Patent Publication Number: US-7719200-B2

Title: Plasma generator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This nonprovisional patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/659,365, filed Mar. 7, 2005, and U.S. Provisional Patent Application Ser. No. 60/691,852, filed Jun. 17, 2005, the disclosures of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   This invention is drawn generally to plasma generators. In particular, the present invention is drawn to a plasma generator capable of producing a plasma plume or jet in open room air. 
   SUMMARY OF THE INVENTION 
   The present invention relates generally to plasma generators. In particular, the present invention relates to a plasma generator capable of producing a relatively long plasma plume or jet in open room air. 
   Non-thermal plasmas, or “cold plasmas”, at or near atmospheric pressures have recently received increased attention because of their use in several emerging novel applications such as excimer light sources, the surface modifications of polymers, and the biological and chemical decontamination of media. Generating plasma in open room air adds the advantage of eliminating the need for an enclosure. Due to the abundant presence of oxygen, nitrogen, and moisture in air, reactive chemical species are produced. Additionally, since the whole process is carried out at atmospheric pressure, no costly and impractical vacuum equipment is necessary. 
   The plasma generator of this invention is capable of producing a relatively long plasma plume or jet in open room air. The generated plasma plume remains at room temperature and can be placed in contact with sensitive materials such as skin, flesh, paper, cloth, etc. without causing any damage. Another advantage of the plasma generator of this invention is its portability. 
   In various exemplary, non-limiting embodiments, the plasma generator, or “plasma pencil”, comprises a cylindrical dielectric tube with a hole at the end where the plasma plume exits. Thus, the plasma pencil can be hand-held like a “pencil” and the generated plume can be applied to the sample under treatment. 
   In various exemplary embodiments, the plasma pencil can be used in applications requiring localized and precise plasma-treatment of materials that cannot withstand the harsh treatment of wet chemicals, high temperatures, or mechanical pressure. The plasma pencil provides a means for disinfection, sterilization, and/or precise cleaning of small surfaces, disinfection of skin or wounds, inactivation of dental bacteria, and the like. The medical field including dentistry is only one exemplary area of use of the plasma pencil. 
   Accordingly, this invention provides a plasma pencil, which can be used for sterilization, plasma-assisted wound healing, and/or cell detachment. 
   This invention separately provides a plasma pencil, which can be used for inactivation of dental bacteria, cleaning of dental caries, and/or sterilization of dental tools. 
   This invention separately provides a plasma pencil, which can be used for modification of surface properties (hydrophilic, oleophilic . . . ), for example, of materials such as polymers. 
   This invention separately provides a plasma pencil, which is portable, scalable, environmentally safe, easy to use, and operates at a relatively low temperature. 
   This invention separately provides a plasma pencil, which allows for the generation of a single cold plasma plume. 
   This invention separately provides a plasma pencil, which allows for the generation of multiple cold plasma plumes simultaneously. 
   This invention separately provides a plasma pencil, which generates one or more plasma plumes at room temperature. 
   This invention separately provides a plasma pencil, which generates one or more plasma plumes that can be placed in contact with sensitive materials such as skin, flesh, paper, cloth, etc. without causing any damage. 
   This invention separately provides a plasma pencil, which may be portable. 
   This invention separately provides a plasma pencil, which has a simplified design. 
   These and other features and advantages of this invention are described in or are apparent from the following detailed description of the exemplary embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein like reference numerals refer to like parts throughout the several views, and wherein: 
       FIG. 1  shows a functional block diagram of a first illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention; 
       FIG. 2  shows a functional block diagram of a second illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention; 
       FIG. 3  shows a functional block diagram of a third illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention; and 
       FIG. 4  shows a functional block diagram of a fourth illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   For simplicity and clarification, the design factors and operating principles of the plasma pencil according to this invention are explained with reference to various exemplary embodiments of a plasma pencil according to this invention. The basic explanation of the design factors and operating principles of the plasma pencil is applicable for the understanding, design, and operation of the plasma pencil of this invention. 
   Furthermore, it should be appreciated that, for simplicity and clarification, the embodiments of this invention will be described with reference to the plasma pencil comprising circular dielectric disks and a cylindrical dielectric tube. However, it should be appreciated that the dielectric disks and dielectric tube or tubes of this invention may comprise circular, oval, rectangular, square, pentagonal, or any other geometric shapes. 
   It should also be appreciated that the term “plasma pencil” is for basic explanation and understanding of the operation of the plasma pencils, methods, and apparatuses of this invention. Therefore, the term “plasma pencil” is not to be construed as limiting the plasma pencils, methods, and apparatuses of this invention. 
   Furthermore, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding both of those included limits are also included in the invention. 
