Optical fiber sensor for detecting acetone concentration and detection method

Abstract

The invention discloses an optical fiber sensor for detecting acetone concentration and a detection method. The optical fiber sensor comprises an acetone detection optical fiber, a coupler coupled with the acetone detection optical fiber, and an acetone sensing unit arranged in the coupler; the acetone sensitive unit comprises a light reflecting mirror directly facing the detection end of the acetone detection optical fiber during use and an acetone sensitive film arranged on the surface of the reflecting surface of the light reflecting mirror; and the acetone sensitive membrane is a ZIF-8 / NPC / APTES (Zeolite Imidazole Acid Frame-8) membrane which is composed of a zeolite imidazole acid framework, nitrogen-doped porous carbon and 3-aminopropyltriethoxysilane. When acetone in an external environment is transmitted to the acetone sensitive film through the coupler, after the acetone sensitive film absorbs the acetone, the refractive index is increased, the absorption intensity of light with the wavelength of 253 nm is enhanced, and the reflectivity is reduced, so that the intensity of light transmitted in the acetone detection optical fiber is reduced; accurate measurement of the acetone concentration in the environment can be realized through the variable quantity between the output light intensity and the input light intensity of the acetone detection optical fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of acetone concentration detection, and particularly to an optical fiber sensor and a detection method for detecting acetone concentration. Background Art

[0002] In the field of cultural relics protection, acetone is widely used as a common solvent, cleaning agent, and sealing and strengthening material. However, acetone has strong volatility, and when its gas reaches a certain concentration, it will cause damage to human health and cultural relics. As a public place, museums have visitors exhaling acetone gas, which will further increase the acetone concentration in the museum and exacerbate the risk of damage to cultural relics. The porous structure of stone and wooden cultural relics makes it easy for acetone to penetrate, resulting in the swelling and deformation of cultural relics and reacting with surface pigments to change color. In addition, acetone has good solubility in organic substances. When it adheres to paper cultural relics, it will dissolve the protective materials and further damage the cultural relics. Therefore, monitoring the acetone concentration in the collection environment is of great significance for protecting cultural relics and maintaining the physical health of visitors and staff.

[0003] Currently, the means for acetone concentration detection include gas chromatography, mass spectrometry, laser spectroscopy, and sensor methods. Gas chromatography, with its high accuracy and sensitivity, is suitable for the analysis of samples with high purity and low acetone content. However, complex samples need to be pretreated to improve the separation effect. Mass spectrometry is often used in combination with chromatography to provide accurate qualitative and quantitative analysis. Laser spectroscopy uses laser technology to perform spectral analysis on acetone gas, with high precision and sensitivity. However, due to the limitations of equipment cost and complexity, it is difficult to be applied to on-site rapid detection. Acetone detection devices based on sensors, such as semiconductor gas sensors, chemiluminescence sensors, electrochemical sensors, and low-frequency alternating current response sensors, etc., achieve quantitative analysis by detecting the change in the electrical signal or optical signal of the acetone concentration in the gas. These sensors have the advantages of small size, low price, high sensitivity, etc., and are suitable for on-site rapid detection and personal use. However, they also have the disadvantages of weak anti-environmental interference ability, poor selectivity, long recovery time, and the risks of discharge or corrosion, etc.

[0004] In recent years, fiber optic sensors have the advantages of no discharge risk, small geometric size, high sensitivity, fast response speed, and distributed measurement, etc., so they have become one of the most promising types of sensors in the field of on-line gas concentration detection technology. Fiber optic sensors have been developed for on-line detection of gas concentrations such as carbon dioxide, hydrogen, acetaldehyde, hydrogen sulfide, ethane, and volatile organic compounds. Among the fiber optic sensors for volatile organic compounds, fiber optic sensors such as the evanescent field type, surface plasmon resonance type, photoacoustic spectroscopy type, and photothermal spectroscopy type have high sensitivity detection capabilities for acetone gas, but their manufacturing processes are complex, the costs are high, they are sensitive to environmental change information, and the sensor selectivity is poor, which limits their wide application. Therefore, it is very necessary to design an acetone gas fiber optic sensor with high efficiency, low cost, strong anti-interference ability, and high selectivity. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the technical problem to be solved by the present invention is: how to provide a fiber optic sensor for detecting acetone concentration. When acetone in the external environment is transmitted to the acetone-sensitive film through the coupler, after the acetone-sensitive film absorbs acetone, its refractive index increases, the absorption intensity of the light with a wavelength of 253 nm increases, and the reflectivity decreases, causing the light intensity transmitted inside the acetone detection optical fiber to decrease, so that the change amount between the output light intensity and the input light intensity of the acetone detection optical fiber can be used to accurately measure the acetone concentration in the environment; and the acetone measurement result is not interfered by other gas components and humidity changes, and there is a linear relationship between the output signal of the fiber optic sensor and the acetone concentration.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A fiber optic sensor for detecting acetone concentration, comprising: an acetone detection optical fiber, a coupler coupled to the acetone detection optical fiber, and an acetone-sensitive unit disposed inside the coupler;

[0008] The acetone-sensitive unit includes a light reflector facing the detection end of the acetone detection optical fiber during use and an acetone-sensitive film disposed on the reflecting surface of the light reflector; the acetone-sensitive film is a ZIF-8 / NPC / APTES film composed of zeolitic imidazolate framework-8, nitrogen-doped porous carbon, and 3-aminopropyltriethoxysilane.

[0009] Preferably, the acetone-sensitive film is prepared by the following steps:

[0010] 1) Add 2-methylimidazole to deionized water, stir evenly and set aside;

[0011] 2) Put dry chrysanthemums into a tubular furnace and sinter in air to obtain nitrogen-doped porous carbon;

[0012] 3) Disperse the nitrogen-doped porous carbon into deionized water and perform ultrasonic treatment to obtain a nitrogen-doped porous carbon solution; dissolve Zn(NO3)2·6H2O into the nitrogen-doped porous carbon solution and stir to obtain a mixed solution;

[0013] 4) Mix the mixed solution with a 2-methylimidazole solution and stir at room temperature to obtain a mixture; transfer the mixture to a polytetrafluoroethylene-lined autoclave for heating; dry the heated product in air to obtain a gray powder, which is the ZIF-8 / NPC composite material;

[0014] 5) After ultrasonically cleaning the optical mirror with an ethanol or acetone solution to remove surface impurities, immerse it in an ethanol solution of 3-aminopropyltriethoxysilane; after taking out the optical mirror, alternately clean it with deionized water and ethanol and dry it for standby;

[0015] 6) Disperse the ZIF-8 / NPC composite material in ethanol to form a uniform suspension; coat it on the surface of the optical mirror by spin coating or dip coating method, and heat and cure the coated optical mirror to obtain the ZIF-8 / NPC / APTES film, which is the acetone-sensitive film.

