Hydrogen sensor, hydrogen detection system, related method and aircraft

Abstract

The invention relates to a hydrogen sensor, a hydrogen detection system comprising the hydrogen sensor, a method for measuring hydrogen concentration and an aircraft. The hydrogen sensor comprises an optical fiber core part, an optical fiber cladding surrounding the optical fiber core part and a hydrogen-sensitive coating arranged on one side of the optical fiber cladding, and the hydrogen-sensitive coating is constructed to be capable of absorbing hydrogen to expand. The optical fiber core part comprises a first half part and a second half part which are divided by a virtual plane extending in the axial direction of the optical fiber core part, and a first Bragg grating and a second Bragg grating with different grating periods are etched in the first half part and the second half part respectively. The optical fiber cladding includes an arcuate outer peripheral surface and a flat outer peripheral surface connected to each other such that the optical fiber cladding has a substantially D-shaped cross-section, and the hydrogen sensitive coating is applied on the flat outer peripheral surface. According to the hydrogen sensor, the hydrogen concentration and temperature at the same spatial position can be measured at the same time, and high sensitivity and reliability are achieved.

Description

Technical Field

[0001] The present disclosure relates to a hydrogen sensor, a detection system and related methods for detecting hydrogen leakage, and also relates to an aircraft including such a detection system. Background Art

[0002] The content of this section only provides background information related to the present disclosure, which may not constitute the prior art.

[0003] Hydrogen is a clean energy source with wide sources, high calorific value and no carbon emissions, and is one of the most promising clean energy sources at present. In particular, hydrogen may at least partially replace existing fossil fuels as the energy source for future aircraft. For example, hydrogen may be directly burned as fuel or made into a fuel cell to supply energy to the aircraft. Such a use of hydrogen raises many specific design considerations. Hydrogen is combustible, has a relatively small molecular weight compared to other fuels, and is colorless and odorless. Therefore, special attention needs to be paid to how to store hydrogen sufficiently without leakage and make any leakage detectable. At normal temperature and pressure, combustion may occur when the hydrogen content in the air is between 4.0% and 75%. Therefore, it is necessary to develop hydrogen sensors with appropriate sensitivity and reliability to quickly and accurately detect hydrogen leakage.

[0004] Optical fiber sensors have the advantages of small size, light weight, low power consumption, corrosion resistance, electromagnetic interference resistance, and suitability for long-distance signal transmission, and can work normally in various complex environments, meeting the technical requirements of hydrogen sensors. Currently, there are hydrogen sensors including fiber Bragg gratings. When light passes through a fiber Bragg grating, the light near a specific central wavelength will be reflected by the grating. The central wavelength of the reflected light is related to the grating period and will shift due to the grating strain and temperature. Such hydrogen sensors may include a hydrogen-sensitive coating coated on the fiber Bragg grating. The hydrogen-sensitive coating absorbs hydrogen and expands, causing strain in the grating. Therefore, the hydrogen concentration can be established as a function of the strain of the grating. Thus, the strain of the grating can be detected by measuring the shift of the central wavelength of the reflected light, and then the hydrogen concentration can be obtained. However, since both the grating strain and temperature will affect the shift of the central wavelength of the reflected light, it is necessary to separate variables to exclude the interference of temperature changes when measuring the grating strain. One current solution is to set two fiber Bragg grating sensors in series or parallel as a control group. However, it is impossible to ensure that two independent gratings at different spatial positions have exactly the same strain or temperature. Therefore, the accuracy of this hydrogen detection solution is relatively low, especially unable to adapt to applications with extremely high safety standards such as aircraft. In addition, setting multiple fiber Bragg grating sensors in series or parallel at different spatial positions requires a large installation space, increasing the complexity and cost of the hydrogen detection system. Summary of the Invention

[0005] One object of the present disclosure is to provide a hydrogen detection solution with high sensitivity and high reliability. Another object of the present disclosure is to eliminate the influence of the cross-sensitivity of the fiber Bragg grating type hydrogen sensor to strain and temperature on the accuracy of hydrogen detection. Still another object of the present disclosure is to provide a hydrogen detection solution with a simple structure and low cost.

