CN113784494A

CN113784494A - High-efficient microwave excitation gas discharge equipment

Info

Publication number: CN113784494A
Application number: CN202111062269.9A
Authority: CN
Inventors: 王清源
Original assignee: Chengdu Jihengte Technology Co ltd
Current assignee: Chengdu Jihengte Technology Co ltd
Priority date: 2021-09-10
Filing date: 2021-09-10
Publication date: 2021-12-10

Abstract

The invention discloses a design scheme of high-efficiency microwave excitation gas discharge equipment. The invention provides a coupling structure capable of switching states in equipment. And then, the coupling structure works in a second state which is almost straight-through, so that almost all microwaves generated by the microwave source are absorbed by the nonlinear device, and the equipment works with high efficiency. The invention can be applied to the disinfection and sterilization treatment of various gases and liquids, and the high-brightness long-life illuminating lamp and the microwave plasma torch.

Description

High-efficient microwave excitation gas discharge equipment

Technical Field

The invention relates to a high-efficiency microwave excitation gas discharge device. In particular to a high-efficiency gas discharge device which realizes the low-power automatic ignition and operation of the gas plasma discharge device by using a coupling structure of two-state operation.

Background

Under the action of high-power microwaves, the gas is ionized, plasma is generated, and light is emitted. The electrodeless ultraviolet lamp lighted by the microwave has the advantages of high brightness, long service life, high luminous efficiency and the like, can be widely used for sterilizing air and drinking water, and can also be used in the fields of industrial waste gas and industrial wastewater treatment and the like. The plasma torch generated by utilizing the microwave ionized gas has the characteristics of high temperature, no pollution and quick start and stop, and has wide application in the aspects of motor vehicle engine ignition, large boiler ignition, metal cutting, surface cleaning and even surgical operation. The microwave plasma thruster generates plasma by utilizing microwave ionized gas, and is expected to provide a new power for space flight.

However, most microwave plasma devices exhibit strong non-linearity in their input impedance, and are strongly non-linear devices. At small signals, the gas is not ionized and the microwave absorption is weak. Most of the microwaves incident on the gas will be reflected. To ionize the gas, a strong microwave field strength is required. For example, at one atmosphere, the breakdown field strength of air is three million volts per meter. Under the action of high-power microwaves, the plasma formed after the gas is ionized can well absorb the microwaves. Early solutions required high power microwaves to ignite the plasma device. When the device is ignited, due to the severe impedance mismatch caused by the significant load change, most of the microwave energy is reflected, the microwave power absorbed by the plasma is small, and the energy efficiency of the device is low. The strong non-linearity of microwave plasma devices also makes low power microwave plasma devices difficult to implement.

Hong et al, 2011 reported a microwave plasma torch [ IEEE transitions ON PLASMA SCIENCE, VOL.39, NO.10, octber 2011, pp.1958-1962 ]. Wherein a moving tungsten filament is used to ignite the microwave plasma device manually. This method is not conducive to the automated operation of the apparatus. Christoph Schopp and Holger Heuermann in 2013 proposed a two-state matching scheme [ 2013, Proceedings of the 43rd European Microwave Conference, pp.881-884 ]. The scheme adopts a lumped parameter matching circuit and utilizes frequency switching to solve the problem of automatic ignition of the gas discharge lamp to a certain extent and improve the energy efficiency of the gas discharge lamp. However, this method has several disadvantages: 1) the insertion loss of the matching circuit is large, and the energy efficiency of the scheme is seriously reduced. 2) In the commonly used microwave frequency band of 2450MHz, the power capacity of the lumped parameter circuit is relatively small. The application of this solution in industrial and environmental fields is limited by the power capacity. 3) For machining errors and parameter errors of components, the scheme lacks adjustability and is difficult to achieve the optimal working state. 4) This solution requires the microwave source to be frequency switched during ignition and operation, increasing the manufacturing cost of the microwave source. 5) For the high-power magnetron with the lowest price per unit power at present, due to the wide frequency spectrum and the unstable operating frequency, the energy efficiency of the matching circuit is further reduced due to the insufficient operating bandwidth.

