Acetylene gas sensor

Abstract

The invention discloses an acetylene gas sensor, and belongs to the technical field of gas detection, the acetylene gas sensor is made based on a photonic crystal fiber, a gas hole structure in the photonic crystal fiber is formed by six large elliptical gas holes and a plurality of small circular gas holes, and the six elliptical gas holes and the plurality of circular gas holes are periodically arranged. A hexagonal lattice of a target lattice period is formed to restrain a transmission light field, on one hand, light field regulation and gas adsorption are optimized by utilizing anisotropy and large inner surface area of six large oval air holes, and the performance is improved; on the other hand, the actual operation difficulty of internal film coating and sensitive material coating processes is greatly reduced due to the large pore size, accurate control over the thickness of the nanogold film and the thickness of the acetylene gas sensitive film is facilitated, the manufacturing complexity of the acetylene gas sensor based on the photonic crystal fiber is reduced, and the yield is increased.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and more particularly to an acetylene gas sensor. Background Technology

[0002] Acetylene has an extremely wide explosive limit range (2.5%~81%), and it is prone to violent explosions when exposed to open flames, high heat, or static electricity, posing a threat to personnel and equipment. Furthermore, high concentrations of acetylene can cause asphyxiation or damage to the central nervous system, with the danger being particularly pronounced in confined spaces. Therefore, real-time monitoring of acetylene concentrations is crucial for preventing catastrophic accidents.

[0003] Photonic crystal fiber (PCF) sensors based on surface plasmon resonance (SPR) technology utilize the SPR effect through their unique microstructure design to respond to subtle changes in the refractive index of the medium, greatly enhancing the interaction between the evanescent field and the analyte gas, and enabling ultra-high sensitivity detection of gases. Compared with traditional electrochemical sensors, their resistance to electromagnetic interference, low transmission loss, and flexible functional modification properties make them more accurate and stable in the real-time monitoring of hazardous gases such as acetylene.

[0004] In the prior art, acetylene gas sensors are mainly based on photonic crystal fiber sensors, which achieve sensing by introducing functional coatings or fillers into their small, densely and periodically arranged circular air holes.

[0005] However, existing photonic crystal fiber sensor-type acetylene gas sensors use small, densely packed circular air holes as sensing units, resulting in a narrow process window for internal coating or material filling, extremely high operational precision requirements, and difficulty in effectively controlling coating thickness and uniformity. Consequently, the fabrication repeatability is poor and the yield is low. At the same time, in order to improve sensitivity, complex air hole arrangements or micro-nano-level auxiliary structures (such as suspended cores, multi-core couplings, etc.) are often relied upon. These designs are prone to introducing deformation and defects during fiber drawing and post-processing, which not only increases the manufacturing difficulty and cost, but also affects the mechanical stability and consistency of the acetylene gas sensor. Summary of the Invention

[0006] Therefore, it is necessary to provide an acetylene gas sensor to address the aforementioned technical problems.

[0007] The present invention adopts the following technical solution: This invention provides an acetylene gas sensor, comprising: a photonic crystal fiber, an acetylene gas sensitive membrane, and a gold nanofilm; The cross-section of the photonic crystal fiber includes six elliptical pores distributed at the center of the cross-section, and multiple circular pores distributed between the elliptical pores and the boundary of the cross-section. The six elliptical pores and the multiple circular pores are arranged periodically to form a hexagonal lattice of the target lattice period, which is used to constrain the transmitted light field; the area of ​​the elliptical pores is larger than the area of ​​the circular pores. A layer of nano-gold film is deposited on the inner surface of the six elliptical pores, and the gold film is used to excite the surface plasmon resonance effect of the photonic crystal fiber. An acetylene gas-sensitive membrane is attached to the inner surface of the gold film. The acetylene gas-sensitive membrane is used to adsorb acetylene gas molecules in the six elliptical pores, so as to modulate the transmission optical field in the photonic crystal fiber based on its own optical property changes. This allows the photonic crystal fiber to convert the concentration of acetylene into the displacement of the acetylene loss spectrum peak based on the transmission optical field and surface plasmon resonance effect.

