Preparation method, stripping method and application method of fiber bragg grating film sensor

Abstract

The invention relates to the technical field of sensors. In particular to a preparation method, a stripping method and an application method of a fiber bragg grating film sensor. The preparation method of the fiber bragg grating film sensor comprises the following steps: preparing the fiber bragg grating film sensor consisting of an optical fiber, a packaging part and a grating film; preprocessing the optical fiber and the packaging part; writing a fiber bragg grating into the preprocessed optical fiber to form a fiber bragg grating sensing element; packaging the fiber bragg grating sensing element through a packaging part to form a fiber bragg grating sensing probe; and coating the fiber grating sensing probe with a grating film to obtain the fiber grating film sensor. The device can be tightly attached to a target monitoring sample, and the monitoring sensitivity and accuracy are improved.

Description

Technical Field

[0001] This application relates to the technical field of sensors, and particularly to a preparation method, a peeling method and an application method of a fiber Bragg grating thin film sensor. Background Art

[0002] Fiber Bragg grating sensors have unique advantages such as corrosion resistance, high sensitivity, and electromagnetic interference resistance. However, when traditional fiber Bragg grating sensors are applied to rock crack monitoring, it is extremely inconvenient to arrange them on the rock surface. The irregular and rough texture of the rock surface makes it difficult for traditional fiber Bragg grating sensors to fit closely. There will inevitably be gaps or poorly adhered areas between the sensor and the rock, resulting in the sensor being unable to accurately perceive the true strain changes on the rock surface and low strain transfer efficiency. This inaccuracy and incompleteness of strain transfer seriously affect the accuracy and reliability of monitoring data, and reduce the accuracy and effectiveness of crack monitoring.

[0003] In summary, the technical problems existing in the related art need to be improved. Summary of the Invention

[0004] The main purpose of the embodiments of this application is to propose a preparation method, a peeling method and an application method of a fiber Bragg grating thin film sensor, which can closely adhere to the target monitoring sample and improve the monitoring sensitivity and accuracy.

[0005] To achieve the above object, on the one hand, an embodiment of this application proposes a preparation method of a fiber Bragg grating thin film sensor, including the following steps:

[0006] Prepare the fiber Bragg grating thin film sensor including an optical fiber, a packaging component and a grating film;

[0007] Pretreat the optical fiber and the packaging component;

[0008] Write a fiber Bragg grating in the pretreated optical fiber to form a fiber Bragg grating sensing element;

[0009] Package the fiber Bragg grating sensing element through the packaging component to form a fiber Bragg grating sensing probe;

[0010] Coat the fiber Bragg grating sensing probe with the grating film to obtain the fiber Bragg grating thin film sensor.

[0011] In some embodiments, the coating of the fiber Bragg grating sensing probe with the grating film includes the following steps:

[0012] Fix the fiber Bragg grating sensing probe on a substrate;

[0013] Drop the grating film solution onto the fiber Bragg grating sensing probe fixed on the substrate;

[0014] Spin-coat the fiber Bragg grating sensing probe onto which the grating film solution is dropped.

[0015] Put the fiber Bragg grating sensing probe with the substrate into an oven for drying and curing to complete the film coating.

[0016] In some embodiments, the substrate includes a transparent glass sheet or a plastic sheet made of polyethylene terephthalate.

[0017] In some embodiments, the grating film solution includes: polymethyl methacrylate, toluene solvent, plasticizer, and light stabilizer.

[0018] In some embodiments, the plasticizer includes dibutyl phthalate, and the light stabilizer includes hindered amine light stabilizers.

[0019] In some embodiments, the spin-coating includes one-stage spin-coating and two-stage spin-coating. The rotation speed of the one-stage spin-coating is less than that of the two-stage spin-coating, and the time of the one-stage spin-coating is less than or equal to that of the two-stage spin-coating. Adjust the acceleration from the one-stage spin-coating to the two-stage spin-coating according to the viscosity of the grating film solution and the distribution of the fiber Bragg grating sensing probe.

[0020] In some embodiments, the grating film contains microcapsules. The microcapsules include a capsule wall and a capsule core, and the capsule wall wraps the capsule core;

[0021] The capsule wall is used to protect the capsule core from leaking when the grating film is not damaged.

[0022] The capsule core is used to fill the damaged gap and repair the grating film when the grating film is damaged.

[0023] To achieve the above object, on the other hand, an embodiment of the present application provides a method for preparing microcapsules of a fiber Bragg grating thin film sensor. The method for preparing microcapsules includes the following steps:

[0024] Dissolve benzotriazole in an organic solvent to form a homogeneous dispersion;

[0025] Add the dispersion to an aqueous phase containing an emulsifier and perform ultrasonic emulsification to form an emulsion system containing tiny droplets;

[0026] Add polyurethane and a diisocyanate cross-linking agent to the emulsion system for cross-linking reaction to form the microcapsules.

[0027] To achieve the above object, on the other hand, an embodiment of the present application provides a method for peeling the grating film of a fiber Bragg grating thin film sensor. The method for peeling the grating film includes the following steps:

[0028] Place the fiber Bragg grating thin film sensor in a sealed container;

[0029] Pour acetone solution into the sealed container so that the grating film is completely immersed;

[0030] Take out the fiber Bragg grating thin film sensor after immersing it for a period of time;

[0031] After the acetone solution attached to the grating film naturally volatilizes, the grating film of the fiber Bragg grating thin film sensor softens, and the grating film is removed.

