A methane detection system based on Fabry-Perot cavity

Abstract

The present invention relates to the field of gas sensing and detection technology, and specifically to a methane detection system based on a Fabry-Perot resonant cavity, comprising a gas pool, a light source, a first optical assembly, an isolation plate, a sensing unit, a second optical assembly, a light detector, an air inlet, and an air outlet. The sensing unit comprises a first limiting film layer, a sensitive layer, and a second limiting film layer arranged in sequence, wherein the first limiting layer, the sensitive layer, and the second limiting layer are provided with through holes. The first limiting film layer, the sensitive layer, and the second limiting film layer constitute a Fabry-Perot resonant cavity. Under the action of methane gas, the refractive index of the sensitive layer changes, thereby causing the resonant wavelength of the Fabry-Perot resonant cavity to shift. Methane gas detection is achieved by shifting the resonant wavelength of the Fabry-Perot resonant cavity. The present invention proposes a new method and mechanism for detecting methane gas concentration, which has good application prospects in the field of methane gas detection and detection.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensing and detection, and in particular to a methane detection system based on a Fabry-Perot resonant cavity. Background Art

[0002] Methane is a colorless, odorless gas. Despite its colorless and odorless nature, it plays a vital role in production and daily life. During coal mining, methane is released from coal seams. When methane concentrations reach 5% or above, combined with oxygen concentrations and open flames, it can cause explosions. Furthermore, methane is a significant greenhouse gas, second only to carbon dioxide, accounting for 20% of global greenhouse gas emissions. Therefore, monitoring methane levels in mines and manufacturing is crucial.

[0003] Infrared absorption spectroscopy is the most common spectroscopic methane detection technology, primarily utilizing methane gas's absorption of infrared light of specific wavelengths for detection. The wavelength of the methane gas absorption spectrum is closely related to the structure of the methane gas molecule, with commonly used absorption bands concentrated at 1.65 microns, 3.31 microns, and 7.66 microns. The infrared absorption spectrum of methane gas is only a few nanometers wide, narrower than the noise of the light source, making it difficult to identify the methane absorption spectrum in the final measured absorption spectrum. Addressing the issue from both the light source and the absorption path would, on the one hand, place higher demands on the light source, and on the other, increase the overall size of the device. Exploring a methane gas concentration detection system with higher accuracy and sensitivity is an urgent issue.

[0004] Years of research have revealed that certain organic compounds possess excellent methane-sensing properties. Cryptophane-A and Cryptophane-E, for example, absorb methane from the environment, causing a change in their refractive index. These methane-sensing compounds offer the potential for achieving even higher-precision and more sensitive methane concentration detection systems. Summary of the Invention

[0005] To address the above issues, the present invention provides a methane detection system based on a Fabry-Perot resonant cavity, comprising a gas pool, a light source, a first optical system, an isolation plate, a sensing unit, a second optical system, a photodetector, an air inlet, and an air outlet. The sensing unit is fixed to the center of the isolation plate. The sensing unit and the isolation plate divide the gas pool into two chambers, with the light source and the first optical system disposed in one chamber, and the second optical system and the photodetector disposed in the other chamber. The air inlet and the air outlet are disposed on the side walls of the two chambers, respectively. The light source emits broadband light, which, after passing through the first optical system, illuminates one side of the sensing unit. After exiting from the other side of the sensing unit, it is converged onto the photodetector through the second optical system. The sensing unit comprises a first confining film layer, a sensitive layer, and a second confining film layer, arranged in sequence. Through holes are provided through the first confining film layer, the sensitive layer, and the second confining film layer.

[0006] The core concept of this invention is to utilize a Fabry-Perot resonant cavity for methane detection. A first confining film layer, a sensitive layer, and a second confining film layer form the Fabry-Perot resonant cavity. The first and second confining films primarily confine light, while the sensitive layer senses methane. When the sensitive layer absorbs methane, its refractive index changes, resulting in a shift in the resonant wavelength of the cavity. A light detector observes the transmission spectrum, and changes in the resonant wavelength reflect the methane concentration.