[0016] Preferably, the acetone detection optical fiber includes an incident optical fiber, several receiving optical fibers, and an optical fiber holder; the first ends of the incident optical fiber and the several receiving optical fibers are fixed together by the optical fiber holder and the several receiving optical fibers are distributed around the incident optical fiber;

[0017] The first ends of the incident optical fiber and the several receiving optical fibers are the detection ends of the ketone detection optical fiber.

[0018] Preferably, an SMA optical fiber connector is connected to the second end of the incident optical fiber;

[0019] The second ends of the several receiving optical fibers fixed together are sequentially connected with an optical fiber collimator and an SMA optical fiber connector.

[0020] Preferably, the coupler is a hollow Teflon round tube with one end open and the other end sealed; the acetone detection optical fiber is coupled with the coupler by inserting it into the open hole of the Teflon round tube through the optical fiber holder, and the first ends of the incident optical fiber and the several receiving optical fibers of the acetone detection optical fiber face the inside of the Teflon round tube.

[0021] Preferably, an opening area is provided on the side wall of the Teflon round tube to communicate the inside of the Teflon round tube with the outside, so that the acetone-containing air can enter the inside of the Teflon round tube through this opening area.

[0022] Preferably, an internal thread is provided on the inner peripheral side wall at the opening position of the Teflon round tube; an external thread is provided on the outer peripheral side wall of the optical fiber holder, which is adapted to the internal thread at the opening position of the Teflon round tube;

[0023] The optical fiber fixator of the acetone detection optical fiber realizes the coupling and fixation with the Teflon round tube through the threaded connection of the external thread and the internal thread.

[0024] A method for detecting acetone concentration based on an optical fiber sensor, implemented based on the optical fiber sensor of the present invention, includes:

[0025] S1: The incident optical fiber of the optical fiber sensor transmits the light beam emitted by the light source;

[0026] S2: The first end of the incident optical fiber of the optical fiber sensor radiates the light beam into the interior of the Teflon round tube with acetone-containing air, and the light beam is transmitted to the acetone-sensitive unit after passing through the acetone-containing air;

[0027] S3: The first ends of the receiving optical fibers of the optical fiber sensor receive the light beam reflected by the acetone-sensitive unit; calculate the output light intensity of the optical fiber sensor based on the light intensities output by the receiving optical fibers;

[0028] S4: Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor;

[0029] S5: Calculate the acetone concentration of the acetone-containing air through the output signal of the optical fiber sensor and the pre-determined calibration relationship between the output signal and the acetone concentration.

[0030] Preferably, in step S3, the output light intensity of the optical fiber sensor is calculated through the following steps:

[0031] S301: Define the light intensity of the light beam radiated by the incident optical fiber as I in ;

[0032] S302: After the light beam with light intensity I in is radiated, two light beams with light intensity I in1 and light intensity I in2 are formed;

[0033] S303: The light beam with light intensity I in1 is transmitted through the acetone-containing air to the surface of the acetone-sensitive film, and part of the light beam is reflected back to the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out1 ;

[0034] The formula is expressed as:

[0035] I out1 = kI in1 R;

[0036] Where:

[0037] R = R0exp[-(4πσ / λ) 2 ;

[0038]

[0039] n2 = K1C + b;

[0040]

[0041] Where: k represents the optical coupling coefficient of the light beam transmitted in the air containing acetone and coupled into the receiving optical fiber; R is the reflectivity of the acetone-sensitive film to light; R0 represents the reflectivity of the acetone-sensitive film under ideal smoothness; σ represents the root mean square roughness of the surface of the acetone-sensitive film; λ represents the optical wavelength of the light beam; n1 represents the refractive index of air; n2 represents the refractive index of the acetone-sensitive film; θ i is the incident angle; θ t is the refraction angle; x is the core spacing between the receiving optical fiber and the incident optical fiber; K1 and b are both constants; C is the acetone concentration;

[0042] S304: The light beam with an intensity of I in2 is transmitted through the air containing acetone to the surface of the acetone-sensitive film, and then coupled into the acetone-sensitive film. After being attenuated by the acetone-sensitive film, it is transmitted to the interface between the acetone-sensitive film and the reflecting surface of the optical mirror; then it is reflected by the reflecting surface of the optical mirror and enters the acetone-sensitive film again; then after being attenuated by the acetone-sensitive film again, it is transmitted to the interface between the acetone-sensitive film and the air containing acetone; finally, the light beam is refracted at the interface between the acetone-sensitive film and the air and enters the air medium containing acetone again, and part of the reflected light beam is coupled into the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ;

[0043] The formula is expressed as:

[0044] I out2 = kI2exp(2ζx / cosθ t );

[0045] Where:

[0046] ζ = 2πε2 / (λn2);

[0047] I out2 = kI2exp[4πε2x / (λn2cosθ t );

[0048] Where: ζ is the attenuation coefficient of the acetone-sensitive film to light; ε2 is the imaginary part of the complex dielectric constant of the acetone-sensitive film;

[0049] S305: Based on the light intensities I out1 and I out2 output by each receiving optical fiber, calculate the output light intensity I out of the fiber optic sensor;

[0050] The formula is expressed as:

[0051]

[0052] In the formula: n represents the number of receiving optical fibers.

[0053] Preferably, based on the output light intensity I of the fiber optic sensor out and the light intensity I of the incident optical fiber receiving the light beam in calculate the absorbance A as the output signal;

[0054] The formula is expressed as:

[0055] A = log(I in / I ou ) = log[I in / n(I out1 +I out2 )].

