Mural monitoring system and method

Abstract

The application discloses a mural monitoring system and method. The mural monitoring system comprises: a fiber assembly comprising a temperature-sensitive optical fiber and a temperature and humidity-sensitive optical fiber arranged side by side; a strain sensing optical fiber configured to be arranged in a mural; a demodulator configured to demodulate a first strain change amount of the temperature-sensitive optical fiber, a second strain change amount of the temperature and humidity-sensitive optical fiber and a Rayleigh scattering frequency shift amount of the strain sensing optical fiber; and a processor configured to obtain a temperature parameter of the mural according to the first strain change amount, obtain a humidity parameter of the mural according to the temperature parameter and the second strain change amount, and obtain a strain parameter of the mural according to the Rayleigh scattering frequency shift amount. The application can monitor the mural in a distributed and high-precision multi-field manner under the premise of ensuring the integrity and cultural relic value of the mural, help explain the changes in various properties of the mural, and provide a reference for predicting mural disasters.

Description

Technical Field

[0001] This invention belongs to the field of soil monitoring in geotechnical engineering, and specifically relates to a mural monitoring system and method. Background Technology

[0002] Cultural relics and murals, due to their attachment to mountains, are relatively fragile and susceptible to factors such as water and salt migration within the surrounding rock and unstable geological structures. Frequent and difficult-to-treat damage to the ground layer and pigment layer poses a global challenge in cultural relic conservation. Currently, domestic and international research institutions mainly focus on the scientific understanding of the mural's production techniques, the analysis of the material composition of the ground layer and pigment layer, and the continuous monitoring of environmental risk factors. Preliminary findings have clarified the mechanisms of major damage and their response to environmental factors, leading to the development of a series of protective and restorative materials and the formation of a complete set of protective reinforcement techniques. To further achieve preventative protection of cultural relics and murals, it is necessary to scientifically control the main risk factors for mural deterioration. In-situ online monitoring of the material composition of the ground layer and pigment layer, as well as the development process of damage, and the construction of a quantitative correlation model of the mural's "body-environment-damage" are crucial for formulating risk factor control strategies. Therefore, multi-field monitoring of the mural, including strain, temperature, and humidity fields, is essential and provides guidance for subsequent comprehensive conservation work.

[0003] In the field of mural conservation, a monitoring and early warning system centered on risk management of the environment in which the murals are situated has been established. However, due to the preciousness and fragility of murals, the application of traditional monitoring technologies and equipment is limited. Currently, there is a lack of in-situ, non-destructive, real-time measurement technologies for shallow surface defects such as the ground layer and pigment layer of murals. Furthermore, the correlation between risk monitoring data and the defects themselves is weak, and the technology for predicting the development of defects is incomplete. These problems severely restrict the accurate assessment of the health status of murals and preventive protection, becoming a global challenge in the field of cultural relic conservation. There is an urgent need to develop specialized sensor equipment to address this common key technological requirement of in-situ online monitoring of murals, enabling systematic monitoring and scientific protection of the mural deterioration process.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a mural monitoring system and method that, while ensuring the integrity and cultural value of the murals, conducts distributed, high-precision, multi-field monitoring of the murals, helps to interpret changes in various properties of the murals, and can also provide a reference for predicting mural disasters.

[0006] The present invention adopts the following technical solution: A mural monitoring system, comprising: An optical fiber assembly configured to be deployed in a mural to provide a path for testing the propagation of a laser within the mural, the optical fiber assembly comprising a temperature-sensitive fiber and a temperature and humidity-sensitive fiber arranged side by side; Strain sensing fiber optic cable, configured to be laid in the mural to provide a propagation path for the test laser within the mural; A demodulator is used to demodulate the first strain change of the temperature-sensitive optical fiber, the second strain change of the temperature and humidity-sensitive optical fiber, and the Rayleigh divergence frequency shift of the strain-sensing optical fiber. A processor is configured to obtain temperature parameters of the mural based on the first strain change; obtain humidity parameters of the mural based on the temperature parameters and the second strain change; and obtain strain parameters of the mural based on the Rayleigh scattering frequency displacement.

[0007] In some preferred embodiments, the optical fiber assembly is disposed in a first measuring hole in the mural, the first measuring hole being opened within the mural and not backfilled; The strain sensing fiber is installed in the second measuring hole of the mural, which is located inside the mural and backfilled by the mural soil.

[0008] In some preferred embodiments, a UV adhesive sheath is provided at one end of the temperature-sensitive optical fiber and at one end of the temperature and humidity-sensitive optical fiber. After being irradiated with ultraviolet light, the UV adhesive sheath fixes the ends of the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber in the first measuring hole. A UV adhesive sheath is provided at one end of the strain sensing fiber, and the UV adhesive sheath fixes the end of the strain sensing fiber in the second measuring hole after being irradiated with ultraviolet light.