   Turning now to  FIG. 1 ,  FIG. 1  shows a functional block diagram of a first illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention. As shown in  FIG. 1 , the plasma pencil  100  comprises a dielectric tube  110  having a first end  112  and a second end  114 . At least one first electrode and one second electrode are placed or formed within or proximate a cavity of the dielectric tube  110 . 
   The first electrode comprises a first dielectric disk  130  having a first dielectric aperture  132  formed therein. In various exemplary embodiments, the first dielectric aperture  132  is formed proximate a center of the first dielectric disk  130 . 
   A first ring electrode  134  is attached or coupled to the first dielectric disk  130  so as to at least partially surround the first dielectric aperture  132 . It should be appreciated that the first ring electrode  134  is attached or coupled to the first dielectric disk  130  such that the first ring electrode  134  does not obstruct the first dielectric aperture  132 . 
   The first ring electrode  134  comprises an electrically conductive material, such as, for example, a metal. In various exemplary embodiments, the first ring electrode  134  may be embedded within the first dielectric disk  130 . 
   In various exemplary embodiments, a diameter of the first ring electrode  134  is smaller than a diameter of the first dielectric disk  130 , but is larger than a diameter of the first dielectric aperture  132 . 
   The first ring electrode  134  is electrically coupled, via an electrical connection  136 , to a power supply  170 . 
   Similarly, the second electrode comprises a second dielectric disk  140  having a second dielectric aperture  142  formed therein. In various exemplary embodiments, the second dielectric aperture  142  is formed proximate a center of the second dielectric disk  140 . 
   A second ring electrode  144  is attached or coupled to the second dielectric disk  140  so as to at least partially surround the second dielectric aperture  142 . It should be appreciated that the second ring electrode  144  is attached or coupled to the second dielectric disk  140  such that the second ring electrode  144  does not obstruct the second dielectric aperture  142 . 
   The second ring electrode  144  comprises an electrically conductive material, such as, for example, a metal. In various exemplary embodiments, the second ring electrode  144  may be embedded within the second dielectric disk  140 . 
   In various exemplary embodiments, a diameter of the second ring electrode  144  is smaller than a diameter of the second dielectric disk  140 , but is larger than a diameter of the second dielectric aperture  142 . 
   The second ring electrode  144  is electrically coupled, via an electrical connection  146 , to the power supply  170 . 
   In various exemplary, non-limiting embodiments, at least a portion of the dielectric tube  110 , the first dielectric disk  130 , and/or the second dielectric disk  140  may be formed of glass, plexiglass, quartz, alumina, ceramic, or the like. However, it should be appreciated that the material that comprises each dielectric disk and the material that comprises the dielectric tube may be the same material or may be a different material. It should also be appreciated that the dielectric tube  110 , the first dielectric disk  130 , and/or the second dielectric disk  140  may be formed of multiple materials. Thus, it should be understood that the material or materials used to form the dielectric tube  110 , the first dielectric disk  130 , and/or the second dielectric disk  140  is a design choice based on the desired appearance, strength, and functionality of the plasma pencil  100 . 
   In various exemplary, non-limiting embodiments, the first end  112  of the dielectric tube  110  is sealed or closed, but for a gas inlet  120 . The first dielectric disk  130  is located within the cavity of the dielectric tube  110 . The second dielectric disk  140  is located within the cavity of the dielectric tube  110 , proximate the second end  114  of the dielectric tube  110 . In various exemplary embodiments, the second dielectric disk  140  is located flush with the second end  114  of the dielectric tube  110 . 
   In various exemplary, non-limiting embodiments, the distance that separates the first dielectric disk  130  from the second dielectric disk  140  is approximately 1-10 mm. 
   Once the plasma pencil  100  is constructed, a carrier gas (or mixture) is injected into the first end  112  of the dielectric tube  110 , via the gas inlet  120 . In various exemplary embodiments, the carrier gas (or mixture) is injected into the plasma pencil at a flow rate of approximately 1-10 ml/min. In various exemplary, non-limiting embodiments, the gas or gas mixtures may comprise helium, helium and oxygen, argon, nitrogen, air, or the like. 
   As the carrier gas (or mixture) is injected into the gas inlet  120 , the gas flows through the cavity of the dielectric tube  110 , through the first dielectric aperture  132  of the first dielectric disk  130 , and finally through the second dielectric aperture  142  of the second dielectric disk  140 . 
   When power is applied to the first ring electrode  134  and the second ring electrode  144 , the injected gas breaks down and a plasma plume  180  is launched through the second dielectric aperture  142  of the second dielectric disk  140 . The generated plasma plume  180  generally extends from the plasma pencil  100  in a direction that is parallel to the main axis of the plasma pencil  100 . The generated plasma plume  180  is at room temperature and remains stable so long as the power is applied to the first ring electrode  134  and the second ring electrode  144  and the carrier gas is flowing. 
