Integrated flexible fiber optic sensing device and its in-situ sensing method

Abstract

This invention proposes an integrated flexible fiber optic sensing device and its in-situ sensing method, belonging to the interdisciplinary field of intelligent sensing and additive manufacturing. It includes: two fixed mechanisms, parallel and spaced apart, for fixing to the surface of the structure being measured; each fixed mechanism has a first groove corresponding to its end face; an elastic substrate, located in the region between the two fixed mechanisms and arranged in a curved shape; the elastic substrate has a second groove on its end face, which is also connected to the first groove on the two fixed mechanisms; and a metallized optical fiber, sequentially embedded in the first and second grooves, with FBG fiber gratings at both ends of the metallized optical fiber in the first groove; the metallized optical fiber is integrally formed with the two fixed mechanisms and the elastic substrate. Metal 3D printing is used to improve manufacturing efficiency, and combined with fiber metallization and fiber-metal integrated forming processes, a rigid connection between the optical fiber and the metal substrate is achieved, improving heat resistance and operability.

Description

Technical Field

[0001] This invention relates to the field of intelligent sensing and additive manufacturing, and in particular to an integrated flexible fiber optic sensing device and its in-situ sensing method. Background Art

[0002] In extreme environments such as those affecting aero-engine turbine blades, which endure long-term exposure to high temperatures, complex aerodynamic loads, and high-cycle fatigue, real-time monitoring of the temperature-strain field is crucial for structural safety. Fiber Bragg grating (FBG) sensors are sensitive to both strain and temperature simultaneously; both factors can cause a shift in the fiber coupling wavelength. As a novel sensing element, FBGs effectively avoid electromagnetic interference compared to electrical sensors and offer advantages such as small size and distributed monitoring capabilities, facilitating integration into the sensor substrate for application in complex environments. Currently, traditional adhesive and soldering methods for sensor packaging suffer from poor heat resistance and operability. Existing sensor placement schemes generally suffer from large substrate sizes and complex fabrication, and neglect the influence of substrate stiffness on strain sensing of the measured structure.

[0003] Therefore, it is essential to provide an integrated flexible fiber optic sensing device and its in-situ sensing method, which improves the shortcomings of conventional bonding and soldering methods by integrating the substrate structure with the fiber optic grating, which have poor heat resistance and are not suitable for high-temperature environments. It also improves the shortcomings of existing sensing and detection equipment, which have small range and low stiffness. Summary of the Invention

[0004] In view of this, the present invention proposes an integrated flexible fiber optic sensing device and its in-situ sensing method that is 3D printed, does not use conventional bonding or welding methods, has good heat resistance, and is suitable for temperature-strain monitoring.

[0005] On one hand, the present invention provides an integrated flexible fiber optic sensing device, comprising:

[0006] Two fixing mechanisms are arranged in parallel and spaced apart for fixing to the surface of the structure being measured. The end faces of the two fixing mechanisms are respectively provided with first grooves.

[0007] An elastic substrate is disposed in the area between two fixed mechanisms and is arranged in a curved shape. A second groove is provided on the end face of the elastic substrate, and the second groove is also connected to the first groove on the two fixed mechanisms.

[0008] Metallized optical fibers are sequentially embedded in the first and second slots. FBG fiber gratings are provided at both ends of the metallized optical fibers located in the first slot. The metallized optical fibers are integrally formed with the two fixing mechanisms and the elastic matrix.

[0009] Based on the above technical solution, preferably, the elastic matrix includes two first arc segments, two second arc segments, and a connecting beam. The connecting beam is located between the two fixed mechanisms and is set at an angle to the longitudinal center plane of the two fixed mechanisms. One end of each of the two first arc segments is fixedly connected to the adjacent side surface of the two fixed mechanisms, and the other end of each of the two first arc segments is fixedly connected to one end of each of the two second arc segments. The other end of each of the two second arc segments is fixedly connected to different ends of the connecting beam.

[0010] Preferably, the initial bending radii of the two first arc segments and the two second arc segments are the same, and the central angle of the first arc segment is 90°, the central angle of the second arc segment is 180°, and the length of the connecting beam is twice the initial bending radius of the first arc segment.