[0009] In some preferred embodiments, the optical fiber assembly further includes a spring sleeved on the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber; The temperature-sensitive optical fiber includes a fiber core and a gold layer covering the fiber core; The temperature and humidity sensitive optical fiber includes a fiber core and a polyimide coating covering the fiber core; The strain sensing fiber is a single-mode fiber.

[0010] In some preferred embodiments, the processor is used to obtain the temperature parameters of the mural according to the following formula (I): (I) In formula (I), This represents the first strain change in the temperature-sensitive optical fiber. The temperature sensitivity coefficient of the temperature-sensitive optical fiber; T The temperature change of the mural; The processor is used to obtain the humidity parameters of the mural according to the following formula (II): (II) In formula (II), This is the second strain change in the P-type temperature and humidity sensitive optical fiber. ΔRH represents the humidity sensitivity coefficient of the temperature and humidity sensitive optical fiber; ΔRH represents the relative humidity change of the mural. The temperature sensitivity coefficient of the temperature and humidity sensitive optical fiber; The processor is used to obtain the strain parameters of the mural according to the following formula (III): (III) In formula (III), The Rayleigh scattering radio frequency shift; v The incident light frequency; The strain coefficient of the strain sensing fiber; This represents the strain variation of the mural.

[0011] The present invention also adopts the following technical solution: A method for monitoring murals, employing the aforementioned mural monitoring system, includes the following steps: S1. Fiber optic components and strain sensing fibers are laid in the mural. One end of the temperature-sensitive fiber and the temperature and humidity-sensitive fiber of the fiber optic component are fixed in the first measuring hole of the mural, and the other end is connected to the demodulator. One end of the strain sensing fiber is fixed in the second measuring hole of the mural, and the other end is connected to the demodulator. S2. Inject a first laser into the temperature-sensitive fiber and the temperature and humidity-sensitive fiber, and inject a second laser into the strain-sensing fiber; S3. The first strain change of the temperature-sensitive optical fiber, the second strain change of the temperature and humidity-sensitive optical fiber, and the Rayleigh divergence of the strain-sensing optical fiber are obtained by demodulation using a demodulator. S4. Obtain the temperature parameters of the mural based on the first strain change; obtain the humidity parameters of the mural based on the temperature parameters and the second strain change; obtain the strain parameters of the mural based on the Rayleigh scattering displacement.

[0012] In some preferred embodiments, in step S1, a first measuring hole is drilled in the mural, a temperature-sensitive fiber and a temperature and humidity-sensitive fiber are inserted into the first measuring hole, one end of the temperature-sensitive fiber and the temperature and humidity-sensitive fiber are fixed to the first measuring hole, the first measuring hole is not backfilled, and there is a gap between the fiber assembly and the hole wall of the first measuring hole. In step S1, a second measuring hole is drilled in the mural, a strain sensing fiber is inserted into the second measuring hole, one end of the strain sensing fiber is fixed to the second measuring hole, and soil slurry of the same type as the mural is injected into the second measuring hole to seal the hole, so that the strain sensing fiber and the mural soil are in contact and coupled.

[0013] In some preferred embodiments, in step S1, a UV adhesive sheath is provided on one end of the temperature-sensitive optical fiber and one end of the temperature and humidity-sensitive optical fiber, and ultraviolet light is applied to cure the UV adhesive sheath, so as to fix the end of the temperature-sensitive optical fiber and the end of the temperature and humidity-sensitive optical fiber in the first measuring hole. A spring is fitted onto at least the portion of the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber located at the first measuring hole. In step S1, a UV adhesive sheath is placed on one end of the strain sensing fiber, and ultraviolet light is applied to cure the UV adhesive sheath, thereby fixing the end of the strain sensing fiber in the second measuring hole.

[0014] In some preferred embodiments, in step S1, an optical fiber with a gold layer is selected as a temperature-sensitive optical fiber, an optical fiber with a polyimide coating is selected as a temperature and humidity-sensitive optical fiber, and a single-mode optical fiber without a coating is selected as a strain-sensing optical fiber; the ends of each optical fiber inserted into the mural are beveled.

[0015] In some preferred embodiments, in step S4, the temperature parameters of the mural are obtained according to the following formula (I): (I) In formula (I), This represents the first strain change in the temperature-sensitive optical fiber. The temperature sensitivity coefficient of the temperature-sensitive optical fiber; T The temperature change of the mural; The humidity parameters of the mural are obtained according to the following formula (II): (II) In formula (II), This is the second strain change in the P-type temperature and humidity sensitive optical fiber. ΔRH represents the humidity sensitivity coefficient of the temperature and humidity sensitive optical fiber; ΔRH represents the relative humidity change of the mural. The temperature sensitivity coefficient of the temperature and humidity sensitive optical fiber; The strain parameters of the mural are obtained according to the following formula (III): (III) In formula (III), The Rayleigh scattering radio frequency shift; v The incident light frequency; The strain coefficient of the strain sensing fiber; This represents the strain variation of the mural.

