Thin film interference type hydrogen sensor and hydrogen tracking detection method

Abstract

The present invention relates to a thin film interference type hydrogen sensor and a hydrogen tracking detection method. It comprises a container with a cavity and an opening on the upper surface, a substrate placed on the lower surface in the cavity, a gasket arranged between an edge of the substrate and the lower surface, a glass plate that closes the opening, and a light source that penetrates the glass plate into the cavity, wherein the glass plate is parallel to the lower surface, an air layer is present between the substrate and the glass plate, a palladium film is provided on the surface of the substrate on one side close to the glass plate, a valve leading to the air layer is provided on the container, and the incident light of the light source is perpendicular to the glass plate. The technical solution provided by the present invention constructs a thin film interference structure in a confined space, and the thickness of the thin film in the interference structure changes with the change of hydrogen concentration, which can be reflected in the change of interference fringes. The designed sensor has a simple structure, sensitive response, low cost and high safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen sensors, and in particular relates to a thin film interference type hydrogen sensor and a hydrogen tracking detection method. Background Art

[0002] A hydrogen sensor is a sensor device that detects hydrogen and generates a signal proportional to the hydrogen concentration. Compared with traditional hydrogen detection methods (gas chromatograph, mass spectrometer), it has the advantages of low cost, small size, and fast response.

[0003] Hydrogen interacts with the sensing element of the hydrogen sensor, which can cause changes in temperature, refractive index, electrical properties, mass or mechanical structure. Depending on the physical quantity detected, hydrogen sensors are divided into catalytic, thermal conductivity, electrochemical, resistive, work function, mechanical, optical and acoustic types. Compared with other types of hydrogen sensors, optical sensors are safer and do not involve circuit risks; secondly, because their original signal is an optical signal rather than an electrical signal, they are less sensitive to electromagnetic noise than other types of sensors; in addition, this type of sensor can perform real-time tracking monitoring.

[0004] There are many types of sensors that use optical changes for detection in the prior art, such as interference type, grating type, etc. The traditional interference type hydrogen sensor is to plate palladium on the interference structure of Mach-Zehnder or Fabry-Perot. When it comes into contact with hydrogen, the palladium film will deform, resulting in the deformation of the interference structure, which in turn causes the spectrum to change. Based on this, hydrogen concentration sensing can be performed. However, the above method is difficult to coat in the fiber interferometer, and the processing repeatability is also poor.

[0005] Thin film interference irradiates a beam of light waves onto a thin film. Due to the different refractive indices, the light waves will be reflected by the upper and lower interfaces of the thin film respectively, and new light waves will be formed due to mutual interference. Compared with the interference structure in the commonly used interferometer, thin film interference has a simpler structure, lower cost and faster feedback. Summary of the invention

[0006] The present invention provides a thin film interference type hydrogen sensor and a hydrogen tracking detection method, which are used to solve the problems of complex structure and high cost of the current interference type hydrogen sensor.

[0007] In order to solve the above technical problems, the technical solution of the present invention is: the thin film interference type hydrogen sensor includes a container with a cavity and an opening on the upper surface, a substrate placed on the lower surface in the cavity, a gasket arranged between an edge of the substrate and the lower surface, a glass plate closing the opening, and a light source penetrating into the cavity through the glass plate, the glass plate is parallel to the lower surface, an air layer is present between the substrate and the glass plate, a palladium film is provided on the surface of the substrate on one side close to the glass plate, the container is provided with a valve leading to the air layer, and the incident light of the light source is perpendicular to the glass plate.

[0008] Optionally, the palladium film has a thickness of 10 nm to 1000 nm, and a thickness non-uniformity of less than 1%.

[0009] Optionally, the substrate is made of glass, metal, silicon wafer, ceramic, crystal, etc., and the palladium film is coated on the surface of the substrate by sputtering, evaporation or pulsed laser deposition process.

[0010] Optionally, the light source is monochromatic light and is a surface light source.

[0011] Optionally, the contact surface between the glass plate and the container is provided with vacuum sealing grease.

[0012] Optionally, a gasket is used to make the angle between the substrate and the lower surface greater than 0° and less than 2°.

[0013] Optionally, the valve includes an air inlet valve and an air outlet valve.

[0014] The present invention also provides a method for hydrogen tracking detection using the above-mentioned thin film interference type hydrogen sensor, which comprises the following steps:

[0015] S1. The light source is incident vertically, and the air layer shows the first interference fringe, and an observation scale is determined within the field of view;

[0016] S2. The gas to be tested is introduced, and the thickness of the palladium film changes with the change of the hydrogen concentration in the gas, and the thickness of the air layer also changes accordingly, and the first interference fringes change to the second interference fringes;

[0017] S3. Observe the displacement of the interference fringes at the scale position to determine the change in the hydrogen concentration in the gas to be measured. Relative to the initial position, if the displacement of the interference fringes increases, the hydrogen concentration increases, and if the displacement decreases, the hydrogen concentration decreases.

[0018] Optionally, the method further comprises calculating the hydrogen concentration in the gas to be measured according to the displacement of the interference fringes.

[0019] Optionally, the calculation method comprises the following steps: introducing several gases with standard hydrogen concentrations to obtain the change in palladium film thickness at the corresponding standard concentrations, fitting a standard curve of the relationship between the change in palladium film thickness and hydrogen concentration, and then substituting the change in air layer thickness obtained in the test process into the standard curve to obtain the corresponding hydrogen concentration; comparing and obtaining the displacement of the first interference fringe and the second interference fringe at the observation scale, and obtaining the change in air layer thickness according to Formula 1:

[0020] ΔH=Dλ / 2L Formula 1;

[0021] Among them, ΔH is the change in the thickness of the air layer, D is the displacement of the interference fringes at the observation scale, λ is the wavelength of the light source, and L is the distance between two adjacent bright fringes or dark fringes.

