Coaxial microwave plasma torch device with tunable resonance frequency

Abstract

The application discloses a coaxial microwave plasma torch device with adjustable resonant frequency, which comprises an outer sleeve, a microwave transmission coaxial unit, an H-section tuning coaxial unit and an L-section tuning coaxial unit arranged in the outer sleeve in sequence along a microwave transmission direction, a tapered end cover arranged at one end of the outer sleeve, and a microwave and gas outlet arranged at the end of the tapered end cover; a first slot, a second slot and a plurality of gas inlets are arranged on the outer wall of the outer sleeve in sequence along the microwave transmission direction; a slotted movable dial unit is installed at the first slot, and the movable dial unit is connected with the H-section tuning coaxial unit; the device further comprises a first positioning pin and a second positioning pin, wherein one end of the first positioning pin is connected with the microwave transmission coaxial unit by penetrating the slot of the movable dial unit, the first slot and the microwave transmission coaxial unit in sequence, and one end of the second positioning pin is connected with the H-section tuning coaxial unit by penetrating the second slot. The device can effectively improve the tuning accuracy and the energy coupling efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetism and plasma, and particularly relates to a coaxial microwave plasma torch device with adjustable resonant frequency. BACKGROUND

[0002] The microwave plasma torch is a device that ionizes gas through high-frequency electromagnetic waves (2.45 GHz) and sprays out a flame-shaped plasma. It can be applied to object surface treatment, gas decomposition and conversion, spectrometers, and metal cutting, and has a wide range of applications in modern industrial production. The microwave plasma torchs currently used in the market can be divided into rectangular waveguides, cylindrical waveguides, and coaxial waveguides according to the transmission mode. Most of them are coupled with gas through electric field to realize gas ionization, regardless of the transmission mode. At present, the rectangular waveguide and the coaxial waveguide are more commonly used. Since the coaxial waveguide designed plasma torch device can transmit TEM waves and is suitable for low-power (<1kW) operation, it can be used for stable molecular gas conversion, such as CO2, and has good applicability in structure. Therefore, the coaxial plasma torch device is more widely used in research and application. In the use of the microwave plasma torch device, the change of working condition parameters will cause the change of electrical parameters at the discharge end, so that the resonant frequency of the plasma torch device also changes. Therefore, it is necessary to adjust (referred to as tuning) the resonant frequency of the plasma torch, so that the plasma torch and the microwave are re-coupled to reach the resonant state and improve the energy utilization rate.

[0003] In the tuning mode, it is mainly divided into active and passive. The active type directly adjusts the frequency of the input microwave without adjusting the resonant frequency of the plasma torch. This method requires a solid-state microwave source with precise adjustable frequency and other equipment, which is high in cost. The passive type directly adjusts the resonant frequency of the microwave plasma device without changing the frequency of the input microwave. Usually, only the geometric properties of the device resonant cavity need to be changed to achieve the tuning purpose, which has the advantages of flexible and diverse tuning mode and low cost, and is more commonly used.

[0004] In the past passive plasma torch tuning, mostly by adjusting the position of the microwave side feed entrance or adjusting the cavity reflection end face position to achieve tuning (such as the publication date is 2014-07-23, the publication number is CN 103945631 A, the application number is 2014101358979, the invention name is "an improved microwave plasma torch device and application" patent). The traditional tuning method only considers one tuning cavity or one tuning variable (i.e. one-way tuning), can only be tuned to odd multiple bands, and it is difficult to achieve tuning within the limited geometric size range, and there are problems of large tuning scale and inconvenient tuning. At the same time, due to the limitation of wavelength and cavity size in the traditional tuning method, only one resonance state of the device under the corresponding working condition is often obtained, and whether this resonance state is the best resonance state cannot be determined, and there is a problem of insufficient tuning accuracy. Even if there are two tuning cavities in the traditional plasma torch tuning, the related dimensions of the two tuning cavities are the same, and the two cavities are related during tuning, and independent tuning in the double variable mode cannot be achieved, and the purpose of accurate tuning cannot be achieved. At the same time, since the traditional plasma torch tuning does not consider the overall equivalent circuit model of the plasma torch device during discharge, and does not realize independent tuning of two different cavities (i.e. two-way tuning) combined with the two-way inductive coupling principle in the circuit, there are problems of imperfect tuning method and insufficient tuning accuracy. SUMMARY

[0005] The purpose of the invention is to provide a coaxial microwave plasma torch device with adjustable resonance frequency, which can effectively improve the tuning accuracy, reduce the tuning scale and improve the energy coupling efficiency in the two-way tuning mode.

[0006] The technical scheme adopted by the present invention is a coaxial microwave plasma torch device with adjustable resonance frequency, which comprises an outer sleeve, a microwave transmission coaxial unit, an H-section tuning coaxial unit and an L-section tuning coaxial unit are arranged in the outer sleeve along the microwave transmission direction in sequence, a conical end cover is arranged at one end of the outer sleeve, and a microwave and gas outlet is arranged at the end of the conical end cover; a first slot, a second slot and a plurality of gas inlets are arranged on the outer wall of the outer sleeve along the microwave transmission direction; a slotted movable dial unit is installed at the first slot, and the movable dial unit is connected with the H-section tuning coaxial unit; further comprising a first positioning pin and a second positioning pin, wherein one end of the first positioning pin passes through the slot of the movable dial unit and the first slot in sequence and is connected with the microwave transmission coaxial unit, the microwave transmission coaxial unit is driven to move by moving the first positioning pin, one end of the second positioning pin passes through the second slot and is connected with the H-section tuning coaxial unit, the H-section tuning coaxial unit is driven to move by moving the second positioning pin.