[0011] Preferably, the deviation of the center wavelength of the FBG fiber gratings at both ends of the metallized optical fiber is 2-5 nm.

[0012] Preferably, the process of integrally molding the metallized optical fiber with the two fixing mechanisms and the elastic substrate includes the following steps:

[0013] Using the fused taper method, a precision motor is used under a microscope to control the stretching speed and displacement of the heated optical fiber, and the diameter of the optical fiber is monitored. Fiber Bragg gratings are placed at both ends of the taper fiber, and the taper fiber and fiber Bragg gratings are fused together to obtain micro / nano fiber. The cladding is removed, and a metal coating is formed on the surface of the micro / nano fiber through chemical plating and metal plating processes to obtain metallized fiber.

[0014] Design a 3D model of two fixed mechanisms and an elastic base using CAD software;

[0015] Use the slicing tool to slice the 3D model and generate layer-by-layer 2D contour data;

[0016] Plan the laser scanning path, set the laser power, scanning speed and powder layer thickness, select a suitable substrate, and clean and preheat the substrate;

[0017] Metal powder is loaded into the powder supply device, and the powder is evenly spread on the substrate using a scraper to achieve the set powder layer thickness; inert gas is then introduced into the printing chamber.

[0018] The laser scans and melts the powder layer based on the slice data. After each powder layer is melted, the substrate thickness decreases by one layer, and the powder-scanning process is repeated. When the powder layer of the first and second slots is printed, the chamber door is opened to sweep away the top metal powder, and the bent metallized optical fiber is placed into the first and second slots. The printing is then carried out layer by layer again until the printing is completely finished, resulting in an integrated metallized optical fiber, two fixing mechanisms, and an elastic substrate.

[0019] Preferably, the depth of the first and second slots is 1.2-1.5 times the diameter of the metallized optical fiber, the width of the first and second slots is 1.1-1.3 times the diameter of the metallized optical fiber, and the cross-sectional shape of the first and second slots is elliptical.

[0020] Preferably, the elastic base and the two fixed mechanisms have the same height, and the width of the elastic base is greater than the height of the elastic base; the angle between the connecting beam and the longitudinal center plane of the two fixed mechanisms is 30°.

[0021] On the other hand, the present invention provides an in-situ sensing method for an integrated flexible fiber optic sensing device, comprising the following steps:

[0022] S1: Configure the above-mentioned integrated flexible fiber optic sensing device; the fiber grating at one end of the metallized fiber is connected to the light source optical path; the metallized fiber is obtained by setting FBG fiber gratings at both ends of the tapered fiber, and then further setting a metal coating on the micro-nano fiber.

[0023] S2: Construct a model for measuring light intensity loss and strain;

[0024] S3: By obtaining the light intensity difference between the fiber gratings at both ends of the metallized optical fiber, the temperature and strain are solved using a wavelength-intensity hybrid demodulation method with dual fiber gratings.

[0025] Preferably, step S2 involves obtaining the bending loss of the FBG fiber grating when it is not subjected to external force; and obtaining the bending loss of the metallized fiber at the first arc segment. x Elongation in the axial direction, metallized optical fiber at the connecting beam x Elongation in the axial direction x The axial direction is the length extension direction of the fixed mechanism, the bending radius of the first arc segment when not subjected to external load, and the bending radius of the first arc segment of the metallized optical fiber after being stretched by external load, to construct the mapping relationship between strain and light intensity loss.

[0026] Preferably, step S3 involves: constructing a mapping relationship between optical intensity loss and the bending radius of the first arc segment of the metallized optical fiber under external load; obtaining a relationship between the center wavelength of the FBG fiber grating and the temperature change; and combining the mapping relationship between optical intensity loss and the bending radius of the first arc segment of the metallized optical fiber under external load, the relationship between temperature change and wavelength drift, and the mapping relationship between strain and optical intensity loss to solve for the strain change and temperature change.

