A microwave cold plasma jet device

Abstract

The present invention discloses a microwave cold plasma jet device, including a cavity part, a microwave coupling part, a tuning part, and an electric field modulation part; the cavity part is a double-resonance cavity structure with one end open, and the microwave transmission mode is a TEM mode; the microwave coupling part can couple microwave energy to the cavity part by means of conductivity coupling, capacitance coupling, magnetic coupling, etc.; the electric field modulation part is realized by an inner electrode wrapped by an insulating layer to which nanosecond pulses (or DC voltage) are applied. Based on the characteristics of microwave cold plasma, such as less ozone generation, higher plasma concentration, richer excited state particles, and nanosecond pulses (or DC) are more likely to form long straight cold plasma, the present invention proposes a microwave cold plasma jet method, that is, applying an auxiliary electric field to the microwave cold plasma, using the auxiliary electric field to pull the charged particles to accelerate the motion, and extending the length of the jet.

Description

Technical Field

[0001] The present invention belongs to the fields of material processing, material testing, plasma biomedicine, clinical medicine, etc. Specifically, it relates to a microwave cold plasma jet device with an auxiliary electric field, which can obtain a stable normal-pressure long straight microwave cold plasma jet. Background Art

[0002] Plasma is composed of electrons, ions, neutral particles, etc. When the temperature of heavy particles is much lower than the electron temperature, it is called cold plasma. At present, atmospheric pressure cold plasma is widely used in waste gas treatment, auxiliary combustion, surface modification, medical sterilization, clinical medicine and other fields. Among them, the atmospheric pressure cold plasma jet is generated in an open space. While transporting active substances and charged particles, it also realizes the separation of the discharge area and the working area, and has higher safety. Therefore, it has good application prospects in biology, clinical medicine and other fields. In practical applications, the jet length is the key parameter to be considered first, which greatly affects and restricts the application of atmospheric pressure cold plasma jets. At the same time, the plasma composition is also a key factor to be considered, which limits the application scenarios of plasma jets.

[0003] Cold plasma can be generated by driving corresponding devices through high voltage, microwave, radio frequency and other means. The driving method and device structure have an important influence on the jet length and composition. Among them, microwave cold plasma jet has the advantages of high electron density, high ionization degree, strong controllability, and low ozone generation. It can be efficiently used in various scenarios such as pathogen inactivation, wound treatment, and human surgery.

[0004] Cold plasma jets are generated in open space, and the influx of air causes the jet length to be shorter. To solve this problem, three approaches are currently used to extend the jet length.

[0005] One is to use a large flow of inert gas (helium, argon, neon, etc.) as the working gas, so that the jet nozzle is in an inert gas environment with a relatively low breakdown field strength threshold, which is conducive to the formation of plasma. At the same time, the high flow of gas can pull the plasma outward; (For example, the 11cm long helium plasma jet proposed by Lu Xinpei's research group in 2008 was generated by a sinusoidal high voltage driving the central electrode wrapped in a quartz tube)

[0006] Both are driven by high-voltage nanosecond pulses, and the plasma jet length is observed to increase significantly under extremely high and fast energy input;

[0007] The third method is to control the plasma jet shape by using a composite coaxial double-wire structure, a dual resonant cavity and dual airflow constraints (corresponding patent number CN201910658894.6).

[0008] 1) When using inert gas as the working gas, a large gas cylinder is required, which is inconvenient to carry and is not suitable for outdoor, grounded material collection and other working environments. In addition, the plasma jet is not suitable for some special environments (such as lung treatment, etc.);

[0009] 2) Among the commonly used working gases, air has a wider application prospect because it does not need to be equipped with gas cylinders, is portable and easy to operate, etc., but it also has problems such as the breakdown field strength threshold is much greater than that of inert gases, and a large amount of ozone is generated when the discharge is stimulated by using high-voltage driven dielectric barrier discharge and other methods. When applied to clinical medicine, it is not conducive to the health of the treated subjects;

[0010] 3) When the plasma jet is ejected by airflow, the pathogens and other medical objects being treated may be separated from their positions due to the disturbance of airflow, which may cause potential problems of biochemical contamination;

[0011] 4) When a microwave cold plasma jet is generated by a composite coaxial double-line and double-gas flow method, since the open ends are all straight tube structures, the electric field strength is not further enhanced, and it is difficult to reach the excitation field strength of air microwave cold plasma, which restricts its application when air is the working gas. Summary of the invention

[0012] In order to solve the above problems existing in the prior art, the present invention proposes a microwave cold plasma jet device.

