A dual-band infrared filter for synchronous detection of methane and carbon monoxide and a preparation method thereof

Abstract

The present application relates to a kind of dual-band infrared filter for methane and carbon monoxide synchronous detection and preparation method, including front film system, substrate and back film system;The front film system and back film system are all alternately stacked by germanium layer and zinc sulfide film layer;The working band of the dual-band infrared filter is 3300-3400nm and 4600-4700nm.The present application is by respectively setting main peak film system structure and secondary peak film system structure on the both sides of substrate, realizes the efficient antireflection of 3300-3400nm (CH4) and 4600-4700nm (CO) two characteristic bands, and the interference light flux of other band is deeply inhibited;Solve the technical problem of high sensitivity, low crosstalk synchronous detection of CH4 and CO in infrared gas sensing system, provide a new scheme for the development of compact, high-performance dual-gas sensor.

Description

Technical Field

[0001] This invention belongs to the field of infrared optical element technology, and specifically relates to a dual-band infrared filter for simultaneous detection of methane and carbon monoxide and its preparation method. Background Technology

[0002] Dual-band infrared filters are selectively highly transparent to two specific wavelengths, while highly cut off to other wavelengths outside their high-transmittance bands. They are primarily used in infrared spectroscopy detection systems. With increasing demands for industrial safety and environmental monitoring, there is an urgent need for infrared sensors capable of simultaneously, rapidly, and accurately detecting multiple hazardous gases. Methane (CH4) and carbon monoxide (CO) are two common and hazardous gases, exhibiting sharp characteristic absorption peaks in the infrared band. The main absorption band of CH4 is around ~3.3µm, and that of CO is around ~4.6µm.

[0003] Currently, infrared gas sensors capable of simultaneously detecting CH4 and CO mostly employ two independent single-band filters, each aligned with its respective absorption peak, achieving spectroscopic detection via a filter wheel or two independent detector channels. This approach results in a complex system structure, large size, high cost, and response speed limited by mechanical switching. While general-purpose dual-band filters exist, their spectral design is typically broad and not optimized for the precise absorption peaks of the specific gas pair CH4 and CO. This leads to insufficient detection sensitivity, inadequate suppression of background stray light, and spectral crosstalk between the two detection channels, ultimately affecting the sensor's detection limit and measurement accuracy. Therefore, there is an urgent need in the field for a dedicated dual-band infrared filter for high-sensitivity, low-crosstalk simultaneous detection of CH4 and CO. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a dual-band infrared filter for simultaneous detection of methane and carbon monoxide and its preparation method, aiming to solve the technical difficulties of high sensitivity and low crosstalk in the simultaneous detection of CH4 and CO gases.

[0005] This invention provides a dual-band infrared filter for simultaneous detection of methane and carbon monoxide, comprising a front film system, a substrate, and a back film system; both the front and back film systems are composed of alternating layers of germanium and zinc sulfide; the operating wavelengths of the dual-band infrared filter are 3300-3400 nm and 4600-4700 nm.

[0006] Preferably, the substrate is a germanium substrate.

[0007] Preferably, the substrate has a diameter of 10-30 mm and a thickness of 0.5-3 mm.

[0008] Preferably, the membrane structure of the front-side membrane system is as follows: Sub / 180.00H 485.50L 260.03H 66.98L 375.54H 759.18L 84.75H 435.83L 228.09H 380.73L 217.32H 431.36L 266.78H 636.61L 225.62H 412.18L 142.91H 439.78L 204.67H 379.50L 286.18H 628.46L 233.07H 376.88L 197.81H 339.97L 132.47H 129.32L 163.33H 300.76L 161.84H 289.49L 137.30H 205.91L 157.91H 324.26L 167.26H 479.61L / Air; where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 1700nm.

[0009] Preferably, the total number of layers in the front film system is 35 to 40.

[0010] Preferably, the membrane structure of the back membrane system is as follows: Sub / 120H 83.57L 946.87H 111.09L 2422.35H 567.58L 408.85H 68.26L 1237.05H 86.94L 681.41H 159.59L 836.67H 482.21L 323.72H 782.3L 342.39H 640.09L 379.02H 616.34L 321.83H 500.95L 354.22H 729.56L 304.6H 716.59L 308.77H 708.98L 332.53H 612.19L 355.36H 531.99L 532.1H 146.55L 79.68H 217.76L 119.56H 183.6L 128.08H 224.81L 151.66H 222.75L 73.5H 282.91L 205.95H 172.86L 88.03H 323.65L 62.09H 191.82L 146.52H 440.8L / Air, where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 5700nm.