[0056] Compared with the prior art, the fiber optic sensor for detecting acetone concentration in the present invention has the following beneficial effects:

[0057] The present invention designs a fiber optic sensor for detecting acetone concentration, which includes an acetone detection optical fiber, an acetone sensitive unit and a coupler. The acetone sensitive unit includes a light reflector and an acetone sensitive film. The acetone sensitive film is an acetone sensitive material coated on the surface of the light reflector. The acetone sensitive material is composed of a zeolitic imidazolate framework-8 / nitrogen-doped porous carbon / 3-aminopropyltriethoxysilane (ZIF-8 / NPC / APTES) composite material: zeolitic imidazolate framework-8 (ZIF-8) has the function of selective adsorption of acetone; nitrogen-doped porous carbon (NPC) is used to improve the adsorption capacity of the ZIF-8 / NPC / APTES composite material for acetone, increase the measurement range of the sensor for acetone and improve the sensitivity of the sensor; 3-aminopropyltriethoxysilane (APTES) is used to enhance the adhesion strength between the ZIF-8 / NPC / APTES film and the light reflector and the mechanical strength of the film, and improve the repeatability and service life of the sensor.

[0058] When the fiber optic sensor works, the light intensity radiated and input into the coupler through the acetone detection optical fiber. When acetone in the external environment is transmitted to the acetone sensitive film (ZIF-8 / NPC / APTES film) through the coupler, the refractive index of the acetone sensitive film increases after absorbing acetone, the absorption intensity of the light intensity with a wavelength of 253 nm increases, and the reflectivity decreases, resulting in a decrease in the light intensity transmitted inside the acetone detection optical fiber, so that the accurate measurement of the acetone concentration in the environment can be realized through the change amount between the output light intensity and the input light intensity of the acetone detection optical fiber; and the acetone measurement result is not interfered by other gas components and humidity changes, and there is a linear relationship between the output signal of the fiber optic sensor and the acetone concentration. Description of the Drawings

[0059] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0060] Figure 1 This is a schematic diagram of the structure of the optical fiber sensor used to detect acetone concentration: Figure 1 (a) is a schematic diagram of the coupler structure. Figure 1 (b) is a schematic diagram of the sensor structure after the acetone detection optical fiber is coupled to the coupler.

[0061] Figure 2 Schematic diagram of the structure of acetone detection optical fiber.

[0062] Figure 3 Schematic diagram of the structure of the acetone sensitive unit.

[0063] Figure 4 Schematic diagram of the optical transmission path of the fiber optic sensor.

[0064] Figure 5 This is the response curve of the sensor to acetone: Figure 5 (a) is the sensor output spectrum at different acetone concentrations. Figure 5 (b) is the relationship curve between the sensor absorbance change and acetone concentration when the light source wavelength is 253nm.

[0065] Figure 6 The selectivity of the optical fiber sensor for acetone.

[0066] The figure marks in the drawings of the specification include: incident optical fiber 1, SMA optical fiber connector 2, optical fiber protective cover 3, optical fiber collimator 4, receiving optical fiber 5, optical fiber holder 6, external thread 7, UV shadowless glue 8, light reflector 9, acetone sensitive film 10, coupler 11, internal thread 12, opening area 13, coupling area 14 of acetone detection optical fiber and coupler. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but only represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0068] It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0069] The following is a more detailed description through specific embodiments:

[0070] Embodiment 1:

[0071] In this embodiment, an optical fiber sensor for detecting acetone concentration is disclosed.

[0072] As Figure 1 shown, an optical fiber sensor for detecting acetone concentration includes: an acetone detection optical fiber, a coupler coupled to the acetone detection optical fiber, and an acetone sensitive unit disposed inside the coupler;

[0073] The acetone sensitive unit includes a light reflecting mirror facing the detection end of the acetone detection optical fiber during use and an acetone sensitive film disposed on the reflecting surface of the light reflecting mirror; the acetone sensitive film is a ZIF-8 / NPC / APTES film composed of zeolitic imidazolate framework-8 (ZIF-8) with acetone selective adsorption function, nitrogen-doped porous carbon (NPC) for improving the adsorption capacity of the acetone sensitive film to acetone, and 3-aminopropyltriethoxysilane (APTES) for enhancing the adhesion strength between the acetone sensitive film and the light reflecting lens and the mechanical strength of the acetone sensitive film.

[0074] Wherein:

[0075] Zeolitic imidazolate framework-8 (ZIF-8) is a porous crystalline material formed by the coordination of zinc ions and 2-methylimidazole.

[0076] Nitrogen-doped porous carbon (NPC) is a functional material formed by sintering nitrogen-containing biomass at high temperature, enabling nitrogen elements to be embedded in the carbon skeleton in the form of chemical bonds while forming a porous structure.

[0077] 3-Aminopropyltriethoxysilane (APTES), also known as silane coupling agent KH-550, is a colorless transparent liquid.

[0078] The acetone-detecting optical fiber (Y-shaped optical fiber) includes an incident optical fiber 1, a plurality of receiving optical fibers 5, and an optical fiber holder 6; the incident optical fiber 2 and the first ends (i.e., the detecting ends) of the plurality of receiving optical fibers 5 are fixed together by the optical fiber holder 6 and the plurality of receiving optical fibers 5 are distributed around the incident optical fiber 2, the second ends of the incident optical fiber 2 and the plurality of receiving optical fibers 5 are separated and the plurality of receiving optical fibers 5 are fixed together;

[0079] The first ends of the incident optical fiber 1 and the plurality of receiving optical fibers 2 are the detecting ends of the acetone-detecting optical fiber.

[0080] In this embodiment, there is one tapered incident optical fiber and six receiving optical fibers.

[0081] The coupler 22 is a hollow Teflon round tube with one end open and the other end sealed; the acetone-detecting optical fiber is inserted into the open hole of the Teflon round tube through the optical fiber holder 6 to achieve coupling with the coupler 11, and the first ends of the incident optical fiber 1 and the plurality of receiving optical fibers 5 of the acetone-detecting optical fiber face the inside of the Teflon round tube.