[0013] The present invention can be implemented through the following technical solutions:

[0014] A microwave cold plasma jet device, consisting of a cavity part, a microwave coupling part, a tuning part and an electric field modulation part;

[0015] The cavity part is an outer tube with one end open, a middle tube with two ends open, and an inner electrode coaxial resonant cavity structure, the outer tube is provided with a microwave feeding port and a tangential flow shielding gas inlet, and the middle tube is provided with a gas inlet;

[0016] The microwave coupling part includes a coupling ring, which couples microwave energy to the cavity part;

[0017] The tuning part is a structure for adjusting the length of the resonant cavity at the tuning end to adjust the field strength at the open end, and the upper end of the tuning end is a reflective end surface; the depth of the cavity part adjusted to the tuning end is Yλ / 4, where λ is the wavelength at the microwave frequency, and Y is a positive odd number;

[0018] The electric field modulation part is connected to the inner electrode by applying nanosecond pulse / DC voltage, and the inner electrode is wrapped by a coaxial insulating layer.

[0019] Furthermore, the outer tube, the middle tube and the inner electrode are all made of metal, and the microwave transmission modes between the outer tube and the middle tube, and between the middle tube and the inner electrode are all TEM modes.

[0020] Furthermore, the axial length of the outer tube is Nλ / 4, wherein λ is the wavelength at the microwave frequency, and N is a positive odd number.

[0021] Furthermore, the upper ends of the outer tube and the middle tube are of a gradual closing structure, the closing angle of the outer tube is 0 to 60 degrees, and the closing angle of the middle tube is 0 to 30 degrees.

[0022] Furthermore, there is a porous coaxial gasket with a metal upper surface between the middle tube and the coaxial insulating layer, and the distance between the upper surface of the porous coaxial gasket and the opening end of the cavity is in the range of Wherein λ is the wavelength at the microwave frequency, and M is a positive odd number.

[0023] Furthermore, the inner electrode is inserted into the cavity of the coaxial insulating layer, and the inner layer of the coaxial insulating layer is coated on the outer side of the inner electrode.

[0024] Furthermore, the upper end of the middle tube is not higher than the outer tube, and the upper ends of the inner electrode and the coaxial insulating layer may be higher / lower than the middle tube.

[0025] Furthermore, the outer tube and the middle tube introduce gas through the shielding gas inlet or the gas inlet.

[0026] Furthermore, the shielding gas inlet is introduced in a tangential flow manner; the gas flow rates of the shielding gas inlet and the gas inlet are controlled at 0 to 20 L / min.

[0027] Furthermore, the distance between the coupling ring and the upper port of the outer tube is adjustable; and the microwave plasma jet device is applicable to electromagnetic wave frequencies ranging from several MHz to several GHz.

[0028] Furthermore, the output pulse width of the nanosecond pulse power supply is 10 to 900 ns, the rising edge is 1 to 200 ns, the amplitude is 3 to 220 kV, the frequency is 1 to 20 kHz, and the duty cycle is 1 to 99%; the output voltage of the DC power supply is 0 to 60 kV or 0 to -60 kV.

[0029] Beneficial Effects

[0030] The present invention uses a microwave source to drive a dual-resonance cavity structure to generate a low-temperature, easy-to-adjust, handheld, normal-pressure microwave cold plasma jet, and on this basis, introduces an auxiliary electric field formed by high voltage to pull the extremely dense charged particles in the microwave plasma to move outside the nozzle, thereby extending the jet length. The present invention uses the electric field to lead the movement of charged particles, effectively avoiding the biochemical pollution that may be caused by airflow disturbance. At the same time, high voltage can drive the generation of cold plasma, which can assist ignition at the port of the torch tube, facilitate the formation of microwave plasma jets and improve their stability. Among them, due to the large difference in the operating frequency of nanosecond pulse / DC high voltage and microwave, the direct current electric field and the microwave field in the plasma resonator can achieve field decoupling. In addition, the microwave cold plasma generation device is based on the deformation of the microwave plasma torch (MPT), and a gradual closing structure is added to the upper end of the outer tube and the middle tube to regulate the electric field at the open end. The insulating layer outside the central electrode can prevent the sheath voltage from being too high to cause the charged particles to bombard the discharge electrode, thereby improving the service life of the electrode, and making the jet device as a whole accessible, thereby improving safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the patent according to the present invention;

[0032] Figure 2 It is another structural schematic diagram according to the patent of the present invention. DETAILED DESCRIPTION

[0033] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Specific embodiment 1

[0035] Specific embodiment 1 provides a composite modulated microwave cold plasma jet device of the present invention, and combines Figure 1 A schematic diagram of one of the typical structures is given below.