[0032] To achieve the above object, another aspect of the embodiments of the present application provides an application method of a fiber Bragg grating thin film sensor, and the application method includes the following steps:

[0033] Connect a plurality of the fiber Bragg grating thin film sensors to a fiber optic transmission line through a connecting component;

[0034] Fix the connected fiber Bragg grating thin film sensors at different target monitoring samples through the grating film;

[0035] Set the strain threshold of the fiber Bragg grating thin film sensor;

[0036] Obtain the strain data of the fiber Bragg grating thin film sensor at different target monitoring samples;

[0037] When the strain data exceeds the strain threshold, determine the crack position of the target monitoring sample by triangulation or the least squares method, and determine the crack length of the target monitoring sample through the strain data.

[0038] The embodiments of the present application at least include the following beneficial effects: The present application provides a preparation method, a peeling method and an application method of a fiber Bragg grating thin film sensor. Through the grating film, the fiber Bragg grating sensing probe is coated, so that the fiber Bragg grating thin film sensor can be closely attached to the target sample with an irregular surface or a rough texture, eliminating the gap between the fiber Bragg grating thin film sensor and the target sample, being able to accurately sense the strain change of the target sample, improving the strain transfer efficiency, and ensuring the accuracy and reliability of the fiber Bragg grating thin film sensor. Description of the Drawings

[0039] Figure 1 is a flowchart of a preparation method of a fiber Bragg grating thin film sensor provided by an embodiment of the present application;

[0040] Figure 2 is Figure 1 a flowchart of step S150 in

[0041] Figure 3It is a flowchart of a method for preparing microcapsules of an optical fiber grating thin film sensor provided by an embodiment of the present application;

[0042] Figure 4 It is a flowchart of a method for stripping a grating film of an optical fiber grating thin film sensor provided by an embodiment of the present application;

[0043] Figure 5 It is a flowchart of an application method of an optical fiber grating thin film sensor provided by an embodiment of the present application;

[0044] Figure 6 It is a schematic structural diagram of a monitoring device of an optical fiber grating thin film sensor provided by an embodiment of the present application. Detailed implementation manners

[0045] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the embodiments of the present application. They are only examples of devices and methods consistent with some aspects of the embodiments of the present application.

[0046] It can be understood that the terms "first", "second", etc. used in the present application may be used herein to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if", "when" as used herein may be interpreted as "when...", "while...", or "in response to determining".

[0047] The terms "at least one", "a plurality of", "each", "any one", etc. used in the present application, at least one includes one, two or more than two, a plurality includes two or more than two, each refers to each of the corresponding plurality, and any one refers to any one of the plurality.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0049] Figure 1 It is a flowchart of a method for preparing an optical fiber grating thin film sensor provided by an embodiment of the present application,Figure 1 The method in

[0050] Step S110: Prepare a fiber Bragg grating thin film sensor including an optical fiber, a packaging component, and a grating film;

[0051] Step S120: Preprocess the optical fiber and the packaging component;

[0052] Step S130: Write a fiber Bragg grating in the preprocessed optical fiber to form a fiber Bragg grating sensing element;

[0053] Step S140: Package the fiber Bragg grating sensing element through the packaging component to form a fiber Bragg grating sensing probe;

[0054] Step S150: Coat the fiber Bragg grating sensing probe with a grating film to obtain a fiber Bragg grating thin film sensor.

[0055] In some embodiments, as Figure 1 shown, an optical fiber, a packaging component, and a grating film are required to prepare the fiber Bragg grating thin film sensor. According to the measurement requirements, an optical fiber such as a common single-mode optical fiber or a polarization-maintaining optical fiber is selected. In this embodiment, a single-mode optical fiber is selected; for applications that require high-precision measurement and long-term stability for the packaging component, a metal material such as stainless steel is selected for packaging. In the preprocessing of the optical fiber, a special optical fiber cleaning tool, such as an alcohol cotton ball, is used to remove impurities such as dust and oil stains on the surface of the optical fiber to ensure that the surface of the optical fiber is clean and smooth. In the preprocessing of the packaging component, if it is a metal packaging component, surface grinding, cleaning, degreasing, etc. are required to improve the reliability and stability of the packaging.

[0056] In some embodiments, in step S130, by the phase mask method, the preprocessed optical fiber is placed behind the phase mask plate, and the position and angle are adjusted to ensure that the ultraviolet light can accurately irradiate the optical fiber; the ultraviolet light source is turned on, and exposure is performed according to the set exposure time and energy, so that the core of the optical fiber generates a periodic refractive index change to form a fiber Bragg grating sensing element. Or by the point-by-point writing method, using a high-precision beam positioning system, the laser beam is accurately focused on the core of the optical fiber; according to the pre-set grating period and length, the irradiation of the laser beam is controlled point by point, so that the refractive index of the optical fiber core material changes at each irradiation point, and gradually constructs a fiber Bragg grating sensing element.

[0057] In some embodiments, in step S140, the packaging component is a metal packaging component. The fiber Bragg grating sensing element is inserted into the inner cavity of the metal packaging shell, the position is adjusted, and a high-temperature resistant adhesive or a welding process is used to fixedly connect the fiber Bragg grating sensing element to the metal shell; an appropriate amount of buffer material can be added at the connection part to reduce the influence of stress on the fiber Bragg grating sensing element.

[0058] Figure 2 Yes Figure 1 is the flowchart of step S150 in Figure 1 Step S150 of includes but is not limited to steps S210 to S240:

[0059] Step S210: Fix the fiber Bragg grating sensing probe on the substrate;

[0060] Step S220: Drop the grating film solution onto the fiber Bragg grating sensing probe fixed on the substrate;

[0061] Step S230: Spin-coat the fiber Bragg grating sensing probe with the dropped grating film solution;

[0062] Step S240: Place the fiber Bragg grating sensing probe with the substrate into an oven for drying and curing to complete film coating.

