A temperature and humidity in-situ detection sensor and a humidity sensor preparation method

Abstract

The present invention discloses an in-situ temperature and humidity detection sensor, comprising a protective layer having an extended groove in the middle thereof, a hydrophobic isolation film fixed to one side of the protective layer having the groove, adhesives applied to the protective layer surfaces on both sides of the hydrophobic isolation film, and a humidity sensor and a temperature sensor arranged in parallel within the groove. The humidity sensor comprises a first fiber Bragg grating (FBG), comprising a first core, a first grating region disposed on the first core, and a first cladding surrounding the grating region, with a PVA film and a composite KGM hydrogel film attached to the periphery of the first cladding in order from the inside out. The temperature sensor comprises a second fiber Bragg grating (FBG), comprising a second core, a second grating region disposed on the second core, and a second cladding surrounding the second grating region. The in-situ temperature and humidity detection sensor of the present invention can accurately detect the temperature and humidity information of a stone cultural relic, and the measurement results are not affected by external factors such as ambient humidity.

Description

Technical Field

[0001] The present invention relates to the technical field of stone cultural relic detection, and in particular to a temperature and humidity in-situ detection sensor and a humidity sensor preparation method. Background Art

[0002] Stone artifacts are invaluable cultural heritage left over from the course of human history, possessing unique historical, cultural, and artistic value. Their proper protection is a necessary requirement for the advancement of our times and a vital part of the continuation of human civilization. Currently, a significant number of stone artifacts remain outdoors for extended periods due to their immovable nature, making them susceptible to a range of physical, chemical, and biological weathering processes, leading to the continued development of various types of damage.

[0003] Numerous previous studies have revealed that water is often a key factor in the deterioration of stone artifacts. In particular, during chemical weathering, water plays a crucial role in the migration of chemical components on the stone surface and the precipitation of salts. Cracks, pores, and joints within the rock mass are often filled with water, making the rock susceptible to dissolution, softening, and collapse. Therefore, accurate online, in-situ temperature and humidity monitoring of stone artifacts is crucial for early warning of deterioration and effective localized preventive protection.

[0004] Currently, the main non-destructive testing technologies for moisture content in masonry materials, both domestically and internationally, include infrared thermal imaging, nuclear magnetic resonance (NMR), microelectrode detection, microwave detection, and fiber optic sensing. Fiber optic sensors, among other technologies, have been extensively researched for measuring relative humidity in air due to their simplicity, long lifespan, and ease of multiplexing. However, current fiber optic sensors often struggle to achieve high accuracy when used for online, in-situ measurement of the binary parameters of temperature and humidity on stone artifacts in semi-dry environments (humidity levels between 40% and 60%) due to interference from the external humidity.

[0005] Therefore, improvements are made based on the existing research on optical fiber humidity sensors to realize an in-situ temperature and humidity detection sensor with higher detection accuracy. Summary of the Invention

[0006] The purpose of the present invention is to provide a temperature and humidity in-situ detection sensor and a humidity sensor preparation method to solve the technical problem in the prior art that when optical fiber sensors are used for online in-situ detection of the binary parameters of temperature and humidity of stone cultural relics in a semi-dry environment, it is often difficult to achieve high-accuracy temperature and humidity detection due to humidity interference from the external environment.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention discloses an in-situ temperature and humidity detection sensor for simultaneously detecting the temperature and humidity of stone cultural relics, comprising a protective layer having an extended groove in the middle of the protective layer, a hydrophobic isolation membrane fixed to one side of the protective layer having the groove, adhesives provided on the protective layer surfaces on both sides of the hydrophobic isolation membrane, and a humidity sensor and a temperature sensor provided in parallel and parallel manner within the groove;

[0009] The humidity sensor includes a first fiber Bragg grating, which includes a first fiber core, a first grating region provided on the first fiber core, a first cladding covering the periphery of the grating region, and a PVA film and a composite KGM hydrogel film attached to the periphery of the first cladding in order from the inside to the outside;

[0010] The temperature sensor includes a second fiber Bragg grating, the second fiber Bragg grating includes a second fiber core, a second grating region is provided on the second fiber core, and the outer periphery of the second grating region is covered with a second cladding.

[0011] The technical solution disclosed in this proposal can be applied to the temperature and humidity detection of stone cultural relics, and is particularly applicable to the temperature and humidity detection of stone cultural relics in a semi-dry environment, wherein the semi-dry environment refers to an environmental condition with a humidity between 40% and 60%.

[0012] The temperature and humidity in-situ detection sensor disclosed in the present invention can avoid the interference of air humidity changes on the humidity measurement of stone cultural relics. It is encapsulated in a packaging structure similar to a "Band-Aid" and has the characteristics of heat and cold resistance, good flexibility and effective isolation from air humidity.

[0013] In practical applications, simply attaching the encapsulated temperature and humidity in-situ detection sensor area to the surface or cracks of a stone artifact allows for accurate online, in-situ measurement of the artifact's humidity. This is because polyvinyl alcohol (PVA) and composite konjac glucomannan gel (KGM) contain a large number of hydroxyl hydrophilic functional groups, which form hydrogen bonds with water molecules, thereby adsorbing and binding to water molecules in the environment. Simultaneously, the area of ​​the first grating region, to which the PVA film and composite KGM hydrogel film are attached, is masked by the encapsulation structure and can only absorb water molecules transmitted from the surface and interior of the stone artifact, unaffected by changes in the external humidity. Simultaneously, the first fiber Bragg grating's two ends are in a freely extended state, avoiding the technical problem of reduced detection accuracy due to external strain when measuring the humidity of stone artifacts.

[0014] Specifically, the PVA film refers to a polyvinyl alcohol film, and the composite KGM hydrogel film refers to a composite konjac glucomannan hydrogel film. The humidity sensor, made of polyvinyl alcohol (PVA) film and composite konjac glucomannan (KGM) hydrogel film, accurately responds to humidity changes in stone cultural relics. It also exhibits high sensitivity and is harmless to the cultural relics, enabling online, in-situ detection of temperature and humidity in semi-arid environments.

[0015] The additional temperature sensor is designed to add a temperature compensation unit to eliminate interference with humidity measurements caused by temperature changes in stone artifacts. When preparing the temperature sensor, a section of fiber Bragg grating (FBG) is used as the second FBG. The second grating region is located on the core of the second FBG. The outer periphery of the second grating region is coated with a second cladding and a second coating, respectively. An optical stripper is used to remove the second coating corresponding to the second grating region, resulting in a temperature sensor for sensing temperature changes.