[0036] The composite field modulated microwave cold plasma jet device is composed of a cavity part, a microwave coupling part, a tuning part and an electric field modulation part;

[0037] See also Figure 1 The microwave cold plasma jet device of the present invention comprises a microwave feeding port 1, an outer tube 2, a tuning end 3, a middle tube 4, a central inner electrode 5, a coupling ring 6, a porous coaxial gasket 7, a coaxial insulating layer 8, a tangential flow shielding gas inlet 9, a nanosecond pulse / DC high voltage input end 10, and a gas inlet 11;

[0038] The cavity part is a coaxial resonant cavity structure of an outer tube 2 with one end open, a middle tube 4 with two ends open, and a central inner electrode 5;

[0039] The outer tube 2, the middle tube 4, and the inner electrode 5 are all made of metal. The microwave transmission modes between the outer tube 2 and the middle tube 4, and between the middle tube 4 and the inner electrode 5 are all TEM modes. The inner electrode 5 is connected to an auxiliary power supply (DC or nanosecond pulse modulation source).

[0040] The axial length of the outer tube 2 is Nλ / 4 (λ is the wavelength at the microwave frequency, and N is a positive odd number);

[0041] The upper ports of the outer tube 2 and the middle tube 4 are of a gradual closing structure, the closing of the outer tube 2 is 0-60°, and the closing of the middle tube 4 is 0-30°. This design is used to adjust the electric field at the port;

[0042] There is a porous coaxial gasket 7 with a metal upper surface between the middle tube 4 and the coaxial insulating layer 8. The distance between the upper surface of the porous coaxial gasket 7 and the opening end of the cavity is (λ is the wavelength at the microwave frequency, and M is a positive odd number);

[0043] The central inner electrode is inserted into the cavity of the coaxial insulating layer 8, and the inner layer of the insulating layer is coated on the outer side of the central inner electrode; the upper end of the coaxial insulating layer 8 is closed, preferably, a quartz tube with a closed upper end is used;

[0044] The upper end of the middle tube 4 is not higher than the outer tube, and the upper ends of the inner electrode 5 and the insulating layer can be higher / lower than the middle tube. Preferably, the upper end of the middle tube 4 is 0-2 mm lower than the upper end of the outer tube, and the upper end of the inner electrode 5 is located at -5-5 mm from the upper end of the middle tube. Figure 1 The upper end of the inner electrode wrapped in the insulating layer is flush with the upper end of the middle tube 4;

[0045] The outer tube 2 and the middle tube 4 can introduce gas, preferably, the shielding gas inlet 9 is introduced in a tangential flow manner; the gas flow rate of the shielding gas inlet 9 and the gas inlet 11 is controlled at 0-20L / min;

[0046] The microwave coupling part can selectively couple the microwave energy to the cavity part by means of conduction coupling, capacitive coupling, etc.; Figure 1 A schematic diagram of the structure of introducing microwave energy into the resonant cavity by conductive coupling is given; the spacing between the coupling ring 6 and the upper port of the outer tube 2 is adjustable; the microwave plasma jet device is suitable for electromagnetic wave frequencies ranging from several MHz to several GHz. Preferably, a stable atmospheric pressure microwave cold plasma jet with a length of 5 to 40 mm is generated at a frequency of 2.45 GHz, and the microwave power conversion efficiency is greater than 80%.

[0047] The tuning part is a structure in which the tuning end 3 adjusts the length of the resonant cavity to adjust the field strength at the open end. The upper end of the tuning end is a reflective end surface, and its material is metal. The depth of the cavity part adjusted to the tuning end is Yλ / 4 (λ is the wavelength at the microwave frequency, and Y is a positive odd number);

[0048] The electric field modulation part is an auxiliary power supply (nanosecond pulse or DC voltage) connected to the inner electrode 5; the output pulse width of the nanosecond pulse power supply is 10-900ns, the rising edge is 1-200ns, the amplitude is 3-220kV, the frequency is 1-20kHz, and the duty cycle is 1-99%; the output voltage of the DC power supply is 0-60kV or 0--60kV;

[0049] The microwave plasma jet device can work in the following 18 ways:

[0050] 1) Microwaves are coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity. The nanosecond pulse power supply is connected to the central inner electrode wrapped in the coaxial insulating tube. The plasma is formed at the axis position of the upper port of the resonant cavity and ejected outward under the drive of the pulse electric field;

