An efficient microwave-excited gas discharge device

Abstract

The present invention discloses a design scheme of an efficient microwave-excited gas discharge device. In the device of the present invention, a coupling structure capable of switching states is provided. During ignition, the coupling structure operates in a first state of weak coupling to form a strong resonance with the same resonant frequency as the operating frequency of the microwave source in the nonlinear device and successfully ignite. Then, the coupling structure operates in a second state of almost direct connection, so that almost all of the microwaves generated by the microwave source are absorbed by the nonlinear device, enabling the device to operate with high efficiency. The present invention can be applied to the disinfection and sterilization treatment of various gases and liquids, high-brightness and long-life lighting lamps, and microwave plasma torches.

Description

Technical Field

[0001] The present invention relates to an efficient microwave-excited gas discharge device. Specifically, it relates to an efficient gas discharge device that uses a coupling structure with dual-state operation to achieve low-power automatic ignition and operation of a gas plasma discharge device. Background Art

[0002] Under the action of high-power microwaves, gas will be ionized to generate plasma and emit light. The electrodeless ultraviolet lamp lit by microwaves has the advantages of high brightness, long life, and high luminous efficiency, and can be widely used for air and drinking water sterilization, and can also be used in the fields of industrial waste gas and industrial wastewater treatment. The microwave plasma torch generated by microwave ionization of gas has the characteristics of high temperature, pollution-free, and can be quickly started and stopped, and has a wide range of applications in motor vehicle engine ignition, large boiler ignition, metal cutting, surface cleaning, and even surgical operations. The microwave plasma thruster uses microwaves to ionize gas to generate plasma, and is expected to provide a new power for space flight.

[0003] However, the input impedance of most microwave plasma devices shows strong nonlinearity and belongs to strongly nonlinear devices. At small signals, the gas is not ionized and has very weak absorption of microwaves. Most of the microwaves projected onto the gas will be reflected. To ionize the gas, a very 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 will absorb microwaves well. In the early solutions, high-power microwaves were required to ignite the plasma device. After the device is ignited, due to a significant change in the load causing severe impedance mismatch, most of the microwave energy is reflected, 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 it difficult to realize small-power microwave plasma devices.

[0004] Yong C. Hong et al. reported a microwave plasma torch in 2011 [IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 10, OCTOBER 2011, pp. 1958 - 1962]. In this case, a moving tungsten wire manual method was used to ignite the microwave plasma device. This method is not conducive to the automatic operation of the equipment. Christoph Schopp and Holger Heuermann proposed a two - state matching scheme in 2013 [Proceedings of the 43rd European Microwave Conference, 2013, pp. 881 - 884]. This scheme uses a lumped - parameter matching circuit and, by using frequency switching, solves the automatic ignition of the gas discharge lamp to a certain extent and improves the energy efficiency of the gas discharge lamp. However, this method has the following disadvantages: 1) The insertion loss of this matching circuit is relatively large, seriously reducing the energy efficiency of this scheme. 2) In the commonly used 2450 MHz microwave 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 the power capacity. 3) For processing errors and parameter errors of components, this scheme lacks adjustability and it is difficult to reach the optimal working state. 4) This scheme requires the microwave source to switch frequencies during ignition and operation, increasing the manufacturing cost of the microwave source. 5) For the high - power magnetron with the lowest unit - power price at present, due to its wide spectrum and unstable operating frequency, the matching circuit further reduces the energy efficiency due to insufficient working bandwidth. Summary of the Invention

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

[0006] An efficient microwave - excited gas discharge device, comprising a microwave source with an operating frequency of f0 and a non - linear device connected in series in sequence; at least one coupling structure is arranged between the microwave source and the non - linear device; the non - linear device has two states according to the magnitude of the microwave signal output by the microwave source, namely a small - signal state and a large - signal state; the coupling structure has two states, the first state of the coupling structure corresponds to a weak - coupling state, and the second state of the coupling structure corresponds to a strong - coupling state; after the non - linear device changes from the small - signal state to the large - signal state, the coupling structure switches between the first state and the second state.