[0007] The features of the present invention are further characterized in that,

[0008] The microwave transmission coaxial unit comprises an inner sleeve arranged in an outer sleeve, an outer wall of the inner sleeve is in a convex shape, a first section shaft is arranged in the inner sleeve, a shaft support is arranged between the first section shaft and the inner wall of the inner sleeve, the inner sleeve and the first section shaft are connected through the shaft support, and the shaft support is in interference fit with the first section shaft and the inner sleeve respectively;

[0009] The H-section tuning coaxial unit comprises a middle sleeve arranged in an outer sleeve, a connecting shaft sleeve is arranged in the middle sleeve, a sleeve support is arranged between the connecting shaft sleeve and the middle sleeve, the middle sleeve and the connecting shaft sleeve are connected through the sleeve support, and the sleeve support is in interference fit with the connecting shaft sleeve and the middle sleeve respectively; one end of a second positioning pin is fixedly connected to the outer wall of the middle sleeve through a third pin hole; the middle sleeve is further connected with a mobile dial unit;

[0010] The L-section tuning coaxial unit comprises a second section shaft and an insulating partition plate arranged in an outer sleeve, the insulating partition plate is sleeved on the outer wall of the second section shaft; the outer sleeve and the second section shaft are connected through the insulating partition plate, the insulating partition plate is in interference fit with the outer sleeve and the second section shaft respectively, and the three parts form an integral whole fixed relative to the inner sleeve and the middle sleeve;

[0011] One end of the middle sleeve is sleeved on the outer wall of the inner sleeve, the inner sleeve and the middle sleeve are in clearance fit, and the two can slide relative to each other; a first end of the connecting shaft sleeve is sleeved on the outer wall of the first section shaft, the first section shaft and the connecting shaft sleeve are in clearance fit, and the two can slide relative to each other; a second end of the connecting shaft sleeve is sleeved on the outer wall of the second section shaft, the second section shaft and the connecting shaft sleeve are in clearance fit, and the two can slide relative to each other.

[0012] The mobile dial unit comprises a curved scale plate covering the first notch, a scale disc notch is formed in the plate body of the curved scale plate, and a scale is arranged on the notch edge of the scale disc notch; the curved scale plate is further provided with a third positioning pin in the direction of the first notch, one end of the third positioning pin is fixedly connected to the outer wall of the middle sleeve through a second pin hole. The curved scale plate is coaxially matched with the outer sleeve, when the middle sleeve moves, the mobile dial unit will slide together with the outer wall of the outer sleeve in the first notch area, and the design purpose of the mobile dial unit is to eliminate the inconvenience of operation caused by relative sliding on the tuning positioning of the H-section tuning area.

[0013] A scale is arranged on the notch edge of the second notch.

[0014] Under the input of microwave with a frequency of 2.45GHz, the displacement adjustment range of the first positioning pin in the scale disc notch is 0-15mm; the displacement adjustment range of the second positioning pin in the second notch is 0-20mm; wherein the total length variation range of the H tuning area and the L tuning area in the axial direction is 45mm~72mm.

[0015] The beneficial effects of the present application are:

[0016] Compared with the traditional device, the resonant frequency adjustable coaxial microwave plasma torch device can change the microwave reflection end face position of two different size cavities by moving two coaxial conductor sleeves according to the impedance coupling matching principle and electromagnetic wave transmission characteristics, so as to change the electrical parameters of different cavities, thereby realizing one-way or two-way tuning. In the two-way tuning mode, the tuning accuracy can be effectively improved, the tuning scale can be reduced, and certain tuning requirements of the microwave plasma torch device under different discharge states can be met. At the same time, multiple resonance states under corresponding working conditions can be obtained, and an optimal resonance state can be found, so that the reflection coefficient is reduced to the lowest, the energy coupling efficiency is improved, and specific tuning rules and specific tuning parameter ranges are obtained according to simulation, so that the axial size and tuning range of the whole plasma torch device are within 3 / 4 wavelength or about 1 / 4 wavelength, and the structure is small. The resonant frequency adjustable coaxial microwave plasma torch device is mainly applied to the decomposition and conversion of CO2, and can help to improve the conversion efficiency of CO2. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the overall assembly schematic diagram of the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0018] Fig. 2 is a main sectional view of the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0019] Fig. 3 is a top view of Figure 2 ;

[0020] Fig. 4 is a structural schematic diagram of the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0021] Figure 5 is the front view of the moving scale disc in the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0022] Figure 6 is the right view of the moving scale disc in the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0023] Figure 7 is the top view of the moving scale disc in the resonant frequency adjustable coaxial microwave plasma torch device of the present application;

[0024] Figure 8 is the working principle diagram of the coaxial microwave plasma torch device with adjustable resonance frequency of the present application;

[0025] Figure 9 is the equivalent circuit principle diagram of the coaxial microwave plasma torch device with adjustable resonance frequency of the present application;

[0026] Figure 10 is the S11 parameter test schematic diagram;

[0027] Figure 11 is the conductivity distribution diagram when the maximum conductivity is 2 (S / m);

[0028] Figure 12 is the conductivity distribution diagram when the maximum conductivity is 10 (S / m);

[0029] Figure 13 is the conductivity distribution diagram when the maximum conductivity is 100 (S / m);

[0030] Figure 14 is the conductivity distribution diagram when the maximum conductivity is 150 (S / m);

[0031] Figure 15 is the conductivity distribution diagram when the maximum conductivity is 1000 (S / m);

[0032] Figure 16 is the conductivity distribution diagram when the maximum conductivity is 3000 (S / m);

