CN115315055A - A microwave cold plasma jet device - Google Patents

Abstract

The invention discloses a microwave cold plasma jet device, comprising a cavity part, a microwave coupling part, a tuning part and an electric field modulation part; the cavity part is a double resonant cavity structure with one end open, and the microwave transmission mode is a TEM mode; the microwave coupling part The microwave energy can be coupled to the cavity part by means of conductance coupling, capacitive coupling, magnetic coupling, etc. The electric field modulation part is realized by the inner electrode wrapped by the insulating layer applying nanosecond pulse (or DC voltage). The invention proposes a microwave cold plasma based on the characteristics of less ozone generation, higher plasma concentration, more excited particles, and easier formation of long direct cold plasma by nanosecond pulse (or DC) in the microwave cold plasma. The jet method is to apply an auxiliary electric field to the microwave cold plasma, and use the auxiliary electric field to drag the charged particles to accelerate the movement, so as to prolong the length of the jet.

Description

A microwave cold plasma jet device

technical field

The invention belongs to the fields of material processing, material detection, plasma biomedicine, clinical medicine, etc., and specifically 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 technique

Plasma is composed of electrons, ions, neutral particles, etc. When the temperature of heavy particles is much lower than that of electrons, it is called cold plasma. At present, atmospheric pressure-cooled plasma is widely used in waste gas treatment, auxiliary combustion, surface modification, medical sterilization, clinical medicine and other fields. Among them, the atmospheric pressure-cooled 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, which has higher safety. Therefore, it has great potential in the fields of biology and clinical medicine. Good application prospects. In practical applications, the jet length is the key parameter to be considered first, which largely 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.

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

The cold plasma jet is generated in an open space, and the influx of air leads to a short jet length. To solve this problem, three methods are currently used to extend the jet length.

One is to use a large flow rate of inert gas (helium, argon, neon, etc.) It can pull the plasma out; (such as the 11cm-long helium plasma jet proposed by Lu Xinpei’s research group in 2008, which is generated by a central electrode wrapped in a quartz tube driven by a sinusoidal high voltage)

The two are driven by high-voltage nanosecond pulses, and the length of the plasma jet is observed to increase significantly under extremely high and extremely fast energy input;

The three are to control the shape of the plasma jet by means of dual resonant cavities and dual airflow constraints through a composite coaxial double-wire structure (corresponding to patent number CN201910658894.6).

1) When using inert gas as the working gas, it needs to be equipped with a large gas cylinder, which is inconvenient to carry, and is not suitable for working environments such as outdoors and grounding materials, and the plasma jet is not suitable for some special environments (such as lung treatment, etc.);

2) Among the commonly used working gases, air has wider application prospects because it does not need to be equipped with gas cylinders, is portable and easy to operate, but there are also methods such as the breakdown field strength threshold is much higher than that of inert gases, and the use of high voltage to drive dielectric barrier discharge. A large amount of ozone is generated when the discharge is excited, which is not conducive to the health of the treated object when it is used in clinical medicine;

3) When the plasma jet is ejected by the leading traction of the air flow, the treated pathogens and other medical objects may leave their positions under the disturbance of the air flow, which may cause potential problems of biochemical pollution;

4) When the microwave cold plasma jet is generated by means of composite coaxial double wires and double air flow, since its opening ends are all straight tube structures, the electric field strength is not further enhanced, and it is difficult to achieve the excitation field strength of air microwave cold plasma , which restricts its application when air is the working gas.

Contents of the invention

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

The present invention can be realized through the following technical solutions:

A microwave cold plasma jet device, which 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 both 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 Entrance;

The microwave coupling portion includes a coupling ring to couple microwave energy to the cavity portion;

The tuning part is a structure in which the tuning end adjusts the length of the resonant cavity to adjust the field strength at the opening end. The wavelength under the microwave frequency, Y is a positive odd number;

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

Further, 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.

Further, the axial length of the outer tube is Nλ/4, where λ is the wavelength at the microwave frequency, and N is a positive odd number.

