Optical fiber hydrogen sensor with D-shaped cross section

Abstract

The invention discloses a hydrogen sensor based on a fiber bragg grating. An optical fiber core part of a sensing optical fiber is a circular cross section and is divided into two half parts, a first Bragg grating and a second Bragg grating with different grating periods are respectively engraved, an optical fiber cladding is D-shaped, and a hydrogen-sensitive coating is arranged on a flat peripheral surface. The inner diameter of the capillary tube is 0.8-1.2 mm, the outer diameter of the capillary tube is 4-6mm, the side wall of the capillary tube is provided with a hydrogen inlet / outlet through hole, and the sensing optical fiber is fixed on the inner wall of the capillary tube and is The sensor inner shell is provided with a first hydrogen inlet and a first hydrogen outlet, and a filter screen is arranged at the inlet and forms a hydrogen inlet and outlet channel together with the sensor outer shell. The sensor utilizes the hydrogen-sensitive coating to adsorb hydrogen and expand, so that the optical fiber core part is strained, and the central wavelength of reflected light of the Bragg grating shifts to detect the hydrogen concentration. The sensor has the advantages of strong electromagnetic interference resistance, high sensitivity, good stability, fast response and the like, and can be widely applied to concentration monitoring of hydrogen related production, storage, transportation and other scenes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogen sensing, and particularly relates to a D-shaped cross-section optical fiber hydrogen sensor. BACKGROUND

[0002] Hydrogen, as a clean energy carrier with great potential and an important chemical raw material, is increasingly widely used in many fields such as energy and chemical industry. However, hydrogen is flammable and explosive, and once its concentration in air exceeds 4% (volume fraction), a combustible mixture can be formed, which can easily cause explosion accidents when encountering a fire source. Therefore, it is crucial to accurately and reliably detect the hydrogen concentration during the production, storage, transportation and use of hydrogen.

[0003] Traditional hydrogen detection methods mainly include electrochemical detection and semiconductor detection. Although electrochemical hydrogen sensors have certain sensitivity, they are susceptible to environmental temperature, humidity and other factors, and the electrodes are easily contaminated or corroded, resulting in a short service life of the sensor and the need for frequent calibration and maintenance. Semiconductor hydrogen sensors perform poorly in stability, and their sensing performance is easily affected by gas impurities, light and other factors, and the accuracy is not ideal when detecting low-concentration hydrogen.

[0004] With the continuous development of optical fiber sensing technology, optical fiber sensors have gradually emerged in the field of gas sensing due to their unique advantages. Optical fiber sensors have many advantages such as strong anti-electromagnetic interference ability, small size, light weight, corrosion resistance, and the ability to realize distributed sensing. In particular, optical fiber grating sensors can convert changes in external physical quantities into changes in optical wavelength through the modulation of Bragg gratings on light signals, and have high sensitivity and accuracy, showing great application potential in hydrogen detection. However, existing hydrogen sensors based on optical fiber gratings still have some room for improvement, such as the need to improve the interaction efficiency between the hydrogen-sensitive coating and the optical fiber grating, and the need to further optimize the overall structure design of the sensor to enhance stability and response speed.

[0005] INVENTION CONTENTS

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the invention to avoid obscuring the purpose of this section, the abstract of the specification and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the patent aims to overcome the deficiencies in the prior art and provide a hydrogen sensor based on fiber Bragg grating, which is characterized by comprising a sensing fiber, a capillary, a sensor inner shell, a filter screen and a sensor outer shell.

[0009] The sensing fiber comprises a fiber core, a fiber cladding, first and second Bragg gratings and a hydrogen-sensitive coating.

[0010] The fiber core has a circular cross-section and is made of quartz and is divided into a first half and a second half along the axial direction.

[0011] The first and second Bragg gratings B1 and B2 are respectively etched in the first and second halves, have different grating periods, the same axial length and a specific spacing.

[0012] The fiber cladding surrounds the fiber core and has a D-shaped cross-section, comprising an arc-shaped outer peripheral surface and a flat outer peripheral surface.