[0006] The first aspect of the present disclosure provides a hydrogen sensor, which includes an optical fiber core, an optical fiber cladding surrounding the optical fiber core, and a hydrogen-sensitive coating provided on one side of the optical fiber cladding. The hydrogen-sensitive coating is configured to be able to absorb hydrogen and expand. The optical fiber core includes a first half and a second half divided by a virtual plane extending along the axial direction of the optical fiber core. A first Bragg grating and a second Bragg grating with different grating periods are respectively etched in the first half and the second half. The optical fiber cladding includes an arc-shaped outer peripheral surface and a flat outer peripheral surface connected to each other, so that the optical fiber cladding has a substantially D-shaped cross section, and the hydrogen-sensitive coating is applied on the flat outer peripheral surface.

[0007] In some embodiments, the distance from the hydrogen-sensitive coating to the central axis of the optical fiber core may be less than the distance from any point on the arc-shaped outer peripheral surface of the optical fiber cladding to the central axis of the optical fiber core.

[0008] In some embodiments, the optical fiber core and the optical fiber cladding may be configured to bend along the central axis of the optical fiber core, and the hydrogen-sensitive coating is provided on the side where the optical fiber cladding protrudes radially outward.

[0009] In some embodiments, the first half and the second half may be symmetric about the central axis of the optical fiber core.

[0010] In some embodiments, the optical fiber core may have a circular cross section, and the first half and the second half may be configured as two semi-circular parts divided along the diameter direction of the optical fiber core.

[0011] In some embodiments, the interface between the first Bragg grating and the second Bragg grating may be perpendicular to the hydrogen-sensitive coating.

[0012] In some embodiments, the hydrogen-sensitive coating may include palladium or a palladium alloy.

[0013] In some embodiments, the axial length of the first Bragg grating may be the same as the axial length of the second Bragg grating.

[0014] The second aspect of the present disclosure provides a hydrogen detection system including the hydrogen sensor of the first aspect.

[0015] In some embodiments, the hydrogen detection system may further include a light source, an optical circulator, a signal processing device, and a pigtail fiber. The light source is connected to the first port of the optical circulator via a first transmission fiber. The second port of the optical circulator is connected to one end of the hydrogen sensor via a second transmission fiber. The opposite end of the hydrogen sensor is connected to the pigtail fiber via a third transmission fiber. The third port of the optical circulator is connected to the signal processing device via a fourth transmission fiber.

[0016] In some embodiments, the signal processing device may include a demodulator configured to convert an optical signal into an electrical signal.

[0017] In some embodiments, the hydrogen detection system may further include a display device connected to the signal processing device for displaying the detection result.

[0018] A third aspect of the present disclosure provides a method for measuring hydrogen concentration. The method includes: setting a hydrogen sensor according to the first aspect above at a position to be measured; passing the light emitted by the light source through the hydrogen sensor; receiving a first optical signal reflected by a first Bragg grating and a second optical signal reflected by a second Bragg grating; measuring an offset amount Δλ of the central wavelength of the first optical signal relative to a predetermined initial reflected light central wavelength of the first Bragg grating 1 and an offset amount Δλ of the central wavelength of the second optical signal relative to a predetermined initial reflected light central wavelength of the second Bragg grating 2 ; based on the offset amount Δλ of the central wavelength of the first optical signal 1 and the offset amount Δλ of the central wavelength of the second optical signal 2 calculate a common strain change amount Δε of the first Bragg grating and the second Bragg grating; and calculate the hydrogen concentration at the position to be measured based on the strain change amount Δε.

[0019] In some embodiments, the strain change amount Δε can be calculated by the following formula:

[0020]

[0021] where K ε1 is the strain coefficient of the first Bragg grating, K ε2 is the strain coefficient of the second Bragg grating, K T1 is the temperature coefficient of the first Bragg grating, K T2 is the temperature coefficient of the second Bragg grating.