[0016] The beneficial effects of this invention are as follows: The mural monitoring system and method of this invention are based on minimally invasive distributed optical fibers deployed in the murals, ensuring the integrity of the murals and having minimal impact on the integrity and cultural value of the mural artifacts. It satisfies the requirement of non-destructive embedding of minimally invasive optical fiber sensors. By establishing the correspondence between Rayleigh dispersion radio frequency shift, strain change and various fields of the mural along the optical fiber, it achieves high spatial resolution multi-field evolution monitoring of the mural, which is of great significance for helping to explain a series of mural disease mechanisms and subsequent cultural relic protection. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a mural monitoring method according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the installation of an optical fiber assembly according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the installation of a strain sensing optical fiber according to an embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of an optical fiber assembly according to an embodiment of the present invention.

[0022] Figure 5 This is a schematic diagram of a calibration test according to an embodiment of the present invention.

[0023] Figure 6 This is a schematic diagram of a mural monitoring system according to an embodiment of the present invention.

[0024] Figure label: 3. Miniature drilling rig; 4. Miniature drill bit; 5. Miniature borehole; 6. Tail fiber optic cable; 7. Ultraviolet lamp; 8. UV adhesive sheath; 9. Strain sensing fiber optic cable; 10. OFDR demodulator; 11. Syringe; 12. Original mural sample filling layer; 13. PI coated fiber optic cable; 14. Au coated fiber optic cable; 15. Spring; 16. Temperature control box. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more readily understood by those skilled in the art. It should be noted that the description of these embodiments is for the purpose of aiding understanding the present invention, but does not constitute a limitation thereof.

[0026] Existing multi-field monitoring methods for murals cannot achieve high-precision, continuous spatial measurement. Neither electrode sensors, remote sensing technology, nor resistivity methods can simultaneously meet the two crucial requirements of high precision and continuous spatial monitoring. Fiber optic Rayleigh scattering demodulation can achieve millimeter-level spatial resolution and enables continuous spatial monitoring. This invention proposes a mural monitoring system and method based on a minimally invasive fiber optic embedding technique. This method minimizes the impact on the integrity and cultural value of the mural artifacts and allows for different deployment methods designed for different monitoring objectives, satisfying the requirement of non-destructive embedding of minimally invasive fiber optic sensors.

[0027] Fiber optic monitoring technology is an emerging soil sensing technology. Compared with traditional monitoring technologies, fiber optic monitoring features distributed, real-time, and stable characteristics. This example addresses various defects in cultural relic murals by designing small-volume, low-modality, and high-sensitivity special optical fibers and optimizing a high-performance optical time-domain reflectometer to improve spatial resolution to the millimeter level. An innovative non-invasive fiber optic attachment technology was developed to ensure high-precision fiber optic sensing signals are acquired while maintaining the integrity of the murals. Furthermore, the coupling mechanism between fiber optics and cultural relic murals was thoroughly studied to establish reliable timeliness criteria, ensuring the accuracy of long-term monitoring data.

[0028] This invention presents a distributed fiber optic deployment method for mural artifacts. While ensuring the integrity and cultural value of the murals, it enables distributed, high-precision, multi-field monitoring of the murals. Analysis of this multi-field data helps interpret changes in various properties of the murals and provides a reference for predicting potential disasters. Therefore, this embodiment provides a distributed, high spatial resolution, and high-precision mural monitoring system and method.

[0029] First, fiber optic cables are laid in the mural; this mainly includes the following steps: (1) Perform micro-drilling. Based on the structure of the mural and the monitoring requirements, micro-drilling equipment is used to drill holes at the preset monitoring points of the mural, controlling the hole diameter and depth to avoid damaging the mural body and the internal soil.

[0030] (2) Fix the bottom fiber and eliminate reflection. Fix the fiber end to the bottom of the hole and use special materials to encapsulate and fix it. At the same time, perform the tail fiber oblique cutting operation and apply the reflection suppression coating to eliminate the signal reflection interference at the fiber end.

[0031] (3) Complete the overall fiber optic deployment by laying the fiber smoothly along the drilled holes, controlling the laying tension to avoid bending and damage to the fiber. For strain sensing fibers, after laying, seal the drilled holes with filling material that matches the mural material to ensure that the deployment does not affect the appearance of the mural and that the fiber can stably sense the relevant parameters of the mural and the surrounding soil. For temperature-sensitive fibers and temperature and humidity-sensitive fibers, do not backfill the holes.

