Normal-pressure microwave plasma jet device

Abstract

The invention is applicable to the technical field of microwave plasmas, and provides a normal-pressure microwave plasma jet device which comprises an outer conductor, an inner conductor coaxially arranged in the outer conductor, a nozzle in threaded connection with the bottom end of the outer conductor, a pin at the end of a radio frequency connector connected with the inner conductor through a connecting conductor, and a gas pipe joint in threaded connection with the outer conductor. The short-circuit plug screw is in threaded connection with the top end of the outer conductor, a short-circuit reflecting surface is arranged at the bottom of a connecting piece installed in the short-circuit plug screw, and the air guide ring is nested on the inner conductor and located between the radio-frequency connector and the air pipe joint; the scheme is simple, reliable and low in cost, stable normal-pressure microwave plasma jet can be obtained without configuring a complex control module to adjust the impedance matching degree of the system, the gas flowing state can be more stable, plasma at an outlet is prevented from being affected, the short-circuit reflecting surface is further designed to be in a threaded up-and-down adjusting mode, and the service life of the system is prolonged. And the impedance matching effect is achieved by finely adjusting the short-circuit reflecting surface.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave plasma, and in particular relates to a normal-pressure microwave plasma jet device. Background Art

[0002] Atmospheric pressure plasma jets have been widely used in biomedicine, material surface treatment, semiconductor technology, environmental protection and other fields. Compared with other discharge excitation methods such as DC, low frequency, and radio frequency, the plasma generated by microwave drive has low breakdown power, high electron density, low electron temperature, and the gas temperature is close to room temperature. At present, the atmospheric pressure plasma jet generating devices that have been maturely used internationally include coaxial resonators, surface wave resonators, microstrip line resonators, hairpin exciters, rectangular waveguides, etc. Among them, the unique inner and outer conductor structure of the coaxial resonator provides a path for gas flow, and the strong electric field environment open outside the open port provides conditions for the generation of jets. The whole body is made of metal and has strong discharge stability.

[0003] In practical applications of coaxial resonator devices, due to the mismatch between the input impedance of the device and the impedance of the power supply system itself, the absolute value of the system return loss decreases, the reflected power of the system increases, and the energy cannot be effectively used. Therefore, it is necessary to adjust certain parameters of the device, such as the position of the short-circuit end face. A microwave electromagnetic field can be generated by a microwave source to provide microwave energy for a microwave plasma torch, and feedback information of the microwave plasma torch can be obtained from a coupled antenna. The microwave source extracts the reflected power value in the feedback information and feeds it back to the control module. The control module sends a control signal to the transmission device according to the reflected power value and a preset parameter relationship curve, and the transmission device drives the adjustment member to move. However, the above scheme requires the configuration of a directional coupler, an attenuator, a detector, and a transmission device, which will not only make the equipment complex and increase the cost, but also reduce the reliability of the system. In addition, the impedance matching degree of the system is affected by many factors. If the short-circuit end face position is simply adjusted, the plasma effect produced is relatively general. Summary of the invention

[0004] The purpose of the embodiment of the present invention is to provide a normal-pressure microwave plasma jet device, which obtains reasonable structural parameters through theoretical calculation, so that the coaxial resonator device and the microwave system impedance are well matched, and a stable normal-pressure microwave plasma jet is obtained without adding an impedance matching adjustment device, aiming to solve the problems existing in the above-mentioned background technology.

[0005] The embodiment of the present invention is implemented as follows: a normal pressure microwave plasma jet device, an outer conductor, characterized in that it also includes: An inner conductor, wherein the inner conductor is arranged inside the outer conductor, and the center lines of the inner conductor and the outer conductor coincide with each other, and a porous flow-guiding structure is provided in the air flow channel formed between the inner conductor and the outer conductor; A nozzle, wherein the nozzle is threadedly connected to the bottom end of the outer conductor, the bottom end face cross-sections of the nozzle and the inner conductor are both conical, and the distance from the bottom end of the inner conductor to the nozzle opening can be adjusted by twisting the inner conductor; A radio frequency connector, wherein the radio frequency connector is fixedly mounted on the outer conductor by means of screws, and a pin at the end of the radio frequency connector is connected to the inner conductor by means of a connecting conductor; An air pipe joint, which is threadedly connected to the outer conductor and communicates with the air flow channel between the outer conductor and the inner conductor; A short-circuit screw plug, wherein the short-circuit screw plug is threadedly connected to the top of the outer conductor, a connector is installed on the inner side of the short-circuit screw plug, the connector is threadedly connected to the inner conductor, the connector is also in contact with the outer conductor, and a short-circuit reflective surface is provided at the bottom of the connector, and the position of the short-circuit reflective surface can be changed by adjusting the short-circuit screw plug; An air guide ring, wherein the air guide ring is nested on the inner conductor and is located between the radio frequency connector and the air pipe joint; The nozzle, the outer conductor, the inner conductor and the short-circuit screw plug together form a coaxial resonant cavity structure.