[0011] Preferably, the total number of layers in the back film system is 50 to 55.

[0012] This invention also provides a method for preparing a dual-band infrared filter for simultaneous detection of methane and carbon monoxide, comprising the following steps:

[0013] (1) The substrate is ultrasonically cleaned and dried;

[0014] (2) Baking and heating the substrate under vacuum conditions;

[0015] (3) The front side of the substrate is treated with a high-energy ion beam, and then a film structure is deposited on the front side of the substrate. Then, annealing is performed. After cooling to the specified temperature, the substrate is first placed and then air is introduced.

[0016] (4) Repeat steps (1) to (3) to deposit a film structure on the back of the substrate to obtain the dual-band infrared filter.

[0017] Preferably, the deposition process in steps (3) and (4) uses an electron beam and 12-hole steric evaporation coating machine with a 12-hole crucible.

[0018] Preferably, the parameters for processing the front side of the substrate with a high-energy ion beam in step (3) are: anode voltage 180V, anode current 4A, cathode current 21A, and bombardment time 15 minutes.

[0019] Preferably, the annealing conditions in step (3) are: annealing temperature of 180℃, constant temperature time of 1 hour, cooling rate of 0.8~1℃ / min, and point venting operation.

[0020] Beneficial effects

[0021] This invention achieves highly efficient anti-reflection in the two characteristic wavelength bands of 3300-3400nm (CH4) and 4600-4700nm (CO) by setting a main peak film structure and a secondary peak film structure on both sides of the substrate, and deeply suppresses the interference light flux in other wavelength bands. It solves the technical problem of high-sensitivity, low-crosstalk synchronous detection of CH4 and CO in infrared gas sensing systems, and provides a new solution for the development of compact, high-performance dual gas sensors. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the dual-band infrared filter of the present invention; wherein, 1-front film system; 2-substrate; 3-back film system.

[0023] Figure 2 This is a graph showing the transmittance of the main peak (front) membrane system in Example 1.

[0024] Figure 3 This is a graph showing the permeability of the secondary peak (back side) membrane system in Example 1.

[0025] Figure 4 The transmittance curve of the dual-band infrared filter prepared in Example 1.

[0026] Figure 5 This is a schematic diagram of the process for preparing the dual-band infrared filter of the present invention. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] Example 1

[0029] Depend on Figure 1 As shown, this embodiment provides a dual-band infrared filter for simultaneous detection of methane and carbon monoxide, comprising a front film system, a substrate, and a back film system; both the front and back film systems are composed of alternating layers of germanium and zinc sulfide; the substrate is a germanium substrate with a diameter of 12.7 mm (0.5 inches) and a thickness of 1.0 mm. The front film system has a total of 38 layers, and the back film system has a total of 52 layers.

[0030] Compared with the prior art, the advantages of this invention are that it achieves high-efficiency anti-reflection in the characteristic band of methane (3300-3400nm) and the characteristic band of carbon monoxide (4600-4700nm), while highly blocking other bands outside the high-reflection band. This provides a core optical element for the dual-gas synchronous detection system, which has significant advantages such as high detection sensitivity and low channel crosstalk.

[0031] Depend on Figure 5 As shown, this embodiment also provides a method for preparing a dual-band infrared filter for simultaneous detection of methane and carbon monoxide, comprising the following steps:

[0032] An electron beam deposition process using a 12-hole crucible and a 12-position resistance evaporation deposition machine was used to prepare the optical film. The germanium material was deposited by electron beam evaporation, and the zinc sulfide material was deposited by molybdenum boat thermal evaporation. The evaporation rate of the germanium film was 6~8 Å / s, and the evaporation rate of the zinc sulfide film was 11~13 Å / s.

[0033] The film layer uses a quartz crystal oscillator signal feedback to adjust the evaporation source power in real time (PID control) to maintain the set evaporation rate, and automatically stops evaporation after the target thickness is reached.

[0034] (1) The substrate is cleaned by fully automatic ultrasonic cleaning, and after cleaning, the substrate is dehydrated by IPA.

[0035] (2) Place the substrate on the umbrella plate in the vacuum chamber of the coating machine, and perform vacuuming and baking heating. The baking temperature is set to 160°C and the baking time is greater than 120 minutes.

[0036] (3) Wait until the vacuum degree reaches 5.0x10 -4 After Pa, high-energy argon ions bombard the front side of the substrate for about 15 minutes. The bombardment parameters are: anode voltage 180V, anode current 4A, and cathode current 21A.