[0032] After the fiber optic cable is laid, a laser is injected into the fiber, propagating forward within the fiber core. Due to the non-uniformity of the fiber material, backscattering of the laser occurs at defect locations. The propagation of Rayleigh scattering is affected by the inherent properties of the fiber. Changes in environmental temperature and humidity, as well as micro-deformations of the mural, can cause changes in the fiber diameter and effective refractive index, leading to variations in the Rayleigh scattering frequency. The demodulator internally combines the Rayleigh scattering frequencies of the measurement and reference fiber segments to obtain the fiber Rayleigh scattering frequency shift caused by changes in the mural's field source.

[0033] Depending on the specific monitoring objective, optimized optical cables are laid within the soil. For strain field monitoring, strain-sensing optical fibers embedded in the mural can detect the strain of the mural. The strain generated by the mural is transmitted to the optical fiber, causing micro-deformation, which in turn leads to additional changes in the Rayleigh scattering frequency shift of the optical fiber. By separating the interference of factors such as temperature and humidity on the frequency shift, and combining this with the optical fiber strain-frequency shift response model, the strain of the mural can be accurately calculated, achieving effective monitoring of the mural's strain.

[0034] Temperature-sensitive optical fibers embedded in soil can monitor soil temperature by sensing changes in Rayleigh scattering frequency shifts. Changes in soil temperature directly lead to corresponding changes in the Rayleigh scattering frequency shifts within the fiber, and the two have a stable functional relationship. This relationship allows for precise calculation of the real-time soil temperature, enabling efficient and accurate monitoring. Similarly, humidity-sensitive optical fibers embedded in soil can monitor soil humidity by sensing changes in Rayleigh scattering frequency shifts. Different soil humidity levels cause different frequency shifts in the fiber. By eliminating the influence of temperature coupling and combining this with a prior model and the frequency shift relationship, efficient and accurate monitoring of soil humidity can be achieved. Rayleigh scattering demodulation has extremely high spatial resolution, reaching the millimeter level. Therefore, the soil moisture content along the fiber can be calculated using the Rayleigh scattering frequency shifts distributed along the fiber, enabling millimeter-level monitoring of moisture field evolution.

[0035] The localization of Rayleigh scattering radio frequency shift depends on the time delay between laser incident and scattered signal reception. t The speed of light propagation in an optical fiber is constant. Knowing the time delay, the distance the light travels in the optical fiber can be calculated, i.e., the location of the Rayleigh scattering frequency shift. The calculation formula is shown in equation (1). In the formula, z The distance between the measurement point and the laser incident point; n g ρ is the refractive index of the optical fiber material; c is the speed of light.

[0036] Spatial resolution of fiber Rayleigh scattering demodulation z Depending on the relationship shown in formula (2), the spatial resolution of the measurement can be adjusted by changing the frequency of the incident laser, thus achieving millimeter-level precision measurement. In the formula, u is the frequency of the incident light emitted by a tunable laser.

[0037] Fiber Rayleigh Dispersion Radio Frequency Displacement With strain change and temperature change T The functional relationship between them is shown in formula (3). In the formula, v The incident light frequency; denoted as the fiber strain plasticity coefficient; a is the fiber thermal expansion coefficient; x is the fiber thermo-optic coefficient. The strain coefficient can be obtained through measurement; C T The temperature coefficient is determined through calibration tests in experiments due to the uncertainties of optical fiber materials and the influence of the coating and sheath on the performance of optical fibers. The aim is to establish an accurate correspondence between Rayleigh scattering radio frequency shift, strain value, and ambient temperature.

[0038] Based on the optical frequency domain reflection (OFDR) distributed optical fiber sensing technology, using polyimide (PI) humidity-sensitive coating and gold (Au) temperature-sensitive coating optical fiber, the PI-coated optical fiber is sensitive to both temperature and relative humidity, while the Au-coated optical fiber is only sensitive to temperature. The strain changes of the two are linearly related to the temperature and humidity changes, and thus the measured relative humidity (RH) can be calculated. The total strain of the PI-coated optical fiber is the superposition of the strain caused by humidity and the strain caused by temperature. The linear expression can be represented by formula (4). Au-coated optical fibers are not sensitive to humidity; strain is caused only by temperature changes, and the linear expression is: In the formula This represents the strain change in the PI-coated optical fiber. ΔRH represents the humidity sensitivity coefficient of the PI-coated optical fiber; ΔRH represents the change in relative humidity of the mural. ΔT represents the temperature sensitivity coefficient of the PI-coated optical fiber; ΔT represents the temperature change of the mural. This represents the strain change in the Au-coated optical fiber. This represents the temperature sensitivity coefficient of Au-coated optical fiber.

