CN115915564A - Coaxial microwave plasma torch device with adjustable resonant frequency - Google Patents
Coaxial microwave plasma torch device with adjustable resonant frequency Download PDFInfo
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Abstract
The invention discloses a coaxial microwave plasma torch device with adjustable resonant frequency, which comprises an outer sleeve, wherein 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 along the microwave transmission direction; the outer wall of the outer sleeve is sequentially provided with a first notch, a second notch and a plurality of gas inlets along the microwave transmission direction; a movable dial unit with a notch is arranged at the first notch, and the movable dial unit is connected with the H-section tuning coaxial unit; the microwave transmission coaxial unit is characterized by further comprising a first positioning pin and a second positioning pin, wherein one end of the first positioning pin sequentially penetrates through the notch of the movable dial unit and the first notch to be connected with the microwave transmission coaxial unit, and one end of the second positioning pin penetrates through the second notch to be connected with the H-section tuning coaxial unit. The device can effectively improve the tuning precision and improve the coupling efficiency of energy.
Description
Technical Field
The invention belongs to the technical field of electromagnetism and plasma, and particularly relates to a coaxial microwave plasma torch device with adjustable resonant frequency.
Background
The microwave plasma torch is a device that ionizes gas by high-frequency electromagnetic waves (2.45 GHz) and emits flame-like plasma. It can be used for object surface treatment, gas decomposition and conversion, spectrometer and metal cutting, etc. and has wide application in modern industrial production. The microwave plasma torches currently applied in the market can be classified into: rectangular waveguide, cylindrical waveguide, coaxial waveguide, whateverMost of the transmission modes are realized by coupling the electric field and the gas to realize the ionization of the gas. At present, rectangular waveguide and coaxial waveguide are more applied, and a plasma torch device designed by the coaxial waveguide can transmit TEM wave and is suitable for low power (C and C)<1 kW) for stable conversion of molecular gases, e.g. CO 2 And the plasma torch device has good applicability in structure, so that the plasma torch device of the same shaft type is more widely applied to research. When the microwave plasma torch device is used, the resonance frequency of the plasma torch device is changed due to the change of working condition parameters, so that the resonance frequency of the plasma torch device needs to be adjusted (tuning for short), the plasma torch and microwaves are recoupled to reach a resonance state, and the utilization rate of energy is improved.
In the tuning mode, the active mode and the passive mode are mainly divided. The active mode is to directly adjust the frequency of the input microwave without adjusting the resonant frequency of the plasma torch, and the mode needs a solid microwave source and other equipment which are accurately adjustable, so the cost is high; the passive mode is to directly adjust the resonant frequency of the microwave plasma device without changing the frequency of the input microwave, and the tuning purpose can be achieved only by changing the geometric attribute of the resonant cavity of the device, so that the passive mode has the advantages of flexible and various tuning modes and low cost, and is more in application.
In most of the conventional passive plasma torch tuning, tuning is realized by adjusting the position of a microwave side feed inlet or the position of a reflecting end surface of a cavity (for example, a patent with publication number 2014-07-23, publication number CN 103945631a, application number 2014101358979, invention name of which is "an improved microwave plasma torch device and application"). The traditional tuning mode only considers one tuning cavity or one tuning variable (namely unidirectional tuning), can only carry out odd-number-times-band tuning, is difficult to realize tuning within a limited geometric size range, and has the problems of large tuning scale and inconvenient tuning. Meanwhile, because the traditional tuning mode is limited by wavelength and cavity size, only one resonance state of the device under the corresponding working condition is often obtained, and whether the resonance state is the optimal resonance state cannot be determined, so that the problem of insufficient tuning precision exists. When the traditional plasma torch is tuned, even if two sections of tuning cavities are distinguished, the related sizes of the two sections of tuning cavities are the same, and the two sections of tuning cavities are correlated with each other during tuning, so that independent tuning in a double-variable mode cannot be realized, and the purpose of accurate tuning cannot be achieved. Meanwhile, when the traditional plasma torch is tuned, an integral equivalent circuit model when the plasma torch device discharges is not considered, and the two-way inductive coupling principle in the circuit is not combined to realize independent tuning (namely two-way tuning) of two sections of different cavities, so that the problems of imperfect tuning mode and insufficient tuning precision exist.
Disclosure of Invention
The invention aims to provide a coaxial microwave plasma torch device with adjustable resonant frequency, which can effectively improve tuning precision, reduce tuning scale and improve energy coupling efficiency in a bidirectional tuning mode.
The invention adopts the technical scheme that the coaxial microwave plasma torch device with adjustable resonant frequency comprises an outer layer sleeve, wherein a microwave transmission coaxial unit, an H-section tuning coaxial unit and an L-section tuning coaxial unit are sequentially arranged in the outer layer sleeve along the microwave transmission direction, a conical end cover is arranged at one end part of the outer layer sleeve, and a microwave and gas outlet is arranged at the end part of the conical end cover; the outer wall of the outer sleeve is sequentially provided with a first notch, a second notch and a plurality of gas inlets along the microwave transmission direction; a movable dial unit with a notch is arranged at the first notch, and the movable dial unit is connected with the H-section tuning coaxial unit; the microwave transmission coaxial unit is characterized by further comprising a first positioning pin and a second positioning pin, wherein one end of the first positioning pin sequentially penetrates through the notch of the movable dial unit and the first notch to be 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 penetrates through the second notch to be connected with the H-section tuning coaxial unit, and the H-section tuning coaxial unit is driven to move by moving the second positioning pin.