[0007] Furthermore, the first optical system includes a convex lens, a plano-concave lens, and a plano-convex lens.

[0008] Furthermore, the second optical system is a convex lens.

[0009] Furthermore, the material of the sensitive layer is X-ray diffraction-A or X-ray diffraction-E.

[0010] Furthermore, the air inlet is arranged in the chamber on one side of the detector, and the air outlet is arranged in the chamber on one side of the light source.

[0011] Furthermore, the air outlet and the light source are arranged on the same side wall.

[0012] Furthermore, the air outlet is arranged at the lower side of the light source.

[0013] Furthermore, local blocks are provided between adjacent through holes, and the material of the local blocks is different from that of the sensitive layer.

[0014] Furthermore, the material of the first limiting film layer and the second limiting film layer is silicon.

[0015] Furthermore, the through holes are distributed periodically.

[0016] Beneficial effects of the present invention:

[0017] (1) The present invention uses a Fabry-Perot resonant cavity to detect methane gas concentration. The sensitive layer material is located in the Fabry-Perot resonant cavity. Under the action of methane gas, the refractive index of the sensitive layer changes, thereby causing the resonant wavelength of the Fabry-Perot resonant cavity to move. Methane gas detection is achieved through the movement of the resonant wavelength of the Fabry-Perot resonant cavity. The present invention proposes a new method and mechanism for detecting methane gas concentration.

[0018] (2) In the present invention, methane gas needs to pass through the through holes penetrating the first limiting film layer, the sensitive layer, and the second limiting film layer in order to reach the gas outlet of another chamber from the gas inlet of one chamber. The sensitive layer is in close contact with the methane gas, which strengthens the interaction between the methane gas and the material in the sensitive layer. The refractive index of the material in the sensitive layer can change more, thereby achieving high-sensitivity and high-precision detection of methane gas concentration.

[0019] (3) The present invention cleverly arranges the positions of the air inlet and the air outlet, and utilizes methane gas to remove the heat generated by the light source, thereby ensuring that the sensing part operates at a lower and more stable temperature, reducing the influence of the heat generated by the system on the resonant wavelength of the Fabry-Perot resonant cavity, and the system operates with high stability, thereby ensuring its high-precision and high-sensitivity operation.

[0020] Based on the above effects, the present invention has good application prospects in the field of methane gas detection and testing.

[0021] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of a methane detection system based on a Fabry-Perot cavity.

[0023] Figure 2 This is a schematic diagram of a sensing unit.

[0024] Figure 3 is a schematic diagram of a first optical system assembly.

[0025] Figure 4 This is a schematic diagram of another sensing unit.

[0026] In the figure: 1. Gas pool; 2. Light source; 3. First optical system; 4. Isolation plate; 5. Sensing part; 6. Second optical system; 7. Photodetector; 8. Air outlet; 9. Air inlet; 31. Convex lens; 32. Plano-concave lens; 33. Plano-convex lens; 51. First limiting film layer; 52. Sensitive layer; 53. Second limiting film layer; 54. Through hole; 55. Local block. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of this application more clear, the application is further described in detail below with reference to the accompanying drawings and examples.