   In various exemplary, non-limiting embodiments, the power supply  170  can supply Alternating Current (AC), Radio Frequency (RF) power, or regulated voltage pulses of varying frequencies to the first ring electrode  134  and the second ring electrode  144 . 
   In various exemplary, non-limiting embodiments, the power supply  170  supplies between 1-20 watts of power to the first ring electrode  134  and the second ring electrode  144 . It should be understood that, in various exemplary embodiments, the power supply  170  may supply up to several hundred watts of power to the first ring electrode  134  and the second ring electrode  144 , based on the desired strength, functionality, and/or size of the generated plasma plume  180  or the plasma pencil  100 . 
   In various exemplary embodiments, the plasma plume  180  may measure 2 inches or more, while the width of the plasma plume  180  is generally determined by the diameter or size of the second dielectric aperture  142 . In various exemplary embodiments, the diameter of the second dielectric aperture  142  may be approximately 1 mm to a few millimeters. 
     FIG. 2  shows a functional block diagram of a second illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention. As shown in  FIG. 2 , the plasma pencil  200  comprises a dielectric tube  210  having a first end  212  and a second end  214 . In various exemplary, non-limiting embodiments, the first end  212  of the dielectric tube  210  is sealed or closed, but for a gas inlet  220 . 
   At least one first electrode and one second electrode are placed or formed within or proximate a cavity of the dielectric tube  210 . The first electrode comprises a first dielectric disk  230  having a first dielectric aperture  232  formed therein and a first ring electrode  234  that at least partially surrounds the first dielectric aperture  232 . The first ring electrode  234  is electrically coupled, via an electrical connection  236 , to a power supply  270 . 
   Similarly, the second electrode comprises a second dielectric disk  240  having a second dielectric aperture  242  formed therein and a second ring electrode  244  that at least partially surrounds the second dielectric aperture  242 . The second ring electrode  244  is electrically coupled, via an electrical connection  246 , to the power supply  270 . 
   It should be understood that each of these elements, if included, corresponds to and operates similarly to the dielectric tube  110 , the first end  112 , the second end  114 , the gas inlet  120 , the first dielectric disk  130 , the first dielectric aperture  132 , the first ring electrode  134 , the electrical connection  136 , the second dielectric disk  140 , the second dielectric aperture  142 , the second ring electrode  144 , the electrical connection  146 , and the power supply  170 , as described above with reference to the plasma pencil  100  of  FIG. 1 . 
   However, as shown in  FIG. 2 , the gas inlet  220  includes a gas delivery tube that extends into the cavity of the dielectric tube  210 . In various exemplary embodiments, the inner diameter of gas delivery tube is approximately equal to the diameter of the first dielectric aperture  232  and/or the second dielectric aperture  242 . In various other exemplary embodiments, the inner diameter of gas delivery tube is larger than the diameter of the first dielectric aperture  232  and/or the second dielectric aperture  242 . 
     FIG. 3  shows a functional block diagram of a third illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention. As shown in  FIG. 3 , the plasma pencil  300  comprises a dielectric tube  310  having a first end  312  and a second end  314 . In various exemplary, non-limiting embodiments, the first end  312  of the dielectric tube  310  is sealed or closed, but for a gas inlet  320 . 
   At least one first electrode and one second electrode are placed or formed within or proximate a cavity of the dielectric tube  310 . The first electrode comprises a first dielectric disk  330  having a first dielectric aperture  332  formed therein and a first ring electrode  334  that at least partially surrounds the first dielectric aperture  332 . The first ring electrode  334  is electrically coupled, via an electrical connection  336 , to a power supply  370 . 
   Similarly, the second electrode comprises a second dielectric disk  340  having a second dielectric aperture  342  formed therein and a second ring electrode  344  that at least partially surrounds the second dielectric aperture  342 . The second ring electrode  344  is electrically coupled, via an electrical connection  346 , to the power supply  370 . 
   It should be understood that each of these elements, if included, corresponds to and operates similarly to the dielectric tube  110 , the first end  112 , the second end  114 , the gas inlet  120 , the first dielectric disk  130 , the first dielectric aperture  132 , the first ring electrode  134 , the electrical connection  136 , the second dielectric disk  140 , the second dielectric aperture  142 , the second ring electrode  144 , the electrical connection  146 , and the power supply  170 , as described above with reference to the plasma pencil  100  of  FIG. 1 . 
   Optionally, the plasma pencil  300  may include a gas delivery tube that extends from the gas inlet  320  into the cavity of the dielectric tube  310 , as described above, with reference to  FIG. 2 . 
