A highly efficient device based on microwave nonlinear devices

Abstract

The present invention discloses a design scheme for an efficient device based on microwave nonlinear devices. Microwave plasma has important applications in high-intensity light sources, microwave ultraviolet air sterilization and industrial waste gas treatment, plasma torches and microwave plasma propulsion. The present invention uses coupling screws and rectangular waveguides, circular waveguides, coaxial lines or other transmission lines to realize two mutually connected resonant cavities, whose resonant frequencies correspond to the operating frequency and ignition frequency of the device respectively. The microwave source first works at the ignition frequency and ignites successfully, and then changes the frequency to the operating frequency to operate efficiently. The present invention can be automatically ignited and can operate efficiently, and can be applied to the fields of disinfection and sterilization of various gases and liquids, microwave plasma torches, microwave plasma vapor deposition, microwave plasma thrusters, etc.

Description

Technical Field

[0001] The present invention relates to a high-efficiency device based on microwave nonlinear devices, and more specifically, to a high-efficiency plasma device that utilizes an impedance matcher and a variable-frequency microwave source to achieve automatic ignition and high-efficiency operation of a gas plasma discharge device. Background Art

[0002] Under the action of high-power microwaves, the gas will be ionized, plasma will be generated and light will be emitted. High-intensity gas discharge lamps realized by microwave-excited plasma have the advantages of high brightness, color spectrum close to sunlight, long life and high luminous efficiency, and can be widely used in automobile headlights, square lighting and greenhouse vegetable light sources. Electrodeless ultraviolet lamps lit by microwaves have the advantages of high brightness, long life and high luminous efficiency, and can be widely used in atmospheric and drinking water sterilization, as well as in industrial waste gas and industrial wastewater treatment. Microwave plasma torches realized by microwave-ionized gas have the characteristics of high temperature, no pollution, and can be started and stopped quickly. They are widely used in motor vehicle engine ignition, large boiler ignition, metal cutting, surface cleaning, and even surgical operations. Microwave plasma thrusters use microwave-ionized gas to generate plasma, which is expected to provide a new power for space flight.

[0003] However, the input impedance of most microwave plasma devices shows strong nonlinearity, and they are strong nonlinear devices. At small signals, the gas is not ionized and the absorption of microwaves is very weak. Most of the microwaves projected onto the gas will be reflected. In order to ionize the gas, a very strong microwave field strength is required. For example, at one atmosphere of pressure, 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 will absorb microwaves very well. Early schemes require high-power microwaves to ignite plasma devices. When the device is ignited, most of the microwave energy is reflected due to the serious impedance mismatch caused by the significant change in the load, and the microwave power absorbed by the plasma is very small, and the energy efficiency of the device is very low. The strong nonlinearity of microwave plasma devices also makes low-power microwave plasma devices difficult to implement.

[0004] Yong C. Hong et al. reported a microwave plasma torch in 2011 [IEEE TRANSACTIONSON PLASMA SCIENCE, VOL. 39, NO. 10, OCTOBER 2011, pp. 1958-1962]. The microwave plasma device was ignited manually by moving tungsten wire. This method is not conducive to the automatic operation of the equipment. Christoph Schopp and Holger Heuermann proposed a dual-state matching scheme in 2013 [2013, Proceedings of the 43rd European Microwave Conference, pp. 881-884]. This scheme adopts lumped parameter matching circuit and frequency switching to solve the problem of automatic ignition and high-efficiency operation of gas discharge lamps. However, this method has the following disadvantages: 1) The insertion loss of the matching circuit is relatively large, which will seriously reduce the energy efficiency of the scheme. 2) In the commonly used 2450MHz microwave frequency band, the power capacity of the lumped parameter circuit is relatively small. The application of this scheme in the industrial and environmental protection fields is limited by power capacity. 3) The matching circuit structure of this solution is complex. Summary of the invention

[0005] The purpose of the present invention is to provide a microwave plasma device with simple structure, low insertion loss and high efficiency. In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A high-efficiency device based on a microwave nonlinear device comprises a microwave source, a regulating circuit, and at least one nonlinear device connected in sequence. The regulating circuit and the nonlinear device constitute a nonlinear load, and the port of the nonlinear load connected to the microwave source is an input port. The nonlinear load has two states, a small signal state and a large signal state. The regulating circuit comprises at least one regulating body and a first coupling structure located at the front end of the regulating body and a second coupling structure located at the rear end of the regulating body. When the signal is small, the first coupling structure, the second coupling structure, and the regulating body between the first coupling structure and the second coupling structure together constitute a first resonant cavity, and the resonant frequency of at least one resonant mode of the first resonant cavity is f1. When the signal is small, the second coupling structure, the regulating body between the second coupling structure and the nonlinear device, and the nonlinear device together constitute a second resonant cavity, and the resonant frequency of at least one resonant mode of the second resonant cavity is f2.