[0063] In some embodiments, the fiber Bragg grating sensing probe is pretreated. Before film coating, the surface of the fiber Bragg grating sensing probe is carefully wiped with acetone to remove impurities such as oil stains and dust, ensuring cleanliness. Then it is placed in a plasma treatment device for surface activation treatment. The treatment time is 3 - 10 minutes and the power is 50 - 200 watts to generate active groups on the surface and enhance the adhesion force with the polymer material.

[0064] In some embodiments, for the preparation of the substrate, a suitable substrate material is selected according to the application scenario and requirements, such as a flat glass sheet or a plastic sheet with good flexibility. Among them, the plastic sheet can be polyethylene terephthalate. The substrate is placed in an ultrasonic cleaning device and ultrasonically cleaned with organic solvents such as ethanol and acetone for 10 - 20 minutes to remove pollutants such as fine particles and organic residue. Then it is dried with high-purity nitrogen or air-dried naturally to ensure that the substrate is dry and clean, providing a good basis for the spin-coating process.

[0065] In some embodiments, for the grating film solution, through a large number of experimental screenings, optical polymer materials such as polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), or polycarbonate (PC) are selected. Taking PMMA as an example, it is accurately weighed and dissolved in toluene solvent, and a 10% - 15% concentration solution is prepared by repeated stirring and appropriate heating. At the same time, an appropriate amount of plasticizer and stabilizer are added according to actual needs. Among them, the plasticizer can be dibutyl phthalate, and the addition amount is 0.5% - 5% of the polymer mass. The stabilizer can be a hindered amine light stabilizer, and the addition amount is 0.1% - 1% of the polymer mass. The flexibility, durability, and anti-aging performance of the grating film are optimized.

[0066] In some embodiments, the polymer material for the grating film solution can also be polystyrene.

[0067] In some embodiments, for the spin-coating process, the pre-treated fiber Bragg grating sensing probe is accurately placed on the prepared substrate and fixed at a specific position by fixing devices such as high-precision clamps or low-viscosity tapes to ensure no deviation or shaking during spin-coating. A micro-syringe is used to slowly and evenly drop the prepared grating film solution onto the substrate, and the dropping amount is controlled at 0.3 - 0.8 milliliters per square centimeter to ensure that the solution covers the fiber Bragg grating sensing probe. During spin-coating, a first-stage spin-coating is carried out first, with a rotation speed of 50 - 200 revolutions per minute for 5 - 30 seconds, so that the grating film solution spreads evenly and infiltrates the fiber Bragg grating sensing probe; then a second-stage spin-coating is carried out, with a rotation speed of 1000 - 5000 revolutions per minute for 30 - 120 seconds, and the excess grating film solution is thrown out under the high-speed centrifugal force to form a high-quality grating film. During the spin-coating process, according to the solution viscosity, substrate properties, and the distribution of fiber Bragg gratings, the spin-coating acceleration is finely adjusted between 50 - 500 revolutions per second to avoid splashing of the grating film solution or uneven thickness of the grating film, ensuring stable and reliable spin-coating and excellent quality of the grating film.

[0068] In some embodiments, in step S240, after spin-coating is completed, the fiber Bragg grating sensing probe with the substrate is immediately placed in a high-precision oven for drying and curing. If the polymer material is PMMA, the oven temperature is set at 60 - 70 °C and the drying time is 10 - 18 hours; if it is PVA, the temperature is adjusted to 50 - 60 °C and the drying time is 8 - 12 hours. During the drying process, the solvent volatilizes, the polymer molecular chains crosslink, the structure of the grating film becomes stable, and the hardness and strength increase, achieving a good curing effect. The cured grating film has good stability and mechanical properties, the fiber Bragg grating is firmly embedded in the grating film, and the adhesion between the two is good, ensuring that the fiber Bragg grating thin film sensor can accurately sense the strain change on the rock surface and convert it into an optical signal during subsequent use.

[0069] Figure 3 It is a flowchart of a method for preparing microcapsules of a fiber Bragg grating thin film sensor provided by an embodiment of the present application. Figure 3 The method in [reference] may include but is not limited to steps S310 to S330:

[0070] Step S310: Dissolve benzotriazole in an organic solvent to form a homogeneous dispersion.

[0071] Step S320: Add the dispersion to an aqueous phase containing an emulsifier and perform ultrasonic emulsification to form an emulsion system containing tiny droplets.

[0072] Step S330: Add polyurethane and a diisocyanate crosslinking agent to the emulsion system for crosslinking reaction to form microcapsules.

[0073] In some embodiments, in order to make the fiber Bragg grating thin film sensor more reliable and durable, microcapsules are added to the grating film so that when the grating film is damaged, the damaged gaps can be filled by the microcapsules to repair the grating film. When moisture, corrosive media, etc. at the target monitoring sample penetrate from the rock surface into the interior of the grating film, they will first reach the area where the microcapsules are located. When the microcapsules are not ruptured, they can serve as a physical barrier themselves to delay the further diffusion rate of harmful media. Once the environmental parameters in the area where the microcapsules are located, such as humidity or pH value, reach their trigger thresholds, the microcapsules will rupture and release protective substances. These protective substances will quickly diffuse in this area and fill the surrounding microscopic pores and channels to form a protective layer. Even after the microcapsules rupture, the protective substances released will form a certain concentration gradient within the grating film. The concentration is higher in the area close to the ruptured microcapsules and gradually decreases as it diffuses towards the fiber Bragg grating sensing element, but it can still provide protection to the fiber Bragg grating sensing element to a certain extent. It can be understood that since the microcapsules are distributed in a certain area, the synergistic effect of multiple microcapsules can ensure relatively comprehensive protection for the fiber Bragg grating sensing element within a large range. Even if the diffusion range of the protective substances is limited after some microcapsules rupture, the other unruptured microcapsules can still form effective protective areas around them to jointly resist the invasion of external harmful factors.