[0039] Based on the above formulas (4) and (5), the calculation relationship between Rayleigh scattering radio frequency displacement and temperature and humidity can be established, as shown in formulas (6) and (7). This calculation formula is derived from the above calculation formulas. Different Rayleigh scattering radio frequency displacements can be obtained by combining different formulas (4) and (5). v Formulas (6) and (7) for calculating the relationship between humidity (RH) and temperature (T): Rayleigh scattering occurs at any point on the fiber. Therefore, when monitoring optical cables with different functions are laid in the soil, the Rayleigh scattering at each point on the fiber will shift due to changes in the external environment. Thus, the field distribution near the entire fiber can be calculated according to formulas (3), (5), and (6).

[0040] The following describes a specific application example.

[0041] Reference Figure 1 As shown, the mural monitoring method generally includes the fiber optic deployment process and the fiber optic monitoring process.

[0042] (I) Fiber Optic Deployment Process The fiber optic deployment process should include at least four core steps: drilling holes in the mural, fixing the bottom, eliminating reflections at the tail end, and overall burial. Firstly, it ensures zero damage to the mural structure during the implantation of the fiber optic sensor; secondly, it guarantees the environmental durability and signal stability of the fiber optic sensing system during long-term monitoring.

[0043] Figure 2 The installation of the strain sensing fiber 9 is shown: (1) A customized micro-drilling rig 3 is used in conjunction with a special micro-drill bit 4 to perform a drilling strategy of vertical wall orientation and constant-speed slow advance. During the drilling process, the drilling pressure and rate must be strictly controlled to ensure the integrity of the wall around the hole and avoid micro-cracks or peeling. After drilling is completed, a small blower is used to thoroughly clean the dust and debris inside the hole to ensure that the hole wall is clean and to provide a foundation for subsequent installation.

[0044] (2) The end of the strain sensing fiber 9 is cut using an optical fiber beveling cutter. Then, the end of the fiber 9 is fixed and encapsulated with a bottom UV adhesive sleeve 8, and irradiated with a UV lamp 7 to ensure that it is quickly fixed to the bottom of the drill hole. This process can not only effectively reduce Fresnel reflection at the end face of the fiber and suppress backscatter noise, but also ensure the high fidelity of the optical signal in long-distance transmission and meet the requirements of high-precision demodulation.

[0045] (3) Connect the processed end of the optical fiber 9 to the demodulator 10 to realize the real-time acquisition and monitoring of strain values ​​through photoelectric conversion.

[0046] (4) Use syringe 11 to extract the undisturbed high-moisture-content mural soil slurry and grout the borehole. This achieves efficient mechanical coupling between the strain sensing fiber and the mural soil, ensuring that the micro-deformation generated by the soil under stress can be transmitted to the fiber 9 without loss, thereby accurately inverting the true strain state of the mural.

[0047] Customized drill rig 3 is an adjustable-speed drill rig, which can adapt to drilling operations on murals of different hardness, effectively ensuring the structural integrity of the murals. Customized drill bit 4 adopts a small-diameter, high-rigidity configuration, which can significantly reduce disturbance to the murals, and the length of the drill bit is matched with the preset embedding depth of the fiber optic sensor.

[0048] The fiber tail beveling process uses a special fiber optic beveling blade to ensure a smooth and clean cut end, effectively reducing fiber reflection and ensuring accurate and lossless optical signal transmission. At the same time, a UV lamp is used to irradiate and cure the UV adhesive sheath at the fiber tail, achieving rapid bonding and further suppressing tail reflection to minimize optical loss.

[0049] The strain sensing fiber 9 uses a small-diameter, single-mode fiber without special coating, which is easy to embed in the borehole and reduces temperature monitoring anomalies caused by coating characteristics.

[0050] When deploying the strain sensing fiber 9, a small-diameter needle is selected when injecting high-moisture-content undisturbed mud into the borehole using a syringe 11 to ensure smooth injection without clogging. When preparing the high-moisture-content undisturbed mud, only clay particles are retained to ensure good fluidity of the slurry. The injection process uses a constant-speed, slow injection to prevent duct blockage. After the borehole is backfilled, it is left to cure statically to allow the fiber 9 to fully couple with the slurry, ensuring strain transfer efficiency and monitoring accuracy.

[0051] Figure 3 The layout of temperature-sensitive fiber and temperature and humidity-sensitive fiber is shown. Specifically, the temperature-sensitive fiber is Au-coated fiber 14, which includes a fiber core and a gold (Au) layer coated on the fiber core; the temperature and humidity-sensitive fiber is Au-coated fiber 13, which includes a fiber core and a polyimide (PI) coating coated on the fiber core.