[0013] The hydrogen-sensitive coating is arranged on the flat outer peripheral surface and is made of palladium or palladium alloy.

[0014] The capillary has a specific inner diameter and outer diameter, a hydrogen inlet and outlet hole in the side wall, and the sensing fiber is fixed to the inner wall.

[0015] The inner cavity of the sensor inner shell is a hydrogen measurement cavity, which has a first hydrogen inlet and a first hydrogen outlet, and the filter screen is installed at the first hydrogen inlet.

[0016] The sensor outer shell has a second hydrogen inlet and a second hydrogen outlet, and together with the sensor inner shell forms a hydrogen inlet and outlet channel.

[0017] The filter screen comprises a stainless steel screen, a particle filter layer, filter cotton and an ePTFE hydrophobic and air-permeable layer.

[0018] The D-shaped cross-section fiber hydrogen sensor has the following beneficial effects: in terms of sensitivity, the special D-shaped fiber cladding cooperates with the Bragg grating, the hydrogen-sensitive coating is close to the grating, and when hydrogen acts, the central wavelength of the grating reflected light can produce more obvious shift, accurately capturing low concentration hydrogen changes, greatly improving the detection sensitivity. In terms of structure, the sensor inner and outer shells and the carefully designed hydrogen inlet and outlet channel and impurity filtering system effectively block water and particulate impurities, protect the hydrogen-sensitive coating and the fiber, enhance the stability and reliability, and prolong the service life. Moreover, the application of double different grating period Bragg gratings, combined with unique optical design and signal processing, can realize accurate measurement and precise quantitative analysis of hydrogen concentration, significantly improve the measurement accuracy and resolution, and show excellent performance and application potential in the field of hydrogen detection. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the structures shown in these drawings without creative labor.

[0020] Figure 1 A schematic cross-sectional structure diagram of a D-shaped cross-section optical fiber hydrogen sensor is provided for the present application.

[0021] Figure 2 A shell structure diagram is provided for the application.

[0022] The purpose of the present application, functional features and advantages will be further described with reference to the embodiments and drawings. DETAILED DESCRIPTION

[0023] The technical solutions in the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and not to limit the present application.

[0024] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail in the following with reference to the embodiments of the present application.

[0025] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0026] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or mutually exclusive of other embodiments.

[0027] As a preferred scheme of the present application, the present application provides a D-shaped cross-section optical fiber hydrogen sensor, which comprises: the present application comprises the following components: a sensing optical fiber 1, an optical fiber core 101, an optical fiber cladding 102, a first Bragg grating B1, a second Bragg grating B2, a hydrogen-sensitive coating 105, a capillary 2, a sensor inner shell 3, a first hydrogen inlet 31, a first hydrogen outlet 32, a filter screen 4, a sensor outer shell 5, a second hydrogen inlet 51, and a second hydrogen outlet 52.

[0028] As a preferred solution of the present application, the optical fiber core 101: adopts a circular cross-section optical fiber core, and the material can be quartz or other materials with good optical performance and stability. The diameter of the optical fiber core can be selected according to actual needs, such as the common 9μm (core diameter) and 125μm (cladding diameter) specifications, and special sizes can also be customized according to specific requirements in some application scenarios.

[0029] As a preferred solution of the present application, the first half 103 and the second half 104: along the axial direction of the optical fiber core 101, it is divided into two symmetrical parts by a virtual plane, namely the first half 103 and the second half 104. The two halves are structurally and functionally related and symmetrical, and together constitute the key area of the optical fiber core for sensing.

[0030] As a preferred solution of the present application, the first Bragg grating B1 and the second Bragg grating B2: respectively in the first half 103 and the second half 104, etching a first Bragg grating B1 and a second Bragg grating B2 with different grating periods. The grating period can be determined according to the specific optical design and hydrogen detection requirements, for example, the grating period of the first Bragg grating B1 is Λ1, and the grating period of the second Bragg grating B2 is Λ2 (Λ1≠Λ2). The axial length of the grating can be set to be the same, for example, both are 4mm-6mm (preferably 5mm), and the distance between the two gratings is 15mm-25mm (preferably 20mm).