[0027] The integrated flexible fiber optic sensing device and its in-situ sensing method provided by this invention have the following advantages compared with the prior art:

[0028] (1) This solution proposes an integrated sensor structure with an elastic substrate, which has the advantages of low stiffness and large range. The elastic substrate used as the substrate and the two fixing mechanisms are processed by metal 3D printing to improve manufacturing efficiency. Combined with fiber metallization and fiber-metal integrated forming process, the rigid connection between the fiber and the metal substrate is realized, which overcomes the problems of poor heat resistance and poor operability caused by traditional adhesive bonding and soldering connection methods. The metallization fiber coating process based on chemical plating and electroplating is used to enhance the interfacial bonding strength between the fiber and the metal substrate and enhance the high temperature resistance of the fiber.

[0029] (2) In terms of signal demodulation mechanism, the sensing device provided by this scheme adopts the dual FBG wavelength-light intensity hybrid demodulation method to solve temperature and strain. It has good effects in the static characteristics, dynamic response, cross coupling and high temperature resistance of temperature and strain. It can realize composite sensing of temperature and strain under the condition of designing specific temperature and strain decoupling.

[0030] (3) The sensing device provided in this solution is particularly suitable for monitoring the structural health of turbine blades and provides a reliable temperature-strain testing method. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0032] Figure 1 This is a top view of the sensing device of the integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention.

[0033] Figure 2(a) is a bottom view of the sensing device of the integrated flexible fiber optic sensing device and its in-situ sensing method of the present invention.

[0034] Figure 2(b) is a left view of the sensing device of the integrated flexible fiber optic sensing device and its in-situ sensing method of the present invention.

[0035] Figure 3 This is a schematic diagram of the structure of the metallized optical fiber in the integrated flexible optical fiber sensing device and its in-situ sensing method of the present invention.

[0036] Figure 4 This is a schematic diagram showing the dimensions of the sensing device of the integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention.

[0037] Figure 5This is a schematic diagram of the structural stress analysis of the integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention.

[0038] Figure 6 This is a perspective view of the sensing device of the integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention.

[0039] Figure 7 This is the modeling strategy for the decoupling model of the integrated flexible fiber optic sensing device and its in-situ sensing method of the present invention.

[0040] Figure 8 This is a schematic diagram of the multi-channel decoupling strategy of an integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention.

[0041] Figure 9 This is a schematic diagram of the multilayer sensing limit learning machine structure of the integrated flexible fiber optic sensing device and its in-situ sensing method according to the present invention. Detailed Implementation

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Fiber Bragg gratings, as a novel sensing element, effectively avoid electromagnetic interference compared to electrical sensors. They also offer advantages such as small size and distributed monitoring capabilities, making them easy to integrate into sensor substrates for use in complex environments. Currently, traditional adhesive and soldering methods for sensor packaging suffer from poor heat resistance and operability. Furthermore, existing sensor placement schemes generally suffer from large substrate sizes and complex fabrication processes, and neglect the impact of substrate stiffness on strain sensing of the measured structure. Therefore, if... Figure 1 Combining Figure 2(a) and Figure 2(b), Figure 3 , Figure 5 and Figure 6 As shown, in one aspect, the present invention provides an integrated flexible fiber optic sensing device, comprising:

[0044] Two fixing mechanisms 4 are arranged in parallel and at intervals for fixing to the surface of the structure being measured. The end faces of the two fixing mechanisms 4 are respectively provided with first grooves 100; the two fixing mechanisms 4 are respectively provided with fixing holes 1 for fixing to the structure being measured.

[0045] The elastic substrate 3 is disposed in the area between the two fixed mechanisms 4 and is arranged in a curved shape. A second groove 200 is provided on the end face of the elastic substrate 3. The second groove 200 is also connected to the first groove 100 on the two fixed mechanisms 4.

[0046] Metallized optical fiber 2 is sequentially embedded in the first slot 100 and the second slot 200. FBG fiber gratings 5 ​​are provided at both ends of the metallized optical fiber 2 located in the first slot 100. The metallized optical fiber 2 is integrally formed with the two fixing mechanisms 4 and the elastic substrate 3. In this embodiment, the FBG fiber gratings 5 ​​at both ends of the metallized optical fiber 2 are identical in size, and the center wavelength deviation between the two FBG fiber gratings 5 ​​is 2-5 nm.