[0028] The present invention provides a methane detection system based on a Fabry-Perot resonant cavity, such as Figure 1 As shown, the methane detection system includes a gas pool 1, a light source 2, a first optical assembly 3, an isolation plate 4, a sensor 5, a second optical assembly 6, a light detector 7, an air inlet 9, and an air outlet 8. Figure 1 In the figure, the gas pool 1 is in the shape of a cuboid. In practical applications, the gas pool 1 can also be in the shape of a cube, cylinder, etc. The material of the gas pool 1 is an infrared absorbing material or the inner wall of the gas pool 1 is coated with an infrared absorbing material to prevent the infrared rays in the external environment from affecting the measurement results. The sensing part 5 is fixed in the middle of the isolation plate 4. The sensing part 5 and the isolation plate 4 are tightly bonded together. The bonding part has good airtightness and methane gas cannot pass through the bonding part. The isolation plate 4 is also tightly bonded or embedded in the inner wall of the gas pool 1; the bonding part between the isolation plate 4 and the inner wall of the gas pool 1 is also not airtight. As Figure 1 As shown, when the gas pool 1 is a rectangular parallelepiped, the overall shape of the isolation plate 4 is rectangular, and the hollowed-out portion of the isolation plate 4 is used to accommodate the sensor unit 5. Thus, the sensor unit 5 and isolation plate 4 divide the gas pool into two chambers: the light source 2 and the first optical train 3 are arranged in the left chamber, and the second optical train 6 and the light detector 7 are arranged in the right chamber. The air inlet 9 and the air outlet 8 are respectively arranged on the side walls of the two chambers. Specifically, as shown in FIG. Figure 1 As shown, the air inlet 9 is arranged in the right chamber, together with the light detector 7 and the second optical system group 6; the air outlet 8 is arranged in the left chamber, together with the light source 2 and the first optical system group 3. The light source 2 is fixed on the left side wall of the gas pool 1, and the first optical system group 3 is fixed on the bottom surface of the gas pool 1 through a bracket. The light detector 7 is fixed on the right side wall of the gas pool 1, and the second optical system group 6 is fixed on the bottom surface of the gas pool 1 through a bracket. The light source 2 is a broadband light source, for example, the light source 2 is a halogen tungsten lamp light source. The light source 2 emits broadband light, which is irradiated to the left side of the sensing part 5 after passing through the first optical system group 3, and after being emitted from the other side of the sensing part 5, it is converged onto the light detector 7 through the second optical system group 6. The light detector 7 includes a spectrometer for measuring the transmission spectrum. As shown Figure 2As shown, the sensing portion 5 includes a first confinement film layer 51, a sensitive layer 52, and a second confinement film layer 53, arranged in sequence. Through holes 54 extend through the first confinement film layer 51, the sensitive layer 52, and the second confinement film layer 53. The first and second confinement film layers 51, 53 are made of silicon or precious metals and have a thickness of less than 2 microns, thereby confining the light field between the first and second confinement film layers 51, 53. The sensitive layer 52 is made of either X-ray diffraction-A or X-ray diffraction-E. The refractive index of X-ray diffraction-A and X-ray diffraction-E changes under the influence of methane gas. The thickness of the sensitive layer 52 is greater than 2 microns. The through holes 54 are circular, with a diameter of less than 1 micron. The through holes 54 are distributed periodically, with a square period.

[0029] In the present invention, a first confining film layer 51, a sensitive layer 52, and a second confining film layer 53 form a Fabry-Perot resonant cavity. The first confining film layer 51 and the second confining film layer 53 are primarily used to confine light, while the sensitive layer 52 is used to sense methane. After the sensitive layer 52 absorbs methane, its refractive index changes, causing the resonant wavelength of the Fabry-Perot resonant cavity to shift. The light detector 7 observes the transmission spectrum, and the shift in the resonant wavelength in the transmission spectrum reflects the methane concentration. The present invention places the sensitive layer 52 within the Fabry-Perot resonant cavity. When the refractive index of the sensitive layer 52 changes, the resonant wavelength of the Fabry-Perot resonant cavity shifts significantly. This shift in the resonant wavelength of the Fabry-Perot resonant cavity enables methane gas detection, thus providing a new method and mechanism for detecting methane gas concentration. In addition, in the present invention, methane gas needs to pass through the through hole 54 that penetrates the first limiting film layer 51, the sensitive layer 52, and the second limiting film layer 53 to reach the gas outlet 8 of another chamber from the gas inlet 9 of one chamber. The sensitive layer 52 can be in close contact with the methane gas, which strengthens the interaction between the methane gas and the material of the sensitive layer 52. The concentration of the methane gas is quickly reflected in the change of the refractive index of the sensitive layer 52, that is, the refractive index of the material of the sensitive layer 52 can change more and more rapidly, thereby achieving high-sensitivity and high-precision methane gas concentration detection.

