KR102499779B1 - Optical gas sensor for hydrogen and hydrogen gas detection system including the same - Google Patents

Abstract

Embodiments include a sensing unit including a sensing material that expands or contracts in response to hydrogen gas; a body case surrounding at least a portion of the sensing unit with a sidewall; a first ferrule disposed at one end of the body case into which the optical fiber is inserted; and a second ferrule disposed at the other end of the body case facing the first ferrule to form a cavity between the first ferrule and the sensing unit passing through the hole of the second ferrule. One end of the sensing unit is disposed in a cavity between the first ferrule and the second ferrule. It relates to an optical sensor and a hydrogen gas sensing system including the same.

Description

Optical hydrogen gas sensor and hydrogen gas detection system including the same

Embodiments relate to a sensor for detecting hydrogen gas, and more particularly, to an optical sensor for detecting hydrogen by using a change in a pattern of an interference wave spectrum generated by a change in volume of a sensing unit that reacts with hydrogen.

Hydrogen gas (H ₂ ) is a material widely used in petroleum, chemical and aerospace industries. Hydrogen gas (H ₂ ) has a high diffusion coefficient (0.16 cm2/s in air), low ignition energy (0.02 mJ), high heat of combustion (285.8 kJ/mol), and a wide explosive concentration range (4–75%). have a high risk Since hydrogen gas (H ₂ ) has colorless, odorless, and tasteless characteristics, it cannot be detected by human senses, and therefore, there is a need for a technology for rapidly detecting hydrogen gas (H ₂ ) with high sensitivity, high accuracy, and high selectivity. Interest is growing.

In the past, a hydrogen sensor operating in an electrical manner was used. However, the electric hydrogen sensor has a limitation in that an electric spark may be generated inside or around the sensor, resulting in a risk of explosion.

Patent Publication No. 10-2020-0070682 (2020.06.18.)

According to one aspect of the present invention, in order to detect hydrogen gas using a change in the pattern of the interference wave spectrum, an optical formula configured to change the wavelength of an interference wave formed by a fiber optic Fabry-Perot interferometer when the sensing unit reacts with hydrogen. A sensor may also be provided.

In addition to this, the optical sensor; and a hydrogen gas detection system that detects the concentration of hydrogen gas based on the change in the pattern of the spectrum of the interfering light of the optical sensor.

An optical sensor for detecting hydrogen by receiving light from a light source through an optical fiber according to an aspect of the present application includes: a sensing unit including a sensing material that expands or contracts in response to hydrogen gas; a body case surrounding at least a portion of the sensing unit with a sidewall; a first ferrule disposed at one end of the body case into which the optical fiber is inserted; and a second ferrule disposed at the other end of the body case facing the first ferrule to form a cavity between the first ferrule and the sensing unit passing through the hole of the second ferrule. One end of the sensing unit is disposed in a cavity between the first ferrule and the second ferrule. The optical sensor forms an interference wave according to a Fabry-Perot interferometer with respect to light output from the optical fiber and propagating through the cavity.

In one embodiment, the sensing unit includes: a support passing through the hole of the second ferrule and extending toward the first ferrule; and a hydrogen reaction layer formed by coating at least a portion of the support. The hydrogen reaction layer may be formed on part or all of the first portion of the support body exposed to the cavity through the hole of the second ferrule.

In one embodiment, the side wall may include at least one aperture. The at least one opening is formed in a portion of the sidewall corresponding to the cavity.

In one embodiment, the interference wave may be formed due to repetitive reflection of light between a surface of the sensing unit and a point where light is emitted from the optical fiber. In the optical sensor, the spectral periodicity of the interference wave is changed as the distance between the surface and the point changes according to the volume change of the sensing material coated in the sensing unit.

In one embodiment, the optical sensor may further include a first fixing body formed at one end of the hole of the second ferrule to fix the sensing unit.

In one embodiment, the hole of the second ferrule may have a larger diameter than the width of the sensing unit so that a gap is formed between the hole of the second ferrule and the sensing unit inside the hole of the second ferrule. there is.

In one embodiment, the hydrogen reaction layer may further include a part or all of a part or all of the second part of the sensing unit inserted into the hole of the second ferrule.

In one embodiment, the support may be an optical fiber.

In one embodiment, the hydrogen reaction layer may be made of a material including palladium.

In one embodiment, the second ferrule hole may further include a second fixture disposed at the other end of the hole opposite to the first ferrule to fix the sensing unit.

In one embodiment, the sensing unit may further include a reflective layer having a higher reflectance than the hydrogen reaction layer, formed on a surface of the sensing unit facing the first ferrule.

In one embodiment, the reflective layer may be made of a material including Au.

In one embodiment, the sensing unit passing through the hole of the second ferrule may be inserted into the hole of the first ferrule so that the sensing unit is fixed across the first ferrule and the second ferrule.

In one embodiment, the hole of the first ferrule may have a larger diameter than the width of the sensing unit so that a gap is formed between the hole of the first ferrule and the sensing unit inside the hole of the first ferrule. .

In one embodiment, the optical sensor may detect hydrogen distributed in gas or fluid.

A hydrogen gas detection system according to a second aspect of the present application includes: an optical sensor according to the above-described embodiments; a light source unit including the light source; optical circulator; and an optical spectrum analyzer for detecting the presence or absence of hydrogen gas or measuring the concentration of hydrogen gas based on a change in spectral periodicity of an interference wave formed by the optical sensor.

In one embodiment, the light source unit may further include an er-doped fiber amplifier (EDFA) for receiving and amplifying the light of the light source.

In one embodiment, the light source may be a single wavelength light source.