[0074] In some embodiments, as Figure 3 shown, for the preparation of microcapsules, the capsule wall and capsule core of the microcapsules need to be determined first. The capsule wall usually selects polymer materials with good film-forming properties, chemical stability, and certain mechanical strength, such as polyurethane, polyurea, polymethyl methacrylate, etc. The capsule core is selected according to the protection requirements. For the anti-corrosion function, corrosion inhibitors such as benzotriazole and sodium molybdate can be selected; for the moisture-proof function, desiccants such as silica gel and calcium chloride can be selected. Specifically, taking the preparation of microcapsules with polyurethane as the capsule wall and benzotriazole as the capsule core as an example, a certain proportion of polyurethane prepolymer and benzotriazole need to be accurately weighed, and appropriate emulsifiers and initiators need to be prepared at the same time. The materials of the capsule core are dissolved or dispersed in an appropriate solvent to form a uniform solution or dispersion. Among them, the appropriate solvent refers to organic solvents such as toluene or ethanol. Then it is added to the water phase containing emulsifiers, and through high-speed stirring or ultrasonic emulsification, etc., the materials of the capsule core form tiny droplets and are uniformly dispersed in the water phase. The water phase with high-speed stirring containing emulsifiers is mainly used for further emulsifying the core material solution or dispersion to form tiny droplets and stably dispersing them.

[0075] More specifically, during the preparation process, the benzotriazole solution is added to the vigorously stirred aqueous phase containing an emulsifier at a certain flow rate. The stirring speed is controlled at 1000 - 5000 revolutions per minute, and stirring is continued for 10 - 30 minutes to form a stable emulsion system, ensuring that the particle size of the capsule core droplets is between 1 - 10 micrometers to obtain good encapsulation effect and release performance. The appropriate solvent can be an organic solvent such as toluene or ethanol. The vigorously stirred aqueous phase containing an emulsifier is mainly used to further emulsify the capsule core solution or dispersion into tiny droplets and form a stable dispersion system. During the emulsification and dispersion process, the capsule core solution or dispersion is added to the aqueous phase. Through the action of vigorous stirring and the emulsifier, the materials of the capsule core form tiny droplets with appropriate particle size and are evenly dispersed in the aqueous phase, so that the polymerization reaction of the capsule wall can be carried out in the aqueous phase subsequently to encapsulate the capsule core and form microcapsules.

[0076] For the polymerization reaction to form the capsule wall, an initiator or crosslinking agent is added to the emulsion system to initiate the polymerization reaction or crosslinking reaction of the polymer of the capsule wall material, and the capsule wall is gradually formed on the surface of the capsule core droplets. Specifically, for example, for polyurethane microcapsules, an appropriate amount of diisocyanate crosslinking agent can be added, and the reaction is carried out at a temperature of 50 - 80 °C for a reaction time of 2 - 6 hours, so that the polyurethane prepolymer polymerizes and crosslinks on the surface of the benzotriazole droplets to form a complete microcapsule structure. During the reaction process, the reaction conditions such as temperature, time, and reactant concentration need to be strictly controlled to ensure the quality and performance of the microcapsules.

[0077] The prepared microcapsules are uniformly mixed with the grating film solution. During the mixing process, it is necessary to ensure that the microcapsules are evenly dispersed in the grating film solution to avoid agglomeration. A method combining low-speed stirring and ultrasonic dispersion is adopted. First, stir at a rotation speed of 100 - 300 revolutions per minute for 30 - 60 minutes to preliminarily disperse the microcapsules in the solution, and then perform ultrasonic treatment. The ultrasonic power is set at 100 to 500 watts, and the ultrasonic time is set at 10 to 30 minutes to further refine the dispersion state of the microcapsules, so that the microcapsules are evenly distributed in the polymer solution. Its concentration is optimized and adjusted according to the protection requirements and sensor performance, generally between 1% - 10% by mass fraction. The polymer solution containing microcapsules is spin-coated on the substrate and embedded in the fiber Bragg grating sensing array network. During the spin-coating process, attention should be paid to controlling the spin-coating parameters, including spin-coating speed, time, and acceleration, etc., to ensure that the microcapsules are evenly distributed in the grating film and do not affect the overall quality and performance of the grating film.

[0078] Specifically, the grating film solution is firstly spread slowly and evenly on the substrate at a low speed of 500-1000 rpm for 5-30 seconds to ensure the initial uniformity of the distribution of the microcapsules, and then the grating film is formed at a high speed of 3000-5000 rpm for 30-120 seconds to shake off the excess solution, so as to form a uniform and dense grating film, so that the microcapsules are firmly embedded in the grating film structure, and can effectively play its protective function during the use of the sensor. The grating film after spin coating is dried and cured. During the curing process, the microcapsules further interact with the polymer grating film and are stabilized in the grating film structure. For grating films made of polymers such as PMMA, they are dried in an oven at 60-70°C for 10-18 hours. During this process, the polymer molecular chains around the microcapsules are cross-linked and solidified, fixing the microcapsules in appropriate positions. At the same time, the capsule walls of the microcapsules can also maintain their integrity and stability, ensuring that during the subsequent use of the sensor, when encountering external environmental stimuli, the microcapsules can release the capsule core in time according to the design requirements, thereby realizing the protection function of the fiber grating sensor probe, extending the service life of the sensor, and improving the reliability of the sensor in complex environments.