The present invention is also characterized in that,
the microwave transmission coaxial unit comprises an inner sleeve arranged in the outer sleeve, the outer wall of the inner sleeve is in a convex shape, a first section of shaft is arranged in the inner sleeve, a shaft support is arranged between the first section of shaft and the inner wall of the inner sleeve, the inner sleeve is connected with the first section of shaft through the shaft support, and the shaft support is in interference fit with the first section of shaft and the inner sleeve respectively; one end part of the first positioning pin is fixedly connected with the outer wall of the inner sleeve through a first pin hole;
the H-section tuning coaxial unit comprises a middle-layer sleeve arranged in the outer-layer sleeve, a connecting shaft sleeve is arranged in the middle-layer sleeve, a sleeve support is arranged between the connecting shaft sleeve and the middle-layer sleeve, the middle-layer sleeve is connected with the connecting shaft sleeve through the sleeve support, and the sleeve support is in interference fit with the connecting shaft sleeve and the middle-layer sleeve respectively; one end part of the second positioning pin is fixedly connected with the outer wall of the middle-layer sleeve through a third pin hole; the middle sleeve is also connected with the movable dial unit;
the L-section tuning coaxial unit comprises a second section shaft arranged in the outer sleeve and an insulating partition plate, and the insulating partition plate is sleeved on the outer wall of the second section shaft; the outer sleeve is connected with the second section shaft through an 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 a whole fixed relative to the inner sleeve and the middle sleeve;
one end part of the middle-layer sleeve is sleeved on the outer wall of the inner-layer sleeve, and the inner-layer sleeve and the middle-layer sleeve are in clearance fit and can slide relatively; the first end part of the connecting shaft sleeve is sleeved on the outer wall of the first section of shaft, the first section of shaft is in clearance fit with the connecting shaft sleeve, and the first section of shaft and the connecting shaft sleeve can slide relatively; the second end part of the connecting shaft sleeve is sleeved on the outer wall of the second section shaft, and the second section shaft is in clearance fit with the connecting shaft sleeve and can slide relatively between the second section shaft and the connecting shaft sleeve.
The movable dial unit comprises a curved scale plate covered at the first notch, a dial notch is formed in the plate body of the curved scale plate, and scales are arranged on the edge of the notch of the dial notch; the curved surface scale plate is provided with a third positioning pin towards the direction of the first notch, and one end of the third positioning pin is fixedly connected with the outer wall of the middle-layer sleeve through a second pin hole. The curved scale plate is coaxially matched with the outer sleeve, the middle sleeve can drive the movable dial unit to slide in the first notch area along the outer wall surface of the outer sleeve when moving, and the movable dial unit is designed to eliminate inconvenience in operation caused by relative sliding to tuning and positioning of an H-section tuning area.
The edge of the notch of the second notch is provided with scales.
Under the condition of microwave input with the frequency of 2.45GHz, the displacement adjusting range of the first positioning pin in the notch of the dial is 0-15mm; the displacement adjusting range of the second positioning pin in the second notch is 0-20mm; wherein the axial total length change range of the H tuning area and the L tuning area is 45 mm-72 mm.
The invention has the beneficial effects that:
compared with the traditional device, the coaxial microwave plasma torch device with the adjustable resonant frequency can change the positions of the microwave reflecting end surfaces of two sections of chambers with different sizes by moving the two coaxial conductor sleeves according to the impedance coupling matching principle and the electromagnetic wave transmission characteristic, thereby achieving the purpose of changing the electrical parameters of different chambers and further realizing unidirectional or bidirectional tuning. In a bidirectional tuning mode, the tuning precision can be effectively improved, the tuning scale can be reduced, certain tuning requirements of the microwave plasma torch device in different discharge states can be met, meanwhile, a plurality of resonance states under corresponding working conditions can be obtained, an optimal resonance state is found from the resonance states, the reflection coefficient is reduced to the minimum, the coupling efficiency of energy is improved, meanwhile, a specific tuning rule and a specific tuning parameter range are obtained according to simulation, the axial size and the tuning range of the whole plasma torch device are within 3/4 wavelength or about 1/4 wavelength, and the structure is small. The coaxial microwave plasma torch device with adjustable resonant frequency is mainly applied to CO 2 Can contribute to the increase of CO 2 The conversion efficiency of (a).