Further, the upper ports of the outer tube and the middle tube have a gradual closing structure, the closing of the outer tube is 0-60°, and the closing of the middle tube is 0-30°.

其中λ为所述微波频率下的波长，M为正奇数。Further, between the middle tube and the coaxial insulating layer, there is a porous coaxial gasket whose upper surface is made of metal, and the distance between the upper surface of the porous coaxial gasket and the port at the opening end of the cavity part is in the range of

Wherein λ is the wavelength at the microwave frequency, and M is a positive odd number.

Further, the inner electrode is inserted into the cavity of the coaxial insulating layer, and the inner layer of the coaxial insulating layer covers the outer side of the inner electrode.

Further, the upper port of the middle tube is not higher than the outer tube, and the upper end of the inner electrode and the coaxial insulating layer can be higher/lower than the middle tube.

Further, the outer tube and the middle tube introduce gas through the shielding gas inlet or the gas inlet.

Further, the shielding gas inlet is introduced in a tangential flow; the gas flow rate of the shielding gas inlet and the gas inlet is controlled at 0-20 L/min.

Further, the distance between the coupling ring 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.

Further, 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 DC power supply The output voltage is 0~60kV or 0~-60kV.

Beneficial effect

The invention uses a microwave source to drive a double-resonant cavity structure to generate a low-temperature, easy-to-adjust, and handheld-operated normal-pressure microwave cold plasma jet, and on this basis, introduces an auxiliary electric field formed by a high voltage to pull the maximum density in the microwave plasma. The charged particles move out of the nozzle, thereby extending the length of the jet. The invention uses the electric field to guide the movement of the charged particles, effectively avoiding the possible biochemical pollution caused by the disturbance of the air flow. At the same time, the high pressure can drive the generation of cold plasma, which can assist ignition at the port of the torch tube, which is beneficial to the formation of microwave plasma jet and improves its stability. Among them, due to the large difference in operating frequency between nanosecond pulse/DC high voltage and microwave, the DC electric field and microwave field can realize field decoupling in the plasma resonator. 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 control the electric field at the opening end. The insulating layer outside the center electrode can prevent the charged particles from bombarding the discharge electrode due to the high voltage of the sheath layer, which improves the service life of the electrode, and makes the jet device as a whole accessible, improving safety.

Description of drawings

Fig. 1 is a structural schematic diagram according to the patent of the present invention;

Fig. 2 is another structural schematic diagram according to the patent of the present invention.

Detailed ways

The implementation of the present invention is described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

Specific embodiment 1

Specific embodiment 1 presents the composite modulation microwave cold plasma jet device of the patent of the present invention, and a typical structural diagram thereof is provided in conjunction with FIG. 1 .

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;

Referring to Fig. 1, the microwave cold plasma jet device of the present invention includes a microwave feed 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 Insulation layer 8, tangential flow shielding gas inlet 9, nanosecond pulse/DC high voltage input terminal 10, gas inlet 11;

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

The outer tube 2, the middle tube 4, and the inner electrode 5 are all made of metal, and 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, and the inner electrode 5 and the inner electrode 5 are all in the TEM mode. Auxiliary power supply (DC or nanosecond pulse modulation source) connection;

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);

The upper ports of the outer tube 2 and the middle tube 4 have 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°, which is designed to adjust the electric field at the ports;

(λ为所述微波频率下的波长，M为正奇数)；Between the middle tube 4 and the coaxial insulating layer 8, there is a porous coaxial gasket 7 whose upper surface is made of metal, and the distance between the upper surface of the porous coaxial gasket 7 and the opening port of the cavity part is

(λ is the wavelength under the microwave frequency, and M is a positive odd number);

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 outside of the central inner electrode; the upper end of the coaxial insulating layer 8 is closed, preferably, a quartz tube with an upper end closed;

The upper port of the middle tube 4 is not higher than the outer tube, and the upper end 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 0-2mm lower than the upper port of the outer tube, and the inner electrode 5 The upper end is located at the upper port of the middle tube -5 ~ 5mm; the upper end of the inner electrode wrapped with the insulating layer in Figure 1 is flush with the upper port of the middle tube 4;

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

The microwave coupling part can optionally couple microwave energy to the cavity part by means of conductance coupling, capacitive coupling, etc.; Figure 1 shows a schematic structural diagram of introducing microwave energy into the resonator cavity by conductance coupling; the coupling ring 6 and the outer tube 2 The distance between the upper ports is adjustable; the microwave plasma jet device is suitable for electromagnetic wave frequency ranges 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 is converted into The efficiency is greater than 80%.

