A spatially distributed optical fiber hydrogen sensor based on array imaging and a measurement method thereof

Abstract

The application belongs to the technical field of optical fiber sensors and gas detection, and specifically provides a spatial distributed optical fiber hydrogen sensor based on array imaging and a measurement method thereof.The sensor comprises a light source module, a light splitting prism, a distributed optical fiber sensing assembly, an image acquisition unit and a signal processing unit, a spatial three-dimensional probe array is constructed by plating an alloy film on the discrete sensing end face of the distributed optical fiber bundle, and the reflectivity change after the film adsorbs hydrogen is used to modulate the reflection signal;combined with a spatial light imaging demodulation architecture, a two-dimensional gray array image is captured, and an image processing algorithm is used to convert the gray scale changes of multiple detection points in a non-coplanar state into the hydrogen concentration of the corresponding physical space in real time.The application breaks the limitation of the traditional array coplanarity, has the advantages of spatial topology flexibility, intrinsic safety and multi-point synchronous monitoring, and can be widely applied to hydrogen safety early warning in complex and limited spaces such as fuel cell cabins and hydrogen storage rooms.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor and gas detection technology, specifically providing a space-distributed fiber optic hydrogen sensor based on array imaging and its measurement method, which utilizes an imaging demodulation architecture to achieve real-time monitoring of hydrogen intensity at multiple discrete points in a complex space. Background Technology

[0002] As a clean energy source, the safety of hydrogen during storage, transportation, and application is central to the hydrogen energy industry chain. Due to its small molecular weight, high permeability, flammability, explosiveness, and wide explosion limits (4.0%~75.0%), hydrogen can easily form explosive mixtures in confined spaces in the event of a leak. Therefore, comprehensive real-time hydrogen monitoring of complex systems (such as fuel cell cabins, aircraft hydrogen storage rooms, and confined spaces in nuclear power plants) is crucial.

[0003] Currently, existing hydrogen detection technologies mainly face the following challenges: 1) Inherent safety is insufficient: Traditional semiconductor or catalytic combustion sensors are electrical sensors, which may generate sparks during detection, making them potential ignition sources. They are also susceptible to interference in complex electromagnetic environments; 2) Low spatial coverage: Existing fiber optic hydrogen sensors (such as FBG and interferometers) are mostly point-based measurements. In distributed scenarios requiring multi-point monitoring, using multiple demodulators significantly increases costs. If multiplexing technology is used, the optical path construction becomes extremely complex, and the sampling frequency and spatial resolution are limited; 3) Poor environmental robustness: Pure palladium (Pd) films undergo significant lattice expansion (α-β phase transition) during hydrogen absorption / dehydrogenation. Long-term operation can lead to cracks or even detachment of the film, i.e., hydrogen embrittlement, which seriously affects the service life of the sensor; 4) Monitoring blind spots: Due to the complex airflow distribution in sealed spaces and the unpredictable location of leaks, existing linear or area array sensors require the sensor head to be on the same plane or straight line, making it difficult to flexibly deploy them to fit complex equipment structures, resulting in serious monitoring blind spots.

[0004] Therefore, developing a distributed hydrogen sensor that can achieve spatial discrete three-dimensional array deployment, is intrinsically safe, and can effectively suppress hydrogen embrittlement has become a pressing issue in the field of hydrogen safety. Summary of the Invention

[0005] The purpose of this invention is to address the inherent safety hazards, susceptibility to hydrogen embrittlement failure, low single-point monitoring coverage, and difficulty in flexible wiring in complex three-dimensional spaces inherent in traditional hydrogen sensors used in hydrogen monitoring scenarios in aerospace, new energy, and power industries. This invention provides a spatially distributed fiber optic hydrogen sensor and measurement method based on array imaging. It aims to overcome the risks of explosion of electrical sensors in hydrogen environments and the shortcomings of ordinary fiber optic sensors in achieving large-scale, non-coplanar multi-point real-time monitoring, thus meeting the requirements of high safety, high spatial resolution, long lifespan, and distributed operation for hydrogen monitoring in complex sealed spaces.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A space-distributed fiber optic hydrogen sensor based on array imaging, characterized in that it comprises: a light source module, a beam splitter prism, a distributed fiber optic sensing component, an image acquisition unit, and a signal processing unit.