Drawings
FIG. 1 is a schematic view of the overall assembly of a coaxial microwave plasma torch device with tunable resonant frequency according to the present invention;
FIG. 2 is a main sectional view of a coaxial microwave plasma torch device whose resonance frequency is adjustable according to the present invention;
FIG. 3 is a top view of FIG. 2;
fig. 4 is a schematic view showing the construction of a coaxial microwave plasma torch device adjustable in resonance frequency according to the present invention;
fig. 5 is a front view of a movable dial in the resonance frequency adjustable coaxial microwave plasma torch apparatus of the present invention;
fig. 6 is a right side view of a movable dial in the resonance frequency adjustable coaxial microwave plasma torch apparatus of the present invention;
fig. 7 is a top view of a movable dial in the resonance frequency adjustable coaxial microwave plasma torch apparatus of the present invention;
fig. 8 is a schematic diagram showing the operation of the resonance frequency adjustable coaxial microwave plasma torch apparatus of the present invention;
fig. 9 is a schematic diagram of an equivalent circuit of the coaxial microwave plasma torch device with adjustable resonant frequency of the present invention;
FIG. 10 is a schematic diagram of the S11 parameter test;
FIG. 11 is a graph of conductivity distribution at a maximum conductivity of 2 (S/m);
FIG. 12 is a graph of conductivity distribution at a maximum conductivity of 10 (S/m);
FIG. 13 is a graph of conductivity distribution at a maximum conductivity of 100 (S/m);
FIG. 14 is a graph of conductivity distribution at a maximum conductivity of 150 (S/m);
FIG. 15 is a graph of conductivity distribution at a maximum conductivity of 1000 (S/m);
FIG. 16 is a graph of conductivity distribution at a maximum conductivity of 3000 (S/m);
FIG. 17 is a graph showing the change in the optimum resonance position when the conductivity is zero;
FIG. 18 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 11;
FIG. 19 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 12;
FIG. 20 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 13;
FIG. 21 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 14;
FIG. 22 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 15;
FIG. 23 is a graph showing the change in the optimum resonance position when the conductivity distribution is as shown in FIG. 16;
fig. 24 is a graph showing how the axial lengths of the H-tuning section and the L-tuning section change to reach the optimum resonance position as the conductivity distribution changes.
In the figure, 1, a first positioning pin, 2, a movable dial unit, 3, a sleeve bracket, 4, a second positioning pin, 5, an outer sleeve, 6, an insulating partition plate, 7, a second section shaft, 8, a connecting shaft sleeve, 9, a middle sleeve, 10, an inner sleeve, 11, a first section shaft, 12, a shaft bracket, 13, a conical end cover, 2-1, a curved scale plate, 2-2, a third positioning pin, 2-3, a dial notch, 5-1, a first notch, 5-2, a second notch, 5-3, a gas inlet, 9-1, a second pin hole, 9-2, a third pin hole, 10-1, a first pin hole, 13-1, a microwave and gas outlet, 14, a microwave generator, 15, a directional coupler, 16, a microwave plasma torch device, 17, a gas cylinder and 18 power detector.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention provides a coaxial microwave plasma torch device with adjustable resonance frequency, which comprises an outer layer sleeve 5, wherein a microwave transmission coaxial unit, an H-section tuning coaxial unit and an L-section tuning coaxial unit are sequentially arranged in the outer layer sleeve 5 along the microwave transmission direction, a conical end cover 13 is arranged at one end part of the outer layer sleeve 5, and a microwave and gas outlet 13-1 is arranged at the end part of the conical end cover 13; the outer wall of the outer sleeve 5 is sequentially provided with a first notch 5-1, a second notch 5-2 and a plurality of gas inlets 5-3 along the microwave transmission direction; a movable dial unit 2 with a notch is arranged at the first notch 5-1, and the movable dial unit 2 is connected with the H-section tuning coaxial unit; the microwave coaxial cable fixing device is characterized by further comprising a first positioning pin 1 and a second positioning pin 4, wherein one end of the first positioning pin 1 sequentially penetrates through a notch of the movable dial unit 2 and a first notch 5-1 to be connected with the microwave transmission coaxial unit, the microwave transmission coaxial unit is driven to move by moving the first positioning pin 1, one end of the second positioning pin 4 penetrates through a second notch 5-2 to be connected with the H-section tuning coaxial unit, and the H-section tuning coaxial unit is driven to move by moving the second positioning pin 4.