[0008] Optionally, the target lattice period is 3.2 μm.

[0009] Optionally, the thickness of the gold film is 38 nm.

[0010] Optionally, the acetylene gas sensitive membrane is an acetylene gas sensitive membrane with a thickness of 200 nm made of tin dioxide.

[0011] Optionally, the ratio of the major axis radius to the semi-major axis radius of the elliptical pore is 1.5:1; the major axis radius is 1.2 μm, and the minor axis radius is 0.8 μm.

[0012] Optionally, the radius of the circular pore is 0.6 μm.

[0013] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: The photonic crystal fiber of this invention features a pore structure consisting of six large elliptical pores and multiple small circular pores arranged periodically to form a hexagonal lattice with a target lattice period, thereby constraining the transmitted light field. On one hand, the anisotropy and large internal surface area of ​​the six large elliptical pores optimize light field modulation and gas adsorption, improving performance without requiring complex pore arrangements or micro / nano-level auxiliary structures, thus enhancing the mechanical stability and consistency of the acetylene gas sensor based on photonic crystal fiber. On the other hand, the larger pore size significantly reduces the practical difficulty of internal coating and sensitive material coating processes, facilitating precise control of the thickness of the nano-gold film and the acetylene gas sensitive film, reducing the manufacturing complexity of the acetylene gas sensor based on photonic crystal fiber, and improving the yield. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0015] Figure 1 A cross-sectional schematic diagram of an acetylene gas sensor provided by the present invention; Figure 2 A schematic diagram illustrating the relationship between acetylene gas volume concentration and the refractive index of a sensitive material, provided by this invention; Figure 3 This invention provides a schematic diagram illustrating the relationship between the size of the lattice period and the acetylene loss spectrum. Figure 4 This invention provides a schematic diagram illustrating the relationship between the thickness of a nano-gold film and the acetylene loss spectrum. Figure 5 A schematic diagram illustrating the relationship between the thickness of an acetylene gas-sensitive membrane and the acetylene loss spectrum provided by this invention; Figure 6 This invention provides a schematic diagram illustrating the relationship between the aperture radius and the acetylene loss spectrum. Figure 7 A schematic diagram of electric field distribution provided by the present invention; Figure 8 A schematic diagram of a height expression provided by the present invention; Figure 9 A schematic diagram illustrating the shift in loss spectrum with varying acetylene concentration, provided by this invention. Figure 10 This is a schematic diagram illustrating the functional relationship between the peak value of the loss spectrum and the change in acetylene concentration, as provided by the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0017] Currently, traditional acetylene gas detection mainly relies on methods such as electrochemical sensors, semiconductor sensors, and traditional fiber optic sensors.

[0018] Although these sensors have achieved the detection of acetylene concentration to a certain extent, they still have the following obvious defects: (1) Limited sensitivity: especially the detection response to ultra-low concentration acetylene (such as below 0.5%) is weak, making it difficult to meet the requirements of high-precision monitoring; (2) Susceptible to electromagnetic interference: electrochemical sensors have poor stability in complex industrial environments and the signal is easily interfered with; (3) Complex structure and high manufacturing cost: some fiber optic sensors rely on complex microstructures, which are difficult to process and not conducive to large-scale preparation; (4) Short service life: the metal sensitive layer is easy to oxidize, resulting in rapid performance decay; (5) Poor real-time performance: traditional sensing methods have slow response speed and cannot achieve real-time monitoring and early warning in a true sense.

[0019] In recent years, thanks to the flexibility of its geometric design and the uniqueness of its light-guiding mechanism, photonic crystal fibers have gradually become an important development direction in related fields due to their excellent scientific research value and market application prospects. Furthermore, by combining surface plasmon resonance technology, their sensing sensitivity has been further improved.

