Fiber grating sensor device for marine steel bar corrosion monitoring and calibration test method

Abstract

The application discloses a kind of optical fiber grating sensor device and calibration test method for marine steel bar corrosion monitoring, by providing a kind of specially designed for marine environment, based on the non-contact magnetic strain principle optical fiber grating sensor device, the device is packaged with full silicon-based material, fundamentally solve long-term corrosion problem;With magnetic non-contact sensing corrosion, avoid the interference caused by direct contact;Through symmetric double-end design, improve reliability and signal quality;Compact structure, easy to install.The application also provides calibration test method matched with the sensor device, by simulating the accelerated electrochemical corrosion test of marine corrosion environment, accurately establish the quantitative mathematical model between sensor output signal and the actual mass loss of steel bar, so as to give the quantitative monitoring ability of sensor, and provide calibration basis for the consistency of different batches of sensors.

Description

Technical Field

[0001] This application relates to the fields of fiber optic sensing technology and measurement and monitoring technology, specifically to a fiber optic grating sensor device and calibration test method for monitoring corrosion of marine engineering steel bars. Background Technology

[0002] Reinforced concrete is the primary building material for modern marine engineering structures, such as cross-sea bridges, deep-water ports, offshore wind power foundations, and drilling platforms. However, the high humidity, high chloride ion content, and effects of wet-dry cycles and freeze-thaw cycles in the marine environment easily induce electrochemical corrosion of the internal reinforcing steel. Steel corrosion not only directly reduces its effective cross-sectional area and load-bearing capacity, but the internal stress generated by the volume expansion of corrosion products is also a major cause of cracking and spalling of the concrete cover, thus accelerating the deterioration of the overall structural performance and seriously threatening the safe service life and long-term durability of the structure. Therefore, real-time and accurate monitoring of the corrosion status of the internal reinforcing steel in marine concrete structures is a key technology for achieving preventative maintenance, assessing remaining service life, and ensuring the safe and economical operation of major projects.

[0003] Existing steel reinforcement corrosion monitoring technologies can be mainly divided into two categories: destructive testing and non-destructive testing. Non-destructive testing is favored because it does not affect the normal use of the structure, and its mainstream methods include:

[0004] Electrochemical monitoring methods, such as half-cell potential method, linear polarization resistance method, and electrochemical impedance spectroscopy, infer corrosion tendency or rate by measuring electrochemical parameters at the steel / concrete interface. Representative products include the CorroWatch system from the Danish company FORCE. Their advantage lies in their relatively mature technology, but they have significant disadvantages: the measurement results are greatly affected by concrete resistivity, moisture content, and temperature; they have poor long-term stability; and they typically only provide qualitative or semi-qualitative corrosion risk assessments, making it difficult to accurately quantify the actual mass loss or remaining cross-sectional area of ​​the steel reinforcement.

[0005] Physical monitoring methods: These methods indirectly assess corrosion by monitoring changes in physical quantities caused by the corrosion, such as ultrasonic thickness measurement, electromagnetic eddy currents, and microwave radar. For example, the electromagnetic guided wave radar sensor from Corrosion RADAR in the UK. These methods are relatively less affected by environmental interference, but they generally suffer from problems such as complex equipment, large size, high cost, difficulty in distributed and integrated deployment within structures, and limited sensitivity to early, minor corrosion.

[0006] In recent years, fiber optic sensing technology, especially fiber Bragg grating (FBG) sensors, has seen rapid development in the field of structural health monitoring due to its unique advantages such as resistance to electromagnetic interference, corrosion resistance, small size, light weight, ease of quasi-distributed measurement, and good long-term stability. Some studies have attempted to apply FBG sensors to monitor rebar corrosion. However, based on existing technologies, fiber grating rebar corrosion sensors applied in marine environments still face the following key challenges and limitations:

[0007] 1. Long-term durability challenges: The marine engineering environment is extremely harsh, and the materials of the sensor body must be able to withstand high chloride ion, high humidity, and acid, alkali, and salt spray corrosion for extended periods. Metal components are prone to corrosion, and organic polymer materials are prone to aging, severely affecting the sensor's lifespan. Existing solutions do not adequately address the long-term corrosion resistance of the sensor body, especially the packaging materials.

[0008] 2. Measurement interference and stability issues: Many sensors transmit strain through physical contact with steel bars. Installation stress, concrete shrinkage and creep, and changes in contact state caused by the accumulation of corrosion products can all introduce uncontrollable interference signals, affecting the stability and accuracy of long-term monitoring.

[0009] 3. Lack of quantitative monitoring capabilities: Most existing FBG corrosion sensors are limited to monitoring "presence" or "relative changes," lacking a systematic and reliable calibration method to establish an accurate and traceable quantitative relationship between the wavelength drift signal of the FBG and the actual physical parameters of the reinforcing steel (such as mass loss and diameter reduction). Without quantitative calibration, true quantitative monitoring and residual bearing capacity assessment cannot be achieved.

[0010] 4. Temperature Cross-Sensitivity: FBG is sensitive to both temperature and strain. Marine structures experience significant diurnal and seasonal temperature variations, and the wavelength drift caused by temperature fluctuations can be far greater than that caused by early corrosion. Achieving stable and reliable temperature compensation in long-term marine engineering monitoring is a crucial engineering challenge that must be addressed.

[0011] 5. Engineering applicability issues: Some sensors have complex structures and large volumes, making them inconvenient to pre-embed or implant before concrete pouring, which limits their large-scale application in engineering projects.

[0012] Therefore, there is an urgent need to develop a new type of fiber optic grating rebar corrosion sensor device and its supporting standardized calibration test method that combines excellent long-term durability, high stability, quantitative monitoring capability, and ease of engineering application. Summary of the Invention

[0013] The main objective of this application is to provide a fiber optic grating sensor device for monitoring corrosion of marine engineering steel reinforcement, comprising:

[0014] The outer shell (1) is a cylindrical quartz structure with a through rectangular hole (1-1) at the center to allow the reinforcing bar to pass through. The inner sides of both ends of the outer shell (1) are machined with a first thread set (1-2).

[0015] Two measurement modules are symmetrically distributed at both ends of the outer casing (1). Each measurement module includes:

[0016] The first base (2) is a stepped shaft structure. The outer side of the first step is machined with a second thread group (2-1), which is fixed to the first thread group (1-2) of the outer shell (1) by thread engagement. The upper side of the second step is machined with a first square hole (2-2). The upper and lower ends of the second step are machined with first U-shaped grooves (2-3). The interior is machined with stepped holes. The other end face of the base is machined with a third thread group (2-4). A first semi-circular boss (2-5) is left in the middle of the threaded hole.

[0017] The magnetic sensing component includes a magnet (5), a magnet shell (6), a first connecting post (9), a high-elastic diaphragm (8), and a first strain measurement fiber grating (10). The magnet (5) is placed in a cylindrical groove (6-1) of the magnet shell (6). The magnet shell (6) is fixed by a fifth threaded group (6-2) and a sixth threaded group (9-1) of the first connecting post (9). The other side boss of the first connecting post (9) is fixed to the center of the high-elastic diaphragm (8). The center of the high-elastic diaphragm (8) is integrated into the first strain measurement fiber grating (10).

[0018] The temperature compensation component includes a support (12) and a first temperature-measuring fiber optic grating (11), wherein the first temperature-measuring fiber optic grating (11) is placed in the middle of the second U-shaped groove (12-1) of the support (12);

[0019] The first cover plate (7) is a cylindrical boss structure, which is fixed to the first base (2) by glass powder. A second through hole (7-1) is processed in the middle, which is in clearance fit with the side wall of the first connecting column (9). The support (12) and the high elastic diaphragm (8) are assembled in the first base (2), and the contact area is fixed with molten silicon powder.

[0020] The base connector (3) is a boss structure. A fourth thread group (3-1) is machined on the outside of the boss for fixing with the third thread group (2-4) of the first base (2). A first through hole (3-2) is machined in the center.

[0021] Waterproof connector (4), the waterproof connector (4) is a cylindrical boss structure, the outer side of the boss is machined with a fourth thread group (4-1) for fixing with the base connector (3), and the center is machined with a through hole for connecting the armored optical cable lead-out optical fiber;

[0022] The magnet (5) is made of neodymium iron boron material, the first strain measurement fiber grating (10) and the first temperature measurement fiber grating (11) are both single-mode optical fibers, the high-elasticity diaphragm (8) is made of aluminosilicate glass material, and the remaining components are made of silicon-based inorganic non-metallic materials.

[0023] In one embodiment, in the magnetic sensing component, the first strain measurement fiber grating (10) is encapsulated inside the high-elasticity diaphragm (8) by placing the fiber grating in the molding mold of the high-elasticity diaphragm (8) and integrally casting it with the molten aluminosilicate glass material constituting the high-elasticity diaphragm (8).

[0024] In one embodiment, the support (12) is fixed inside the first base (2), and a U-shaped groove (12-1) is provided thereon. The first temperature measuring fiber optic grating (11) is loosely disposed in the U-shaped groove (12-1) and is fixed to the support (12) only at both ends of the fiber optic grating by molten silica adhesive.

[0025] In one embodiment, the first base (2) is fixed to the inner side of the outer shell (1) by threaded connection, and the end of the first base (2) is also connected in sequence to a base connector (3) for leading out optical fibers and a waterproof connector (4).

[0026] In one embodiment, the steps for preparing the high-elasticity diaphragm (8) include:

[0027] (a) Place a fiber optic grating at the center of the high-elasticity diaphragm mold;

[0028] (b) Pour the high-elasticity glass material into the mold;

[0029] (c) Place the mold in a heating furnace and heat it to the preset temperature at a preset heating rate;

[0030] (d) After the device is cooled and the mold is opened, high-elasticity tempering treatment is immediately carried out. After heat preservation, it is taken out and air-cooled to obtain a high-elasticity thin silicon wafer (8) containing the fiber grating.

[0031] In one embodiment, the step of fixing the first connecting post (9) to the high-elastic diaphragm (8) includes:

[0032] (a) Mix silica glass powder and pure water in a preset mass ratio to form a molten state and then apply a thin layer to the center point of the high-elastic film (8);

[0033] (b) Press the boss of the first connecting post (9) perpendicularly into contact with the center of the high-elastic diaphragm (8) and apply a preset pressure;

[0034] (c) Place the parts on a heating table and heat them to 400°C. Hold them at the temperature for a preset time. Once the silica powder has cooled, the parts will adhere firmly.