[0008] The distributed optical fiber sensing component consists of multiple independent optical fibers. One end of the optical fibers is bundled together to form a flat coplanar end, which constitutes a two-dimensional optical fiber imaging array. The other end serves as a hydrogen probe. Multiple hydrogen probes are distributed in the space to be measured at predetermined detection positions and are in a non-coplanar state, thus constructing a three-dimensional spatial probe array.

[0009] The light source module outputs an optical signal, which is shaped by a beam shaping element and then incident on a beam splitter. The beam splitter then directs the signal to the coplanar end of the distributed fiber optic sensing component and distributes it to each hydrogen probe. The hydrogen probe senses the hydrogen concentration and modulates a reflected light signal carrying local concentration information. The reflected light signal returns along the original path and converges at the coplanar end. After passing through the beam splitter again, it is collected by the beam shaping element. The image acquisition unit then captures the grayscale image on the two-dimensional fiber optic imaging array and transmits it to the signal processing unit.

[0010] Furthermore, each hydrogen probe is coated with a Pd alloy thin film doped with noble metals. The Pd alloy thin film reacts with hydrogen to produce a change in complex refractive index, which modulates a reflected light signal carrying local concentration information.

[0011] Furthermore, the Pd alloy thin film is specifically one of Pd-Au, Pd-Ag, and Pd-Co alloy thin films, wherein the atomic ratio of Pd to the doped noble metal is 2:1 to 5:1.

[0012] Furthermore, the length and wiring path of each optical fiber in the distributed optical fiber sensing component are customized according to the distribution of potential leakage points in the space under test, so as to realize synchronous monitoring of multiple discrete locations in the space.

[0013] Furthermore, the image acquisition unit includes a CCD camera or a CMOS image sensor.

[0014] Furthermore, the signal processing unit uses a Raspberry Pi.

[0015] Furthermore, the image acquisition unit acquires a two-dimensional grayscale array image of the fiber bundle end face in real time. The signal processing unit extracts the region of interest (ROI) and quantifies the grayscale to obtain the grayscale information of each array element. Then, the hydrogen concentration information is obtained through the grayscale-concentration mapping table. At the same time, the real-time concentration of each predetermined detection position in the space to be measured is obtained through the two-dimensional grayscale array-three-dimensional spatial coordinate mapping.

[0016] Meanwhile, the present invention also provides a measurement method based on the aforementioned array-based imaging space-distributed fiber optic hydrogen sensor, characterized by comprising the following steps:

[0017] Let N be the number of hydrogen probes in the distributed fiber optic sensing component. Distribute N-1 hydrogen probes at predetermined detection positions in the space to be measured, and place the remaining 1 hydrogen probe in a sealed vacuum tube as a reference. At the same time, a two-dimensional grayscale array-three-dimensional spatial coordinate mapping is formed.

[0018] The light source module is activated, and the image acquisition unit acquires a two-dimensional grayscale array image of the coplanar end of the distributed fiber optic sensing component in real time.

[0019] The signal processing unit extracts the region of interest (ROI) from the two-dimensional grayscale array image to obtain a spot array. After median filtering preprocessing, it extracts the real-time grayscale value of each spot and performs calibration based on a reference benchmark. Based on the calibrated grayscale value, it obtains the hydrogen concentration information of each spot according to the prior grayscale-concentration mapping table, and then feeds back the real-time concentration information of the detection position corresponding to each spot according to the two-dimensional grayscale array-three-dimensional spatial coordinate mapping.

[0020] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0021] This invention provides a space-distributed fiber optic hydrogen sensor and measurement method based on array imaging. It utilizes imaging demodulation to achieve real-time monitoring of hydrogen intensity at multiple discrete points within a complex space, offering the following advantages:

[0022] 1. Extremely flexible spatial topology: Breaking the limitation that traditional sensor arrays must be coplanar, by utilizing the bendable characteristics of distributed fiber bundles, the sensing end face can be discretized according to the actual leakage risk points (such as valves, flanges, welds), realizing blind-zone-free monitoring in three-dimensional space. This invention achieves decoupling of detection points in three-dimensional spatial topology by freely configuring the length and path of each independent fiber branch.