In one embodiment, the light circulator may have first, second, and third ports. The light output from the light source unit is output to the optical sensor connected to the second port, and is formed in the optical sensor. The interference wave input through the second port is output to the optical spectrum analyzer connected to the third port.

In one embodiment, the light source emits light for a first time and does not emit light for a second time, and the second time is such that the light emitted during the first time is reflected from the surface of the sensing unit. It may also include the time to proceed to the optical spectrum analyzer.

An optical sensor for detecting hydrogen gas according to an aspect of the present invention detects hydrogen by using an interference wave caused by light. The optical sensor has the same level of sensitivity, accuracy, selectivity, and detection speed as conventional electronic device-based sensors, and there is no risk of explosion because there is no fear of generating an electric spark.

In addition, the optical sensor may detect not only hydrogen in the air but also hydrogen dissolved in a fluid. Since the optical sensor operates based on a Fabry-Perot cavity formed between optical fibers (or inside an optical fiber ferrule) that has excellent durability against the external environment, a sensing target such as a surrounding gas or liquid is mixed. It can also operate in a variety of harsh environments and can also detect hydrogen gas.

1 is a diagram for explaining the principle of an optical fiber Fabry-Perot interferometer.
2 is a schematic structural diagram of a hydrogen gas detection system according to an embodiment of the present invention.
3 is a schematic diagram of an operating principle of an optical sensor according to an embodiment of the present invention.
4 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.
5A to 5C are diagrams for explaining characteristics of the optical sensor of FIG. 4 .
6 is a diagram illustrating an effect of a reflective layer according to an embodiment of the present invention.
7 is a diagram for explaining a sensing and restoring aspect according to a diameter of a hole of a ferrule and a diameter of a sensing unit according to an embodiment of the present invention.
8 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.
9A and 9B are diagrams for explaining characteristics of the optical sensor of FIG. 8 .
10 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.
FIG. 11 is a diagram for explaining changes when the optical sensor of FIG. 10 is placed in a fluid.
12A to 12B are diagrams for explaining characteristics of the optical sensor of FIG. 10 .

It should be noted that the technical terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. In addition, technical terms used in this specification should be interpreted in terms commonly understood by those of ordinary skill in the technical field disclosed in this specification, unless specifically defined otherwise in this specification, and are overly inclusive. It should not be interpreted in a positive sense or in an excessively reduced sense. In addition, when technical terms used in this specification are erroneous technical terms that do not accurately express the spirit of the technology disclosed in this specification, they should be replaced with technical terms that those skilled in the art can correctly understand.

Also, singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise. As used herein, “consists of.” or "includes." Such terms should not be construed as necessarily including all of the various components or steps described in the specification, and some of the components or steps may not be included, or additional components or steps may be included. It should be interpreted as being more inclusive.

In addition, the suffix “part” for components used in this specification is given or used interchangeably in consideration of only the ease of writing the specification, and does not itself have a meaning or role distinct from each other.

In addition, in describing the technology disclosed in this specification, if it is determined that a detailed description of a related known technology may obscure the gist of the technology disclosed in this specification, the detailed description will be omitted. In addition, it should be noted that the accompanying drawings are only intended to facilitate understanding of the spirit of the technology disclosed in this specification, and should not be construed as limiting the spirit of the technology by the accompanying drawings.

Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the accompanying drawings.

1 is a diagram for explaining the principle of an optical fiber Fabry-Perot interferometer.

Fiber Febry-Parot interferometer (FFPI) has periodicity in the spectrum of interference waves reflected from two reflective films, and the distance between the two films or the refractive index of the material constituting the interferometer changes Then, the periodicity also changes. The fiber optic Fabry-Perot interferometer uses the principle of analyzing the spectrum using this change in periodicity. A detailed description of this is as follows.

FIG. 1A shows a case in which two reflective films 132 and 134 have a distance L0 and a space between the films is filled with a material having a refractive index n0.

The two films 132 and 134 are a region 120 and a first film 132 which is an interface for the material between the two films 132 and 134 and an inner area 110 between the films 132 and 134. ) and the second film 134, which is the boundary between the outer region 130. The first layer 132 and the second layer 134 have a reflectance R lower than 1.

Light E0 having an arbitrary wavelength λ proceeds from a region 120 connected to one surface of the first layer 132 and is irradiated onto the first layer 132 . The light passing through the first layer 132 is incident on a region 130 between the first layer 132 and the second layer 134 .

Light incident to the area 110 proceeds to the second film 134 again. The light moving along the movement path as described above is caused by a difference in refractive index of the regions 110, 120, and 130 and/or a difference in reflectance of the films 132 and 134, which causes the first film 132 and the second film 132 to pass through. Some or all of it is reflected at (134). Depending on the characteristics of the second film 134, some of the propagated light may be transmitted to the outside. The reflected light passes through the first film 132 and travels back to the region 120 .

Accordingly, light repeatedly reflected and transmitted between the two films 132 and 134 forms a plurality of reflected waves Er1 , Er2 , Er3 . . . returning to the area 120 . The plurality of reflected waves Er1 , Er2 , and Er3 cause interference with each other within the region 120 , and the finally determined interference wave is formed due to the interference.

Figure 1b is a diagram showing the spectrum of the interference wave of Figure 1a.

The interference wave has a constant wavelength, and the spectrum of the interference wave exhibits periodicity according to the wavelength, and this periodicity is expressed as a function of the distance between the two layers 132 and 134 and the refractive index.

As shown in FIG. 1B, the spectrum of the interference wave has the same peak position regardless of the component included in the incident light. Specifically, the position of the peak does not vary depending on the wavelength (component) of the incident light, but the intensity of the peak may change due to a difference in transmittance and reflectance at the boundary of the reflective film.