[0051] 2) The microwave is coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity, and high voltage (positive / negative)

[0052] The power source is connected to the central inner electrode wrapped in the coaxial insulating tube, and the plasma is formed at the axis position of the upper port of the resonant cavity and ejected outwards driven by the high voltage electric field;

[0053] 3) The microwave is coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity, and the plasma is formed at the axis position of the upper port of the resonant cavity and ejected outward;

[0054] 4) A nanosecond pulse power source is connected to the central inner electrode wrapped in a coaxial insulating tube, and plasma is formed at the upper end of the inner electrode and ejected outward;

[0055] 5) A DC high voltage (positive / negative) power supply is connected to the central inner electrode wrapped in a coaxial insulating tube, and plasma is formed at the upper end of the inner electrode and ejected outward;

[0056] 6) Based on method 1), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0057] 7) Based on method 2), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0058] 8) Based on method 4), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0059] 9) Based on method 5), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0060] 10) Based on method 1), gas (single / mixed) is input through inlet 9 and inlet 11, and a microwave plasma jet is driven to be ejected by a pulse electric field, and the plasma composition is adjusted;

[0061] 11) Based on method 2), gas (single / mixed) is input through inlet 9 and inlet 11, and microwave plasma jet is driven to be ejected in coordination with high voltage electric field, and plasma composition is adjusted;

[0062] 12) Based on method 3), gas (single / mixed) is input through inlet 9 and inlet 11, microwave plasma jet is ejected, and plasma composition is adjusted;

[0063] 13) Based on method 4), gas (single / mixed) is input through inlet 9 and inlet 11, a cold plasma jet driven by a nanosecond pulse is ejected, and the plasma composition is adjusted;

[0064] 14) Based on method 5), gas (single / mixed) is input through inlet 9 and inlet 11, a cold plasma jet driven by a nanosecond pulse is ejected, and the plasma composition is adjusted;

[0065] 15) Based on method 1), the coaxial insulating layer is an insulating coating;

[0066] 16) Based on method 2), the coaxial insulating layer is an insulating coating;

[0067] 17) Based on method 4), the coaxial insulating layer is an insulating coating;

[0068] 18) Based on method 5), the coaxial insulating layer is an insulating coating; Specific embodiment 2

[0070] Figure 2 Another schematic diagram of the structure according to the present invention is given, which supports the coordinated modulation of microwave cold plasma jet length by dual resonant cavities, auxiliary electric fields and three gas flows;

[0071] The composite field modulated microwave cold plasma jet device is composed of a cavity part, a microwave coupling part, a tuning part and an electric field modulation part;

[0072] See also Figure 2 The composite field modulated microwave cold plasma jet device of the present invention comprises a microwave feeding port 1, an outer tube 2, a tuning end 3, a middle tube 4, a coupling ring 6, a porous coaxial gasket 7, a tangential flow shielding gas inlet 9, a nanosecond pulse / DC high voltage input end, a middle tube air inlet 11, a capillary air inlet 12, a capillary inner electrode 13, and a coaxial insulating tube 14;

[0073] The cavity part is a coaxial resonant cavity structure of an outer tube 2, a middle tube 4, and a capillary inner electrode 13;

[0074] The outer tube, the middle tube, and the capillary inner electrode are all made of metal. The outer tube, the middle tube, and the reflection end form a coaxial resonant cavity 1 with one end open. The middle tube, the capillary inner electrode, and the reflection end form a coaxial resonant cavity 2 with one end open. Both places form a TEM standing wave field inside.

[0075] The electrode inside the capillary is connected to an auxiliary power source (DC or nanosecond pulse modulation source);

[0076] The axial length of the outer tube is (λ is the wavelength at the microwave frequency, and N is a positive odd number);

[0077] The upper ports of the outer tube and the middle tube are of a gradual closing structure, the closing of the outer tube is 0-60°, and the closing of the middle tube is 0-30°. This design is used to adjust the electric field at the port;

[0078] There is a porous coaxial gasket with a metal upper surface between the middle tube and the coaxial insulating tube 14. The distance between the upper surface of the porous gasket and the opening end of the cavity is (λ is the wavelength at the microwave frequency, and M is a positive odd number);

[0079] The inner surface of the coaxial insulating tube 14 is wrapped around the outer surface of the capillary inner electrode, and its axial length is consistent with the capillary inner electrode, and its inner diameter is consistent with the outer diameter of the capillary inner electrode. Preferably, a quartz insulating tube is used to wrap the outer surface of the capillary inner electrode;