[0035] A calibration and testing method for a fiber optic grating sensor device for monitoring corrosion of marine engineering steel bars, the method comprising the following steps:

[0036] (a) Place the acrylic bracket (21) at the bottom of the rust basin (19) and fix it with UV glue. Fix the fiber optic grating sensor device and the two ends of the steel bar (14) to the upper groove of the acrylic bracket (21).

[0037] (b) Connect the positive and negative terminals of the power supply (15) to the steel bar (14) and the stainless steel plate (18) respectively through wires;

[0038] (c) Turn on the power switch (15) to make the wire (17), steel bar (14), 3.5% NaCl solution (20), stainless steel plate (18) and power supply (15) form a closed circuit, and the steel bar (14) begins to corrode faster.

[0039] (d) A fiber optic demodulator (16) is used to connect the fiber optic sensor device (13) to monitor the center wavelength changes of the first strain measurement fiber optic grating (10) and the first temperature measurement fiber optic grating (11);

[0040] (e) Apply a constant current of 2A to the steel bar (14) using a power supply (15) and keep the test environment temperature at 25±2℃;

[0041] (f) After 8 days of rusting of the steel bar (14), the fiber optic grating demodulator (16) recorded data at a frequency of 5 Hz.

[0042] (g) Take out the steel bar (14) every 24 hours to remove rust and weigh it, and record the mass loss of the steel bar (14). To remove rust, soak it in 10% hydrochloric acid solution for 10 minutes, then remove the surface rust with a wire brush, rinse with clean water, dry and weigh it.

[0043] (h) By recording the center wavelength signal of the fiber optic grating sensor device (13) and the mass loss data of the steel bar (14), establish the sensitivity relationship of the corrosion change of the steel bar (14) and complete the calibration test.

[0044] In one embodiment, the bottom of the acrylic bracket (21) is coated with UV waterproof adhesive and is strongly fixed to the bottom of the rust basin (19); the axis of the steel bar (14) coincides with the center line of the through rectangular hole; a fixing groove is provided on the acrylic bracket (21), and the initial distance between the surface of the steel bar (14) and the magnet (5) in the fiber optic grating sensor device (13) is set to 5mm.

[0045] In one embodiment, the calibration test method is performed in a constant temperature environment, and the sensitivity relationship of the corrosion change of the steel bar (14) is a linear model. The corresponding relationship between the wavelength change of the fiber optic grating and the strain can be expressed as:

[0046]

[0047] in This is the net corrosion strain wavelength shift of the fiber grating. The strain sensitivity coefficient of the fiber optic grating is given by the first strain measurement fiber optic grating (10), where the axial strain is... , For the effective photoelastic coefficient, This indicates a temperature change. When the fiber grating is bent, the change in its curvature directly affects the amount of wavelength shift.

[0048] Therefore, this application has the following beneficial effects:

[0049] This application provides a fiber optic grating sensor device for monitoring corrosion of marine steel bars. The fiber optic grating sensor device includes: a housing (1), which is a cylindrical quartz structure with a through rectangular hole (1-1) at the center to allow steel bars to pass through it; and a first thread group (1-2) is processed on the inner sides of both ends of the housing (1).

[0050] Two measuring modules are symmetrically distributed at both ends of the outer shell (1). Each measuring module includes: a first base (2), which is a stepped shaft structure. A second thread group (2-1) is machined on the outer side of the first step, and is fixed to the first thread group (1-2) of the outer shell (1) by thread engagement; a first square hole (2-2) is machined on the upper side of the second step; a first U-shaped groove (2-3) is machined on the upper and lower ends of the second step; a stepped hole is machined inside; a third thread group (2-4) is machined on the other end face of the base; a first semi-circular boss (2-5) is left in the middle of the thread hole; and a magnetic induction component, including a magnet. (5) A magnet shell (6), a first connecting post (9), a high-elastic diaphragm (8), and a first strain measurement fiber grating (10). The magnet (5) is placed in the cylindrical groove (6-1) of the magnet shell (6). The magnet shell (6) is fixed to the sixth thread (9-1) of the first connecting post (9) by the fifth thread (6-2). The other side boss of the first connecting post (9) is fixed to the center of the high-elastic diaphragm (8). The center of the high-elastic diaphragm (8) is integrated into the first strain measurement fiber grating (10). A temperature compensation component includes a support (12) and a first temperature measuring fiber grating (11). A warm fiber optic grating (11) is placed in the middle of the second U-shaped groove (12-1) of the support (12); a first cover plate (7), the first cover plate (7) is a cylindrical boss structure, fixed to the first base (2) by glass powder, and a second through hole (7-1) is processed in the middle, which is clearance-fitted with the side wall of the first connecting column (9); wherein, the support (12) and the high-elastic diaphragm (8) are assembled in the first base (2), and the contact area is fixed by molten silicon powder; a base connector (3), the base connector (3) is a boss structure, and a fourth thread group (3-1) is processed on the outside of the boss, which is used to connect with the first base (12) 2) The third thread group (2-4) is fixed, and the center is machined with a first through hole (3-2); waterproof connector (4), the waterproof connector (4) is a cylindrical boss structure, the outer side of the boss is machined with a fifth thread group (6-1), which is used to fix with the base connector (3), and the center is machined with a through hole, which is used to connect the armored optical cable lead-out optical fiber; wherein, the magnet (5) is made of neodymium iron boron material, the first strain measurement fiber grating (10) and the first temperature measurement fiber grating (11) are both single-mode optical fibers, the high elastic diaphragm (8) is made of silicon aluminum glass material, and the remaining parts are all made of silicon-based inorganic non-metallic materials.

[0051] The present application discloses a fiber Bragg grating sensor device and a calibration test method for monitoring the corrosion of steel bars in marine engineering. By providing a fiber Bragg grating sensor device designed specifically for the marine environment and based on the principle of non-contact magnetostrictive strain, the device is encapsulated with all-silicon-based materials, fundamentally solving the problem of long-term corrosion resistance; using magnetic force to sense corrosion non-contact, avoiding interference caused by direct contact; improving reliability and signal quality through a symmetric double-end design; and having a compact structure, facilitating installation. Another important object of the present application is to provide a set of calibration test methods supporting the sensor device. Through an accelerated electrochemical corrosion test simulating the marine corrosion environment, a quantitative mathematical model between the sensor output signal and the actual mass loss of the steel bar is accurately established, thereby endowing the sensor with the ability of quantitative monitoring and providing a calibration basis for the consistency of different batches of sensors. BRIEF DESCRIPTION OF THE DRAWINGS 16>

[0052] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 is a schematic diagram and a cross-sectional view of a fiber Bragg grating corrosion monitoring device based on magnetic force sensing provided by the present application;

[0054] Figure 2 is a schematic diagram of the outer shell of the fiber Bragg grating sensor of the present application;

[0055] Figure 3 is a schematic diagram of the structure of the first base of the present application;

[0056] Figure 4 is a schematic diagram of the structure of the base joint of the present application;

[0057] Figure 5 is a schematic diagram and a cross-sectional view of the waterproof joint of the present application;

[0058] Figure 6 is a schematic diagram of the structure of the magnet shell of the present application;

[0059] Figure 7 is a schematic diagram of the structure of the first cover plate of the present application;

[0060] Figure 8 is a schematic diagram of the structure of the first connecting column of the present application;

[0061] Figure 9 is a schematic diagram of the structure of the support of the present application;

[0062] Figure 10This is a diagram of a calibration and testing device for a fiber optic grating corrosion monitoring device.

[0063] Figure 11 This is a graph of sensor experimental data obtained in this application (sensor 1-1).

[0064] Figure 12 This is a graph of the sensor experimental data obtained in this application (sensor 1-2).

[0065] Identification: 1. Outer shell, 2. First base, 3. Base connector, 4. Waterproof connector, 5. Magnet, 6. Magnet shell, 7. First cover plate, 8. High-elastic diaphragm, 9. First connecting column, 10. First strain measurement fiber optic grating, 11. First temperature measurement fiber optic grating, 12. Support, 13. Diaphragm type fiber optic grating corrosion sensor (fiber optic grating sensor device of this application), 14. Reinforcing bar, 15. Power supply, 16. Fiber optic grating demodulator, 17. Wire, 18. Stainless steel plate, 19. Corrosion basin, 20. NaCl solution, 21. Acrylic bracket;

[0066] 1-1 Through rectangular hole; 1-2 First thread set;

[0067] 2-1 Second thread group, 2-2 First square hole, 2-3 First U-shaped groove, 2-4 Third thread group, 2-5 First semi-circular boss;

[0068] 3-1 Third thread group, 3-2 First through hole;

[0069] 4-1 Fourth thread group;

[0070] 6-1 Cylindrical groove, 6-2 Fifth thread set

[0071] 7-1 Second through hole;

[0072] 9-1 Sixth thread group;

[0073] 12-1 Second U-shaped groove. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0075] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0076] To address the shortcomings of existing sensors in harsh marine engineering environments, such as insufficient long-term durability, susceptibility to interference from installation stress and interface changes, difficulty in quantitative monitoring of rebar corrosion, poor temperature compensation, and limited engineering applicability, this application provides an innovative fiber optic grating sensor device for monitoring rebar corrosion in marine engineering. This device aims to achieve long-term, stable, and high-precision quantitative monitoring of rebar corrosion. Its core design concept lies in all-silicon-based non-contact magnetic sensing, and through material innovation and structural innovation, it systematically solves the aforementioned technical bottlenecks.

[0077] The core improvements of this device are primarily reflected in the revolutionary choice of materials and integrated packaging technology. All main structural components, including the outer shell, base, connecting columns, and diaphragm supports, are manufactured using highly chemically stable silicon-based inorganic non-metallic materials such as quartz glass and aluminosilicate glass. These components are bonded together using high-temperature molten glass powder, forming a fully sealed, fully inert, and robust whole. This design fundamentally eliminates the risks of electrochemical corrosion of metal components and aging and degradation of organic polymer materials, giving the sensor an ultra-long service life comparable to marine concrete structures and completely solving the long-term durability problem.