[0007] In the present invention, the so-called "ignition" means that the gas in the nonlinear device is broken down and becomes plasma.

[0008] The small signal and large signal here can have different definitions for different nonlinear devices. For example, for a gas discharge device, the small signal refers to the signal when the gas is not broken down. The two states of the nonlinear load correspond to the state when the gas is not broken down and the state after the gas is broken down. Generally speaking, a signal less than 1 milliwatt is a signal, and a large signal has a power greater than 1 watt.

[0009] The resonant frequencies of the first resonant cavity and the second resonant cavity may vary greatly depending on the state of the nonlinear device. Here, f2 and f1 specifically refer to the resonant frequencies of a resonant mode of the second resonant cavity and the first resonant cavity respectively when the signal is small.

[0010] After the microwave source is turned on, the center frequency of the microwave output by the microwave source changes from f2 to a certain frequency f3 at least once. In general, f3 equal to f1 may not be the best choice, because when the nonlinear device is in a large signal state, the resonant frequency of the resonant mode of the first resonant cavity will deviate to a certain extent from the resonant frequency of the resonant mode of the nonlinear device in a small signal state. Therefore, we can set f3 equal to f1, but changing it within a range of less than 5% relative error with f1 to find the best f3 frequency may achieve better results.

[0011] The input impedance of the nonlinear device varies significantly with the output power of the microwave source. For example, when the output power of the microwave source is 1 milliwatt, the nonlinear device is in a small signal mode, and its input impedance is mainly reactance. When the output power of the microwave source is 100 watts, the nonlinear device is in a large signal mode, and its input impedance is close to the characteristic impedance of the output end of the microwave source. The nonlinear device here can include a plasma discharge device with a discharge gas disposed inside, such as a gas discharge lamp bulb, an electrodeless ultraviolet lamp, a dielectric tube with a gas flowing inside, etc.

[0012] The center frequency of the microwave output by the microwave source here needs to change from f2 to f3 at least once. There are two ways of "changing". If the microwave source is a solid-state source, the "change" here refers to "switching". If the microwave source is an electric vacuum oscillator, the "change" here refers to "drift". For example, after the most typical electric vacuum oscillator magnetron is started, the frequency of its output microwave will gradually decrease due to the temperature rise of its resonant cavity until it finally stabilizes.

[0013] Taking microwave plasma nonlinear devices as an example, the working principle of the present invention is briefly described as follows. In general, before the gas breaks down, the nonlinear device has very weak absorption of microwaves and is in a small signal state. The input impedance of the nonlinear device is mainly reactance. Almost all microwaves entering the nonlinear device are reflected back. The amplitude of the microwave electric field felt by the gas in the nonlinear device is very small. The gas cannot be broken down.

[0014] The present invention sets a second coupling structure between the nonlinear device and the microwave source, and forms a second resonant cavity together with the nonlinear device. Before the gas breaks down, the loss of this resonant cavity is very small, and its Q value is very high. In order to effectively break down the gas therein, we need to meet two conditions: first, the frequency of the microwave source is equal to the frequency of this resonant cavity, both are f2, or as close as possible. Second, the impedance of the microwave source and the resonant cavity at resonance is matched as much as possible. For the second requirement, we need to appropriately set the coupling coefficient of the second coupling structure. Since the Q value of the resonant cavity is very high, the coupling coefficient of the second coupling structure will be very low.

[0015] After the gas is broken down, the nonlinear device is in a large signal state. The second resonant cavity that is matched at a small signal is no longer matched, and most of the microwaves will be reflected. The operating efficiency of the device will be very low. The present invention sets a first coupling structure in front of the second coupling structure, so that the first coupling structure and the second coupling structure together form a first coupling cavity and the frequency of the first coupling cavity is f1, and adjusts the coupling coefficient of the first coupling structure so that the microwave source, the first coupling cavity, and the nonlinear device in the large signal state are matched at the frequency f1. Considering that the second coupling structure is in a weak coupling state, the first coupling structure must also be in a weak coupling state.

[0016] In order to realize that the nonlinear device effectively changes from the small signal state to the large and small signal state, and then operates efficiently, the first coupling structure and the second coupling structure are both in a weak coupling state. In the small signal state, the Q values ​​of the first resonant cavity and the second resonant cavity in the small signal state should be relatively high. In a specific case, the Q values ​​of the first resonant cavity and the second resonant cavity are related to the absorption performance of the nonlinear device to microwaves in the small signal state, for example, both Q values ​​are greater than 100 and less than 10000.

