Fiber bragg grating hydrogen sensing system based on amorphous palladium-based alloy and sensor

A sensing system and fiber grating technology, applied in the field of hydrogen sensors, can solve the problems of fiber grating strain and temperature cross-sensitivity, large loss of coreless fiber, decreased accuracy, etc., to improve hydrogen embrittlement phenomenon, strong hydrogen permeability, The effect of low production cost

Inactive Publication Date: 2021-02-05
安徽伯华氢能源科技有限公司
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AI-Extracted Technical Summary

Problems solved by technology

[0005] However, fiber gratings have the problem of cross-sensitivity between strain and temperature. In order to achieve high-precision measurement, it is usually necessary to perform temperature compensation on the fiber grating sensing system.
Patent CN105841840A proposes an optical fiber sensor capable of simultaneously measuring hydrogen gas concentration and temperature. Its essence is to realize simultaneous measurement of hydrogen gas concentration and temperature by monitoring the interference spectrum generated by the coreless fiber and the reflect...
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Method used

Referring to accompanying drawing 1, corrode the fiber cladding (2) engraved with fiber Bragg grating (1) with hydrofluoric acid, make its thickness reduce, thereby improve sensor sensitivity. With the corroded cladding as the substrate, a certain thickness of polyimide film and Ni film are coated successively as the adhesion layer (3), the purpose is to increase the adhesion between the sensing layer and the optical fiber cladding to prevent hydrogen Sensitive material falls off. The amorphous palladium-based alloy film coated on the outside of the adhesion layer constitutes the outermost sensing layer (4) of the hydrogen-sensitive probe. The Pd-Cu-Si amorphous alloy film is selected as the hydrogen-sensitive material, and its preparation method is as follows: coating The method uses the vacuum magnetron sputtering method, the target material is a Pd target with a purity of 99.99% and a CuSi alloy target with a purity of 99.9%, and the atomic ratio of the CuSi alloy target is Cu:Si=5:17; the Pd target is connected to a DC power supply CuSi target Connect the radio frequency power supply; control the thickness of the film by changing the current of the DC power supply and the power of the radio frequency power supply, and finally anneal the film. It should be pointed out that the ratio of the cross-sectional area of ​​the film to the optical fiber will directly affect the sensitivity and time response of the sensor. The sensitivity increases with the increase of the ratio, but the response time decreases with the increase of the film thickness. In order to obtain a fast-response fiber-optic hydrogen sensor, the thickness of the film layer in this example is selected as 30 nm. In order to increase the sensitivity and ensure the mechanical strength, the diameter o...
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Abstract

The invention discloses a fiber bragg grating hydrogen sensing system based on amorphous palladium-based alloy. The fiber bragg grating hydrogen sensing system is formed by welding a first fiber bragggrating and a second fiber bragg grating which have different central wavelengths in series, wherein the surface of the second fiber bragg grating is coated with a sensing film layer to form a hydrogen sensitive probe, and the sensing film layer is an amorphous palladium-based alloy film. Byutilizing the principle that the stress and the refractive index are changed after the sensing film layer absorbs hydrogen, the hydrogen concentration in the environment is converted into the offset of the central wavelength of a substrate, and the material has both the reversible hydrogen absorption performance of metal palladium and the excellent hydrogen permeability of amorphous alloy, so that the stability and sensitivity of a sensing system can be greatly improved. The surface of the first grating is exposed and used for temperature measurement and temperature compensation, and the inherent temperature cross sensitivity problem of the fiber grating sensor is eliminated. Aiming at the type ofthe second grating, the invention further provides two sensors loading the hydrogen sensing system based on reflection and transmission spectra respectively.

Application Domain

Material analysis by optical meansConverting sensor output optically

Technology Topic

Alloy thin filmTransmittance spectra +6

Image

  • Fiber bragg grating hydrogen sensing system based on amorphous palladium-based alloy and sensor
  • Fiber bragg grating hydrogen sensing system based on amorphous palladium-based alloy and sensor
  • Fiber bragg grating hydrogen sensing system based on amorphous palladium-based alloy and sensor

Examples

  • Experimental program(2)