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 opening end. The upper end of the tuning end is a reflective end surface, and its material is a metal material; the depth of the tuning end adjusted to the cavity part is Yλ /4 (λ is the wavelength under the microwave frequency, Y is a positive odd number);

In the electric field modulation part, an auxiliary power supply (nanosecond pulse or DC voltage) is connected to the inner electrode 5; the output pulse width of the nanosecond pulse power supply is 10-900 ns, the rising edge is 1-200 ns, and the amplitude is 3-220 kV. 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;

The described microwave plasma jet device can work in the following 18 ways:

1) The microwave is coupled into the resonant cavity through the microwave coupling part, and a TEM standing wave is formed in the resonant cavity. The nanosecond pulse power supply is connected to the central inner electrode wrapped in the coaxial insulating tube, and the plasma is formed at the axial position of the upper port of the resonant cavity, and Driven by a pulsed electric field, it is ejected outward;

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

The power supply is connected to the central inner electrode wrapped in the coaxial insulating tube, and the plasma is formed at the axial position of the upper port of the resonant cavity, and is ejected outwards driven by a high-voltage electric field;

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 axial position of the upper port of the resonant cavity and ejected outward;

4) The nanosecond pulse power supply is connected to the central inner electrode wrapped in the coaxial insulating tube, and the plasma is formed on the upper end of the inner electrode and ejected outward;

5) The DC high-voltage (positive/negative) power supply is connected to the central inner electrode wrapped in the coaxial insulating tube, and the plasma is formed on the upper end of the inner electrode and ejected outward;

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

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

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

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

10) Based on method 1), the gas (single/mixed) is input from the inlet 9 and the inlet 11, and the microwave plasma jet is driven by the pulsed electric field to eject, and the plasma composition is adjusted;

11) Based on method 2), the gas (single/mixed) is input from the inlet 9 and the inlet 11, and the high-voltage electric field is used to drive the microwave plasma jet to eject and adjust the plasma composition;

12) Based on method 3), the gas (single/mixed) is input from the inlet 9 and the inlet 11, and the microwave plasma jet is pulled to be ejected, and the plasma composition is adjusted;

13) Based on method 4), the gas (single/mixed) is input from the inlet 9 and the inlet 11, and the cold plasma jet driven by nanosecond pulse is drawn to eject, and the plasma composition is adjusted;

14) Based on method 5), the gas (single/mixed) is input from the inlet 9 and the inlet 11, and the cold plasma jet driven by the nanosecond pulse is pulled out, and the plasma composition is adjusted;

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

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

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

18) Based on method 5), the coaxial insulating layer is an insulating coating;

Specific embodiment 2

Figure 2 shows another structural schematic diagram according to the patent of the present invention, which supports dual resonant cavities, auxiliary electric field and three airflows to coordinately modulate the length of the microwave cold plasma jet;

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;

Referring to Fig. 2, the composite field modulated microwave cold plasma jet device of the present invention includes a microwave feed port 1, an outer tube 2, a tuning end 3, a middle tube 4, a coupling ring 6, a porous coaxial gasket 7, and a tangential flow shield Gas inlet 9, nanosecond pulse/DC high voltage input end, middle tube air inlet 11, capillary air inlet 12, capillary inner electrode 13, coaxial insulating tube 14;

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

The outer tube, the middle tube, and the inner electrode of the capillary are all made of metal, and the outer tube, the middle tube, and the reflective end form a coaxial resonant cavity 1 with one end open, and the middle tube, the capillary inner electrode, and the reflective end form a coaxial resonant cavity with one end open. Cavity 2, both of which form TEM standing wave fields inside;