[0079] In some embodiments, when the fiber Bragg grating thin film sensor containing microcapsules is installed, it is more appropriate to place the microcapsules in the inner layer close to the grating film, within a range of 10-50 microns from the surface of the fiber Bragg grating sensor element. When the environment in which the target monitoring sample is located begins to erode the grating film and penetrate into the fiber Bragg grating sensor element, the microcapsules can respond quickly and release protective substances, forming a protective layer on the surface of the fiber Bragg grating sensor element, effectively blocking further intrusion of harmful factors.

[0080] In some embodiments, when installing a fiber grating film sensor containing microcapsules, some microcapsules can be arranged in the area 50-100 microns inside the grating film at the interface where the grating film contacts the rock. Because this area is where the environmental factors of the target monitoring sample first act, when the water and chemicals on the rock surface try to penetrate into the grating film, the microcapsules here can take the lead in taking effect.

[0081] Figure 4 is a flow chart of a grating film stripping method for a fiber grating thin film sensor provided in an embodiment of the present application, Figure 4 The method may include but is not limited to steps S410 to S440:

[0082] Step S410: placing the fiber grating thin film sensor in a sealed container;

[0083] Step S420: pouring the acetone solution into a sealed container so that the grating film is completely immersed;

[0084] Step S430: immerse the fiber grating thin film sensor for a period of time and then take it out;

[0085] Step S440: After the acetone solution attached to the grating film naturally volatilizes, the grating film of the fiber Bragg grating thin film sensor softens, and the grating film is removed.

[0086] In some embodiments, when the substrate is not suitable for monitoring the subsequent target monitoring sample, such as insufficient flexibility or adhesion, the cured grating film needs to be peeled off from the substrate. The diluted silicone release agent can be evenly applied to the interface between the grating film and the substrate, or the peeling angle can be precisely controlled between 30° and 60°, and the force can be controlled to separate slowly and evenly to avoid damaging the grating film and the fiber Bragg grating sensing probe.

[0087] In some embodiments, when the fiber Bragg grating thin film sensor after peeling off the substrate is cut into a suitable shape, such as a rectangle, a circle or other customized shapes, by a laser cutting machine or a sharp blade according to the shape and size of the monitoring area, so as to accurately fit the monitoring area on the rock surface. When cutting the grating film with a blade, in order to ensure that the grating is not damaged during the cutting process and the sensor can still be used continuously, it is necessary to select a suitable cutting tool, such as a sharp scalpel or a special grating film cutting tool. Before use, carefully check the cutting edge of the tool to ensure that there are no notches, bluntness, etc., and perform grinding treatment if necessary to ensure the sharpness of the cutting edge. For example, for a grating film with a relatively thin thickness, a scalpel with a fine cutting edge can be selected, which can cut under a relatively small acting force and reduce the impact on the fiber Bragg grating. Fix the grating film to be cut firmly on a flat workbench by using double-sided tape or a vacuum adsorption device, etc., to ensure that the grating film does not move during the cutting process. At the same time, according to the shape and size to be cut, use measuring tools and marking tools to accurately draw cutting lines on the grating film to determine the cutting path and improve the cutting accuracy. During the cutting process, control the cutting speed and maintain a slow and uniform cutting motion. Too fast cutting speed may cause the tool to generate a large impact force on the grating film and the fiber Bragg grating sensing probe, which is likely to cause damage to the fiber Bragg grating sensing probe; while too slow speed may affect the cutting efficiency and may cause the tool to stay on the grating film for too long, increasing the potential risk to the fiber Bragg grating sensing probe. For example, for general grating film materials, the cutting speed can be controlled at 5-10 centimeters per minute. Apply appropriate cutting pressure, and the pressure should be uniform and moderate. Excessive pressure may directly break the fiber Bragg grating sensing probe or cause irreversible deformation to it, while too small pressure may not be able to cut off the grating film smoothly, resulting in uneven cutting edges and even possibly damaging the fiber Bragg grating sensing probe when pulling the grating film. During the cutting process, adjust the cutting pressure according to the material and thickness of the grating film through hand feeling and experience. Observe the cutting area in real time, and tools such as a magnifying glass or a microscope can be used to closely monitor the relative position of the fiber Bragg grating sensing probe and the tool. Once it is found that the tool is approaching the fiber Bragg grating sensing probe or there is an abnormal displacement of the fiber Bragg grating sensing probe, etc., immediately stop cutting, adjust the position of the tool and then continue the operation. For example, when cutting near the fiber Bragg grating sensing probe, observe through a microscope to ensure that the tool maintains a safety distance of at least 0.5 millimeters from the fiber Bragg grating sensing probe. After cutting is completed, immediately conduct an appearance inspection on the fiber Bragg grating. Under sufficient light conditions, carefully check whether there are damages such as scratches, cracks, fractures, etc. on the surface of the fiber Bragg grating. For impurities such as dust and debris attached to the surface, use a clean and soft non-woven fabric or cotton ball dipped in a small amount of anhydrous ethanol to gently wipe, to avoid further affecting the performance of the fiber Bragg grating. Use a simple test device, such as an optical fiber optical power meter, to conduct a preliminary performance test on the sensor. Input the optical signal into the fiber Bragg grating sensing element, measure the output optical power and compare it with the data before cutting.If a significant decrease in optical power or other abnormal conditions are found, further check whether the connection parts of the fiber Bragg grating sensing elements are loose and whether there is damage inside the optical fiber. For some minor performance problems, try to repair them by reconnecting the fiber bundle jumpers, adjusting the parameters of relevant equipment, etc.; for serious damage, it may be necessary to replace part or the entire sensor of the damaged fiber Bragg grating sensing element.