[0047] Figure 1 and Figure 6 The elastic substrate 3 shown resembles a figure-eight or S-shape. Specifically, the elastic substrate 3 mainly comprises three parts: two first arc segments 31, two second arc segments 32, and a connecting beam 33. The connecting beam 33 is located between the two fixed mechanisms 4 and is set at an angle to the longitudinal center plane of the two fixed mechanisms 4, with the included angle being [angle value missing]. θ One end of each of the two first arc segments 31 is fixedly connected to the side surfaces adjacent to the two fixed mechanisms 4, and the other end of each of the two first arc segments 31 is fixedly connected to one end of each of the two second arc segments 32, and the other end of each of the two second arc segments 32 is fixedly connected to different ends of the connecting beam 33.

[0048] In this embodiment, to simplify the structure and reduce the amount of calculation, the initial bending radii of the two first circular arc segments 31 and the two second circular arc segments 32 are made the same, that is... Figure 4 radius in R 2 and R 3 are equal, let R 2= R 3= R Furthermore, the central angle of the first arc segment 31 is 90°, the central angle of the second arc segment 32 is 180°, and the length of the connecting beam 33 is twice the initial bending radius of the first arc segment 31.

[0049] To better optimize the structure of the elastic substrate 3 and the two fixing mechanisms 4 used as the substrate, when the metal substrate is mounted on the surface of the structure under test, the stiffness of the substrate will introduce constraint reaction forces that affect the deformation of the structure under test. To reduce and quantify this effect, the influence factor is defined as... q .

[0050] Establish x Directional external load F Mapping relationship with impact factor x The axial direction is the length extension direction of the fixed mechanism 4, where ,like Figure 5As shown, based on the principle of energy method in mechanics of materials, it can be obtained that the elastic matrix 3 and the two fixed mechanisms 4 are in... x The total deformation in the direction is: ,in A Let be the cross-sectional area of ​​the elastic matrix 3. , b The width of the cross-section of the elastic matrix 3 is given by [reference to a specific matrix]. h The height of the elastic matrix 3; E It is the elastic modulus; I For the moment of inertia, ; L For elastic matrix 3 in x Total length in the axial direction, Therefore, the impact factor can be obtained as follows: .

[0051] During the optimization of the elastic matrix structure, multi-objective constraints can be set according to actual needs, such as the angle between the connecting beam 33 and the vertical direction. θ Cross-sectional area A and the initial bending radius of the first circular arc segment 31 R Such adjustments require multi-parameter coordinated optimization to adjust the substrate stiffness. For example, in this embodiment, analysis reveals the height of the elastic substrate 3. h and the cross-sectional width of the elastic matrix 3 b The increase of the sensor's influence factor q It will increase; the included angle θ and initial bending radius R Increase, Influence Factor q Will decrease.

[0052] In one embodiment, the overall dimensions of the elastic matrix are 20mm × 10.5mm × 0.55mm, and the initial bending radius is... R It is 2mm, with an included angle. θ The angle is 30°, the height of the elastic substrate 3 and the two fixing mechanisms 4 are the same, and the width of the elastic substrate 3 is greater than the height of the elastic substrate 3. By limiting the elastic substrate 3 to bend inward, the overall size of the elastic substrate can be reduced while maintaining sufficient sensitivity and ease of installation, thus meeting the requirements of small-size configuration.

[0053] As shown in Figures 2(a) and 2(b), the depth of the first slot 100 and the second slot 200 is 1.2-1.5 times the diameter of the metallized optical fiber 2, the width of the first slot 100 and the second slot 200 is 1.1-1.3 times the diameter of the metallized optical fiber 2, and the cross-sectional shape of the first slot 100 and the second slot 200 is elliptical.