[0080] The upper end of the middle tube is not higher than the outer tube, and the upper end of the capillary electrode can be higher / lower than the middle tube. Preferably, the upper end of the middle tube is 0-2 mm lower than the upper end of the outer tube, and the upper end of the capillary electrode is located -5-5 mm from the upper end of the middle tube. Figure 2 The upper port of the electrode in the middle capillary is flush with the upper port of the middle tube;

[0081] Gas can be introduced into the outer tube, the middle tube, and the capillary inner electrode. Preferably, the shielding gas inlet 9 is introduced in a tangential flow manner; the gas flow rate of the gas inlet 9 and the gas inlet 11 is controlled at 0-20 L / min, and the gas flow rate of the gas inlet 12 is controlled at 0-1 L / min;

[0082] The microwave coupling part can selectively couple the microwave energy to the cavity part by means of conduction coupling, capacitive coupling, etc.; Figure 2 A schematic diagram of the structure of introducing microwave energy into the resonant cavity by conductive coupling is given; the spacing between the coupling ring 6 and the upper port of the outer tube is adjustable; the microwave plasma jet device is suitable for electromagnetic wave frequencies ranging from several MHz to several GHz. Preferably, a stable atmospheric pressure microwave cold plasma jet with a length of 5 to 40 mm is generated at a frequency of 2.45 GHz, and the microwave power conversion efficiency is greater than 80%.

[0083] The tuning part is a structure in which the tuning end 3 adjusts the length of the resonant cavity to adjust the field strength at the open end. The upper end of the tuning end is a reflective end surface, and its material is metal. The depth of the cavity part adjusted to the tuning end is Yλ / 4 (λ is the wavelength at the microwave frequency, and Y is a positive odd number);

[0084] The electric field modulation part is an auxiliary power supply (nanosecond pulse or DC voltage) connected to the capillary electrode 13; the output pulse width of the nanosecond pulse power supply is 10-900ns, the rising edge is 1-200ns, the amplitude is 3-220kV, the frequency is 1-20kHz, and the duty cycle is 1-99%; the output voltage of the DC power supply is 0-60kV or 0--60kV;

[0085] The microwave plasma jet device can work in the following 18 ways:

[0086] 1) The microwave is coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity, and the nanosecond pulse power supply is connected to the electrode inside the capillary. The plasma is formed at the axis position of the upper port of the resonant cavity and ejected outward under the drive of the pulse electric field;

[0087] 2) The microwave is coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity, and the high-voltage (positive / negative) power supply is connected to the electrode inside the capillary. The plasma is formed at the axis position of the upper port of the resonant cavity and ejected outward under the drive of the high-voltage electric field;

[0088] 3) The microwave is coupled into the resonant cavity through the microwave coupling part, forming a TEM standing wave in the resonant cavity, and the plasma is formed at the axis position of the upper port of the resonant cavity and ejected outward;

[0089] 4) A nanosecond pulse power source is connected to the inner electrode of the capillary, and plasma is formed at the upper end of the inner electrode and ejected outward;

[0090] 5) A DC high voltage (positive / negative) power supply is connected to the inner electrode of the capillary, and plasma is formed at the upper end of the inner electrode and ejected outward;

[0091] 6) Based on method 1), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0092] 7) Based on method 2), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0093] 8) Based on method 4), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0094] 9) Based on method 5), the outer tube is not connected to the ground wire, and the infinite end is used as the ground wire;

[0095] 10) Based on method 1), gas (single / mixed) is input through inlet 9, inlet 11, and inlet 12, and a microwave plasma jet is driven to be ejected by a pulse electric field, and the plasma composition is adjusted;

[0096] 11) Based on method 2), gas (single / mixed) is input through inlet 9, inlet 11, and inlet 12, and a microwave plasma jet is driven to be ejected in coordination with a high voltage electric field, and the plasma composition is adjusted;

[0097] 12) Based on method 3), gas (single / mixed) is input through inlet 9, inlet 11, and inlet 12, microwave plasma jet is ejected, and plasma composition is adjusted;

[0098] 13) Based on method 4), gas (single / mixed) is input through inlet 9, inlet 11, and inlet 12, and a cold plasma jet driven by a nanosecond pulse is ejected, and the plasma composition is adjusted;

[0099] 14) Based on method 5), gas (single / mixed) is input through inlet 9, inlet 11, and inlet 12, and a cold plasma jet driven by a nanosecond pulse is ejected, and the plasma composition is adjusted;

