A Real-Time Defect Monitoring System for Insulating Sling Composites Using Multimode Fiber Arrays

Abstract

This invention discloses a real-time monitoring system for defects in insulating suspender composites using a multi-mode fiber optic array, belonging to the field of fiber optic defect detection technology. It addresses the challenge of traditional defect detection techniques in health monitoring of composite structures, which often struggle to achieve comprehensive multi-channel and multi-mode detection and localization. The three-channel sensing structure possesses multi-level and multi-angle defect localization capabilities, significantly improving the accuracy and reliability of defect detection in insulating suspender composites. By combining distributed acoustic sensing, fiber Bragg gratings, and an optical time-domain reflectometer, this structure effectively achieves coarse localization, step detection, refined window generation, and precise localization. The coarse localization of defects using distributed acoustic sensing, through window expansion and correction, enhances adaptability to unknown or complex defect types. Furthermore, relying on the acoustic intensity characteristics of typical defects in the database further improves the stability and accuracy of detection.

Description

Technical Field

[0001] This invention relates to the field of optical fiber defect detection technology, and more specifically, to a real-time monitoring system for defects in the insulating strap composite of a multimode optical fiber array. Background Technology

[0002] Currently, defect detection of insulating sling composites mainly relies on traditional non-destructive testing technologies such as ultrasound, X-ray, and infrared imaging. Fiber Bragg grating technology has been widely used in many structural health monitoring applications. By measuring the changes in reflected wavelengths in optical fibers, it is possible to monitor stress and temperature changes in structures. Optical time domain reflectometers can be used to accurately locate damage points in optical fibers and are an important optical fiber testing tool.

[0003] The existing technology has the following shortcomings:

[0004] Traditional defect detection technologies often struggle to achieve comprehensive multi-channel, multi-modal detection and localization in the health monitoring of composite structures. Specifically, existing technologies frequently suffer from insufficient defect localization accuracy, particularly in the detection of complex materials, where the exact location and type of defects often remain undetermined. For instance, while single-mode fiber Bragg grating technology can provide real-time monitoring of stress and temperature, its accuracy remains limited for detecting minute defects and complex damage. Conversely, relying solely on optical time-domain reflectometry (OTDR), although offering higher precision localization, typically requires a large sensing area and complex equipment setup.

[0005] To address the above problems, this invention proposes a solution. Summary of the Invention

[0006] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a real-time monitoring system for defects in insulating sling composites of multimode fiber arrays, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A real-time monitoring system for defects in insulating sling composites using a multimode fiber array includes a three-channel sensor construction module, a step detection refinement module, a threshold adjustment and update module, and a defect location module, with signal connections between the modules;

[0009] The three-channel sensing construction module constructs a three-channel sensing structure based on distributed acoustic sensing, fiber Bragg gratings, and optical time-domain reflectometers. It focuses and locates defects in the insulating sling composite material step by step, generates a coarse positioning window based on distributed acoustic sensing, and adds preset diffusion to obtain an extended window.

[0010] The step detection refinement module performs step detection on the expansion window. If two adjacent gratings change abruptly in the same direction and the amplitude exceeds the step threshold, the step is located and refined to obtain a narrow window. If there is no step, strain voids are marked. The expansion ratio is calculated by combining the step significance and the insulation acoustic damping ratio. The preset diffusion is corrected and widened to obtain a new expansion window.

[0011] When the threshold adjustment and update module still has no step change in the new expanded window, the distributed acoustic sensing is re-triggered. Using the acoustic intensity characteristics corresponding to typical defects in the defect response database as a reference, the detection threshold is adaptively lowered or raised, the initial threshold value is updated, and the coarse positioning is re-coordinated. The narrow window is then repeatedly acquired.

[0012] The defect location module uses an optical time domain reflectometer (OTDR) to determine the specific defect location of the insulating sling composite material based on a narrow window. If the step test still fails, the OTD is used to directly locate the intersection of multiple strain voids. If the intersection of strain voids still cannot be located, the entire sensing fiber is traversed for defect location.

[0013] In a preferred embodiment, the three-channel sensing building block includes the following:

[0014] A sensing optical fiber is embedded along the length of the insulating sling composite to be monitored as a distributed acoustic sensing channel to collect acoustic vibration signals inside the insulating sling composite in real time. Several equally spaced fiber Bragg grating sensors are set up to form a fiber Bragg grating sensing network. The sensing optical fiber is connected to the optical time domain reflectometer unit to construct a three-channel sensing structure of optical-grating-optical.