The electrode in the capillary is connected to the auxiliary power supply (DC or nanosecond pulse modulation source);

(λ为所述微波频率下的波长，N为正奇数)；The axial length of the outer tube is

(λ is the wavelength under the microwave frequency, and N is a positive odd number);

The upper ports of the outer tube and the middle tube have a gradual closing structure, the closing of the outer tube is 0-60°, and the closing of the middle tube is 0-30°, which is designed to adjust the electric field at the ports;

(λ为所述微波频率下的波长，M为正奇数)；There is a porous coaxial gasket with an upper surface made of metal between the middle pipe and the coaxial insulating pipe 14, and the distance range between the upper surface of the porous gasket and the opening port of the cavity part is

(λ is the wavelength under the microwave frequency, and M is a positive odd number);

The inner surface of the coaxial insulating tube 14 is wrapped around the outer surface of the capillary inner electrode, 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;

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

The outer tube, the middle tube, and the inner electrode of the capillary can introduce gas. Preferably, the shielding gas inlet 9 is introduced in a tangential flow; the gas flow rate of the gas inlet 9 and gas inlet 11 is controlled at 0-20L /min, the gas flow rate at the air inlet 12 is controlled at 0-1L/min;

The microwave coupling part can optionally couple microwave energy to the cavity part by means of conductance coupling, capacitive coupling, etc.; Figure 2 shows a schematic structural diagram of introducing microwave energy into the resonator cavity by conductance coupling; the coupling ring 6 is connected to the outer tube The port spacing is adjustable; the microwave plasma jet device is suitable for electromagnetic wave frequency ranges 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%.

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 opening end. The upper end of the tuning end is a reflective end surface, and its material is a metal material; the depth of the tuning end adjusted to the cavity part is Yλ /4 (λ is the wavelength under the microwave frequency, Y is a positive odd number);

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

The described microwave plasma jet device can work in the following 18 ways:

1) The microwave is coupled into the resonant cavity through the microwave coupling part, and a TEM standing wave is formed in the resonant cavity. The nanosecond pulse power supply is connected to the inner electrode of the capillary, and the plasma is formed at the axial position of the upper port of the resonant cavity, and is driven downward by the pulse electric field. Outer spray;

2) The microwave is coupled into the resonant cavity through the microwave coupling part, and a TEM standing wave is formed in the resonant cavity. The high-voltage (positive/negative) power supply is connected to the inner electrode of the capillary, and the plasma is formed at the axial position of the upper port of the resonant cavity, and is controlled by the high-voltage electric field Driven to spray out;

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 axial position of the upper port of the resonant cavity and ejected outward;

4) The nanosecond pulse power supply is connected to the inner electrode of the capillary, and the plasma is formed on the upper end of the inner electrode and ejected outward;

5) The DC high-voltage (positive/negative) power supply is connected to the inner electrode of the capillary, and the plasma is formed on the upper end of the inner electrode and ejected outward;

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

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

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

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

10) Based on method 1), the gas (single/mixed) is input from the inlet 9, the inlet 11, and the inlet 12, and the microwave plasma jet is driven by the pulsed electric field to eject, and the plasma composition is adjusted;

11) Based on method 2), the gas (single/mixed) is input from the inlet 9, the inlet 11, and the inlet 12, and the high-voltage electric field drives the microwave plasma jet to eject, and adjusts the plasma composition;

12) Based on method 3), the gas (single/mixed) is input from the inlet 9, the inlet 11, and the inlet 12, and the microwave plasma jet is pulled to be ejected, and the plasma composition is adjusted;

13) Based on method 4), the gas (single/mixed) is input from the inlet 9, the inlet 11, and the inlet 12, and the cold plasma jet driven by the nanosecond pulse is drawn to eject, and the plasma composition is adjusted;