[0033] Figure 17 is the optimal resonance position change rule diagram when the conductivity is zero;

[0034] Figure 18 is the optimal resonance position change rule diagram when the conductivity distribution is as shown in Figure 11 ;

[0035] Figure 19 is the optimal resonance position change rule diagram when the conductivity distribution is as shown in Figure 12 ;

[0036] Figure 20 is the optimal resonance position change rule diagram when the conductivity distribution is as shown in Figure 13 ;

[0037] Figure 21 is the optimal resonance position change rule diagram when the conductivity distribution is as shown in Figure 17 ;

[0038] Figure 22 is the optimal resonance position change rule diagram when the conductivity distribution is as shown in Figure 18 ;

[0039] Figure 23 is the best resonance position change rule when the conductivity distribution is as shown in Figure 19 ;

[0040] Figure 24 is the axial length change rule of H tuning section and L tuning section when the conductivity distribution changes to reach the best resonance position.

[0041] In the figure, 1. first positioning pin, 2. moving scale disc unit, 3. sleeve support, 4. second positioning pin, 5. outer sleeve, 6. insulating partition, 7. second section shaft, 8. connecting shaft sleeve, 9. middle sleeve, 10. inner sleeve, 11. first section shaft, 12. shaft support, 13. conical end cover, 2-1. curved scale plate, 2-2. third positioning pin, 2-3. scale disc notch, 5-1. first notch, 5-2. second notch, 5-3. gas inlet, 9-1. second pin hole, 9-2. third pin hole, 10-1. first pin hole, 13-1. microwave and gas outlet, 14. microwave generator, 15. directional coupler, 16. coaxial microwave plasma torch device, 17. gas cylinder, 18. power detector. DETAILED DESCRIPTION

[0042] The present application will be described in detail below in conjunction with the drawings and specific embodiments.

[0043] The present application provides a coaxial microwave plasma torch device with adjustable resonance frequency, as shown in Figures 1-7 , comprising an outer sleeve 5, a microwave transmission coaxial unit, an H-section tuning coaxial unit and an L-section tuning coaxial unit are sequentially arranged in the outer sleeve 5 along the microwave transmission direction, a conical end cover 13 is arranged at one end of the outer sleeve 5, and a microwave and gas outlet 13-1 is arranged at the end of the conical end cover 13; a first notch 5-1, a second notch 5-2 and a plurality of gas inlets 5-3 are sequentially arranged on the outer wall of the outer sleeve 5 along the microwave transmission direction; a notched moving scale disc unit 2 is installed at the first notch 5-1, and the moving scale disc unit 2 is connected with the H-section tuning coaxial unit; further comprising a first positioning pin 1 and a second positioning pin 4, wherein one end of the first positioning pin 1 sequentially passes through the notch of the moving scale disc unit 2 and the first notch 5-1 and is connected with the microwave transmission coaxial unit, the microwave transmission coaxial unit is moved by moving the first positioning pin 1, one end of the second positioning pin 4 passes through the second notch 5-2 and is connected with the H-section tuning coaxial unit, the H-section tuning coaxial unit is moved by moving the second positioning pin 4.

[0044] The microwave transmission coaxial unit comprises an inner sleeve 10 arranged in the outer sleeve 5, the outer wall of the inner sleeve 10 is in the shape of a Chinese character "N", a first section shaft 11 is arranged in the inner sleeve 10, a shaft support 12 is arranged between the first section shaft 11 and the inner wall of the inner sleeve 10, the inner sleeve 10 and the first section shaft 11 are connected through the shaft support 12, and the shaft support 12 is in interference fit with the first section shaft 11 and the inner sleeve 10 respectively; one end of the first positioning pin 1 is fixedly connected with the outer wall of the inner sleeve 10 through the first pin hole 10-1;

[0045] The H-section tuning coaxial unit comprises a middle sleeve 9 arranged in the outer sleeve 5, a connecting shaft sleeve 8 is arranged in the middle sleeve 9, a sleeve support 3 is arranged between the connecting shaft sleeve 8 and the middle sleeve 9, the middle sleeve 9 and the connecting shaft sleeve 8 are connected through the sleeve support 3, and the sleeve support 3 is in interference fit with the connecting shaft sleeve 8 and the middle sleeve 9 respectively; one end of the second positioning pin 4 is fixedly connected with the outer wall of the middle sleeve 9 through the third pin hole 9-2; the middle sleeve 9 is further connected with the mobile dial unit 2;

[0046] The L-section tuning coaxial unit comprises a second section shaft 7 and an insulating partition plate 6 arranged in the outer sleeve 5, the insulating partition plate 6 is sleeved on the outer wall of the second section shaft 7; the outer sleeve 5 and the second section shaft 7 are connected through the insulating partition plate 6, the insulating partition plate 6 is in interference fit with the outer sleeve 5 and the second section shaft 7 respectively, and the three parts form an integral body relative to the inner sleeve 10 and the middle sleeve 9;

[0047] One end of the middle sleeve 9 is sleeved on the outer wall of the inner sleeve 10, the inner sleeve 10 and the middle sleeve 9 are in clearance fit and can slide relative to each other; the first end of the connecting shaft sleeve 8 is sleeved on the outer wall of the first section shaft 11, the first section shaft 11 and the connecting shaft sleeve 8 are in clearance fit and can slide relative to each other; the second end of the connecting shaft sleeve 8 is sleeved on the outer wall of the second section shaft 7, the second section shaft 7 and the connecting shaft sleeve 8 are in clearance fit and can slide relative to each other. The shaft radius of the first section shaft 11 is the same as that of the second section shaft 7;