[0015] Coarse positioning detection of insulating sling composites is performed using distributed acoustic sensing channels. The acoustic response of the sensing fiber is continuously monitored, and once it exceeds an initial threshold, the system will detect the problem. The acoustic event indicates that the sound source location point has a defect, and a fiber optic region surrounding the sound source location point is defined as a coarse location window.

[0016] Based on the coarse positioning window, a preset diffusion is introduced to expand it. The coarse positioning window is expanded to both sides by a preset diffusion length to obtain the expanded window.

[0017] In a preferred embodiment, the step detection refinement module includes the following:

[0018] The strain distribution in the region is step-detected using fiber Bragg grating sensors deployed within the extended window. The current strain values ​​of all fiber Bragg grating sensors within the extended window are obtained and compared with the strain distribution baseline under normal conditions in the region.

[0019] When the strain difference between two adjacent fiber Bragg grating sensors exceeds the step threshold and the strain change corresponding to the difference is in the same direction, it is determined that there is an abnormal strain step between the two sensors, and a section of optical fiber between the two adjacent fiber Bragg grating sensors is defined as a narrow window.

[0020] Once the strain step is successfully detected and the narrow window is obtained, the system can directly enter the defect location module, where the optical time domain reflectometer will perform the final defect location on the narrow window.

[0021] If the strain difference between all adjacent fiber Bragg grating sensors within the extended window does not exceed the step threshold, or the corresponding strain changes are not in the same direction, then a strain hole is introduced to mark the extended window segment.

[0022] In response to the occurrence of strain voids, an expansion factor λ is calculated based on the combined step significance and insulation acoustic damping ratio to modify and relax the original preset diffusion.

[0023] The ratio of the maximum adjacent strain difference observed within the current extended window to the step threshold is denoted as the step significance. The ratio of the acoustic emission signal intensity detected at the coarse acoustic positioning point to the acoustic signal intensity at the boundary of the coarse positioning window is denoted as the insulation acoustic damping ratio. ;

[0024] The expansion ratio is calculated by combining the significance of the step and the acoustic damping ratio of the insulation: ; where α and β are weighting coefficients, determined by experience and experiments, used to balance the influence of step significance and acoustic damping ratio on window adjustment;

[0025] By applying the calculated expansion ratio to the original preset diffusion length, the adjusted new diffusion length is obtained as the product of the preset diffusion and the expansion ratio. Based on this, the initial coarse positioning window is further widened to both sides.

[0026] After obtaining the new extended window, the step detection is repeated to compare the strain readings of adjacent fiber Bragg grating sensors within the new window. If a step change is detected at this time, the defect location is located and the narrow window is refined according to the aforementioned method, and the process directly enters the defect location module.

[0027] Conversely, if the new extended window still does not detect a step change, it proceeds to the next module.

[0028] In a preferred embodiment, the threshold adjustment and update module includes the following:

[0029] If the new expanded window still does not detect a valid step signal, refer to the acoustic intensity characteristics of the defect response database;

[0030] Let the effective amplitude of the background noise be N, and the initial threshold value be... Where k corresponds to the required initial signal-to-noise ratio, and the typical defect signal found by referring to the defect response database needs to be at least... When reliable detection requires multiples of the noise amplitude, the updated initial threshold value is expressed as follows: Update the acoustic threshold; repeatedly re-trigger coarse localization based on the new acoustic threshold, add a preset diffusion length to form a new extended window, and trigger the step detection refinement module again to perform strain step detection on the region to obtain a new narrow window;

[0031] The number of executions is set. If a narrow window is still not obtained after multiple threshold adjustments and repeated detections, the area where the strain void is obtained in each detection will be recorded, and the intersection of the strain voids obtained multiple times will be recorded as the intersection area of ​​the multiple strain voids.

[0032] In a preferred embodiment, the defect location module includes the following:

[0033] The optical time domain reflectometer is used to accurately locate defects, which includes the following three types of location logic;

[0034] Firstly, once a narrow window has been obtained, the optical time domain reflectometer can be used directly to locate defects in the sensing fiber corresponding to the narrow window.