[0082] The working logic of the optical fiber sensor is as follows:

[0083] 1) The second end of the incident optical fiber receives the light beam for detecting acetone;

[0084] 2) The first end of the incident optical fiber radiates the light beam into the inside of the Teflon round tube with acetone-containing air, and the light beam is transmitted to the acetone-sensitive unit after passing through the acetone-containing air;

[0085] 3) The first ends of each receiving optical fiber receive the light beam reflected by the acetone-sensitive unit and transmit it to the second end, and the output light intensity of the optical fiber sensor is calculated based on the light intensity output from the second ends of each receiving optical fiber;

[0086] 4) Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor;

[0087] 5) Calculate the acetone concentration in the acetone-containing air based on the output signal of the fiber optic sensor and the calibrated relationship between the output signal and the acetone concentration determined in advance.

[0088] The present invention designs a fiber optic sensor for detecting acetone concentration, which includes an acetone detection optical fiber, an acetone sensitive unit, and a coupler. The acetone detection optical fiber consists of an incident optical fiber, six receiving optical fibers, and an optical fiber holder with seven holes. The incident optical fiber and the receiving optical fibers are fixed in the optical fiber holder, and the receiving optical fibers are distributed around the incident optical fiber. The optical fiber holder has an external thread, and the optical fiber and the holder are fixed and encapsulated with UV curable glue. The acetone sensitive unit includes a light reflector and an acetone sensitive film. The acetone sensitive film is an acetone sensitive material coated on the surface of the light reflector. The acetone sensitive material is composed of a zeolitic imidazolate framework-8 / nitrogen-doped porous carbon / 3-aminopropyltriethoxysilane (ZIF-8 / NPC / APTES) composite material: zeolitic imidazolate framework-8 (ZIF-8) has the function of selectively adsorbing acetone; nitrogen-doped porous carbon (NPC) is used to improve the adsorption capacity of the ZIF-8 / NPC / APTES composite material for acetone, increase the measurement range of the sensor for acetone, and improve the sensitivity of the sensor; 3-aminopropyltriethoxysilane (APTES) is used to enhance the adhesion strength between the ZIF-8 / NPC / APTES film and the light reflector lens and the mechanical strength of the film, and improve the repeatability and service life of the sensor. The coupler is a hollow Teflon round tube with an opening at one end and sealed at the other end. The opening area of the Teflon round tube facilitates the free passage of acetone in the environment through the Teflon round tube. The acetone sensitive unit is fixed at the end of the coupler with UV curable glue, and the coupler and the acetone detection optical fiber are fixed by threaded coupling to form a fiber optic sensor for acetone measurement.

[0089] When the fiber optic sensor works, the light intensity radiated into the coupler through the acetone detection optical fiber. When acetone in the external environment is transmitted to the acetone sensitive film (ZIF-8 / NPC / APTES film) through the coupler, the refractive index of the acetone sensitive film increases after absorbing acetone, the absorption intensity of the light intensity with a wavelength of 253 nm increases, and the reflectivity decreases, resulting in a decrease in the light intensity transmitted inside the acetone detection optical fiber. Thus, the accurate measurement of the acetone concentration in the environment can be achieved by the change amount between the output light intensity and the input light intensity of the acetone detection optical fiber; and the acetone measurement result is not interfered by other gas components and humidity changes, and there is a linear relationship between the output signal of the fiber optic sensor and the acetone concentration.

[0090] To better introduce the technical solution of the present invention, this embodiment is described through the following several parts.

[0091] I. Acetone Detection Optical Fiber (Y-shaped Optical Fiber)

[0092] First, seven quartz optical fibers with a length of 0.3 - 5 m and a diameter of 100 - 5000 μm are intercepted. After the end faces of the optical fibers are polished smoothly using optical fiber polishing paper, the surfaces of the optical fibers are rinsed clean with deionized water and dried with high-purity nitrogen for standby. Then, one incident optical fiber and six receiving optical fibers are fixed in an optical fiber holder made of plastic with a length of 10 - 100 mm and a diameter of 5 - 30 mm, and having an external thread 7 at the first end. The diameters of the seven holes in the holder are 110 - 5100 μm, and the length of the external thread 7 is 5 - 50 mm; the receiving optical fibers are distributed around the incident optical fiber, and the distance between the cores of the receiving optical fibers and the core of the incident optical fiber is 2 - 5 mm; the space between the optical fibers and the holder is filled, fixed, and encapsulated with UV-curable adhesive 8. Then, the second ends of the incident optical fiber and the receiving optical fibers are fixed in the optical fiber protective sleeve 3 for standby. Finally, an SMA optical fiber connector 2 is connected to the first end of the incident optical fiber, and an optical fiber collimator 4 and an SMA optical fiber connector 2 are successively connected to the first end of the receiving optical fibers to form an acetone detection optical fiber (Y-shaped optical fiber), as Figure 2 shown.

[0093] In the specific implementation process, for the preparation of the acetone detection optical fiber (Y-shaped optical fiber):

[0094] The length of the quartz optical fiber is 1 m, the diameter of the incident optical fiber is 1000 μm, the diameters of the six receiving optical fibers are 440 μm, and the distance between the incident optical fiber and the receiving optical fibers is x = 1 mm. The length of the optical fiber holder with an external thread is 50 mm and the diameter is 5 mm. The diameter of the middle hole in the holder is 1010 μm, and the diameters of the other six holes are 450 μm. The length of the external thread is 30 mm. The first ends of the receiving optical fibers are inserted into the middle hole of the optical fiber holder, and the first ends of the six receiving optical fibers are respectively inserted into the other six holes of the optical fiber holder. The space between the optical fibers and the holder is filled, fixed, and encapsulated with UV-curable adhesive, and an SMA optical fiber connector is connected to the first end of the incident optical fiber, and an optical fiber collimator and an SMA optical fiber connector are successively connected to the first end of the receiving optical fibers to form an acetone detection optical fiber (Y-shaped optical fiber).

[0095] II. Acetone Sensing Unit

[0096] The preparation steps of the acetone sensing unit include:

[0097] Zeolitic imidazolate framework-8 (ZIF-8) has advantages such as a large specific surface area, an ordered pore structure, and good chemical stability; at the same time, the pore size of ZIF-8 can be regulated, and it can selectively adsorb acetone molecules. Nitrogen-doped porous carbon (NPC) has a low preparation cost, is environmentally friendly, and has a porous structure that can increase the adsorption sites of acetone. Therefore, the combination of ZIF-8 and NPC can achieve the selective adsorption of acetone gas molecules, and has a high adsorption capacity, which helps to improve the detection range and sensitivity of the sensor.