[0054] The process of integrally forming the metallized optical fiber 2 with the two fixing mechanisms 4 and the elastic substrate 3 includes the following steps:

[0055] Using the fused ablation taper method, the stretching speed and displacement of the heated optical fiber are controlled by a precision motor under a microscope, and the diameter of the fiber is monitored. FBG fiber gratings are placed at both ends of the taper fiber, and the taper fiber and the fiber gratings are fused together to obtain a micro / nano fiber. The cladding on the surface of the micro / nano fiber is removed, and a metal coating is formed on the surface of the micro / nano fiber through chemical plating and metal plating processes to obtain metallized fiber 2. If the coating layer is removed from the fiber using wire strippers, a nickel layer is deposited on the surface of the fiber through activation, sensitization, chemical plating, and electroplating processes. The diameter of the taper fiber is 5μm, and the coating thickness at the taper fiber is 45μm, that is, the diameter after coating is 50μm. The length of the FBG fiber grating is 1mm, and the diameter after coating is 125μm. The nickel layer is used to enhance the interfacial bonding strength between the metallized fiber and the substrate, and to enhance the high-temperature resistance of the metallized fiber.

[0056] Design a 3D model of the two fixed mechanisms 4 and the elastic base 3 using CAD software; and export it as an STL file.

[0057] The 3D model is sliced ​​using SLM software to generate layer-by-layer 2D contour data.

[0058] A substrate structure was prepared using aluminum alloy powder (AlSi10Mg), the laser scanning path was planned, the laser power, scanning speed and powder layer thickness were set, a suitable substrate was selected, and the substrate was cleaned and preheated.

[0059] Metal powder is loaded into the powder supply device, and a scraper is used to spread the powder evenly on the substrate to achieve the set powder layer thickness; inert gas is filled into the printing chamber; the high-purity inert gas atmosphere can prevent metal oxidation.

[0060] The laser scans and melts the powder layer according to the slice data. After each powder layer is melted, the substrate thickness decreases by one layer, and the powder-scanning process is repeated. When the powder layer of the first slot 100 and the second slot 200 is printed, the chamber door is opened to sweep away the top metal powder, and the bent metallized optical fiber 2 is placed into the first slot 100 and the second slot 200. The printing is carried out layer by layer again until the printing is completely finished, and the integrated metallized optical fiber 2, the two fixing mechanisms 4 and the elastic substrate 3 are obtained.

[0061] In this embodiment, a laser power of 350 W, a scanning speed of 1000 mm / s, and a layer thickness of 50 μm are used to ensure the interfacial bonding performance and high-temperature stability between the optical fiber and the metal substrate; the laser scanning path is set to a checkerboard pattern. The depth of the first groove 100 and the second groove 200 is 0.3 mm.

[0062] After implanting metallized optical fibers with a dual FBG fiber grating structure into the substrate, in-situ temperature-strain sensing of the measured structure can be achieved. Light experiences intensity loss when passing through the bending structure of the elastic substrate 3 to reach the second FBG fiber grating, creating an intensity difference. In-situ strain measurement is performed using this intensity difference, and in-situ temperature measurement is performed using the wavelength shift of the FBG fiber grating. For example... Figure 1 and Figure 5 As shown, the light intensity variation of the first FBG fiber grating on the left is caused by the power fluctuation of the light source and the bending disturbance of the transmission fiber. The light intensity fluctuation of the second FBG fiber grating on the right is coupled with the light intensity variation of the first FBG fiber grating and the light intensity variation caused by the bending of the fiber between the two FBG fiber gratings. The light intensity difference between the two can effectively measure the strain.

[0063] According to Marcuse's principle, the initial fiber bending loss coefficient is expressed as: , It is a constant. p When it is 0 It is 2. p When not 0 =1; and These are the radially normalized phase constant and the radially normalized attenuation constant, respectively. V For normalized frequency, d The radius of the tapered optical fiber, Let be the axial propagation constant. and They are respectively v -1st order and v +1 order modified Bessel function.

[0064] On the other hand, the present invention provides an in-situ sensing method for an integrated flexible fiber optic sensing device, comprising the following steps:

[0065] S1: Configure the aforementioned integrated flexible fiber optic sensing device; the fiber grating at one end of the metallized fiber 2 is connected to the light source optical path; the metallized fiber 2 is obtained by setting FBG fiber gratings 5 ​​at both ends of the tapered fiber, and then further setting a metal coating on the resulting micro / nano fiber. The optimization of the substrate structure, the preparation of the metal coating, and the 3D printing to form the integrated flexible fiber optic sensing device are as described above.

