may replace the microwave source 233, where each microwave
power head may transmit microwaves to the microwave cavity 250. In
such embodiment, two microwaves may have different wavelengths and
amplitudes, and as a consequence, the intervals 264a and 264b may
be different from each other. Likewise, the widths 266a and 266b of
the high-energy regions may be different from each other.
[0079] FIG. 9 is a schematic diagram of a microwave cavity and
waveguides, collectively shown at 270, for generating high-energy
regions in a two-dimensional array form in accordance with still
another embodiment of the present invention. As illustrated, a
microwave cavity 276 may receive four microwaves 274a to 274d
traveling through four waveguides 272a to 272d, respectively. The
phases of the microwaves may be controlled by a corresponding one
of four non-rotating phase shifters (not shown in FIG. 9) coupled
to the waveguides 272a to 272d, respectively. The four microwaves
274a to 274d may be generated by one or more microwave power heads.
Each of four microwaves 274a to 274d may be generated by a
corresponding one of the four microwave power heads, respectively.
In an alternative embodiment, two microwave power heads generate
microwaves, where each microwave is split into two microwaves. In
another alternative embodiment, one microwave power head may be
split into four microwaves using a power splitter having four
outlets. It is noted that these three embodiments are provided for
exemplary purposes only. Thus, it should be apparent to those of
ordinary skill that any suitable system with the capability of
providing four microwaves may be used with the microwave waveguides
272a to 272d without deviating from the present invention.
[0080] Various embodiments of nozzles in FIGS. 6A-6F and walls of
microwave cavities in FIG. 4B-4D that form gas flow channels may be
also applied to the systems described in FIG. 9. For simplicity,
such embodiments have not been shown.
[0081] Referring back to FIG. 8, the intervals 264a and 264b
between two neighboring nozzles in x- and z-directions may be half
wavelengths of the microwaves shown by the waveforms 260a and 260b,
respectively. In some applications, these half-wavelength intervals
may introduce fluctuations in plasma characteristics along the x-
and z-directions and, as a consequence, smaller intervals may be
required. For example, FIG. 10 schematically shows an alternative
interference pattern of the high-energy regions found within the
microwave cavity of the systems depicted in FIGS. 7 and 9. As
illustrated, each high-energy region 268' may contain more than one
nozzle 256' providing smaller intervals between neighboring
nozzles. By reducing the intervals, the nozzle array coupled to the
microwave cavity 250' may be able to generate a plasma having an
enhanced uniformity in both x- and z-directions. As in the case of
FIG. 8, the width 266a' of each high energy region 268' may be
controlled by adjusting the phase difference between two microwaves
260a' and 261a', while the width 266b' may be controlled by
adjusting the phase difference between two microwaves 260b' and
261b'.
[0082] FIG. 11 is a schematic diagram of a system shown at 310 and
having a plasma nozzle array 337 in accordance with still another
embodiment of the present invention. As illustrated, the system
shown at 310 is quite similar to the system shown at 10 (FIG. 1)
with the difference that nozzles 336 in a nozzle array 337 may
receive gas directly from a gas tank 334. The gas line 370 from the
gas tank 334 may have a plurality of branches 371, wherein each
branch may be coupled to one of the nozzles 336 and formed of a
conventional gas tube.
[0083] FIG. 12 shows a cross-sectional view of the microwave cavity
332 and nozzle array 337 taken along a direction normal to the
z-axis in FIG. 11. As illustrated, a nozzle 336 may includes: a gas
flow tube 358; a grounded shield 360 for reducing microwave loss
through gas flow tube 358 and sealed with the cavity wall 332, the
gas flow tube 358 being tightly fitted into the grounded shield
360; a rod-shaped conductor 352 having a portion 354 disposed in
the microwave cavity 332 for receiving microwaves from within the
microwave cavity 332; a position holder 356 disposed between the
rod-shaped conductor 352 and the grounded shield 360 and configured
to securely hold the rod-shaped conductor 352 relative to the
ground shield 360; and a gas feeding mechanism 362 for coupling the
branch 371 to the grounded shield 360. The position holder 356,
grounded shield 360 and rod-shaped conductor 352 may be made of the
same materials as those of the vortex guide 146 (FIG. 4D), grounded
shield 178 (FIG. 6B) and rod-shaped conductor 152 (FIG. 4D),
respectively. For example, the grounded shield 360 may be made of
metal and preferably copper.
[0084] As illustrated in FIG. 12, the nozzle 336 may receive gas
through the gas feeding mechanism 362. The gas feeding mechanism
362 may be a pneumatic one-touch fitting (model No. KQ2H05-32) made
by SMC Corporation of America, Indianapolis, Ind. One end of the
gas feeding mechanism 362 has a threaded bolt that mates with the
female threads formed on the edge of a hole 364 in the grounded
shield 360 as illustrated in FIG. 13. It should be apparent to
those of ordinary skill that the present invention may be practiced
with other suitable types of gas feeding mechanisms. Several
embodiments of the nozzles 336 and the microwave cavity 332 that
may be used for the system 310 are discussed in the previously
referred PCT Application entitled "Microwave Plasma Nozzle with
Enhanced Plume Stability and Heating Efficiency," filed on Jul. 7,
2005.
