Broadband normal-pressure microwave plasma torch

Abstract

The invention relates to the technical field of microwave plasma, in particular to a broadband normal-pressure microwave plasma torch, which adopts the structure provided by the invention and mainly comprises an outer conductor, an inner conductor, a radio frequency connector and a discharge device, the column body is connected between the first conical end and the second conical end, the first conical end is connected with the radio frequency connector, and the second conical end is connected with the discharging device. By means of the structure, the tail end of the inner conductor (electrode) is amplified, namely the second conical end, the electric field flux is increased, the excitation area of the plasma torch is enlarged, stable excitation of large-flow and large-size plasma flames is achieved, impedance matching is unbalanced due to the enlargement of the electrode, two gradually-changed impedance matching structures are additionally arranged on the design of the torch body, and the impedance matching effect is improved. And the disc at the tail end of the electrode is well matched with the coaxial structure.

Description

Technical Field

[0001] The present invention relates to the field of microwave plasma technology, in particular to a broadband atmospheric pressure microwave plasma torch. Background Art

[0002] Microwave plasma has the characteristics of high electron density, high efficiency and high electron temperature. Therefore, microwave plasma torches are widely used in surface treatment, chemical industry, material processing and other fields.

[0003] Plasma torches have attracted widespread attention from both academia and industry due to their widespread application in fields such as material synthesis, thin film fabrication, directional etching, spray coating, and welding. High-flow plasma jets, in particular, have become a hot topic in plasma research due to their high gas flow rate, large flame volume, and ability to process larger amounts of material in a single pass. To achieve high-flow gas excitation, a resonant structure is often a good choice. This structure allows the maximum amount of microwave power to propagate into the cavity, generating a strong electric field and depositing power into the plasma. However, this also results in a smaller jet excitation zone in conventional resonant cavity structures, preventing the production of a large plasma flame. Once the plasma ignites, the excitation zone is further compressed. Consequently, conventional coaxial resonant cavity plasma jets have a thinner and shorter flame, which is clearly unsuitable for surface treatment of large quantities of materials. Therefore, the development and design of plasma devices capable of exciting high-flow and large-volume plasmas under the same conditions has become an urgent need. Summary of the Invention

[0004] The purpose of the present invention is to provide a broadband atmospheric pressure microwave plasma torch to solve the above problems in the prior art.

[0005] The present invention is achieved through the following technical solutions: A broadband atmospheric pressure microwave plasma torch comprises an outer conductor, an inner conductor, a radio frequency connector, and a discharge device. The inner conductor is disposed within the outer conductor, one end of the inner conductor being connected to the radio frequency connector and the other end being connected to the discharge device. The radio frequency connector and the discharge device are respectively connected to the two ends of the outer conductor. The inner conductor includes a first tapered end, a cylinder, and a second tapered end. The cylinder is connected between the first tapered end and the second tapered end. The first tapered end is connected to the RF connector, and the second tapered end is connected to the discharge device. The maximum bottom area of ​​the first tapered end is less than or equal to the minimum bottom area of ​​the second tapered end.

[0006] Preferably, the discharge device includes an air intake device, a quartz tube and a mesh tube, the bottom of the mesh tube is detachably connected to the outer conductor, the quartz tube is arranged in the mesh tube, one end of which is connected to the inner conductor, and the air intake device is arranged at the connection between the quartz tube and the inner conductor.

[0007] Preferably, the air intake device includes two air intake pipes, one end of each air intake pipe is connected to the quartz tube.

[0008] Preferably, through holes are respectively provided on both sides of the outer conductor, and the air inlet pipe passes through the outer conductor through the through holes.

[0009] Preferably, the two air inlet pipes are connected to both sides of the quartz tube in a rotationally symmetrical manner, and the angle between the two air inlet pipes and the horizontal direction is 15 degrees.

[0010] Preferably, a plurality of through holes are provided on the side of the mesh cylinder.

[0011] Preferably, one end of the mesh tube is detachably connected to the outer conductor via a bolt.

[0012] Preferably, the radio frequency connector includes a connecting seat and a thread provided on the connecting seat.