[0022] In some embodiments, the method may further include based on the offset amount Δλ of the central wavelength of the first optical signal 1 and the offset amount Δλ of the central wavelength of the second optical signal 2Calculate the common temperature change ΔT of the first Bragg grating and the second Bragg grating. The temperature change ΔT can be calculated by the following formula:

[0023]

[0024] where K ε1 is the strain coefficient of the first Bragg grating, K ε2 is the strain coefficient of the second Bragg grating, K T1 is the temperature coefficient of the first Bragg grating, K T2 is the temperature coefficient of the second Bragg grating.

[0025] In some embodiments, the method may further include calibrating the hydrogen concentration as a function of the common strain of the first Bragg grating and the second Bragg grating.

[0026] The fourth aspect of the present disclosure provides an aircraft including the hydrogen detection system according to the second aspect.

[0027] In various embodiments of the present disclosure, two Bragg gratings with different grating periods are etched into the same section of optical fiber, whereby two optical signals can be reflected simultaneously, so that the hydrogen concentration and temperature at the same spatial position can be measured simultaneously based on these two optical signals, improving the sensitivity and reliability of the sensor. In addition, the hydrogen sensor according to the present disclosure is constructed of an optical fiber having a substantially D-shaped cross section, and the hydrogen-sensitive coating is applied at the flat surface of the substantially D-shaped optical fiber, whereby the hydrogen-sensitive coating can be made closer to the two Bragg gratings in the optical fiber core, thus effectively improving the sensitivity of the hydrogen sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The embodiments of the present disclosure will be described hereinafter only by way of example with reference to the drawings. In the drawings, the same features or components are denoted by the same reference numerals, and the drawings are not necessarily drawn to scale. In the drawings:

[0029] Figure 1 shows a schematic longitudinal sectional view taken along the central axis of a hydrogen sensor according to an embodiment of the present disclosure;

[0030] Figure 2 shows a cross-sectional view taken along a direction perpendicular to the central axis of a hydrogen sensor according to an embodiment of the present disclosure;

[0031] Figure 3 shows a schematic diagram of a hydrogen sensor according to another embodiment of the present disclosure;

[0032] Figure 4 shows a schematic diagram of a hydrogen detection system according to an embodiment of the present disclosure; and

[0033] Figure 5 FIG. 1 shows a schematic view of an aircraft according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, and uses. It should be understood that in all these figures, like reference numerals indicate the same or similar parts and features. Each figure schematically shows the concept and principle of the embodiment of the present disclosure, and does not necessarily show the specific dimensions and their ratios of each embodiment of the present disclosure. Specific parts in a specific figure may be exaggerated to illustrate relevant details or structures of the embodiment of the present disclosure.

[0035] In the description of the embodiments of the present disclosure, the orientation terms related to "upper", "lower", etc. are described based on the upper and lower positions of the views shown in the drawings. In actual applications, the "upper", "lower", etc. position relationships used herein can be defined according to the actual situation, and these relationships can be reversed with each other and are not intended to limit the scope of the present disclosure.

[0036] Figure 1 FIG. 2 shows a schematic longitudinal sectional view taken along the central axis of a hydrogen sensor 10 according to an embodiment of the present disclosure. Figure 2 FIG. 3 shows a cross-sectional view taken along a direction perpendicular to the central axis of the hydrogen sensor 10 according to an embodiment of the present disclosure.