[0023] 2. Intrinsic safety and high reliability: The sensing front end is completely electricity-free and is composed of glass / quartz and metal alloy thin films, making it suitable for flammable and explosive hydrogen environments;

[0024] 3. Cost advantage of single-end demodulation: It reuses the imaging demodulation architecture, which reduces the concentration information of the complex "three-dimensional probe array" in space to a "two-dimensional fiber imaging array" of the demodulation segment. Only one set of CCD and signal processing unit is needed to simultaneously demodulate the information of hundreds or thousands of detection points. The cost of single-point monitoring is far lower than that of traditional multiplexed fiber optic hydrogen sensors, which has extremely high engineering application value.

[0025] 4. Outstanding level of intelligence: The system integrates spatial location mapping and concentration gradient analysis functions, which can not only quantitatively detect concentration, but also quickly locate the initial leak source through image processing algorithms, realizing a leap from detection to diagnosis. Attached Figure Description

[0026] Figure 1 This is a structural block diagram of the space-distributed fiber optic hydrogen sensor based on array imaging in this invention.

[0027] Figure 2 This is a schematic diagram of the space-distributed detection topology of the space-distributed fiber optic hydrogen sensor based on array imaging in this invention.

[0028] Figure 3 This is a schematic diagram of the multilayer thin film structure at the end face of the optical fiber in this invention.

[0029] Figure 4 This is a mapping diagram of grayscale and hydrogen concentration at the end face of the optical fiber bundle in this invention.

[0030] Figure 5 This is a measurement result diagram of a space-distributed fiber optic hydrogen sensor based on array imaging in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] This embodiment provides a spatially distributed fiber optic hydrogen sensor based on array imaging for monitoring hydrogen leaks inside the powertrain chassis of a fuel cell vehicle. This scenario has a complex spatial structure, including the fuel cell stack, hydrogen circulation pump, pressure reducing valve, and various pipeline joints, and is subject to high-frequency electromagnetic interference generated by the motor controller and vibrations generated during fuel cell stack operation. In this embodiment, the sensor is constructed by discretizing key leakage points (such as hydrogen inlet flange, circulation pump interface, etc.) within the chassis to build a highly customized three-dimensional spatial probe array, enabling synchronous monitoring of hydrogen concentration at multiple points in space.

[0033] Specifically, the space-distributed fiber optic hydrogen sensor includes: a light source module, a beam splitter prism, a distributed fiber optic sensing component, an image acquisition unit, and a data processing unit, such as... Figure 1 As shown; wherein, the distributed optical fiber sensing component is used to sense the hydrogen concentration at multiple points in space and modulate the distribution of reflected light intensity. One end of the component is bundled into an uncoated optical fiber bundle with a flat end face and connected to the beam splitter prism to form a two-dimensional optical fiber imaging array; the other end is decomposed into multiple independent optical fiber branches, and the ends of each branch form an array of coated ends dispersed at different detection positions in the space to be measured and in a non-coplanar state, constructing a three-dimensional spatial probe array, such as... Figure 2 As shown; each optical fiber end face of the arrayed coating end is coated with a Pd alloy thin film doped with noble metals. The Pd alloy is selected from one or more of Pd-Au, Pd-Ag, and Pd-Co, and the atomic ratio of Pd to the doped noble metal is 2:1 to 5:1; the signal processing unit integrates a spatial mapping demodulation module, which is configured to convert the two-dimensional grayscale array image captured by the image acquisition unit into a hydrogen concentration signal with corresponding physical coordinates for output.

[0034] The sensor achieves concentration sensing through directional transmission and feedback of the optical path: the light emitted by the light source module is shaped by the beam shaping element, redirected by the beam splitter, and enters the distributed optical fiber sensing component, which transmits it to the spatial three-dimensional probe array deployed at various potential leakage points in space; the reflection light signal carrying local concentration information is modulated by the change in complex refractive index caused by the reaction of the Pd alloy thin film with hydrogen and returns along the original path, is shaped by the beam splitter and beam shaping element, and is captured in real time by the image acquisition unit to form a two-dimensional grayscale array image corresponding to the spatial topology; the signal processing unit performs region of interest (ROI) extraction, grayscale quantization, and concentration and spatial coordinate mapping processing on the two-dimensional grayscale array image to obtain the real-time hydrogen concentration at each detection point.

