A room-temperature and room-pressure microwave low-temperature plasma jet excitation device

Abstract

This invention proposes a room-temperature and ambient-pressure microwave low-temperature plasma jet excitation device, relating to the field of plasma. It includes a resonant cavity comprising a coaxial outer cavity and an inner cavity. A copper core tube is fixedly mounted in the upper half of the inner cavity, with its top end extending beyond the top opening of the inner cavity. A gas guide hole is also provided at the bottom of the inner cavity. A gas guide port and a microwave feed port are provided on the side of the outer cavity, and an air inlet channel is also provided at the bottom of the outer cavity. This invention, by employing a double-layered open coaxial resonant cavity structure and setting specific parameter ratios, enables the efficient and stable excitation of a stable and controllable low-temperature plasma jet with extremely low power under ambient temperature and pressure conditions. It also reveals the working mechanism, solving the problems of traditional technologies such as dependence on low gas pressure, high excitation power, poor jet stability, and low microwave absorption efficiency, and broadening the application scenarios of low-temperature plasma technology.

Description

Technical Field

[0001] This invention relates to the field of plasma technology, and more specifically, to a room-temperature and room-pressure microwave low-temperature plasma jet excitation device. Background Technology

[0002] Low-temperature plasma possesses unique non-thermal equilibrium characteristics, is rich in various active and charged particles, and its overall temperature can be maintained at levels close to or even lower than room temperature. Compared to high-temperature plasma, it generates significantly less thermal effect when processing target materials, thus demonstrating unique technological competitiveness. This advantage not only greatly expands the application fields of plasma technology but also gives it broad application prospects in multiple areas such as materials processing, medical treatment, environmental remediation, agriculture and food, and electromagnetic protection.

[0003] In high-frequency discharge, microwave discharge is a form of electrodeless discharge with unique advantages. Existing technology includes a microwave plasma generator that uses a coaxial resonant cavity. Plasma is excited in the uncovered gaps of the conductor by placing a non-metallic tube as a gas flow path at the center of the central conductor. While this device can operate at near atmospheric pressure, it still has some shortcomings: its core structural design makes it sensitive to load changes before and after plasma excitation, requiring complex feedback circuits (such as detecting the internal electromagnetic field and feeding back to control the magnetron anode voltage and excitation current) to stabilize the frequency, resulting in a complex system. Furthermore, its microwave feeding method (antenna coupling) and cavity structure still need improvement in achieving low-power, high-efficiency excitation and generating stable, controllable, slender jets.

[0004] In the existing technology, how to achieve stable, low-power microwave-excited plasma jets at room temperature and pressure, and how to flexibly control the jet state, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a room-temperature and room-pressure microwave low-temperature plasma jet excitation device. By adopting a double-layer open coaxial resonant cavity structure and setting specific parameter ratios, it can achieve efficient excitation of stable and controllable low-temperature plasma jets with extremely low power (minimum 22W) under room-temperature and room-pressure conditions. The invention also reveals its working mechanism, solving the problems of traditional technologies such as dependence on low gas pressure, high excitation power, poor jet stability, and low microwave absorption efficiency, and broadening the application scenarios of low-temperature plasma technology.

[0006] The embodiments of the present invention are implemented as follows: This invention provides a room temperature and pressure microwave low-temperature plasma jet excitation device, including a resonant cavity. The resonant cavity includes a coaxial outer cavity and an inner cavity. A copper core tube is fixedly provided in the upper half of the inner cavity, and the top end of the copper core tube extends out of the top opening of the inner cavity. A gas guide hole is also provided at the bottom of the inner cavity. A gas guide port and a microwave feed port are provided on the side of the outer cavity. An air inlet channel is also provided at the bottom of the outer cavity.

[0007] In a preferred embodiment, the ratio of the radius of the inner cavity to the radius of the outer cavity is 1:2.3.

[0008] In a preferred embodiment, the top of the air intake channel is connected to the bottom of the inner cavity, and the diameter of the air guide hole is 0.3-0.8 mm, preferably 0.5 mm.

[0009] In a preferred embodiment, the radius of the copper core tube is 1 mm, and the length of the copper core tube extending out of the inner cavity is 1 mm.