[0078] Secondly, this device employs a non-contact magnetic sensing mechanism. The sensor couples with the reinforcing steel bar being measured via a built-in permanent magnet, converting the minute diameter changes caused by steel bar corrosion (leading to changes in the magnetic air gap) into changes in magnetic force. This magnetic force is transmitted through a rigid connecting column to a specially designed high-elasticity diaphragm, causing its deformation. Crucially, the first strain measurement fiber grating of the sensing element is integrally encapsulated within the center of the high-elasticity diaphragm using a pre-embedded casting process, achieving efficient and hysteresis-free strain transmission from the diaphragm substrate to the fiber grating. This non-contact method completely avoids signal drift and failure caused by installation stress, concrete shrinkage, or the accumulation of corrosion products in traditional adhesive or wrapped contact sensors, significantly improving the stability and accuracy of long-term monitoring.

[0079] To overcome the challenge of temperature cross-sensitivity, this device integrates an independent temperature compensation unit within each measurement module. This unit contains a temperature-sensing fiber optic grating encapsulated on a dedicated support. This encapsulation method makes it extremely insensitive to mechanical strain, responding precisely only to changes in ambient temperature. This provides a pure temperature reference signal for real-time compensation of the temperature's influence on strain measurement signals, ensuring the reliability of monitoring data under complex ambient temperature fields.

[0080] Furthermore, the device features a compact cylindrical structure with a through hole in the center of the outer shell, allowing it to be conveniently fitted onto the reinforcing steel bars and cast together, much like a "sleeve." This simplifies installation and minimizes interference with construction. Combined with the standardized electrochemical accelerated corrosion calibration test method provided in this application, a precise quantitative relationship model between sensor optical wavelength drift and actual steel bar mass loss can be pre-established. This represents a leap from qualitative early warning to quantitative assessment, providing direct and reliable quantitative data support for the safety status assessment and life prediction of engineering structures.

[0081] This application provides a fiber optic grating sensor device for monitoring corrosion of marine engineering steel bars, referring to... Figure 1 , Figure 1 This application provides a schematic diagram and cross-sectional view of a fiber optic grating corrosion monitoring device based on magnetic sensing. The fiber optic grating sensor device includes:

[0082] The outer shell (1) is a cylindrical quartz structure with a through rectangular hole (1-1) at the center to allow the reinforcing bar to pass through. The inner sides of both ends of the outer shell (1) are machined with a first thread set (1-2).

[0083] Two measurement modules are symmetrically distributed at both ends of the outer casing (1). Each measurement module includes:

[0084] The first base (2) is a stepped shaft structure. The outer side of the first step is machined with a second thread group (2-1), which is fixed to the first thread group (1-2) of the outer shell (1) by thread engagement. The upper side of the second step is machined with a first square hole (2-2). The upper and lower ends of the second step are machined with first U-shaped grooves (2-3). The interior is machined with stepped holes. The other end face of the base is machined with a third thread group (2-4). A first semi-circular boss (2-5) is left in the middle of the threaded hole.

[0085] The magnetic sensing component includes a magnet (5), a magnet shell (6), a first connecting post (9), a high-elastic diaphragm (8), and a first strain measurement fiber grating (10). The magnet (5) is placed in a cylindrical groove (6-1) of the magnet shell (6). The magnet shell (6) is fixed by a fifth threaded group (6-2) and a sixth threaded group (9-1) of the first connecting post (9). The other side boss of the first connecting post (9) is fixed to the center of the high-elastic diaphragm (8). The center of the high-elastic diaphragm (8) is integrated into the first strain measurement fiber grating (10).

[0086] The temperature compensation component includes a support (12) and a first temperature-measuring fiber optic grating (11), wherein the first temperature-measuring fiber optic grating (11) is placed in the middle of the second U-shaped groove (12-1) of the support (12);

[0087] The first cover plate (7) is a cylindrical boss structure, which is fixed to the first base (2) by glass powder. A second through hole (7-1) is processed in the middle, which is in clearance fit with the side wall of the first connecting column (9). The support (12) and the high elastic diaphragm (8) are assembled in the first base (2), and the contact area is fixed with molten silicon powder.

[0088] The base connector (3) is a boss structure. A fourth thread group (3-1) is machined on the outside of the boss for fixing with the third thread group (2-4) of the first base (2). A first through hole (3-2) is machined in the center.

[0089] Waterproof connector (4), the waterproof connector (4) is a cylindrical boss structure, the outer side of the boss is machined with a fourth thread group (4-1) for fixing with the base connector (3), and the center is machined with a through hole for connecting the armored optical cable lead-out optical fiber;

[0090] The magnet (5) is made of neodymium iron boron material, the first strain measurement fiber grating (10) and the first temperature measurement fiber grating (11) are both single-mode optical fibers, the high-elasticity diaphragm (8) is made of aluminosilicate glass material, and the remaining components are made of silicon-based inorganic non-metallic materials.

[0091] Specifically, in this embodiment, a fiber optic grating sensor device for monitoring steel reinforcement corrosion in marine engineering is provided. The device is cylindrical in shape, compact in structure, and easy to embed in concrete structures. Its core design concept is to sense minute diameter changes caused by steel reinforcement corrosion through non-contact magnetic force changes, and to convert the mechanical signal into a high-precision optical signal for measurement using a fiber optic grating encapsulated within a silicon-based elastic element. Simultaneously, an independent temperature compensation unit is integrated to eliminate environmental temperature interference. The fiber optic grating sensor device mainly consists of a cylindrical outer shell (1) and two identical measurement modules symmetrically installed at both ends inside it.

[0092] The outer casing (1), serving as the protective and mounting body of the device, is made of high-purity quartz glass through precision machining. As shown in the figure, Figure 2 This is a schematic diagram of the fiber optic grating sensor housing of this application. A rectangular through hole (1-1) is machined through the center of the housing (1) along its axial direction. The size of the through hole is designed to be slightly larger than the diameter of the steel bar to be monitored, so that the steel bar can pass through smoothly and ensure that a preset non-contact gap is maintained between the steel bar and the sensitive element inside the sensor. Precision internal threads are machined on the inner sidewalls at both ends of the housing (1), forming the first thread group (1-2), which is used for fixed connection with the measurement module.

[0093] Each measurement module is the core functional unit of the sensor, and its specific composition is as follows:

[0094] First base (2): As the main support and mounting reference of the module, it is made of quartz glass and processed into a stepped shaft structure, as shown in the figure. Figure 3 This is a schematic diagram of the structure of the first base of this application. The outer cylindrical surface of its first step (larger diameter end) is machined with an external thread, namely the second thread set (2-1), which is used to engage with the first thread set (1-2) of the outer shell (1), thereby fixing the entire module inside the outer shell. A first square hole (2-2) is milled out on the upper side of the second step, and a first U-shaped groove (2-3) is milled out at each of the symmetrical upper and lower ends. These holes and grooves serve as the routing channels for optical fibers. The interior of the first base (2) is machined with precision stepped holes for accommodating and positioning other components. At the center of its other end face, a third thread set (2-4) (internal thread) is machined for connecting subsequent lead-out interfaces; at the entrance of the third thread set (2-4), a raised first semi-circular boss (2-5) is provided to separate and protect the two optical fibers passing through it, preventing mutual interference or excessive bending.

[0095] Magnetic induction component: This component is responsible for converting the magnetic force changes caused by steel corrosion into mechanical strain of the elastic element, specifically including:

[0096] Magnet (5): High-performance neodymium iron boron permanent magnets are used, which are cylindrical in shape and provide a stable magnetic field source.

[0097] Magnet shell (6): Made of quartz glass, it has a cylindrical structure, as shown in the figure. Figure 6 This is a schematic diagram of the structure of the magnet shell of this application; a cylindrical groove (6-1) is machined on one end face to precisely accommodate and fix the magnet (5). It is usually fixed by a gap fit with a small amount of high temperature resistant adhesive to protect the magnet and ensure its long-term stability. The other end face of the magnet shell (6) is machined with a fifth thread group (6-2) (external thread).

[0098] First connecting post (9): A cylinder made of quartz glass, serving as a force transmission rod. One end of it is machined with a sixth thread group (9-1) (internal thread), used to screw and fix it to the fifth thread group (6-2) of the magnet shell (6); the other end of it is machined with a small boss.

[0099] High-elasticity diaphragm (8): This is the key elastic sensing element of this application, made of aluminosilicate glass. After appropriate heat treatment, this material has good elasticity, high strength and excellent corrosion resistance. The high-elasticity diaphragm (8) has a circular thin sheet structure.

[0100] The first strain measurement fiber Bragg grating (10): As the core sensing element, it is a single-mode fiber Bragg grating. Its unique feature is that the encapsulation method is not simply pasted on the surface of the diaphragm, but rather encapsulated inside its geometric center area during the manufacturing process of the high-elastic diaphragm (8) through a "pre-embedded casting integrated molding" process. The specific preparation method is as follows: First, the bare fiber Bragg grating with the coating stripped is precisely fixed to the center position of the molding mold of the high-elastic diaphragm; then, molten aluminosilicate glass is poured into the mold; after it cools and solidifies and undergoes annealing and chemical tempering treatment, it is demolded to obtain the high-elastic diaphragm (8) with the fiber Bragg grating perfectly encapsulated in the center area. This encapsulation method ensures efficient and lossless strain transfer from the diaphragm to the fiber Bragg grating, and the interface remains stable and reliable for a long time.

[0101] The small protrusion at the end of the first connecting post (9) is bonded and fixed to the back of the central area (i.e., the area encapsulated with FBG) of the high-elastic diaphragm (8) by high-temperature molten silica glass powder. In specific operation, the prepared glass powder slurry is thinly coated on the center of the diaphragm, then the connecting post protrusion is vertically aligned and lightly pressed into contact, and finally placed on a heating table and heated to about 400°C to melt and sinter the glass powder. After cooling, a strong chemical bond is formed. Figure 8 This is a schematic diagram of the structure of the first connecting post of this application. The magnet shell (6) and the first connecting post (9) are connected by threads, thereby mechanically coupling the magnet (5) to the center of the high-elastic diaphragm (8).