[0035] The sensor's operating procedure is as follows:

[0036] Optical signal distribution and transmission: The light source module starts and outputs light, which is shaped by the beam shaping element and coupled to the distributed fiber bundle by the beam splitter. The light is transmitted along each branch to the spatial three-dimensional probe array distributed in different locations in space.

[0037] Multi-point concentration modulation: The reflectivity of the Pd alloy film at each detection site changes in real time according to the local hydrogen concentration at its location, forming reflected signal light of varying intensity.

[0038] Image capture and analysis: The reflected light from each path converges back to the end face of the fiber bundle along the original path, and after passing through the beam splitter, it is shaped by the beam shaping element and projected onto the image acquisition unit to form a two-dimensional grayscale array image; the signal processing unit performs noise reduction, grayscale extraction and nonlinear concentration analysis on the image, and converts the brightness and darkness changes of the two-dimensional grayscale array image into a three-dimensional hydrogen concentration distribution map to complete real-time online monitoring.

[0039] More specifically, in this embodiment, the fiber optic sensing component uses distributed multimode silica fiber with a specification of 62.5 / 125μm. First, each detection end face of the fiber optic sensing array is sequentially subjected to rough grinding and fine grinding with an abrasive wheel, and then polished with diamond polishing fluid to ensure the flatness of the end face meets optical reflection requirements. Then, a magnetron sputtering process is used to deposit a Ti target on the polished fiber end face. First, a Ti adhesion layer of approximately 4nm thickness is formed by sputtering a Ti target at 100W power for 30s. Subsequently, a Pd and Ag target co-sputtering process is used, with a power ratio set at 60W:35W, for continuous sputtering for 300s, ultimately forming a Pd-Ag alloy thin film with a total thickness of approximately 40nm. Figure 3 As shown, the atomic ratio of Pd to Ag in the alloy film is approximately 4.2:1. This ratio effectively suppresses phase transformation stress during hydrogen absorption and improves resistance to hydrogen embrittlement. In this embodiment, 18 detection optical fibers are arranged at key locations within the chassis, and an additional coated optical fiber housed in a sealed vacuum tube serves as a reference for temperature and light source fluctuations. The fiber bundle's junction is secured to a flange with high-temperature resistant sealant to ensure coaxiality between the fiber axis and the demodulation optical path. The light source module uses a green collimated LED light source with a center wavelength of 532nm. Its collimated output ensures efficient light signal incidence onto the beam splitter and coupling into the fiber bundle. The image acquisition unit uses an industrial-grade CCD camera with a pixel resolution of 1920×1080 and a frame rate of 30fps. The signal processing unit uses a Raspberry Pi 4B, integrating a spatial mapping demodulation algorithm.

[0040] During sensor assembly and installation, the prepared 18-channel sensing optical fiber is routed along the inner wall of the chassis to each potential leakage point and fixed with high-temperature resistant clips. Then, the fiber bundle end is connected to the beam splitter prism, and the beam splitter prism angle is adjusted so that the CCD can clearly capture the 19 light spot array formed by the bundle end face, including 1 reference fiber. Finally, a two-dimensional grayscale array-three-dimensional spatial coordinate mapping is established in the Raspberry Pi. During hydrogen monitoring, 532nm spatial light is coupled into a distributed optical fiber via a beam splitter prism. The optical signal is transmitted to the end faces at various locations in space. When a hydrogen leak occurs in a local environment, the Pd-Ag thin film at that location absorbs hydrogen atoms, causing a change in the film's complex refractive index and resulting in a decrease in reflected light intensity. The CCD captures the two-dimensional grayscale array image formed by the reflection in real time and transmits it to a Raspberry Pi. After median filtering preprocessing, the Raspberry Pi extracts the real-time grayscale value of each detection point, compares it with the intensity of the reference optical fiber, eliminates interference from light source fluctuations, and calculates the grayscale change (light intensity). Finally, based on a preset grayscale change-hydrogen concentration mapping table, the specific concentration value at that point is calculated.

[0041] This embodiment specifies the mapping relationship between grayscale change and hydrogen concentration within the concentration range of 0-4%, as follows: Figure 4 As shown, exemplary measurement results are as follows: Figure 5 As shown, performance tests show that under typical fuel cell operating conditions, the identification response time for 4% hydrogen (lower explosion limit) is ≤60s, the measurement error is ≤±0.5%, and the spatial positioning accuracy depends on the location of the sampling points, which can accurately locate minute leakage sources. In summary, this embodiment verifies the feasibility of array imaging demodulation architecture in complex hydrogen energy scenarios.