The microwave transmission coaxial unit comprises an inner sleeve 10 arranged in an outer sleeve 5, the outer wall of the inner sleeve 10 is in a convex shape, 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 is connected with the first section shaft 11 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 a first pin hole 10-1;
the H-section tuning coaxial unit comprises a middle-layer sleeve 9 arranged in the outer-layer sleeve 5, a connecting shaft sleeve 8 is arranged in the middle-layer sleeve 9, a sleeve support 3 is arranged between the connecting shaft sleeve 8 and the middle-layer sleeve 9, the middle-layer sleeve 9 is connected with the connecting shaft sleeve 8 through the sleeve support 3, and the sleeve support 3 is in interference fit with the connecting shaft sleeve 8 and the middle-layer sleeve 9 respectively; one end part of the second positioning pin 4 is fixedly connected with the outer wall of the middle-layer sleeve 9 through a third pin hole 9-2; the middle sleeve 9 is also connected with the movable dial unit 2;
the L-section tuning coaxial unit comprises a second section shaft 7 arranged in the outer sleeve 5 and an insulating partition plate 6, and the insulating partition plate 6 is sleeved on the outer wall of the second section shaft 7; the outer sleeve 5 is connected with the second section shaft 7 through an 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 a whole fixed relative to the inner sleeve 10 and the middle sleeve 9;
one end part of the middle layer sleeve 9 is sleeved on the outer wall of the inner layer sleeve 10, and the inner layer sleeve 10 is in clearance fit with the middle layer sleeve 9 and can slide relatively between the two; the first end part of the connecting shaft sleeve 8 is sleeved on the outer wall of the first section of shaft 11, the first section of shaft 11 is in clearance fit with the connecting shaft sleeve 8, and the first section of shaft 11 and the connecting shaft sleeve 8 can slide relatively; the second end part of the connecting shaft sleeve 8 is sleeved on the outer wall of the second section of shaft 7, and the second section of shaft 7 is in clearance fit with the connecting shaft sleeve 8 and can slide relatively between the second section of shaft and the connecting shaft sleeve 8. The shaft radius of the first section shaft 11 is the same as that of the second section shaft 7;
as shown in fig. 5-7, the movable dial unit 2 comprises a curved scale plate 2-1 covered at a first notch 5-1, a dial notch 2-3 is formed on a plate body of the curved scale plate 2-1, and scales are arranged at the notch edge of the dial notch 2-3; the curved scale plate 2-1 is also provided with a third positioning pin 2-2 towards the first notch 5-1, and one end part of the third positioning pin 2-2 is fixedly connected with the outer wall of the middle-layer sleeve 9 through a second pin hole 9-1. The curved scale plate 2-1 is coaxially matched with the outer sleeve 5, the middle sleeve 9 can drive the movable dial unit 2 to slide together along the outer wall surface of the outer sleeve 5 in the first notch 5-1 area when moving, and the movable dial unit 2 is designed to eliminate the inconvenience in operation caused by relative sliding.
The notch edge of the second notch 5-2 is provided with a scale.
The radius ratio of the second section shaft 7 to the inner wall of the outer sleeve 5 is 5.5, the radius 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 radius ratio of the first section shaft 11 to the inner wall of the inner sleeve 10 is 2.2.
Under the condition of microwave input with the frequency of 2.45GHz, the displacement adjusting range of the first positioning pin 1 in the groove opening 5-3 of the dial plate is 0-15mm; the displacement adjusting range of the second positioning pin 4 in the second notch 5-2 is 0-20mm; wherein the axial total length change range of the H tuning area and the L tuning area is 45 mm-72 mm.
Three coaxial regions are distributed in a stepped manner along the microwave transmission direction in sequence along the microwave transmission direction and respectively consist of a microwave transmission region, an H-section tuning region and an L-section tuning region, wherein the L-section tuning region comprises a shrinkage hole discharge region at the position of a conical end cover 13, the axial lengths of the H-section tuning region and the L-section tuning region are adjustable, the radial outer wall of the H-section tuning region is the inner wall of a middle-layer sleeve 9, the radial inner wall is the outer wall of a connecting shaft sleeve 8, and the axial length of the H-section tuning region is adjusted by a movable inner-layer sleeve 10 and a first section shaft; the radial outer wall of the L-section tuning area is the inner wall of the outer sleeve 5, the surface of a second section of shaft 7 of the radial inner wall, and the axial length of the L-section tuning area is adjusted by a movable middle-layer sleeve 9 and a connecting shaft sleeve 8; the microwave transmission coaxial area formed by the inner layer sleeve 10 and the first section shaft 11, the H-section tuning coaxial area formed by the middle layer sleeve 9 and the connecting shaft sleeve 8 and the L-section tuning coaxial area formed by the outer layer sleeve 5 and the second section shaft 7 are enclosed. The connecting shaft sleeve 8 and the middle layer sleeve 9 surround to form a coaxial region for H-section tuning, the inner layer sleeve 10 and the first section shaft 11 are moved simultaneously through the first positioning pin 1, the axial length of an H-section tuning region can be changed, and H-section tuning is realized; the second section shaft 7 and the outer sleeve 5 are surrounded to form a coaxial region of L section tuning, the shaft sleeve 8 and the outer sleeve 5 are connected through the second positioning pin 4 in a moving mode, the axial length of an L section tuning area can be changed, and L section tuning is achieved. According to the equivalent circuit schematic diagram shown in fig. 9, the impedance characteristics of the H-band tuning region and the L-band tuning region can be adjusted according to different conductivity distribution changes of the discharge end caused under different working conditions, so that the coaxial microwave plasma torch device reaches a required resonance state.