A fiber optic Fabry-Perot interferometer (FPPI) is used for purposes such as sensing a material by using a change in the spectral periodicity of the final interference wave thus formed.

If a reflection surface on one side reacts with a specific external material and the corresponding reflection surface is deformed, the periodic pattern of the spectrum can be changed if the distance L forming the interferometer is changed.

As a result, the fiber optic Fabry-Perot interferometer can sense external influences that cause material change in the fiber optic Fabry-Perot interferometer by the spectral periodicity change of the interfering wave.

FIG. 1C shows a case in which the distance L between the two layers 132 and 134 changes from L0 to L1 as the distance between the two layers 132 and 134 increases by ΔL.

When the distance between the two films 132 and 134 is changed, the number of final standing waves formed by reflection of the incident wave increases as the resonance length increases, so the spectral period of the interference wave also becomes shorter. Therefore, on the spectrum, it is possible to observe a phenomenon in which the peaks and valleys of the observed spectrum shift to one side.

If at least a portion of one of the two films 132 and 134 is deformed and the distance between the two films 132 and 134 increases, the period of the interference wave with respect to the wavelength λ of the incident wave The amount of change in wavelength (Δλ) according to the change is shown in Equation 1 below.

Here, Δλ is the change in the wavelength of the interference wave with respect to the wavelength of the incident wave, λ is the wavelength of the incident wave, n ₀ is the refractive index of the material between the two films, ΔL is the change in the distance between the two films, and L ₀ is the difference between the two films represents the distance of

In this way, the fiber optic Fabry-Perot interferometer is based on the change in the wavelength of the interference wave (Δλ) according to the change in the distance between the two arbitrary films 132 and 134 and the corresponding change in the spectral periodicity, the two films 132 and 134 ) It is possible to detect an external influence that causes a change in the distance of the material 110 filling the gap.

Hereinafter, an optical sensor for detecting hydrogen gas using the principle of an optical fiber Fabry-Perot interferometer will be described.

2 is a schematic structural diagram of a hydrogen gas detection system according to an embodiment of the present invention.

Referring to FIG. 2 , the hydrogen gas detection system 1 includes a light source unit 100; circulator 300; and an optical sensor 400; and an optical spectrum analyzer (OSA) 500. Components 100 , 300 , 400 , and 500 of the hydrogen gas detection system 1 are optically connected through an optical fiber 200 .

The light source unit 100 includes a light source that supplies light to the optical sensor 400 . Light generated from the light source unit 100 may be irradiated to an input port of the circulator 300 . In addition, the light may be irradiated to the optical sensor 400 through the circulator 300 .

In one embodiment, the light source may be configured to emit white light or broadband light. For example, the light source may be a laser diode or a broadband light source. In the above embodiment, the light source unit 100 including the light source may further include an er-doped fiber amplifier (EDFA).

In one embodiment, the light source may be configured to emit a single wavelength optical signal. When the light source unit 100 is configured to utilize a single wavelength optical signal instead of EDFA, when the optical sensor 400 detects hydrogen, the change in intensity of the optical signal due to the shift of the interferometer according to the reaction with the optical sensor 400 is proportional to the ER (extinction ratio) of

Light emitted from the light source unit 100 travels along the optical fiber 200 to other components 300, 400, and 500.

The optical fiber 200 may provide a movement path of light formed in the light source unit 100 using total internal reflection. The optical fiber 200 may connect each component constituting the system 1 and provide an optical movement path for light generated from the light source to move between the components.

Specifically, in the optical fiber 200, the light formed in the light source is irradiated to the optical sensor through the circulator 300, and the interference wave formed in the optical sensor 400 passes through the circulator 300. It can be irradiated with the optical spectrum analyzer 500.

The optical fiber 200 radiates light to the sensor 400 with minimal energy loss. The optical fiber 200 may be composed of a core and a cladding that induce total reflection of light.

In alternative embodiments, each of the components 100, 300, 400, and 500 in System 1 may be connected through a planar optical waveguide instead of the optical fiber 200. Then, the optical waveguide has a shorter length and a much thinner thickness than the optical fiber 200, thereby providing an intensive configuration of the optical sensor 400 and the hydrogen gas detection system 1 including the optical sensor 400 This is possible and may be useful for changing the diameter of light formed in the light source.

The circulator 300 may have first to third ports. The circulator 300 may be configured to output light input through the first port to the second port and output light input through the second port to the third port. The circulator 300 may include a mirror or a polarization control element that reflects light to control the path of the light.

The first port of the circulator 300 is connected to the light source unit 100. The second port of the circulator 300 is connected to the optical sensor 400. The third port of the circulator 300 is connected to the analyzer 500.

The circulator 300 is positioned between the light source unit 100, the optical sensor 400, and the optical spectrum analyzer 500, and can change a path of light generated from the light source unit 100. At this time, the first port of the circulator 300 is connected to the light source unit 100, the second port is connected to the optical sensor 400, and the third port is connected to the optical spectrum analyzer 500. can be connected with

In one embodiment, the circulator 300 outputs the light emitted from the light source unit 100 input to the first port to the optical sensor 400 connected to the second port, and the optical sensor ( 400) and outputs the interference wave input to the second port to the optical spectrum analyzer 500 connected to the third port.

In one embodiment, the light source unit 100 may be turned on to emit light for a first time and turned off to not emit light for a second time. In the second time, the light emitted during the first time is input to the optical sensor 400, and an interference wave generated is output from the optical sensor 400 and passes through the circulator 300 to the optical spectrum analyzer ( 500). During the first time on the light path of the hydrogen gas detection system 1, light travels from the light source unit 100 to the optical sensor 400 through the circulator 300. In addition, light travels from the optical sensor 400 to the optical spectrum analyzer 500 through the circulator 300 for the second time on the light path of the hydrogen gas detection system 1 .