[0006] Preferably, a microwave feed port is provided on the outer conductor corresponding to the RF connector, and the distance between the microwave feed port and the short-circuit reflection surface is L1; The distance between the microwave feed inlet and the opening of the nozzle is L2; L1+L2=(2n-1)λ / 4, λ is the wavelength of microwave, n=1, 2, 3...; Among them, αL1 / sin 2 (βL1)+αL2 / cos 2 (βL2)≈1, β=2π / λ, α is the microwave attenuation coefficient.

[0007] Preferably, when λ is 122.5 mm, for 2.45 GHz microwaves, one set of solutions is L1=63.7 mm, L2=28.2 mm.

[0008] Preferably, the radius of the outer conductor is b, the radius of the inner conductor is a, and the ratio b / a between the two is in the range of [2 4].

[0009] Preferably, the diameter of the opening of the nozzle is [2 6] mm.

[0010] Preferably, the air guide ring is made of polytetrafluoroethylene.

[0011] Preferably, a plurality of ventilation holes are evenly arranged on the air guide ring along the circumferential direction.

[0012] The atmospheric pressure microwave plasma jet device provided by the embodiment of the present invention has the following advantages: 1. The whole structural scheme is simple, reliable and low-cost. It does not need to configure a complex control module to adjust the impedance matching degree of the system. Reasonable structural parameters are obtained through theoretical calculation to ensure good impedance matching between the coaxial resonator device and the microwave system, so as to obtain a stable atmospheric pressure microwave plasma jet; 2. A new porous guide structure is installed in the air flow channel between the outer conductor and the inner conductor, which can make the gas flow state more stable and avoid the influence of air flow turbulence on the plasma at the outlet; 3. The short-circuit reflective surface is designed to be adjustable up and down by thread. In actual operation, if the structural parameters deviate from the design parameters due to processing and assembly errors, the impedance matching effect can be achieved by fine-tuning the short-circuit reflective surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A cross-sectional view of a normal-pressure microwave plasma jet device provided by an embodiment of the present invention; Figure 2 A three-dimensional structural diagram of a normal-pressure microwave plasma jet device provided in an embodiment of the present invention; Figure 3 A front view of a gas guide ring in a normal-pressure microwave plasma jet device provided by an embodiment of the present invention; In the attached drawings: 1-nozzle; 2-outer conductor; 3-RF connector; 4-air guide ring; 5-inner conductor; 6-trachea joint; 7-short-circuit screw plug; 8-connector; 9-short-circuit reflective surface; 10-vent. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0015] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0016] like Figures 1 to 3As shown, it is a structural diagram of a normal-pressure microwave plasma jet device provided by an embodiment of the present invention, comprising an outer conductor 2, an inner conductor 5, a nozzle 1, a radio frequency connector 3, an air pipe joint 6, a short-circuit screw plug 7 and an air guide ring 4, wherein the inner conductor 5 is arranged inside the outer conductor 2, and the center lines of the inner conductor 5 and the outer conductor 2 coincide, and a porous flow guide structure is provided in the air flow channel formed between the inner conductor 5 and the outer conductor 2; the nozzle 1 is threadedly connected to the bottom end of the outer conductor 2, and the bottom end face cross-sections of the nozzle 1 and the inner conductor 5 are both conical, and the distance from the bottom end of the inner conductor 5 to the opening of the nozzle 1 is adjusted by twisting the inner conductor 5; the radio frequency connector 3 is fixedly mounted on the outer conductor 2 by screws, and the radio frequency The pin at the end of the connector 3 is connected to the inner conductor 5 through a connecting conductor, and the RF connector 3 is also connected to an external microwave source through a RF cable; the air pipe joint 6 is threadedly connected to the outer conductor 2 and communicates with the air flow channel between the outer conductor 2 and the inner conductor 5; the short-circuit screw plug 7 is threadedly connected to the top of the outer conductor 2, and a connecting piece 8 is also installed on the inner side of the short-circuit screw plug 7, the connecting piece 8 is threadedly connected to the inner conductor 5, the connecting piece 8 also abuts against the outer conductor 2, and a short-circuit reflecting surface 9 is provided at the bottom of the connecting piece 8, and the position of the short-circuit reflecting surface 9 is changed by adjusting the short-circuit screw plug 7; the air guide ring 4 is nested on the inner conductor 5, and the air guide ring 4 is located between the RF connector 3 and the air pipe joint 6.