[0007] The strong coupling state corresponding to the second state of the coupling structure may be a state where the microwave source is directly connected to the nonlinear device, which is equivalent to a state where the coupling structure is completely removed. For a coupling screw, it is equivalent to completely withdrawing it from the nonlinear device.

[0008] In the present invention, so-called "ignition" means that the gas inside the nonlinear device is broken down into plasma.

[0009] 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 mW, the nonlinear device is in a small-signal mode, and its input impedance is almost a pure reactance. When the output power of the microwave source is 100 W, 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 may include a plasma discharge device with a discharge gas inside, such as a gas discharge lamp bulb, a microwave ultraviolet lamp, a dielectric tube with gas flowing through it, etc.

[0010] Taking the microwave plasma nonlinear device as an example, the working principle of the present invention is briefly described as follows. Generally, before the gas breakdown, the nonlinear device absorbs very little microwave and is in a small-signal state. The input impedance of the nonlinear device is almost a pure reactance. Almost all the microwaves entering the nonlinear device are reflected back. The amplitude of the microwave electric field felt by the gas inside the nonlinear device is very small. The gas cannot be broken down.

[0011] The present invention provides a coupling structure between the nonlinear device and the microwave source, which together with the nonlinear device forms a resonant cavity. Before the gas breakdown, the loss of this resonant cavity is very small and its Q value is very high. To effectively break down the gas inside, we need to meet two conditions: First, the frequency of the microwave source is equal to or as close as possible to the frequency of this resonant cavity, both being f0. Second, the impedance of the microwave source and the resonant cavity at resonance should be as matched as possible. For the second requirement, we need to appropriately set the coupling coefficient of the coupling structure. Since the Q value of this resonant cavity is very high, the coupling coefficient of the coupling structure will be very low.

[0012] After the gas is broken down, the nonlinear device is in a large-signal state. The resonant cavity that was matched in the small-signal state 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 arranges to change the coupling structure from the first state to the second state, that is, to make the microwave source directly communicate with the nonlinear device. Since the nonlinear load is close to matching with the microwave source in the large-signal state and can absorb microwaves well, changing the coupling structure to its second state can make the device operate efficiently.

[0013] Generally, there is gas inside the non-linear device, which can be broken down to generate plasma under the action of microwaves with high enough power.

[0014] Regarding the coupling structure, we have three designs:

[0015] In the first design, the coupling structure is a metal column. The first state of the coupling structure is that the metal column is inserted into the non-linear device to a certain depth, and the second state of the coupling structure is that the metal column withdraws from the non-linear device. In cooperation with the coupling structure, we are provided with at least one spring; after manually compressing the spring, the coupling structure is in the first state, and after releasing the spring, the coupling structure is in the second state. In cooperation with the coupling structure, we can also set up a motor. By driving the metal column with the motor, the coupling structure is changed from its first state to its second state.

[0016] In the second design, the coupling structure is a metal screw. The first state of the coupling structure is that the metal screw is screwed into the non-linear device to a certain depth, and the second state of the coupling structure is that the metal screw is screwed out of the non-linear device.

[0017] In the first state of the coupling structure, the depth X of the metal column or the metal screw entering the non-linear device is greater than 2 / 3 of the maximum stroke of the metal column or the metal screw inside the non-linear device. The maximum stroke of the metal column or the metal screw inside the non-linear device is defined as the maximum length that the metal column or the metal screw can reach inside the non-linear device, provided that the top of the metal column or the metal screw and the inner surface of the non-linear device opposite thereto do not come into contact.

[0018] In the third solution, the coupling structure is a diode spanning between two opposite inner surfaces of the non-linear device. The first state of the diode is a certain degree of conduction state, and the second state of the diode is a fully disconnected state. The two opposite inner surfaces respectively refer to the first cross-section where microwaves enter the non-linear device and the second cross-section opposite to the first cross-section.