[0048] As shown in Figures 5-7 The mobile dial unit 2 comprises a curved scale plate 2-1 covering the first notch 5-1, a dial slot 2-3 is formed in the plate body of the curved scale plate 2-1, and a scale is arranged on the notch edge of the dial slot 2-3; the curved scale plate 2-1 is further provided with a third positioning pin 2-2 in the direction of the first notch 5-1, and one end of the third positioning pin 2-2 is fixedly connected with the outer wall of the middle sleeve 9 through the second pin hole 9-1. The curved scale plate 2-1 is coaxially connected with the outer sleeve 5, and when the middle sleeve 9 moves, the mobile dial unit 2 will slide along the outer wall of the outer sleeve 5 in the first notch 5-1 area, and the design purpose of the mobile dial unit 2 is to eliminate the inconvenience caused by relative sliding.

[0049] The notch edge of the second notch 5-2 is provided with a scale.

[0050] The ratio of the second section shaft 7 to the inner wall radius of the outer sleeve 5 is 5.5, the ratio of the outer wall of the connecting sleeve 8 to the inner wall radius of the middle sleeve 9 is 3.9, and the ratio of the first section shaft 11 to the inner wall radius of the inner sleeve 10 is 2.2.

[0051] Under the input of 2.45GHz microwave, the displacement adjustment range of the first positioning pin 1 in the scale notch 2-3 is 0-15mm; the displacement adjustment range of the second positioning pin 4 in the second notch 5-2 is 0-20mm; and the total axial length change range of the H tuning area and the L tuning area is 45mm~72mm.

[0052] Along the microwave transmission direction, there are three coaxial areas distributed in a stepped manner along the microwave transmission direction, which are the microwave transmission area, the H section tuning area and the L section tuning area, respectively. The L section tuning area includes a contraction hole discharge area at the tapered end cover 13, and the axial lengths of the H section and the L section tuning area are both adjustable. The radial outer wall of the H section tuning area is the inner wall of the middle sleeve 9, and the radial inner wall is the outer wall of the connecting sleeve 8. The axial length of the H section tuning area is adjusted by the movable inner sleeve 10 and the first section shaft 11. The radial outer wall of the L section tuning area is the inner wall of the outer sleeve 5, and the radial inner wall is the surface of the second section shaft 7. The axial length of the L section tuning area is adjusted by the movable middle sleeve 9 and the connecting sleeve 8. The microwave transmission coaxial area surrounded by the inner sleeve 10 and the first section shaft 11, the H section tuning coaxial area surrounded by the middle sleeve 9 and the connecting sleeve 8, and the L section tuning coaxial area surrounded by the outer sleeve 5 and the second section shaft 7. The H section tuning coaxial area surrounded by the connecting sleeve 8 and the middle sleeve 9, by moving the inner sleeve 10 and the first section shaft 11 simultaneously through the first positioning pin 1, the axial length of the H section tuning area can be changed to realize H section tuning. The L section tuning coaxial area surrounded by the second section shaft 7 and the outer sleeve 5, by moving the connecting sleeve 8 and the outer sleeve 5 simultaneously through the second positioning pin 4, the axial length of the L section tuning area can be changed to realize L section tuning. Figure 9 According to the equivalent circuit principle diagram shown, according to the different conductivity distribution changes caused by the discharge end under different working conditions, the impedance characteristics of the H section tuning area and the L section tuning area are adjusted to make the coaxial microwave plasma torch device reach the required resonance state.

[0053] The inner sleeve 10 is installed between the first section shaft 11 near the microwave inlet and the middle sleeve 9, and is fixedly connected with the first section shaft 11 through the shaft support 12 and can be moved simultaneously, with a displacement adjustment range of 0-15mm; the middle sleeve 9 is installed between the outer sleeve 5 near the discharge end and the inner sleeve 10, and is coaxially matched with the inner and outer sleeves 5 and 10 and can slide relative to each other, with a displacement adjustment range of 0-20mm; the outer sleeve 5 is fixedly connected with the second section shaft 7 through the insulating partition plate 6 and is fixed relative to the inner sleeve 10 and the middle sleeve 9 without displacement; the first section shaft 11 and the second section shaft 7 are connected through the connecting shaft sleeve 8 and are gap matched and can slide relative to each other; the insulating partition plate 6 divides the L tuning area into a discharge area and a non-discharge area, so that the ionized gas during discharge does not affect the operation of the tuning area; the gas flows in through the gas inlet 5-3 of the outer sleeve 5, only passes through the conical end cover 13, and directly flows out from the microwave and gas outlet 13-1 after ionization; the microwave inlet is a coaxial area between the first section shaft 11 and the inner sleeve 10 on the other side of the discharge port.

[0054] The inner sleeve 10 is connected with the first section shaft 11 through the shaft support 12, the shaft support 12 is interference fitted with the first section shaft 11 and the inner sleeve 10 respectively, and the three form a whole that is fixed relative to each other during movement; the first section shaft 11 is gap fitted with the connecting shaft sleeve 8 and can slide relative to each other; the inner sleeve 10 is gap fitted with the middle sleeve 9 and can slide relative to each other; the first positioning pin 1 is fixedly connected with the inner sleeve 10 through the first pin hole 10-1 and can slide in the moving scale disc slot 2-3 area in the first slot 5-1 area by moving the first positioning pin 1, for tuning and positioning; the connecting shaft sleeve 8 is gap fitted with the first section shaft 11 and the second section shaft 7 respectively and can slide relative to each other.