The optical sensor 400 forms an interference wave according to the principle of a fiber optic Fabry-Perot interferometer. The optical sensor 400 may form the interference wave according to the principle of a fiber optic Fabry-Perot interferometer with respect to the light irradiated from the light source unit 100 .

3 is a schematic diagram of an operating principle of an optical sensor according to an embodiment of the present invention.

Referring to FIG. 3 , the optical sensor 400 is configured to form a first reflective film and a second reflective film that act as two films of an optical fiber Fabry-Perot interferometer to form the interference wave. Light traveling through the optical fiber 200 of System 1 is incident on the first reflective film and proceeds toward the second reflective film. At least some of the light traveling toward the second reflective film is reflected and passes through the first reflective film again. Light traveling in this way can form an interference wave having an arbitrary wavelength and spectral periodicity by repetitive reflection between the two films.

The first reflective film is formed at an output end of an optical fiber 200 emitting light traveling toward the optical sensor 400 .

The second reflective film is formed in a portion of the sensing material that expands or contracts in response to hydrogen gas. The second reflective film may be implemented as a surface of the sensing material itself or a surface of another component in contact with the sensing material.

The sensing material may be a material that expands by adsorbing hydrogen gas or contracts when not combined with the hydrogen gas. In one embodiment, the sensing material may include palladium (Pd).

A change in the volume of the sensing material causes a change in the distance between the first reflective layer and the second reflective layer. The wavelength of the interference wave may change as the distance at which light travels between the first and second reflection films changes.

The structure of the optical sensor 400 will be described in more detail with reference to FIG. 4 below.

The optical spectrum analyzer 500 detects the existence of hydrogen gas and/or measures the hydrogen gas concentration based on the wavelength change of the interference wave. That is, the optical spectrum analyzer 500 observes the spectrum of the interference wave formed by the optical sensor 400, and determines whether or not the hydrogen gas exists based on whether the spectrum periodicity changes or not, and/or hydrogen valence. concentration can be calculated.

To this end, the optical spectrum analyzer 500 may measure the spectrum of the interference wave. The optical spectrum analyzer 500 may display the spectrum of the interference wave incident to the optical spectrum analyzer 500 on a display. The characteristics of light by the optical spectrum analyzer 500 may include wavelength, periodicity, light intensity, and the like.

Not all components of the hydrogen gas detection system shown in FIG. 2 are essential components, and the hydrogen gas detection system 1 may be implemented with more or fewer components than those shown in FIG. 2 .

4 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.

Referring to FIG. 4 , the optical sensor 400 includes a sensing unit 410; body case 420; a first ferrule 430; and a second ferrule 440 .

The optical sensor 400 receives light from the light source unit 100 through the optical fiber 200 . The received light propagates toward the sensing unit 410 . The propagated light is reflected from one surface of the sensing unit 410 facing the output end of the optical fiber 200 and proceeds to the optical fiber 200 again.

The sensing unit 410 includes: a support 411; and a hydrogen reaction layer 413 .

The support 411 is a structure extending along one axis. The support 411 supports the hydrogen reaction layer 413 formed on a part of the support 411 .

In one embodiment, the support 411 may be a single mode fiber (SMF).

The hydrogen reaction layer 413 is made of a sensing material that expands or contracts in response to hydrogen gas. The hydrogen reaction layer 413 may be formed by coating a portion of the support 411 with palladium, for example. A portion of the support 411 includes one end of both ends of the support 411 facing the optical fiber 200 . A surface of the coated palladium layer 413 facing the optical fiber 200 functions as a second reflective film in FIG. 3 .

The body case 420 is a housing having a side wall and one end and the other end passing therethrough, and having a space inside the side wall. The body case 420 functions as a sleeve pipe for the sensing unit 410 to be disposed in the inner space. The body case 420 has various planar shapes such as a cylinder, an ellipse, and a polygon. For example, the body case 420 may have a cylindrical shape as shown in FIG. 4 .

The body case 420 has a plane width greater than that of the sensing unit 410 . As shown in FIG. 4 , the cylindrical body case 420 has a larger diameter than the inner width of the sensing unit 410 .

The body case 420 may surround the entire sensing unit 410 or partially. For example, as shown in FIG. 4 , the body case 420 may surround the sensing unit 410 so that a part of the support 411 of the sensing unit 410 is exposed to the outside.

The first ferrule 430 and the second ferrule 440 are components having a hole in the center in the form of a cylindrical tube used for alignment of optical fibers in a connection such as an optical connector. The first ferrule 430 and the second ferrule 440 are partially or wholly inserted into one end of the body case 410 . For example, as shown in FIG. 4 , portions of the first ferrule 430 and the second ferrule 440 may be inserted into the sidewall of the body case 410 .

The first ferrule 430 and the second ferrule 440 are disposed to face each other. The optical sensor 400 has a cavity formed by the sidewall of the body case 410, the first ferrule 430 and the second ferrule 440.

The first ferrule 430 supports the optical fiber 200 through which light of the light source unit 100 is input. The optical fiber 200 is inserted into the hole of the first ferrule 430 . The optical sensor 400 is coupled to one end of the optical fiber 200 by the first ferrule 430 .

The hole of the first ferrule 430 may match the diameter of the optical fiber 200 as shown in FIG. 4, or may be wider to have a gap between the optical fibers 200 as shown in FIG. 10 below. there is.

In one embodiment, the first ferrule 430 and one end of the optical fiber 200 may be polished perpendicular to the direction of light output from the optical fiber 200 . One surface of the first ferrule 430 is polished to face the sensing unit 410 .