[0030] In the present invention, the air inlet 9 is arranged on one side of the light detector 7, and the air outlet 8 is arranged on one side of the light source 2. Methane gas is used to carry away the heat generated by the light source 2, thereby ensuring that the sensing part 5 operates at a lower and more stable temperature, reducing the influence of the heat generated by the system on the resonant wavelength of the Fabry-Perot cavity, and the system operation is highly stable, thereby ensuring its high-precision and high-sensitivity operation.

[0031] The fabrication method for the sensing portion 5 includes forming a first confining film layer 51, a sensitive layer 52, a second confining film layer 53, and a through hole 54. First, the first confining film layer 51 is formed using physical vapor deposition (PVD). Then, the sensitive layer 52 is formed using PVD or spin-on coating. Finally, the second confining film layer 53 is formed using PVD. Finally, the through hole 54 is formed using ion beam etching or chemical etching. After fabrication, the sensing portion 5 is adhered to the hole in the center of the isolation plate 4.

[0032] In the present invention, the isolation plate 4 may or may not be provided with a through hole. This depends on the power of the air pump at the air inlet 9. When the power of the air pump is relatively low, no through hole is provided on the isolation plate 4, and the methane gas only passes through the through hole 54 on the sensing part 5. When the power of the air pump is relatively high, in order to prevent the pressure damage caused by the methane gas to the sensing part 5, a through hole is provided on the isolation plate 4, and the methane gas can also pass through the through hole on the isolation plate 4, thereby reducing the damage to the sensing part 5 caused by the methane gas. Therefore, in the present invention, a relatively low-power air pump can be selected, as long as there is sufficient methane gas to pass through the sensing part 5. Therefore, the present invention only requires a relatively low-power air pump, and the power consumption is low.

[0033] Preferably, an elastic baffle is provided on the isolation plate 4, which can be opened or closed. At the beginning of the measurement, the elastic baffle is opened to quickly remove the gas in the gas pool; during the actual measurement, the elastic baffle is closed, and methane gas only passes through the through hole 54.

[0034] Preferably, to enhance the strength of the sensor 5, the sensor 5 is adhered to a film with a through hole, which does not absorb the light emitted by the light source; or the sensor 5 is adhered to a wire mesh, which has high strength and can pass methane gas.

[0035] like Figure 3 As shown, the first optical train 3 includes a convex lens 31, a plano-concave lens 32, and a plano-convex lens 33. After emitting a spherical wave from the light source 2, it is converted into parallel light by the convex lens 31. This parallel light then passes through the plano-concave lens 32 and the plano-convex lens 33 to form an expanded beam of parallel light. This means that the first optical train 3 implements a beam expansion function. This allows for more through holes 54 to be provided in the sensing unit 5 to facilitate the passage of methane gas. The light detector 7 then detects the transmission spectrum of a larger area of the Fabry-Perot resonant cavity, resulting in more accurate measurement results.

[0036] In the present invention, the second optical system 6 is a convex lens. Light emitted from the right side of the sensor 5 passes through the second optical system 6 and is then focused on the probe of the light detector 7.

[0037] Preferably, the air outlet 8 and the light source 2 are arranged on the same side wall of the gas pool 1 where the light source is arranged. If the light source 2 is arranged on the left side wall of the gas pool 1, the air outlet 8 is also arranged on the left side wall of the gas pool 1, the air outlet 8 is closer to the light source 2, and the heat generated by the light source 2 is more easily carried away from the gas pool 1 by the methane gas. Furthermore, the air outlet 8 is arranged on the lower side of the light source 2. The molecular weight of methane gas is 16, which is less than the average molecular weight of air, and the methane gas is more located on the upper side of the gas pool 1. By arranging the air outlet 8 on the lower side of the light source 2, the methane gas can pass through the area where the light source 2 is located more and take away more heat generated by the light source 2, thereby lowering the temperature in the gas pool 1, reducing the influence of the heat generated by the system on the optical characteristics of the sensing part 5, and further improving the stability of the system operation.