[0055] The middle sleeve 9 is connected with the connecting shaft sleeve 8 through the sleeve support 3, the sleeve support 3 is interference fitted with the connecting shaft sleeve 8 and the middle sleeve 9 respectively, and the three form a whole that is fixed relative to each other during movement; the middle sleeve 9 is gap fitted with the outer sleeve 5 and the inner sleeve 10 respectively and can slide relative to each other; the middle sleeve 9 is fixedly connected with the second positioning pin 4 through the third pin hole 9-2, and the positioning pin 4 can slide in the second slot 5-2 area for tuning or positioning; the third positioning pin 2-2 of the moving scale disc unit 2 is connected with the middle sleeve 9 through the second pin hole 9-1, the curved scale plate 2-1 is coaxially matched with the outer sleeve 5, and the middle sleeve 9 moves to drive the moving scale disc unit 2 to slide together along the outer wall surface of the outer sleeve 5 in the first slot 5-1 area; the design purpose of the moving scale disc is to eliminate the inconvenience of operation caused by relative sliding for tuning and positioning of the H section coaxial area;

[0056] The outer sleeve 5 is connected with the second section shaft 7 through the insulating partition 6, the insulating partition 6 is in interference fit with the outer sleeve 5 and the second section shaft 7 respectively, and the three parts form a whole fixed relative to the inner sleeve 10 and the middle sleeve 9;

[0057] The two tuning regions of the device can be one-way tuned by moving the inner sleeve 10 and the middle sleeve 9 respectively, and can be two-way tuned by moving the inner sleeve 10 and the middle sleeve 9 simultaneously, so as to obtain the best resonance state. In the setting of the plasma torch geometric parameters, the ratio of the inner wall radius of the second section shaft 7 to the outer sleeve 5 is 5.5, the ratio of the outer wall of the connecting shaft sleeve 8 to the inner wall of the middle sleeve 9 is 3.9, and the ratio of the inner wall of the first section shaft 11 to the inner sleeve 10 is 2.2. Through simulation research, the best resonance parameters of the coaxial microwave plasma torch under different conductivity distribution conditions are obtained. When the load is empty, the axial length of the L tuning region is 22.7mm, which is about 1 / 4 wavelength, and the axial length of the H tuning region is 49.6mm, so that under the same working condition parameters, the strongest electric field in the discharge area and the smallest energy reflection coefficient can be obtained; when the maximum temperature of the discharge gas is stabilized at about 7000K and the maximum conductivity is about 1000S / m, the axial length of the L tuning region is 9.5mm, the axial length of the H tuning region is 41.2mm, and the smallest energy reflection coefficient can be obtained; when the maximum temperature of the discharge gas is stabilized at about 10000K and the maximum conductivity is 3000S / m, the axial length of the L tuning region is 7.6mm, the axial length of the H tuning region is 38mm, and the lowest energy reflection coefficient can be obtained. In the gas discharge, the axial length of the L tuning region and the H tuning region is gradually reduced when the maximum conductivity changes from 10S / m to 3000S / m, so that better impedance matching can be obtained.

[0058] In terms of movement mode, the inner sleeve 10 is fixedly connected with the first section shaft 11 through the shaft support 12, and is fixedly connected with the positioning pin 1, so that the axial length of the H tuning coaxial region surrounded by the middle sleeve 9 and the connecting shaft sleeve 8 can be adjusted by moving the positioning pin 1 to drive the inner sleeve 10; the middle sleeve 9 is fixedly connected with the connecting shaft sleeve 8 through the sleeve support 3, and is fixedly connected with the positioning pin 4 and the moving scale disc unit 2, so that the axial length of the L tuning coaxial region surrounded by the outer sleeve 5 and the second section shaft 7 can be adjusted by moving the positioning pin 4 to drive the connecting shaft sleeve 8 and the middle sleeve 9; the axial lengths of the H tuning coaxial region and the L tuning coaxial region can be independently adjusted by the first positioning pin 1 and the second positioning pin 4 respectively; the outer sleeve 5 is fixedly connected with the second section shaft 7 through the insulating partition 6 to form a fixed whole without relative displacement.

[0059] The injection positions of the microwave and the gas are as shown in Figure 8As shown, microwaves enter the tuning section cavity through the coaxial region surrounded by the inner sleeve 10 and the first shaft 11, and are finally scattered out from the microwave and gas outlet 13-1 of the conical end cap 13 at one end of the outer sleeve 5; gas flows in through the gas inlet 5-3 of the outer sleeve 5, passes through the conical end cap 13, and flows out directly from the outlet 13-1.

[0060] The equivalent circuit model of the tuning device is as follows: Figure 9 As shown, there are mainly two tuning area circuits: the H-segment and the L-segment. These two tuning area circuits are connected together via inductive coupling. The H-segment tuning area circuit corresponds to... Figure 8 Equivalent circuit parameters of the H-segment cavity, Z H C represents the impedance introduced by the walls and medium when microwaves propagate in the H-segment cavity. H The capacitance between the coaxial cavities in segment H is represented; the tuning region circuit in segment L mainly corresponds to the equivalent circuit parameters of the segment L cavity in Figure 8 and the impedance parameters of the plasma, Z. L C represents the impedance introduced by the walls and medium when microwaves propagate in the L-segment cavity. L C represents the capacitance between the L-segment coaxial cavities. open Z represents the capacitance when the terminal is open in the undischarged state. plasma This represents the impedance generated by the plasma during discharge. In the H-segment tuning circuit, element Z... H First, connect it in series with the induction coil L1, and then connect it with component C. H It is connected in parallel with microwave generator 14; in the L-segment tuning circuit, Z L First with C open and Z plasma The two components form a parallel circuit connected in series, and then connected to component C. L It is connected in parallel with induction coil L2. Induction coils L1 and L2 are placed side by side in parallel to achieve inductive coupling, but they are not directly connected electrically.