[0020] Traditional photonic crystal fiber acetylene sensors of this type often suffer from the following structural limitations: First, they typically use small, densely packed circular air holes as sensing elements, resulting in a narrow process window for internal coating or material filling, extremely high operational precision requirements, and difficulty in effectively controlling coating thickness and uniformity, thus leading to poor fabrication repeatability and low yield. Second, to improve sensitivity, they often rely on complex air hole arrangements or micro / nano-level auxiliary structures (such as suspended cores, multi-core couplings, etc.). These designs are prone to introducing deformation and defects during fiber drawing and post-processing, which not only increases manufacturing difficulty and cost but also affects the mechanical stability and consistency of the sensor. Third, most structures do not adequately consider the protection of the sensing layer and metal layer during long-term use. The metal layer, directly exposed to the test environment, is prone to oxidation and failure, leading to rapid performance degradation of the sensor.

[0021] This invention addresses the problems of poor real-time performance in current single-gas concentration detection and limited accuracy in detecting small molecule compounds and ultra-low concentration analytes. It proposes and simulates a six-hole PCF-SPR acetylene sensor based on a composite thin film filling. First, a gold film is deposited inside the elliptical pores to excite surface plasmon resonance. Then, a SnO2 thin film is added. This film not only enhances the gas detection sensitivity as an acetylene-sensitive material but also isolates oxygen to slow down the oxidation of the metal layer, effectively extending the service life of the photonic crystal fiber. Combined with a side-hole structure, this sensor measures the acetylene concentration by measuring the displacement of the loss peak, exhibiting high accuracy. The maximum sensitivity was obtained by simulating the loss spectrum curve of acetylene (0–0.5%) using COMSOL.

[0022] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Figure 1 This is a cross-sectional schematic diagram of an acetylene gas sensor according to the present invention. Figure 1 In the diagram, yellow represents the gold layer (TM), and green represents the acetylene gas-sensitive membrane (TC). The elliptical pores have a minor axis radius of a1 (preferably 0.8 μm) and a major axis radius of b1 (preferably 1.2 μm), while the small circular pores have a radius of r, and the lattice period is a. Figure 1 As can be seen, the acetylene gas sensor includes: a photonic crystal fiber.

[0024] The cross-section of the photonic crystal fiber includes six elliptical pores distributed at the center of the cross-section, and multiple circular pores distributed between the elliptical pores and the boundary of the cross-section.

[0025] Six elliptical pores and multiple circular pores are arranged periodically to form a hexagonal lattice of the target lattice period, which is used to constrain the transmitted light field; the area of ​​the elliptical pores is larger than the area of ​​the circular pores.

[0026] A layer of nano-gold film is coated on the inner surface of the six elliptical pores. This gold film is used to excite the surface plasmon resonance effect of the photonic crystal fiber.

[0027] An acetylene gas-sensitive membrane is attached to the inner surface of the gold film. This acetylene gas-sensitive membrane is used to adsorb acetylene gas molecules in six elliptical pores. Based on the changes in its own optical properties, it modulates the transmission optical field in the photonic crystal fiber, so that the photonic crystal fiber converts the concentration of acetylene into the displacement of the acetylene loss spectrum peak based on the transmission optical field and surface plasmon resonance effect.

[0028] In the photonic crystal fiber-based acetylene gas sensor of this invention, the elliptical vent serves as a key structure supporting the gold nanofilm and the acetylene gas-sensitive film. Its size must maximize the contact area with the gas to be measured while ensuring the stability of the fiber structure and effective mode field constraint. In one or more embodiments of this invention, the ratio of the major and minor axes of the elliptical vent can be 1.5:1. At this ratio, the elliptical vent provides sufficient surface area for uniformly coating the functional thin film. Simultaneously, maintaining the structural integrity with the surrounding small circular vents and the outer edge of the fiber is beneficial for exciting a stable and strong surface plasmon resonance effect.