Disclosure of Invention

The invention aims to provide a microwave plasma device with simple structure, low insertion loss and high efficiency. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

an efficient microwave-excited gas discharge device comprises a microwave source with the working frequency of f0 and a nonlinear device which are sequentially communicated; at least one coupling structure is arranged between the microwave source and the nonlinear device; the nonlinear device has two states, namely a small signal state and a large signal state according to the size of the microwave signal output by the microwave source; the coupling structure has two states, a first state of the coupling structure corresponding to a weak coupling state and a second state of the coupling structure corresponding to a strong coupling state; the coupling structure switches between a first state and a second state after the nonlinear device changes from a small signal state to a large signal state.

The strong coupling state corresponding to the second state of the coupling structure may be a state in which the microwave source is directly connected to the nonlinear device, which is equivalent to a state in which the coupling structure is completely removed. For the coupling screw, it is equivalent to completely withdraw it from the nonlinear device.

In the present invention, the term "ignition" means that the gas in the nonlinear device is broken down to become plasma.

The input impedance of the nonlinear device varies significantly with the magnitude of the microwave source output power. For example, at an output power of 1 milliwatt of the microwave source, the nonlinear device is in a small signal mode, and its input impedance is almost purely reactive. When the output power of the microwave source is 100 watts, the nonlinear device is in a large signal mode, and the input impedance of the nonlinear device is close to the characteristic impedance of the output end of the microwave source. The non-linear device herein may include a plasma discharge device having a discharge gas disposed therein, such as a gas discharge lamp bulb, an electrodeless ultraviolet lamp, a dielectric tube having a gas flowing therethrough, and the like.

Taking a microwave plasma nonlinear device as an example, the working principle of the invention is briefly described as follows. In general, before gas breakdown, the nonlinear device absorbs microwaves weakly and is in a small-signal state. The input impedance of the nonlinear device is almost purely reactive. The microwaves entering the nonlinear device are almost totally reflected back. The amplitude of the microwave electric field felt by the gas within the nonlinear device is small. The gas cannot be broken down.

The invention arranges a coupling structure between the nonlinear device and the microwave source, and forms a resonant cavity together with the nonlinear device. Before the gas breakdown, the loss of the resonant cavity is very small, and the Q value is very high. In order to effectively break down the gas therein, we need to satisfy two conditions: first, the frequency of the microwave source is equal to the frequency of the cavity, both at f0, or as close as possible. Secondly, the impedance of the microwave source and the resonant cavity is matched as much as possible when the microwave source and the resonant cavity are in resonance. For the second requirement, we need to set the coupling coefficient of the coupling structure appropriately. Due to the high Q-value of the cavity, the coupling coefficient of the coupling structure will be low.

After the gas is broken down, the nonlinear device is in a large signal state. The matching cavities are no longer matched for small signals and most of the microwaves will be reflected. The operation efficiency of the apparatus will be low. The present invention arranges for the coupling structure to be changed from a first state to a second state, i.e. a state in which the microwave source is in direct communication with the nonlinear device. Since the nonlinear load is closely matched to the microwave source in the large signal state, microwaves are well absorbed, changing the coupling structure to its second state allows the device to operate efficiently.

Generally, the nonlinear device has gas inside, and can be broken down to generate plasma under the action of microwave with high enough power.

With respect to the coupling structure, we have three designs:

in a first design, the coupling structure is a metal pillar, the first state of the coupling structure is that the metal pillar is inserted into the nonlinear device to a certain depth, and the second state of the coupling structure is that the metal pillar is withdrawn from the nonlinear device. In cooperation with the coupling structure, we have at least one spring; the coupling structure is in a first state after the spring is manually compressed, and the coupling structure is in a second state after the spring is released. In cooperation with the coupling structure, a motor may also be provided. The metal column is driven by a motor to change the coupling structure from the first state to the second state.

In a second embodiment, the coupling structure is a metal screw. The first state of the coupling structure is that the metal screw is screwed into the nonlinear device to a certain depth, and the second state of the coupling structure is that the metal screw is screwed out of the nonlinear device.

In the first state of the coupling structure, the depth X of the metal post or metal screw into the nonlinear device is greater than 2/3 of the maximum travel of the metal post or metal screw inside the nonlinear device. The maximum stroke of the metal column or the metal screw inside the nonlinear device is defined as the maximum length which can be reached by the metal column or the metal screw inside the nonlinear device, if the top end of the metal column or the metal screw and the inner surface of the nonlinear device opposite to the top end cannot be contacted.