   However, as shown in  FIG. 3 , the plasma pencil  100  includes a dielectric applicator tube  346  that extends from the second dielectric aperture  342  of the second dielectric disk  340 . In various exemplary embodiments, the diameter of the applicator tube  346  is larger than the diameter of the second dielectric aperture  342 , but equal to or smaller than the diameter of the second ring electrode  344 . 
   In various exemplary embodiments, the dielectric applicator tube  346  has a closed distal end and includes a plurality of apertures  348  formed around its circumference at locations where desired plasma plumes  380  are to extend from the dielectric applicator tube  346 . In various exemplary embodiments, the diameter of the apertures  348  is approximately 1-3 mm. 
   When the plasma pencil  300  is in use, plasma plumes  380  extend from each of the apertures  348 . It should be appreciated that these plasma plumes  380  may extend in a direction perpendicular to the main axis of the plasma pencil  300 . Alternatively, the plasma plumes  380  may extend in a direction that is at an obtuse angle to the main axis of the plasma pencil  300 . In still other exemplary embodiments, the plasma plumes  380  may extend in a direction that is at an acute angle to the main axis of the plasma pencil  300 . 
     FIG. 4  shows a functional block diagram of a fourth illustrative, non-limiting embodiment of a plasma generator, or plasma pencil, according to this invention. As shown in  FIG. 4 , the plasma pencil  400  comprises a dielectric tube  410  having a first end  412  and a second end  414 . In various exemplary, non-limiting embodiments, the first end  412  of the dielectric tube  410  is sealed or closed, but for a gas inlet  420 . 
   At least one first electrode and one second electrode are placed or formed within or proximate a cavity of the dielectric tube  410 . The first electrode comprises a first dielectric disk  430  having at least one first dielectric aperture  432  formed therein and a first ring electrode  434  that at least partially surrounds the at least one first dielectric aperture  432 . The first ring electrode  434  is electrically coupled, via an electrical connection  436 , to a power supply  470 . 
   Similarly, the second electrode comprises a second dielectric disk  440  having at least one second dielectric aperture  442  formed therein and a second ring electrode  444  that at least partially surrounds the at least one second dielectric aperture  442 . The second ring electrode  444  is electrically coupled, via an electrical connection  446 , to the power supply  470 . 
   It should be understood that each of these elements, if included, corresponds to and operates similarly to the dielectric tube  110 , the first end  112 , the second end  114 , the gas inlet  120 , the first dielectric disk  130 , the first dielectric aperture  132 , the first ring electrode  134 , the electrical connection  136 , the second dielectric disk  140 , the second dielectric aperture  142 , the second ring electrode  144 , the electrical connection  146 , and the power supply  170 , as described above with reference to the plasma pencil  100  of  FIG. 1 . 
   Optionally, the plasma pencil  400  may include at least one dielectric applicator tube (not shown) that extends from one, from each, or collectively from all of the at least one apertures  442  of the second dielectric disk  440 , as described above, with reference to  FIG. 3 . 
   However, as shown in  FIG. 4 , a dielectric chamber wall  423  is included within the cavity of the dielectric tube  410 . The chamber wall  423  includes a plurality of gas inlet apertures  422  and creates a gas regulating chamber  421  within the cavity of the dielectric tube  410 . In various exemplary embodiments, each gas inlet aperture  422  includes a gas delivery tube that extends from the chamber wall  423  towards the second end  414 . The gas delivery tubes, if included, direct the flow of gas towards the apertures in the first dielectric disk  430  and the second dielectric disk  440 . 
   The gas regulating chamber  421  allows gas from the gas inlet  420  to be more evenly distributed to the plurality of gas inlet apertures  422 . 
   The number, shape, and size of the aperture(s)  432  and the aperture(s)  442  is a design choice based on the desired number, shape, and size of the generated plasma plumes  480 . The first ring electrode  434  and the second ring electrode  444  may be formed so as to surround the aperture(s)  432  and the aperture(s)  442 , respectively, without obstructing them. Alternatively, the first ring electrode  434  and the second ring electrode  444  may be formed so as to separately surround each of the aperture(s)  432  and the aperture(s)  442 , respectively, without obstructing them. 
   While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, the plasma pencil of this invention may comprise a plurality of dielectric disks spaced apart in the dielectric tube. Likewise, the gas regulating chamber, as described above, with reference to  FIG. 4 , may optionally be included in any of the exemplary embodiments of the plasma pencil described herein. 
   Such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed exemplary embodiments. It is to be understood that the phraseology of terminology employed herein is for the purpose of description and not of limitation. Accordingly, the foregoing description of the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes, modifications, and/or adaptations may be made without departing from the spirit and scope of this invention.