[0088] In some embodiments, when the substrate of the fiber Bragg grating thin film sensor is peeled off from the fiber Bragg grating sensing probe, the grating film can be adjusted by softening the optical fiber film. According to the characteristics of the grating film material, select appropriate heating temperature and time. For the PMMA grating film, it can be heated to near the glass transition temperature. Generally, the glass transition temperature of PMMA is about 105°C. Note that the temperature cannot be too high to avoid excessive softening or even decomposition of the grating film. Oven heating can be used. Heat the grating film to the target temperature at a heating rate of 1-2°C per minute and keep it for 10-30 minutes to gradually soften the grating film. During the heating process, the temperature can be monitored in real time through a temperature sensor to ensure the accuracy and stability of the temperature.

[0089] In some embodiments, when softening the grating film by toluene fumigation. Place the PMMA grating film in a sealed container and place a small amount of toluene at the bottom of the container. The vapor generated by the volatilization of toluene will gradually penetrate into the PMMA grating film to soften it. The fumigation time depends on the thickness of the grating film and the required softening degree. Generally, for a grating film with a thickness of 0.3-0.8 mm, fumigation for 2-6 hours is more appropriate. However, toluene is toxic and volatile, and the operation must be carried out in a well-ventilated fume hood, and the dosage of toluene must be strictly controlled to prevent potential safety hazards and environmental pollution caused by its excessive volatilization.

[0090] In some embodiments, as Figure 4 shown, when softening the grating film by acetone solution. Immerse the PMMA grating film in the acetone solution. The immersion time should not be too long, generally 1-5 minutes, to avoid excessive dissolution of the thin grating film. After taking it out, let the acetone volatilize naturally in a ventilated environment. As the acetone volatilizes, the grating film will gradually soften. During the immersion process, ensure that the grating film is completely immersed in the acetone solution, but do not stir or knead the grating film excessively to prevent damage to the grating film structure.

[0091] Figure 5 is a flowchart of an application method of a fiber Bragg grating thin film sensor provided by an embodiment of the present application, Figure 5 The method in

[0092] Step S510: Connect a plurality of fiber Bragg grating thin film sensors to the optical fiber transmission line through connection components;

[0093] Step S520: fixing the connected fiber grating thin film sensors at different target monitoring samples through the grating films;

[0094] Step S530: setting the strain threshold of the fiber grating thin film sensor;

[0095] Step S540: Acquire strain data of the fiber grating thin film sensor at different target monitoring samples;

[0096] Step S550: When the strain data exceeds the strain threshold, the crack position of the target monitoring sample is determined by triangulation or least square method, and the crack length of the target monitoring sample is determined by the strain data.

[0097] In some embodiments, Figure 5 As shown, in step S510, a plurality of fiber grating thin film sensors are connected to the optical fiber transmission line through a connecting component, and the connection process can form a sensor array network in the form of series connection or parallel connection.

[0098] In some embodiments, grating thin film sensors are arranged. Before arranging grating thin film sensors, it is necessary to comprehensively consider multiple factors such as the geological characteristics of the rock structure, the characteristics of the force distribution, and the historical monitoring data of the target monitoring sample, and use advanced numerical simulation analysis technology and field survey experience to accurately predict the key positions where cracks may appear, wherein the numerical simulation analysis technology can be finite element analysis. Then the prepared fiber grating thin film sensor is tightly attached to the predetermined position on the rock surface. A high-strength, high-adhesive adhesive is used, and the operation is strictly in accordance with the instructions for use to ensure that the adhesive is evenly applied and of moderate thickness. After curing, a firm bonding layer is formed, so that the sensor can accurately sense the small strain changes on the rock surface, wherein the adhesive can be a two-component epoxy resin adhesive or a cyanoacrylate adhesive. The arrangement method can be flexibly selected. If it is necessary to fully grasp the strain distribution on the rock surface, an array arrangement is adopted, such as a rectangular or circular array, and the array spacing is adjusted between 5-20 cm according to the monitoring accuracy requirements to achieve large-area all-round monitoring; for weak parts of the rock structure, such as joints, crack development areas, or stress concentration areas, sensors are arranged in a focused manner to improve the monitoring sensitivity of crack initiation and expansion in key areas.

[0099] In some embodiments, for the data collection and connection method of the fiber grating thin film sensor, a high-precision, multi-channel fiber grating demodulator is used to collect sensor data, usually with 8-32 channels. The end of the fiber bundle of the fiber grating thin film sensor is accurately connected to each channel of the demodulator through the fiber bundle jumper head. When connecting, the fiber end face is kept clean and free of dust and oil to ensure the efficiency of optical signal transmission. It is understandable that the end face is cleaned with a professional fiber cleaning tool before connection, and then connected with a high-precision fiber connector to ensure stable connection and low loss.