[0029] In simulating the acetylene gas sensor provided by this invention, in order to accurately calculate the limiting loss of light during transmission, a perfectly matched layer (PML) is applied to the periphery of the photonic crystal fiber, and the PML is set to 1µm.

[0030] Unlike traditional photonic crystal fiber sensor designs, this invention incorporates six large-scale elliptical pores within the cladding. Elliptical pores offer significant advantages over circular pores in photonic crystal fiber sensors, primarily due to their anisotropic geometric properties. By adjusting the ratio of the major and minor axes and the orientation of the elliptical pores, the birefringence and dispersion characteristics of the fiber can be flexibly controlled, thereby enhancing the interaction between light and the analyte (acetylene) and improving sensing sensitivity—a particularly noticeable effect in surface plasmon resonance sensors. Furthermore, the elliptical pores provide a larger internal surface area, and their specific arrangement imparts a negative Poisson's ratio effect to the fiber structure, enhancing its resistance to compression and deformation. Ultimately, this invention enables the acetylene gas sensor to achieve high sensitivity and selectivity while possessing superior design freedom and mechanical stability.

[0031] This invention simultaneously coats gold and acetylene gas-sensitive materials to enhance the response of the loss spectrum to acetylene gas concentration. Since the coating process is carried out within large pores, the actual operational difficulty is significantly reduced compared to small pores, which facilitates more precise control of the coating thickness during actual operation. Simultaneously, the relatively large distance between the six elliptical pores and the fiber boundary ensures the stability of the fiber structure, simplifies the drawing difficulty of the fiber fundamental mode, and reduces the complexity of the manufacturing process. Furthermore, it mitigates, to some extent, the asymmetry caused by fiber deformation due to external pressure, thereby reducing refractive index errors and improving detection accuracy.

[0032] This invention employs a coating process to construct a nano-gold film on the inner surface of an elliptical air hole to excite a surface plasmon resonance effect. Based on this, a tin dioxide functional thin film is further modified. This tin dioxide thin film not only serves as a sensitive layer for acetylene gas, significantly improving detection sensitivity through its refractive index variation with gas concentration, but also effectively blocks oxygen from the environment, inhibiting the oxidation process of the metal layer and thus extending the lifespan of the photonic crystal fiber sensor. Combined with the side-hole structure design, this sensor achieves high-precision and high-accuracy measurement of acetylene gas concentration by monitoring the shift of the loss peak position in the transmission spectrum.

[0033] The following is a separate explanation of each part, including the acetylene gas sensitive layer: The detection of acetylene gas is highly dependent on the gas-sensitive material; however, such materials often possess broad-spectrum sensitivity, responding to a variety of gases. This invention uses tin dioxide as the acetylene gas-sensitive material, and the acetylene-sensitive material exhibits a linear relationship with the volume concentration of acetylene gas, such as... Figure 2 As shown, Figure 2 This is a schematic diagram illustrating the relationship between acetylene gas volume concentration and the refractive index of a sensitive material in this invention. Figure 2The horizontal axis represents the volume concentration of acetylene gas, set within the low concentration range of 0-0.5%; the vertical axis represents the refractive index of the acetylene gas-sensitive material.

[0034] When the volume fraction of acetylene is 0-0.5%, the refractive index of this sensitive material is... It is negatively correlated with acetylene gas concentration, that is: (1).

[0035] In the formula, This represents the volume fraction of acetylene gas.

[0036] Quartz crystal: The primary background material of the sensing device is fused silica. For silica, its wavelength-dependent refractive index can be calculated using the Sellmeier equation, as shown in the following formula: (2) In the formula, The wavelength-dependent refractive index of fused silica. The incident wavelength; , , , , and All are constants in the Sellmeier equation. Their related dielectric constants can be calculated using the Drude-Lorentz formula, i.e.:

[0037] (3) In the formula, and These are the relevant dielectric constants of the metals. The real and imaginary parts, the dielectric constant of the metal The value is 9.84. The frequency of the incident wavelength, The plasma frequency is 1.36 × 10⁻⁶. 16 rad / s; The damping frequency is 1.45 × 10⁻⁶. 14 rad / s.