[0037] (4) A main peak film structure is deposited on the front side of the substrate, the main peak film structure comprising: Sub / 180.00H485.50L 260.03H 66.98L 375.54H 759.18L 84.75H 435.83L 228.09H 380.73L 217.32H431.36L 266.78H 636.61L 225.62H 412.18L 142.91H 439.78L 204.67H 379.50L286.18H 628.46L 233.07H 376.88L 197.81H 339.97L 132.47H 129.32L 163.33H 300.76L 161.84H 289.49L 137.30H 205.91L 157.91H 324.26L 167.26H 479.61L / Air; where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 1700nm. The obtained main peak film structure is composed of Figure 2 As shown, it meets the technical requirements of achieving high transmittance at 3300-3400nm & 4600-4700nm under the conditions of 23℃ and incident angle of 0°; and T≤1% at 2230-3190nm & 3510-4490nm.

[0038] (5) After the main peak film structure is deposited, the infrared filter is annealed at a temperature of 180°C for 1 hour and a cooling rate of 0.8~1°C / min.

[0039] (6) When the temperature drops to 80°C, manually release the air 6 times and then continue to introduce air into the vacuum chamber. The release should be 2 seconds and then 8 seconds.

[0040] (7) Clean the coated product with fully automatic ultrasonic cleaning. After cleaning, use IPA to dehydrate the substrate.

[0041] (8) Place the substrate on the umbrella plate in the vacuum chamber of the coating machine, and perform vacuuming and baking heating. The baking temperature is set to 160°C and the baking time is greater than 120 minutes.

[0042] (9) Wait until the vacuum degree reaches 5.0x10 -4 After Pa, a back-side sub-peak film structure is deposited on the other side of the substrate, including: Sub / 120H 83.57L 946.87H 111.09L 2422.35H 567.58L 408.85H 68.26L 1237.05H 86.94L 681.41H 159.59L 836.67H 482.21L 323.72H 782.3L 342.39H 640.09L 379.02H 616.34L 321.83H 500.95L 354.22H 729.56L 304.6H 716.59L 308.77H 708.98L 332.53H 612.19L 355.36H 531.99L 532.1H 146.55L 79.68H 217.76L 119.56H 183.6L 128.08H 224.81L 151.66H 222.75L 73.5H 282.91L 205.95H 172.86L 88.03H 323.65L 62.09H 191.82L 146.52H 440.8L / Air, where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 5700nm. The obtained secondary peak film structure is composed of Figure 3 As shown, it meets the technical requirements of achieving high transmittance at 3300-3400nm & 4600-4700nm under the conditions of 23℃ and incident angle of 0°; and T≤1% in visible light -2250nm & 4810-6820nm.

[0043] (10) After the back film structure is deposited, the infrared filter is annealed at a temperature of 180°C for 1 hour and a cooling rate of 0.8~1°C / min.

[0044] (11) When the temperature drops to 80°C, manually release the air 6 times and then continue to introduce air into the vacuum chamber. The release should be 2 seconds and then 8 seconds.

[0045] Depend on Figure 4 As shown, the substrate described in this embodiment, after being coated on both sides, meets the technical requirements of T≥90% and Tavg≥92% for 3300-3400nm & 4600-4700nm under the conditions of 23℃ and incident angle of 0°; and T≤1% for visible light -3180nm & 3520-4480nm & 4820-6800nm. This dual-band infrared filter is marked and denoted as sample A.

[0046] Comparative Example 1

[0047] Fabrication of a universal dual-band filter

[0048] To verify the superiority of this invention in the detection of specific gases, a comparative filter was prepared. This comparative filter employs a different film system design than that of this invention, with a passband of the common 3800-4800 nm & 8000-10000 nm. It is designated as Sample B.

[0049] Performance testing and comparative analysis:

[0050] Sample A (the present invention) and sample B (the comparative example) were integrated onto the same non-dispersive infrared (NDIR) gas sensor platform. A standard mixed gas containing 500 ppm CH4 and 300 ppm CO was introduced into the sensor's gas chamber, and detection was performed under the same conditions.

[0051] Test method:

[0052] Record the output voltage signals of the two channels (corresponding to two passbands). The signal-to-noise ratio (SNR) is calculated as the ratio of the signal voltage to the noise voltage (measured when the target gas is absent). Crosstalk is calculated as the percentage of the signal generated in the other gas channel compared to the target channel signal when only one gas is present.

[0053] Test results: The test results are shown in the table below.