[0100] In some embodiments, when the fiber Bragg grating thin film sensor collects data, when the target monitoring sample is a rock and the internal cracks in the rock cause strain changes on the rock surface, the fiber Bragg grating sensing element in the fiber Bragg grating thin film sensor is sensitively responsive to strain due to its optical properties, manifested as a significant change in the reflection spectrum. The multi-channel fiber Bragg grating demodulator collects the reflection spectrum signal, including key information such as the light intensity values at different wavelengths. Based on the principle of the fiber Bragg grating strain-spectral relationship, when the fiber Bragg grating is subjected to strain, its internal microstructure changes, the refractive index of the optical fiber and the grating period change, and according to the Bragg condition, the Bragg wavelength drifts. The quantitative relationship between the strain and the wavelength drift amount is:

[0101]

[0102] where Δλ is the wavelength drift amount, P e is the effective elasto-optic coefficient, ε is the strain, and λ B is the initial Bragg wavelength of the fiber Bragg grating. By accurately measuring the wavelength drift amount of the reflection spectrum and the light intensity change, data related to the strain on the rock surface is obtained. When there is no strain normally, the fiber Bragg grating reflection spectrum has a peak at a specific wavelength λ0. When strain occurs, the peak wavelength drifts to λ0 + Δλ, and the light intensity changes from I0 to I0 + ΔI. The demodulator collects these change data in real time, providing a basis for subsequent crack monitoring and analysis.

[0103] In some embodiments, the spectral data collected by the multi-channel fiber Bragg grating demodulator is sent to the data receiving terminal through the wireless transmission module. The wireless transmission module can be Wi-Fi, Bluetooth, or ZigBee, and the data receiving terminal can be a computer or a server. When there is a perfect Wi-Fi network at the construction site, Wi-Fi transmission is preferred. Its transmission rate can reach 10 - 100 Mbps, the transmission distance is far, and the data transmission is stable, meeting the real-time high-speed transmission requirements of a large amount of monitoring data. Conventional Wi-Fi transmission can reach more than 100 meters in an obstacle-free environment. In remote mountainous areas or where there is no Wi-Fi network, low-power, short-distance wireless transmission technologies such as Bluetooth or ZigBee can play a better role. Bluetooth is suitable for short-distance monitoring scenarios within 10 to 100 meters, with a small amount of data and low power consumption requirements. Long-distance transmission can be achieved by setting multiple relay nodes; ZigBee has strong self-organizing capabilities and a large network capacity, can support hundreds of nodes, and has low power consumption. It is suitable for data transmission in large-scale sensor networks. In complex environments such as mountain tunnels or underground mines, it can build a stable and reliable wireless transmission network, and the transmission distance is generally between 10 and 1000 meters.

[0104] In some embodiments, the wireless transmission module can select radio frequency transmission as the transmission method according to the application environment.

[0105] In some embodiments, after the receiving end receives a wireless signal, a receiving device such as a wireless network card, a Bluetooth receiver, or a ZigBee coordinator receives and decodes it to restore it to the original spectral data. Then, it is processed using specialized data analysis software. First, the data is cleaned, and median filtering or mean filtering algorithms are used to remove noise and outliers to ensure data quality. Next, interpolation processing is performed, and linear interpolation or spline interpolation is used to ensure the continuity of the wavelength data for subsequent analysis. Strain data is calculated according to the strain-spectral relationship model, and the collected wavelength drift amount is substituted into the quantitative relationship formula between strain and wavelength drift amount to calculate the preliminary strain value. At the same time, considering the relationship between light intensity change and strain, the preliminary strain value is corrected and supplemented through a pre-calibrated light intensity-strain relationship model. For example, the light intensity-strain relationship model is a quadratic function relationship: I = aε 2 + bε + c, where a, b, and c are calibration coefficients. Thus, more accurate strain data is obtained, which accurately reflects the actual strain situation on the rock surface and provides reliable basic data for crack monitoring and analysis.

[0106] In some embodiments, such as Figure 5 shown, the strain data is processed using data analysis software, and a strain threshold is set. The strain threshold is controlled between 0.005 and 0.01. When the strain in a certain area exceeds the threshold, it is determined that a crack has occurred. Through the strain data of multiple sensors, positioning algorithms such as triangulation and the least squares method are used to determine the crack position. According to the strain change amplitude and distribution, the crack length and propagation direction are calculated in combination with an empirical formula. The empirical formula is: L = k × Δε, where L is the crack length, k is the calibration coefficient, and Δε is the strain change amplitude. A monitoring report is generated regularly, and the content includes the crack development trend, the evaluation of the rock structure stability, etc., providing a decision-making basis for engineering maintenance.

[0107] In some embodiments, in order to process the sensing data obtained by the fiber Bragg grating thin film sensor, the data analysis can be completed through a crack recognition algorithm based on machine learning to judge the crack situation.

[0108] In some embodiments, such as Figure 6As shown, when the fiber Bragg grating thin film sensor 3 is applied to monitoring, the fiber Bragg grating thin film sensor 3 is tightly connected to the target monitoring sample 1 through the adhesive layer 2 prepared by an adhesive. A cushion layer 4 is provided on the other side of the fiber Bragg grating thin film sensor 3. The fiber Bragg grating thin film sensor 3 is connected to a multi-channel fiber Bragg grating demodulator 6 through a fiber bundle jumper 5. The data obtained by the fiber Bragg grating thin film sensor 3 is sent to a data receiving terminal 8 through a wireless transmission module 7, and the obtained data is analyzed in real time by data analysis software 9. Among them, the data analysis software 9 can be an operating software embedded in the data receiving terminal 8; when the fiber Bragg grating thin film sensor 3 is arranged between two rocks to obtain strain data, the cushion layer 4 is used because the rock surface is often rough and has various sharp protrusions or depressions. The cushion layer 4 can effectively reduce the direct pressure and wear caused by the unevenness of the rock surface to the fiber Bragg grating thin film sensor 3, thereby achieving buffering and protection. The cushion layer 4 can also increase the friction and adhesion between the fiber Bragg grating thin film sensor 3 and the rock surface, assist the adhesive to better fix the fiber Bragg grating thin film sensor 3 for auxiliary fixation and optimize strain transfer. Moreover, the cushion layer 4 can make the strain on the rock surface be transmitted to the fiber Bragg grating thin film sensor 3 more evenly, optimizing the strain transfer.