[0042] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A space-distributed fiber optic hydrogen sensor based on array imaging, characterized in that, include: Light source module, beam splitter, distributed fiber optic sensing components, image acquisition unit and signal processing unit; The distributed optical fiber sensing component consists of multiple independent optical fibers. One end of the optical fibers is bundled together to form a flat coplanar end, which constitutes a two-dimensional optical fiber imaging array. The other end serves as a hydrogen probe. Multiple hydrogen probes are distributed in the space to be measured at predetermined detection positions and are in a non-coplanar state, thus constructing a three-dimensional spatial probe array. The light source module outputs an optical signal, which is shaped by a beam shaping element and then incident on a beam splitter. The beam splitter then directs the signal to the coplanar end of the distributed fiber optic sensing component and distributes it to each hydrogen probe. The hydrogen probe senses the hydrogen concentration and modulates a reflected light signal carrying local concentration information. The reflected light signal returns along the original path and converges at the coplanar end. After passing through the beam splitter again, it is collected by the beam shaping element. The image acquisition unit then captures the grayscale image on the two-dimensional fiber optic imaging array and transmits it to the signal processing unit.

2. The space-distributed fiber optic hydrogen sensor according to claim 1, characterized in that, Each hydrogen probe has a Pd alloy thin film doped with noble metals deposited on its end face. The Pd alloy thin film reacts with hydrogen to produce a change in complex refractive index, which modulates a reflected light signal carrying local concentration information.

3. The space-distributed fiber optic hydrogen sensor according to claim 2, characterized in that, Specifically, the Pd alloy thin film is one of Pd-Au, Pd-Ag, or Pd-Co alloy thin films, wherein the ratio of the number of Pd atoms to the number of doped noble metal atoms is 2:1 to 5:

1.

4. The space-distributed fiber optic hydrogen sensor according to claim 1, characterized in that, In the distributed optical fiber sensing component, the length and wiring path of each optical fiber are customized according to the distribution of potential leakage points in the space to be tested, so as to realize synchronous monitoring of multiple discrete locations in the space.

5. The space-distributed fiber optic hydrogen sensor according to claim 1, characterized in that, The image acquisition unit includes a CCD camera or a CMOS image sensor.

6. The space-distributed fiber optic hydrogen sensor according to claim 1, characterized in that, The signal processing unit uses a Raspberry Pi.

7. The space-distributed fiber optic hydrogen sensor according to claim 1, characterized in that, The image acquisition unit acquires a two-dimensional grayscale array image of the coplanar end of the distributed optical fiber sensing component in real time. The signal processing unit extracts the region of interest (ROI) and quantifies the grayscale to obtain the grayscale information of each array element. Then, the hydrogen concentration information is obtained through the grayscale-concentration mapping table. At the same time, the real-time concentration of each predetermined detection position in the space to be measured is obtained through the two-dimensional grayscale array-three-dimensional spatial coordinate mapping.

8. The measurement method of the space-distributed fiber optic hydrogen sensor based on array imaging according to claim 1, characterized in that, Includes the following steps: Let N be the number of hydrogen probes in the distributed fiber optic sensing component. Distribute N-1 hydrogen probes at predetermined detection positions in the space to be measured. Place the remaining 1 hydrogen probe in a sealed vacuum tube as a reference. At the same time, establish a two-dimensional grayscale array-three-dimensional spatial coordinate mapping. The light source module is activated, and the image acquisition unit acquires a two-dimensional grayscale array image of the coplanar end of the distributed fiber optic sensing component in real time. The signal processing unit extracts the region of interest (ROI) from the two-dimensional grayscale array image to obtain the light spot array, and extracts the real-time grayscale value of each light spot after median filtering preprocessing, while performing calibration based on a reference benchmark. Based on the calibrated grayscale values, the hydrogen concentration information of each light point is obtained according to the prior grayscale-concentration mapping table, and then the real-time concentration information of the detection position corresponding to each light point is fed back according to the two-dimensional grayscale array-three-dimensional spatial coordinate mapping.

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