The inner sleeve 10 is arranged between a first section of shaft 11 close to a microwave inlet and the middle sleeve 9, is fixedly connected with the first section of shaft 11 through a shaft bracket 12, can move simultaneously, and has a displacement adjusting range of 0-15mm; the middle sleeve 9 is arranged between the outer sleeve 5 and the inner sleeve 10 which are close to the discharge end, is in coaxial clearance fit with the inner sleeve 5 and the outer sleeve 5, and can slide relatively, and the displacement adjusting range of the middle sleeve 9 is 0-20mm; the outer sleeve 5 is fixedly connected with the second section shaft 7 through an insulating partition plate 6 and is fixed without displacement relative to the inner sleeve 10 and the middle sleeve 9; the first section of shaft 11 and the second section of shaft 7 are connected through a connecting shaft sleeve 8, are in clearance fit and can slide relatively; the L tuning area is divided into a discharge area and a non-discharge area by the insulating partition plate 6, so that ionized gas does not influence the operation of the tuning area during discharge; gas flows in through a gas inlet 5-3 of the outer sleeve 5 and only passes through the conical end cover 13, and directly flows out from a microwave and gas outlet 13-1 after ionization; the microwave inlet is the coaxial region between the first section axis 11 and the inner sleeve 10, on the other side of the discharge port.
The inner layer sleeve 10 is connected with the first section shaft 11 through a shaft support 12, the shaft support 12 is in interference fit with the first section shaft 11 and the inner layer sleeve 10 respectively, and a relatively fixed whole body is formed among the three parts during movement; the first section of shaft 11 is in clearance fit with the connecting shaft sleeve 8 and can slide relatively, and the inner layer sleeve 10 is in clearance fit with the middle layer sleeve 9 and can slide relatively; the first positioning pin 1 is fixedly connected with the inner layer sleeve 10 through a first pin hole 10-1, and can slide in the area of a movable dial notch 2-3 in the area of a first notch 5-1 by moving the first positioning pin 1 to perform tuning and positioning; the connecting shaft sleeve 8 is in clearance fit with the first section shaft 11 and the second section shaft 7 respectively and can slide relatively.
The middle-layer sleeve 9 is connected with the connecting shaft sleeve 8 through the sleeve support 3, the sleeve support 3 is respectively in interference fit with the connecting shaft sleeve 8 and the middle-layer sleeve 9, and a relatively fixed whole body is formed among the three during movement; the middle sleeve 9 is in clearance fit with the outer sleeve 5 and the inner sleeve 10 respectively and can slide relatively, the middle sleeve 9 and the second positioning pin 4 are fixedly connected through a third pin hole 9-2, and can slide in the second notch 5-2 area through the positioning pin 4 to perform tuning or positioning; the third positioning pin 2-2 of the movable dial unit 2 is connected with the middle-layer sleeve 9 through the second pin hole 9-1, the curved scale plate 2-1 is coaxially matched with the outer-layer sleeve 5, the middle-layer sleeve 9 can drive the movable dial unit 2 to slide in the first notch 5-1 area along the outer wall surface of the outer-layer sleeve 5 when moving, and the movable dial is designed to eliminate the inconvenience in operation brought to H-section coaxial area tuning positioning due to relative sliding;
the outer sleeve 5 is connected with the second section shaft 7 through an 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 a whole fixed relative to the inner sleeve 10 and the middle sleeve 9;
the two tuning areas arranged in the device can realize unidirectional tuning by respectively and independently moving the inner sleeve 10 and the middle sleeve 9, and can also realize bidirectional tuning by simultaneously moving the inner sleeve 10 and the middle sleeve 9, so as to obtain the optimal resonance state. In the geometrical parameter setting of the plasma torch, the ratio of the radius of the inner wall of the outer sleeve 5 to the second section shaft 7 is 5.5, the ratio of the radius of the inner wall of the middle sleeve 9 to the outer wall of the connecting shaft sleeve 8 is 3.9, and the ratio of the radius of the inner wall of the inner sleeve 10 to the first section shaft 11 is 2.2. The optimal resonance parameters of the coaxial microwave plasma torch under different conductivity distribution conditions are obtained through simulation research, and when the coaxial microwave plasma torch is in no load, the axial length of an L tuning region is 22.7mm and is about 1/4 wavelength, and the axial length of an H tuning region is 49.6mm, so that the strongest electric field and the smallest energy reflection coefficient of a discharge region can be obtained under the same working condition parameters; 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 an L tuning region is 9.5mm and the axial length of an H tuning region is 41.2mm, and the minimum 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 lowest energy reflection coefficient can be obtained by taking the axial length of the L tuning region as 7.6mm and the axial length of the H tuning region as 38 mm. In the gas discharge, the axial length of the L-section tuning area and the H-section tuning area is gradually reduced in the process of changing the maximum conductivity from 10S/m to 3000S/m, so that better impedance matching can be obtained.