[0031] As a preferred solution of the present application, the optical fiber cladding 102: The optical fiber cladding surrounds the optical fiber core 101 and provides protection and optical isolation for the optical fiber core. Its material can be matched with the optical fiber core to ensure good optical coupling and signal transmission. The thickness of the optical fiber cladding can be designed according to the overall size and performance requirements of the optical fiber, generally between several tens of microns to several hundred microns.

[0032] As a preferred solution of the present application, the arc-shaped outer peripheral surface 102a and the flat outer peripheral surface 102b: The optical fiber cladding has a generally D-shaped cross-section, including the arc-shaped outer peripheral surface 102a and the flat outer peripheral surface 102b. The arc-shaped outer peripheral surface 102a is coaxial with the optical fiber core 101, and the flat outer peripheral surface 102b is used to apply the hydrogen-sensitive coating 105. This special cross-sectional design allows the hydrogen-sensitive coating 105 to be closer to the Bragg grating in the optical fiber core, thereby improving the sensitivity of the sensor.

[0033] As a preferred solution of the present application, the hydrogen-sensitive coating 105: hydrogen-sensitive coating 105 is arranged on the flat outer peripheral surface 102b of the optical fiber cladding 102, and the material thereof can be selected from materials such as palladium (Pd) or palladium alloy, which have good adsorption and expansion characteristics for hydrogen. The thickness of the hydrogen-sensitive coating 105 can be determined according to specific sensitivity requirements and process conditions, and is generally between tens of nanometers and hundreds of nanometers, for example, 50 nm. When the hydrogen-sensitive coating 105 absorbs hydrogen, it will expand radially and axially, thereby causing the optical fiber core 101 to produce strain, which in turn causes the center wavelength of the reflected light of the Bragg grating to shift.

[0034] As a preferred solution of the present application, the sensor inner shell 3: for mounting and protecting the capillary 2, and the inner cavity thereof serves as a hydrogen measurement cavity. The sensor inner shell 3 is provided with a first hydrogen inlet 31 and a first hydrogen outlet 32 at positions corresponding to the hydrogen inlet and outlet holes 21, respectively, and a filter screen 4 is mounted at the first hydrogen inlet 31 for filtering impurities in the hydrogen, and a filter screen can also be provided at the first hydrogen outlet 32. The sensor inner shell 3 can include a cavity 301 and a partition plate 302, which connects the outer wall of the cavity 301 and the inner wall of the sensor outer shell 5, and divides the space between the cavity 301 and the sensor outer shell 5 into two parts.

[0035] As a preferred solution of the present application, the sensor outer shell 5: for packaging and protecting the entire sensor assembly, and the sensor outer shell 5 is provided with a second hydrogen inlet 51 and a second hydrogen outlet 52, which together with the sensor inner shell 3 form a hydrogen inlet and outlet channel.

[0036] As a preferred solution of the present application, the filter screen 4: is mounted at the first hydrogen inlet 31 (and optionally at the first hydrogen outlet 32), and the filter screen 4 includes, in sequence along the flow direction of the hydrogen, a layer of stainless steel screen, a layer of particulate filter layer, a layer of filter cotton, and a layer of ePTFE hydrophobic and air-permeable layer, for filtering water vapor and particles in the hydrogen, and improving measurement accuracy.

[0037] As a preferred solution of the present application, the capillary 2: if a hydrogen sensing mechanism based on fiber grating is used in combination with the capillary structure, a capillary 2 with an inner diameter of 0.8mm-1.2mm (preferably 1mm) and an outer diameter of 4mm-6mm (preferably 5mm) can be selected, and the side wall thereof is provided with hydrogen inlet and outlet holes 21. The core of the sensing optical fiber 1 is formed into a first fiber grating 11 and a second fiber grating 12 by etching, and is fixed to the inner wall of the capillary 2, and the sensing optical fiber 1 is coated with a palladium layer at a portion corresponding to the second fiber grating 12. The open end of the capillary 2 abuts against the inner wall of the sensor inner shell 3, and hydrogen can only enter and exit the capillary 2 from the hydrogen inlet and outlet holes 21.