[0098] 1. Preparation steps of ZIF-8 / NPC composite material:

[0099] 1) Add 2 - 5 g of 2-methylimidazole to 50 - 100 mL of deionized water, stir evenly and set aside.

[0100] 2) Put dry chrysanthemum into a tube furnace, sinter in air at 500℃ - 600℃ for 3 - 4 hours to obtain NPC.

[0101] 3) Disperse 30 - 100 mg of NPC into 5 - 20 mL of deionized water, ultrasonically treat for 4 - 8 hours to obtain a uniform NPC solution; dissolve 0.1 - 0.5 g of Zn(NO3)2·6H2O into the NPC solution, stir for 6 - 7 hours to obtain a mixed solution.

[0102] 4) Mix the mixed solution with the 2-methylimidazole solution, stir at room temperature for 5 - 10 minutes, then transfer the mixture to a polytetrafluoroethylene-lined autoclave, treat at 100 - 150℃ for 5 - 10 hours; dry the product in air at 50 - 100℃ for 12 - 20 hours to obtain a gray powder, which is the ZIF-8 / NPC composite material.

[0103] 2. Preparation steps of ZIF-8 / NPC / APTES film:

[0104] 5) To achieve uniform attachment of the sensitive material on the surface of the optical mirror, enhance its adhesion strength with the optical mirror and the mechanical strength of the film, ultrasonically clean the lens with ethanol or acetone solution to remove surface impurities, then immerse it in an ethanol solution of 3-aminopropyltriethoxysilane (APTES) with a concentration of 2 - 10 mg / mL for 2 - 5 hours, take it out and alternately clean and dry it with deionized water and ethanol for standby.

[0105] 6) Disperse 50 - 100 mg of the prepared ZIF-8 / NPC powder in 10 - 20 mL of ethanol to form a uniform suspension; uniformly coat it on the surface of the optical mirror by spin coating or dip coating method, and heat and cure the coated optical mirror at 60 - 80℃ for 1 - 3 hours to obtain a ZIF-8 / NPC / APTES film with a thickness of 20 - 100 μm, which is the acetone-sensitive film. The optical mirror coated with the acetone-sensitive film is the acetone-sensitive unit, as Figure 3 shown.

[0106] In the specific implementation process, preparation of the acetone-sensitive unit:

[0107] 1. The preparation steps of the ZIF-8 / NPC composite material are as follows: First, add 4.5 g of 2-methylimidazole to 60 mL of deionized water, stir evenly and set aside. Then, put the dried chrysanthemum into a tubular furnace and sinter it in air at 550 °C for 3 hours to obtain NPC. Next, disperse 60 mg of NPC into 10 mL of deionized water and ultrasonically treat it for 5 hours to obtain a uniform NPC solution. Secondly, dissolve 0.29 g of Zn(NO3)2·6H2O into the NPC solution, stir for 6 hours to obtain a mixed solution. Mix this mixed solution with the 2-methylimidazole solution, stir at room temperature for 5 minutes, and then transfer the mixture to a polytetrafluoroethylene-lined autoclave and treat it at 120 °C for 6 hours. Finally, vacuum-dry the product at 80 °C for 15 hours to obtain the ZIF-8 / NPC composite material. 2. The preparation steps of the ZIF-8 / NPC / APTES film are as follows: First, ultrasonically clean the lens with an ethanol or acetone solution to remove surface impurities, then immerse it in an ethanol solution of 5 mg / mL 3-aminopropyltriethoxysilane (APTES) and treat it for 2 hours. After taking it out, wash it alternately with deionized water and ethanol and dry it for standby. Disperse 50 mg of the prepared ZIF-8 / NPC powder in 10 mL of ethanol to form a uniform suspension. Finally, uniformly coat it on the lens surface by spin coating or dip coating. The coated lens is heated and cured at 60 °C for 2 hours to obtain an acetone-sensitive film with a thickness of 30 μm; The optical mirror coated with the ZIF-8 / NPC / APTES film is an acetone-sensitive unit.

[0108] The above solution is the optimal ratio of various components when preparing the acetone-sensitive unit (see Case 3 in Table 1). Through this optimal ratio, the absorption intensity and reflectivity of the acetone-sensitive film can be best balanced.

[0109] In other preferred embodiments, the acetone-sensitive unit can also be prepared by the component ratios of other cases in Table 1. However, compared with Case 3, in Case 1 and Case 2, the absorption intensity of the acetone-sensitive film is better, but the reflectivity effect is worse; in Case 4 and Case 5, the absorption intensity of the acetone-sensitive film is better, but the reflectivity effect is worse; only Case 3 can make both the absorption intensity and reflectivity of the acetone-sensitive film excellent.

[0110]

[0111] III. Coupler

[0112] In order to obtain a reflective acetone concentration optical fiber sensor, firstly, a Teflon rod with a diameter of 10 to 35 mm and a length of 10 to 200 mm is cut. Then, a hole with a diameter of 6 to 22 mm and a depth of 8 to 190 mm is drilled at one end of the Teflon rod. Secondly, in order to facilitate the free entry and exit of the substances in the Teflon hole and the substances outside the Teflon, an opening area 13 is opened on both sides of the Teflon central area with a hole, and the width of the opening area 13 is 3 to 15 mm and the length is 4 to 150 mm, that is, the side wall of the Teflon round tube is opened to connect the inside of the Teflon round tube with the outside, so that the acetone-containing air can enter the inside of the Teflon round tube through the opening area 13. Next, one end of the Teflon material with a hole drilled inside and an opening on the side is processed into an internal thread 12 by turning. The diameter of the internal thread 12 is 5 to 30 mm and the length is 5 to 50 mm. The internal thread 12 matches the structural dimensions of the external thread 7 of the optical fiber holder. The Teflon material with the internal thread is a coupler, such as Figure 1 Finally, the acetone sensitive unit is fixed to the bottom of the coupler by UV shadowless glue, and the coupler (Teflon tube) and the optical fiber holder are coupled and fixed by screw rotation (coupling area 14 between the acetone detection optical fiber and the coupler), forming an optical fiber sensor for acetone measurement. The structure of the optical fiber sensor for selective acetone concentration detection is shown in FIG. Figure 1 (b) as shown.