[0038] Furthermore, if Figure 4 As shown, a local block 55 is provided between adjacent through holes 54. The material of the local block 55 is different from that of the sensitive layer 52. The material of the local block 55 is silicon or precious metal. The local block 55 limits Figure 4 The light field distribution in the up-down direction generates a stronger light field distribution at the through hole 54. When the refractive index of the sensitive layer 52 changes, the resonance wavelength of the Fabry-Perot cavity moves more, thereby achieving higher sensitivity in detecting the methane gas concentration.

[0039] Preferably, the present invention further comprises a dust filter, which is arranged on the air inlet 9 to filter out dust and prevent dust from clogging the through hole.

[0040] Preferably, the through hole 54 is truncated cone-shaped, with a larger bottom area on the side of the air inlet 9 and a smaller bottom area on the side of the air outlet 8. This allows more methane gas molecules to accumulate within the through hole 54, which can further change the refractive index of the sensitive layer 52 and thus the resonant wavelength of the Fabry-Perot cavity, thereby achieving more sensitive methane gas concentration detection.

[0041] In summary, the present invention uses a Fabry-Perot resonant cavity to achieve methane gas concentration detection. The material in the sensitive layer 52 is located in the Fabry-Perot resonant cavity. Under the action of methane gas, the refractive index of the sensitive layer 52 changes, thereby causing the resonant wavelength of the Fabry-Perot resonant cavity to shift. Methane gas detection is achieved through the shift of the resonant wavelength of the Fabry-Perot resonant cavity. The present invention proposes a new method and mechanism for detecting methane gas concentration, and also achieves high-precision and high-sensitivity detection of methane gas concentration.

[0042] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A methane detection system based on a Fabry-Perot cavity, characterized by: The invention comprises a gas pool, a light source, a first optical system, an isolation plate, a sensing part, a second optical system, a light detector, an air inlet, and an air outlet; the sensing part is fixed in the middle of the isolation plate, the sensing part and the isolation plate divide the gas pool into two chambers, the light source and the first optical system are arranged in one chamber, the second optical system and the light detector are arranged in the other chamber, the air inlet and the air outlet are respectively arranged on the side walls of the two chambers; the light source emits broadband light, and the broadband light passes through the first optical system and then enters the gas pool; Light is irradiated onto one side of the sensing portion, exits from the other side of the sensing portion, and then converges onto the light detector via the second optical assembly. The sensing portion includes a first limiting film layer, a sensitive layer, and a second limiting film layer arranged in sequence. Through holes are provided in the first limiting layer, the sensitive layer, and the second limiting layer. The material of the sensitive layer is Xuefan-A or Xuefan-E. The through holes are periodically distributed and truncated cone-shaped. The bottom area of the through holes is larger on the air inlet side and smaller on the air outlet side.

2. The methane detection system based on a Fabry-Perot cavity according to claim 1, wherein: The first optical system includes a convex lens, a plano-concave lens, and a plano-convex lens.

3. The methane detection system based on the Fabry-Perot cavity according to claim 1, wherein: The second optical system is a convex lens.

4. The methane detection system based on a Fabry-Perot cavity according to claim 1, wherein: The air inlet is arranged in the cavity on one side of the detector, and the air outlet is arranged in the cavity on one side of the light source.

5. The methane detection system based on the Fabry-Perot cavity according to claim 4, characterized in that: The air outlet and the light source are arranged on the same side wall.

6. The methane detection system based on the Fabry-Perot cavity according to claim 5, characterized in that: The air outlet is arranged at the lower side of the light source.

7. The methane detection system based on a Fabry-Perot cavity according to claim 1, wherein: Local blocks are provided between adjacent through holes, and the material of the local blocks is different from that of the sensitive layer.

8. The methane detection system based on a Fabry-Perot cavity according to any one of claims 1 to 7, characterized in that: The first limiting film layer and the second limiting film layer are made of silicon.

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