[0013] Preferably, a through hole is provided on a side of the outer conductor close to the RF connector, for one end of the inner conductor to pass through the outer conductor and be connected to the RF connector.

[0014] Preferably, one end of the second tapered end is provided with a groove, and one end of the quartz tube is provided with a protrusion, and the protrusion is provided in the groove.

[0015] The technical solution of the present invention has at least the following advantages and beneficial effects: The structure provided by the present invention primarily comprises an outer conductor, an inner conductor, an RF connector, and a discharge device. The inner conductor comprises a first tapered end, a cylinder, and a second tapered end. The cylinder is connected between the first and second tapered ends. The first tapered end is connected to the RF connector, and the second tapered end is connected to the discharge device. This structure increases the electric field flux and expands the excitation area of ​​the plasma torch, enabling stable excitation of high-flow, large-volume plasma flames. However, the enlargement of the electrode can lead to an imbalance in impedance matching. Two gradually varying impedance matching structures are added to the torch body to ensure a good match between the disc at the end of the electrode and the coaxial structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a schematic cross-sectional view of the present invention; Figure 3 For the present invention Figure 1 Left view of; Figure 4 is a schematic cross-sectional view of the inner conductor of the present invention; Figure 5 Schematic diagram of the structure of the inner conductor of the present invention; Figure 6 is a schematic cross-sectional view of the outer conductor of the present invention; Figure 7 Schematic diagram of the structure of the outer conductor of the present invention; Figure 8 It is a structural schematic diagram of the net cylinder of the present invention; Figure 9 A top view of the net cylinder of the present invention; Figure 10 Schematic cross-sectional view of the net cylinder of the present invention; Figure 11 This is a schematic diagram of the structure of the present invention without the outer conductor; Figure 12 Schematic diagram of the gas flow direction of the air intake of the present invention; Figure 13 The distribution change of the microwave electric field (V / m) at different times of the present invention; Figure 14 is the distribution change of the electron number density (1 / m³) at different times in the present invention.

[0018] Icon: 1-RF connector, 2-outer conductor, 3-air inlet pipe, 4-mesh tube, 5-inner conductor, 6-quartz tube. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0020] Please refer to Figures 1-11 The present invention provides a broadband atmospheric pressure microwave plasma torch, comprising an outer conductor 2, an inner conductor 5, a radio frequency connector 1, and a discharge device. The inner conductor 5 is disposed within the outer conductor 2, one end of the inner conductor 5 being connected to the radio frequency connector 1 and the other end being connected to the discharge device. The radio frequency connector 1 and the discharge device are respectively connected to both ends of the outer conductor 2. Specifically, the outer conductor 2 is a hollow cylindrical structure with one end open. The open end is connected to the discharge device, and the other end is connected to the RF connector 1. The RF connector 1 is used to connect to the input of an external microwave source.

[0021] The inner conductor 5 includes a first tapered end, a cylinder, and a second tapered end. The cylinder is connected between the first tapered end and the second tapered end. The first tapered end is connected to the RF connector 1, and the second tapered end is connected to the discharge device. The maximum bottom area of ​​the first tapered end is less than or equal to the minimum bottom area of ​​the second tapered end.

[0022] Specifically, the inner conductor 5 usually serves as a high-voltage electrode (positive or negative), forming a strong electric field with an external electrode (such as a nozzle or a ground electrode), and ionizing the working gas (such as argon, nitrogen or air) through high-voltage discharge to generate plasma.

[0023] Among them, the first tapered end, the cylinder and the second tapered end are an integrated structure. From the first tapered end to the second tapered end, the cross-sectional area of ​​the inner conductor 5 is in a gradually increasing shape. The first tapered end and the second tapered end are both approximately in the shape of a truncated cone. The upper surface area and the lower surface area of ​​the truncated cone constitute the two bottom areas of the truncated cone. The smallest bottom area of ​​the first tapered end, that is, the fixed top of the first tapered end is connected to the RF connector 1. The largest bottom area of ​​the first tapered end constitutes one end face of the cylinder, and the other end face of the cylinder constitutes the end face with the smallest bottom area of ​​the second tapered end. The largest bottom area of ​​the second tapered segment constitutes the bottom face of the entire structure of the inner conductor 5. By gradually increasing the shape of the inner conductor 5 from one end to the other, a gradually transitioning impedance matching structure is formed, which can reduce reflection and improve microwave energy efficiency.