[0017] The regulating body and the nonlinear device can be of any spatial shape. In a preferred design, the regulating body is a section of a transmission line, or more than one section of interconnected transmission lines. The transmission line can be a rectangular waveguide. The transmission line can also include a coaxial line inner conductor, which is a coaxial line.

[0018] In order to realize a plasma spray gun, there is an empty tube inside the inner conductor of the coaxial line, and a metal head is arranged at the tail end of the outer conductor of the transmission line away from the microwave source. There is an air outlet in the center of the metal head. The empty tube inputs gas from the outside through at least one air inlet pipe, and the gas is ejected from the air outlet in the center of the metal head.

[0019] In a preferred implementation, the first coupling structure and the second coupling structure are both coupling screws, the depth of the coupling screw entering the adjusting body can be changed from the outside and fixed by a nut, and the depth of the coupling screw entering the adjusting body is greater than 2 / 3 of the maximum stroke of the coupling screw inside the adjusting body. The maximum stroke of the coupling screw inside the adjusting body is defined as the maximum length that the coupling screw can reach inside the adjusting body, provided that the top of the coupling screw and the inner surface of the adjusting body opposite thereto cannot contact each other.

[0020] In order to achieve weak coupling, the coupling screw needs to enter the adjusting body deeply enough.

[0021] In another implementation, the first coupling structure and the second coupling structure are both metal diaphragms with through holes, and at least in one direction of the cross section, the size of the through hole is less than 1 / 3 of the size of the metal diaphragm. The metal diaphragm refers to a metal plate of a certain thickness and a certain shape, in which there are through holes. In order to achieve weak coupling, the size of the through hole needs to be small enough.

[0022] In another implementation, in the first coupling structure and the second coupling structure, either one is a metal diaphragm or a coupling screw with a through hole, and the other is a metal diaphragm or a coupling screw with a through hole.

[0023] The applications of the present invention can be simply divided into three categories:

[0024] The first application is that at least one gas discharge lamp is arranged in the nonlinear device. The invention can provide a high-quality light source with high brightness, long life, high luminous efficiency and a color spectrum close to sunlight. In this case, a plurality of small holes are opened on the shell of the nonlinear device, which can effectively prevent microwave leakage and allow visible light to be fully emitted.

[0025] The second application is that discharge gas passes through the nonlinear device. The invention can provide a type of efficient plasma torch or microwave plasma thruster.

[0026] The third type of application is that at least one electrodeless ultraviolet lamp is arranged in the nonlinear device. The electrodeless ultraviolet lamp is efficiently lit by microwaves, allowing air or water, especially waste or waste water, to pass through the electrodeless lamp in the nonlinear device, and the bacteria, viruses and harmful substances therein are effectively killed or degraded by ultraviolet light. At this time, at least two holes are opened on the shell of the nonlinear device, which can effectively prevent microwave leakage and allow gas and liquid to enter and flow out of the nonlinear device.

[0027] For convenience, the electromagnetic wave source here mainly uses the microwave frequency band. The present invention can also use millimeter waves or even terahertz frequencies with higher frequencies than microwaves, as well as radio frequency frequencies with lower frequencies than microwaves. At the same time, the nonlinear devices here are not limited to gas discharge and plasma. Relying on the strong nonlinear effect, other devices with significantly different load impedances before and during operation can be effectively started and run efficiently using the present invention.

[0028] The present invention has the beneficial effects:

[0029] The present invention discloses a design scheme for an efficient device based on microwave nonlinear devices. Microwave plasma has important applications in high-intensity light sources, microwave ultraviolet air sterilization and industrial waste gas treatment, plasma torches and microwave plasma propulsion. The present invention uses coupling screws and rectangular waveguides, circular waveguides, coaxial lines or other transmission lines to realize two mutually connected resonant cavities, whose resonant frequencies correspond to the operating frequency and ignition frequency of the device respectively. The microwave source first works at the ignition frequency and ignites successfully, and then changes the frequency to the operating frequency to operate efficiently. The present invention can be automatically ignited and can operate efficiently, and can be applied to the fields of disinfection and sterilization of various gases and liquids, microwave plasma torches, microwave plasma vapor deposition, microwave plasma thrusters, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A side cross-sectional schematic diagram of the present invention and implementation example 1

[0031] Figure 2 A top view of Example 2

[0032] Figure 3 A top view of Example 3

[0033] Figure 4 A side cross-sectional view of Example 4

[0034] Figure 5 A side cross-sectional schematic diagram of implementation example 5

[0035] Figure 6 A side cross-sectional schematic diagram of implementation example 6

[0036] The corresponding names of the numbers in the accompanying drawings are: 1-microwave source, 2-regulating circuit, 21-regulating body, 21A-first coupling structure, 21B-second coupling structure, 23-coaxial line inner conductor, 24-empty tube, 25-inlet pipe, 3-non-linear device, 31-dielectric tube, 32-electrodeless lamp tube, 33-supporting dielectric plate, 34-metal head, 35-air outlet. DETAILED DESCRIPTION

[0037] Implementation Example 1

[0038] like Figure 1 and Figure 2 shown.