[0052] Similar to the installation process of strain sensing fiber 9, a customized micro drill 3 and a customized micro drill bit 4 are used to drill holes. Then, the holes are cleaned to ensure that the hole walls are clean. The tails of fibers 13 and 14 are beveled and fixed and encapsulated with UV adhesive sheaths 8. Then, they are connected to demodulator 10 to install PI-coated fiber 13 and Au-coated fiber 14. Subsequent measurements are then performed without the need for backfilling the drilled holes.

[0053] Figure 4 The structure of the optical fiber assembly is shown. For example... Figure 4 As shown, the fiber optic assembly mainly consists of three parts. The outermost part is a custom-designed small-diameter spring 15. This spring 15 has a preset elastic tension, which ensures efficient temperature and humidity exchange between the inner and outer spaces of the spring 15, guaranteeing the stable implementation of the fiber optic assembly's temperature and humidity monitoring function. Furthermore, since fiber optic monitoring signals are susceptible to both temperature and strain, the external spring 15 provides stable protection for the internal fibers 13 and 14, preventing external wall deformation from transmitting to the fibers and causing additional strain shifts. This ensures that the signal shift in the fiber optics is only caused by temperature and humidity changes, structurally eliminating strain interference with temperature and humidity monitoring. The custom-designed spring 15 contains one PI-coated fiber 13 and one Au-coated fiber 14. The PI-coated fiber 13 is a polyimide humidity-sensitive coated fiber, and the Au-coated fiber 14 is a gold temperature-sensitive coated fiber. Utilizing the different physical sensitivity characteristics of the two coatings, decoupled temperature and humidity monitoring is achieved. The PI-coated fiber 13 is sensitive to both temperature and relative humidity, while the Au-coated fiber 14 is only sensitive to temperature. Furthermore, the strain changes of both fibers exhibit a linear functional relationship with the corresponding temperature and humidity changes. The total strain of the PI-coated optical fiber 13 is composed of the superposition of humidity-induced strain and temperature-induced strain. Combined with the pure temperature strain response characteristics of the Au-coated optical fiber 14, the relative humidity (RH) and temperature values ​​of the monitoring area can be calculated through equations (4) and (5), thus achieving accurate measurement of temperature and humidity. The optical fiber assembly is buried in the preset monitoring position of the mural. After the deployment is completed, long-term effective monitoring of the temperature and humidity of the mural and the surrounding medium can be achieved.

[0054] (II) Parameter calibration of strain sensing fiber, temperature sensing fiber, and temperature and humidity sensing fiber Before monitoring, the temperature-frequency shift relationship, strain-frequency shift relationship, and humidity-frequency shift relationship of the optical fiber should be calibrated, i.e., the unknown coefficients in equations (3), (4), and (5). Determined values. In some other embodiments, calibration may be omitted, and the parameters provided by the fiber optic manufacturer may be used directly.

[0055] Reference Figure 5As shown, the specific calibration experiment was conducted in a constant-temperature environmental chamber 16 to ensure that the fiber offset was not affected by temperature. Five different supersaturated salt solutions were used in the chamber to provide a stable and repeatable relative humidity environment. These salt solutions were lithium chloride (LiCl), magnesium chloride (MgCl2), sodium bromide (NaBr), sodium chloride (NaCl), and potassium sulfate (K2SO4), which correspond to approximately 11%, 33%, 58%, 75%, and 97% relative humidity at different temperatures, respectively. To prevent crystallization or unsaturation due to temperature changes, excess solid salt was added during the preparation process to maintain dynamic equilibrium and ensure the stability of relative humidity during the experiment. First, the fiber was passed through a five-perforated sealed box (the box was not sealed at this time) at a temperature of 20°C, and the sealed box and the fiber tip were fixed to avoid strain affecting the fiber measurement results during subsequent solution addition and sealing. After fixing the fiber, the initial value was scanned under these conditions, and the temperature and humidity values ​​in the environmental chamber at the time of the initial value scan were recorded. Subsequently, the prepared salt solutions were sequentially injected into the sealed box, which was then sealed and left to stand for approximately 30 minutes to ensure uniform humidity distribution and complete moisture absorption equilibrium between the optical fiber and the environment. At this point, the effective strain value generated by the optical fiber was measured. After humidity calibration, the temperature sensitivity coefficient of the optical fiber was determined. Thus, the temperature and humidity sensitivity coefficient under relative humidity conditions can be measured.

[0056] (III) Fiber Optic Monitoring Process like Figure 6 As shown, single-mode fiber jumpers connecting strain sensing fiber 9, PI-coated fiber 13, and Au-coated fiber 14 are connected to Rayleigh scattering demodulator 10. Rayleigh scattering demodulator 10 is then connected to a data processing computer, and laser light is introduced into each fiber. First, Rayleigh scattering demodulator 10 continuously receives and demodulates the Rayleigh divergence in strain sensing fiber 9 and the strain changes in Au-coated fiber 14 and PI-coated fiber 13, using these as the basis for calculating the divergence.