[0035] Secondly, when a narrow window is not obtained but multiple strain cavity regions overlap, the detection range of the optical time domain reflectometer is focused on the overlapping region of multiple strain cavities to locate the defect in this section of the sensing fiber.

[0036] Third, when the optical time domain reflectometer fails to locate the defect in the intersection area of ​​multiple strain voids, a global scan is performed along the entire sensing fiber to finally determine the location of the defect.

[0037] The technical effects and advantages of the real-time monitoring system for defects in insulating sling composites using a multimode fiber optic array, as described in this invention:

[0038] This three-channel sensing structure has multi-level and multi-angle defect localization capabilities, which can significantly improve the accuracy and reliability of defect detection in insulating sling composites. By combining distributed acoustic sensing, fiber Bragg gratings and optical time-domain reflectometers, this structure can effectively realize multiple steps such as coarse localization, step detection, refined window generation, and precise localization.

[0039] Furthermore, the use of distributed acoustic sensing for coarse defect localization, through window expansion and modification, enhances adaptability to unknown or complex defect types. The threshold adjustment and update module, relying on the acoustic intensity characteristics of typical defects in the database, adaptively adjusts detection sensitivity under different environments and conditions, further improving detection stability and accuracy. Finally, the optical time-domain reflectometer (OTDR) can accurately determine defect locations within a narrow window, reducing errors and complexity. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the process for a real-time monitoring system for defects in insulating sling composites using a multimode fiber array, according to the present invention.

[0041] Figure 2 This is a schematic diagram of a real-time monitoring system module for defects in insulating sling composites using a multimode fiber array, according to the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example

[0044] Please see Figures 1-2 As shown, this invention discloses a real-time monitoring system for defects in insulating sling composites using a multimode fiber array, comprising a three-channel sensor construction module, a step detection refinement module, a threshold adjustment and update module, and a defect location module, with signal connections between the modules.

[0045] The three-channel sensing construction module constructs a three-channel sensing structure based on distributed acoustic sensing, fiber Bragg gratings, and optical time-domain reflectometers. It focuses and locates defects in the insulating sling composite material step by step, generates a coarse positioning window based on distributed acoustic sensing, and adds preset diffusion to obtain an extended window.

[0046] The step detection refinement module performs step detection on the expansion window. If two adjacent gratings change abruptly in the same direction and the amplitude exceeds the step threshold, the step is located and refined to obtain a narrow window. If there is no step, strain voids are marked. The expansion ratio is calculated by combining the step significance and the insulation acoustic damping ratio. The preset diffusion is corrected and widened to obtain a new expansion window.

[0047] When the threshold adjustment and update module still has no step change in the new expanded window, the distributed acoustic sensing is re-triggered. Using the acoustic intensity characteristics corresponding to typical defects in the defect response database as a reference, the detection threshold is adaptively lowered or raised, the initial threshold value is updated, and the coarse positioning is re-coordinated. The narrow window is then repeatedly acquired.

[0048] The defect location module uses an optical time domain reflectometer (OTDR) to determine the specific defect location of the insulating sling composite material based on a narrow window. If the step test still fails, the OTD is used to directly locate the intersection of multiple strain voids. If the intersection of strain voids still cannot be located, the entire sensing fiber is traversed for defect location.

[0049] In the three-channel sensing construction module, a three-channel sensing structure of optical-grating-optical is constructed based on distributed acoustic sensing, fiber Bragg gratings, and optical time-domain reflectometers. This structure progressively focuses and locates defects in the insulating sling composite material. A coarse positioning window is generated based on distributed acoustic sensing, and a preset diffusion is added to obtain an expanded window. Specific details include:

[0050] A sensing optical fiber is embedded along the length of the insulating sling composite to be monitored, serving as a distributed acoustic sensing channel to collect acoustic vibration signals inside the insulating sling composite in real time. Several equally spaced fiber Bragg grating sensors are also set up to form a fiber Bragg grating sensing network to acquire strain data at multiple discrete locations.

[0051] The sensing fiber is connected to the optical time domain reflectometer unit as an optical time domain reflectance detection channel to identify scattering changes along the fiber.

[0052] With the above configuration, a multimode fiber optic sensing system with a three-channel sensing structure of light-grating-light is formed. Each channel cooperates with the other and gives full play to its own advantages to achieve all-round monitoring of the condition of the insulating sling composite structure.

[0053] First, a coarse positioning detection of the insulating sling composite material is performed using a distributed acoustic sensing channel.