[0039] A high-efficiency device based on a microwave nonlinear device comprises a microwave source 1, a regulating circuit 2, and a nonlinear device 3 connected in sequence. The regulating circuit 2 and the nonlinear device 3 constitute a nonlinear load, and the port of the nonlinear load connected to the microwave source 1 is an input end. The nonlinear load has two states, a small signal state and a large signal state. The regulating circuit 2 comprises at least one regulating body 21, a first coupling structure 21A located at the front end of the regulating body 21, and a second coupling structure 21B located at the rear end of the regulating body 21. When the signal is small, the first coupling structure 21A, the second coupling structure 21B, and the regulating body 21 between the first coupling structure 21A and the second coupling structure 21B together constitute a first resonant cavity, and the resonant frequency of at least one resonant mode of the first resonant cavity is f1. When the signal is small, the second coupling structure 21B, the regulating body 21 between the second coupling structure 21B and the nonlinear device 3, and the nonlinear device 3 together constitute a second resonant cavity, and the resonant frequency of at least one resonant mode of the second resonant cavity is f2. After the high-efficiency device based on microwave nonlinear devices changes from a small signal state to a large signal state, the center frequency of the microwave output by the microwave source 1 changes from f2 to f3 at least once.

[0040] After the microwave source 1 is turned on, the center frequency of the microwave output by the microwave source 1 changes at least once from f2 to a certain frequency f3. The relative error between F3 and f1 is less than 5%.

[0041] In the small signal state, the Q values ​​of the first resonant cavity and the second resonant cavity are both greater than 100 and less than 10,000.

[0042] The first coupling structure 21A and the second coupling structure 21B are both weakly coupled.

[0043] The regulating body 21 is a section of transmission line.

[0044] The transmission line is a rectangular waveguide.

[0045] The first coupling structure 21A and the second coupling structure 21B are both coupling screws. The depth of the coupling screws entering the adjusting body 21 can be changed from the outside and fixed by a nut. The depth of the coupling screws entering the adjusting body 21 is greater than 2 / 3 of the maximum stroke of the coupling screws inside the adjusting body 21.

[0046] Implementation Example 2

[0047] like Figure 2 shown.

[0048] Compared with Implementation Example 1, the only difference is:

[0049] The first coupling structure 21A and the second coupling structure 21B are both metal diaphragms. In the width direction of the rectangular waveguide, the size of the through hole is less than 1 / 3 of the size of the metal film.

[0050] Implementation Example 3

[0051] like Figure 3 shown.

[0052] Compared with implementation example 2, the nonlinear device includes a one-to-four equal-amplitude and equal-phase power divider and a nonlinear sub-device connected to the four output ends thereof respectively.

[0053] Implementation Example 4

[0054] like Figure 4 shown.

[0055] Compared with Example 1, the only difference is:

[0056] The nonlinear device includes a short-circuited rectangular waveguide and a dielectric tube 31. The dielectric tube 31 passes through the rectangular waveguide from the wide side of the rectangular waveguide from bottom to top, and gas passes through the dielectric tube and can be ionized by microwaves inside the rectangular waveguide. The plasma generated after ionization is ejected upward. This embodiment is a plasma torch.

[0057] Implementation Example 5

[0058] like Figure 5 shown.

[0059] Compared with Implementation Example 1, the only difference is:

[0060] The transmission line of the regulating circuit 2 is a coaxial line section including a coaxial inner conductor 23. The nonlinear device is a short-circuited circular waveguide section, in which an electrodeless lamp 32 and two supporting dielectric plates 33 at both ends of the electrodeless lamp are arranged along its axis.

[0061] Implementation Example 6

[0062] like Figure 6 shown.

[0063] Compared with Implementation Example 5, the only difference is:

[0064] There are no induction lamps 32.