In a third aspect, the coupling structure is a diode spanning between two opposite inner surfaces of the nonlinear device, a first state of the diode is a certain conduction state, a second state of the diode is a full off state, and the two opposite inner surfaces respectively refer to a first cross section where the microwave enters the nonlinear device and a second cross section opposite to the first cross section.

The nonlinear device can also be a one-division-multiple equal-amplitude equal-phase power divider, and each output end of the power divider is connected with a nonlinear sub-device which is identical to each other. This arrangement is suitable for providing microwave energy to a plurality of non-linear sub-devices simultaneously using a relatively powerful microwave source such as a magnetron.

The output end of the microwave source and the input end of the nonlinear device can be rectangular waveguide, or circular waveguide, or ridge waveguide, or coaxial line, etc.

A dielectric tube is arranged in the nonlinear device and penetrates through the nonlinear device, gas passes through the dielectric tube, and the device is a plasma torch.

The application of the invention can be simply divided into three categories:

in a first type of application, at least one gas discharge lamp is arranged in the non-linear device. The invention can provide a high-quality light source with high brightness, long service life, high luminous efficiency and color spectrum close to sunlight. At this time, the casing of the nonlinear device is provided with a plurality of small holes, which can not only effectively prevent the microwave from leaking, but also can fully emit visible light.

In a second type of application, the non-linear device is passed through a discharge gas. The invention can provide a high-efficiency plasma torch or microwave plasma thruster.

In the third application, at least one electrodeless ultraviolet lamp tube is arranged in the nonlinear device. The electrodeless ultraviolet lamp tube is efficiently lightened by microwaves, so that air or water, particularly waste or wastewater, passes through the electrodeless lamp tube in a nonlinear device, and bacteria, viruses and harmful substances in the electrodeless ultraviolet lamp tube are effectively killed or degraded by ultraviolet light. At this time, the housing of the nonlinear device is provided with at least two holes, which can not only effectively prevent the microwave from leaking, but also allow gas and liquid to enter and flow out of the nonlinear device.

The invention has the following beneficial effects:

the invention discloses a design scheme of high-efficiency microwave excitation gas discharge equipment. The invention provides a coupling structure capable of switching states in equipment. Before ignition, the coupling structure works in a weak coupling state, strong resonance with the same resonant frequency as the working frequency of the microwave source is formed in the nonlinear device, ignition is smoothly performed, then the coupling structure works in a second almost straight-through state, almost all microwaves generated by the microwave source are absorbed by the nonlinear device, and the equipment works with high efficiency. The invention can be applied to the disinfection and sterilization treatment of various gases and liquids, and the high-brightness long-life illuminating lamp and the microwave plasma torch.

Drawings

FIG. 1 is a schematic side sectional view of the invention and example 1

FIG. 2 is a schematic side sectional view of EXAMPLE 2

FIG. 3 is a schematic side sectional view of EXAMPLE 3

FIG. 4 is a schematic top view of embodiment example 4

The reference numbers in the drawings correspond to the names: 1-microwave source, 22-coupling structure, 4-nonlinear device, 41-medium tube.

Detailed Description

Examples 1

As shown in fig. 1.

An efficient microwave excitation gas discharge device comprises a microwave source 1 with the working frequency of f0 and a micro nonlinear device 4 which are sequentially communicated; the micro nonlinear device 4 has two states, namely a small signal state and a large signal state according to the size of the microwave signal output by the microwave source 1; a coupling structure 22 is arranged between the microwave source 1 and the micro nonlinear device 4; the coupling structure 22 has two states, a first state of the coupling structure 22 corresponding to a weak coupling state and a second state of the coupling structure 22 corresponding to a strong coupling state; after the micro non-linear device 4 changes from a small signal state to a large signal state, the coupling structure 22 switches between a first state and a second state.

The micro nonlinear device 4 has gas inside, and can generate plasma by breakdown under the action of microwave with high enough power.

The coupling structure 22 is a metal pillar, the first state of which is inserted into the micro non-linear device 4 to a certain depth, and the second state of which is completely withdrawn from the micro non-linear device 4.

The change of the coupling structure 22 from its first state to its second state is here accomplished by manually ejecting the metal posts all the way out of the micro-nonlinear device 4.