[0010] In a preferred embodiment, the length of the outer cavity is 90-100mm, preferably 92.2mm; the length of the inner cavity is 27-30mm, preferably 28.8mm; and the height of the microwave feed port from the bottom of the outer cavity is 34-38mm, preferably 36.5mm.

[0011] As a preferred embodiment, the outer wall of the upper half of the outer cavity is also provided with annular heat dissipation fins.

[0012] In some embodiments of the present invention, a fairing is also included, which is detachably disposed at the opening of the outer cavity.

[0013] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: 1. This invention employs a double-layer open coaxial resonant cavity structure with one end short-circuited and the other end open, and combines it with inner cavity, outer cavity, microwave feed port and copper core tube with specific parameters. This enables the generation of stable low-temperature plasma jets with low power under normal temperature and pressure conditions, solving the problem of dependence on low gas pressure in traditional technologies. 2. The jet macroscopic temperature of the present invention is low, which is consistent with the characteristics of low temperature plasma. The jet length increases linearly with microwave power. The return loss is stable at around -12dB in the range of 35W-80W. There is no filamentary discharge phenomenon. The stability performance is excellent. Furthermore, the jet state can be flexibly controlled by adjusting the airflow velocity and microwave power. 3. The electric field distribution of the present invention is uniform, the microwave absorption efficiency is high, and the reflectivity is ≤6%, which is lower than the existing microwave reflection level. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention; Figure 2 This is a cross-sectional view of the excitation device in Embodiment 1 of the present invention; Figure 3 This is an enlarged view of point A in Embodiment 1 of the present invention; Figure 4 This is a comparison diagram of the electric field distribution at the top of the copper core tube at different frequencies in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the fairing structure in Embodiment 3 of the present invention; Figure 6 The image shows the jet flow diagrams of the microwave low-temperature plasma jet excitation device at different powers when the inner cavity flow rate is 2 L / min and the outer cavity flow rate is 1 L / min in Embodiment 3 of the present invention. Figure 7 for Figure 6 The corresponding reflection coefficient and jet length as a function of power are shown in the graph. Figure 8 The image shows the jet flow diagrams of the microwave low-temperature plasma jet excitation device under different powers when the inner cavity flow rate is 1 L / min and the outer cavity flow rate is 0.1 L / min in Embodiment 3 of the present invention. Figure 9 for Figure 8 The corresponding reflection coefficient and jet length as a function of power are shown in the graph. Figure 10 The image shows the jet flow diagrams of the microwave low-temperature plasma jet excitation device at different powers when the inner cavity flow rate is 0.5 L / min and the outer cavity flow rate is 0.5 L / min, as described in Embodiment 3 of the present invention. Figure 11 for Figure 10 The corresponding reflection coefficient and jet length as a function of power are shown in the graph. Figure 12 This is a jet diagram of the microwave low-temperature plasma jet excitation device under the rectifier in Embodiment 3 of the present invention; Figure 13 for Figure 12 The corresponding reflection coefficient and jet length as a function of power are shown in the graph. Figure 14 This is a graph showing the curves of different microwave feed heights and return losses in Embodiment 3 of the present invention.

[0016] Icons: 1-Outer cavity; 2-Inner cavity; 3-Copper core tube; 4-Air duct; 5-Air inlet; 6-Microwave feed port; 7-Air intake channel; 8-Annular heat dissipation fins; 9-Flat cover. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] Example 1 Please refer to Figures 1-3 This embodiment provides a room-temperature and room-pressure microwave low-temperature plasma jet excitation device, including a resonant cavity. The resonant cavity, as the core device for excitation, is divided into a coaxial outer cavity 1 and an inner cavity 2. The outer cavity 1 is made of copper-nickel alloy and has an overall length of 92.2 mm. The top of the outer cavity 1 is open, and the bottom is closed. An inner cavity 2 and an air inlet channel 7 are located along the central axis of the outer cavity 1. The inner cavity 2 is made of brass and has a similar structure to the outer cavity 1, with an open top and a closed bottom. Its overall length is 28.8 mm. The inner cavity 2 and the outer cavity 1 together form a double-layered open coaxial resonant cavity structure with one end short-circuited and the other open. In addition, a copper core tube 3 is fixed along the central axis of the inner cavity 2. The bottom end of the copper core tube 3 is fixed to the bottom surface of the inner cavity 2, and the top end extends out of the top of the inner cavity 2 by 1 mm. Furthermore, to avoid distortion of the electric field at the tip, the tip of the copper core tube 3 is rounded.