[0038] The formula for calculating fiber core loss L is: (4) In the formula, The effective refractive index of the optical fiber The imaginary part.

[0039] Gold film: For gold nanofilm materials, the relationship between their dielectric constant and refractive index can be described by the Drude model, as follows: (5) (6) in, , and These represent the dielectric constant of gold, plasma wavelength, and collision wavelength, respectively. and All are constants, and their values ​​are respectively = 1.4541×10 -7 m、 = 1.7614×10 -5 m. The real and imaginary parts of the complex refractive index of the gold nanofilm are nm and km, respectively, where nm is the real part of the complex refractive index, corresponding to the phase velocity of light propagating in the material; km is the imaginary part of the complex refractive index, corresponding to the absorption (extinction) characteristics of the material, and its light intensity transmittance. for:

[0040] (7) In the formula, For reference dielectric constant, The thickness of the gold film is given by the formula; the larger the imaginary part, the stronger the absorption and the lower the transmittance; the greater the thickness, the more severe the light attenuation. 。

[0041] Simulation parameter optimization: Given that minute changes in the structural parameters of photonic crystal fibers will significantly affect their optical properties and directly determine the performance of sensors, this invention also conducts parameter analysis. Combining images from a one-dimensional plotting group, it focuses on analyzing three key design factors: lattice period size, nano-gold film thickness, and acetylene gas sensitive layer thickness. The response law of parameter changes to sensor performance is discussed in detail, aiming to provide a clear theoretical basis for the optimized design of high-performance sensors.

[0042] Regarding the size of the lattice period Figure 3 This is a schematic diagram illustrating the relationship between the size of the lattice period and the acetylene loss spectrum in this invention. Figure 3The horizontal axis represents the wavelength, typically within the range of 0.56-0.6 μm, in µm; the vertical axis represents the lattice period, also in µm. The lattice period directly determines the bandgap position and optical field confinement capability of the photonic crystal fiber, ultimately affecting the sensor's operating wavelength, sensitivity, and the interaction strength between the mode field and the analyte. In this study, different parameter selections of the sensor's lattice period 'a' were investigated. It was found that when the lattice period 'a' was adjusted from 2.8 μm to 3.6 μm, the loss spectrum did not exhibit a blue shift or red shift. However, the confinement loss decreased with increasing lattice period. To prevent excessively high confinement loss from adversely affecting the sensing range, a lattice period 'a' of 3.2 μm is preferred as the optimal parameter.

[0043] Regarding the thickness of the nano gold film Figure 4 This is a schematic diagram illustrating the relationship between the thickness of a nano-gold film and the acetylene loss spectrum in this invention. Figure 4 The horizontal axis represents the wavelength, set within the common range of 0.56-0.6 nm; the vertical axis represents the thickness of the gold nanofilm, in nm. The thickness (tm) of the gold nanofilm is a crucial factor in exciting surface plasmon resonance in photonic crystal fibers. This invention, through simulation, reveals the influence of the gold nanofilm thickness on the loss spectral characteristics. The study found that in acetylene photonic crystal fiber sensors, when the thickness (tm) of the coated metal film increases from 34 nm to 42 nm, the loss spectrum exhibits a significant redshift, while the confinement loss amplitude decreases significantly and the full width at half maximum (FWHM) expands significantly. To optimize the center wavelength position and select a suitable confinement loss for detection, a gold nanofilm thickness of 38 nm is preferably considered the optimal parameter.