[0066] S2: Construct a model for measuring light intensity loss and strain.

[0067] Step S2 involves setting the FBG fiber gratings 5 ​​at both ends of the metallized fiber 2 to FBG1 and FBG2, respectively. The reflected light intensities of the FBG fiber gratings 5 ​​in the initial state of the integrally formed metallized fiber 2 are respectively... The reflected light intensities of the FBG fiber grating 5 in its unbent state before being embedded with the two fixing mechanisms 4 and the elastic matrix 3 are respectively The bending loss of FBG fiber grating 5 when not subjected to external force is: ,in, r The initial bending radius for embedding the metallized optical fiber 2 into the first slot 100 and the second slot 200; The length of the metallized optical fiber 2 corresponding to the initial bending radius of the first arc segment 31 is the proportion of the circumference of the virtual circle corresponding to the initial bending radius. Given the initial fiber bending loss coefficient, the bent metallized fiber 2 at the first arc segment 31... x Elongation in the axial direction And the metallized optical fiber 2 at the connecting beam 33 x Elongation in the axial direction The following relationship is satisfied: x The axial direction is the length extension direction of the fixed mechanism 4. R 0 represents the bending radius of the first arc segment 31 of the metallized optical fiber 2 after being stretched under an external load. The angle between the two ends of the first arc segment 31 is... ;strain The relationship between the bending radius of the metallized optical fiber 2 and the following formula is: , L For elastic matrix 3 in x Total length in the axial direction, R The bending radius of the first circular arc segment 31 when it is not subjected to external load. , The angle between the longitudinal center planes of the connecting beam 33 and the two fixed mechanisms 4; strain With light intensity loss The mapping relationship is as follows: .

[0068] S3: By obtaining the light intensity difference between the fiber gratings at both ends of the metallized fiber 2, the temperature and strain are solved using a wavelength-intensity hybrid demodulation method with dual fiber gratings.

[0069] Step S3 states that when subjected to an external load, the optical intensity loss coefficient of the metallized fiber 2 is... The relationship between optical intensity loss and the bending radius of the first circular arc segment 31 of the current metallized optical fiber 2 is as follows: ,in These are the peak light intensities of the FBG fiber gratings 5 ​​at both ends of the metallized optical fiber 2 under external load. The current bending radius of the first circular arc segment 31 after being subjected to external load. RThe length of the metallized fiber 2 corresponding to 0 is the proportion of the circumference of the virtual circle corresponding to the initial bending radius; The bending loss coefficient of optical fiber under external load ;make , The change in center wavelength of FBG fiber grating 5 with temperature Proportional , These represent the center wavelength shifts of the FBG fiber gratings 5 ​​at both ends of the metallized fiber 2, respectively. These are the center wavelengths of the FBG fiber gratings 5 ​​at both ends of the metallized fiber 2. The coefficient of thermal expansion is... Thermo-optic coefficient, The temperature change is considered in relation to the wavelength shift and strain. With light intensity loss The mapping relationship is obtained. , and As a constant, the strain change is obtained by acquiring the center wavelength shift of FBG fiber grating 5. and temperature change Therefore, it is only necessary to first determine the constant. K T , K ε , and ∆ can then be determined based on the change in the center wavelength of the reflected light from the fiber grating. ε ∆ T This means that it can achieve combined measurement of structural temperature and strain under different environments.

[0070] The integrated flexible fiber optic sensing device in this embodiment operates in a temperature range of 20°C to 500°C. Within the 500°C operating temperature range, the temperature linearity is better than 0.9878, and the temperature and strain decoupling performance is good. By constructing light intensity-wavelength composite sensing data and processing it through a neural network algorithm, the maximum decoupling error is less than 8%.