[0020] Furthermore, in this embodiment, the radius ratio (excluding the thickness of the outer shell) of the inner cavity 2 and the outer cavity 1 is 1:2.3. Preferably, the radius of the inner cavity 2 is 1 mm, and the radius of the outer cavity 1 is 2.3 mm. This ratio design ensures that the resonant cavity achieves stable resonance at the target operating frequency. The bottom of the inner cavity 2 is sealed to the air intake channel 7, and the bottom of the inner cavity 2 is also provided with several air guide holes 4, the diameter of which is set to 0.5 mm. The bottom end of the air intake channel 7 penetrates the bottom surface of the outer cavity 1.

[0021] Optionally, in this embodiment, there are four air vents 4, which are distributed along the bottom circumference of the inner cavity 2.

[0022] Furthermore, a gas inlet 5 with a diameter of 3mm is provided in the lower half of the outer cavity 1. This, along with the gas inlet channel 7 and the gas guide hole 4 at the bottom of the inner cavity 2, enables dual-channel gas input. It is worth noting that in this embodiment, the working gas is 99.99% high-purity argon. Operators can control the argon flow rate by adjusting the pressure difference between the inner cavity 2 and the outer cavity 1 (preferably controlling the argon flow rate in the inner cavity 2 to 0.5L / min and the argon flow rate in the outer cavity 1 to 0.5L / min). This effectively prevents filamentary discharge of argon gas within the resonant cavity, ensuring the uniformity and stability of the plasma jet.

[0023] Furthermore, a microwave feed port 6 is provided in the lower half of the outer cavity 1. The microwave feed port 6 uses a 2.45GHz microwave source directly coupled to the outer cavity 1 via a 50Ω coaxial cable, with the feed port height 36.5mm from the bottom surface of the outer cavity 1. This design employs a λ / 4 impedance inversion characteristic to achieve impedance matching with the plasma load, enabling return loss to be below -12dB, effectively reducing microwave energy reflection and improving microwave energy utilization.

[0024] Optionally, in this embodiment, the outer cavity 1 can also be equipped with annular heat dissipation fins 8 to increase the heat dissipation area, accelerate heat dissipation, and ensure that the temperature of the device remains within a reasonable range under normal temperature and pressure operating conditions. In addition, the top of the outer cavity 1 is also provided with a detachable shroud 9 to constrain the loss of high-energy particles and improve electron density and jet length.

[0025] The specific working principle of this invention is as follows: After the device is started, 99.99% high-purity argon gas is first supplied to the inner cavity 2 and the outer cavity 1 through the air inlet channel 7 and the air guide port 5, respectively. The pressure difference is adjusted to stabilize the argon gas flow rate in the inner cavity 2 at 0.5 L / min and the argon gas flow rate in the outer cavity 1 at 0.5 L / min. Then, a 2.45 GHz microwave source is started. The microwave is coupled to the outer cavity 1 through a 50 Ω coaxial line via a feed port, and then coupled to the inner cavity 2 from the outer cavity 1. Under the resonance effect of the inner cavity 2 and the outer cavity 1, an intensity greater than 5 × 10⁻⁶ is formed on the surface of the central copper core tube 3 (within 1 / 3 of the range from the opening). 6 A uniform strong electric field of V / m is generated; this strong electric field breaks down argon gas at room temperature and pressure, exciting the generation of plasma. The plasma forms a stable jet under the constraint of the rectifier 9. During operation, the brass inner cavity 2 is coupled with microwaves, and the copper-nickel alloy outer cavity 1 and the annular heat dissipation fins 8 work together to dissipate heat, ensuring stable device temperature, efficient utilization of microwave energy, and stable and continuous excitation of plasma.

[0026] Example 2 This embodiment first explores the comparison of the electric field distribution at the top of the copper core tube 3 at different frequencies using the device prepared in Embodiment 1, including the following steps: An EFS-3000 electric field strength meter (measuring range 1×10⁻⁶) was used. 5 V / m ~ 1×10 7 V / m, measurement accuracy ±1%, paired with a three-dimensional moving platform (positioning accuracy ±0.01mm), used for precise measurement of electric field strength on the surface of the copper core and at different locations in the working area; the measurement environment is maintained at normal temperature and pressure (25℃, 1 standard atmosphere), and the environmental electromagnetic interference is ≤1×10 4 V / m, to avoid external interference affecting the measurement results; the working gas supply is kept consistent with that in Example 1 (99.99% high-purity argon, flow rate of 0.5L / min in inner cavity 2 and 0.5L / min in outer cavity 1) to ensure consistency of measurement conditions.