[0037] As Figure 1 and Figure 2 shown, the hydrogen sensor 10 is constructed of a section of optical fiber, including an optical fiber core 101 and an optical fiber cladding 102 surrounding the optical fiber core 101. The optical fiber core 101 may include a first half 103 and a second half 104 divided by a virtual plane extending along its axial direction. Preferably, the first half 103 and the second half 104 are symmetric about the central axis of the optical fiber core 101. In this embodiment, the optical fiber core 101 has a circular cross-section, so the first half 103 and the second half 104 are configured as two semi-circular portions divided along the diameter direction of the optical fiber core 101. In other embodiments, an optical fiber core with a non-circular cross-section may also be used. As Figure 2 best shown, the optical fiber cladding 102 includes an arc-shaped outer peripheral surface 102a and a flat outer peripheral surface 102b connected to each other. Thus, the optical fiber cladding 102 has a generally D-shaped asymmetric cross-section. The arc-shaped outer peripheral surface 102a of the optical fiber cladding 102 may be coaxial with the circular optical fiber core 101. A first Bragg grating B1 and a second Bragg grating B2 are respectively etched in the first half 103 and the second half 104. The first Bragg grating B1 has a first grating period Λ 1, the second Bragg grating 103 has a second grating period Λ different from the first grating period Λ 1 of the second grating period Λ 2 . The axial length of the first Bragg grating B1 can be substantially the same as the axial length of the second Bragg grating B2. The hydrogen sensor 10 further includes a hydrogen-sensitive coating 105. As Figure 1 and Figure 2 shown, the hydrogen-sensitive coating 105 is disposed on the flat outer peripheral surface 102b of the optical fiber cladding 102. The hydrogen-sensitive coating 105 is configured to absorb hydrogen and expand, causing axial and radial deformations of the optical fiber cladding 102 and the optical fiber core 101, thereby generating strain in the first Bragg grating B1 and the second Bragg grating B2. The hydrogen-sensitive coating 105 may include, for example, a thin film made of palladium (Pd) or a palladium alloy. Figure 1 and Figure 2 show two different arrangements of the hydrogen-sensitive coating 105 relative to the first Bragg grating B1 and the second Bragg grating B2. Preferably, as Figure 2 shown, the flat outer peripheral surface 102b of the optical fiber cladding 102 and the hydrogen-sensitive coating 105 thereon can be arranged perpendicular to the interface 106 between the first Bragg grating B1 and the second Bragg grating B2. Thus, the influence of the deformation of the hydrogen-sensitive coating 105 on the first Bragg grating B1 and the second Bragg grating B2 can be made more uniform. However, the hydrogen-sensitive coating 105 can also be arranged closer to either the first Bragg grating B1 or the second Bragg grating B2. In other words, the hydrogen-sensitive coating 105 can be at any angle relative to the interface 106 between the first Bragg grating B1 and the second Bragg grating B2, and can even be parallel to the interface 106 as Figure 1 shown. Regardless of how the hydrogen-sensitive coating 105 is arranged relative to the first Bragg grating B1 and the second Bragg grating B2, reliable detection performance can be obtained after calibrating the hydrogen sensor 10.

[0038] Compared with a configuration in which the optical fiber cladding has a circular cross-section and the hydrogen-sensitive coating is uniformly distributed on the radial outer side of the optical fiber cladding, the optical fiber cladding 102 with a substantially D-shaped cross-section in the present disclosure allows the hydrogen-sensitive coating 105 to be closer to the optical fiber core 101, and thus closer to the first Bragg grating B1 and the second Bragg grating B2. In particular, the hydrogen-sensitive coating 105 can be arranged such that the distance from the hydrogen-sensitive coating 105 to the central axis of the optical fiber core 101 is less than the distance from any point on the arcuate outer peripheral surface 102a of the optical fiber cladding 102 to the central axis of the optical fiber core 101. The closer the hydrogen-sensitive coating 105 is to the first Bragg grating B1 and the second Bragg grating B2, the greater the strain that the deformation of the hydrogen-sensitive coating 105 can cause in the first Bragg grating B1 and the second Bragg grating B2 at the same hydrogen concentration, and the higher the sensitivity of the hydrogen sensor 10.

[0039] When manufacturing the hydrogen sensor 10, a part of the material of the optical fiber cladding 102 with a circular cross-section can be removed (for example, by chemical etching or machining) to form a flat outer peripheral surface 102b. This step can be carried out before or after the step of etching the Bragg grating. When etching the Bragg grating, the second half 104 of the optical fiber core 101 can be masked first, and the first Bragg grating B1 can be laser-etched in the first half 103, then the etched first half 103 can be masked and the second Bragg grating B2 can be laser-etched in the second half 104. Alternatively, the first Bragg grating B1 and the second Bragg grating B2 with high consistency and stability can also be etched by a single exposure by making the laser pass through a two-dimensional spatial phase mask with a double periodic structure. After etching the first Bragg grating B1 and the second Bragg grating B2, a hydrogen-sensitive coating 105 can be applied on the flat outer peripheral surface 102b of the optical fiber cladding 102.