[0085] FIG. 13 is an exploded perspective view of the nozzle 336
shown in FIG. 12. As illustrated, the rod-shaped conductor 352 and
the grounded shield 360 can engage the inner and outer perimeters
of the position holder 356, respectively. The rod-shaped conductor
352 may have a portion 354 that acts as an antenna to collect
microwaves from the microwave cavity 332. The collected microwave
may travel along the rod-shaped conductor 352 and generate plasma
338 using the gas flowing through the gas flow tube 358. The term
rod-shaped conductor is intended to cover conductors having various
cross sections such as circular, oval, elliptical, or an oblong
cross section, or any combinations thereof.
[0086] The microwaves may be collected by the portion 354 of the
rod-shaped conductor 352 that extends into the microwave cavity
332. These microwaves travel down the rod-shaped conductor toward
the tapered tip. More specifically, the microwaves are received by
and travel along the surface of the rod-shaped conductor 352. The
depth of the skin responsible for microwave penetration and
migration is a function of the microwave frequency and the
conductor material. The microwave penetration distance can be less
than a millimeter. Thus, a rod-shaped conductor 400 of FIG. 14A
having a hollow portion 401 is an alternative embodiment for the
rod-shaped conductor 352.
[0087] It is well known that some precious metals are good
microwave conductors. Thus, to reduce the unit price of the device
without compromising the performance of the rod-shaped conductor,
the skin layer of the rod-shaped conductor can be made of precious
metals that are good microwave conductors while cheaper conducting
materials can be used for inside of the core. FIG. 14B is a
cross-sectional view of another alternative embodiment of a
rod-shaped conductor, wherein a rod-shaped conductor 402 includes
skin layer 406 made of a precious metal and a core layer 404 made
of a cheaper conducting material.
[0088] FIG. 14C is a cross-sectional view of yet another
alternative embodiment of the rod-shaped conductor, wherein a
rod-shaped conductor 408 includes a conically-tapered tip 410.
Other cross-sectional variations can also be used. For example,
conically-tapered tip 410 may be eroded by plasma faster than
another portion of rod-conductor 408 and thus may need to be
replaced on a regular basis.
[0089] FIG. 14D is a cross-sectional view of another alternative
embodiment of the rod-shaped conductor, wherein a rod-shaped
conductor 412 has a blunt-tip 414 instead of a pointed tip to
increase the lifetime thereof.
[0090] FIG. 14E is a cross-sectional view of another alternative
embodiment of the rod-shaped conductor, wherein a rod-shaped
conductor 416 has a tapered section 418 secured to a cylindrical
portion 420 by a suitable fastening mechanism 422 (in this case,
the tapered section 418 can be screwed into the cylindrical portion
420 using the screw end 422) for easy and quick replacement
thereof.
[0091] FIGS. 14F-14I show cross-sectional views of further
alternative embodiments of the rod-shaped conductor. As
illustrated, rod-shaped conductors 421, 424, 428 and 434 are
similar to their counterparts 352 (FIG. 13), 400 (FIG. 14A), 402
(FIG. 14B) and 416 (FIG. 14E), respectively, with the difference
that they have blunt tips for reducing the erosion rate due to
plasma. It is noted that the various embodiments of rod-shaped
conductor depicted in FIGS. 14A-14I can be used in any embodiment
of the nozzle described in FIGS. 1 and 3-13.
[0092] FIG. 15 shows a flowchart 500 illustrating exemplary steps
for configuring a microwave plasma nozzle array in accordance with
at least one embodiment of the present invention. At step 502, the
first pair of microwaves is directed into a microwave cavity in
opposing directions along a first axis. Next, at step 504, the
second pair of microwaves is directed into the microwave cavity in
opposing directions along a second axis, where the first axis is
normal to the second axis such that the first and the second pairs
of microwaves interfere to yield high-energy regions that are
stationary within the microwave cavity. Then, a phase of at least
one microwave selected from the first and second pair of microwaves
is adjusted to control the high-energy regions at step 506.
Finally, at step 508, a nozzle array is coupled to the microwave
cavity, where one or more nozzle elements of the nozzle array are
configured to collect the microwave energy from a corresponding one
of the high-energy regions.
[0093] While the present invention has been described with a
reference to the specific embodiments thereof, it should be
understood, of course, that the foregoing relates to preferred
embodiments of the invention and that modifications may be made
without departing from the spirit and the scope of the invention as
set forth in the following claims.
[0094] In addition, many modifications may be made to adapt a
particular situation, systems, process, process step or steps, to
the objective, the spirit and the scope of the present invention.
All such modifications are intended to be within the scope of the
claims appended hereto.
* * * * *
References