[0065] An empty tube 24 is arranged inside the inner conductor of the coaxial line. As a nonlinear device, a metal head 34 is arranged at the tail end of the outer conductor of the coaxial line away from the microwave source 1, and an air outlet 35 is arranged in the center of the metal head. The empty tube 24 inputs gas from the outside through an air inlet pipe 25, and the gas is ejected from the air outlet 35 in the center of the metal head 34. By setting the frequency of the solid source 1 to the ignition frequency, turning on the solid source 1 and setting its frequency to f1, the gas can be successfully broken down near the metal head 34 to generate plasma. By switching the frequency of the solid source 1 to the operating frequency, the temperature and length of the plasma flame can be optimized. Generally, the material of the air inlet pipe 25 is preferably dielectric. In order to facilitate ignition, there is a gap between the metal head 34 and the inner conductor 23 of the coaxial line, and the gap should be as small as possible.

[0066] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. In order to facilitate the debugging of the device, some conventional technologies, such as adding an impedance adapter between the microwave source and the adjustment circuit, and setting a tuning device in the first resonant cavity and the second resonant cavity, may be useful. According to the technical essence of the present invention, within the spirit and principle of the present invention, any modification, equivalent replacement, addition of any conventional technology, etc. made to the above embodiments that deviate from the optimal design still falls within the protection scope of the technical solution of the present invention.

Claims

1. A high-efficiency device based on microwave nonlinear devices, characterized in that: The invention comprises a microwave source (1), a regulating circuit (2), and at least one nonlinear device (3) which are connected in sequence; the regulating circuit (2) and the nonlinear device (3) constitute a nonlinear load, and the port of the nonlinear load connected to the microwave source (1) is an input port; the nonlinear load has two states, a small signal state and a large signal state; the regulating circuit (2) comprises at least one regulating body (21), a first coupling structure (21A) located at the front end of the regulating body (21), and a second coupling structure (21B) located at the rear end of the regulating body (21); when the signal is small, the first coupling structure (21A), the second coupling structure (21B), and the regulating body (21) between the first coupling structure (21A) and the second coupling structure (21B) together constitute a first resonant cavity, and the resonant frequency of at least one resonant mode of the first resonant cavity is f1; when the signal is large, the second coupling structure (21B), the regulating body (21) between the second coupling structure (21B) and the nonlinear device (3), and the nonlinear device (3) together constitute a second resonant cavity, and the resonant frequency of at least one resonant mode of the second resonant cavity is f2 ; The first coupling structure (21A) and the second coupling structure (21B) are coupling screws or metal diaphragms with through holes or a combination thereof; when the first coupling structure (21A) or the second coupling structure (21B) is a coupling screw, the depth of the coupling screw entering the adjusting body (21) can be changed and fixed from the outside, and the depth of the coupling screw entering the adjusting body (21) is greater than 2 / 3 of the maximum stroke of the coupling screw inside the adjusting body (21); when the first coupling structure (21A) or the second coupling structure (21B) is a metal diaphragm with a through hole, at least in one direction of the cross section, the size of the through hole is less than 1 / 3 of the size of the metal diaphragm.

2. The high-efficiency device based on microwave nonlinear devices according to claim 1, characterized in that: After the microwave source (1) is turned on, the central frequency of the microwaves output by the microwave source (1) changes at least once from f2 to a certain frequency f3.

3. The high-efficiency device based on microwave nonlinear devices according to claim 2, characterized in that: Where f3 is equal to f1, or the relative error between f3 and f1 is less than five percent.

4. The high-efficiency device based on microwave nonlinear devices according to claim 1, characterized in that: In the small signal state, the Q values ​​of the first resonant cavity and the second resonant cavity are both greater than or equal to 100 and less than or equal to 10,000.

5. The high-efficiency device based on microwave nonlinear devices according to claim 1, characterized in that: The first coupling structure (21A) and the second coupling structure (21B) are both in a weak coupling state.

6. The high-efficiency device based on microwave nonlinear devices according to claim 1, characterized in that: The regulating body (21) is a section of a transmission line, or more than one section of transmission lines that are interconnected.

7. The high-efficiency device based on microwave nonlinear devices according to claim 6, characterized in that: The transmission line is a rectangular waveguide.

8. The high-efficiency device based on microwave nonlinear devices according to claim 6, characterized in that: The transmission line also includes a coaxial line inner conductor (23), and the transmission line is a coaxial line.

9. The high-efficiency device based on microwave nonlinear devices according to claim 8, characterized in that: An empty tube (24) is provided inside the inner conductor (23) of the coaxial line; a metal head (34) is provided at the tail end of the outer conductor of the transmission line away from the microwave source (1); an air outlet (35) is provided at the center of the metal head (34); gas is input from the outside into the empty tube (24) through at least one air inlet pipe (25), and the gas is ejected from the air outlet (35) at the center of the metal head (34).

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