14) Based on method 5), the gas (single/mixed) is input from the inlet 9, the inlet 11, and the inlet 12, and the cold plasma jet driven by the nanosecond pulse is drawn to eject, and the plasma composition is adjusted;

15) Based on method 1), the capillary inner electrode can be a ring-shaped inner electrode flush with the upper port of the coaxial insulating tube, the outer surface of the ring electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the ring electrode is consistent with the inner diameter of the coaxial insulating tube;

16) Based on method 2), the capillary inner electrode may be a ring-shaped inner electrode flush with the upper port of the coaxial insulating tube, the outer surface of the ring electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the ring electrode is consistent with the inner diameter of the coaxial insulating tube;

17) Based on method 4), the inner electrode of the capillary can be a ring-shaped inner electrode flush with the upper port of the coaxial insulating tube, the outer surface of the ring electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the ring electrode is consistent with the inner diameter of the coaxial insulating tube;

18) Based on method 5), the inner electrode of the capillary can be a ring-shaped inner electrode flush with the upper port of the coaxial insulating tube, the outer surface of the ring electrode is wrapped by the inner surface of the insulating tube, and the outer diameter of the ring electrode is consistent with the inner diameter of the coaxial insulating tube;

The invention prolongs the length of the microwave cold plasma jet, can intelligently generate specific cold plasma in combination with different driving parameters and gas parameters, and improves its operability and practicability in clinical hospitals and other fields.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (11)

1. A microwave cold plasma jet device, characterized in that, 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 both 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 microwave coupling portion includes a coupling ring to couple microwave energy to the cavity portion; The tuning part is a structure in which the tuning end adjusts the length of the resonant cavity to adjust the field strength at the opening end. The wavelength under the microwave frequency, Y is a positive odd number; The electric field modulation part is connected to the internal electrode for applying nanosecond pulse/DC voltage, and the internal electrode is wrapped by a coaxial insulating layer. 2. a kind of microwave cold plasma jet device according to claim 1, is characterized in that, described outer pipe, middle pipe, inner electrode are all metal materials, between outer pipe and middle pipe, middle pipe and inner electrode The microwave transmission modes among them are all TEM modes. 3. a kind of microwave cold plasma jet device according to claim 1, is characterized in that, the axial length of described outer tube is Nλ/4, and wherein, λ is the wavelength under described microwave frequency, and N is positive odd number. 4. A microwave cold plasma jet device according to claim 1, characterized in that, the upper port of the outer tube and the middle tube is a gradual closing structure, the closing of the outer tube is 0-60°, the middle tube The closing of the tube is 0-30°. 5. A kind of microwave cold plasma jet device according to claim 1, characterized in that, there is a porous coaxial washer 7 whose upper surface is a metal material between the middle tube and the coaxial insulating layer, and the porous coaxial The distance range of the upper surface of the gasket 7 from the open end port of the cavity part is

Wherein λ is the wavelength at the microwave frequency, and M is a positive odd number. 6 . The microwave cold plasma jet device according to claim 1 , wherein the inner electrode is inserted into the cavity of the coaxial insulating layer, and the inner layer of the coaxial insulating layer covers the outer side of the inner electrode. 7. A microwave cold plasma jet device according to claim 1, characterized in that the upper port of the middle tube is not higher than the outer tube, and the upper end of the inner electrode and the coaxial insulating layer can be higher/lower than the middle Tube. 8. 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. 9. a kind of microwave cold plasma jet device according to claim 8, is characterized in that, described shielding gas entrance place is introduced with the mode of tangential flow; The gas velocity of described shielding gas entrance, gas inlet is controlled at 0 ~20L/min. 10. A microwave cold plasma jet device according to claim 8, 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 frequency ranges from several MHz to several GHz. 11. A microwave cold plasma jet device according to claim 8, characterized in that the output pulse width of the nanosecond pulse power supply is 10-900 ns, the rising edge is 1-200 ns, and the amplitude is 3-220 kV, The frequency is 1-20kHz, and the duty ratio is 1-99%. The output voltage of the DC power supply is 0-60kV or 0-60kV.

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