[0057] The initial monitoring time should not be less than 5 minutes to ensure that the Rayleigh scattering radio frequency shift during the stable phase can represent the true condition of the soil at that time. Adjust the pump light frequency emitted by the Rayleigh scattering demodulator and select an appropriate spatial resolution and sampling time interval to achieve high-quality monitoring.

[0058] The 5-minute Rayleigh scattering frequency shift measured in this stage can be used to obtain a representative baseline reference value, namely the initial Rayleigh scattering frequency shift, through a weighted average. v 0.

[0059] After completing the initial frequency shift of Rayleigh scattering vAfter the initial measurement, corresponding physical quantities can be measured according to the different functions of the buried optical fiber. The Rayleigh scattering demodulator 10 is used to monitor the changes in Rayleigh scattering frequency shift or strain in the single-mode fiber during the corresponding process. By measuring the change in Rayleigh scattering frequency shift at the time when data acquisition is required, the Rayleigh scattering frequency shift at that time point can be obtained. v Then Δv can be calculated, such as By combining equations (I), (II), and (III), the strain, humidity, and temperature values ​​of the mural at that time can be calculated. This process should be completed using a data processing computer.

[0060] (I) (II) (III) Equation (I) is the same as expression (5) above. Equation (II) is the same as expression (4) above. Equation (III) is based on expression (3) above. In this embodiment, since the strain sensing fiber and the mural soil are efficiently mechanically coupled through glue injection, the temperature change has a very small effect on the strain measured by the fiber. Therefore, the relationship between the strain of the mural and the Rayleigh scattering frequency shift of the strain sensing fiber is simplified to equation (III).

[0061] Furthermore, based on the parameters obtained by demodulating the temperature-sensitive fiber and the temperature and humidity-sensitive fiber using the demodulator during the monitoring process, the humidity and temperature of the mural are directly calculated according to the above expressions (6) and (7).

[0062] By performing the above steps regularly according to monitoring needs, the non-destructive installation of fiber optic sensors for multi-field monitoring of murals can be achieved, along with subsequent data analysis and processing, enabling high spatial resolution monitoring of the multi-field evolution of murals.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0064] As indicated in this specification and claims, the terms "comprising" and "including" only indicate the inclusion of expressly identified steps and elements, and these steps and elements do not constitute an exclusive list; the method or apparatus may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the associated listed items.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0066] Any step described in any method or process claim may be performed in any order, and is not limited to the order presented in the claims. The limitation of method + function or step + function is used only if all of the following conditions are met in a particular claim: a) it expressly states "method for..." or "step for..."; b) it expressly states the corresponding function. Structures, materials, or actions supporting the method + function are expressly described in the description herein. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given herein.

[0067] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are preferred embodiments. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A mural monitoring system, characterized in that, include: An optical fiber assembly configured to be deployed in a mural to provide a path for testing the propagation of a laser within the mural, the optical fiber assembly comprising a temperature-sensitive fiber and a temperature and humidity-sensitive fiber arranged side by side; Strain sensing fiber optic cable, configured to be laid in the mural to provide a propagation path for the test laser within the mural; A demodulator is used to demodulate the first strain change of the temperature-sensitive optical fiber, the second strain change of the temperature and humidity-sensitive optical fiber, and the Rayleigh divergence frequency shift of the strain-sensing optical fiber. A processor is configured to obtain temperature parameters of the mural based on the first strain change; obtain humidity parameters of the mural based on the temperature parameters and the second strain change; and obtain strain parameters of the mural based on the Rayleigh scattering frequency shift.

2. The mural monitoring system according to claim 1, characterized in that, The optical fiber assembly is installed in the first measuring hole of the mural, which is located inside the mural and has not been backfilled. The strain sensing fiber is installed in the second measuring hole of the mural, which is located inside the mural and backfilled by the mural soil.

3. The mural monitoring system according to claim 2, characterized in that, A UV adhesive sheath is provided at one end of the temperature-sensitive optical fiber and at one end of the temperature and humidity-sensitive optical fiber. After being irradiated with ultraviolet light, the UV adhesive sheath fixes the ends of the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber in the first measuring hole. A UV adhesive sheath is provided at one end of the strain sensing fiber, and the UV adhesive sheath fixes the end of the strain sensing fiber in the second measuring hole after being irradiated with ultraviolet light.

4. The mural monitoring system according to claim 1, characterized in that, The optical fiber assembly also includes a spring, which is sleeved on the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber; The temperature-sensitive optical fiber includes a fiber core and a gold layer covering the fiber core; The temperature and humidity sensitive optical fiber includes a fiber core and a polyimide coating covering the fiber core; The strain sensing fiber is a single-mode fiber.