[0109] The embodiments described in the embodiments of the present application are for more clearly explaining the technical solutions of the embodiments of the present application, and do not constitute a limitation to the technical solutions provided by the embodiments of the present application. Those skilled in the art know that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

[0110] Those skilled in the art can understand that the technical solutions shown in the figures do not constitute a limitation to the embodiments of the present application, and may include more or fewer steps than shown in the figures, or combine some steps, or different steps.

[0111] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0112] Those of ordinary skill in the art can understand that all or some of the steps in the methods disclosed above, and the functional modules / units in the systems and devices can be implemented as software, firmware, hardware and their appropriate combinations.

[0113] In several embodiments provided by the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the above division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections between each other can be through some interfaces. The indirect couplings or communication connections of devices or units can be in electrical, mechanical or other forms.

[0114] The preferred embodiments of the embodiments of the present application have been described above with reference to the accompanying drawings. However, this does not limit the scope of the rights of the embodiments of the present application. Any modifications, equivalent replacements, and improvements made by those skilled in the art without departing from the scope and essence of the embodiments of the present application shall fall within the scope of the rights of the embodiments of the present application.

Claims

1. A method for preparing a fiber grating thin film sensor, characterized in that: The following steps are involved: Prepare the fiber grating thin film sensor comprising an optical fiber, a packaging component and a grating film; Preprocessing the optical fiber and the packaging component; Writing a fiber grating into the pre-processed optical fiber to form a fiber grating sensing element; The fiber Bragg grating sensor element is packaged by the packaging component to form a fiber Bragg grating sensor probe; The fiber grating sensor probe is coated with the grating film to obtain the fiber grating thin film sensor.

2. The preparation method according to claim 1, characterized in that: The step of coating the fiber grating sensor probe with the grating film comprises the following steps: Fixing the fiber grating sensor probe on a substrate; Dropping the grating film solution onto the fiber grating sensing probe fixed on the substrate; Spin coating the fiber grating sensing probe to which the grating film solution is dropped; The fiber grating sensor probe with the substrate is placed in an oven for drying and curing to complete the coating.

3. The preparation method according to claim 2, characterized in that: The substrate includes a transparent glass sheet or a plastic sheet made of polyethylene terephthalate.

4. The preparation method according to claim 2, characterized in that: The grating film solution comprises: polymethyl methacrylate, toluene solvent, plasticizer and light stabilizer.

5. The preparation method according to claim 4, characterized in that: The plasticizer includes dibutyl phthalate, and the light stabilizer includes a hindered amine light stabilizer.

6. The preparation method according to claim 2, characterized in that: The spin coating includes one-stage spin coating and two-stage spin coating, the rotation speed of the one-stage spin coating is less than the rotation speed of the two-stage spin coating, the time of the one-stage spin coating is less than or equal to the time of the two-stage spin coating, and the acceleration from the one-stage spin coating to the two-stage spin coating is adjusted according to the viscosity of the grating film solution and the distribution of the fiber grating sensor probe.

7. The preparation method according to claim 1, characterized in that: The grating film comprises a microcapsule, wherein the microcapsule comprises a capsule wall and a capsule core, wherein the capsule wall wraps the capsule core; The capsule wall is used to protect the capsule core from leaking when the grating film is not damaged; The capsule core is used to fill the damaged gaps and repair the grating film when the grating film is damaged.

8. A method for preparing microcapsules of fiber grating thin film sensors, characterized in that: The microcapsule preparation method is applied to the fiber grating thin film sensor prepared by the preparation method according to any one of claims 1 to 7, and the microcapsule preparation method comprises the following steps: dissolving benzotriazole in an organic solvent to form a uniform dispersion; Adding the dispersion into a water phase containing an emulsifier to perform ultrasonic emulsification to form an emulsion system containing tiny droplets; Polyurethane and diisocyanate crosslinking agent are added into the emulsion system to carry out crosslinking reaction to form the microcapsules.

9. A method for stripping a grating film of a fiber grating thin film sensor, characterized in that: The grating film stripping method is applied to the fiber grating thin film sensor prepared by the preparation method according to any one of claims 1 to 7, and the grating film stripping method comprises the following steps: Placing the fiber grating thin film sensor in a sealed container; Pour the acetone solution into the sealed container so that the grating film is completely immersed; immersing the fiber grating thin film sensor for a period of time and then taking it out; When the acetone solution to which the grating film is attached naturally evaporates, the grating film of the fiber grating thin film sensor softens, and the grating film is removed.

10. An application method of a fiber grating thin film sensor, characterized in that: The application method comprises the following steps: Connecting a plurality of the fiber grating thin film sensors prepared by the preparation method according to any one of claims 1 to 7 to a fiber transmission line through a connecting component; Fixing the connected fiber grating thin film sensors at different target monitoring samples via the grating films; Setting a strain threshold of the fiber grating thin film sensor; Acquiring strain data of the fiber grating thin film sensor at different target monitoring samples; When the strain data exceeds the strain threshold, the crack position of the target monitoring sample is determined by triangulation or least square method, and the crack length of the target monitoring sample is determined by the strain data.

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