[0102] Temperature compensation component: used for real-time monitoring of ambient temperature to compensate for the effect of temperature changes on the signal of the first strain measurement fiber optic grating (10), specifically including:

[0103] Support (12): Made of quartz glass, it has a round boss structure. An annular boss is provided on its end face to support the edge of the high-elasticity diaphragm (8). A second U-shaped groove (12-1) is machined along the axial direction of the support (12), as shown in the figure. Figure 9 This is a structural schematic diagram of the support in this application.

[0104] The first temperature-sensing fiber grating (11) is also a single-mode FBG. Its encapsulation method is designed to isolate mechanical strain and is only sensitive to temperature. Specifically, the fiber grating is placed in the middle of the second U-shaped groove (12-1) of the support (12) while in a relaxed state (leaving a small excess length to avoid tension). Then, molten silica glass powder is coated only at both ends of the fiber grating (away from the grating area), and after heating and curing, a "two-point" fixation is achieved. In this way, the grating area is suspended in the groove and is almost unaffected by the mechanical deformation of the support, thus accurately reflecting changes in ambient temperature.

[0105] First cover plate (7): A cylindrical boss structure made of quartz glass, as shown in the figure. Figure 7This is a schematic diagram of the structure of the first cover plate of this application. A second through hole (7-1) is machined in the center of the cover plate. The through hole is clearance-fitted with the rod body of the first connecting post (9), allowing the connecting post to move freely in the axial direction to transmit magnetic force, while restricting its radial sway and ensuring the linearity of the movement. The first cover plate (7) is fixed to the first base (2) by coating its contact ring with high-temperature glass powder and heating and curing it.

[0106] Base connector (3): Usually a metal or high-strength ceramic boss structure, as shown in the figure. Figure 4 This is a schematic diagram of the base connector of this application; a fourth thread group (3-1) (external thread) is machined on its outer side, which is used to screw and fix with the third thread group (2-4) of the first base (2). A first through hole (3-2) is machined in the center of the base connector (3) for two optical fiber pigtails to pass through.

[0107] Waterproof connector (4): A standardized cylindrical boss structure waterproof seal with a fifth thread group (4-1) machined on its outer side. As shown in the figure. Figure 5 This is a schematic diagram and cross-sectional view of the waterproof connector of this application. The waterproof connector (4) is screwed onto the base connector (3), and its interior is usually equipped with an elastic sealing ring (such as a rubber or silicone O-ring), which presses the optical fiber and interface together when tightened to achieve a reliable waterproof and dustproof seal. The optical fiber can finally be led out through the through hole in the center of the waterproof connector (4) and connected to the armored optical cable.

[0108] The internal assembly process of the sensor device in this embodiment is as follows:

[0109] First, the support (12) is placed into the stepped hole inside the first base (2), and molten silica glass powder is applied to the contact surface and then heated and cured to achieve fixation. Then, the high-elastic diaphragm (8) with integrated magnetic sensing components is placed on the support (12), with its edge resting on the annular support protrusion on the end face of the support (12). Next, the first cover plate (7) is covered, and its second through hole (7-1) is fitted into the first connecting post (9). The contact surfaces between the first cover plate (7) and the first base (2) and the contact areas between the edge of the high-elastic diaphragm (8) and the support (12) are all bonded and fixed at high temperature using molten silica glass powder. At this point, the edge of the high-elastic diaphragm (8) is firmly clamped and fixed, and the central area becomes a sensitive area that can be freely bent with changes in magnetic force. Finally, the pigtails of the first strain measurement fiber grating (10) and the first temperature measurement fiber grating (11) are carefully passed through the first square hole (2-2), the first U-shaped groove (2-3), and around the first semi-circular boss (2-5) to the outside of the end face of the first base (2).

[0110] Two fully assembled measurement modules, as described above, are screwed into the outer shell (1) from both ends. The second thread group (2-1) of the first base (2) is symmetrically fastened to the inside of the outer shell by the thread engagement between the second thread group (2-1) and the first thread group (1-2) of the outer shell (1), thus forming the complete sensor device of this application.

[0111] The working principle of the sensor device in this application is as follows: the reinforcing bar to be monitored is passed through the rectangular through hole (1-1) of the sensor housing (1), the sensor position is adjusted so that the reinforcing bar is located in the center of the hole, and a preset fixed air gap (e.g., 5 mm) is maintained between it and the internal magnet (5). Then, the sensor is cast into the concrete along with the reinforcing bar. A magnetic attraction is generated between the magnet (5) and the ferromagnetic reinforcing bar. This force acts on the center of the high-elastic diaphragm (8) through the first connecting column (9), causing it to produce initial bending strain, which in turn causes the center wavelength of the first strain measurement fiber optic grating (10) encapsulated therein to drift accordingly. When the reinforcing bar rusts, its diameter decreases by micrometers due to rust damage, causing the air gap between the magnet (5) and the reinforcing bar to increase slightly, and the magnetic force decreases accordingly. This change causes the strain of the high-elastic diaphragm (8) to decrease, thereby causing the wavelength of the first strain measurement fiber optic grating (10) to drift in the opposite direction. By monitoring the amount of this wavelength drift using a high-precision fiber optic grating demodulator, the state of the reinforcing bar corrosion can be inferred. At the same time, the first temperature-measuring fiber optic grating (11) monitors the ambient temperature in real time. Its wavelength change signal is used to accurately subtract the temperature effect from the total wavelength change of the first strain-measuring fiber optic grating (10) to obtain the strain signal caused purely by corrosion, thus achieving accurate temperature compensation.

[0112] In the sensor device of this embodiment, all major structural components in contact with the corrosive environment (outer shell 1, first base 2, magnet shell 6, first connecting column 9, support 12, first cover plate 7, and high-elastic diaphragm 8) are made of silicon-based inorganic non-metallic materials such as quartz glass or aluminosilicate glass, and are connected by high-temperature molten glass powder to form a fully sealed, fully inert, and robust whole. This structure fundamentally eliminates the risks of electrochemical corrosion of metal components and aging of organic materials, giving the sensor an ultra-long service life and extremely high measurement stability in harsh marine environments. The non-contact magnetic sensing method avoids interference from installation stress and interface changes caused by direct contact with reinforcing steel, improving the accuracy and reliability of measurements.

[0113] In one embodiment, in the magnetic sensing component, the first strain measurement fiber grating (10) is encapsulated inside the high-elasticity diaphragm (8) by placing the fiber grating in the molding mold of the high-elasticity diaphragm (8) and integrally casting it with the molten aluminosilicate glass material constituting the high-elasticity diaphragm (8).

[0114] Specifically, in this embodiment, the core of the magnetic sensing component, namely the integration of the first strain measurement fiber grating (10) and the high-elastic diaphragm (8), is achieved through an advanced micro-nano glass forming process. The core of this process lies in directly embedding the fiber optic sensing element into the body of the high-performance aluminosilicate glass elastomer, realizing true integration of mechanical and optical functional units at the material level, rather than simple surface bonding or mechanical fixation.

[0115] First, mold preparation and fiber positioning are performed. High-purity graphite or high-temperature resistant ceramic materials are selected to precisely machine a molding mold that matches the shape and size of the final high-elastic diaphragm (8), such as a mold with a circular cavity (e.g., diameter Φ20mm, depth 0.8mm). Before the mold is put into use, it needs to be preheated to reduce thermal stress. The next step is the extremely critical fiber positioning step: a single-mode fiber Bragg grating (10) (usually operating near the 1550nm band) with the polymer coating removed and temporary protective connectors at both ends is carefully placed in the mold cavity. Special micro-optical adjustment frame or precision clamps are required to accurately, horizontally, and without tension suspend and fix the grating area of ​​the fiber grating (usually about 10-15mm long) in the geometric center plane of the cavity. The accuracy of this step directly determines the consistency and symmetry of the final sensor sensitivity. The grating axis must be parallel to the diaphragm plane and centered, and the error must be controlled within the micrometer level.

[0116] Next, molten glass is poured and integrally molded. The selected grade of aluminosilicate glass (e.g., glass with excellent elasticity and chemical stability) is placed in a specialized crucible and heated in a high-temperature furnace under a controlled atmosphere to above its melting temperature (e.g., approximately 850°C) until it is completely melted and reaches a homogeneous, moderately fluid state. The preheated mold is placed stably, and using precision casting equipment or methods, the molten aluminosilicate glass is smoothly and continuously poured into the mold cavity where the fiber Bragg grating has been fixed, ensuring that the molten glass completely fills the cavity and submerges the grating area, while avoiding the formation of bubbles or turbulence impacting the fiber position.

[0117] Next comes controlled cooling and precision annealing. After casting, the mold containing the molten glass and optical fiber is transferred as a whole to a temperature-controlled annealing furnace. A carefully designed annealing temperature profile is executed: first, the temperature is slowly lowered to pass through the glass transition temperature region, and then held at that temperature for a sufficient time to minimize residual stress caused by glass cooling shrinkage and non-uniform temperature fields. This annealing process is crucial for ensuring the uniformity of the mechanical properties, optical quality, and long-term spectral stability of the final high-elasticity film (8) and fiber optic grating (10). After annealing, the film is slowly cooled to room temperature.

[0118] Finally, demolding and functional enhancement are performed. After the mold has completely cooled, the demolding operation is carefully carried out to obtain a silicon-aluminum glass preform with the fiber grating (10) completely embedded in the central area. To give the preform better elastic response and durability, it can be chemically tempered: the glass preform is immersed in a high-temperature molten salt bath (e.g., potassium nitrate) for a period of time, and a dense compressive stress layer is formed on its surface through an ion exchange process. This treatment not only significantly improves the mechanical strength (bending resistance, impact resistance) of the film, but also gives it better fatigue resistance under repeated stress, thus obtaining the final high-elasticity film (8).

[0119] In one embodiment, the support (12) is fixed inside the first base (2), and a U-shaped groove (12-1) is provided thereon. The first temperature measuring fiber optic grating (11) is loosely disposed in the U-shaped groove (12-1) and is fixed to the support (12) only at both ends of the fiber optic grating by molten silica adhesive.