[0071] The neural network algorithm mentioned here is used in practical applications where temperature and strain need to be measured simultaneously. However, due to the coupling effect between the two, decoupling is achieved through neural networks and other algorithms. In this embodiment, the sensor adopts a dual FBG fiber grating structure: the incident light is first reflected by the left FBG fiber grating FBG1 to form a light intensity signal. I 1. Subsequently, the light is transmitted to the right-hand FBG fiber grating FBG2 via a flexible bending structure defined by an elastic matrix. The bending deformation of the flexible structure causes optical loss, resulting in a decrease in the optical intensity signal of the right-hand FBG fiber grating FBG2. I2. Strain-dependent attenuation occurs, therefore the light intensity difference exhibits a nonlinear mapping relationship with strain. Simultaneously, the center wavelength shift Δ of any FBG fiber grating... λ While it can characterize temperature changes, the thermal expansion effect simultaneously causes wavelength shift and thermal strain, leading to cross-coupling interference. Therefore, it is necessary to establish a [mechanism / mechanism] based on Δ... I and Δ λ This is a decoupling algorithm that takes strain and temperature as inputs and outputs. The following section will describe this neural network decoupling algorithm in detail.

[0072] In modeling the algorithm structure, since temperature also causes thermal strain, but strain is mainly caused by external forces, the two output variables, strain and temperature, are both correlated and different. Therefore, neither independent nor coupled modeling strategies are ideal for algorithm structure modeling. This invention proposes a decoupling algorithm modeling strategy to improve decoupling accuracy. The structure is as follows: Figure 1 As shown, in this strategy, the established model includes a shared part and multiple decoupled parts, where the decoupled parts correspond to the output variables. The shared part and the decoupled parts in the model represent, to some extent, the correlation and differences between the output variables.

[0073] Depend on Figure 7 The decoupling strategy described in the embodiment constructs a decoupling model where the inputs are identical (light intensity difference and center wavelength shift) and the outputs are strain and temperature. Figure 8 and Figure 9 As shown, a decoupled network of a multilayer sensing multichannel extreme learning machine (MLM) is established. This model mainly consists of three channels of an MLM with the same multilayer sensing. Each channel outputs predicted strain and temperature, and the final strain and temperature are the weighted average of the outputs from these three channels. The multichannel architecture helps the model obtain more stable prediction results. For a specific channel of the MLM structure, there are two hidden layers. The first layer is a shared part with 100 neurons, and the second layer contains two decoupled parts, corresponding to strain and temperature respectively, with 50 and 35 neurons respectively. The ReLU activation function is used.

[0074] Temperature and strain were solved using a dual FBG wavelength-intensity hybrid demodulation method. By constructing a model for intensity loss and strain measurement, the strain measurement range was extended to 37.520 με, and the FBG wavelength could accurately map the ambient temperature.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An integrated flexible fiber optic sensing device, characterized in that, include: Two fixing mechanisms are arranged in parallel and spaced apart for fixing to the surface of the structure being measured. The end faces of the two fixing mechanisms are respectively provided with first grooves. An elastic substrate is disposed in the area between two fixed mechanisms and is arranged in a curved shape. A second groove is provided on the end face of the elastic substrate, and the second groove is also connected to the first groove on the two fixed mechanisms. Metallized optical fibers are sequentially embedded in the first and second slots. FBG fiber gratings are provided at both ends of the metallized optical fibers located in the first slot. The metallized optical fibers are integrally formed with the two fixing mechanisms and the elastic matrix. The process of integrally molding the metallized optical fiber with two fixing mechanisms and an elastic substrate includes the following steps: Using the fused taper method, a precision motor is used under a microscope to control the stretching speed and displacement of the heated optical fiber, and the diameter of the optical fiber is monitored. Fiber Bragg gratings are placed at both ends of the taper fiber, and the taper fiber and fiber Bragg gratings are fused together to obtain micro / nano fiber. The cladding is removed, and a metal coating is formed on the surface of the micro / nano fiber through chemical plating and metal plating processes to obtain metallized fiber. Design a 3D model of two fixed mechanisms and an elastic base using CAD software; Use the slicing tool to slice the 3D model and generate layer-by-layer 2D contour data; Plan the laser scanning path, set the laser power, scanning speed and powder layer thickness, select a suitable substrate, and clean and preheat the substrate; Metal powder is loaded into the powder supply device, and the powder is evenly spread on the substrate using a scraper to achieve the set powder layer thickness; inert gas is then introduced into the printing chamber. The laser scans and melts the powder layer based on the slice data. After each powder layer is melted, the substrate decreases by one thickness, and the powder-scanning process is repeated. When the powder layer of the first and second slots is printed, the chamber door is opened to sweep away the metal powder on the top layer, and the bent metallized optical fiber is placed into the first and second slots. The printing is then carried out layer by layer until the printing is completely finished, resulting in an integrated metallized optical fiber, two fixing mechanisms and an elastic substrate.