[0040] Figure 3 FIG. shows a schematic diagram of a hydrogen sensor 10' according to another embodiment of the present disclosure, in which the technical features that are the same or similar to those in the foregoing embodiment are denoted by the same reference numerals with an apostrophe. The optical fiber core 101' and the optical fiber cladding 102' of the hydrogen sensor 10' are arranged to be bent along the central axis, the flat outer peripheral surface 102b' of the optical fiber cladding 102' is arranged on the radially outward protruding side of the optical fiber cladding 102', and the hydrogen-sensitive coating 105' is applied on the flat outer peripheral surface 102b'. Thus, the hydrogen-sensitive coating 105' can be arranged closer to the first Bragg grating B1' and the second Bragg grating B2', thereby further improving the sensitivity of the hydrogen sensor. Other aspects of this embodiment may be the same as or similar to those of the hydrogen sensor 10 described above, and will not be elaborated here.

[0041] Figure 4 FIG. shows a schematic diagram of a hydrogen detection system 1 according to an embodiment of the present disclosure. Figure 4Schematically shown is that the hydrogen detection system 1 includes the aforementioned hydrogen sensor 10. It should be understood that the hydrogen sensor 10 can also be replaced by a hydrogen sensor 10'. The hydrogen detection system 1 may further include a light source 20, an optical circulator 30, a signal processing device 40, and a pigtail 50. The hydrogen sensor 10 is arranged at the position to be measured, for example, it can be arranged in a closed or semi-closed gas chamber 60. The arrangement of the gas chamber 60 can prevent dust and the like from affecting the sensing accuracy of the hydrogen sensor. The light source 20 can be configured as a broadband laser source (BBS). An optical circulator is a multi-port optical device with non-reciprocal characteristics. In this embodiment, the optical circulator 30 has three ports. When an optical signal is input from any port, the optical signal will output from the next port with very little loss, that is, the optical signal input from the first port 301 of the optical circulator 30 can only output from the second port 302, and the optical signal input from the second port 302 can only output from the third port 303, and so on. The light source 20 is connected to the first port 301 of the optical circulator 30 via a first transmission optical fiber 701. One end of the hydrogen sensor 10 is connected to the second port 302 of the optical circulator 30 via a second transmission optical fiber 702, and the opposite end of the hydrogen sensor 10 is connected to the pigtail 50 via a third transmission optical fiber 703. The signal processing device 40 is connected to the third port 303 of the optical circulator 30 via a fourth transmission optical fiber 704. The signal processing device 40 is configured to receive the optical signal output from the third port 303 and calculate the hydrogen concentration accordingly. The signal processing device 40 may include, for example, a demodulator configured to convert the optical signal into an electrical signal. The hydrogen sensor 10 may further include a display device 80 for displaying the detection result, and the display device may be connected to the signal processing device 40. The display device 80 can display data such as the center wavelength of the reflected light, temperature, hydrogen concentration, etc.

[0042] The principle of using the hydrogen detection system 1 to measure the hydrogen concentration will be specifically described below. The hydrogen sensor 10 includes two Bragg gratings with different grating periods. A Bragg grating is a narrowband filter with a periodic microstructure, which has a strong reflection effect only on light with a very narrow spectrum near a specific center wavelength (also known as the Bragg wavelength), and the remaining light waves will continue to propagate through the Bragg grating. The center wavelength λ of the reflected light satisfies the Bragg equation:

[0043] λ = 2nΛ

[0044] where n is the refractive index and Λ is the grating period (i.e., the distance between two adjacent grooves in the Bragg grating).

[0045] When the optical fiber with a Bragg grating is stretched or compressed, the grating period Λ of the Bragg grating will change accordingly. In addition, the sensitivity to temperature is another characteristic of the Bragg grating. On the one hand, the thermo-optic effect will cause a change in the refractive index n. On the other hand, the thermal expansion of the grating will cause a change in the grating period Λ. Since the refractive index n and the grating period Λ are affected by the grating strain and the ambient temperature around the grating, the central wavelength of the reflected light reflected by the Bragg grating will also change with the changes in strain and temperature. Therefore, the change in the corresponding physical quantity of the part to be measured can be determined according to the offset of the central wavelength of the reflected light relative to the predetermined initial central wavelength of the reflected light. For example, the central wavelength of the reflected light at a temperature of 0 °C and a grating strain of 0 can be used as the initial central wavelength of the reflected light. The offset Δλ of the central wavelength of the reflected light can be calculated by Equation (1):

[0046] Δλ = K ε *Δε + K T *ΔT (1)

[0047] where K ε is the strain coefficient, Δε is the strain change of the Bragg grating, and K T is the temperature coefficient, and ΔT is the ambient temperature change.