[0120] Specifically, in this embodiment, the encapsulation and fixing method of the first temperature-sensing fiber optic grating (11) and the support (12) is the key to achieving accurate and stable temperature sensing. The core design idea of ​​this method is "mechanical strain isolation, temperature response retention", that is, through specific mechanical structures and encapsulation processes, the first temperature-sensing fiber optic grating (11) is insensitive to the mechanical strain caused by the force or corrosion expansion of the surrounding structures (such as the first base (2) and the high-elastic diaphragm (8)), while it can sense changes in ambient temperature without damping, thereby providing a pure and reliable temperature reference signal for the entire sensor device. The implementation process is as follows:

[0121] First, preparation and positioning are carried out. The support (12), as the carrier of the temperature sensing unit, is made of precision-machined quartz glass. The dimensions of the U-shaped groove (12-1) on it need to be precisely designed: the groove width is slightly larger than the diameter of the bare optical fiber (for example, if the optical fiber diameter is 125μm, the groove width is about 130-150μm), and the groove depth needs to ensure that the top of the optical fiber is slightly lower than or flush with the end face of the support (12) after placement, so as to avoid being compressed by other components during subsequent assembly. Before the encapsulation operation, the support (12) and the first temperature-sensing fiber grating (11) need to be cleaned. The middle grating section (i.e., the sensitive section) of the first temperature-sensing fiber grating (11) is placed loosely and without pre-stress at the bottom center of the U-shaped groove (12-1). Here, a slight reverse tension is applied to both ends of the optical fiber and then released through a precision fine-tuning device to ensure that the grating area is in a relaxed state of natural bending in the groove, leaving a micron-level excess length, which is the physical basis for achieving strain isolation.

[0122] Next, a precise point fixing process is performed. The fixing points are selected at a certain distance (usually greater than 10 mm) from both ends of the grating area in the fiber coating. Using a precision dispensing device or a micro-manipulation needle tip, a small amount of pre-mixed molten silica adhesive is drawn. This adhesive is usually made of ultrafine quartz powder mixed with silica sol or a specific high-temperature adhesive, and its coefficient of thermal expansion matches that of the quartz glass support (12) and the optical fiber itself. The adhesive is precisely applied to the two preset fixing points, so that it wraps around the optical fiber and forms a connection with the groove walls on both sides of the U-shaped groove (12-1). This operation must ensure that the adhesive does not touch the grating area itself to maintain the free state of the grating area. This two-point fixing method is like fixing the two ends of a string while keeping the middle section relaxed, which can effectively isolate the compressive or tensile strain transmitted along the axis of the support (12).

[0123] Then, thermal curing and stress relief are performed. The components (support (12) and optical fiber) that have been fixed with adhesive are placed in a programmed temperature-controlled heating device. The adhesive is heated to its melting and sintering temperature (e.g., about 400°C) at a controlled heating rate (e.g., 5-10°C / min) and held at this temperature for a period of time (e.g., 10-15 minutes). During this process, the silica adhesive melts, flows and wets the contact surface, and then solidifies during cooling, forming a strong chemical bond with the silica surface of the quartz glass support (12) and the optical fiber. More importantly, this matching heat treatment process helps to eliminate local residual stress introduced by adhesive application and the difference in the coefficients of thermal expansion of the materials. After cooling, the first temperature-measuring fiber grating (11) is firmly fixed to the support (12), and its grating area is effectively mechanically decoupled from the support (12) body due to the fixed constraints at both ends and its own relaxed state.

[0124] It is particularly important to note that the first temperature-sensing fiber optic grating (11) packaged using the above process has the following significant features and beneficial effects:

[0125] Excellent strain isolation. When the outer shell (1) or the first base (2) deforms due to external loads, concrete shrinkage or rust expansion, the deformation is transmitted to the two fixed points through the support (12), but since the grating area is relaxed, its length is hardly forced to change, thus ensuring that its reflection center wavelength hardly responds to these mechanical disturbances.

[0126] Temperature sensitivity is fully preserved. Since the thermo-optical effect and thermal expansion effect of the grating material itself (quartz) are not affected by the encapsulation, changes in ambient temperature can directly and completely cause changes in the grating period and refractive index, thereby generating accurate wavelength drift signals.

[0127] High long-term stability. Utilizing an all-silicon-based material system and high-temperature chemical bonding, the fixed-point interface is stable, and there is no aging of organic adhesives, ensuring the long-term reliability of the temperature compensation signal.

[0128] In one embodiment, the first base (2) is fixed to the inner side of the outer shell (1) by threaded connection, and the end of the first base (2) is also connected in sequence to a base connector (3) for leading out optical fibers and a waterproof connector (4).

[0129] Specifically, in this embodiment, the mechanical connection between the first base (2) and the outer shell (1) and the sealed lead-out of the optical fiber are key links to ensure the overall structural stability, long-term sealing reliability and engineering maintainability of the sensor device.

[0130] First, the threaded connection between the first base (2) and the outer shell (1) is explained. The second thread set (2-1) machined on the outer side of the first step of the first base (2) forms a precision-fit threaded pair with the first thread set (1-2) on the inner side of the outer shell (1). Fine threads (such as M30×1.5) are usually selected to provide a larger contact area and better locking force, while also facilitating accurate axial positioning in a limited space. During assembly, a special tool or torque wrench is required to symmetrically screw the first base (2) of the two measuring modules into the outer shell (1) from both ends until the preset tightening torque is reached. This design achieves a detachable rigid connection between each sensing module and the housing (1), bringing significant advantages: First, it has a high degree of modularity, allowing the two sensing modules to be assembled, tested, and calibrated independently before being integrated with the housing, facilitating quality control and fault replacement; Second, the symmetrical locking structure can effectively resist vibration and stress during concrete pouring and service, ensuring the long-term stability of the relative positions of the internal sensitive components (such as high-elastic diaphragms and fiber optic gratings); Third, a thin layer of high-temperature resistant and anti-aging silicone-based sealant can be pre-coated between the threaded mating surfaces, further enhancing the static sealing ability of the interface against the intrusion of corrosive media.

[0131] Next, the sealing interface structure of the optical fiber lead-out end is described. On the end face of the first base (2), its third threaded group (2-4) is used to connect the base connector (3). The base connector (3) is usually made of stainless steel or high-strength corrosion-resistant alloy, and the diameter of its central first through hole (3-2) is optimized to allow two optical fiber pigtails to pass through smoothly while minimizing the gap to reduce subsequent sealing pressure. The main function of the base connector (3) is to provide a reliable mechanical transition from the brittle quartz glass substrate to the external flexible armored optical cable and to serve as the basis for secondary sealing. At the end of the base connector (3), a waterproof connector (4) is connected by threads on its outer side. The waterproof connector (4) is a standardized industrial-grade component, usually made of brass or stainless steel, and integrates an elastic sealing structure, such as a rubber O-ring, silicone gasket, or injection-molded sealing core. When the waterproof connector (4) is tightened, its internal sealing element is compressed, thereby tightly wrapping the optical fiber leading out from the base connector (3) and filling all possible tiny gaps where water may seep in, achieving a dynamic seal with an IP67 or higher protection level. The leading optical fiber is then connected to the armored optical cable, whose outer sheath is firmly clamped to the tail of the waterproof connector (4), forming a third layer of protection, which together ensures the integrity and reliability of the sensor signal transmission line in a long-term immersion environment in damp, saline-alkali concrete.

[0132] In one embodiment, the steps for preparing the high-elasticity diaphragm (8) include:

[0133] (a) Place a fiber optic grating at the center of the high-elasticity diaphragm mold;

[0134] (b) Pour the high-elasticity glass material into the mold;

[0135] (c) Place the mold in a heating furnace and heat it to the preset temperature at a preset heating rate;

[0136] (d) After the device is cooled and the mold is opened, high-elasticity tempering treatment is immediately carried out. After heat preservation, it is taken out and air-cooled to obtain a high-elasticity thin silicon wafer (8) containing the fiber grating.

[0137] Specifically, in this embodiment, the fabrication of the high-elasticity diaphragm (8) is a precise micro-nano glass processing and functional integration process. Its core lies in using a fiber Bragg grating (10) as an embedded sensing element, achieving material-level fusion with a high-performance aluminosilicate glass substrate at high temperatures, thereby creating a composite sensing unit that combines excellent elasticity, long-term stability, and high sensitivity. The specific steps include:

[0138] (a) Mold pretreatment and fiber optic grating precision positioning

[0139] First, high-purity graphite or special high-temperature resistant ceramic materials are selected and precision-machined into a molding mold with a specific cavity (e.g., circular, diameter Φ20mm, depth 1.0mm). The inner surface of the mold needs to be highly smooth and preheated to eliminate adsorbed moisture and reduce thermal shock. Then, the critical fiber positioning is performed: a single-mode fiber grating (10) with its coating removed and temporary protective connectors at both ends (e.g., center wavelength 1550nm) is precisely and stress-free suspended in the geometric center plane of the mold cavity using a high-precision micro-displacement platform and a microscopic vision system. The positioning accuracy needs to reach the micrometer level to ensure that the grating axis is parallel to the diaphragm plane and centered, which is the basis for ensuring the symmetry and consistency of sensor sensitivity. After positioning, the two ends of the fiber are slightly fixed outside the mold with a high-temperature resistant clamp to prevent displacement in subsequent steps.

[0140] (b) Pretreatment and casting of high-elasticity glass material

[0141] The "high-elasticity glass material" refers to a silica-alumina glass powder (such as the Pyrex 7740 series) with specific composition that has undergone pre-melting and pulverization. Before casting, the glass powder needs to be preheated to a certain temperature (e.g., 300°C) in a dry environment to remove adsorbed gases and moisture. Subsequently, under a controlled environment (e.g., a dry nitrogen atmosphere), the preheated glass powder is smoothly and evenly poured into the mold cavity where the optical fiber has been positioned. During the pouring process, it is necessary to avoid impacting the optical fiber and ensure that the powder completely fills the cavity and covers the grating area. A vibration table can also be used to assist in making the powder denser and reducing internal voids.

[0142] (c) High-temperature melting and integrated molding heat treatment

[0143] The mold containing glass powder and optical fiber is transferred as a whole to a temperature-controlled high-temperature furnace (such as a muffle furnace). A precise heat treatment profile is then executed: first, the temperature is raised at a slow rate (such as 5°C / min) to above the sintering temperature of the glass powder (e.g., 850°C), and held at this temperature for a sufficient time (e.g., 1-2 hours). During this stage, the glass powder particles melt at the interface, bond together, and gradually densify, ultimately forming a completely transparent and homogeneous glass melt that completely encapsulates and wets the fiber grating, which is a heterogeneous material. This high-temperature melting process causes slight interdiffusion between the silica cladding of the optical fiber and the aluminosilicate glass matrix at the interface, forming a strong physicochemical bond. Subsequently, a precision annealing stage is entered: following the specific annealing temperature profile of the aluminosilicate glass, the glass transition temperature region is cooled at an extremely slow rate (e.g., 0.5-1°C / min), and isothermal holding may be performed in this region to minimize residual internal stress introduced by uneven cooling and material differences. Stress relief is crucial for preventing spontaneous cracking of the diaphragm, ensuring optical uniformity, and maintaining long-term dimensional stability.