[0054] When defects occur inside composite materials, they are often accompanied by stress waves or acoustic emission signals. Distributed acoustic sensing channels can sensitively capture these abnormal acoustic activities and determine the location of the sound source along the optical fiber through time delay and phase demodulation.

[0055] The acoustic response of the sensing fiber is continuously monitored, and once it exceeds the initial threshold value... The acoustic event is identified as a defect, and the location of the event along the optical fiber is located accordingly. Since the distributed acoustic sensing channel itself has distributed positioning capabilities, it can locate the event point within a range of tens of meters or even longer. However, its positioning accuracy is limited by factors such as the system sampling rate and signal-to-noise ratio, and is generally on the order of meters. Therefore, what is obtained is the approximate area of ​​the defect, rather than the precise location.

[0056] The approximate location of the defect provided by the distributed acoustic sensing channel, that is, a section of optical fiber surrounding the sound source location point, is defined as the coarse location window.

[0057] To improve the robustness of subsequent detection, a preset diffusion is introduced to expand the coarse positioning window. The coarse positioning window is expanded to both sides by a preset diffusion length to obtain the expanded window. The preset diffusion is a pre-set length tolerance used to cover the possible positioning error and defect influence range.

[0058] The extended window has a larger range than the coarse positioning window, ensuring that even if the area affected by the deviation or defect in the positioning of the distributed acoustic sensing channel exceeds the coarse positioning window, it can still be covered by subsequent fine detection.

[0059] In the step detection refinement module, step detection is performed on the expanded window. If two adjacent gratings abruptly change in the same direction and the amplitude exceeds the step threshold, the step is located and refined to obtain a narrow window. If there is no step, strain voids are marked. The expansion ratio is calculated by combining the step significance and the insulation acoustic damping ratio. The preset diffusion is then corrected and widened to obtain a new expanded window. Specific details include:

[0060] After coarse positioning and determining the extended window, fiber Bragg grating sensors deployed within the extended window are used to perform step detection on the strain distribution in that area. Fiber Bragg grating sensors can measure local strain. When defects exist within the insulating sling composite, the load transfer path and strain field will change, often resulting in abnormal strain gradients or abrupt changes near the defects. By analyzing the differences in strain readings between adjacent fiber Bragg grating sensors within the extended window, the presence of a strain step change can be detected.

[0061] Specifically, step detection is performed on the extended window to obtain the current strain values ​​of all fiber Bragg grating sensors within the extended window, and these values ​​are compared with the strain distribution baseline under normal conditions in that region.

[0062] When an internal defect exists, the defect will interrupt the force transmission path, causing a sudden change in strain at the defect and in the surrounding area: the material on one side of the defect may be suddenly unloaded or the load reduced, while the other side maintains a high strain, thus creating a discontinuity in strain values ​​at the location of the defect.

[0063] Since fiber Bragg grating sensors are discretely arranged sensing points, the difference in readings between two adjacent fiber Bragg grating sensors can reflect whether there is a sudden change in strain between them. If the difference in strain values ​​between a pair of adjacent fiber Bragg grating sensors suddenly increases within a short distance, and the two change in the same direction, i.e., a sudden change in the same direction, for example, both strain values ​​decrease or increase relative to their respective previous references, but the amplitudes are significantly different, it indicates that there may be a step change in the strain field between the two sensors.

[0064] A step threshold is preset to determine whether the "abrupt amplitude" is significant. The step threshold can be set based on the sensor accuracy and typical values ​​of strain abrupt changes caused by historical defects. When the strain difference between adjacent fiber Bragg grating sensors exceeds the step threshold and the strain change corresponding to the difference is in the same direction, it can be determined that there is an abnormal strain step between the two sensors, and a section of optical fiber between the two adjacent fiber Bragg grating sensors is defined as a narrow window.

[0065] The narrow window is much smaller than the expanded window and is concentrated at the suspected defect, providing a focused area for subsequent precise analysis using an optical time domain reflectometer. Thus, if the strain step is successfully detected and the narrow window is refined, the monitoring process in this embodiment can directly enter the defect location module, where the optical time domain reflectometer performs the final defect location on the narrow window.