[0019] The non-linear device can also be a power divider that divides one into multiple equal-amplitude and equal-phase paths, and each output end of the power divider is connected to a non-linear sub-device that is exactly the same as each other. This solution is suitable for using a microwave source with relatively high power, such as a magnetron, to provide microwave energy to multiple non-linear sub-devices simultaneously.

[0020] The output end of the microwave source and the input end of the non-linear device can be a rectangular waveguide, or a circular waveguide, or a ridged waveguide, or a coaxial cable, etc.

[0021] A dielectric tube is provided in the non-linear device. The dielectric tube passes through the non-linear device, and gas passes through the dielectric tube. This device is a plasma torch.

[0022] The applications of the present invention can be simply divided into three categories:

[0023] For the first category of applications, at least one gas discharge lamp is provided inside the non-linear device. The invention can provide a type of high-brightness, long-life, high luminous efficiency light source with a chromatogram close to sunlight. At this time, several small holes are opened on the outer shell of the non-linear device, which can effectively prevent microwave leakage and allow visible light to be emitted fully.

[0024] For the second category of applications, discharge gas passes through the non-linear device. The invention can provide a type of efficient plasma torch or microwave plasma thruster.

[0025] For the third category of applications, at least one electrodeless ultraviolet lamp tube is provided inside the non-linear device. The electrodeless ultraviolet lamp tube is efficiently lit by microwaves, and air or water, especially waste gas or wastewater, passes outside the electrodeless lamp tube in the non-linear device, and 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 outer shell of the non-linear device, which can effectively prevent microwave leakage and allow gas and liquid to enter and flow out of the non-linear device.

[0026] The beneficial effects of the present invention are:

[0027] The present invention discloses a design scheme of an efficient microwave-excited gas discharge device. The present invention is provided with a coupling structure that can switch states in the device. Before ignition, the coupling structure works in a weak coupling state, a strong resonance with the same resonant frequency as the working frequency of the microwave source is formed in the non-linear device and ignition is successful, and then the coupling structure works in a second state that is almost direct-through, so that almost all the microwaves generated by the microwave source are absorbed by the non-linear device, and the device works with high efficiency. The present invention can be applied to the disinfection and sterilization treatment of various gases and liquids, high-brightness and long-life lighting lamps, and microwave plasma torches. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic side sectional view of the present invention and Embodiment 1

[0029] Figure 2 It is a schematic side sectional view of Embodiment 2

[0030] Figure 3 It is a schematic side sectional view of Embodiment 3

[0031] Figure 4 It is a schematic top view of Embodiment 4

[0032] Names corresponding to the reference numerals in the drawings: 1 - microwave source, 22 - coupling structure, 4 - non-linear device, 41 - dielectric tube. Detailed implementation manners

[0033] Implementation example 1

[0034] As Figure 1 shown.

[0035] An efficient microwave-excited gas discharge device includes a microwave source 1 with an operating frequency of f0 and a micro non-linear device 4 connected in sequence; the micro non-linear device 4 has two states, a small-signal state and a large-signal state, according to the magnitude of the microwave signal output by the microwave source 1; a coupling structure 22 is provided between the microwave source 1 and the micro non-linear device 4; the coupling structure 22 has two states, the first state of the coupling structure 22 corresponds to a weak coupling state, and the second state of the coupling structure 22 corresponds to a strong coupling state; after the micro non-linear device 4 changes from the small-signal state to the large-signal state, the coupling structure 22 switches between the first state and the second state.

[0036] There is gas inside the micro non-linear device 4, and plasma can be generated by breakdown under the action of microwaves with high enough power.

[0037] The coupling structure 22 is a metal column. The first state of the metal column is to insert into the micro non-linear device 4 to a certain depth, and the second state of the metal column is to completely withdraw from the micro non-linear device 4.

[0038] The change of the coupling structure 22 from its first state to the second state here is completed by manually withdrawing the metal column completely from the micro non-linear device 4.

[0039] Implementation example 2

[0040] As Figure 2 shown.

[0041] Compared with implementation example 1, the difference is only that:

[0042] The coupling structure 22 is a diode.

[0043] Implementation example 3

[0044] As Figure 3 shown.