[0016] Preferably, the first grating region and the second grating region are arranged in a groove region corresponding to the hydrophobic isolation film.

[0017] In this way, during detection, the humidity sensor only receives humidity from the stone cultural relics, avoiding humidity errors caused by the external environment.

[0018] Preferably, the mathematical relationship between the temperature change and humidity value in the temperature and humidity in-situ detection sensor and the drift of the Bragg wavelength of the temperature sensor and the humidity sensor is as follows:

[0019]

[0020] Where ΔT is the change in temperature, RH is the humidity, K T1 and K T2 are the temperature sensitivity coefficients of the humidity sensor and temperature sensor, K RH is the humidity sensitivity coefficient of the humidity sensor, Δλ1 and Δλ2 are the Bragg wavelength drifts of the humidity sensor and temperature sensor respectively;

[0021] Among them, K RH =λ B (1-P e )β,λ B is the first fiber Bragg grating resonant center wavelength, P e is the elastic-optical coefficient of the first fiber Bragg grating, and β is the wet expansion coefficient of the first fiber Bragg grating attached with the PVA film and the composite KGM hydrogel film.

[0022] In a second aspect, the present invention further discloses a method for preparing a humidity sensor, which is used to prepare the humidity sensor in the temperature and humidity in-situ detection sensor as described above, comprising the following steps:

[0023] S1, taking a fiber Bragg grating and performing preprocessing to obtain a first fiber Bragg grating for preparing a humidity sensor, wherein the first fiber Bragg grating has a first grating region;

[0024] S2, performing silane treatment on the first fiber Bragg grating pretreated in step S1 to enhance the adhesion strength between the optical fiber with the coating removed and the moisture-sensitive material in subsequent steps;

[0025] S3. Add polyvinyl alcohol powder to deionized water and heat in a water bath until the polyvinyl alcohol powder is completely dissolved, and prepare a PVA solution with a mass percentage of 10% to 15% for later use;

[0026] S4, slowly adding KGM powder to the prepared HPC solution to obtain a KGM hydrogel mixture containing HPC;

[0027] S5, adding nano-carbon powder to the prepared KGM hydrogel mixture containing HPC, wherein the mass percentage of the nano-carbon powder in the KGM hydrogel mixture containing HPC is 1-4%, stirring, ultrasonically oscillating, and standing at room temperature to obtain a composite KGM hydrogel containing carbon nano-powder;

[0028] S6. Repeatedly scrape-coat the PVA solution on the surface of the first cladding layer corresponding to the first grating region according to a preset thickness of the PVA film and dry the PVA solution until the PVA film reaches a preset thickness, thereby obtaining a first fiber Bragg grating with the PVA film attached thereto.

[0029] S7. Depositing a composite KGM hydrogel containing carbon nanopowder on the surface of the PVA film and freeze-drying the film to shape the composite KGM hydrogel containing carbon nanopowder into a composite KGM hydrogel film, thereby obtaining a humidity sensor having the PVA film and the composite KGM hydrogel film attached thereto in sequence.

[0030] The preparation method of the humidity sensor disclosed in the present invention has the following technical effects: the preparation method is simple and easy to operate, and the obtained humidity sensor with the PVA film and the composite KGM hydrogel film attached sequentially from the inside to the outside has high sensitivity and high measurement accuracy.

[0031] Preferably, in step S1, the fiber Bragg grating is pre-processed using the following method: the first grating region is located on the core of the first fiber Bragg grating, and the periphery of the first grating region is respectively covered with a first cladding and a first coating layer; the first coating layer corresponding to the first grating region is removed by an optical stripper, and then the first grating region is partially immersed in anhydrous ethanol and deionized water in turn, and ultrasonically cleaned for 8 to 10 minutes, and then set aside after cleaning.

[0032] Preferably, in step S2, the method for silane-treating the first fiber Bragg grating pretreated in step S1 is: first, immersing the first grating area in a NaOH solution, then rinsing it with deionized water and drying it for later use, then placing the first grating area in a silane coupling agent with a mass percentage concentration of 10-15%, taking it out and placing it in a vacuum drying oven for later use.

[0033] Preferably, in step S4, a 0.5% mass fraction HPC solution is first prepared, and the pH of the HPC solution is adjusted to 8.5; then KGM powder is slowly added to the prepared HPC solution to obtain an HPC-KGM hydrogel mixture, wherein the mass percentage of KGM in the mixture is 1.5-4.5%.

[0034] Preferably, a 0.5% mass fraction HPC solution is prepared by the following method: 20-30% of a predetermined amount of water is heated to 60° C., HPC is slowly added under sufficient stirring, and after all HPC is added, the remaining predetermined amount of water is added, stirred until the HPC is completely dissolved, and allowed to stand to obtain a clear HPC solution.

[0035] Preferably, the specific operation method of step S6 is: first, use tweezers to clamp the PVA solution, and use a scraping method to pull it along the cladding surface corresponding to the first grating area, so as to deposit the PVA on the cladding surface corresponding to the first grating area; then, place the coated first fiber Bragg grating in a vacuum drying oven at 75 to 85°C and dry it for 3 to 5 minutes; repeat this operation multiple times until the PVA film reaches a preset thickness and stop scraping to obtain a first fiber Bragg grating with a PVA film attached.

[0036] In this way, by controlling the pulling times to obtain PVA films of different thicknesses on the cladding surface corresponding to the first grating region, the sensitivity of the humidity sensor can be controlled according to actual needs.

[0037] Preferably, the specific operation method of step S7 is: using a shaping tube, and sleeved on the outer periphery of the first fiber Bragg grating corresponding to the first grating area, while ensuring that the first grating area is located at the center of the shaping tube; then evenly filling the shaping tube with a composite KGM hydrogel containing carbon nanopowder, and placing it in a refrigerator for freezing and shaping, and then freeze-drying to obtain a humidity sensor with a PVA film and a composite KGM hydrogel film attached thereto from the inside to the outside.