[0144] (d) Cooling, demolding and high-elasticity tempering reinforcement treatment

[0145] After annealing, the mold is cooled to near room temperature in the furnace or at a controlled rate, and then carefully demolded to obtain a glass preform with embedded fiber gratings. Immediately afterwards, the preform is subjected to high-elasticity tempering treatment to significantly improve its mechanical properties: chemical tempering is usually used. The preform is immersed in a high-temperature molten salt bath (e.g., potassium nitrate KNO3 molten salt at around 400°C) and held for several hours (e.g., 6-10 hours). During this process, smaller ions in the glass surface layer exchange ions with larger ions in the molten salt. As the larger ions occupy more space, a dense compressive stress layer is formed on the glass surface. After the heat treatment is completed, the sample is removed and cooled in air. This chemical tempering treatment significantly enhances the surface hardness, bending strength, impact resistance and fatigue life of the preform, making it a high-elasticity film capable of withstanding long-term cyclic stress (8).

[0146] In one embodiment, the step of fixing the first connecting post (9) to the high-elastic diaphragm (8) includes:

[0147] (a) Mix silica glass powder and pure water in a preset mass ratio to form a molten state and then apply a thin layer to the center point of the high-elastic film (8);

[0148] (b) Press the boss of the first connecting post (9) perpendicularly into contact with the center of the high-elastic diaphragm (8) and apply a preset pressure;

[0149] (c) Place the parts on a heating table and heat them to 400°C. Hold them at the temperature for a preset time. Once the silica powder has cooled, the parts will adhere firmly.

[0150] Specifically, in this embodiment, the fixation between the first connecting post (9) and the high-elastic diaphragm (8) is the key mechanical interface for achieving precise and reliable transmission of magnetic force to strain. This step employs a special bonding process based on high-temperature molten silica glass powder, aiming to form a chemical bond between the two silicon-based materials, quartz glass (connecting post) and aluminosilicate glass (diaphragm), which possesses high strength, excellent durability, outstanding creep resistance, and near-perfect matching of thermal expansion coefficients. The implementation process is precise and controllable, as detailed below:

[0151] (a) Adhesive preparation and precision coating

[0152] First, the silica glass powder adhesive is prepared. The selected silica glass powder should be high-purity, ultrafine-particle (e.g., particle size D50 of 5-10 micrometers) quartz glass powder, and its chemical composition and coefficient of thermal expansion must be highly compatible with the main materials of the first connecting column (9) and the high-elastic diaphragm (8). The glass powder of a predetermined mass is mixed with high-purity deionized water (or a specific organic carrier) at a predetermined precise mass ratio (e.g., powder: liquid = 3:1 to 4:1). The mixture is stirred in a controlled environment using a precision stirring device to form a uniform, bubble-free paste with a certain viscosity and fluidity. The state of this paste is crucial; if it is too thin, the adhesive layer will be too thin and lack strength, while if it is too thick, it will affect the uniformity and wettability of the coating. Subsequently, precise quantitative coating is performed: using a micro-dispensing system or high-precision coating tool, the prepared slurry is coated at a very thin, uniform, and controllable thickness (e.g., a target dry film thickness of 30-50 micrometers) onto the precise geometric center point of the back side (the side not opposite the reinforcing bar) of the high-elastic diaphragm (8). This center point must be strictly aligned with the area of ​​the first strain measurement fiber grating (10) encapsulated inside the diaphragm to ensure that the force transmission path acts directly on the sensing core.

[0153] (b) Alignment assembly and pressure preloading

[0154] Immediately after the slurry is applied, high-precision alignment and pre-pressing are performed. The side of the first connecting post (9) with the protrusion is precisely and vertically aligned with the center area of ​​the coated high-elastic diaphragm (8) using an optically assisted alignment system or precision clamp. Then, a preset, constant, slight pressure (e.g., between 0.1 and 0.5 MPa) is applied axially. This step serves three purposes: first, to ensure initial and complete tight contact between the connecting post protrusion and the diaphragm surface, eliminating most of the air between the interfaces; second, to allow the slurry to spread evenly, forming a continuous and uniformly thick adhesive layer; and third, to establish initial mechanical positioning to prevent displacement during subsequent transfer and heating. The pressure needs to be optimized to ensure good contact while avoiding excessive pressure that could cause significant deformation of the high-elastic diaphragm (8) or damage to the internal fiber grating before bonding.

[0155] (c) High-temperature sintering and interfacial chemical bonding formation

[0156] After pre-pressing, the assembly (first connecting post (9) and high-elasticity diaphragm (8)) is transferred as a whole to a precision heating stage or high-temperature furnace with programmed temperature control. A critical heat treatment sintering procedure is performed: the assembly is slowly heated to a preset sintering temperature of 400°C at a controlled heating rate (e.g., 3-5°C / min), and held at this temperature for a precisely preset time (e.g., 15-30 minutes). After holding at this temperature, the assembly is cooled to room temperature at a slow, controlled rate (e.g., 1-2°C / min). Slow cooling helps release thermal stress that may be caused by small differences in thermal expansion between materials, ensuring the long-term stability of the bonded interface. After complete cooling, the silica glass powder adhesive has transformed into a dense, robust, and chemically stable glass interlayer, thereby firmly bonding the first connecting post (9) and the high-elasticity diaphragm (8) into a single unit.

[0157] A calibration and testing method for a fiber optic grating sensor used for monitoring corrosion of marine engineering steel reinforcement, the method comprising the following steps:

[0158] (a) Place the acrylic bracket (21) at the bottom of the rust basin (19) and fix it with UV glue. Fix the fiber optic grating sensor device and the two ends of the steel bar (14) to the upper groove of the acrylic bracket (21).

[0159] (b) Connect the positive and negative terminals of the power supply (15) to the steel bar (14) and the stainless steel plate (18) respectively through wires;

[0160] (c) Turn on the power switch (15) to make the wire (17), steel bar (14), 3.5% NaCl solution (20), stainless steel plate (18) and power supply (15) form a closed circuit, and the steel bar (14) begins to corrode faster.

[0161] (d) A fiber optic demodulator (16) is used to connect the fiber optic sensor (13) to monitor the center wavelength changes of the first strain measurement fiber optic grating (10) and the first temperature measurement fiber optic grating (11);

[0162] (e) Apply a constant current of 2A to the steel bar (14) using a power supply (15) and keep the test environment temperature at 25±2℃;

[0163] (f) After 8 days of rusting of the steel bar (14), the fiber optic grating demodulator (16) recorded data at a frequency of 5 Hz.

[0164] (g) Take out the steel bar (14) every 24 hours to remove rust and weigh it, and record the mass loss of the steel bar (14). To remove rust, soak it in 10% hydrochloric acid solution for 10 minutes, then remove the surface rust with a wire brush, rinse with clean water, dry and weigh it.

[0165] (h) By recording the center wavelength signal of the fiber optic grating sensor device (13) and the mass loss data of the steel bar (14), establish the sensitivity relationship of the corrosion change of the steel bar (14) and complete the calibration test.

[0166] Specifically, in this embodiment, the calibration test method for the fiber optic grating sensor used for monitoring corrosion of marine steel reinforcement is a systematic and repeatable laboratory procedure. It aims to accurately quantify the mapping relationship between the sensor's optical response (wavelength drift) and the physical state of the steel reinforcement (mass loss) by simulating the marine chloride ion corrosion environment and accelerating the corrosion process, thereby establishing a calibration benchmark for quantitative monitoring in engineering fields. This method combines electrochemical accelerated corrosion, high-frequency optical signal synchronous acquisition, and intermittent precision mass measurement techniques. Specific implementation details are as follows:

[0167] (a) System setup and precise sample positioning

[0168] First, prepare a plastic corrosion basin (19) of suitable volume as the reaction vessel. Use laser-cut acrylic brackets (21), with V-shaped or arc-shaped positioning grooves on the top that match the diameter of the sensor housing and the diameter of the reinforcing bar. Use UV-curing adhesive to firmly attach two sets (four in total) of acrylic brackets (21) symmetrically and horizontally to the predetermined positions at the bottom of the corrosion basin (19), ensuring that the axes of the two sets of brackets are strictly aligned. Place a section of reinforcing bar sample (14) (e.g., HRB400, 20mm in diameter) with its initial diameter, length, and initial mass M0 (accuracy up to 0.01g) precisely measured, after grinding, degreasing, acid pickling activation, and drying pretreatment, horizontally in the groove of the bottom set of brackets. Place the fiber optic grating sensor device (13) to be calibrated horizontally in the groove of the top set of brackets. Precise calibration using a dial indicator or laser alignment instrument ensures that the axis of the reinforcing bar (14) passes precisely through the center of the rectangular through hole (1-1) in the sensor housing (1), and that the initial calibration air gap (e.g., 5.00 ± 0.10 mm) is maintained between the magnet (5) inside the sensor and the surface of the reinforcing bar (14). This step is the physical basis for ensuring the consistency of all sensor calibration conditions and the validity of subsequent data.

[0169] (b) Electrochemical circuit connection

[0170] The stainless steel plate (18) (as an auxiliary cathode) is vertically fixed to one side of the inner wall of the rust basin (19). Using an insulated wire (17), the positive output terminal of the DC regulated power supply (15) is securely connected to one end of the reinforcing bar (14) (welding or conductive clamps can be used), and the negative output terminal of the power supply (15) is connected to the upper end of the stainless steel plate (18). Check to ensure that all electrical connections are secure, have good conductivity, and are free from short-circuit risks.