2. The integrated flexible fiber optic sensing device according to claim 1, characterized in that, The elastic matrix includes two first arc segments, two second arc segments, and a connecting beam. The connecting beam is located between the two fixed mechanisms and is set at an angle to the longitudinal center plane of the two fixed mechanisms. One end of each of the two first arc segments is fixedly connected to the adjacent side surface of the two fixed mechanisms, and the other end of each of the two first arc segments is fixedly connected to one end of each of the two second arc segments. The other end of each of the two second arc segments is fixedly connected to different ends of the connecting beam.

3. The integrated flexible fiber optic sensing device according to claim 2, characterized in that, The initial bending radii of the two first circular arc segments and the two second circular arc segments are the same, and the central angle of the first circular arc segment is 90°, the central angle of the second circular arc segment is 180°, and the length of the connecting beam is twice the initial bending radius of the first circular arc segment.

4. The integrated flexible fiber optic sensing device according to claim 2, characterized in that, The center wavelength deviation of the FBG fiber gratings at both ends of the metallized optical fiber is 2-5 nm.

5. The integrated flexible fiber optic sensing device according to claim 1, characterized in that, The depth of the first and second slots is 1.2-1.5 times the diameter of the metallized optical fiber, the width of the first and second slots is 1.1-1.3 times the diameter of the metallized optical fiber, and the cross-sectional shape of the first and second slots is elliptical.

6. The integrated flexible fiber optic sensing device according to claim 2, characterized in that, The elastic base and the two fixed mechanisms have the same height, and the width of the elastic base is greater than its height; the angle between the connecting beam and the longitudinal center plane of the two fixed mechanisms is 30°.

7. An in-situ sensing method for an integrated flexible fiber optic sensing device, characterized in that, Includes the following steps: S1: The integrated flexible fiber optic sensing device as described in any one of claims 3-6 is configured; the fiber grating at one end of the metallized fiber is connected to the light source optical path; the metallized fiber is obtained by setting FBG fiber gratings at both ends of the tapered fiber to obtain micro-nano fiber and then further setting a metal coating. S2: Construct a model for measuring light intensity loss and strain; S3: By obtaining the light intensity difference between the fiber gratings at both ends of the metallized optical fiber, the temperature and strain are solved using a wavelength-intensity hybrid demodulation method with dual fiber gratings.

8. The in-situ sensing method of the integrated flexible fiber optic sensing device according to claim 7, characterized in that, Step S2 involves obtaining the bending loss of the FBG fiber grating when it is not subjected to external force; and obtaining the bending loss of the metallized fiber at the first arc segment. x Elongation in the axial direction, metallized optical fiber at the connecting beam x Elongation in the axial direction x The axial direction is the length extension direction of the fixed mechanism, the bending radius of the first arc segment when not subjected to external load, and the bending radius of the first arc segment of the metallized optical fiber after being stretched by external load, to construct the mapping relationship between strain and light intensity loss.

9. The in-situ sensing method of the integrated flexible fiber optic sensing device according to claim 8, characterized in that, Step S3 involves constructing a mapping relationship between optical intensity loss and the bending radius of the first arc segment of the metallized optical fiber under external load; obtaining a relationship between the center wavelength of the FBG fiber grating and the temperature change; and solving for the strain change and temperature change by combining the mapping relationship between optical intensity loss and the bending radius of the first arc segment of the metallized optical fiber under external load, the relationship between temperature change and wavelength drift, and the mapping relationship between strain and optical intensity loss.

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