[0027] Then, the device was started, and the working gas flow rate was adjusted to a stable state to ensure no filamentary discharge. The microwave source output frequency was adjusted to 2.4GHz, 2.45GHz, and 2.5GHz respectively, and the microwave output power was kept stable at 100W at each frequency. After the device had been running stably for 5 minutes, the measurement began. Using a three-dimensional moving platform, the probe of the electric field strength tester was moved to within 1 / 3 of the distance from the opening of the resonant cavity (0~9.6mm). A measurement point was selected every 0.5mm along the axial direction of the copper core surface. Each measurement point was measured three times, and the average value was taken as the measured value of the electric field strength at that point. The electric field strength data of all measurement points at each frequency were recorded. The experimental results are as follows. Figure 4 As shown, at 2.4 GHz, the high-intensity electric field is concentrated in a small region at the top of the copper core; at 2.5 GHz, the high-intensity electric field is distributed below the opening; and at 2.45 GHz, the high-intensity electric field surrounds the upper half of the copper core, is uniformly distributed, and has an intensity of 5.4 × 10⁻⁶. 6 The V / m is 10.9 times that at 2.4 GHz and 49.1 times that at 2.5 GHz. This comparison verifies that the present invention can achieve better electric field distribution and excitation efficiency at the frequency of 2.45 GHz.

[0028] Therefore, it can be seen that the ambient temperature and pressure microwave low-temperature plasma jet excitation device prepared in Embodiment 1 of the present invention can form a resonant system with a uniform high-intensity electric field at a frequency of 2.45 GHz under ambient temperature and pressure.

[0029] Example 3 This embodiment further compares and verifies the experimental effects of the device in Embodiment 1, including the following schemes: 1) First, investigate the effect of argon flow rate on the plasma jet. This includes the following steps: The flow rate in inner cavity 2 was adjusted to 2 L / min and the flow rate in outer cavity 1 was adjusted to 1 L / min. The state of the plasma jet generated under different microwave powers was observed, and the reflection coefficient S was also observed. 11 The relationship between the jet length and the experimental results is as follows. Figure 6 and Figure 7 As shown, at this flow rate, the generated plasma will exhibit a scattered pattern and cannot generate stable, elongated plasma. The magnitude of microwave power only affects the length of the generated plasma.

[0030] Furthermore, the flow rate in inner cavity 2 was adjusted to 1 L / min and the flow rate in outer cavity 1 was adjusted to 0.1 L / min. The state of the plasma jet generated under different microwave powers was observed, and the reflection coefficient S was also observed. 11 The relationship between the jet length and the experimental results is as follows. Figure 8 and Figure 9 As shown, the generated plasma is linear with no scattering, and the plasma jet length exhibits a trend of "first increasing and then stabilizing" with microwave power. Specifically, in the range of 30-65W, the plasma jet length increases approximately linearly, while in the range of 65-80W, the jet length remains stable at 11.0 mm, no longer changing with increasing power. Furthermore, although the return loss S... 11 The reflection performance fluctuates periodically with changes in microwave power, but overall it is higher than -5.6dB, indicating relatively poor reflection performance.

[0031] Furthermore, the flow rate in inner cavity 2 was adjusted to 0.5 L / min, and the flow rate in outer cavity 1 was also adjusted to 0.5 L / min. The state of the plasma jet generated under different microwave powers was observed, and the relationship between the reflection coefficient S11 and the jet length was also observed. The experimental results are as follows: Figure 10 and Figure 11 As shown, under this argon flow rate, the length of the generated plasma jet is positively correlated with the microwave power, and the plasma jet length and shape are better. Furthermore, at a power of 30-65W, the return loss S... 11 It exhibits periodic fluctuations with changes in microwave power, but the fluctuation range is not large, and it can basically stabilize at around -11.6dB. Its reflection performance is relatively good and can meet the impedance matching requirements of the device.