[0066] If no effective strain step change is detected within the extended window, that is, the strain difference between all adjacent fiber Bragg grating sensors does not exceed the step threshold and no obvious discontinuity occurs, it indicates that there is no serious defect causing a sudden strain change within the extended window. A strain void is introduced to mark this segment of the extended window, indicating that there may be a non-sudden defect within this range.

[0067] Strain voids refer to abnormal "blank" areas in the strain distribution, where the strain readings of fiber Bragg grating sensors are significantly lower or nearly constant compared to normal conditions, lacking the expected gradient changes, as if there were a void in the strain field.

[0068] In the case of strain voids, the original preset diffusion needs to be modified and relaxed. An expansion factor λ is calculated by combining the step significance and the insulation acoustic damping ratio to redefine a larger expansion window range.

[0069] Step significance Defined as the ratio of the maximum adjacent strain difference observed within the current extended window to the step threshold, it is used to measure the significance of strain step signs: a step significance close to 1 indicates that although the threshold has not been reached, it is close to the critical state of a step, while a step significance closer to 0 indicates that there are almost no signs of strain abrupt change within the extended window.

[0070] Insulation acoustic damping ratio Reflecting the local attenuation characteristics of the sound source signal in the insulating composite material, it is defined as the ratio of the intensity of the acoustic emission signal detected at the coarse acoustic positioning point to the intensity of the acoustic signal at the boundary of the coarse positioning window. The larger the insulation acoustic damping ratio, the more confined the acoustic event is to the vicinity of the coarse positioning point. The closer the insulation acoustic damping ratio is to 1, the more uniform the acoustic signal is distributed or the attenuation is slow along the optical fiber, which means that there is a deviation or defect in the sound source positioning and the influence range of the sound field is large.

[0071] Based on the above parameters, the expansion ratio is calculated as follows: Where α and β are weighting coefficients, determined empirically and experimentally, used to balance the influence of step significance and acoustic damping ratio on window adjustment. Characterizing the relative insufficiency of the strain step signal, Characterizes the relative insufficiency of local concentration of acoustic signals;

[0072] When no obvious strain step is found within the expansion window and the acoustic signal distribution is not concentrated, a larger value is taken, so that the expansion factor is significantly greater than 1, thereby greatly widening the expansion window and expanding the search range; conversely, if a step almost appears within the expansion window and the acoustic event is highly localized, the expansion factor is only slightly higher than 1, and the expansion window only needs to be slightly expanded.

[0073] By applying the calculated expansion ratio to the original preset diffusion length, the adjusted new diffusion length is obtained as the product of the preset diffusion and the expansion ratio. Based on this, the initial coarse positioning window is further widened to both sides, and a new expansion window is redefined.

[0074] After obtaining the new extended window, the step detection is repeated. The strain readings of adjacent fiber Bragg grating sensors within the new window are compared to find abrupt change signals. If a step change is detected at this time, the defect location is located and the narrow window is refined according to the aforementioned method, and the defect location module is directly entered.

[0075] Conversely, if the new extended window still fails to detect a valid step signal, it indicates that even with the expanded range, the presence of the defect cannot be directly identified. In this case, either the defect does not have a significant impact on the strain field, or the previous acoustic coarse localization may have been incorrect. Therefore, proceed to the next module to redetermine the coarse localization window and the extended window by reusing the distributed acoustic sensing channels and adjusting the parameters.

[0076] In the threshold adjustment and update module, when there is still no step in the new extended window, the distributed acoustic sensing is re-triggered. Referring to the acoustic intensity characteristics corresponding to typical defects in the defect response database, the detection threshold is adaptively decreased or increased, and the initial threshold value is updated for re-coarse positioning. The narrow window is repeatedly obtained, and the specific content includes:

[0077] If no valid step signal is still detected in the new extended window, it means that the current detection threshold may be too high, causing weak defect signals to fail to trigger the detection. Then, the detection threshold is appropriately decreased to improve the sensitivity of the acoustic channel and increase the probability of capturing weak defect acoustic emissions. On the contrary, if the amplitude of the event signal that triggered the acoustic coarse positioning in the previous round is very low, and it is confirmed through subsequent strain detection that there is no abnormal change in strain associated with this event, this indicates that this event is likely environmental noise or a harmless event, belonging to a false trigger situation, suggesting that the threshold may be set too low. Then, the detection threshold is increased to reduce the possibility of such noise events being triggered again and enhance the discrimination ability of the acoustic channel for real defect events;