[0048] The light emitted by the light source 20 is transmitted to the hydrogen sensor 10 via the first transmission optical fiber 701, the first port 301 and the second port 302 of the optical circulator 30, and the second transmission optical fiber 702. At the hydrogen sensor 10, the first Bragg grating B1 and the second Bragg grating B2 will respectively reflect the first optical signal and the second optical signal near the corresponding central wavelengths. These two reflected optical signals are output to the signal processing device 40 via the second transmission optical fiber 702 and the third port 303 of the optical circulator 30. The remaining light that is not reflected passes through the hydrogen sensor 10 and continues to be transmitted to the pigtail 50 via the third transmission optical fiber 703.

[0049] When the hydrogen-sensitive coating 105 of the hydrogen sensor 10 absorbs hydrogen, it will expand radially and axially, thereby causing strain in the optical fiber core 101 etched with the first Bragg grating B1 and the second Bragg grating B2. Therefore, the central wavelengths of the reflected lights corresponding to the first Bragg grating B1 and the second Bragg grating B2 shift relative to their initial values. Since the first Bragg grating B1 and the second Bragg grating B2 are etched in two halves of the same section of optical fiber, that is, at the same spatial point, the first Bragg grating B1 and the second Bragg grating B2 have substantially the same ambient temperature change amount ΔT, and have substantially the same strain change amount Δε when the optical fiber deforms. Then, the offset Δλ 1 of the central wavelength of the reflected light of the first Bragg grating B1 2 and the offset Δλ

[0050]

[0051] wherein, K ε1 is the strain coefficient of the first Bragg grating B1, K ε2 is the strain coefficient of the second Bragg grating B2, K T1 is the temperature coefficient of the first Bragg grating B1, K T2 is the temperature coefficient of the second Bragg grating B2. These coefficients can be determined, for example, through a calibration test.

[0052] The strain change Δε and the temperature change ΔT can be solved from Equation (2), as shown in Equations (3) and (4):

[0053]

[0054]

[0055] Based on the change amounts and initial values of the strain and temperature of the grating, the current strain ε and temperature T of the grating can be determined. Since the strain of the grating is caused by the expansion of the hydrogen-sensitive coating 105 absorbing hydrogen, the hydrogen concentration C H can be calibrated as a function of the strain ε, as shown in Equation (5):

[0056] C H = f(ε) (5)

[0057] Therefore, the hydrogen detection system 1 according to the present disclosure can separate and calculate two variables respectively, that is, the strain change Δε and the temperature change ΔT, so that the hydrogen concentration and temperature at the same spatial position can be accurately measured simultaneously, excluding the interference of the temperature factor in the process of measuring the hydrogen concentration through the shift amount of the center wavelength of the reflected light.

[0058] In an existing conventional hydrogen detection system that uses two fiber optic sensors in series or parallel as a control group, the two fiber optic sensors measure the temperature and strain at two different spatial positions. Therefore, it is impossible to completely separate the effects of temperature and strain on the offset of the central wavelength of the detected reflected light. In the hydrogen detection system 1 according to the present disclosure, the two Bragg gratings are etched in the same section of optical fiber, thus enabling the simultaneous measurement of the temperature and strain at the same spatial position, accurately eliminating the influence of temperature changes on the measurement result of hydrogen concentration, and improving the detection sensitivity and reliability. If the two Bragg gratings are symmetrically arranged with respect to the central axis in the fiber core and have substantially the same axial length, consistent strain of the two Bragg gratings can be ensured in the case of deformation of the optical fiber in any direction, which is beneficial to further improving the detection sensitivity and reliability. In addition, arranging the two Bragg gratings in the same section of optical fiber significantly simplifies the structure of the hydrogen detection system, reduces the space occupied by the hydrogen detection system, and lowers the cost. Additionally, the optical fiber with a substantially D-shaped cross-section used in the present disclosure reduces the distance between the hydrogen-sensitive coating and the two Bragg gratings, thus improving the sensitivity of the hydrogen sensor.