[0038] The present invention has the following beneficial effects: in actual application, the temperature and humidity in-situ detection sensor disclosed by the present invention only needs to adhere the encapsulated temperature and humidity in-situ detection sensor area to the surface or cracks of stone cultural relics to achieve online in-situ accurate measurement of the humidity of the stone cultural relics. Since the area of ​​the first grating area to which the PVA film and the composite KGM hydrogel film are attached is covered by the encapsulation structure, it can only absorb water molecules transmitted on the surface and inside of the stone cultural relics and is not affected by changes in the humidity of the external environment. Moreover, the humidity sensor's humidity-sensitive material uses polyvinyl alcohol (PVA) film and composite konjac glucomannan (KGM) hydrogel film, which can accurately respond to information on changes in the humidity of the stone cultural relics. When responding to humidity, it has high sensitivity and does not damage the cultural relics. It can smoothly achieve online in-situ detection of the temperature and humidity of the stone cultural relics in a semi-dry environment. In short, the temperature and humidity in-situ detection sensor disclosed by the present invention can accurately detect the temperature and humidity information of the stone cultural relics, and the measurement results are not affected by external factors such as ambient humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the purpose, technical solutions 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:

[0040] Figure 1 It is a schematic structural diagram of the temperature and humidity in-situ detection sensor of the present invention.

[0041] Figure 2 This is a schematic diagram of the packaging structure of the temperature and humidity in-situ detection sensor of the present invention.

[0042] Figure 3 It is a schematic structural diagram of the humidity sensor of the present invention.

[0043] Figure 4 It is a schematic diagram of the temperature sensor structure of the present invention.

[0044] Figure 5 Schematic diagram of the installation of the temperature and humidity in-situ detection sensor for detecting the temperature and humidity of stone cultural relics in an embodiment of the present invention.

[0045] Figure 6 : is the relationship between the Bragg wavelength drift and temperature of the temperature sensor and the humidity sensor in the embodiment of the present invention.

[0046] Figure 7 : This is the relationship between the Bragg wavelength drift of the temperature sensor and the humidity sensor and the humidity of the stone cultural relic in the embodiment of the present invention (temperature is 25°C).

[0047] Explanation of the accompanying drawings: 101, protective layer; 102, groove; 103, hydrophobic isolation film; 104, adhesive; 107, supporting plate; 201, first fiber Bragg grating; 202, first fiber core; 203, first grating region; 204, first cladding; 205, first coating layer; 206, PVA film; 207, composite KGM hydrogel film; 301, second fiber Bragg grating; 302, second fiber core; 303, second grating region; 304, second cladding; 305, second coating layer; 400, stone cultural relic. DETAILED DESCRIPTION

[0048] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0049] 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 require further definition or explanation in subsequent figures. In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the figures, or the orientations or positional relationships in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and are not to be construed as indicating or implying relative importance. Furthermore, terms such as "horizontal" and "vertical" do not imply that a component must be absolutely horizontal or overhanging, but rather may be slightly tilted. For example, "horizontal" simply refers to a direction that is more horizontal than "vertical," and does not imply that the structure must be completely horizontal, but rather may be slightly tilted. In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0050] The present invention can be applied to in-situ online detection of stone cultural relics, solving the technical problem in the prior art that optical fiber sensors are often difficult to achieve high-accuracy temperature and humidity detection due to humidity interference from the external environment when performing online in-situ detection of the binary parameters of temperature and humidity of stone cultural relics in a semi-dry environment.

[0051] First, see Figures 1 to 4 Based on the technical problems solved above, the present invention discloses an in-situ temperature and humidity detection sensor for simultaneously detecting the temperature and humidity of stone cultural relics, comprising a protective layer 101, wherein the middle portion of the protective layer 101 has an extended groove 102, a hydrophobic isolation membrane 103 is fixed to one side of the protective layer 101 having the groove 102, adhesives 104 are respectively provided on the surfaces of the protective layer 101 on both sides of the hydrophobic isolation membrane 103, and a humidity sensor and a temperature sensor are arranged side by side and in parallel in the groove 102.

[0052] See also Figure 3 The humidity sensor includes a first fiber Bragg grating 201, which includes a first fiber core 202. A first grating region 203 is provided on the first fiber core 202. The outer periphery of the grating region is covered with a first cladding 204. The outer periphery of the first cladding 204 is sequentially attached with a PVA film 206 and a composite KGM hydrogel film 207 from the inside to the outside.

[0053] See also Figure 4 The temperature sensor includes a second fiber Bragg grating 301 , which includes a second fiber core 302 , a second grating region 303 is provided on the second fiber core 302 , and the outer periphery of the second grating region 303 is covered with a second cladding 304 .

[0054] The technical solution disclosed in this solution can be applied to the temperature and humidity detection of stone cultural relics 400, and is particularly applicable to the temperature and humidity detection of stone cultural relics 400 in a semi-dry environment, wherein the semi-dry environment refers to an environmental condition with a humidity between 40% and 60%.

[0055] The temperature and humidity in-situ detection sensor disclosed in the present invention can avoid the interference of air humidity changes on the humidity measurement of the stone cultural relic 400 body. It is encapsulated in a packaging structure similar to a "Band-Aid" and has the characteristics of heat and cold resistance, good flexibility and effective isolation from air humidity.

[0056] In actual applications, only the encapsulated temperature and humidity in-situ detection sensor region needs to be adhered to stone cultural relics 400 surfaces or cracks, so as to realize the online in-situ accurate measurement of stone cultural relics 400 body humidity. The reason is that there are a large amount of hydroxyl hydrophilic functional groups in polyvinyl alcohol (PVA) and compound konjac glucomannan gel (KGM), these hydrophilic functional groups can form hydrogen bonds with water molecules, and then the water molecules in the adsorption environment are combined, while the region of the first grating area 203 attached with PVA film 206 and compound KGM hydrogel film 207 is covered by the encapsulation structure, can only absorb the water molecules on stone cultural relics 400 surfaces and internal transmission, not subject to the influence of external environment humidity change. The first fiber Bragg grating 201 two ends are in free extension state simultaneously, avoid the technical problem that the detection accuracy rate that sensor brings due to external strain declines when measuring stone cultural relics 400 humidity.

[0057] Specifically, the PVA film 206 is a polyvinyl alcohol film, and the composite KGM hydrogel film 207 is a composite konjac glucomannan hydrogel film. The humidity sensor, which utilizes polyvinyl alcohol (PVA) film and composite konjac glucomannan (KGM) hydrogel film as its humidity-sensitive materials, can accurately respond to humidity changes in the stone artifact 400. It also exhibits high sensitivity and is harmless to the artifact, enabling online, in-situ detection of the temperature and humidity of the stone artifact 400 in a semi-arid environment.