In the movement mode, the inner sleeve 10 is fixedly connected with the first section shaft 11 through the shaft support 12 and is also fixedly connected with the positioning pin 1, and the axial length of an H-section tuning coaxial area formed by surrounding 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-layer sleeve 9 is fixedly connected with the connecting shaft sleeve 8 through the sleeve support 4 and is also fixedly connected with the positioning pin 4 and the movable dial unit 2, and the connecting shaft sleeve 8 and the middle-layer sleeve 9 can be driven by the positioning pin 4 to realize the axial length adjustment of an L-section tuning coaxial area formed by the outer-layer sleeve 5 and the second-section shaft 7 in an enclosing manner; the axial lengths of the H-section tuning coaxial area and the L-section tuning coaxial area can be independently adjusted through 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 plate 6 to form a fixed whole without relative displacement.
The injection position of the microwave and the gas is shown in fig. 8, the microwave enters the cavity of the tuning section through the coaxial region surrounded by the inner sleeve 10 and the first section shaft 11, and finally is scattered out from the microwave and gas outlet 13-1 of the conical end cover 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 directly flows out of the outlet 13-1.
The equivalent circuit model of the tuning device is mainly provided with an H-section tuning area circuit and an L-section tuning area circuit as shown in figure 9, and the two-section tuning area circuit is connectedAre connected together in an over-inductive coupling manner. Wherein the H-section tuning region circuit corresponds to the equivalent circuit parameter, Z, of the H-section cavity in FIG. 8 H Represents the impedance of the wall and the medium when the microwave propagates in the H-section cavity, C H Capacitance representing presence between H-section coaxial cavities; the L-section tuning region circuit mainly corresponds to the equivalent circuit parameter of the L-section cavity in FIG. 8 and the impedance parameter of the plasma, Z L C represents the impedance of wall surface and medium when the microwave propagates in the L-section cavity L Capacitance, C, representing the presence between L sections of coaxial cavities open Representing the capacitance in the undischarged state, Z, at which the terminals are open plasma Representing the impedance of the plasma generated at the time of discharge. In H-band tuning-zone circuits, element Z H First and induction coil L 1 Connected in series and then connected with element C H Is connected with the microwave generator 14 in parallel; in the L-stage tuning-zone circuit, Z L First with C open And Z plasma The parallel circuit formed by the two elements is connected in series and then connected with the element C L And an induction coil L 2 And (4) connecting in parallel. Induction coil L 1 And L 2 The inductive coupling function is realized by parallel arrangement, and no direct connection relation exists electrically.
Because the coaxial cavity has linear impedance in the axial direction, the impedance can be matched and adjusted by changing the axial length parameters of the L-section cavity and the H-section cavity. The equivalent circuit model of fig. 9 and the inductive coupling relationship between the equivalent circuit models can be analyzed, and under the condition that the coupling coefficients of the circuits of the two tuning regions are not changed, when the working condition parameters are changed, such as the plasma discharge intensity is increased, the circuit impedance corresponding to the L tuning region is reduced, which is equivalent to the reduction of the axial length of the L-section cavity, at this time, the current of the L-tuning region is increased, the coupling induces the circuit of the H-tuning region, and the current of the corresponding H-tuning region is reduced, namely, the axial length of the H-section cavity is required to be increased to increase the impedance. By the tuning mode, better impedance matching can be realized, and meanwhile, the analysis result of the equivalent circuit model has good corresponding relation with the change rule of the curves in the graphs of fig. 17-23.
On the material arrangement, the shaft bracket 12, the positioning pin 4, the sleeve bracket 3 and the insulating partition plate 6 are made of quartz; the first section of shaft 11, the inner layer sleeve 10, the middle layer sleeve 9, the connecting shaft sleeve 8, the second section of shaft 7 and the outer layer sleeve 5 are made of stainless steel, and the surfaces of the first section of shaft, the inner layer sleeve 10, the middle layer sleeve 9, the connecting shaft sleeve 8, the second section of shaft and the outer layer sleeve 5 are all provided with copper coatings.
The specific tuning mode is realized by using the experimental testing apparatus shown in fig. 10, and the specific connection relationship is that the microwave generator 14 is connected in series with the directional coupler 15 and then directly connected with the microwave plasma torch apparatus 16; the bypass of the directional coupler 15 is connected with a power detector 18 in parallel, so that an S11 value can be obtained through real-time testing; the gas of the microwave plasma torch device 16 comes directly from the injection of the gas cylinder 17. In the use of the device, the experimental configuration and the connection mode can be combined, 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 value displayed by the experimental instrument 18 is observed, and the displacement adjustment range of the first positioning pin 1 and the second positioning pin 4 is gradually reduced by comparing the S11 values of the two tuning operations before and after, so that the microwave plasma torch device can obtain the minimum S11 value and reach the optimal resonance state. The calculation formula of the S11 parameter in the experimental test is as follows:
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 good or bad degree of impedance matching, wherein P R To reflect power, P I Is the incident power.
The assumed conductivity distribution model of the coaxial microwave plasma torch at the initial discharge is shown in fig. 11 and 12. In a certain working condition range (frequency 2.45GHz, pressure 1atm, power 50W-500W, 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 fig. 13-16. The diagrams corresponding to the variation of the resonance position with the length of H and L as shown in FIGS. 17 to 23 under different conductivity distribution models are obtained through COMSOL simulation, and the S11 parameter obtained through software calculation in the diagrams is equivalent to the S11 value obtained through calculation in experiments.