[0061] Because the coaxial cavity has linear impedance in the axial direction, impedance matching can be achieved by changing the axial length parameters of the L-segment and H-segment cavities. This can be achieved by adjusting the axial length parameters of the L-segment and H-segment cavities. Figure 9 Analysis of the equivalent circuit model and the inductive coupling relationship between them reveals that, with the coupling coefficients of the two tuning regions remaining constant, when the operating parameters change, such as an increase in plasma discharge intensity, the circuit impedance of the L-tuning region decreases, which is equivalent to a decrease in the axial length of the L-section cavity. At this time, the current in the L-tuning region increases, which is coupled to the H-tuning region circuit. The corresponding current in the H-tuning region circuit should decrease, meaning the axial length of the H-section cavity needs to be increased to increase its impedance. This tuning method achieves better impedance matching, and the analysis results of the equivalent circuit model are consistent with... Figure 17 — Figure 23The change rule of the curve has a good corresponding relationship.

[0062] The materials of the shaft support 12, the positioning pin 4, the sleeve support 3 and the insulation partition 6 are quartz, and the materials of the first section shaft 11, the inner sleeve 10, the middle sleeve 9, the connecting shaft sleeve 8, the second section shaft 7 and the outer sleeve 5 are stainless steel, and the surfaces of the shafts are coated with copper.

[0063] The specific tuning mode is implemented by using the experimental test device as shown in Figure 10 The specific connection relationship is that the microwave generator 14 is connected with the directional coupler 15 in series and then directly connected with the microwave plasma torch device 16; the bypass of the directional coupler 15 is connected with the power detector 18 in parallel, so that the S11 value can be obtained in real time; and the gas of the microwave plasma torch device 16 directly comes from the injection of the gas cylinder 17. In the use of the device, the S11 value displayed by the experimental instrument 18 can be observed after the first positioning pin 1 and the second positioning pin 4 of the microwave plasma torch device 16 are adjusted each time, the S11 values of the two tuning operations are compared, the displacement adjustment range of the first positioning pin 1 and the second positioning pin 4 is gradually reduced, so that the microwave plasma torch device can obtain the smallest S11 value and reach the best resonance state. The calculation formula of the S11 parameter in the experimental test is as follows:

[0064]

[0065] The S11 parameter of the microwave plasma torch is the ratio of the reflected power to the incident power, which is a dB value, and is a parameter for describing the degree of impedance matching, wherein is the reflected power, is the incident power.

[0066] The assumed conductivity distribution model of the coaxial microwave plasma torch in the initial discharge is as shown in Figure 11 and Figure 12 . In a certain working condition range (frequency 2.45 GHz, pressure 1 atm, power 50 W~500 W, gas flow 5 l / min~15 l / min), when the discharge is in the outward injection stage, the assumed conductivity distribution is as shown in Figures 13 to 16 . Through COMSOL simulation, the law diagram of the resonance position changing with the length of H and L under different conductivity distribution models is obtained as shown in Figures 17 to 23 . In the diagram, the S11 parameter calculated by the software is equivalent to the S11 value calculated in the experiment.

[0067] In the diagram as shown in Figures 17 to 23 , each curve has a corresponding minimum point, which corresponds to the resonance position under different parameters, wherein the smaller the S11 parameter value is, the higher the energy coupling efficiency is, and the better the matching effect is. From the diagram, it can be seen that the resonance position of the coaxial microwave plasma torch is related to the length of the inner sleeve 10, the middle sleeve 9 and the outer sleeve 5, and the length of the first section shaft 11 and the second section shaft 7.Figures 17 to 23 Each graph in the diagram also shows that, with the plasma conductivity distribution remaining constant and the total length of the two tuning regions within 3 / 4 of the wavelength, gradually increasing the axial length of the H tuning region shifts the resonant position to the left, meaning the axial length of the L tuning region decreases. Based on this principle, an optimal resonant position can be obtained during tuning, which is the minimum value of the minimum value of each curve in each graph. Since the minimum point of each curve in each graph represents a resonant state of the device, the purpose of tuning is to find the location of the minimum point. However, whether the obtained minimum point is the true minimum value is not reflected in traditional tuning methods. Traditional tuning methods only perform unidirectional tuning with a single variable, obtaining only one curve in the graph. The minimum point of that curve is not necessarily the minimum minimum value we need for tuning. Therefore, the main drawback of traditional tuning methods is that it is difficult to obtain the optimal resonant state of the device, resulting in low tuning accuracy.

[0068] The specific tuning parameters obtained through simulation are described and analyzed as follows.

[0069] When the conductivity distribution of the coaxial microwave plasma torch is zero, the following is obtained: Figure 17 The diagram showing the variation of the resonant position with H and L indicates that when H = 49.6 mm and L = 22.7 mm, the coaxial microwave plasma torch reaches the optimal resonant position, the reflection coefficient of the microwave port reaches its minimum value, and the electric field strength reaches its maximum value, which is more conducive to plasma ignition and improves energy coupling efficiency.