[0058] The reason for providing an additional temperature sensor is to add a temperature compensation unit to eliminate interference caused by temperature changes of the stone artifact 400 on the humidity measurement. When preparing the temperature sensor, a section of fiber Bragg grating is used as the second fiber Bragg grating 301. The second grating region 303 is located on the core of the second fiber Bragg grating 301. The outer periphery of the second grating region 303 is respectively coated with a second cladding layer 304 and a second coating layer 305. The second coating layer 305 corresponding to the second grating region 303 is removed using an optical stripper, thus obtaining a temperature sensor for sensing temperature changes.

[0059] Specifically, when detecting the temperature and humidity of the stone cultural relic 400, the humidity sensor can simultaneously respond to the temperature and humidity change information of the stone cultural relic 400. The temperature fiber Bragg grating is a fiber Bragg grating with the coating removed, which is used to test the temperature response of the stone cultural relic 400 and eliminate the influence of temperature changes on the humidity measurement results.

[0060] In addition, the present invention can be widely applied to the online real-time in-situ monitoring of temperature and humidity in the fields of stone cultural relics, concrete, rock structure health, etc.

[0061] As a preference, see Figure 1 and Figure 2 The first grating region 203 and the second grating region 303 are arranged in the groove 102 area corresponding to the hydrophobic isolation film 103.

[0062] In this way, during detection, the humidity sensor only receives the humidity from the stone cultural relic 400, thereby avoiding humidity errors caused by the external environment.

[0063] For details, please refer to Figure 1 A support sheet 107 is further provided on one side of the groove 102 corresponding to the adhesive 104 , for relatively fixing the positions of the first fiber Bragg grating 201 and the second fiber Bragg grating 301 .

[0064] The theoretical analysis of the temperature and humidity in-situ detection sensor is as follows.

[0065] The first fiber Bragg grating resonant center wavelength λ B and the effective refractive index n of the optical fiber eff and the grating period Λ satisfies,

[0066] λ B =2n eff Λ (1)

[0067] In formula (1), λ B is the first fiber Bragg grating resonant center wavelength, n eff is the effective refractive index of the optical fiber, and Λ is the grating period.

[0068] When broadband incident light enters an optical fiber, light of a specific wavelength is reflected by the fiber Bragg grating (FBG), while light of other wavelengths is transmitted through the fiber Bragg grating. The wavelength of the reflected light is called the Bragg wavelength. Changes in temperature and strain will cause changes in the grating period and effective refractive index, resulting in a shift in the Bragg wavelength, which is expressed as follows:

[0069] Δλ B =λ B {[(1-P e )α+ξ]ΔT+(1-P e )ε} (2)

[0070] In formula (2), ΔλB B is the change of the Bragg wavelength of the first fiber Bragg grating, λ B is the resonant center wavelength of the first fiber Bragg grating, α is the thermal expansion coefficient of the first fiber Bragg grating, ξ is the thermo-optic coefficient of the first fiber Bragg grating, ΔT is the temperature change, P eis the elastic-optical coefficient of the first fiber Bragg grating, and ε is the strain generated on the first fiber Bragg grating. In addition, under constant temperature conditions, ΔT = 0, and the first term on the right side of equation (2) can be ignored.

[0071] Polyvinyl alcohol (PVA) and composite konjac glucomannan gel (KGM) contain a large number of hydroxyl hydrophilic functional groups. These hydrophilic functional groups will form hydrogen bonds with water molecules, thereby being able to adsorb and bind water molecules in the environment. To make the first fiber Bragg grating sensitive to humidity, it is necessary to apply the humidity-sensitive materials polyvinyl alcohol and composite konjac glucomannan gel to the grating area of ​​the FBG twice to form a humidity-sensitive unit, forming a uniform humidity-sensitive coating on the fiber surface. This coating can expand or contract in volume according to changes in the molecular weight of water in the environment, thereby causing axial strain in the first fiber Bragg grating and causing the resonant center wavelength of the first fiber Bragg grating to drift. This strain is caused by changes in humidity and is therefore called humidity strain, and is expressed by the following formula:

[0072] ε=β·ΔRH (3)

[0073] In equation (3), β is the coefficient of expansion of the first fiber Bragg grating with the humidity-sensitive coating, and ΔRH is the difference between the process humidity and the humidity used for calibration. Since the humidity calibration standard used for this sensor is 0%, the humidity difference ΔRH is equal to the actual humidity value RH.

[0074] When the ambient temperature remains constant during the test, formula (2) is simplified to:

[0075] Δλ RH =λ B (1-P e )β·RH (4)

[0076] Let K RH =λ B (1-P e )β, then formula (4) can be simplified as:

[0077] Δλ RH =K RH ·RH (5)

[0078] In formula (4) and formula (5), K RH is the humidity sensitivity coefficient of the humidity sensor, Δλ RH is the shift of the Bragg wavelength of the first fiber Bragg grating caused by humidity.

[0079] As can be seen from equation (5), under constant temperature conditions, the humidity value can be completely derived by constructing a one-to-one correspondence between the Bragg wavelength drift and humidity through a function. Therefore, humidity can be measured by detecting the drift of the first fiber Bragg grating resonant center wavelength.

[0080] However, since the ambient temperature during the test is not constant, the Bragg wavelength drift caused by temperature changes should be eliminated. This can be done by introducing a bare fiber Bragg grating as a temperature compensation unit to eliminate the influence of ambient temperature changes.

[0081] When the humidity remains constant, temperature changes will cause both the humidity-sensitive coating and the optical fiber to expand or contract, which will cause the Bragg wavelength to drift:

[0082] ε T =λ B [(1-P e )α+ξ]ΔT (6)

[0083] In formula (6), ε T is the strain value of the first fiber Bragg grating with the humidity sensitive coating attached due to thermal expansion or contraction, λ B is the first fiber Bragg grating resonant center wavelength, P e is the elastic-optical coefficient of the first fiber Bragg grating, α is the thermal expansion coefficient of the first fiber Bragg grating, ξ is the thermo-optical coefficient of the first fiber Bragg grating, and ΔT is the temperature change.

[0084] Let K T =λ B [(1-P e )α+ξ], is the temperature sensitivity coefficient of the humidity sensor. The Bragg wavelength change of the first fiber Bragg grating is determined by the RH and temperature changes. Further simplifying equations (1) and (2), we can derive the following equation:

[0085] Δλ B =K T ΔT+K RH ·RH (7)

[0086] In formula (7), Δλ B is the change of the Bragg wavelength of the first fiber Bragg grating, K T is the set temperature sensitivity coefficient, K RH is the humidity sensitivity coefficient of the humidity sensor, ΔT is the temperature change, RH is the humidity value, and the humidity in formula (7) is a constant value.