EXAMPLES example 2

As shown in fig. 2.

Compared with the embodiment example 1, the difference is only that:

the coupling structure 22 is a diode.

EXAMPLE 3

As shown in fig. 3.

Compared with the embodiment example 1, the difference is only that:

the high-efficiency microwave excitation gas discharge equipment is a plasma torch. The output end of the microwave source and the nonlinear device 4 are both rectangular waveguides. A dielectric tube 41 is arranged in the rectangular waveguide, and the dielectric tube 41 penetrates through the waveguide. In the waveguide, gas is input from one end of the dielectric tube 41, ionized by the dielectric tube 41, formed into high-temperature plasma, and ejected from the other end of the dielectric tube 41.

EXAMPLE 4

As shown in fig. 4.

Compared with the embodiment 1, the difference is only that:

the nonlinear device 4 is formed by connecting an H-plane four-way equiamplitude equiphase rectangular waveguide power divider and four nonlinear sub-devices. The output end of the microwave source and the input end of the nonlinear sub-device are both rectangular waveguides. The four non-linear sub-devices are almost identical to each other.

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. To facilitate commissioning of the apparatus, conventional techniques such as adding an impedance tuner between the microwave source and the non-linear device, providing a tuning device on the non-linear device, etc. may be useful. Any modification, equivalent replacement, addition of any conventional technology, etc. to the above embodiment without departing from the best design, within the spirit and principle of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. An efficient microwave-excited gas discharge apparatus, comprising a microwave source (1) having an operating frequency f0 and a nonlinear device (4) connected in series; the nonlinear device (4) has two states, namely a small signal state and a large signal state according to the size of the microwave signal output by the microwave source (1); at least one coupling structure (22) is arranged between the microwave source (1) and the nonlinear device (4); the coupling structure (22) has two states, a first state of the coupling structure (22) corresponding to a weak coupling state and a second state of the coupling structure (22) corresponding to a strong coupling state; the coupling structure (22) changes from a first state to a second state after the nonlinear device (4) changes from a small signal state to a large signal state.

2. A high efficiency microwave excited gas discharge apparatus as claimed in claim 1, wherein the non-linear device (4) has a gas inside, and the gas breaks down under the action of microwaves to produce a plasma.

3. A high efficiency microwave excited gas discharge apparatus as claimed in claim 1 wherein the coupling structure (22) is a metal post, the first state of the coupling structure being insertion of the metal post into the nonlinear device to a depth X, and the second state of the coupling structure being withdrawal of the metal post from the nonlinear device.

4. A high efficiency microwave excited gas discharge apparatus as claimed in claim 3 wherein at least one spring is provided; the coupling structure (22) is in a first state after compression of the spring and the coupling structure (22) is in a second state after release of the spring.

5. An efficient microwave excited gas discharge apparatus according to claim 1, wherein the coupling structure (22) is a metal screw, the first state of the coupling structure is the insertion of the metal screw into the non-linear device (4) to a depth X, and the second state of the coupling structure is the withdrawal of the metal screw from the non-linear device (4).

6. A high efficiency microwave excited gas discharge apparatus as claimed in claim 3 or 5 wherein at least one motor is provided; the motor may move the coupling structure (22) between a first state and a second state of the coupling structure (22).

7. A high efficiency microwave excited gas discharge apparatus as claimed in claim 3, wherein in the first state of the coupling structure, the depth X is greater than 2/3 of the maximum travel of the metal column inside the nonlinear device (4).

8. A high efficiency microwave excited gas discharge apparatus as claimed in claim 5, wherein in the first state of the coupling structure, the depth X is greater than 2/3 of the maximum travel of the metal screw inside the non-linear device (4).

9. A high efficiency microwave excited gas discharge apparatus as claimed in claim 1, wherein the coupling structure (22) is a diode spanning between two opposing internal surfaces of the nonlinear device (4), a first state of the diode being a somewhat on state and a second state of the diode being an off state, the two opposing internal surfaces being respectively a first cross section where microwaves enter the nonlinear device (4) and a second cross section opposite the first cross section.

10. A high efficiency microwave excited gas discharge apparatus as claimed in claim 1, wherein a dielectric tube (41) is provided in the non-linear device (4), the dielectric tube (41) passing through the non-linear device (4), the dielectric tube (41) having a gas passing therethrough.