In the graphs shown in fig. 17 to 23, each curve has a corresponding minimum value 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. It can be seen from each of fig. 17 to 23 that, under the condition that the plasma conductivity distribution is not changed, and when the total length of the two tuning regions is within the 3/4 wavelength range, the axial length of the H tuning region is gradually increased, the resonance position is shifted to the left, that is, the axial length of the L tuning region is decreased, and according to this rule, an optimal resonance position, that is, the minimum value of each curve in each graph, can be obtained in the tuning process. Since the minima point of each curve in each figure represents a resonant state of the device, the aim of our tuning is to find the minima point position of the curve. Whether the obtained minimum value point is the minimum value point or not is not reflected in the traditional tuning mode, the traditional tuning mode only has single-variable unidirectional tuning and can only obtain a certain curve in the graph, and the minimum value point of the curve is not necessarily the minimum value point required by tuning, so that the traditional tuning mode has the main defects that the optimal resonance state of the device is not easy to obtain and the tuning precision is low.
The specific tuning parameters obtained by simulation were analyzed as described below.
When the conductivity distribution of the coaxial microwave plasma torch is zero, a regular graph of the change of the resonance position along with H and L as shown in fig. 17 is obtained, when H =49.6mm and L =22.7mm, the coaxial microwave plasma torch reaches the optimal resonance position, the reflection coefficient of a microwave port reaches the minimum value, and meanwhile, the electric field intensity also reaches the maximum value, so that the coaxial microwave plasma torch is more beneficial to ignition of plasma and the energy coupling efficiency is improved.
When the conductivity profile of the torch device is as shown in fig. 11, a graph of the variation law as shown in fig. 18 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =36mm, L =23.2 mm; when the conductivity distribution is as shown in fig. 12, a graph of the change law as shown in fig. 19 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =35.5mm, L =23.2 mm; when the conductivity distribution is as shown in fig. 13, a graph of the change law as shown in fig. 20 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =43mm, L =17.4 mm; when the conductivity distribution is as shown in fig. 14, a graph of the change law as shown in fig. 21 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =43mm, L =14.2 mm; when the conductivity distribution is as shown in fig. 15, a graph of the change law as shown in fig. 22 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =41.2mm, L =9.5mm; when the conductivity distribution is as shown in fig. 16, a graph of the change law as shown in fig. 23 is obtained, from which it can be obtained that the device reaches the optimum resonance position at H =38mm, L =7.6 mm. Therefore, as can be seen from the simulation results of fig. 17 to 23, the designed and adopted bidirectional tuning mode of the coaxial microwave plasma torch device with adjustable resonant frequency of the present invention can meet the tuning requirements under different discharge states, is not limited by odd-number multiple wave bands, can obtain a plurality of resonance states within a certain geometric length range, and can determine the optimal resonance state or the optimal resonance position of the device, thereby effectively improving the tuning accuracy and the coupling efficiency of energy.
Through statistical analysis of the parameters of the optimal resonance positions in fig. 17 to 23, the H and L parameter variation rules corresponding to the optimal resonance positions when the distribution of the plasma conductivity changes as shown in fig. 24 are obtained. From the figure, when the maximum conductivity is more than 10S/m, the axial size of the cavities of the H tuning section and the L tuning section is gradually reduced along with the increase of the conductivity, so that the optimal resonance state can be obtained, and the rule provides meaningful guidance and theoretical support for the operation of the coaxial microwave plasma torch device with the adjustable resonance frequency. When the conductivity distribution is more than 10S/m, the variation range of the axial dimension of the H-section cavity is 35-50 mm, and the displacement range of the first positioning pin 1 in the notch 2-3 of the movable dial is 0-15mm; the axial size change range of the L-section cavity is 5-25 mm, and the displacement range of the corresponding second positioning pin 4 in the second notch 5-2 is 0-20mm; the axial total length change range of the L-section cavity and the H-section cavity is 45-72 mm within 3/4 of the wavelength band length, so that the device is good in usability.
The coaxial microwave plasma torch device with the adjustable resonant frequency is suitable for working conditions that the frequency is 2.45GHz, the power range is 50W-500W, the air pressure is 1atm, and the gas flow is 5 l/min-15 l/min. When the film is unloaded, taking H =49.6mm, L =22.7mm can obtain the minimum reflection coefficient; when the power is about 220W, the gas flow is 12l/min, the corresponding maximum gas temperature is about 7000K, and the conductivity distribution is as shown in FIG. 15, the change rule of the optimal resonance position is as shown in FIG. 22, taking H =41mm and L =9.5mm; when the power is about 500W, the gas flow is 15l/min, the corresponding maximum gas temperature is about 10000K, and the conductance distribution is shown in FIG. 16, the change rule of the optimal resonance position is shown in FIG. 23, and H =38mm and L =8mm are taken. For other operating condition parameters within the operating condition range, reference values can be obtained through the optimal resonance position change rule of fig. 17 to 24 or experiments and simulations, and tuning is performed by combining the testing device shown in fig. 10.