The second ferrule 430 supports the sensing unit 410 . The sensing unit 410 is inserted through the hole of the second ferrule 440 . Also, the other end of the sensing unit 410 may be disposed outside the hole of the second ferrule 440 (ie, outside the optical sensor 400).

In certain embodiments, as shown in FIG. 4 , one end of the sensing unit 410 penetrating the hole of the second ferrule 440 may be disposed in the inner cavity.

Also, the optical sensor 400 may include at least one fixing body to fix the sensing unit 410 .

In certain embodiments, the optical sensor 400 may further include the first stator 451 and the second stator 453 as shown in FIG. 4 .

The fixing bodies 451 and/or 453 are formed at one end and/or the other end of the hole of the second ferrule 440 to fix the sensing unit 410 passing through the hole of the second ferrule 440. .

The fixtures 451 and 453 may be made of, for example, resin such as epoxy, but are not limited thereto.

The fixture 451 is disposed at one end of the hole of the second ferrule 440 that contacts the outside of the optical sensor 400 .

The fixture 453 is disposed at the other end of the hole of the second ferrule 440, which is in contact with the inner cavity of the optical sensor 400. The fixture 453 opposes the first ferrule 430 .

In certain embodiments, the sidewall of the body case 420 may include at least one aperture 421 . The at least one opening 421 is formed in a portion of the sidewall corresponding to the cavity. As shown in FIG. 4 , the at least one opening 421 is formed in a side wall portion forming an internal cavity.

When hydrogen gas is distributed around the optical sensor 400 , the sensing unit 410 inside the body case 420 is exposed to the hydrogen gas introduced through the side wall opening 421 . Then, the volume of the hydrogen reaction layer 413 of the sensing unit 410 changes.

In certain embodiments, the hydrogen reaction layer 413 may be formed on part or all of the support 411 exposed to the internal cavity through the hole of the second ferrule 440 . That is, the hydrogen reaction layer 413 may be formed in a portion exposed to the internal cavity of the support 411 .

In other specific embodiments, the hydrogen reaction layer 413 may be additionally formed on part or all of the support 411 inserted into and penetrating the hole of the second ferrule 440 . That is, the hydrogen reaction layer 413 may be formed over the exposed portion of the internal cavity and the inserted portion of the hole in the support 411 . This will be described in more detail with reference to FIG. 8 below.

When light is incident on the optical sensor 400 having the structure of FIG. 4 , interference waves are formed due to repeated light reflection between the surface of the sensing unit 10 and the point where the light is emitted from the optical fiber 200 . do. This interference wave is repeatedly reflected between the first reflective film formed on the optical fiber 200 and the first ferrule 430 and the second reflective film formed on the surface (eg, hydrogen reaction layer 413) of the sensing unit 410. is formed

Due to repeated reflection and transmission of light between the first and second reflective films, periodic constructive interference occurs, forming a plurality of standing waves between the two reflective films, and as a result, final interference waves having a constant periodicity on the spectrum are formed. will do An interference wave formed through an optical fiber Fabry-Perot interferometer composed of two reflective films may have an arbitrary wavelength depending on a distance between the two reflective films.

The spectral periodicity of the interfering wave changes according to the volume change of the sensing material. Specifically, the interference wave is generated by reacting with hydrogen gas introduced into the inner cavity, and the distance between the surface and the point (ie, between the first reflective film and the second reflective film) according to the change in volume of the sensing material coated in the sensing unit. distance) changes. Then, the spectral periodicity of the interfering wave changes due to a change in distance due to a change in volume.

The optical sensor 400 may be used to detect hydrogen through whether or not the spectral period of the interference wave changes.

When hydrogen gas does not exist outside, the volume of the sensing material of the hydrogen reaction layer 413 does not change. Therefore, the distance D of the cavity between the first reflective film and the second reflective film does not change.

Meanwhile, when the sensing material of the hydrogen reaction layer 413 is expanded by being combined with external hydrogen gas, the volume of the hydrogen reaction layer 413 changes. For example, when the sensing material absorbs hydrogen gas, the distance between the reflective films decreases from D to D'(=D+ΔD), and eventually the periodicity of the spectrum of the interference wave of the fiber optic Fabry-Perot interferometer changes. may be

The change in periodicity of the spectrum of the interference wave may be expressed as a shift in the position of the peak of the spectrum of the interference wave.

5A to 5C are diagrams for explaining characteristics of the optical sensor of FIG. 4 . The graphs of FIGS. 5A to 5C are obtained by injecting hydrogen gas around the optical sensor 400 .

FIG. 5A shows the intensity and wavelength of an interference wave generated by the optical sensor 400 of FIG. 4 , and FIG. 5B shows a resonance peak point in the spectrum of an interference wave generated by the optical sensor 400 of FIG. 4 . The shift interval of is shown according to the exposure time.

Referring to FIG. 5A , when hydrogen gas is injected into the vicinity of the optical sensor 400, the hydrogen gas flows into the inner cavity of the optical sensor 400 through the opening 421 and reacts with the sensing unit 410. As the distance of the Fabry-Parott interferometer changes, a wavelength shift occurs as indicated by the arrow in FIG. 5A. Referring to FIG. 5B , as the time for which the optical sensor 400 is exposed to hydrogen gas increases, the degree of shift of the interference wave gradually increases.

Meanwhile, when the injection of the hydrogen gas is completed and the measurement environment is refreshed, the shifted wavelength of the interference wave returns to the position before the shift.