Example Embodiment

[0033]Example 1
[0034]See attachedfigure 1 , Use hydrofluoric acid to etch the fiber cladding (2) engraved with fiber Bragg grating (1) to reduce its thickness, thereby improving the sensitivity of the sensor. The corroded cladding is used as the substrate, and a certain thickness of polyimide film and Ni film are successively coated as the adhesion layer (3). The purpose is to increase the adhesion between the sensor layer and the optical fiber cladding and prevent hydrogen Sensitive material falls off. The amorphous palladium-based alloy film coated on the outside of the adhesion layer constitutes the outermost sensing layer (4) of the hydrogen sensitive probe. The Pd-Cu-Si amorphous alloy film is selected as the hydrogen sensitive material. The preparation method is as follows: The method uses vacuum magnetron sputtering method, the target materials are 99.99% purity Pd target and 99.9% CuSi alloy target, the atomic ratio of CuSi alloy target is Cu:Si=5:17; the Pd target is connected to the DC power supply CuSi target Connect the radio frequency power supply; control the film thickness by changing the DC power supply current and the radio frequency power supply power, and finally the film is annealed. It should be pointed out that the ratio of the cross-sectional area of ​​the film to the optical fiber will directly affect the sensitivity and time response of the sensor. The sensitivity increases with the increase of the ratio, but the response time decreases with the increase of the film thickness. In order to obtain a fast-response optical fiber hydrogen sensor, the thickness of the film layer in this embodiment is selected as 30 nm. In order to increase the sensitivity while ensuring the mechanical strength, the diameter of the corroded optical fiber is 50 μm.
[0035]See attachedfigure 2 , A fiber grating hydrogen sensor based on amorphous palladium-based alloy (the second grating is Bragg grating), composed of light source (5), sensing fiber (6), coupler (7), measuring gas chamber (8), and transmission Sensor system (9), signal detection system (12), pigtail (13), computer (14), cable (15). Among them, the sensing system (9) placed in the measuring gas chamber (8) consists of a hydrogen sensitive probe and a temperature probe. The structure of the hydrogen sensitive probe is shown in the attached file.figure 1 As shown, the type of the second grating (11) in the hydrogen sensitive probe is a Bragg grating, and the type of the first grating (10) in the temperature probe is also a Bragg grating, but the center wavelengths of the two gratings are separated by 5 nm. When the light emitted by the light source (5) enters the sensing system (9), if the temperature or hydrogen concentration in the measuring gas chamber (8) changes, the change in the reflection spectrum obtained by the monitoring signal detection system (12) And calculate with formula 1 and 2, can get temperature and hydrogen concentration data. The end face of the pigtail (13) is polished or coated with a refractive index matching gel to avoid Fresnel reflection. A cable (15) is used to connect the signal detection system (12) and the computer (14) to realize the analysis, processing and display of the data. The temperature compensation mechanism provided by the present invention not only solves the cross-sensitivity problem of the temperature of the fiber grating sensor to the hydrogen concentration measurement, but also realizes the simultaneous monitoring of the temperature and the hydrogen concentration.

Example Embodiment

[0036]Example 2
[0037]In addition to etching or using ultra-fine Bragg gratings to improve the sensitivity of fiber gratings, the strategy of using long-period gratings instead of Bragg gratings has also received widespread attention. Because the long-period grating wavelength changes not only due to strain, but also due to changes in the refractive index of the cladding and coating. And if the coating thickness is small enough, the effect of strain on the wavelength shift can be ignored. Therefore, in this example, the second grating type is chosen to be long-period grating. Moreover, because LPG itself has a higher sensitivity than FBG, the thickness of the Pd-Cu-Si thin layer in this embodiment is selected as 15 nm to obtain a shorter response and recovery time. Except for the above two parameters, the preparation method of the sensing system (9) is the same as that of Example 1.
[0038]However, because LPG is the coupling between the core fundamental mode and the cladding mode transmitted in the same direction, there is no reverse transmission. Therefore, when the second grating is a long-period grating, the fiber grating hydrogen sensor structure of the present invention is shown in the appendix.image 3. With attachedfigure 2 Compared with the sensor structure shown, the second grating type is changed from Bragg grating to long period grating (11), and the coupler (7) and pigtail (13) are removed, and the transmission obtained by the monitoring signal detection system (12) The change of the spectrum is calculated using formulas 1 and 2, and the temperature and hydrogen concentration data can be obtained.
[0039]Further, the selection of sensor structure during the implementation of the present invention (attachedfigure 2 Or withimage 3) Is determined by the selection type of the second grating. The type of grating (ie, the first grating) used by the temperature probe can be Bragg grating or long period grating. FBG has lower production cost and higher reusability, while LPG has a larger temperature coefficient.

PUM

PropertyMeasurementUnit
Thickness1.0 ~ 80.0µm
Thickness0.0 ~ 20.0µm
Thickness0.0 ~ 100.0nm

Description & Claims & Application Information

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