[0044] Regarding the thickness of the acetylene gas-sensitive membrane Figure 5 This is a schematic diagram illustrating the relationship between the thickness of an acetylene gas-sensitive membrane and the acetylene loss spectrum in this invention. Figure 5The wavelength is still used as the horizontal axis, ranging from 0.56 to 0.6 nm; the vertical axis is changed to the thickness of the acetylene gas-sensitive film, in nm. The acetylene gas-sensitive film (tc) is a key component that gives photonic crystal fiber optic sensors selectivity and functionality. It modulates the transmitted light field in the fiber by specifically adsorbing target gas molecules, causing changes in its optical properties, and converting gas concentration information into a highly sensitive and specific optical signal, ultimately achieving accurate detection by the sensor. Research has found that when the acetylene gas-sensitive film thickness (tc) is adjusted from 180 nm to 220 nm, the loss resonant wavelength shifts towards longer wavelengths, exhibiting a significant redshift, while the loss peak continuously increases. With an acetylene gas-sensitive film thickness of 200 nm, the loss spectrum curve as a function of wavelength shows high smoothness, demonstrating superior performance in acetylene gas concentration detection. Therefore, when designing sensors, it is preferable to set the acetylene gas-sensitive film thickness to 200 nm.

[0045] Regarding the size of the aperture of a circular pore Figure 6 This is a schematic diagram illustrating the relationship between the aperture radius and the acetylene loss spectrum in this invention. Figure 6 The mid-wavelength remains on the horizontal axis, ranging from 0.56 to 0.6 μm; the vertical axis represents the aperture radius, also in μm. The aperture radius directly determines the mode field distribution and evanescent field intensity of the photonic crystal fiber. Studies have shown that increasing the aperture enhances the interaction between light and the analyte, thus improving sensitivity; however, excessive enlargement may weaken the light confinement or alter the phase-matching conditions. In this study, when the aperture radius *r* in the acetylene photonic crystal fiber sensor changed from 0.5 μm to 0.7 μm, the loss spectrum did not exhibit a blue-shift or red-shift. The confinement loss decreased slightly with increasing lattice period. Therefore, to enhance measurement accuracy and sensitivity, a aperture radius of 0.6 μm is preferred in the model.

[0046] Table 1 illustrates the effect of model parameters on acetylene loss spectra. Table 1. Effect of model parameters on acetylene loss spectrum Key parameters of the model were optimized, and an optimal parameter combination was determined. This parameter combination significantly improved the accuracy of the sensor in acetylene detection and ensured optimal detection results. Specific parameter selections are detailed in Table 2.

[0047] Table 2 Selection of Sensor Model Parameters Simulation results and analysis: Based on the foregoing, a simulation experiment was conducted using COMSOL simulation software. The main purpose was to verify the accuracy and feasibility of the surface plasmon resonance (SPR) acetylene gas sensor in a six-hole photonic crystal fiber. According to plasmon resonance theory, a significant SPR effect will occur when the real part of the effective refractive index of the fiber core fundamental mode is equal to the real part of the effective refractive index of the surface plasmon resonance mode. Figure 7 and Figure 8 The diagrams show the electric field distribution and height expression of the sensor model at a wavelength of 580 nm under optimal parameter configuration. The diagrams demonstrate that the acetylene photonic crystal fiber sensor exhibits uniform energy distribution, proving the rationality of its structural design.

[0048] This invention simulates and analyzes acetylene gas concentration. Given the extremely wide explosion limit range of acetylene gas, this invention sets the acetylene gas concentration within the range of 0–0.5%, and performs successive scans at 0.1% intervals. Because there is a linear correlation between the refractive index of the acetylene gas-sensitive membrane and the acetylene concentration, this invention achieves accurate measurement of acetylene gas concentration by measuring the shift of the loss spectrum peak at different acetylene concentrations. Figure 9 This is a schematic diagram illustrating the shift in the loss spectrum of the present invention as the acetylene concentration changes. The wavelength is used as the horizontal axis, with the range set between 0.56 and 0.6 μm. The vertical axis represents the acetylene gas concentration, which is set at a lower concentration, i.e., between 0 and 0.5%.