[0087] Equation (7) includes both temperature and humidity changes and explores the impact of their numerical changes on the Bragg wavelength drift.

[0088] Based on the above analysis, the expression formula of humidity and temperature of the humidity sensor is obtained as follows:

[0089]

[0090] In formula (8), K T1 and K T2 are the temperature sensitivity coefficients of the humidity sensor and temperature sensor, K RH is the humidity sensitivity coefficient of the humidity sensor, Δλ1 and Δλ2 are the Bragg wavelength drifts of the humidity sensor and temperature sensor respectively. RH It is not a constant value, but a one-to-one correspondence between the Bragg wavelength drift and humidity can be constructed through a function. The mathematical relationship between the temperature change and humidity value in the temperature and humidity in-situ detection sensor and the Bragg wavelength drift of the temperature sensor and humidity sensor is as follows:

[0091]

[0092] In formula (9), ΔT is the change in temperature, RH is the humidity value, K T1 and K T2 are the temperature sensitivity coefficients of the humidity sensor and temperature sensor, K RH is the humidity sensitivity coefficient of the humidity sensor, Δλ1 and Δλ2 are the Bragg wavelength drifts of the humidity sensor and temperature sensor, respectively.

[0093] Before conducting temperature and humidity testing on stone artifacts, it is first necessary to determine the one-to-one correspondence between Bragg wavelength drift and humidity through experiments on sandstone samples. This involves the following steps:

[0094] First, measure the response characteristics of the humidity sensor and temperature sensor to temperature at constant humidity, and calculate K T1 and K T2 The value of

[0095] Then, at a constant temperature, multiple standard humidity values ​​were set, and the humidity of the sandstone sample body was changed according to the set standard humidity values. The response characteristics of the humidity sensor to humidity were measured, and a one-to-one correspondence between the drift of the humidity sensor's Bragg wavelength and humidity was obtained.

[0096] Then, in practical applications, when detecting the changes in humidity and temperature of stone cultural relics, the fiber Bragg grating demodulator is used to measure the resonant center wavelength drifts Δλ1 and Δλ2 of the first fiber Bragg grating and the second fiber Bragg grating in the humidity sensor and the temperature sensor, respectively. Then, combined with formula (9), the in-situ accurate measurement of the changes in the binary parameters of humidity and temperature of the stone cultural relics can be achieved.

[0097] The temperature and humidity in-situ detection sensor disclosed in the present invention has the following technical effects:

[0098] 1. In practical applications, the temperature and humidity in-situ detection sensor disclosed in the present invention only needs to adhere the packaged temperature and humidity in-situ detection sensor area to the surface or cracks of stone cultural relics to achieve online in-situ accurate measurement of the humidity of the stone cultural relics.

[0099] 2. The first grating area, where the PVA film and composite KGM hydrogel film are attached, is masked by the encapsulation structure and can only absorb water molecules transmitted from the surface and interior of the stone artifact, unaffected by changes in the external humidity. Furthermore, the humidity sensor's hygroscopic materials, made of polyvinyl alcohol (PVA) film and composite konjac glucomannan (KGM) hydrogel film, accurately respond to humidity changes within the stone artifact itself. This humidity response is highly sensitive and harmless to the artifact, enabling online, in-situ detection of the temperature and humidity of stone artifacts in semi-dry environments.

[0100] 3. Both ends of the first fiber Bragg grating are in a free extension state, which avoids the technical problem of reduced detection accuracy caused by external strain when the sensor measures the humidity of stone cultural relics.

[0101] 4. By setting up an additional temperature sensor, the influence of temperature on the detection results of the humidity sensor can be eliminated.

[0102] In summary, the temperature and humidity in-situ detection sensor disclosed in the present invention can accurately detect the temperature and humidity information of the stone cultural relic body, and the measurement results are not affected by external factors such as ambient humidity.

[0103] Second, see Figure 3 The present invention also discloses a method for preparing a humidity sensor, which is used to prepare the humidity sensor in the temperature and humidity in-situ detection sensor as described above, comprising the following steps:

[0104] S1, taking a fiber Bragg grating and performing preprocessing to obtain a first fiber Bragg grating 201 for preparing a humidity sensor, wherein the first fiber Bragg grating 201 has a first grating region 203;

[0105] S2, performing silane treatment on the first fiber Bragg grating 201 pretreated in step S1 to enhance the adhesion strength between the optical fiber with the coating removed and the moisture-sensitive material in subsequent steps;

[0106] S3. Add polyvinyl alcohol powder to deionized water and heat in a water bath until the polyvinyl alcohol powder is completely dissolved, and prepare a PVA solution with a mass percentage of 10% to 15% for later use;

[0107] S4, slowly adding KGM powder to the prepared HPC solution to obtain a KGM hydrogel mixture containing HPC;

[0108] S5, adding nano-carbon powder to the prepared KGM hydrogel mixture containing HPC, wherein the mass percentage of the nano-carbon powder in the KGM hydrogel mixture containing HPC is 1-4%, stirring, ultrasonically oscillating, and standing at room temperature to obtain a composite KGM hydrogel containing carbon nano-powder;

[0109] S6. Repeatedly scrape the PVA solution onto the surface of the first cladding layer 204 corresponding to the first grating region 203 according to the preset thickness of the PVA film 206 and dry it until the PVA film 206 reaches the preset thickness, and then stop scraping to obtain the first fiber Bragg grating 201 attached with the PVA film 206.

[0110] S7. Depositing a composite KGM hydrogel containing carbon nanopowder on the surface of the PVA film 206 and freeze-drying the composite KGM hydrogel containing carbon nanopowder to form a composite KGM hydrogel film 207, thereby obtaining a humidity sensor having the PVA film 206 and the composite KGM hydrogel film 207 attached thereto in sequence.

[0111] Specifically, in step S1, the fiber Bragg grating is pre-processed using the following method: the first grating region 203 is located on the core of the first fiber Bragg grating 201, and the periphery of the first grating region 203 is respectively covered with a first cladding 204 and a first coating layer 205; an optical stripper is used to remove the first coating layer 205 corresponding to the first grating region 203, and then the first grating region 203 is partially immersed in anhydrous ethanol and deionized water in turn, and ultrasonically cleaned for 8 to 10 minutes, and then set aside for use after cleaning.