[0024] The structure provided by the present invention primarily comprises an outer conductor 2, an inner conductor 5, an RF connector 1, and a discharge device. The inner conductor 5 comprises a first tapered end, a cylinder, and a second tapered end. The cylinder is connected between the first and second tapered ends. The first tapered end is connected to the RF connector 1, and the second tapered end is connected to the discharge device. This structure increases the electric field flux and expands the excitation area of ​​the plasma torch, enabling stable excitation of high-flow, large-volume plasma flames. However, the enlargement of the electrode can lead to an imbalance in impedance matching. Therefore, two gradually varying impedance matching structures are added to the torch body to ensure a good match between the disc at the end of the electrode and the coaxial structure.

[0025] In this invention, the jet is treated as a filter with a narrow bandwidth and resonant frequency. It is fed directly through a coaxial structure, achieving maximum efficiency through impedance matching. From an electrical perspective, the impedance matching structure is sensitive to small changes in the electrical load (e.g., plasma). The plasma is ignited at one frequency and operated at a resonant frequency that varies due to changes in plasma impedance. Therefore, the operating network within the jet is said to be bi-stable (ignited and operated). This is achieved by adding a short matching circuit between the jet (without active plasma) and the coaxial inner conductor 5.

[0026] Another effect is a change in impedance matching, which is affected by the presence of conductive material. If the matching wire is sufficiently wide, it will act as an antenna, radiating a portion of the electromagnetic wave. This creates a large electric field flux at the resonant cavity open circuit, significantly improving the efficiency of plasma excitation. However, this also affects the impedance matching. Ignition of the plasma further increases the complexity of the system. Changes in the electrical length of the matching disk are expected to result in a shift to lower frequencies, but due to the complex interactions, it is impossible to precisely calculate the magnitude. Simulations of the system allow for an approximate estimation of these changes.

[0027] In an exemplary embodiment of the present invention, the discharge device includes an air intake device, a quartz tube 6 and a mesh tube 4, the bottom of the mesh tube 4 is detachably connected to the outer conductor 2, the quartz tube 6 is arranged in the mesh tube 4, one end of which is connected to the inner conductor 5, and the air intake device is arranged at the connection between the quartz tube 6 and the inner conductor 5.

[0028] Specifically, the quartz tube 6 is a cylindrical structure with one open end and the other closed, with a hollow interior. A protrusion is provided on the closed end, and a groove is provided at the bottom of one end of the inner conductor 5, i.e., the second tapered end. The quartz tube 6 is connected to the groove at the second tapered end via the protrusion. The quartz tube 6 physically isolates the inner conductor 5 (the high-voltage electrode) from the external electrode (such as the grounded nozzle or reaction chamber), preventing direct short circuits and ensuring that high-voltage discharge occurs only through the gaseous medium. The quartz tube 6 acts as a dielectric barrier, facilitating dielectric barrier discharge. Its insulating properties confine the discharge to the interior or exterior of the tube, forming a uniform low-temperature plasma and avoiding the intense energy concentration associated with arc discharge.

[0029] Secondly, the air intake device includes two air intake pipes 3 , one end of each air intake pipe 3 is connected to the quartz tube 6 .

[0030] Through holes are respectively opened on both sides of the outer conductor 2, and the air inlet pipe 3 passes through the outer conductor 2 through the through holes. The two air inlet pipes 3 are connected to both sides of the quartz tube 6 in a rotationally symmetrical manner. In addition, the angle between the two air inlet pipes 3 and the horizontal direction is 15 degrees, and the gas feed tangential direction is staggered with the axis of the cylinder. Figure 12It can be seen that this air intake method can generate a spiral upward airflow and improve the uniformity of the airflow in the glass tube.

[0031] In an exemplary embodiment of the present invention, a plurality of through holes are opened on the side of the mesh tube 4 , and one end of the mesh tube 4 is detachably connected to the outer conductor 2 via bolts.