[0070] When the conductivity distribution of the plasma torch device is as follows Figure 11 As shown, the following was obtained: Figure 18 The graph shows the variation pattern. From the graph, it can be seen that the device reaches the optimal resonance position when H=36mm and L=23.2mm; when the conductivity distribution is as shown... Figure 12 As shown, the following was obtained: Figure 19 The graph shows the variation pattern. From the graph, it can be seen that the device reaches the optimal resonance position when H=35.5mm and L=23.2mm; when the conductivity distribution is as shown... Figure 13 As shown, the following was obtained: Figure 20 The graph shows the variation pattern. From the graph, it can be seen that the device reaches the optimal resonance position when H=43mm and L=17.4mm; when the conductivity distribution is as shown... Figure 14 As shown, the following was obtained: Figure 21 The graph shows the variation pattern. From the graph, it can be seen that the device reaches the optimal resonance position when H=43mm and L=14.2mm; when the conductivity distribution is as shown... Figure 15 As shown, the following was obtained: Figure 22 The graph shows the variation pattern. From the graph, it can be seen that the device reaches the optimal resonance position when H=41.2mm and L=9.5mm; when the conductivity distribution is as shown...Figure 16 The change rule diagram shown in the figure is obtained, and from the figure, it can be obtained that the device reaches the optimal resonance position when H=38mm and L=7.6mm. Figure 23 The simulation results of formula (1) and formula (2) show that the resonant frequency adjustable coaxial microwave plasma torch device of the application can meet the tuning requirements under different discharge states, is not limited by odd multiple wave bands, can obtain multiple resonance states within a certain geometric length range, can determine the optimal resonance state or the optimal resonance position of the device, and can effectively improve the tuning accuracy and the energy coupling efficiency. Figure 17 Figure 23 The simulation results of formula (1) and formula (2) show that the resonant frequency adjustable coaxial microwave plasma torch device of the application can meet the tuning requirements under different discharge states, is not limited by odd multiple wave bands, can obtain multiple resonance states within a certain geometric length range, can determine the optimal resonance state or the optimal resonance position of the device, and can effectively improve the tuning accuracy and the energy coupling efficiency.

[0071] Through statistical analysis of the optimal resonance position parameters of formula (1) and formula (2), the change rule of the H and L parameters corresponding to the optimal resonance position when the plasma conductivity distribution changes is obtained, as shown in the figure. Figures 17 to 23 From the figure, it can be obtained that when the maximum conductivity is greater than 10S / m, the axial size of the H tuning section and the L tuning section is gradually reduced with the increase of the conductivity, and the optimal resonance state can be obtained, which provides meaningful guidance and theoretical support for the operation of the resonant frequency adjustable coaxial microwave plasma torch device of the application. When the conductivity distribution is greater than 10S / m, from the figure, it can be obtained that the axial size of the H section cavity changes in the range of 35mm~50mm, corresponding to the displacement range of 0~15mm of the first positioning pin 1 in the moving scale disc slot 2-3; the axial size of the L section cavity changes in the range of 5mm~25mm, corresponding to the displacement range of 0~20mm of the second positioning pin 4 in the second slot 5-2; and the axial total length of the L section cavity and the H section cavity changes in the range of 45mm~72mm, which is within the length of the 3 / 4 wave band, so that the device has good usability. Figure 24 The resonant frequency adjustable coaxial microwave plasma torch device of the application is suitable for working conditions with a frequency of 2.45GHz, a power range of 50W~500W, a gas pressure of 1atm and a gas flow of 5l / min~15l / min. When the load is empty, H=49.6mm and L=22.7mm can obtain the minimum reflection coefficient; when the power is about 220W and the gas flow is 12l / min, the maximum gas temperature is about 7000K, the conductivity distribution is as shown in the figure, the optimal resonance position change rule is as shown in the figure, H=41mm and L=9.5mm are taken; when the power is about 500W and the gas flow is 15l / min, the maximum gas temperature is about 10000K, the conductivity distribution is as shown in the figure, and the optimal resonance position change rule is as shown in the figure.

[0072] Figure 15 The resonant frequency adjustable coaxial microwave plasma torch device of the application is suitable for working conditions with a frequency of 2.45GHz, a power range of 50W~500W, a gas pressure of 1atm and a gas flow of 5l / min~15l / min. When the load is empty, H=49.6mm and L=22.7mm can obtain the minimum reflection coefficient; when the power is about 220W and the gas flow is 12l / min, the maximum gas temperature is about 7000K, the conductivity distribution is as shown in the figure, the optimal resonance position change rule is as shown in the figure, H=41mm and L=9.5mm are taken; when the power is about 500W and the gas flow is 15l / min, the maximum gas temperature is about 10000K, the conductivity distribution is as shown in the figure, and the optimal resonance position change rule is as shown in the figure. Figure 22 Figure 16 The resonant frequency adjustable coaxial microwave plasma torch device of the application is suitable for working conditions with a frequency of 2.45GHz, a power range of 50W~500W, a gas pressure of 1atm and a gas flow of 5l / min~15l / min. When the load is empty, H=49.6mm and L=22.7mm can obtain the minimum reflection coefficient; when the power is about 220W and the gas flow is 12l / min, the maximum gas temperature is about 7000K, the conductivity distribution is as shown in the figure, the optimal resonance position change rule is as shown in the figure, H=41mm and L=9.5mm are taken; when the power is about 500W and the gas flow is 15l / min, the maximum gas temperature is about 10000K, the conductivity distribution is as shown in the figure, and the optimal resonance position change rule is as shown in the figure. Figure 23 ​​​As shown, take H = 38mm, L = 8mm.For other working condition parameters in the working condition range, the reference value can be obtained through the optimal resonance position variation law or experiment and simulation, and tuning is carried out in combination with the test device as shown in Figures 17 to 24 The test device is shown in Figure 6. Figure 10 The test device is shown in Figure 6.