[0112] Specifically, in step S2, the method of treating the first fiber Bragg grating pretreated in step S1 with silane is as follows: first, immersing the first grating region in 1 mol·L -1The first grating area is placed in a NaOH solution for 30 to 60 minutes, rinsed with deionized water and dried for later use. The first grating area is then placed in a silane coupling agent with a mass percentage concentration of 10 to 15% and soaked for 20 to 40 minutes. After taking it out, it is placed in a vacuum drying oven at 90 to 110°C and dried for 10 to 15 minutes for later use.

[0113] Specifically, in step S3, the water bath temperature is 90-95° C., and the water bath heating time is 4-5 hours.

[0114] Specifically, in step S4, a 0.5% mass fraction hydroxypropyl cellulose (HPC) solution is first prepared, and the pH of the HPC solution is adjusted to 8.5; then KGM powder is slowly added to the prepared HPC solution to obtain a KGM hydrogel mixture containing HPC, wherein the mass percentage of KGM in the mixture is 1.5 to 4.5%.

[0115] Specifically, a 0.5% mass fraction hydroxypropyl cellulose (HPC) solution is prepared by the following method: 20-30% of a predetermined amount of water is heated to 60° C., and HPC is slowly added under sufficient stirring. After all HPC is added, the remaining predetermined amount of water is added, and the mixture is stirred for 10-30 minutes. After the HPC is completely dissolved, the mixture is allowed to stand for a period of time to obtain a clear HPC solution.

[0116] Specifically, the pH of the HPC solution is adjusted by dropwise adding NaOH solution to the HPC solution.

[0117] Specifically, in step S5, after adding the nano-carbon powder to the prepared HPC-containing KGM hydrogel mixture, it is necessary to continue to stir vigorously for 8 to 12 hours, place it in an ultrasonic oscillator for 2 to 4 hours, and finally stand it at room temperature for a set time to obtain a composite KGM hydrogel containing carbon nano-powder.

[0118] Specifically, in step S6, in order to better control the thickness of the PVA film attached to the cladding surface corresponding to the first grating area, the following method is used: first, a small amount of PVA solution is clamped with tweezers, and the solution is slowly pulled along the cladding surface corresponding to the first grating area using a scraping method to deposit the PVA on the cladding surface corresponding to the first grating area; then, the coated first fiber Bragg grating is placed in a vacuum drying oven and dried at 75-85°C for 3-5 minutes; the operation is repeated multiple times until the PVA film reaches a preset thickness and the scraping is stopped to obtain a first fiber Bragg grating attached with a PVA film.

[0119] In this way, by controlling the pulling times to obtain PVA films of different thicknesses on the cladding surface corresponding to the first grating region, the sensitivity of the humidity sensor can be controlled according to actual needs.

[0120] Specifically, in step S7, in order to facilitate the uniform deposition of the composite KGM hydrogel containing carbon nanopowder on the surface of the PVA film, the following method is adopted: a shaping tube is used and is sleeved on the outer periphery of the first fiber Bragg grating corresponding to the first grating area, while ensuring that the first grating area is located at the center of the shaping tube; then the composite KGM hydrogel containing carbon nanopowder is evenly filled into the shaping tube, and placed in a refrigerator for freezing and shaping, and then freeze-dried to obtain a humidity sensor with a PVA film and a composite KGM hydrogel film attached thereto from the inside to the outside.

[0121] As one of the implementation methods of the shaping tube, the shaping tube adopts a cylindrical PTFE tube. In order to facilitate shaping, the cylindrical PTFE tube is longitudinally cut along the center line of the tube to form two symmetrical semi-cylindrical tube bodies;

[0122] When filling the composite KGM hydrogel containing carbon nanopowder, first fill one of the two semi-cylindrical tubes and shape it, then take out and fill the other two semi-cylindrical tubes and shape them to obtain a complete composite KGM hydrogel film.

[0123] As one embodiment of the PTFE tube, the inner diameter of the PTFE tube is 0.8 mm and the outer diameter is 1.5 mm.

[0124] Specifically, in step S7, the refrigerator temperature is less than or equal to -4°C, and the freezing and setting time is 8 to 12 hours.

[0125] Specifically, in step S7, the freeze-drying time is 8 to 12 hours.

[0126] The preparation method of the humidity sensor disclosed in the present invention has the following technical effects: the preparation method is simple and easy to operate, and the obtained humidity sensor with the PVA film and the composite KGM hydrogel film attached sequentially from the inside to the outside has high sensitivity and high measurement accuracy.

[0127] Example

[0128] In order to further illustrate the temperature and humidity in-situ detection sensor of the present invention, the present invention discloses the following application embodiments.

[0129] This embodiment discloses a method for preparing a temperature and humidity in-situ detection sensor:

[0130] A1. Preparation of humidity sensor:

[0131] (1) A fiber Bragg grating (FBG) was obtained, and a first coating layer with a grating region length of 15 mm was removed using an optical stripper. The grating region was then sequentially immersed in anhydrous ethanol and deionized water for ultrasonic cleaning for 10 minutes, thereby obtaining a first fiber Bragg grating for preparing a humidity sensor, wherein the first fiber Bragg grating had a first grating region.

[0132] (2) In order to enhance the adhesion strength between the first grating area and the humidity sensitive material, the first grating area is first immersed in 1 mol·L -1 The first grating area was placed in a NaOH solution for 30 minutes, rinsed with deionized water and dried for later use, and then the first grating area was placed in a 10% by mass concentration silane coupling agent for 40 minutes, taken out and dried in a vacuum drying oven at 90°C for 15 minutes for later use;

[0133] (3) Add polyvinyl alcohol powder to deionized water and heat in a water bath (90°C) for 5 hours until the polyvinyl alcohol powder is completely dissolved, and prepare a 15% by weight PVA solution for later use;

[0134] (4) Prepare a 0.5% mass fraction of hydroxypropyl cellulose (HPC) solution. Take 30% of the predetermined amount of water and heat it to 60°C. Slowly add the HPC under sufficient stirring. After all the HPC is added, add the remaining predetermined amount of water and stir for 20 minutes until it is completely dissolved. Let it stand for a period of time to obtain a clear solution. Adjust the pH of the HPC solution to 8.5 by adding NaOH solution dropwise.

[0135] (5) KGM powder was slowly added to the HPC solution, and gelation occurred within 2 minutes to obtain a KGM hydrogel mixture containing HPC, in which the mass percentage of KGM in the mixture was 3%.