[0017] The application provides a normal-pressure microwave plasma jet device, the entire structural scheme is simple and reliable, the cost is low, and there is no need to configure a complex control module to adjust the impedance matching degree of the system. Reasonable structural parameters are obtained through theoretical calculation to ensure that the impedance matching between the coaxial resonator device and the microwave system is good, so that a stable normal-pressure microwave plasma jet can be obtained; and a porous guide structure is added in the air flow channel between the outer conductor 2 and the inner conductor 5, which can make the gas flow state more stable and avoid the influence of air flow turbulence on the plasma at the outlet; the short-circuit reflecting surface 9 is also designed to be threaded up and down. In the actual operation process, if the structural parameters deviate from the design parameters due to processing and assembly errors, the impedance matching effect can be achieved by fine-tuning the short-circuit reflecting surface 9.

[0018] In one embodiment of the present invention, the diameter of the opening of the nozzle 1 is [2 6] mm, and a plurality of ventilation holes 10 are evenly arranged along the circumferential direction on the air guide ring 4, and the diameter of the ventilation holes 10 is [1 3] mm; in addition, the range of the short-circuit reflection surface 9 is adjusted to [-5 5] mm by turning the short-circuit screw plug 7.

[0019] like Figure 1 and Figure 2As shown, as a preferred embodiment of the present invention, a microwave feed port is provided on the outer conductor 2 corresponding to the RF connector 3, and the distance between the microwave feed port and the short-circuit reflective surface 9 is L1; The distance between the microwave feeding port and the opening of the nozzle 1 is L2; L1+L2=(2n-1)λ / 4, λ is the wavelength of microwave, n=1, 2, 3...; Among them, αL1 / sin 2 (βL1)+αL2 / cos 2 (βL2)≈1, β=2π / λ, α is the microwave attenuation coefficient.

[0020] In one example of the present invention, for 2.45GHz microwaves, when λ is 122.5mm, the length of the coaxial line is 3 / 4λ=91.9mm, and one set of optimal solutions is L1=63.7mm, L2=28.2mm; during the test, when the air flow rate is 3L / min and the microwave source power is gradually increased from 0 to 50W, a stable normal-pressure microwave plasma can be generated.

[0021] like Figure 2 As shown, as another preferred embodiment of the present invention, the radius of the outer conductor 2 is b, the radius of the inner conductor 5 is a, and the ratio b / a between the two is in the range of [2 4].

[0022] In one embodiment of the present invention, according to the theoretical calculation formula of the characteristic impedance of the coaxial transmission line, when the ratio of the radius of the outer conductor 2 and the radius of the inner conductor 5 needs to be controlled [2 4], the additional impedance matching system can be eliminated.

[0023] like Figure 2 and Figure 3 As shown, as another preferred embodiment of the present invention, the air guide ring 4 is made of polytetrafluoroethylene material.

[0024] In one embodiment of the present invention, by selecting polytetrafluoroethylene as the processing material, the heat resistance and cold resistance of the air guide ring 4 can be improved, and it can be used for a long time at [-180 260] degrees Celsius. At the same time, it also has the characteristics of low friction coefficient and can play a lubricating role.

[0025] To sum up, during operation, gas flows in from the gas pipe joint 6, flows through the gas guide ring 4 and is evenly dispersed before flowing out from the nozzle 1. The microwave energy of the microwave source is fed into the interior of the device through the RF cable and the RF connector 3. The gas is ignited in the tapered part of the inner conductor 5, thereby generating plasma, which is ejected from the opening of the nozzle 1 to form a jet plasma.