FIG. 5C shows that the resonance peak in the spectrum of the interference wave generated by the optical sensor 400 of FIG. 4 shifts when the time interval of exposure to hydrogen gas is repeated. Other gases (eg, N ₂ ) may be injected during different time intervals when the concentration-controlled exposure of hydrogen gas is completed. In one experimental example, the graph of FIG. 5C may be obtained when hydrogen gas diluted with nitrogen to a maximum concentration of 4% (minimum explosive concentration of hydrogen) is used.

Even when the optical sensor 400 of FIG. 4 is repeatedly exposed to hydrogen gas for several tens of minutes, the spectrum of the interference wave shifts. Therefore, the optical sensor 400 can repeatedly detect hydrogen.

The hydrogen gas detection system 1 including the optical sensor 400 obtains an interference wave output from the optical sensor 400 using the optical spectrum analyzer 500 . The obtained interference wave may be an interference wave in which the period of the spectrum is changed by changing the wavelength. The optical spectrum analyzer 500 may output the presence or absence of hydrogen gas and/or the detected concentration of hydrogen gas when the spectrum period changes according to the analysis result.

For example, when the wavelength has changed compared to when the hydrogen gas is not present, the hydrogen gas detection system 1 may determine that the hydrogen gas is present in the air.

Also, the hydrogen gas detection system 1 may measure the concentration of hydrogen gas based on the degree of wavelength change. The degree to which the periodicity of the spectrum of the interfering wave changes corresponds to ΔD. Since the wavelength of the peak of the interference spectrum is different for each concentration of hydrogen gas, the hydrogen gas detection system 1 may detect the hydrogen concentration based on the detection result of the wavelength of the peak of the interference spectrum. For example, the hydrogen gas detection system 1 detects the wavelength of a peak in the interference wave spectrum, and converts the concentration of hydrogen gas corresponding to the wavelength of the detected peak into the concentration of hydrogen gas detected by the optical sensor 400. may decide

To this end, the hydrogen gas detection system 1 may store in advance the relationship between peak wavelengths for each hydrogen concentration (eg, in the optical spectrum analyzer 500). For example, the optical spectrum analyzer 500 may store a relationship between peak wavelengths for each hydrogen concentration. For example, when a value of a specific wavelength of a peak is detected, the system 1 may measure the current concentration of hydrogen gas with a value of concentration corresponding to the value of the specific wavelength.

After detecting the hydrogen gas, when the detected hydrogen gas is removed and the measurement environment is refreshed, the moved interference wave spectrum returns to the position before the movement.

The hydrogen gas detection system 1 may determine that the concentration of hydrogen gas is lowered when the change in the interfering wave spectrum indicates a return to the previous position. In addition, the hydrogen gas detection system 1 may determine that the concentration of hydrogen gas has returned to the previous state when the interference wave spectrum has returned to the previous position after being changed.

The hydrogen gas detection system 1 may provide the user with hydrogen gas analysis results, including the presence or absence of hydrogen gas, the concentration of hydrogen gas, and/or the change state of the hydrogen gas concentration. For example, the user may know that the leaked hydrogen gas has been removed.

In one embodiment, the sensing unit 410 may further include a reflective layer 415 . As shown in FIG. 4 , the reflective layer 415 is formed on a surface of the hydrogen reactive layer 413 facing the optical fiber 200 through coating or the like.

The reflective layer 415 is made of a material having higher reflectance than the sensing material. The reflective layer 415 may be made of, for example, a material including gold (Au), but is not limited thereto. In this case, the surface of the reflective layer 415 functions as a second reflective film in FIG. 3 .

6 is a diagram illustrating an effect of a reflective layer according to an embodiment of the present invention.

Referring to FIG. 6 , when the optical sensor 400 includes the reflective layer 415, the interference wave has a higher ER value. That is, due to the reflective layer 415, light loss in the sensor 400 is reduced, and reliability of hydrogen sensing data of System 1 is increased.

In certain embodiments, the second ferrule 440 may be configured such that a gap is formed between the inside of the hole of the second ferrule 440 and the sensing unit 410 penetrating the hole. The hole of the second ferrule 440 has a larger diameter than the width of the sensing unit 410, that is, the width of the portion including the outermost hydrogen reaction layer 413.

The gap between the inside of the hole of the second ferrule 440 and the sensing unit 410 penetrating this hole is formed by the reaction of the palladium layer 413 coated on the support 411 of the sensing unit 410 with surrounding hydrogen, Even if the cross-sectional diameter of the sensing unit 410 increases due to the expansion of the second ferrule 440, it has a gap that does not come into contact with the inner diameter of the hole.

In certain embodiments, a difference between the diameter of the hole of the second ferrule 440 and the diameter of the support 411 of the sensing unit 410 may be greater than or equal to 1 μm and less than or equal to 9 μm. In some embodiments, a difference between the diameter of the hole of the second ferrule 440 and the diameter of the support 411 of the sensing unit 410 may be 3 μm or less.

7 is a view for explaining a detection and restoration aspect according to a diameter of a hole of a ferrule and a diameter of a support body according to an embodiment of the present invention.

The graph on the left side of FIG. 7 shows a case where the diameter of the hole of the second ferrule 440 and the diameter of the sensing unit match. Here, the diameter matching is the same as the diameter of the hole of the second ferrule 440 and the diameter of the sensing unit 410, the palladium layer 413 coated on the support 411 of the sensing unit 410 When the cross-sectional diameter of the sensing unit 410 increases by reacting with the surrounding hydrogen and expanding in volume, the inner diameter of the second ferrule 440 matches the contact between the palladium layer 413 coated on the support 411. means the degree For example, if the difference between the diameter of the hole of the second ferrule 440 and the diameter of the sensing unit 410 is 1 μm or less, the diameters may be regarded as matching.