[0032] In addition, the RF connector 1 includes a connecting seat and a thread provided on the connecting seat. A through hole is provided on one side of the outer conductor 2 close to the RF connector 1 for one end of the inner conductor 5 to pass through the outer conductor 2 and connect to the RF connector 1 .

[0033] Based on the above structure of the present invention, a plasma simulation was performed, and additional simulations were performed in the finite element simulator COMSOL to evaluate whether the principle can be applied to active plasma.

[0034] In order to better show the state of plasma in the glass tube, a rotational symmetry method is used. Figure 14 It can be seen that microwave power breakdown first occurs at the edge of the matching disk, which is the open circuit point of the coaxial resonant cavity. The microwave energy will be concentrated at the open circuit point. As time goes by, the discharge area concentrates towards the center of the glass tube and the volume gradually increases. When the discharge time reaches When the discharge reaches 0.05 seconds, the discharge becomes stable and the shape of the plasma column no longer changes with time.

[0035] Figure 13 It shows the change of microwave electric field distribution during the discharge process. The electron number density per second is / m³, which is far less than the critical number density of microwave plasma In the initial state, the microwaves are totally reflected by the open-circuit equivalent coaxial line, so they are only in the cavity and near the open-circuit point.

[0036] like Figure 14 As shown, when the electron density exceeds a critical value, the plasma exhibits metallic properties, shielding electromagnetic waves. A thin layer of quartz tube 6 exists between the plasma and the metal wall. This acts as a dual-conductor transmission line for electromagnetics. Electromagnetic waves propagate along the glass column wall and are ultimately dissipated in the plasma.

[0037] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A broadband atmospheric pressure microwave plasma torch, characterized in that: The invention comprises an outer conductor (2), an inner conductor (5), a radio frequency connector (1) and a discharge device, wherein the inner conductor (5) is arranged in the outer conductor (2), one end of the inner conductor (5) is connected to the radio frequency connector (1), and the other end is connected to the discharge device, and the radio frequency connector (1) and the discharge device are respectively connected to the two ends of the outer conductor (2); The inner conductor (5) comprises a first tapered end, a column, and a second tapered end, the column being connected between the first tapered end and the second tapered end, the first tapered end being connected to the radio frequency connector (1), the second tapered end being connected to the discharge device, and the maximum bottom area of ​​the first tapered end being less than or equal to the minimum bottom area of ​​the second tapered end.

2. A broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that: The discharge device comprises an air intake device, a quartz tube (6) and a mesh tube (4); the bottom of the mesh tube (4) is detachably connected to the outer conductor (2); the quartz tube (6) is arranged in the mesh tube (4) and one end of the quartz tube is connected to the inner conductor (5); and the air intake device is arranged at the connection between the quartz tube (6) and the inner conductor (5).

3. A broadband atmospheric pressure microwave plasma torch according to claim 2, characterized in that: The air intake device comprises two air intake pipes (3), one end of each air intake pipe (3) is connected to the quartz tube (6).

4. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that: Through holes are respectively provided on both sides of the outer conductor (2), and the air inlet pipe (3) passes through the outer conductor (2) through the through holes.

5. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that: The two air inlet pipes (3) are connected to both sides of the quartz tube (6) in a rotationally symmetrical manner, and the angle between the two air inlet pipes (3) and the horizontal direction is 15 degrees.

6. A broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that: A plurality of through holes are provided on the side surface of the mesh cylinder (4).

7. The broadband atmospheric pressure microwave plasma torch according to claim 3, characterized in that: One end of the mesh cylinder (4) is detachably connected to the outer conductor (2) via a bolt.

8. The broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that: The radio frequency connector (1) comprises a connecting seat and a thread arranged on the connecting seat.

9. The broadband atmospheric pressure microwave plasma torch according to claim 1, characterized in that: A through hole is provided on one side of the outer conductor (2) close to the radio frequency connector (1), for one end of the inner conductor (5) to pass through the outer conductor (2) and connect to the radio frequency connector (1).

10. The broadband atmospheric pressure microwave plasma torch according to claim 2, characterized in that: One end of the second tapered end is provided with a groove, and one end of the quartz tube (6) is provided with a protrusion, and the protrusion is arranged in the groove.

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