[0026] The nozzle 1, the outer conductor 2, the inner conductor 5 and the short-circuit plug 7 together constitute a coaxial resonant cavity structure. In order to make the microwave resonate, a strong standing wave electric field can be formed in the conical part of the inner conductor 5. It must satisfy L1+L2=(2n-1)λ / 4. For 2.45GHz microwaves, λ=122.5mm, n=1, 2, 3...; the standing wave electric field size can be increased by adjusting the output power of the microwave source. As long as the electric field is strong enough, the value is not less than the air breakdown field strength of 3×10 6 V / m, then plasma can be ignited at the opening of the nozzle 1.

[0027] In order to reduce the reflected power of the system and eliminate the additional impedance matching system, the input impedance of the microwave plasma jet device should be as close as possible to the output impedance of the microwave source. The output characteristic impedance of the microwave source is usually 50Ω. According to theoretical calculations, the input impedance of the microwave plasma jet device can be: 50×[αL1 / sin 2 (βL1)+αL2 / cos 2 (βL2)]^(-1), therefore, when αL1 / sin2(βL1)+αL2 / cos2(βL2)≈1, the input impedance of the device is closest to the output impedance of the microwave source. At this time, the system reflected power is minimum and the system does not need to be additionally configured with an impedance matching device.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0029] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A normal pressure microwave plasma jet device, outer conductor, characterized in that: Also includes: An inner conductor, wherein the inner conductor is arranged inside the outer conductor, and the center lines of the inner conductor and the outer conductor coincide with each other, and a porous flow-guiding structure is provided in the air flow channel formed between the inner conductor and the outer conductor; A nozzle, wherein the nozzle is threadedly connected to the bottom end of the outer conductor, the bottom end face cross-sections of the nozzle and the inner conductor are both conical, and the distance from the bottom end of the inner conductor to the nozzle opening can be adjusted by twisting the inner conductor; A radio frequency connector, wherein the radio frequency connector is fixedly mounted on the outer conductor by means of screws, and a pin at the end of the radio frequency connector is connected to the inner conductor by means of a connecting conductor; An air pipe joint, which is threadedly connected to the outer conductor and communicates with the air flow channel between the outer conductor and the inner conductor; A short-circuit screw plug, wherein the short-circuit screw plug is threadedly connected to the top of the outer conductor, a connector is installed on the inner side of the short-circuit screw plug, the connector is threadedly connected to the inner conductor, the connector is also in contact with the outer conductor, and a short-circuit reflective surface is provided at the bottom of the connector, and the position of the short-circuit reflective surface can be changed by adjusting the short-circuit screw plug; An air guide ring, wherein the air guide ring is nested on the inner conductor and is located between the radio frequency connector and the air pipe joint; The nozzle, the outer conductor, the inner conductor and the short-circuit screw plug together form a coaxial resonant cavity structure.

2. The atmospheric pressure microwave plasma jet device according to claim 1, characterized in that: A microwave feed port is provided on the outer conductor at a position corresponding to the RF connector, and a distance between the microwave feed port and the short-circuit reflective surface is L1; The distance between the microwave feed inlet and the opening of the nozzle is L2; L1+L2=(2n-1)λ / 4, λ is the wavelength of microwave, n=1, 2, 3...; Among them, αL1 / sin 2 (βL1)+αL2 / cos 2 (βL2)≈1, β=2π / λ, α is the microwave attenuation coefficient.

3. The atmospheric pressure microwave plasma jet device according to claim 2, characterized in that: When λ is 122.5 mm, for 2.45 GHz microwaves, one set of solutions is L1=63.7 mm, L2=28.2 mm.

4. The atmospheric pressure microwave plasma jet device according to claim 1, characterized in that: The radius of the outer conductor is b, the radius of the inner conductor is a, and the ratio b / a between the two is in the range of [2 4].

5. The atmospheric pressure microwave plasma jet device according to claim 1, characterized in that: The diameter of the nozzle opening is [2 6] mm.

6. The atmospheric pressure microwave plasma jet device according to claim 1, characterized in that: The air guide ring is made of polytetrafluoroethylene material.

7. The atmospheric pressure microwave plasma jet device according to claim 1, characterized in that: The air guide ring is evenly provided with a plurality of air vents along the circumferential direction.

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