[0078] The adjustment of the threshold is carried out according to the dynamic adjustment method of the signal-to-noise ratio. The background noise level of the distributed acoustic sensing channel is evaluated in real time, and the detection threshold is defined as a certain multiple of the background noise amplitude or an equivalent decibel margin. Let the effective amplitude of the background noise be N, and the initial threshold value , where k corresponds to the required initial signal-to-noise ratio. By referring to the defect response database, it is found that typical defect signals usually require at least times the noise amplitude to be reliably detected. Then, the target signal-to-noise ratio is set to . If < k, it means that the signal-to-noise ratio required by the initial threshold is too high, and the threshold should be decreased; if > k, the initial threshold is too low, and the threshold is increased. The new threshold is obtained through the adjustment of the proportional coefficient, and the updated initial threshold value is expressed as: .

[0079] The distributed acoustic sensing channel is used again to conduct coarse positioning detection on the insulation sling composite material. Under the new threshold setting, continuously monitor the acoustic emission signals from inside the composite material: when an acoustic event exceeding the new threshold is captured, it is determined that a defect event has reappeared, and the position of this event on the optical fiber is located to obtain a new coarse positioning window. Subsequently, based on this coarse positioning window, a preset diffusion length is added to form a new extended window, and the step detection refinement module is triggered again to conduct strain step detection on this area to attempt to obtain a new narrow window.

[0080] It should be noted that the threshold adjustment and update module can be executed multiple times when necessary; that is, the threshold adjustment and acoustic detection-strain refinement process can be repeated multiple times. Each round of adjustment refers to the defect response database and previous detection results to fine-tune the threshold, gradually approaching the threshold level that best suits the current defect signal characteristics, until a strain step is detected and a narrow window is obtained.

[0081] The number of executions is set. If a narrow window is still not obtained after multiple threshold adjustments and repeated detections, the area where the strain void is obtained in each detection will be recorded, and the intersection of the strain voids obtained multiple times will be recorded as the intersection area of ​​the multiple strain voids.

[0082] In the defect location module, an optical time-domain reflectometer (OTDR) is used to determine the specific defect location of the insulating sling composite material based on a narrow window. If the step test still fails, the ORT is used to directly locate the intersection of strain voids multiple times. If the intersection of strain voids still cannot be located, the defect location is performed by traversing the entire sensing fiber. The specific content includes:

[0083] Based on the aforementioned window information, an optical time-domain reflectometer is used to accurately locate the defect. Specifically, this involves the following three types of location logic:

[0084] Firstly, when a narrow window has been obtained: a high-resolution scan of the sensing fiber corresponding to the narrow window can be directly performed using an optical time-domain reflectometer (OTDR) to accurately determine the location of the defect. The ORT can identify anomalies in the local scattering characteristics of the fiber by sending optical pulses into the fiber and detecting changes in the backscattered signal during propagation along the fiber.

[0085] When defects exist within a narrow window region, these defects often affect the sensing fiber embedded in that region—for example, causing micro-bending, refractive index perturbations, or increased reflection. This produces observable changes in the backscattering curve of an optical time-domain reflectometer (OTDR). Because the narrow window is small and known, the OTD can perform precise measurements on this fiber segment, increasing the sampling rate and signal averaging to obtain a clear scattering distribution. By analyzing the variation characteristics of the OTD signal relative to the normal baseline at the narrow window, the distance to the anomaly point can be accurately determined, i.e., the specific location of the defect. Using a narrow window for focused scanning with the OTD not only offers high positioning accuracy and speed but also limits the detection range to the vicinity of the suspected defect, reducing interference from irrelevant information.

[0086] Secondly, when a narrow window is not obtained but multiple strain cavity regions overlap: focus the detection range of the optical time domain reflectometer on the overlapping region of multiple strain cavities, and perform a focused scan on this section of the sensing fiber to try to directly discover the defect;

[0087] The intersection region of multiple strain holes refers to a common fiber segment marked as a strain hole in each expansion window after multiple rounds of threshold adjustment and detection. Although no obvious strain abrupt change signal was detected in this region, the acoustic coarse localization repeatedly pointed the possible location of the defect to this nearby area, suggesting that the defect may exist in this intersection region without causing significant strain anomalies. To address this, an optical time-domain reflectometer (OTDR) can implement more sensitive scanning measures in the intersection region, such as appropriately shortening the spatial sampling interval of the OTD and increasing the signal averaging times to improve signal change detection capabilities. Within the intersection region, if there are subtle defects that previously failed to cause strain abrupt changes, a highly sensitive OTD scan is expected to capture subtle backscattering anomalies relative to the surrounding background at that location. By comparing the OTD echo curve of this region with the baseline curve under healthy conditions, any abnormal changes in scattering intensity can be used to determine the presence and location of the defect. Thus, even if the defect does not produce obvious strain field characteristics, it can still be located in its possible region using optical methods.