[0073] In view of the deficiencies of the existing microwave plasma torch device, the resonant frequency adjustable coaxial microwave plasma torch device designed by the application can realize one-way tuning and two-way tuning by moving the axial conductor sleeve within the range of 3 / 4 wavelength, has small volume, is simple to operate, and can meet the tuning requirements within a certain working condition range.The tuning cavity size variation range and variation law obtained through simulation make the resonant frequency adjustable coaxial microwave plasma torch device of the application simple to operate, small in tuning scale, have good applicability, can effectively improve the tuning precision, further improve the energy coupling efficiency, and also enhance the impedance matching stability and the stability of the plasma torch discharge.

Claims

1. A coaxial microwave plasma torch device with adjustable resonant frequency, characterized in that, The outer sleeve (5) includes a microwave transmission coaxial unit, an H-segment tuning coaxial unit, and an L-segment tuning coaxial unit arranged sequentially along the microwave transmission direction inside the outer sleeve (5). A conical end cap (13) is provided at one end of the outer sleeve (5), and a microwave and gas outlet (13-1) is provided at the end of the conical end cap (13). A first slot (5-1), a second slot (5-2), and several gas inlets (5-1, 5-2, 5-1) are arranged sequentially along the microwave transmission direction on the outer wall of the outer sleeve (5). 3) A movable dial unit (2) with a slot is installed at the first slot (5-1). The movable dial unit (2) is connected to the H-segment tuning coaxial unit. It also includes a first positioning pin (1) and a second positioning pin (4). One end of the first positioning pin (1) passes through the slot of the movable dial unit (2) and the first slot (5-1) in sequence and is connected to the microwave transmission coaxial unit. One end of the second positioning pin (4) passes through the second slot (5-2) and is connected to the H-segment tuning coaxial unit. The microwave transmission coaxial unit includes an inner sleeve (10), and a first shaft (11) is provided inside the inner sleeve (10); the H-segment tuning coaxial unit includes a middle sleeve (9), and a connecting shaft sleeve (8) is provided inside the middle sleeve (9); the L-segment tuning coaxial unit includes a second shaft (7); the first end of the connecting shaft sleeve (8) is fitted on the outer wall of the first shaft (11), and the two can slide relative to each other; the second end of the connecting shaft sleeve (8) is fitted on the outer wall of the second shaft (7), and the two can slide relative to each other.

2. The coaxial microwave plasma torch device with adjustable resonant frequency according to claim 1, characterized in that, The microwave transmission coaxial unit includes an inner sleeve (10) disposed inside an outer sleeve (5). The outer wall of the inner sleeve (10) is convex. A first shaft (11) is disposed inside the inner sleeve (10). A shaft support (12) is disposed between the first shaft (11) and the inner wall of the inner sleeve (10). The inner sleeve (10) and the first shaft (11) are connected by the shaft support (12). The shaft support (12) is press-fitted with the first shaft (11) and the inner sleeve (10) respectively. One end of the first positioning pin (1) is fixedly connected to the outer wall of the inner sleeve (10) through the first pin hole (10-1). The H-segment tuning coaxial unit includes a middle sleeve (9) disposed inside the outer sleeve (5), a connecting shaft sleeve (8) disposed inside the middle sleeve (9), a sleeve bracket (3) disposed between the connecting shaft sleeve (8) and the middle sleeve (9), the middle sleeve (9) and the connecting shaft sleeve (8) being connected by the sleeve bracket (3), the sleeve bracket (3) being press-fitted with the connecting shaft sleeve (8) and the middle sleeve (9) respectively; one end of the second positioning pin (4) is fixedly connected to the outer wall of the middle sleeve (9) through the third pin hole (9-2); the middle sleeve (9) is also connected to the movable dial unit (2); The L-segment tuning coaxial unit includes a second-segment shaft (7) and an insulating partition (6) disposed inside the outer sleeve (5). The insulating partition (6) is sleeved on the outer wall of the second-segment shaft (7). The outer sleeve (5) and the second-segment shaft (7) are connected through the insulating partition (6). The insulating partition (6) is interference-fitted with the outer sleeve (5) and the second-segment shaft (7) respectively. One end of the middle sleeve (9) is fitted onto the outer wall of the inner sleeve (10), and the inner sleeve (10) and the middle sleeve (9) are in clearance fit; the first end of the connecting shaft sleeve (8) is fitted onto the outer wall of the first section shaft (11), and the first section shaft (11) and the connecting shaft sleeve (8) are in clearance fit; the second end of the connecting shaft sleeve (8) is fitted onto the outer wall of the second section shaft (7), and the second section shaft (7) and the connecting shaft sleeve (8) are in clearance fit.

3. The coaxial microwave plasma torch device with adjustable resonant frequency according to claim 2, characterized in that, The movable dial unit (2) includes a curved dial plate (2-1) covering the first slot (5-1). The curved dial plate (2-1) has a dial slot (2-3) on its plate body, and the edge of the dial slot (2-3) is provided with a scale. The curved dial plate (2-1) is also provided with a third positioning pin (2-2) facing the first slot (5-1). One end of the third positioning pin (2-2) is fixedly connected to the outer wall of the middle sleeve (9) through the second pin hole (9-1).

4. The coaxial microwave plasma torch device with adjustable resonant frequency according to claim 1, characterized in that, The second slot (5-2) has graduations on its edge.

5. The coaxial microwave plasma torch device with adjustable resonant frequency according to claim 2, characterized in that, Under a microwave input of 2.45 GHz, the displacement adjustment range of the first positioning pin (1) in the dial slot (2-3) is 0-15 mm; the displacement adjustment range of the second positioning pin (4) in the second slot (5-2) is 0-20 mm.

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