[0054]

[0055] Results analysis:

[0056] As shown in the table above, sample A, designed using the specific band of this invention, exhibits an extremely high signal-to-noise ratio (>48 dB) in the detection of CH4 and CO, indicating its extremely high detection sensitivity. Sample B, using a general band, suffers from a wide and complete passband (3800-4800nm ​​& 8000-10000nm), failing to precisely align with the sharp absorption lines of CH4 (~3.3µm) and CO (~4.6µm). This results in extremely weak characteristic absorption signals received by the detector, leading to a low signal-to-noise ratio (<5 dB) and rendering effective detection impossible. The filter of this invention (sample A) exhibits less than 1% crosstalk between the two channels, demonstrating its excellent band isolation capability.

[0057] in conclusion:

[0058] The above experiments fully demonstrate that this invention, by precisely aligning the dual-band wavelengths with the characteristic absorption peaks of CH4 and CO (3300-3400nm & 4600-4700nm), and combining this with specific film system design and fabrication processes, achieves highly sensitive, low-crosstalk simultaneous detection of these two gases. Its performance far surpasses that of general-purpose filters with mismatched wavelengths. Therefore, this invention provides an optimal optical solution for specific gas detection applications.

[0059] In addition, the reliability of the film layer of sample A was verified by constant temperature and humidity test at 85℃ and 85% relative humidity (referring to JESD22-A101 or related standards), and no film layer peeling was found.

[0060] In addition, sample A was subjected to three tensile tests using 3M 600 tape that meets the requirements of ASTM D3359 standard. No film peeling was found, indicating that the film of the filter has reliable adhesion.

[0061] It should be understood that the embodiments disclosed in this invention are only for illustrating the essence of the invention, and their details should not constitute a limitation on the scope of protection. For those skilled in the art, any modifications, substitutions, or variations made to the described embodiments without departing from the concept and principles of this invention, such as equivalent substitutions in membrane structure or process parameters, that achieve the same goal of highly sensitive simultaneous detection of methane and carbon monoxide, should be considered to be included within the scope defined by the claims of this invention.

Claims

1. A dual-band infrared filter for simultaneous detection of methane and carbon monoxide, characterized in that, It includes a front film system, a substrate, and a back film system; both the front and back film systems are composed of alternating layers of germanium and zinc sulfide; the operating wavelengths of the dual-band infrared filter are 3300-3400nm and 4600-4700nm. The membrane structure of the front-side membrane system is as follows: Sub / 180.00H 485.50L 260.03H 66.98L 375.54H 759.18L 84.75H 435.83L 228.09H 380.73L 217.32H 431.36L 266.78H 636.61L 225.62H 412.18L 142.91H 439.78L 204.67H 379.50L 286.18H 628.46L 233.07H 376.88L 197.81H 339.97L 132.47H 129.32L 163.33H 300.76L 161.84H 289.49L137.30H 205.91L 157.91H 324.26L 167.26H 479.61L / Air; where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 1700nm; The membrane structure of the back-side membrane system is as follows: Sub / 120H 83.57L 946.87H 111.09L 2422.35H 567.58L 408.85H 68.26L 1237.05H 86.94L 681.41H 159.59L 836.67H 482.21L 323.72H 782.3L 342.39H 640.09L 379.02H 616.34L 321.83H 500.95L 354.22H 729.56L 304.6H 716.59L 308.77H 708.98L 332.53H 612.19L 355.36H 531.99L 532.1H 146.55L 79.68H 217.76L 119.56H 183.6L 128.08H 224.81L 151.66H 222.75L 73.5H 282.91L 205.95H 172.86L 88.03H 323.65L 62.09H 191.82L 146.52H 440.8L / Air, where Sub represents the substrate, Air represents air, H represents the physical thickness of the germanium film layer, L represents the physical thickness of the zinc sulfide film layer, and the numbers in the film structure formula represent the physical thickness of the film layer in nm; the design wavelength of the film structure is 5700nm.

2. The dual-band infrared filter according to claim 1, characterized in that, The substrate is a germanium substrate.

3. The dual-band infrared filter according to claim 1, characterized in that, The substrate has a diameter of 10~30mm.

4. A method for preparing a dual-band infrared filter for simultaneous detection of methane and carbon monoxide as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) The substrate is ultrasonically cleaned and dried; (2) Baking and heating the substrate under vacuum conditions; (3) The front side of the substrate is treated with a high-energy ion beam, and then a film structure is deposited on the front side of the substrate. Then, annealing is performed. After cooling to the specified temperature, the substrate is first placed and then air is introduced. (4) Repeat steps (1) to (3) to deposit a film structure on the back of the substrate to obtain the dual-band infrared filter.

5. The preparation method according to claim 4, characterized in that, The deposition process in steps (3) and (4) uses an electron beam and 12-hole steric evaporation deposition machine with a 12-hole crucible.

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