When the diameter of the hole of the second ferrule 440 matches the diameter of the sensing unit, due to friction between the palladium-coated sensing unit 410 and the hole of the second ferrule 440, the sensor structure after exposure to hydrogen gas is not restored to its original state.

On the other hand, as shown in the graph on the right of FIG. 7, the optical sensor 400 is a sensor according to the expansion/contraction of palladium due to the gap between the inside of the hole of the second ferrule 440 and the sensing unit 410. The performance of the sensor 400 does not deteriorate, and the stability of the sensor 400 can be ensured.

In other specific embodiments, the optical sensor 400 may be configured so that the inner space of the hole of the second ferrule 440 and the inner cavity of the optical sensor 400 form a single space. To this end, the optical sensor 400 may not include the second fixture 453.

8 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.

Since the structure of the optical sensor 400 of FIG. 8 is similar to that of the optical sensor 400 of FIG. 4, differences will be mainly described.

Referring to FIG. 8, as described above, in the optical sensor 400, the hydrogen reaction layer 413 may be formed over a part or all of the exposed portion of the internal cavity and the inserted portion of the hole in the support 411. . For example, as shown in FIG. 8 , the hydrogen reaction layer 413 may be formed over the entire insertion portion of the second ferrule 440 and the entire exposed portion of the internal cavity in the support 411 . Here, the insertion part corresponds to the length of the hole.

As shown in FIG. 8 , the second ferrule 440 may be configured such that a gap is formed between the inside of the hole of the second ferrule 440 and the sensing unit 410 passing through the hole. Under this structure, since the space inside the hole of the second ferrule 440 and the space of the inner cavity are not blocked, the space where the hydrogen reaction layer 413 can be exposed to hydrogen is expanded compared to FIG. 4 . As a result, the area of the hydrogen reaction layer 413 that is exposed to hydrogen gas and reacts with hydrogen is expanded by a portion inside the hole of the second ferrule 440 . As a result, the volume change amount of the hydrogen reaction layer 413 according to the reaction with hydrogen increases.

9A and 9B are diagrams for explaining characteristics of the optical sensor of FIG. 8 .

FIG. 9A shows the intensity and wavelength of the interference wave generated by the optical sensor 400 of FIG. 8, and FIG. 9B shows the resonance peak point in the spectrum of the interference wave generated by the optical sensor 400 of FIG. The shift interval of is shown according to the exposure time. Referring to FIGS. 5 and 9 , the optical sensor 400 of FIG. 8 in which a reaction area is increased by expanding a space exposed to hydrogen gas has higher hydrogen sensitivity than the optical sensor 400 of FIG. 4 .

In yet other specific embodiments, the optical sensor 400 may be configured such that the sensing unit 410 is fixed across the first ferrule 430 and the second ferrule 440 .

10 is a schematic structural diagram of an optical sensor according to an embodiment of the present invention.

Since the structure of the optical sensor 400 of FIG. 10 is similar to that of the optical sensor 400 of FIG. 4, differences will be mainly described.

Referring to FIG. 10 , the optical sensor 400 passes through the hole of the second ferrule 440 so that the sensing unit 410 is fixed across the first ferrule 430 and the second ferrule 440 . The sensing unit 410 may be inserted into the hole of the first ferrule 430 . Then, one end of the sensing unit 410 is disposed inside the hole of the first ferrule 430 instead of the inner cavity.

In addition, the first ferrule 430 may be configured such that a gap is formed between the inside of the hole of the first ferrule 430 and the sensing unit 410 inserted into the hole. To this end, the hole of the first ferrule 430 has a larger diameter than the width of the sensing unit 410, that is, the width of the portion including the outermost hydrogen reaction layer 413.

In one embodiment, the holes of the first ferrule 430 and the second ferrule 440 may correspond to each other. For example, when a gap is formed between the inside of the hole of the second ferrule 440 and the sensing unit 410 penetrating therethrough, the first ferrule 430 is formed between the inside of the hole of the first ferrule 430 and the second ferrule 430. A gap may be formed between the sensing units 410 inserted into the holes.

In alternative embodiments, the optical sensor 400 of FIG. 10 may be configured to include a stator 451 and not include a stator 453 . That is, the optical sensor 400 of FIG. 10 may be implemented by inserting one end of the sensing unit 410 of the optical sensor 400 of FIG. 8 into the hole of the first ferrule 430 .

In this way, when the sensing unit 410 is fixed across both the first ferrule 430 and the second ferrule 440, the optical sensor 400 has higher data reliability.

Also, the optical sensor 400 may detect hydrogen dissolved in the fluid.

FIG. 11 is a diagram for explaining changes when the optical sensor of FIG. 10 is placed in a fluid. The graph of FIG. 11 is obtained using the optical sensor 400 of FIG. 10 in an environment in which hydrogen gas diluted to 4% in nitrogen is dissolved in oil through a diffuser.

Referring to FIG. 11, the FSR of the result of using the optical sensor 400 of FIG. 10 in electrical insulating oil (ie, fluid) used in a power transformer is the FSR of the result of using the same optical sensor 400 of FIG. 10 in air. same. That is, in the optical sensor 400 of FIG. 10 , the Fabry-Parrot resonance characteristics are maintained even when used in a fluid as in the case of being used in air.

That is, the optical sensor 400 of FIG. 10 may detect hydrogen distributed in a fluid or gas.

FIG. 12A FIG. 12B is a diagram for explaining characteristics of the optical sensor of FIG. 10 .