Aiming at the design defects of the existing microwave plasma torch device, the coaxial microwave plasma torch device with the adjustable resonant frequency, which is designed by the invention, can realize unidirectional tuning and bidirectional tuning by moving the axial conductor sleeve in a 3/4 wavelength range, has small volume and simple operation, and can meet tuning requirements in a certain working condition range. The size change range and the change rule of the tuning cavity are obtained through simulation, so that the coaxial microwave plasma torch device with the adjustable resonant frequency, disclosed by the invention, is simple in operation mode, small in tuning size and good in applicability, can effectively improve tuning precision, further improves the coupling efficiency of energy, and simultaneously enhances the impedance matching stability and the discharge stability of the plasma torch.
Claims (5)
1. The coaxial microwave plasma torch device with the adjustable resonant frequency is characterized by comprising an outer sleeve (5), wherein 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 a 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); the outer wall of the outer sleeve (5) is sequentially provided with a first notch (5-1), a second notch (5-2) and a plurality of gas inlets (5-3) along the microwave transmission direction; a movable dial unit (2) with a notch is arranged at the first notch (5-1), and the movable dial unit (2) is connected with the H-section tuning coaxial unit; the microwave tuning coaxial unit is characterized by further comprising a first positioning pin (1) and a second positioning pin (4), wherein one end of the first positioning pin (1) sequentially penetrates through a notch of the movable dial unit (2) and the first notch (5-1) to be connected with the microwave transmission coaxial unit, and one end of the second positioning pin (4) penetrates through the second notch (5-2) to be connected with the H-section tuning coaxial unit.
2. The resonance frequency adjustable coaxial microwave plasma torch device according to claim 1, wherein the microwave transmitting coaxial unit comprises an inner sleeve (10) arranged in the outer sleeve (5), the outer wall of the inner sleeve (10) is in a convex shape, 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) is connected with the first section shaft (11) through the shaft support (12), and the shaft support (12) is respectively in interference fit with the first section shaft (11) and the inner sleeve (10); one end part of the first positioning pin (1) is fixedly connected with the outer wall of the inner sleeve (10) through a first pin hole (10-1);
the H-section tuning coaxial unit comprises a middle-layer sleeve (9) arranged in an outer-layer sleeve (5), a connecting shaft sleeve (8) is arranged in the middle-layer sleeve (9), a sleeve support (3) is arranged between the connecting shaft sleeve (8) and the middle-layer sleeve (9), the middle-layer sleeve (9) is connected with the connecting shaft sleeve (8) through the sleeve support (3), and the sleeve support (3) is in interference fit with the connecting shaft sleeve (8) and the middle-layer sleeve (9) respectively; one end part of the second positioning pin (4) is fixedly connected with the outer wall of the middle-layer sleeve (9) through a third pin hole (9-2); the middle sleeve (9) is also connected with the movable dial unit (2);
the L-section tuning coaxial unit comprises a second section shaft (7) arranged in the outer sleeve (5) and an insulating partition plate (6), and the insulating partition plate (6) is sleeved on the outer wall of the second section shaft (7); the outer sleeve (5) is connected with the second section shaft (7) through an insulating partition plate (6), and the insulating partition plate (6) is in interference fit with the outer sleeve (5) and the second section shaft (7) respectively;
one end part of the middle layer sleeve (9) is sleeved on the outer wall of the inner layer sleeve (10), and the inner layer sleeve (10) is in clearance fit with the middle layer sleeve (9); the first end part of the connecting shaft sleeve (8) is sleeved on the outer wall of the first section of shaft (11), and the first section of shaft (11) is in clearance fit with the connecting shaft sleeve (8); the second end part of the connecting shaft sleeve (8) is sleeved on the outer wall of the second section shaft (7), and the second section shaft (7) is in clearance fit with the connecting shaft sleeve (8).
3. The resonance frequency adjustable coaxial microwave plasma torch apparatus as claimed in claim 2, wherein the movable dial unit (2) comprises a curved scale plate (2-1) covering the first notch (5-1), the body of the curved scale plate (2-1) is provided with a dial notch (2-3), and the edge of the notch of the dial notch (2-3) is provided with a scale; the curved surface scale plate (2-1) is further provided with a third positioning pin (2-2) towards 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-layer sleeve (9) through a second pin hole (9-1).
4. The coaxial microwave plasma torch device with adjustable resonance frequency according to claim 1, wherein the notch edge of the second notch (5-2) is provided with a scale.
5. The resonance frequency adjustable coaxial microwave plasma torch device according to claim 2, characterized in that the displacement adjustment range of the first positioning pin (1) in the dial notch (5-3) is 0-15mm at a frequency of 2.45GHz microwave input; the displacement adjusting range of the second positioning pin (4) in the second notch (5-2) is 0-20mm.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116419464A (en) * | 2023-06-09 | 2023-07-11 | 安徽农业大学 | Plasma torch device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116419464A (en) * | 2023-06-09 | 2023-07-11 | 安徽农业大学 | Plasma torch device |
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