[0049] The study found that as the concentration of acetylene gas increases, the peak value of the loss spectrum decreases and shifts slightly towards shorter wavelengths, exhibiting a linear trend. The peak wavelength was measured given the acetylene concentration, and a plot was then created. With concentration change The slope of the fitted straight line is the sensitivity K, which is the scatter plot of the data. Figure 10 This is a schematic diagram illustrating the functional relationship between the peak value of the loss spectrum and the change in acetylene concentration in this invention. Figure 10 The horizontal axis represents the acetylene concentration; the vertical axis represents the magnitude of the loss spectrum peak.

[0050] Using the concentration range of 0.1% to 0.5% and its corresponding peak wavelength, the sensor sensitivity K can be calculated to be -8 nm / %. Furthermore, the acetylene concentration can be measured based on the displacement of the loss peak per unit wavelength, as shown in the following formula: (8) The sensor designed in this invention determines the concentration of acetylene gas by measuring the displacement of the loss peak, exhibiting strong anti-interference capabilities and high measurement accuracy. Furthermore, this sensor incorporates surface plasmon resonance technology, overcoming the limitations of the traditional diffraction limit and significantly improving transmission performance. Compared to acetylene gas sensors currently on the market, the sensor designed in this invention achieves a significant improvement in stability and possesses higher sensitivity.

[0051] This invention designs and studies a six-hole photonic crystal fiber acetylene sensor based on a gold film and a tin dioxide gas-sensitive film coating. To enhance the response of the loss spectrum to acetylene concentration, six ultra-large elliptical pores are introduced into the cladding, within which a nano-gold film and an acetylene-sensitive film are added from the inside out. By combining surface plasmon resonance technology, the sensitivity and selectivity of acetylene gas detection are significantly improved.

[0052] The influence of key structural parameters such as lattice period, gold film thickness, gas-sensitive film thickness, and aperture radius on sensor performance was analyzed using the finite element simulation software COMSOL. An optimal parameter combination (a=3.2μm, tm=38 nm, tc=200 nm, r=0.6μm) was optimized. Simulation results show that the sensor exhibits good electric field distribution uniformity and a significant SPR effect at a wavelength of 580 nm, verifying the rationality of its structural design and its detection feasibility. Furthermore, this invention establishes a linear relationship between the shift of the acetylene loss spectrum peak and the change in acetylene concentration. Through least squares fitting, the function of the loss peak shift and acetylene concentration is obtained, leading to a sensor sensitivity of -8nm / %. This invention provides a novel fiber optic sensing solution for high-precision, high-stability real-time monitoring of acetylene gas, with promising application prospects in fields such as chemical safety production and environmental monitoring.

[0053] The perforation structure in the photonic crystal fiber of this invention consists of six large elliptical pores and multiple small circular pores, arranged periodically to form a hexagonal lattice with a target lattice period, thereby constraining the transmitted optical field. On one hand, the anisotropy and large internal surface area of ​​the six large elliptical pores optimize optical field modulation and gas adsorption, improving performance. On the other hand, the larger pore size significantly reduces the practical difficulty of internal coating and sensitive material coating processes, facilitating precise control of the thickness of the nano-gold film and the acetylene gas sensitive film. This reduces the manufacturing complexity of the acetylene gas sensor based on the photonic crystal fiber and improves the yield. A high-sensitivity and high-precision detection of low-concentration acetylene has been achieved: By employing a composite structure in which a gold film and a SnO2 sensitive layer are sequentially coated in an elliptical large-aperture cavity, and by exciting a surface plasmon resonance effect, the interaction between the evanescent field and acetylene gas is significantly enhanced. This structure can linearly convert changes in acetylene concentration (0~0.5%) into a precise shift of the loss spectrum peak position (sensitivity up to -8nm / %), thus overcoming the technical bottleneck of insufficient accuracy of traditional sensors for detecting small molecules and ultra-low concentration analytes.