[0113] In the specific implementation process, for the reflective acetone concentration optical fiber sensor packaging:

[0114] First, a Teflon rod with a diameter of 12mm and a length of 40mm is cut. Then, a hole with a diameter of 8mm and a depth of 30mm is drilled in the center of the Teflon rod. Then, opening areas connected to the outside are set on both sides of the Teflon center area with a hole, and the width of the opening area is 7mm and the length is 50mm. Secondly, one end of the Teflon material with a hole drilled inside and an opening on the side is processed into an internal thread by turning. The diameter of the internal thread is 8mm and the length is 15mm. The Teflon material with the internal thread is a coupler. UV shadowless glue is used again to fix the acetone sensitive unit at the bottom of the coupler. Finally, the coupler and the optical fiber holder are fixed by threaded rotation coupling, and the distance between the optical fiber end face and the light reflection mirror surface is kept at y=2mm. The packaged and fixed sensor is the optical fiber sensor for selective measurement of acetone concentration.

[0115] Embodiment 2:

[0116] This embodiment discloses an acetone concentration detection method based on an optical fiber sensor, which is implemented based on the optical fiber sensor in the first embodiment.

[0117] A method for detecting acetone concentration based on an optical fiber sensor, comprising:

[0118] S1: The second end of the incident optical fiber of the fiber optic sensor transmits the light beam emitted by the light source;

[0119] S2: The first end of the incident optical fiber of the fiber optic sensor radiates the light beam into the interior of the Teflon circular tube containing acetone-containing air, and the light beam is transmitted to the acetone-sensitive unit after passing through the acetone-containing air;

[0120] S3: The first ends of the receiving optical fibers of the fiber optic sensor receive the light beam reflected by the acetone-sensitive unit and transmit it to the second end; calculate the output light intensity of the fiber optic sensor based on the light intensity output from the second ends of the receiving optical fibers;

[0121] S4: Calculate the corresponding output signal based on the output light intensity of the fiber optic sensor;

[0122] S5: Calculate the acetone concentration of the acetone-containing air through the output signal of the fiber optic sensor and the pre-determined calibration relationship between the output signal and the acetone concentration.

[0123] In the first embodiment, the reflective fiber optic acetone concentration sensor mainly utilizes the fact that after the acetone-sensitive membrane (ZIF-8 / NPC / APTES membrane) selectively adsorbs acetone gas molecules, the refractive index increases, resulting in a decrease in the light intensity transmitted to the receiving optical fiber. By measuring the change information of the output signal of the receiving optical fiber, the selective measurement of the acetone concentration is realized. The schematic diagram of the optical transmission path of the sensor is as Figure 4 shown.

[0124] Combined with Figure 4 shown, the output light intensity of the fiber optic sensor is calculated through the following steps:

[0125] S301: Define the light intensity of the light beam radiated by the incident optical fiber as I in ;

[0126] S302: After the light beam with light intensity I in radiates, two light beams with light intensity I in1 and light intensity I in2 are formed; I in =I in1 +I in2 ;

[0127] S303: The light beam with light intensity I in1 is transmitted through the acetone-containing air to the surface of the acetone-sensitive membrane, and part of the light beam is reflected back to the receiving optical fiber. The light intensity received by the receiving optical fiber is I out1 ;

[0128] For the light intensity I1 output from the incident optical fiber reaching the surface of the acetone-sensitive membrane and being reflected, the light intensity received by the receiving optical fiber can be expressed as:

[0129] I out1 =kIin1 R; (1)

[0130] Wherein:

[0131] R = R0exp[-(4πσ / θ) 2 ; (2)

[0132] When the refractive index of air is n1, the refractive index of the acetone-sensitive film is n2, and the incident angle is θ i , and the refraction angle is θ t , R0 can be expressed by the Fresnel formula as:

[0133]

[0134] In Equation (3), n1sinθ i = n2sinθ t ; θ i = arctan(x / y), where x is the core distance between the receiving optical fiber and the incident optical fiber, and y is the distance between the incident optical fiber and the acetone-sensitive thin film.

[0135] Since the refractive index n2 of the acetone-sensitive film is a function of the acetone concentration c, the functional relationship between n2 and c can be described as:

[0136] n2 = K1C + b; (4)

[0137]

[0138] In the formula: k represents the optical coupling coefficient of the light beam transmitted in the acetone-containing air and coupled into the receiving optical fiber; R is the light reflectivity of the acetone-sensitive film; R0 represents the reflectivity of the acetone-sensitive film under ideal smoothness; σ represents the root mean square roughness of the surface of the acetone-sensitive film; λ represents the optical wavelength of the light beam; n1 represents the refractive index of air; n2 represents the refractive index of the acetone-sensitive film; θ i is the incident angle; θ t is the refraction angle; x is the core distance between the receiving optical fiber and the incident optical fiber; K1 and b are both constants; C is the acetone concentration;

[0139] S304: After the light beam with an intensity of I in2 is transmitted through the acetone-containing air to the surface of the acetone-sensitive film, it is coupled into the acetone-sensitive film, and after being attenuated by the acetone-sensitive film, it is transmitted to the interface between the acetone-sensitive film and the reflecting surface of the optical mirror; then it is reflected by the reflecting surface of the optical mirror and enters the acetone-sensitive film again; then after being attenuated by the acetone-sensitive film again, it is transmitted to the interface between the acetone-sensitive film and the acetone-containing air; finally, the light beam is refracted at the interface between the acetone-sensitive film and the air and enters the acetone-containing air medium again, and the partially reflected light beam is coupled into the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ;

[0140] After the light intensity I2 output from the incident optical fiber is transmitted into the acetone-sensitive film, light attenuation will occur. The light intensity of the beam after attenuation by the acetone-sensitive film and coupled into the output optical fiber can be described as follows:

[0141] I out2 = kI2exp(2ζx / cosθ t ); (6)

[0142] Where:

[0143] ζ = 2πε2 / (λn2); (7)

[0144] Substituting Equation (7) into Equation (6), the light intensity coupled into the output optical fiber after the light intensity I2 output from the incident optical fiber is absorbed by the acetone-sensitive film can be obtained as follows:

[0145] I out2 = kI2exp[4πε2x / (λn2cosθ t ); (8)

[0146] In the formula: ζ is the attenuation coefficient of the acetone-sensitive film for light, which is related to the refractive index n2 of the acetone-sensitive film; ε2 is the imaginary part of the complex dielectric constant of the acetone-sensitive film (ZIF-8 / NPC / APTES film);

[0147] S305: Calculate the output light intensity I of the fiber optic sensor based on the light intensities I out1 and I out2 ; out ;

[0148] The formula is expressed as:

[0149]

[0150] In the formula: n represents the number of receiving optical fibers, and n is set to 6 in this embodiment.