[0171] (c) Construction of the simulated environment and accelerated corrosion initiation

[0172] Slowly pour a pre-prepared 3.5% (mass percentage) NaCl solution (20) into the corrosion basin (19) until the liquid surface completely submerges the steel bar sample (14) and the sensitive parts of the fiber optic grating sensor device (13), and extends at least 20 mm above the upper surface of the steel bar to simulate a seawater immersion environment. Then, close the power supply (15) switch. At this point, a complete electrochemical corrosion circuit is formed by the wire (17), steel bar (14) (anode), NaCl solution (20) (electrolyte), stainless steel plate (18) (cathode), and power supply (15), as shown in the figure. Figure 10 This is a diagram of a calibration test device for a fiber optic grating corrosion monitoring device. Subsequently, the reinforcing bar (14) undergoes forced dissolution under the action of anodic current, and its corrosion rate is much higher than that under natural conditions, thereby achieving the purpose of accelerating corrosion.

[0173] The reinforcing bar (14) and the fiber optic grating sensor device (13) are connected by magnetic force, thus establishing a relationship between changes in magnetic force and the center wavelength of the fiber optic grating. The structure is equipped with a temperature-compensated fiber optic grating, which can automatically compensate for frequent temperature changes. To ensure the stability of the calibration data, the entire calibration test scheme is conducted in a constant temperature laboratory environment. During corrosion, the relative positions of the fiber optic grating sensor device (13) and the reinforcing bar (14) do not change.

[0174] (df) Synchronous optical monitoring and constant current and temperature control

[0175] Immediately connect the fiber optic output of the fiber optic sensor device (13) to the fiber optic demodulator (16) using a fiber optic patch cord. Set the fiber optic demodulator (16) to continuously scan and record the center wavelength data of the first strain measurement fiber optic grating (10) and the first temperature measurement fiber optic grating (11) at a sampling frequency of 5 Hz. Simultaneously, set the DC power supply (15) to output a constant current of 2 A. The current value is chosen to ensure a sufficiently fast corrosion rate to shorten the experimental cycle, while avoiding excessive current density that could distort the corrosion mechanism or generate excessive heat. The entire calibration test process should be conducted in a constant temperature environment (25 ± 2℃) to eliminate the interference of drastic temperature fluctuations on the FBG signal and ensure data stability. The total duration of continuous power-on accelerated corrosion is 8 days (192 hours). The fiber Bragg grating sensor device (13) and the fiber Bragg grating demodulator (16) were connected by jumpers. A constant current of 2A was applied to the reinforcing bar (14) using a power supply (15) to achieve a stable test effect. When the liquid level in the corrosion basin (19) dropped, a 3.5% NaCl solution (20) was added to simulate a more realistic marine environment. The reinforcing bar (14) was corroded for a total of 8 days. The recording frequency of the fiber Bragg grating demodulator (16) was 5Hz to test the strain response performance. The corresponding performance of the fiber Bragg grating sensor device (13) to the changes in the corrosion of the reinforcing bar was obtained through the test, and the calibration test of the fiber Bragg grating corrosion sensor was completed.

[0176] (g) Precise measurement of intermittent mass loss

[0177] During the power-on process, the process is paused every 24 hours. The specific operation is as follows: turn off the power (15), carefully remove the steel bar sample (14), and rinse it initially with deionized water. Then immerse it in a 10% (volume ratio) hydrochloric acid solution (a small amount of hexamethylenetetramine can be added as a corrosion inhibitor to prevent over-corrosion of the substrate) for 10 minutes to completely dissolve the loose and dense rust products attached to the surface. Then gently scrub the surface with a wire brush to remove any residue and rinse with plenty of water. Immediately afterwards, immerse the steel bar in a dilute sodium carbonate solution to neutralize the residual acid, rinse with water, and finally dehydrate with anhydrous ethanol and dry in a 60-70℃ oven for 2 hours. After cooling to room temperature, weigh it using a precision analytical balance, record the current mass, and calculate the cumulative mass loss at that time point. This process strictly follows the standard metal corrosion weight loss test method to ensure the accuracy and comparability of the mass loss data. After measurement, return the steel bar to its original position, replenish the evaporated solution to the original liquid level, and reconnect the power to continue the experiment.

[0178] (h) Data processing and sensitivity calibration model establishment

[0179] After the experiment, all data were compiled. First, using the data from the first temperature-measuring fiber grating (11), the wavelength data of the first strain-measuring fiber grating (10) was temperature-compensated to obtain the net wavelength drift caused only by corrosion. Then, the net wavelength drift corresponding to each 24-hour time point was correlated with the cumulative mass loss of the reinforcing steel. Generally, within a certain corrosion range, the two show a good linear relationship. The corresponding calibration equation can be established by fitting methods such as the least squares method. The wavelength change of the corresponding fiber grating and the strain relationship can be expressed as:

[0180]

[0181] in This is the net corrosion strain wavelength shift of the fiber grating. The strain sensitivity coefficient of the fiber optic grating is given by the first strain measurement fiber optic grating (10), where the axial strain is... , For the effective photoelastic coefficient, The slope K (unit: pm / g) represents the temperature change. When the fiber grating is bent, the change in its curvature directly affects the wavelength shift. This slope directly reflects the sensor's optical response intensity to corrosion of a unit mass of reinforcing steel. It is a crucial conversion parameter in subsequent engineering applications, used to convert the real-time monitored wavelength change into the actual amount of corrosion (mass loss) of the reinforcing steel, thus completing the quantitative calibration test of the sensor. This method is efficient and reliable, providing a solid metrological foundation for the engineering application of the sensor.

[0182] In one embodiment, the bottom of the acrylic bracket (21) is coated with UV waterproof adhesive and is strongly fixed to the bottom of the rust basin (19); the axis of the steel bar (14) coincides with the center line of the through rectangular hole; a fixing groove is provided on the acrylic bracket (21), and the initial distance between the surface of the steel bar (14) and the magnet (5) in the fiber optic grating sensor device (13) is set to 5mm.

[0183] Specifically, in the calibration test method of this embodiment, the fixing of the acrylic bracket (21), the precise alignment of the steel bar (14) and the fiber optic sensor device (13), and the accurate setting of the initial air gap are the three core physical prerequisites for ensuring the consistency of calibration experimental conditions, data accuracy, and repeatability. The specific implementation is as follows:

[0184] The bottom surface of the selected acrylic support (21) must be flat and clean. Before fixing, determine the precise positions of the two support points at the bottom of the rust basin (19). Apply UV-curing waterproof adhesive evenly to the entire bottom surface of the acrylic support (21). This type of adhesive can cure rapidly under ultraviolet light of a specific wavelength, forming a cured product with excellent water resistance and bonding strength. Press the adhesive-coated support (21) into the predetermined position and immediately use a UV lamp to irradiate it to firmly fix it. This fixing method is not only firm and reliable, able to withstand solution immersion and slight disturbance, but also cures quickly, facilitating efficient preparation of experimental equipment.

[0185] The pre-treated reinforcing bar (14) is placed in the fixed bottom bracket groove. Then, the fiber optic grating sensor device (13) is placed in the corresponding upper bracket groove. The position of the fiber optic grating sensor device (13) is finely adjusted using a precision adjustment system (such as a fine-tuning platform equipped with a dial indicator or an optical projection alignment instrument). The goal of the adjustment is to make the axis of the reinforcing bar (14) completely coincide with the geometric center line of the rectangular through-hole (1-1) on the sensor housing (1). This is typically achieved by measuring and equalizing the distances between the surface of the reinforcing bar and the inner wall of the rectangular hole in four orthogonal directions. Alignment accuracy must be controlled at a high level (e.g., deviation less than 0.5 mm) to ensure that the reinforcing bar maintains a symmetrical spatial relationship with the magnetic sensing components inside the sensor during subsequent corrosion, avoiding measurement errors introduced by eccentric torque.

[0186] After completing the axis alignment, the most crucial step is to set and verify the initial air gap distance between the surface of the reinforcing bar (14) and the working surface of the magnet (5) inside the fiber optic grating sensor device (13). According to the design, this distance is set to 5 mm in this embodiment. To achieve this, a high-precision feeler gauge set or laser rangefinder is required. By fine-tuning the height or angle of the fiber optic grating sensor device (13) on the upper support, measurements and adjustments are made at multiple measurement points (usually at least at both ends and the middle along the reinforcing bar axis) to ensure that the air gap value at all measurement points is 5 mm, with the error controlled within ±0.1 mm. This precise initial air gap is the benchmark for establishing a quantitative relationship between magnetic force change and corrosion amount, and its accuracy directly determines the effectiveness and universality of the calibration coefficient (sensitivity K). After completing the above three steps, the physical configuration of the entire calibration system before electrolyte injection is precisely established, laying a solid foundation for subsequent repeatable and highly reliable accelerated corrosion and synchronous monitoring experiments. Figure 11 and Figure 12 As shown, during the experiment simulating steel bar corrosion, the center wavelength of the two measurement modules of the fiber optic grating corrosion sensor showed good linearity with the steel bar mass loss; when the amount of corrosion changed slightly, the center wavelength of the grating also showed a significant response, indicating that the device has high sensitivity.

[0187] In one embodiment, the calibration test is performed in a constant temperature environment, and the sensitivity relationship of the corrosion change of the steel bar (14) is a linear model. The corresponding relationship between the wavelength change of the fiber optic grating and the strain can be expressed as:

[0188]

[0189] in This is the net corrosion strain wavelength shift of the fiber grating. The strain sensitivity coefficient of the fiber optic grating is given by the first strain measurement fiber optic grating (10), where the axial strain is... , For the effective photoelastic coefficient, This indicates a temperature change. When the fiber grating is bent, the change in its curvature directly affects the amount of wavelength shift.

[0190] Specifically, in this embodiment, the calibration test process is conducted in a constant temperature laboratory environment, with the ambient temperature controlled at 25±1℃. This strict temperature control measure aims to minimize the interference of ambient temperature fluctuations on the fiber Bragg grating sensing signal, thereby ensuring that in subsequent data analysis, the strain signal purely caused by steel corrosion can be clearly separated and quantified, guaranteeing the accuracy, stability, and repeatability of the calibration results.

[0191] Using the calibration test method described in this application, a correlation analysis was conducted between the experimentally measured and temperature-compensated net wavelength drift data and the cumulative mass loss data of the reinforcing steel. The analysis revealed an excellent linear relationship between the two within the range of corrosion variation. Therefore, the sensitivity relationship to changes in reinforcing steel corrosion can be simplified to a linear model.