[0088] Third, when the optical time domain reflectometer fails to locate the defect in the intersection area of ​​multiple strain voids, it will automatically traverse the entire sensing fiber for a global scan to finally determine the location of the defect.

[0089] Instead of being limited to the area previously indicated by coarse acoustic localization, the system now performs optical time-domain reflectometry (OTDR) detection across the entire range of the sensing fiber from start to finish. This full-range scanning allows for a comprehensive acquisition of the backscattering intensity distribution along the fiber, enabling the detection of any anomalous signals. If an unidentified defect exists in the insulating sling composite, even if it wasn't captured by acoustic and strain analyses earlier, its impact on the sensing fiber (e.g., causing slight scattering gain or localized loss) will be reflected in the global ODR curve: typically, a scattering signal pattern different from the normal background will appear at the corresponding defect location (e.g., a small reflection spike, or additional attenuation in the backscattering curve after that location). By identifying the anomaly's position on the fiber length coordinates, the system can determine the final defect location. While full-fiber scanning may be relatively resource-intensive in terms of time and data processing, it serves as a last resort, ensuring that even if previous localized detection was flawed or missed, the defect can still be captured through a comprehensive scan, leaving no blind spots.

[0090] By combining the above three positioning logics, regardless of whether the defect will cause an obvious strain step signal, the location of the defect can be locked and output.

[0091] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0092] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0093] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0094] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0095] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0096] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time monitoring system for defects in insulating sling composites using a multimode fiber optic array, characterized in that, Signal connection between modules; The three-channel sensing module constructs a light-grating-light three-channel sensing structure based on distributed acoustic sensing, fiber Bragg grating, and optical time domain reflectometer, and gradually focuses and locates defects of the insulating sling composite material. Coarse positioning is performed based on distributed acoustic sensing to generate a coarse positioning window, and a preset diffusion is added to obtain an extended window. The step detection refinement module performs step detection on the extended window. If the adjacent two gratings mutate in the same direction and the amplitude exceeds the step threshold, the step is located and refined to obtain a narrow window. If there is no step, a strain void is marked, and the extended multiple is calculated by combining the step significance and the insulating acoustic damping ratio. The preset diffusion is corrected and relaxed to obtain a new extended window. The threshold adjustment and update module re-triggers the distributed acoustic sensing when there is still no step in the new extended window. The acoustic intensity characteristics of typical defects in the defect response database are used as a reference to adaptively lower or raise the detection threshold. The initial threshold value is updated to re-coarsely position and repeatedly obtain a narrow window. The defect positioning module uses the optical time domain reflectometer to judge the specific insulating sling composite material defect positioning based on the narrow window. If the step fails, the intersection part of the strain void is directly positioned by the optical time domain reflectometer multiple times. If the intersection part of the strain void still cannot be positioned, the entire sensing optical fiber is traversed to locate the defect.

2. The insulating sling composite material defect real-time monitoring system of a multi-modal optical fiber array according to claim 1, characterized in that: A sensing optical fiber is embedded in the insulating sling composite material to be monitored along the length direction thereof as a distributed acoustic sensing channel, and acoustic vibration signals inside the insulating sling composite material are collected in real time. A plurality of fiber Bragg grating sensors are arranged at equal intervals to form a fiber Bragg grating sensing network, and the sensing optical fiber is connected to an optical time domain reflectometer unit to construct a light-grating-light three-channel sensing structure.

3. The insulating sling composite material defect real-time monitoring system of a multi-modal optical fiber array according to claim 2, characterized in that: Using a distributed acoustic sensing channel to perform coarse localization detection on an insulated sling composite material, continuously monitoring the acoustic response of the sensing optical fiber, once an acoustic event exceeding an initial threshold value is detected , it is determined that a defect has occurred at the acoustic source localization point, and a section of the optical fiber region around the acoustic source localization point is defined as a coarse localization window; A preset diffusion is introduced on the basis of the coarsely positioned window to expand the coarsely positioned window by a preset diffusion length on both sides to obtain an extended window.