[0100] 15) Based on method 1), the capillary inner electrode may be an annular inner electrode flush with the upper end of the coaxial insulating tube, the outer surface of the annular electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the annular electrode is consistent with the inner diameter of the coaxial insulating tube;

[0101] 16) Based on method 2), the capillary inner electrode may be an annular inner electrode flush with the upper end of the coaxial insulating tube, the outer surface of the annular electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the annular electrode is consistent with the inner diameter of the coaxial insulating tube;

[0102] 17) Based on method 4), the capillary inner electrode may be an annular inner electrode flush with the upper end of the coaxial insulating tube, the outer surface of the annular electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the annular electrode is consistent with the inner diameter of the coaxial insulating tube;

[0103] 18) Based on method 5), the capillary inner electrode may be an annular inner electrode flush with the upper end of the coaxial insulating tube, the outer surface of the annular electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the annular electrode is consistent with the inner diameter of the coaxial insulating tube;

[0104] The present invention prolongs the length of microwave cold plasma jet, and can intelligently generate specific cold plasma by coordinating different driving parameters and gas parameters, thereby improving its operability and practicability in clinical hospitals and other fields.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A microwave cold plasma jet device, characterized in that: It consists of a cavity part, a microwave coupling part, a tuning part and an electric field modulation part; The cavity part is an outer tube with one end open, a middle tube with two ends open, and an inner electrode coaxial resonant cavity structure. The outer tube is provided with a microwave feeding port and a tangential flow shielding gas inlet, and the middle tube is provided with a gas inlet; the axial length of the outer tube is Nλ / 4, wherein λ is the wavelength at the microwave frequency, and N is a positive odd number; The microwave coupling part includes a coupling ring, which couples microwave energy to the cavity part; The tuning part is a structure for adjusting the length of the resonant cavity at the tuning end to adjust the field strength at the open end, and the upper end of the tuning end is a reflective end surface; the depth of the cavity part adjusted to the tuning end is Yλ / 4, where λ is the wavelength at the microwave frequency, and Y is a positive odd number; The electric field modulation part is connected to the inner electrode by applying nanosecond pulse / DC voltage, and the inner electrode is wrapped by a coaxial insulating layer; there is a porous coaxial gasket with a metal upper surface between the middle tube and the coaxial insulating layer, and the distance between the upper surface of the porous coaxial gasket and the opening end of the cavity part is Wherein λ is the wavelength at the microwave frequency, and M is a positive odd number.

2. A microwave cold plasma jet device according to claim 1, characterized in that: The outer tube, the middle tube and the inner electrode are all made of metal, and the microwave transmission modes between the outer tube and the middle tube and between the middle tube and the inner electrode are all TEM modes.

3. A microwave cold plasma jet device according to claim 1, characterized in that: The upper ends of the outer tube and the middle tube are of a gradual closing structure, the closing angle of the outer tube is 0 to 60 degrees, and the closing angle of the middle tube is 0 to 30 degrees.

4. A microwave cold plasma jet device according to claim 1, characterized in that: The inner electrode is inserted into the cavity of the coaxial insulating layer, and the inner layer of the coaxial insulating layer is coated on the outer side of the inner electrode.

5. A microwave cold plasma jet device according to claim 1, characterized in that: The upper end of the middle tube is not higher than the outer tube, and the upper ends of the inner electrode and the coaxial insulating layer can be higher / lower than the middle tube.

6. A microwave cold plasma jet device according to claim 1, characterized in that: The outer tube and the middle tube introduce gas through the shielding gas inlet or the gas inlet.

7. A microwave cold plasma jet device according to claim 6, characterized in that: The shielding gas inlet is introduced in a tangential flow manner; the gas flow rates of the shielding gas inlet and the gas inlet are controlled at 0 to 20 L / min.

8. A microwave cold plasma jet device according to claim 6, characterized in that: The distance between the coupling ring and the upper port of the outer tube is adjustable; the microwave plasma jet device is applicable to electromagnetic wave frequencies ranging from several MHz to several GHz.

9. A microwave cold plasma jet device according to claim 6, characterized in that: The output pulse width of the nanosecond pulse power supply is 10 to 900 ns, the rising edge is 1 to 200 ns, the amplitude is 3 to 220 kV, the frequency is 1 to 20 kHz, and the duty cycle is 1 to 99%; the output voltage of the DC power supply is 0 to 60 kV or 0 to -60 kV.

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