5. The mural monitoring system according to any one of claims 1 to 4, characterized in that, The processor is used to obtain the temperature parameters of the mural according to the following formula (I): （I） In formula (I), This represents the first strain change in the temperature-sensitive optical fiber. The temperature sensitivity coefficient of the temperature-sensitive optical fiber; T The temperature change of the mural; The processor is used to obtain the humidity parameters of the mural according to the following formula (II): (II) In formula (II), This is the second strain change in the P-type temperature and humidity sensitive optical fiber. ΔRH represents the humidity sensitivity coefficient of the temperature and humidity sensitive optical fiber; ΔRH represents the relative humidity change of the mural. The temperature sensitivity coefficient of the temperature and humidity sensitive optical fiber; The processor is used to obtain the strain parameters of the mural according to the following formula (III): (III) In formula (III), The Rayleigh scattering radio frequency shift; v The incident light frequency; The strain coefficient of the strain sensing fiber; This represents the strain variation of the mural.

6. A method for monitoring murals, characterized in that, The mural monitoring system as described in claim 1, wherein the mural monitoring method comprises the following steps: S1. Fiber optic components and strain sensing fibers are laid in the mural. One end of the temperature-sensitive fiber and the temperature and humidity-sensitive fiber of the fiber optic components are fixed in the first measuring hole of the mural, and the other end is connected to the demodulator. One end of the strain sensing fiber is fixed in the second measuring hole of the mural, and the other end is connected to the demodulator. S2. Inject a first laser into the temperature-sensitive fiber and the temperature and humidity-sensitive fiber, and inject a second laser into the strain-sensing fiber; S3. The first strain change of the temperature-sensitive optical fiber, the second strain change of the temperature and humidity-sensitive optical fiber, and the Rayleigh divergence of the strain-sensing optical fiber are obtained by demodulation using a demodulator. S4. Obtain the temperature parameters of the mural based on the first strain change; obtain the humidity parameters of the mural based on the temperature parameters and the second strain change; obtain the strain parameters of the mural based on the Rayleigh scattering displacement.

7. The mural monitoring method according to claim 6, characterized in that, In step S1, a first measuring hole is drilled in the mural, and a temperature-sensitive fiber and a temperature and humidity-sensitive fiber are inserted into the first measuring hole. One end of the temperature-sensitive fiber and the temperature and humidity-sensitive fiber is fixed to the first measuring hole. The first measuring hole is not backfilled, and there is a gap between the fiber assembly and the hole wall of the first measuring hole. In step S1, a second measuring hole is drilled in the mural, a strain sensing fiber is inserted into the second measuring hole, one end of the strain sensing fiber is fixed to the second measuring hole, and soil slurry of the same type as the mural is injected into the second measuring hole to seal the hole, so that the strain sensing fiber and the mural soil are in contact and coupled.

8. The mural monitoring method according to claim 7, characterized in that, In step S1, a UV adhesive sheath is applied to one end of the temperature-sensitive optical fiber and one end of the temperature and humidity-sensitive optical fiber, and ultraviolet light is applied to cure the UV adhesive sheath, so as to fix the ends of the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber in the first measuring hole. A spring is fitted onto at least the portion of the temperature-sensitive optical fiber and the temperature and humidity-sensitive optical fiber located at the first measuring hole. In step S1, a UV adhesive sheath is placed on one end of the strain sensing fiber, and ultraviolet light is applied to cure the UV adhesive sheath, thereby fixing the end of the strain sensing fiber in the second measuring hole.

9. The mural monitoring method according to claim 6, characterized in that, In step S1, an optical fiber with a gold layer is selected as a temperature-sensitive optical fiber, an optical fiber with a polyimide coating is selected as a temperature and humidity-sensitive optical fiber, and a single-mode optical fiber without a coating is selected as a strain-sensing optical fiber. The ends of each optical fiber inserted into the mural are beveled.

10. The mural monitoring method according to claim 6, characterized in that, In step S4, the temperature parameters of the mural are obtained according to the following formula (I): （I） In formula (I), This represents the first strain change in the temperature-sensitive optical fiber. The temperature sensitivity coefficient of the temperature-sensitive optical fiber; T The temperature change of the mural; The humidity parameters of the mural are obtained according to the following formula (II): (II) In formula (II), This is the second strain change in the P-type temperature and humidity sensitive optical fiber. ΔRH represents the humidity sensitivity coefficient of the temperature and humidity sensitive optical fiber; ΔRH represents the relative humidity change of the mural. The temperature sensitivity coefficient of the temperature and humidity sensitive optical fiber; The strain parameters of the mural are obtained according to the following formula (III): (III) In formula (III), The Rayleigh scattering radio frequency shift; v The incident light frequency; The strain coefficient of the strain sensing fiber; This represents the strain variation of the mural.

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