4. The insulating sling composite material defect real-time monitoring system of a multi-modal optical fiber array according to claim 3, characterized in that: The strain distribution in the extended window is detected by the fiber Bragg grating sensors arranged in the extended window range. The current strain values of all the fiber Bragg grating sensors in the extended window are obtained and compared with the strain distribution baseline in the normal state of the region. If the strain difference between adjacent fiber Bragg grating sensors exceeds the step threshold and the strain change corresponding to the difference is in the same direction, it is determined that there is an abnormal strain step between the two sensors, and a segment of the optical fiber region between the two adjacent fiber Bragg grating sensors is defined as a narrow window. If the strain step is successfully detected and the narrow window is refined, the defect positioning module can directly perform final defect positioning on the narrow window by the optical time domain reflectometer. If the strain difference of all adjacent FBG sensors in the extended window does not exceed the step threshold value, or the corresponding strain change is not in the same direction, the strain void is introduced to mark the extended window.

5. The real-time monitoring system for defects of the insulated suspension composite material of the multi-modal fiber array according to claim 4, characterized in that: For the case of strain void, the step significance and the insulation acoustic damping ratio are combined to calculate an expansion factor λ to modify the original preset diffusion; The ratio of the maximum difference in adjacent strains observed within the current extension window to the step threshold is denoted as the step significance The ratio of the acoustic emission signal strength detected at the acoustic coarse positioning point to the acoustic signal strength at the boundary of the coarse positioning window is denoted as the insulating acoustic damping ratio ; The expansion ratio calculation is expressed as a combination of the step significance and the insulation acoustic damping ratio: wherein a and β are weight coefficients determined by experience and experiment to balance the influence degree of the step significance and the acoustic damping ratio on the window adjustment. By applying the calculated expansion factor to the original preset diffusion length, the adjusted new diffusion length is obtained as the product of the preset diffusion and the expansion factor, and the initial coarse positioning window is further widened on both sides accordingly.

6. The real-time monitoring system for defects of the insulated suspension composite material of the multi-modal fiber array according to claim 4, characterized in that: After obtaining the new extended window, the step detection is repeated, and the strain reading difference of adjacent FBG sensors in the new window is compared. If a step mutation is detected at this time, the defect position is located according to the aforementioned method and refined to obtain a narrow window, and the defect positioning module is directly entered; On the contrary, if the new extended window still does not detect a step mutation, the next module is entered.

7. A real-time monitoring system for defects in an insulated overhead composite of a multi-modal fiber array as claimed in claim 6, wherein ； If the new extended window still does not detect an effective step signal, the acoustic intensity characteristics of the defect response database are referred to; Let the effective amplitude of the background noise be N, and the initial threshold value where k corresponds to the required initial signal-to-noise ratio, and the reference defect response database reveals that a typical defect signal requires at least times the noise amplitude to be reliably detected, the initial threshold value is updated to represent: the updated acoustic threshold.

8. A real time monitoring system for defects in an insulated pendant composite of a multi-modal fiber array as claimed in claim 7, wherein The coarse positioning is triggered multiple times based on the new acoustic threshold, and the preset diffusion length is added to form a new extended window. The strain step detection module is triggered again to detect the strain step in this area, and a new narrow window is obtained; The number of executions is set. If the narrow window is still not obtained after multiple threshold adjustments and repeated detections, the region where the strain void is located is recorded each time, and the intersection of multiple strain voids is recorded as the intersection region of multiple strain voids.

9. The real-time monitoring system for defects of the insulated suspension composite material of the multi-modal fiber array according to claim 1, characterized in that: Optical time domain reflectometer is used for precise positioning of defects, including the following three types of positioning logic; First, when the narrow window is obtained, the optical time domain reflectometer is directly used to position the defect corresponding to the sensing fiber of the narrow window; Second, when the narrow window is not obtained but the intersection region of multiple strain voids exists, the detection range of the optical time domain reflectometer is focused on the intersection region of multiple strain voids, and the defect is positioned in this section of sensing fiber; Third, when the intersection region of multiple strain voids is still not positioned by the optical time domain reflectometer, the whole sensing fiber is scanned to finally determine the position of the defect point.

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