[0151] Based on the output light intensity I of the fiber optic sensor out and the light intensity I of the beam radiated by the incident optical fiber in calculate the absorbance as the output signal of the fiber optic sensor. Calculate the absorbance A as the output signal of the fiber optic sensor through the following formula:

[0152] According to the Lambert-Beer law, the absorbance A of the sensor output signal can be described as:

[0153] A = log(I in / I out ) = log[I in / n(I out1 +I out2 )]. (10)

[0154] In this embodiment, when the acetone-sensitive film selectively absorbs acetone molecules, the refractive index n2 of the acetone-sensitive film increases, resulting in a decrease in θ t and an increase in cosθ t . Since n1≈1 and θ i is constant, I out1 and I out2 decrease as the acetone concentration C in the external environment increases, that is, I out decreases as the acetone concentration C in the external environment increases; the sensor output signal (absorbance A) increases as the acetone concentration C in the external environment increases, that is, A∝C. Therefore, by measuring the change in the absorbance A, the measurement of the acetone concentration C can be achieved.

[0155] It should be noted that the above calculation logic is an introduction to the internal working principle of the fiber optic sensor, which is mainly applied when determining the calibration relationship between the output signal and the acetone concentration. During the actual detection process, the fiber optic sensor can directly obtain the light intensity of the received beam and the light intensity of the output beam, and then use formula (11) to calculate the absorbance, that is, the output signal, and determine the acetone concentration through the calibration relationship between the output signal and the acetone concentration.

[0156] When the fiber optic sensor works, the light intensity radiated into the coupler through the acetone detection optical fiber. When acetone in the external environment is transmitted to the acetone-sensitive film (ZIF-8 / NPC / APTES film) through the coupler, the refractive index of the acetone-sensitive film increases after absorbing acetone, the absorption intensity of the light intensity with a wavelength of 253nm increases, and the reflectivity decreases, resulting in a decrease in the light intensity transmitted inside the acetone detection optical fiber, enabling the accurate measurement of the acetone concentration in the environment through the change between the output light intensity and the input light intensity of the acetone detection optical fiber; and the acetone measurement result is not interfered by other gas components and humidity changes, and there is a linear relationship between the sensor output signal and the acetone concentration.

[0157] Sensor detection of acetone performance test

[0158] The response absorption spectrum of the prepared sensor to acetone concentrations of 0 - 500 ppm in the environment and the relationship curve between the change in the sensor absorbance and the acetone concentration are as Figure 5 shown. The selectivity result diagram of the sensor to other gas concentrations of 500 ppm in the environment is as Figure 6 shown.

[0159] As Figure 5As shown in (a), the sensor produced a characteristic absorption peak at 253 nm, and the absorbance increased with the increase of acetone concentration. The reason is that with the increase of acetone concentration, the number of acetone molecules adsorbed by the sensitive material increases, resulting in an increase in the refractive index of the acetone-sensitive film, causing an increase in the light attenuation of the sensor. Therefore, the absorbance of the output spectrum of the sensor increases, which is consistent with the theoretical model analysis result of formula (10). As Figure 5 shown in (b), when the light source wavelength is 253 nm, there is a linear relationship between the output signal (absorbance) of the sensor and the acetone concentration, A = 0.00421 + 0.000286c (R 2 = 0.99756), and the sensitivity of the sensor reaches 0.000286 AU / ppm. The reason is that ZIF-8 and NPC are porous structures and have many acetone adsorption sites. When acetone molecules are transported to the acetone-sensitive film, they will be adsorbed, thereby increasing its refractive index and causing light attenuation. The higher the acetone concentration, the greater the refractive index increment and the greater the light attenuation, and the greater the absorbance A of the sensor.

[0160] As Figure 6 shown, the sensor has different absorption characteristic light wavelengths for 500 ppm of SO2, CO2, N2, acetone, formic acid, and the calculated gas, and the response sensitivity of the sensor to acetone with the same concentration is higher than that of other gases. The reason is that ZIF-8 / NPC has high selectivity for acetone.

[0161] Comprehensively Figure 5 and Figure 6 show that the fiber optic sensor of the present invention can selectively and accurately detect the acetone concentration at a light wavelength of 253 nm.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solution should be covered within the scope of the claims of the present invention.

Claims

1. An optical fiber sensor for detecting acetone concentration, characterized in that: include: An acetone detection optical fiber, a coupler coupled to the acetone detection optical fiber, and an acetone sensitive unit disposed inside the coupler; The acetone sensitive unit includes a light reflector facing the detection end of the acetone detection optical fiber when in use and an acetone sensitive film arranged on the reflection surface of the light reflector; the acetone sensitive film is a ZIF-8 / NPC / APTES film composed of zeolite imidazolate framework-8, nitrogen-doped porous carbon and 3-aminopropyltriethoxysilane.

2. The optical fiber sensor for detecting acetone concentration according to claim 1, characterized in that: The acetone sensitive membrane was prepared by the following steps: 1) Add 2-methylimidazole to deionized water, stir well and set aside; 2) placing the dried chrysanthemum in a tube furnace and sintering in air to obtain nitrogen-doped porous carbon; 3) dispersing nitrogen-doped porous carbon into deionized water and subjecting it to ultrasonic treatment to obtain a nitrogen-doped porous carbon solution; dissolving Zn(NO3)2·6H2O into the nitrogen-doped porous carbon solution and stirring to obtain a mixed solution; 4) mixing the mixed solution with the 2-methylimidazole solution, stirring at room temperature to obtain a mixture; transferring the mixture to a polytetrafluoroethylene-lined autoclave for heating; drying the heated product in air to obtain a gray powder, which is the ZIF-8 / NPC composite material; 5) After ultrasonically cleaning the light reflector with ethanol or acetone solution to remove surface impurities, immerse it in 3-aminopropyltriethoxysilane ethanol solution; after taking out the light reflector, wash it alternately with deionized water and ethanol and dry it for later use; 6) dispersing the ZIF-8 / NPC composite material in ethanol to form a uniform suspension; coating it on the surface of the light reflector by spin coating or dip coating, and heating and curing the coated light reflector to obtain a ZIF-8 / NPC / APTES film, i.e., an acetone sensitive film.