The graph of FIG. 12 is obtained in an environment in which hydrogen gas is injected into electrical insulating oil used in a power transformer. 12a shows the intensity and wavelength of the interference wave generated by the optical sensor 400 of FIG. 10 according to the injection of hydrogen and the end of injection, respectively, and FIG. 12b shows the intensity and wavelength of the interference wave generated by the optical sensor 400 of FIG. The shift interval of the resonance peak point in the spectrum of the interference wave is shown according to the exposure time.

Referring to FIG. 12A, when hydrogen is injected into electrical insulating oil, the resonant wavelength shifts as shown by the arrow on the left graph. And when hydrogen injection is stopped, the resonant wavelength is restored to the original position as indicated by the arrow on the right graph.

Referring to FIG. 12B , the optical sensor 400 maintains Fabry-Farat resonance characteristics even under fluid conditions. The resonance characteristics of this Fabry-Parrot are stably maintained for several tens of minutes, particularly for 10 minutes or more.

In this way, the optical sensor 400 may detect not only hydrogen in the air but also hydrogen dissolved in a fluid. The optical sensor may sense hydrogen gas without being affected by the surrounding environment, such as a surrounding gas or liquid.

Those skilled in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed according to the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

1: hydrogen gas detection system
100: light source
200: optical fiber
300: circulator
400: optical sensor
410: sensing unit
411: support
413: hydrogen reaction layer
415: reflective layer
420: body case
421: aperture
430, 440: ferrule
451, 453: fixture
500: optical spectrum analyzer

Claims (20)

In an optical sensor for detecting hydrogen by receiving light from a light source through an optical fiber,
a sensing unit including a sensing material that expands or contracts in response to hydrogen gas;
a body case surrounding at least a portion of the sensing unit with a sidewall;
a first ferrule disposed at one end of the body case into which the optical fiber is inserted; and
A second ferrule disposed at the other end of the body case facing the first ferrule and forming a cavity between the first ferrule and the sensing unit passing through a hole of the second ferrule to detect the sensing unit. One end of the unit is disposed in a cavity between the first ferrule and the second ferrule,
Forming an interference wave according to a Fabry-Perot interferometer with respect to light output from the optical fiber and traveling through the cavity;
The sensing unit:
a support body passing through the hole of the second ferrule and extending toward the first ferrule; And a hydrogen reaction layer formed by coating at least a portion of the support, wherein the hydrogen reaction layer is formed on part or all of the first portion of the support exposed to the cavity through the hole of the second ferrule,
The optical sensor of claim 1, further comprising a reflective layer formed on a surface of the sensing unit facing the first ferrule and having a higher reflectance than the hydrogen reactive layer.
delete According to claim 1,
the sidewall includes at least one aperture;
The optical sensor according to claim 1 , wherein the at least one opening is formed in a portion of the sidewall corresponding to the cavity.
According to claim 3,
The interference wave is formed due to repeated reflection of light between a surface of the sensing unit and a point where light is emitted from the optical fiber,
An optical sensor according to claim 1 , wherein the spectral periodicity of the interference wave is changed as a distance between the surface and a point changes according to a change in volume of the sensing material coated in the sensing unit.
According to claim 1,
The optical sensor of claim 1, further comprising a first fixing body formed at one end of the hole of the second ferrule to fix the sensing unit.
According to claim 1,
The hole of the second ferrule has a diameter larger than the width of the sensing unit so that a gap between the hole of the second ferrule and the sensing unit is formed inside the hole of the second ferrule Optical sensor, characterized in that .
According to claim 6,
The optical sensor according to claim 1 , wherein the hydrogen reaction layer is formed on a part or all of a part or all of the second part of the sensing unit inserted into the hole of the second ferrule.
According to claim 1,
The optical sensor, characterized in that the support is an optical fiber.
According to claim 1,
The hydrogen reaction layer is an optical sensor, characterized in that made of a material containing palladium.
According to claim 1,
The optical sensor of claim 1, further comprising a second fixing body disposed at the other end of the hole opposite to the first ferrule in the hole of the second ferrule to fix the sensing unit.
delete According to claim 1,
The reflective layer is an optical sensor, characterized in that made of a material containing Au.
According to claim 6,
The optical sensor according to claim 1 , wherein the sensing unit passing through the hole of the second ferrule is inserted into the hole of the first ferrule so that the sensing unit is fixed across the first ferrule and the second ferrule.
According to claim 13,
The optical sensor of claim 1 , wherein the hole of the first ferrule has a larger diameter than the width of the sensing unit so that a gap is formed between the hole of the first ferrule and the sensing unit inside the hole of the first ferrule.
According to claim 13,
The optical sensor is an optical sensor, characterized in that for detecting hydrogen distributed in the gas or fluid.
An optical sensor according to any one of claims 1, 3 to 10, and 12 to 15;
a light source unit including the light source;
optical circulator; and
and an optical spectrum analyzer for detecting the presence or absence of hydrogen gas or measuring the concentration of hydrogen gas based on a change in the spectral periodicity of the interference wave formed by the optical sensor.
According to claim 16,
The light source unit: Hydrogen gas detection system, characterized in that further comprising an EDFA (Er-doped fiber amplifier) for receiving and amplifying the light of the light source.
According to claim 16,
The light source is a hydrogen gas detection system, characterized in that the single wavelength light source.
According to claim 16,
The optical circulator has first, second, and third ports,
Outputting the light output from the light source unit to the optical sensor connected to the second port, and outputting the interference wave formed by the optical sensor and input to the second port to the optical spectrum analyzer connected to the third port A hydrogen gas detection system, characterized in that.
According to claim 16,
the light source emits light for a first time and does not emit light for a second time;
The hydrogen gas detection system of claim 1 , wherein the second time period includes a time period in which light emitted during the first time period is reflected from a surface of the sensing unit and travels to the optical spectrum analyzer.

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