[0045] Compared with implementation example 1, the difference is only that:

[0046] The efficient microwave-excited gas discharge device is a plasma torch. The output end of the microwave source and the non-linear device 4 are both rectangular waveguides. A dielectric tube 41 is arranged in the rectangular waveguide, and the dielectric tube 41 penetrates the waveguide. In the waveguide, gas is input from one end of the dielectric tube 41, is ionized through the dielectric tube 41, forms high-temperature plasma and ejects from the other end of the dielectric tube 41.

[0047] Embodiment 4

[0048] As Figure 4 shown.

[0049] Compared with Embodiment 1, the difference lies only in that:

[0050] The non-linear device 4 is composed of an H-plane four-way equal-amplitude and equal-phase rectangular waveguide power divider connected to four non-linear sub-devices. The output end of the microwave source and the input ends of the non-linear sub-devices are both rectangular waveguides. The four non-linear sub-devices are almost exactly the same.

[0051] As mentioned above, these are only the preferred embodiments of the present invention and do not impose any formal restrictions on the present invention. For the convenience of debugging this device, some conventional techniques, such as adding an impedance matcher between the microwave source and the non-linear device, and setting a tuning device on the non-linear device, may be useful. According to the technical essence of the present invention, any modifications that deviate from the optimal design, equivalent replacements, and addition of any conventional techniques to the above embodiments within the spirit and principles 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 device, characterized in that, It includes a microwave source (1) with an operating frequency of f0 and a non-linear device (4) connected in sequence; a dielectric tube (41) is provided in the non-linear device (4), the dielectric tube (41) passes through the non-linear device (4), gas passes through the dielectric tube (41), and the non-linear device (4) has two states according to the magnitude of the microwave signal output by the microwave source (1), namely the small-signal state and the large-signal state; at least one coupling structure (22) is provided between the microwave source (1) and the non-linear device (4); the coupling structure (22) has two states, the first state of the coupling structure (22) corresponds to the weak-coupling state and forms a resonant cavity together with the non-linear device, and the second state of the coupling structure (22) corresponds to the strong-coupling state and the state where the microwave source (1) and the non-linear device (4) are directly connected, which is equivalent to the state where the coupling structure is completely removed; after the non-linear device (4) changes from the small-signal state to the large-signal state, the coupling structure (22) changes from the first state to the second state.

2. The efficient microwave-excited gas discharge device according to claim 1, characterized in that, The coupling structure (22) is a metal post. The first state of the coupling structure is that the metal post is inserted into the non-linear device to a depth of X, and the second state of the coupling structure is that the metal post withdraws from the non-linear device.

3. The efficient microwave-excited gas discharge device according to claim 2, characterized in that, At least one spring is provided; the coupling structure (22) is in the first state after the spring is compressed, and the coupling structure (22) is in the second state after the spring is released.

4. The efficient microwave-excited gas discharge device according to claim 1, characterized in that, The coupling structure (22) is a metal screw. The first state of the coupling structure is that the metal screw is inserted into the non-linear device (4) to a depth of X, and the second state of the coupling structure is that the metal screw withdraws from the non-linear device (4).

5. The efficient microwave-excited gas discharge device according to claim 2 or 4, characterized in that, At least one motor is provided; the motor can drive the coupling structure (22) to change between the first state and the second state of the coupling structure (22).

6. The efficient microwave-excited gas discharge device according to claim 2, characterized in that, In the first state of the coupling structure, the depth X is greater than 2 / 3 of the maximum travel of the metal post inside the non-linear device (4).

7. The efficient microwave-excited gas discharge device according to claim 4, characterized in that, 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).

8. The efficient microwave-excited gas discharge device according to claim 1, characterized in that, The coupling structure (22) is a diode spanning between two opposite inner surfaces of the non-linear device (4). The first state of the diode is a certain degree of conduction state, and the second state of the diode is the off state. The two opposite inner surfaces respectively refer to the first cross-section where the microwave enters the non-linear device (4) and the second cross-section opposite to the first cross-section.

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