[0059] As Figure 5 Schematically shown, the hydrogen sensors 10, 10' according to the present disclosure or the hydrogen detection system 1 including the hydrogen sensors can be applied in the aircraft 2. The aircraft 2 can be an aircraft that directly uses hydrogen as fuel for combustion or uses a hydrogen fuel cell for power supply. The hydrogen sensor 10 can be arranged, for example, near the hydrogen storage tank or the hydrogen fuel cell (not shown) of the aircraft 2. The display device 80 of the hydrogen detection system 1 can be arranged, for example, in the cockpit 202 of the aircraft 2.

[0060] Herein, exemplary embodiments of the hydrogen sensor, hydrogen detection system, aircraft, and related methods according to the present disclosure have been described in detail. However, it should be understood that the present disclosure is not limited to the specific embodiments described and illustrated above in detail. Without departing from the gist and scope of the present disclosure, those skilled in the art can make various modifications and variations to the present disclosure. All such modifications and variations fall within the scope of the present disclosure. Moreover, all the components described herein can be replaced by other technically equivalent components.

Claims

1. A hydrogen sensor (10) includes an optical fiber core (101), an optical fiber cladding (102) surrounding the optical fiber core (101), and a hydrogen-sensitive coating (105) provided on one side of the optical fiber cladding (102). The hydrogen-sensitive coating (105) is configured to absorb hydrogen and expand. Characterized in that, The optical fiber core (101) includes a first half (103) and a second half (104) divided by a virtual plane extending in the axial direction of the optical fiber core (101). A first Bragg grating (B1) and a second Bragg grating (B2) with different grating periods are respectively etched in the first half (103) and the second half (104). The optical fiber cladding (102) includes an arc-shaped outer peripheral surface (102a) and a flat outer peripheral surface (102b) connected to each other, so that the optical fiber cladding (102) has a substantially D-shaped cross-section. The hydrogen-sensitive coating (105) is applied on the flat outer peripheral surface (102b).

2. The hydrogen sensor (10) according to claim 1, Characterized in that, The distance from the hydrogen-sensitive coating (105) to the central axis of the optical fiber core (101) is less than the distance from any point on the arc-shaped outer peripheral surface (102a) of the optical fiber cladding (102) to the central axis of the optical fiber core (101).

3. The hydrogen sensor according to claim 1, Characterized in that, The optical fiber core and the optical fiber cladding are configured to be bent along the central axis of the optical fiber core, and the hydrogen-sensitive coating is provided on the radially outward protruding side of the optical fiber cladding.

4. The hydrogen sensor (10) according to any one of claims 1 to 3, Characterized in that, The first half (103) and the second half (104) are symmetric about the central axis of the optical fiber core (101).

5. The hydrogen sensor (10) according to any one of claims 1 to 3, Characterized in that, The optical fiber core has a circular cross-section, and the first half (103) and the second half (104) are configured as two semi-circular parts divided along the diameter direction of the optical fiber core.

6. The hydrogen sensor (10) according to any one of claims 1 to 3, Characterized in that, The interface (106) between the first Bragg grating (B1) and the second Bragg grating (B2) is perpendicular to the hydrogen-sensitive coating (105).

7. The hydrogen sensor (10) according to any one of claims 1 to 3, Characterized in that, The hydrogen-sensitive coating (105) includes palladium or a palladium alloy.

8. The hydrogen sensor (10) according to any one of claims 1 to 3, Characterized in that, The axial length of the first Bragg grating (B1) and the axial length of the second Bragg grating (B2) are the same.

9. A hydrogen detection system (1), Characterized in that, The hydrogen detection system includes the hydrogen sensor (10) according to any one of claims 1 to 8.