[0136] (6) Adding nano-carbon powder to the prepared KGM hydrogel and vigorously stirring the mixed solution for 12 h, wherein the mass percentage of nano-carbon powder in the HPC-containing KGM hydrogel mixture is 1%, and placing it in an ultrasonic oscillator for 2 h, and finally standing at room temperature for a period of time to obtain a composite KGM hydrogel containing carbon nano-powder;

[0137] (7) Repeatedly scraping the PVA solution onto the surface of the first cladding layer corresponding to the first grating region according to the preset thickness of the PVA film and drying the solution until the PVA film reaches the preset thickness, thereby obtaining a first fiber Bragg grating with the PVA film attached thereto;

[0138] Specifically, during scraping, a small amount of PVA solution was taken with tweezers and slowly pulled along the first grating area using a scraping method; during drying, the solution was dried in a vacuum drying oven at 80° C. for 5 minutes;

[0139] (8) A composite KGM hydrogel containing carbon nanopowder is deposited on the surface of a PVA film and freeze-dried to shape the composite KGM hydrogel containing carbon nanopowder into a composite KGM hydrogel film, thereby obtaining a humidity sensor with a PVA film and a composite KGM hydrogel film attached in sequence.

[0140] Specifically, in order to facilitate the uniform deposition of the composite KGM hydrogel containing carbon nanopowder on the surface of the PVA film, the following method is adopted: a shaping tube is used and is sleeved on the outer periphery of the first fiber Bragg grating corresponding to the first grating area, while ensuring that the first grating area is located at the center of the shaping tube; the composite KGM hydrogel containing carbon nanopowder is then evenly filled in the shaping tube, placed in a refrigerator for freezing and shaping, and then freeze-dried to obtain a humidity sensor with a PVA film and a composite KGM hydrogel film attached thereto from the inside out; the shaping tube adopts a cylindrical PTFE tube with an inner diameter of 0.8 mm and an outer diameter of 1.5 mm; for the convenience of shaping, the cylindrical PTFE tube is longitudinally cut along the center line of the tube to form two symmetrical semi-cylindrical tube bodies; when filling the composite KGM hydrogel containing carbon nanopowder, one of the two semi-cylindrical tube bodies is first filled and shaped, and then the other two semi-cylindrical tube bodies are taken out and shaped to obtain a complete composite KGM hydrogel film.

[0141] A2. Preparation of temperature sensor:

[0142] To eliminate the interference caused by temperature changes of stone cultural relics on humidity measurement, a temperature compensation unit was introduced. A section of fiber Bragg grating was used as the second fiber Bragg grating. The second grating region was located on the core of the second fiber Bragg grating. The outer periphery of the second grating region was respectively coated with a second cladding layer and a second coating layer. The second coating layer corresponding to the second grating region was removed with an optical stripper, thus obtaining a temperature sensor for sensing temperature changes.

[0143] A3. Prepare the packaging structure.

[0144] In order to avoid the interference of air humidity changes on the humidity measurement of stone cultural relics, a "Band-Aid" type packaging structure is designed for encapsulating fiber Bragg gratings coated with humidity-sensitive materials. The structure has the characteristics of heat and cold resistance, good flexibility and effective isolation from air humidity. The packaging structure includes a protective layer, the middle part of the protective layer has an extended groove, the side of the protective layer with the groove is fixed with a hydrophobic isolation membrane, the surfaces of the protective layer on both sides of the hydrophobic isolation membrane are respectively provided with adhesives, and a humidity sensor and a temperature sensor are arranged side by side and in parallel in the groove. The first grating area and the second grating area are arranged in the groove area corresponding to the hydrophobic isolation membrane, thereby obtaining an in-situ temperature and humidity detection sensor for simultaneously detecting the temperature and humidity of stone cultural relics.

[0145] Before using the prepared in-situ temperature and humidity detection sensor to detect temperature and humidity on stone artifacts, it is first necessary to determine the one-to-one correspondence between the Bragg wavelength drift and humidity through experiments on sandstone samples. This includes the following steps:

[0146] First, measure the response characteristics of the humidity sensor and temperature sensor to temperature at constant humidity, and calculate K T1 and K T2 The value of

[0147] Then, at a constant temperature, multiple standard humidity values ​​were set, and the humidity of the sandstone sample body was changed according to the set standard humidity values. The response characteristics of the humidity sensor to humidity were measured, and a one-to-one correspondence between the drift of the humidity sensor's Bragg wavelength and humidity was obtained.

[0148] Then, in practical applications, when detecting the changes in humidity and temperature of stone cultural relics, the fiber Bragg grating demodulator is used to measure the resonant center wavelength drifts Δλ1 and Δλ2 of the first fiber Bragg grating and the second fiber Bragg grating in the humidity sensor and the temperature sensor, respectively. Then, combined with formula (9), the in-situ accurate measurement of the changes in the binary parameters of humidity and temperature of the stone cultural relics can be achieved.

[0149] See also Figure 5 The temperature and humidity in-situ detection sensor prepared in this embodiment is attached to the surface or cracks of stone cultural relics to detect the Bragg wavelength drift of the temperature sensor and the humidity sensor.

[0150] from Figure 6 It can be seen that when the temperature of the stone cultural relic changes, the drift of the resonant center wavelength (Bragg wavelength) of the temperature sensor and the humidity sensor increases with the increase of temperature.

[0151] from Figure 7 It can be seen that when the temperature of the stone artifact is constant at 25°C, the drift of the temperature sensor's resonant center wavelength (Bragg wavelength) remains constant when the humidity of the stone artifact increases, indicating that the temperature sensor is insensitive to changes in the water content of the stone artifact; the drift of the humidity sensor's resonant center wavelength (Bragg wavelength) increases with increasing humidity, and its humidity Bragg wavelength drift Δλ RH =-805.44*exp(-RH / 50.19)+805.44.

[0152] also, Figure 6 and Figure 7 It shows that the temperature sensor in the temperature and humidity in-situ detection sensor used in this embodiment only responds to the temperature change information of stone cultural relics, and its temperature sensitivity coefficient is K T2=9.9pm / ℃, according to Figure 6 The measurement results of the humidity sensor can be used to obtain the temperature sensitivity coefficient K of the humidity sensor. T1 =10.3pm / ℃. Therefore, formula (9) can be further described as:

[0153]

[0154] Therefore, in practical applications, by utilizing the drift of the fiber Bragg grating resonance center wavelength (Bragg wavelength) corresponding to the temperature sensor and humidity sensor in the temperature and humidity in-situ detection sensor of the present invention, and combining it with formula (10), it is possible to accurately measure the temperature and humidity change information of the stone cultural relic body online.