[0054] Possessing excellent anti-electromagnetic interference capability and long-term stability: This invention is based on the all-optical photonic crystal fiber sensing principle, fundamentally avoiding the defects of electrochemical sensors that are susceptible to environmental electromagnetic interference. At the same time, the tin dioxide sensitive layer not only serves as a gas response medium, but also isolates oxygen and prevents oxidation of the internal gold film, thereby effectively delaying the degradation of sensor performance, significantly extending its service life, and overcoming the problems of easy aging and short lifespan of existing metal-based sensors.

[0055] The structural design balances high performance with good process feasibility: by using six specifically arranged elliptical side holes as functional areas, the anisotropy and large internal surface area are utilized to optimize light field modulation and gas adsorption, thereby improving performance. On the other hand, the larger hole size greatly reduces the actual operational difficulty of internal coating and coating of sensitive materials, which is conducive to achieving precise control of the thickness of gold film and sensitive layer, and solves the problems of complex manufacturing and low yield of traditional micro-nano structure sensors.

[0056] This solution provides a fast and reliable real-time monitoring solution. The sensor detects acetylene gas based on the optical loss peak shift, offering a rapid response and enabling quantitative analysis by establishing a direct functional relationship between wavelength and concentration. This approach overcomes the shortcomings of some existing sensors, such as slow response and high signal delay, and can meet the urgent needs of real-time, online monitoring of acetylene gas in fields such as chemical safety and environmental monitoring.

[0057] In summary, this invention systematically solves the key deficiencies of existing acetylene sensors in terms of sensitivity, anti-interference, durability, and real-time performance through an innovative composite thin film-filled six-hole photonic crystal fiber structure, providing a new gas sensing solution that is highly accurate, highly stable, and easy to implement.

[0058] It should also be noted that the terms "comprising," "including," or any other variations thereof in this invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in this invention, other elements not expressly listed may also be included.

[0059] The various embodiments in this invention are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0060] The above description is merely an embodiment of the present invention and is not intended to limit the 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 principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. An acetylene gas sensor, characterized by: Photonic crystal fiber, acetylene gas sensitive membrane, and gold nanofilm; The cross-section of the photonic crystal fiber includes six elliptical pores distributed at the center of the cross-section, and multiple circular pores distributed between the elliptical pores and the boundary of the cross-section. The six elliptical pores and the multiple circular pores are arranged periodically to form a hexagonal lattice of the target lattice period, which is used to constrain the transmitted light field; the area of ​​the elliptical pores is larger than the area of ​​the circular pores. A layer of nano-gold film is deposited on the inner surface of the six elliptical pores, and the gold film is used to excite the surface plasmon resonance effect of the photonic crystal fiber. An acetylene gas-sensitive membrane is attached to the inner surface of the gold film. The acetylene gas-sensitive membrane is used to adsorb acetylene gas molecules in the six elliptical pores, so as to modulate the transmission optical field in the photonic crystal fiber based on its own optical property changes. This allows the photonic crystal fiber to convert the concentration of acetylene into the displacement of the acetylene loss spectrum peak based on the transmission optical field and surface plasmon resonance effect.

2. The acetylene gas sensor as described in claim 1, characterized in that, The target lattice period is 3.2 μm.

3. The acetylene gas sensor as described in claim 1, characterized in that, The thickness of the gold film is 38 nm.

4. The acetylene gas sensor as described in claim 1, characterized in that, The acetylene gas sensitive membrane is an acetylene gas sensitive membrane with a thickness of 200 nm made of tin dioxide.

5. The acetylene gas sensor as described in claim 1, characterized in that, The ratio of the major axis radius to the semi-major axis radius of the elliptical pore is 1.5:1; the major axis radius is 1.2 μm, and the minor axis radius is 0.8 μm.

6. The acetylene gas sensor as described in claim 1, characterized in that, The radius of the circular pore is 0.6 μm.

Images