10. The hydrogen detection system (1) according to claim 9, Characterized in that, the hydrogen detection system (1) further includes a light source (20), an optical circulator (30), a signal processing device (40) and a pigtail fiber (50), wherein, the light source (20) is connected to the first port (301) of the optical circulator (30) via a first transmission optical fiber (701), the second port (302) of the optical circulator (30) is connected to one end of the hydrogen sensor (10) via a second transmission optical fiber (702), the opposite end of the hydrogen sensor (10) is connected to the pigtail fiber (50) via a third transmission optical fiber (703), and the third port (303) of the optical circulator (30) is connected to the signal processing device (40) via a fourth transmission optical fiber (704).

11. The hydrogen detection system (1) according to claim 10, Characterized in that, the signal processing device (40) includes a demodulator configured to convert an optical signal into an electrical signal.

12. The hydrogen detection system (1) according to claim 10, Characterized in that, the hydrogen detection system (1) further includes a display device (80) connected to the signal processing device (40) for displaying the detection result.

13. A method for measuring hydrogen concentration, Characterized in that, the method includes: setting a hydrogen sensor (10) at a position to be measured, the hydrogen sensor (10) includes an optical fiber core (101), an optical fiber cladding (102) surrounding the optical fiber core (101), and a hydrogen-sensitive coating (105) provided on one side of the optical fiber cladding (102), the hydrogen-sensitive coating (105) is configured to be able to absorb hydrogen and expand, wherein, the optical fiber core (101) includes a first half (103) and a second half (104) divided by a virtual plane extending along the axial direction of the optical fiber core (101), a first Bragg grating (B1) and a second Bragg grating (B2) with different grating periods are respectively etched in the first half (103) and the second half (104), the optical fiber cladding (102) includes an arc-shaped outer peripheral surface (102a) and a flat outer peripheral surface (102b) connected to each other, so that the optical fiber cladding (102) has a substantially D-shaped cross section, and the hydrogen-sensitive coating (105) is applied on the flat outer peripheral surface (102b), making the light emitted by the light source (20) pass through the hydrogen sensor (10); receiving a first optical signal reflected by the first Bragg grating (B1) and a second optical signal reflected by the second Bragg grating (B2); Measuring the offset Δλ of the central wavelength of the first optical signal relative to the predetermined initial reflected light central wavelength of the first Bragg grating (B1) 1 and the offset Δλ of the central wavelength of the second optical signal relative to the predetermined initial reflected light central wavelength of the second Bragg grating (B2) 2 ; The offset Δλ based on the central wavelength of the first optical signal 1 and the offset Δλ based on the central wavelength of the second optical signal 2 calculate the common strain change amount (Δε) of the first Bragg grating (B1) and the second Bragg grating (B2); and calculating the hydrogen concentration at the position to be measured based on the strain change amount Δε.

14. The method according to claim 13, Characterized in that, the strain change amount (Δε) is calculated by the following formula: where K ε1 is the strain coefficient of the first Bragg grating (B1), K ε2 is the strain coefficient of the second Bragg grating (B2), K T1 is the temperature coefficient of the first Bragg grating (B1), K T2 is the temperature coefficient of the second Bragg grating (B2).

15. The method according to claim 13, Characterized in that, The method further includes calculating a common temperature change amount (ΔT) of the first Bragg grating (B1) and the second Bragg grating (B2) based on the offset amount (Δλ 1 ) of the central wavelength of the first optical signal and the offset amount (Δλ 2 ) of the central wavelength of the second optical signal, and the temperature change amount (ΔT) is calculated by the following formula: where, K ε1 is the strain coefficient of the first Bragg grating (B1), K ε2 is the strain coefficient of the second Bragg grating (B2), K T1 is the temperature coefficient of the first Bragg grating (B1), K T2 is the temperature coefficient of the second Bragg grating (B2).

16. The method according to claim 13, Characterized in that, the method further includes calibrating the hydrogen concentration as a function of the common strain (ε) of the first Bragg grating (B1) and the second Bragg grating (B2).

17. An aircraft (2), characterized in that, the aircraft includes a hydrogen detection system (1) according to any one of claims 9 to 12.

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