3. The optical fiber sensor for detecting acetone concentration according to claim 1, characterized in that: The acetone detection optical fiber includes an incident optical fiber, a plurality of receiving optical fibers and an optical fiber holder; the first ends of the incident optical fiber and the plurality of receiving optical fibers are fixed together by the optical fiber holder and the plurality of receiving optical fibers are distributed around the periphery of the incident optical fiber; The first ends of the incident optical fiber and the plurality of receiving optical fibers are detection ends of the ketone detection optical fibers.

4. The optical fiber sensor for detecting acetone concentration according to claim 3, characterized in that: The second end of the incident optical fiber is connected with an SMA optical fiber connector; The second ends of the plurality of receiving optical fibers fixed together are connected in sequence with an optical fiber collimator and an SMA optical fiber connector.

5. The optical fiber sensor for detecting acetone concentration according to claim 3, characterized in that: The coupler is a hollow Teflon tube with an opening at one end and a sealed end at the other end; the acetone detection optical fiber is inserted into the opening of the Teflon tube through an optical fiber holder to achieve coupling with the coupler, and the incident optical fiber of the acetone detection optical fiber and the first ends of several receiving optical fibers are facing the inside of the Teflon tube.

6. The optical fiber sensor for detecting acetone concentration according to claim 5, characterized in that: An opening area is provided on the side wall of the Teflon round tube to connect the inside of the Teflon round tube with the outside, so that the acetone-containing air can enter the inside of the Teflon round tube through the opening area.

7. The optical fiber sensor for detecting acetone concentration according to claim 5, characterized in that: An internal thread is arranged on the inner peripheral side wall of the opening position of the Teflon round tube; an external thread matching the internal thread of the opening position of the Teflon round tube is arranged on the outer peripheral side wall of the optical fiber holder; The optical fiber holder of the acetone detection optical fiber is coupled and fixed to the Teflon round tube through a threaded connection of an external thread and an internal thread.

8. A method for detecting acetone concentration based on an optical fiber sensor, characterized in that: The optical fiber sensor according to claim 1 is implemented as follows: S1: The incident optical fiber of the optical fiber sensor transmits the light beam emitted by the light source; S2: The first end of the incident optical fiber of the optical fiber sensor radiates the light beam to the inside of the Teflon tube containing acetone air, and the light beam is transmitted to the acetone sensitive unit after passing through the acetone air; S3: The first end of each receiving optical fiber of the optical fiber sensor receives the light beam reflected by the acetone sensitive unit; the output light intensity of the optical fiber sensor is calculated based on the light intensity output by each receiving optical fiber; S4: Calculate the corresponding output signal based on the output light intensity of the optical fiber sensor; S5: Calculate the acetone concentration of the acetone-containing air through the output signal of the optical fiber sensor and a predetermined calibration relationship between the output signal and the acetone concentration.

9. The method for detecting acetone concentration based on an optical fiber sensor according to claim 8, characterized in that: In step S3, the output light intensity of the optical fiber sensor is calculated by the following steps: S301: Define the light intensity of the incident optical fiber radiation as I in ; S302: Light intensity is I in The light beam radiates to form a light intensity of I in1 and light intensity is I in2 Two types of beams; S303: Light intensity is I in1 The light beam is transmitted to the surface of the acetone sensitive film through the acetone-containing air, and part of the light beam is reflected back to the receiving optical fiber. The light intensity received by the receiving optical fiber is I out1 ; The formula is: I out1 =kI in1 R; in: R=R0exp[-(4π / λ) 2 ; n2=K1C+b; Where: k represents the optical coupling coefficient of the light beam transmitted in the acetone-containing air coupled into the receiving optical fiber; R is the reflectivity of the acetone sensitive film to light; R0 represents the reflectivity of the acetone sensitive film under ideal smoothness; σ represents the root mean square roughness of the acetone sensitive film surface; λ represents the wavelength of the light beam; n1 represents the refractive index of air; n2 represents the refractive index of the acetone sensitive film; θ i is the incident angle; θ t is the refraction angle; x is the core spacing between the receiving fiber and the incident fiber; K1 and b are both constants; C is the acetone concentration; S304: Light intensity is I in2 After the light beam is transmitted to the surface of the acetone sensitive film through the acetone-containing air, it is coupled into the acetone sensitive film, and after being attenuated by the acetone sensitive film, it is transmitted to the interface between the acetone sensitive film and the reflective surface of the light reflector; then it is reflected by the reflective surface of the light reflector and enters the acetone sensitive film again; then it is attenuated again by the acetone sensitive film and transmitted to the interface between the acetone sensitive film and the acetone-containing air; finally, the light beam is refracted at the interface between the acetone sensitive film and the air and enters the acetone-containing air medium again, and the partially reflected light beam is coupled into the inside of the optical fiber by the receiving optical fiber, and the light intensity received by the receiving optical fiber is I out2 ; The formula is: I out2 =kI2exp(2ζx / cosθ t ); in: ζ=2πε2 / (λn2); I out2 =kI2exp[4πε2x / (λn2cosθ t ); Where: ζ is the attenuation coefficient of the acetone sensitive film to light; ε2 is the imaginary part of the complex dielectric constant of the acetone sensitive film; S305: Based on the light intensity I output by each receiving optical fiber out1 and I out2 Calculate the output light intensity I of the optical fiber sensor out ; The formula is: Where: n represents the number of receiving optical fibers.

10. The method for detecting acetone concentration based on an optical fiber sensor according to claim 9, characterized in that: Output light intensity I based on optical fiber sensor out and the light intensity I of the incident optical fiber receiving light beam in Calculate the absorbance A as the output signal; The formula is: A=log(I in / I ou )=log[I in / n(I out1 +I ou )]。

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