[0155] It will be understood that the present invention is described through some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. Under the guidance of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. The embodiments described in the present invention are some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein may 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 merely represents selected embodiments of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a humidity sensor, for preparing a humidity sensor for an in-situ temperature and humidity detection sensor, wherein the in-situ temperature and humidity detection sensor is used to simultaneously detect the temperature and humidity of stone cultural relics, comprising a protective layer having an extended groove in the middle of the protective layer, a hydrophobic isolation membrane fixed to one side of the protective layer having the groove, adhesives provided on surfaces of the protective layer on both sides of the hydrophobic isolation membrane, a humidity sensor and a temperature sensor provided in parallel and parallel within the groove; the humidity sensor comprising a first fiber Bragg grating, the first fiber Bragg grating comprising a first core, a first grating region provided on the first core, a first cladding covering the periphery of the grating region, a PVA film and a composite KGM hydrogel film attached to the periphery of the first cladding in order from the inside out; the temperature sensor comprising a second fiber Bragg grating, the second fiber Bragg grating comprising a second core, a second grating region provided on the second core, a second cladding covering the periphery of the second grating region; The preparation method of the humidity sensor comprises the following steps: S1, taking a fiber Bragg grating and performing preprocessing to obtain a first fiber Bragg grating for preparing a humidity sensor, wherein the first fiber Bragg grating has a first grating region; S2, performing silane treatment on the first fiber Bragg grating pretreated in step S1; S3. Add polyvinyl alcohol powder to deionized water and heat in a water bath until the polyvinyl alcohol powder is completely dissolved, and prepare a PVA solution with a mass percentage of 10% to 15% for later use; S4. Slowly adding KGM powder to the prepared HPC solution to obtain a KGM hydrogel mixture containing HPC; wherein, in step S4, first preparing a 0.5% mass fraction HPC solution, and adjusting the pH of the HPC solution to 8.5; then slowly adding KGM powder to the prepared HPC solution to obtain a KGM hydrogel mixture containing HPC, wherein the mass percentage of KGM in the mixture is 1.5-4.5%; the preparation of the 0.5% mass fraction HPC solution is carried out by the following method: taking 20-30% of a predetermined amount of water and heating it to 60° C., slowly adding HPC under sufficient stirring, and after all the HPC is added, adding the remaining predetermined amount of water, stirring until the HPC is completely dissolved, and then standing to obtain a clear HPC solution; S5, adding nano-carbon powder to the prepared KGM hydrogel mixture containing HPC, wherein the mass percentage of the nano-carbon powder in the KGM hydrogel mixture containing HPC is 1-4%, stirring, ultrasonically oscillating, and standing at room temperature to obtain a composite KGM hydrogel containing carbon nano-powder; S6. Repeatedly scrape-coat the PVA solution on the surface of the first cladding corresponding to the first grating region according to a preset thickness of the PVA film and dry the solution until the PVA film reaches a preset thickness, thereby obtaining a first fiber Bragg grating with a PVA film attached thereto. The specific operation of this step is as follows: first, use tweezers to clamp the PVA solution, and use a scraping method to pull the solution along the surface of the cladding corresponding to the first grating region to deposit the PVA on the surface of the cladding corresponding to the first grating region; then, place the coated first fiber Bragg grating in a vacuum drying oven at 75-85° C. and dry it for 3-5 minutes; repeat this operation multiple times until the PVA film reaches a preset thickness, thereby obtaining a first fiber Bragg grating with a PVA film attached thereto. S7. Depositing a composite KGM hydrogel containing carbon nanopowder on the surface of the PVA film, and freeze-drying and shaping it, so that the composite KGM hydrogel containing carbon nanopowder becomes a composite KGM hydrogel film, and obtaining a humidity sensor with the PVA film and the composite KGM hydrogel film attached in sequence; the specific operation method of this step is: using a shaping tube, and sleeved on the outer periphery of the first fiber Bragg grating corresponding to the first grating area, while ensuring that the first grating area is located at the center of the shaping tube; then evenly filling the shaping tube with the composite KGM hydrogel containing carbon nanopowder, and placing it in a refrigerator for freezing and shaping, and then freeze-drying, to obtain a humidity sensor with the PVA film and the composite KGM hydrogel film attached in sequence from the inside to the outside.

2. The method for preparing a humidity sensor according to claim 1, wherein: The first grating region and the second grating region are arranged in the groove region corresponding to the hydrophobic isolation film.

3. The method for preparing a humidity sensor according to claim 2, wherein: The mathematical relationship between the temperature change and humidity value in the temperature and humidity in-situ detection sensor and the drift of the Bragg wavelength of the temperature sensor and humidity sensor is as follows: D T = D λ 2 / K T2 ; K RH · RH = D λ 1- ( K T1 / K T2 ) D λ 2; Where, Δ T is the change in temperature, RH is the humidity value, K T1 and K T2 are the temperature sensitivity coefficients of the humidity sensor and temperature sensor respectively, K RH is the humidity sensitivity coefficient of the humidity sensor, Δ λ 1 and Δ λ 2 are the Bragg wavelength drifts of the humidity sensor and temperature sensor respectively; in, K RH = λ B (1 - P e ) β , λ B is the first fiber Bragg grating resonant center wavelength, P e is the elastic-optical coefficient of the first fiber Bragg grating, β is the wet expansion coefficient of the first fiber Bragg grating attached with the PVA film and the composite KGM hydrogel film.

4. The method for preparing a humidity sensor according to claim 1, wherein: In step S1, the fiber Bragg grating is pretreated using the following method: the first grating region is located on the core of the first fiber Bragg grating, and the periphery of the first grating region is respectively covered with a first cladding layer and a first coating layer; the first coating layer corresponding to the first grating region is removed using an optical stripper, and then the first grating region is partially immersed in anhydrous ethanol and deionized water in turn, and ultrasonically cleaned for 8 to 10 minutes, and then set aside after cleaning.

5. The method for preparing a humidity sensor according to claim 1 or 4, wherein: In step S2, the method for silane treatment of the first fiber Bragg grating pretreated in step S1 is as follows: first, immersing the first grating area in a NaOH solution, then rinsing with deionized water and drying for standby use, then statically immersing the first grating area in a silane coupling agent with a mass percentage concentration of 10-15%, taking it out and placing it in a vacuum drying oven for drying before standby use.

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