[0038] It should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A fiber grating based hydrogen sensor, characterized in that, The application relates to a hydrogen sensor, which comprises the following components: a sensing optical fiber (1) having: an optical fiber core (101) with a circular cross section, made of quartz material, divided into a first half (103) and a second half (104) by a virtual plane in the axial direction; a first Bragg grating (B1) etched in the first half (103) and having a specific grating period Lambda 1; a second Bragg grating (B2) etched in the second half (104) and having a grating period Lambda 2 different from Lambda 1, and the axial length of the first Bragg grating (B1) and the second Bragg grating (B2) is between 4 mm and 6 mm and preferably 5 mm, and the distance between the two is between 15 mm and 25 mm and preferably 20 mm; an optical fiber cladding (102) surrounding the optical fiber core (101) and having a substantially D-shaped cross section, comprising an arc-shaped outer peripheral surface (102a) coaxial with the optical fiber core (101) and a flat outer peripheral surface (102b), and a hydrogen-sensitive coating (105) is arranged on the flat outer peripheral surface (102b), the hydrogen-sensitive coating (105) is made of palladium or palladium alloy material and has a thickness of tens of nanometers to hundreds of nanometers and preferably 50 nm; a capillary tube (2) with an inner diameter of 0.8 mm to 1.2 mm and preferably 1 mm and an outer diameter of 4 mm to 6 mm and preferably 5 mm, and the side wall is provided with hydrogen inlet and outlet through holes (21), the fiber core of the sensing optical fiber (1) is fixed on the inner wall of the capillary tube (2) by etching to form a first fiber grating (11) and a second fiber grating (12), and the sensing optical fiber (1) is coated with a palladium layer at the part corresponding to the second fiber grating (12), and the open end of the capillary tube (2) abuts against the inner wall of the sensor inner shell (3), and hydrogen can only enter and exit the capillary tube (2) from the hydrogen inlet and outlet through holes (21); a sensor inner shell (3) with an inner cavity serving as a hydrogen measurement cavity, and a first hydrogen inlet (31) and a first hydrogen outlet (32) are arranged at positions corresponding to the hydrogen inlet and outlet through holes (21), respectively, and a filter screen (4) is arranged at the first hydrogen inlet (31); the filter screen (4) is arranged at the first hydrogen inlet (31) and sequentially comprises a layer of stainless steel screen, a layer of particle filter layer, a layer of filter cotton and a layer of ePTFE hydrophobic and air-permeable layer along the flow direction of hydrogen; a sensor outer shell (5) for packaging and protecting the whole sensor assembly, and a second hydrogen inlet (51) and a second hydrogen outlet (52) are arranged on the sensor outer shell (5) to form a hydrogen inlet and outlet channel together with the sensor inner shell (3).

2. The fiber-optic grating-based hydrogen sensor of claim 1, wherein, The diameter specification of the optical fiber core (101) includes common 9 mu m fiber core diameter and 125 mu m cladding diameter, or special sizes customized according to specific requirements.

3. The fiber-optic grating-based hydrogen sensor of claim 1, wherein, The thickness of the optical fiber cladding (102) is designed according to the overall size and performance requirements of the optical fiber, and ranges from tens of microns to hundreds of microns.

4. The fiber-optic grating-based hydrogen sensor of claim 1, wherein, A filter screen (4) can be optionally arranged at the first hydrogen outlet (32).

5. The fiber-optic grating-based hydrogen sensor of claim 1, wherein, The sensor inner shell (3) comprises a cavity (301) and a partition plate (302) connecting the outer wall of the cavity (301) and the inner wall of the sensor outer shell (5) to divide the space between the cavity (301) and the sensor outer shell (5) into two parts.

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