[0032] 2) This scheme further determined that, under the conditions of a flow rate of 0.5 L / min in inner cavity 2 and a flow rate of 0.5 L / min in outer cavity 1, if... Figure 5 The effect of the fairing 9 (preferably an acrylic fairing) on ​​the jet is shown. Experimental results are as follows: Figure 12 and Figure 13 As shown, it can be seen that after adding the rectifier 9, the length of the generated plasma jet is positively correlated with the microwave power, and the return loss S11 It is negatively correlated with microwave power. However, overall, with the addition of the rectifier 9, the jet length is longer than without the rectifier 9, and the return loss S... 11 It is even lower; at microwave frequencies of 30-80W, it is generally below -12.2dB, resulting in better reflection performance.

[0033] 3) This scheme also measured the effect of the height of microwave feed port 6 on return loss, including: The device from Scheme 2 was selected, and different feed port heights were set. The entire device was operated at a frequency of 2.45 GHz. A network analyzer was connected to the microwave input feed port. After calibrating the instrument, the return loss S11 value was measured. The average value corresponding to each feed port height was recorded, and the relationship curve between feed port height and return loss was plotted. The experimental results are as follows: Figure 14 As shown, the height of the microwave feed port 6 has a significant impact on the return loss, exhibiting a general pattern of "first decreasing and then increasing." Specifically, as the feed port height increases from 30mm to 36.5mm, the absolute value of the return loss S11 gradually increases (while the numerical value gradually decreases), and microwave energy reflection gradually decreases. When the feed port height exceeds 36.5mm, as the height continues to increase, the absolute value of the return loss S11 gradually decreases (while the numerical value gradually increases), and microwave energy reflection gradually increases. However, overall, a return loss S11 ≤ -12dB meets the impedance matching requirements of the device. When the feed port height is 36.5mm, the return loss is the lowest (S11 is approximately 26dB), the impedance matching effect is optimal, and the microwave energy reflectivity is the lowest.

[0034] In summary, the embodiments of the present invention provide a room temperature and pressure microwave low-temperature plasma jet excitation device. By adopting a double-layer open coaxial resonant cavity structure with one end short-circuited and the other end open, and in conjunction with an inner cavity 2, an outer cavity 1, a microwave feed port 6, and a copper core tube 3 with specific parameters, it is possible to generate a stable low-temperature plasma jet with low power under room temperature and pressure, thus solving the problem of dependence on low gas pressure in traditional technologies. The jet of this invention has a low macroscopic temperature, which conforms to the characteristics of low-temperature plasma. The jet length increases linearly with microwave power. The return loss is stable at around -12dB in the range of 35W-80W. There is no filamentary discharge phenomenon. It has excellent stability performance. Furthermore, the jet state can be flexibly controlled by adjusting the airflow velocity and microwave power. The electric field distribution of this invention is uniform, the microwave absorption efficiency is high, and the reflectivity is ≤6%, which is lower than the existing microwave reflection level.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A room-temperature and room-pressure microwave low-temperature plasma jet excitation device, characterized in that, The resonant cavity includes a coaxial outer cavity and an inner cavity. A copper core tube is fixedly installed in the upper half of the inner cavity, and the top end of the copper core tube extends out of the top opening of the inner cavity. A vent hole is also provided at the bottom of the inner cavity. A vent port and a microwave feed port are provided on the side of the outer cavity. An air inlet channel is also provided at the bottom of the outer cavity.

2. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 1, characterized in that, The ratio of the radius of the inner cavity to the radius of the outer cavity is 1:2.

3.

3. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 2, characterized in that, The top of the air intake channel is connected to the bottom of the inner cavity, and the diameter of the air guide hole is 0.3-0.8mm, preferably 0.5mm.

4. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 3, characterized in that, The copper core tube has a radius of 1 mm and extends 1 mm beyond the inner cavity.

5. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 4, characterized in that, The length of the outer cavity is 90-100mm, preferably 92.2mm; the length of the inner cavity is 27-30mm, preferably 28.8mm; the height of the microwave feed port from the bottom of the outer cavity is 34-38mm, preferably 36.5mm.

6. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 1, characterized in that, The outer wall of the upper half of the outer cavity is also provided with annular heat dissipation fins.

7. The ambient temperature and pressure microwave low-temperature plasma jet excitation device according to claim 6, characterized in that, It also includes a fairing, which is detachably disposed at the opening of the outer cavity.

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