[0192] A reinforcing bar is passed through a rectangular hole in the center of the sensor housing, and the device is cast into concrete. A magnet maintains a 5mm air gap with the reinforcing bar, generating axial magnetic force. The high-elastic diaphragm deforms under axial tension from the first connecting column, causing the first strain-measuring optical fiber, encapsulated in molten glass powder on the surface of the diaphragm, to bend and deform. When the reinforcing bar corrodes, the change in the magnet's magnetic force causes a change in the strain of the first strain-measuring optical fiber. This structure incorporates a temperature-compensated fiber Bragg grating for automatic compensation in environments with frequent temperature changes. Magnetic induction principle:

[0193] Select cross-sectional area as A cylindrical magnet is used as the sensing probe, and the air gap magnetic flux density is defined as... Then the expression for magnetic force is:

[0194]

[0195] in The magnetic permeability represents vacuum. When the steel bar (14) corrodes, the air gap between the magnet and the steel bar (14) changes, and the magnetic flux at the operating point of the magnet can be expressed as:

[0196]

[0197] in Let be the length of the magnet in the magnetization direction. It is the cross-sectional area of ​​the magnet. It is the remanent magnetic flux density of the magnet. The air gap spacing, The relative permeability of the magnetic material. The residual magnetic field strength. When the reinforcing steel corrodes, the mass loss can be expressed as:

[0198]

[0199] in Let be the original diameter of the reinforcing bar, and ΔD be the diameter change of the corroded reinforcing bar. Combining the above three formulas, the change in magnetic force caused by the corrosion of reinforcing bar (14) can be expressed as:

[0200]

[0201] Under magnetic stretching, the deflection of the high-elastic diaphragm (8) can be expressed as:

[0202]

[0203] Where E d Let be the elastic modulus of the diaphragm material, v be the Poisson's ratio of the diaphragm material, R be the outer radius of the diaphragm, and r be the fixed inner radius of the diaphragm. For strain measurement optical fibers, the change in axial strain can be expressed as:

[0204]

[0205] Where L f The length of the optical fiber encapsulated in the high-elasticity diaphragm; the relationship between the wavelength change of the fiber grating and the strain can be expressed as:

[0206]

[0207] Where K ε The strain sensitivity coefficient of a fiber optic grating, K T The effective photoelasticity coefficient is approximately 0.22 at room temperature, and ΔT represents the temperature change.

[0208] As the formula shows, when a fiber optic grating is bent, the change in its curvature directly affects the wavelength shift. Generally, the greater the curvature, the greater the wavelength shift. This is because when the fiber is bent, the propagation path of light changes, causing a change in the grating's refractive index modulation period, which in turn causes a shift in the center wavelength.

[0209] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0210] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0211] It should be particularly noted that, through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, or of course, by hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A fiber optic grating sensor device for monitoring corrosion of marine engineering steel bars, characterized in that, The fiber Bragg grating sensor device includes: The outer shell (1) is a cylindrical quartz structure with a through rectangular hole (1-1) at the center to allow the reinforcing bar to pass through. The inner sides of both ends of the outer shell (1) are machined with a first thread set (1-2). Two measurement modules are symmetrically distributed at both ends of the outer casing (1). Each measurement module includes: The first base (2) is a stepped shaft structure. The outer side of the first step is machined with a second thread group (2-1), which is fixed to the first thread group (1-2) of the outer shell (1) by thread engagement. The upper side of the second step is machined with a first square hole (2-2). The upper and lower ends of the second step are machined with first U-shaped grooves (2-3). The interior is machined with stepped holes. The other end face of the base is machined with a third thread group (2-4). A first semi-circular boss (2-5) is left in the middle of the threaded hole. The magnetic sensing component includes a magnet (5), a magnet shell (6), a first connecting post (9), a high-elastic diaphragm (8), and a first strain measurement fiber grating (10). The magnet (5) is placed in a cylindrical groove (6-1) of the magnet shell (6). The magnet shell (6) is fixed by a fifth threaded group (6-2) and a sixth threaded group (9-1) of the first connecting post (9). The other side boss of the first connecting post (9) is fixed to the center of the high-elastic diaphragm (8). The center of the high-elastic diaphragm (8) is integrated into the first strain measurement fiber grating (10). The temperature compensation component includes a support (12) and a first temperature-measuring fiber optic grating (11), wherein the first temperature-measuring fiber optic grating (11) is placed in the middle of the second U-shaped groove (12-1) of the support (12); The first cover plate (7) is a cylindrical boss structure, which is fixed to the first base (2) by glass powder. A second through hole (7-1) is processed in the middle, which is in clearance fit with the side wall of the first connecting column (9). The support (12) and the high elastic diaphragm (8) are assembled in the first base (2), and the contact area is fixed with molten silicon powder. The base connector (3) is a boss structure. A fourth thread group (3-1) is machined on the outside of the boss for fixing with the third thread group (2-4) of the first base (2). A first through hole (3-2) is machined in the center. Waterproof connector (4), the waterproof connector (4) is a cylindrical boss structure, the outer side of the boss is machined with a fourth thread group (4-1) for fixing with the base connector (3), and the center is machined with a through hole for connecting the armored optical cable lead-out optical fiber; The magnet (5) is made of neodymium iron boron material, the first strain measurement fiber grating (10) and the first temperature measurement fiber grating (11) are both single-mode optical fibers, the high-elasticity diaphragm (8) is made of aluminosilicate glass material, and the remaining components are made of silicon-based inorganic non-metallic materials.

2. The fiber Bragg grating sensor device according to claim 1, characterized in that, In the magnetic sensing component, the first strain measurement fiber grating (10) is encapsulated inside the high-elasticity diaphragm (8) by placing the fiber grating in the molding mold of the high-elasticity diaphragm (8) and integrally casting it with the molten aluminosilicate glass material constituting the high-elasticity diaphragm (8).

3. The fiber Bragg grating sensor device according to claim 1, characterized in that, The support (12) is fixed inside the first base (2), and a U-shaped groove (12-1) is provided on it. The first temperature measuring fiber optic grating (11) is loosely disposed in the U-shaped groove (12-1) and is fixed to the support (12) only at both ends of the fiber optic grating by molten silica adhesive.

4. The fiber Bragg grating sensor device according to claim 1, characterized in that, The first base (2) is fixed to the inner side of the outer shell (1) by threaded connection. The end of the first base (2) is also connected in sequence to a base connector (3) for leading out optical fiber and a waterproof connector (4).

5. The fiber Bragg grating sensor device according to claim 1 or 2, characterized in that, The steps for preparing the high-elasticity diaphragm (8) include: (a) Place a fiber optic grating at the center of the high-elasticity diaphragm mold; (b) Pour the high-elasticity glass material into the mold; (c) Place the mold in a heating furnace and heat it to the preset temperature at a preset heating rate; (d) After the device is cooled and the mold is opened, high-elasticity tempering treatment is immediately carried out. After heat preservation, it is taken out and air-cooled to obtain a high-elasticity thin silicon wafer (8) containing the fiber grating.

6. The fiber Bragg grating sensor device according to claim 1, characterized in that, The steps for fixing the first connecting post (9) to the high-elastic diaphragm (8) include: (a) Mix silica glass powder and pure water in a preset mass ratio to form a molten state and then apply a thin layer to the center point of the high-elastic film (8); (b) Press the boss of the first connecting post (9) perpendicularly into contact with the center of the high-elastic diaphragm (8) and apply a preset pressure; (c) Place the parts on a heating table and heat them to 400°C. Hold them at the temperature for a preset time. Once the silica powder has cooled, the parts will adhere firmly.

7. A calibration and testing method for a fiber optic grating sensor device for monitoring corrosion of marine engineering steel bars, characterized in that, The method includes the following steps: (a) Place the acrylic bracket (21) at the bottom of the rust basin (19) and fix it with UV glue. Fix the fiber optic grating sensor device and the two ends of the steel bar (14) to the upper groove of the acrylic bracket (21). (b) Connect the positive and negative terminals of the power supply (15) to the steel bar (14) and the stainless steel plate (18) respectively through wires; (c) Turn on the power switch (15) to make the wire (17), steel bar (14), 3.5% NaCl solution (20), stainless steel plate (18) and power supply (15) form a closed circuit, and the steel bar (14) begins to corrode faster. (d) A fiber optic demodulator (16) is used to connect to a fiber optic sensor device (13) to monitor the change in the center wavelength of the first strain measurement fiber optic grating (10) and the first temperature measurement fiber optic grating (11); (e) Apply a constant current of 2A to the steel bar (14) using a power supply (15) and keep the test environment temperature at 25±2℃; (f) After 8 days of rusting of the steel bar (14), the fiber optic grating demodulator (16) recorded data at a frequency of 5 Hz. (g) Take out the steel bar (14) every 24 hours to remove rust and weigh it, and record the mass loss of the steel bar (14). To remove rust, soak it in 10% hydrochloric acid solution for 10 minutes, then remove the surface rust with a wire brush, rinse with clean water, dry and weigh it. (h) By recording the center wavelength signal of the fiber optic grating sensor device (13) and the mass loss data of the steel bar (14), establish the sensitivity relationship of the corrosion change of the steel bar (14) and complete the calibration test.

8. The calibration and testing method for the fiber Bragg grating sensor device according to claim 7, characterized in that, The bottom of the acrylic bracket (21) is coated with UV waterproof adhesive and is strongly fixed to the bottom of the rust basin (19); the axis of the steel bar (14) coincides with the center line of the through rectangular hole; a fixing groove is provided on the acrylic bracket (21), and the initial distance between the surface of the steel bar (14) and the magnet (5) in the fiber optic grating sensor device (13) is set to 5mm.

9. The calibration test method according to claim 7, characterized in that, The calibration test method is carried out in a constant temperature environment. The sensitivity relationship of the corrosion change of the steel bar (14) is a linear model. The corresponding relationship between the wavelength change of the fiber optic grating and the strain can be expressed as: ； in This is the net corrosion strain wavelength shift of the fiber grating. The strain sensitivity coefficient of the fiber optic grating is given by the first strain measurement fiber optic grating (10), where the axial strain is... , For the effective photoelastic coefficient, This indicates a temperature change. When the fiber grating is bent, the change in its curvature directly affects the amount of wavelength shift.

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