[0022] Optionally, by adjusting the thickness and / or position of the gasket, the angle between the substrate and the lower surface is adjusted, and finally the resolution of the thin film interference type hydrogen sensor is adjusted.

[0023] The technical solution provided by the present invention constructs a thin film interference structure in a confined space. The thickness of the thin film in the interference structure will change with the change of hydrogen concentration, which can be reflected in the change of interference fringes. The designed sensor has a simple structure, sensitive response, low cost and high safety. It is particularly suitable for intuitive monitoring of hydrogen concentration in areas with complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a specific embodiment of the thin film interference type hydrogen sensor of the present invention;

[0025] Figure 2 It is a schematic flow chart of the hydrogen tracking method of the present invention;

[0026] Figure 3 It is a schematic flow chart of the hydrogen concentration detection method of the present invention.

[0027] As shown in the figure:

[0028] 10 - container, 11 - bottom plate, 12 - side wall, 13 - cavity, 20 - substrate, 30 - palladium film, 40 - gasket, 50 - glass plate, 60 - light source, 70 - air layer, 81 - air inlet valve, 82 - air outlet valve. DETAILED DESCRIPTION

[0029] For ease of understanding, the thin film interference type hydrogen sensor and the hydrogen tracking detection method are described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0030] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation and positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] like Figure 1 As shown, the thin film interference type hydrogen sensor includes a rectangular container 10, a substrate 20 arranged in the container 10, a palladium film 30 arranged on the upper surface of the substrate 20, a gasket 40 arranged under the substrate 20, a glass plate 50 arranged on the container 10, and a light source 60 arranged above the glass plate 50.

[0033] Continue to see Figure 1 The container 10 includes a bottom plate 11, a side wall 12 arranged on the bottom plate 11, an internal cavity 13 and an opening on the cavity 13. The substrate 20 is placed on the lower surface of the cavity 13, that is, the bottom plate 11. The gasket 40 is located between an edge of the substrate 20 and the bottom plate 11. The glass plate 50 is provided with vacuum sealing grease around the contact with the side wall 12, so that the cavity 13 becomes a closed space.

[0034] Continue to see Figure 1 The area between the palladium film 30 and the glass plate 50 is an air layer 70. The glass plate is parallel to the bottom plate 11. The light source 60 is incident vertically from above the glass plate 50 and penetrates into the air layer 70 through the glass plate. The gasket 40 forms an angle between the substrate 20 and the bottom plate 11, so the air layer 70 is a wedge-shaped flat plate. The air layer 70 is equivalent to a thin film. The incident light is reflected at the upper and lower interfaces of the air layer 70 respectively, and interference fringes of equal thickness with alternating light and dark are formed due to mutual interference.

[0035] Continue to see Figure 1 An air inlet valve 81 leading to the air layer 70 is disposed on one side of the side wall 12, and an air outlet valve 82 connecting the air layer 70 to the outside is disposed on the other side.

[0036] The palladium film 30 has a thickness of 10 nm to 1000 nm, and a thickness non-uniformity of less than 1%.

[0037] The substrate 20 is made of glass, metal, silicon wafer, ceramic, crystal, etc. The palladium film 30 is coated on the upper surface of the substrate 20 by a sputtering deposition process.

[0038] The light source 60 is monochromatic light, which can improve the contrast of interference fringes, and is an LED surface light source.

[0039] The angle between the substrate 20 and the bottom plate 11 is approximately between 0° and 2°.

[0040] Hydrogen tracking can be performed using the thin film interference type hydrogen sensor, which includes the following steps:

[0041] S1. The light source 60 is incident vertically, and the air layer 70 shows a first interference fringe, and an observation scale is determined within the field of view;

[0042] S2. Open the air inlet valve 81 and the air outlet valve 82 to allow the measured air flow to continue to flow. Palladium has a specific characteristic of expanding when absorbing hydrogen and contracting when desorbing. Therefore, the thickness of the surface of the palladium film 30 changes after contacting hydrogen, and the thickness of the air layer 70 also changes accordingly, and the first interference fringe changes to the second interference fringe;

[0043] S3. Observe the displacement of the interference fringes at the scale position to determine the change in the hydrogen concentration in the gas to be measured. Relative to the initial position, if the displacement of the interference fringes increases, the hydrogen concentration increases, and if the displacement decreases, the hydrogen concentration decreases. When there is no hydrogen in the gas flow, the position of the interference fringes remains unchanged.

[0044] The thin film interference type hydrogen sensor can be used to estimate the hydrogen concentration while tracking, which includes the following steps:

[0045] S1. Passing a number of hydrogen gas of standard concentrations to obtain the change in the thickness of the palladium film at the corresponding standard concentration, and fitting a standard curve of the relationship between the change in the thickness of the palladium film and the hydrogen concentration. The specific process is as follows:

[0046] S11. The initial film thickness of the palladium film 30 is measured by a probe scanning method to be 100 nm. The container 10 is evacuated, the inlet valve 81 and the outlet valve 82 are closed, and the light source 60 is incident vertically;

[0047] S12. A mixture of hydrogen and nitrogen is introduced, wherein the standard concentration of hydrogen is 4%, the thickness of the palladium film 30 changes, and the thickness change value of the palladium film 30 is measured after removal to construct a corresponding data of the hydrogen concentration and the thickness change value of the palladium film 30;

[0048] S13. After evacuating the vacuum again, repeat steps S11 and S12 to obtain corresponding data of a number of standard hydrogen concentrations and thickness changes of the palladium film 30, and then fit the change curve using discrete points in the coordinate axis, such as using the least squares method;

[0049] S2. Evacuate the container, close the outlet valve 82, and introduce the gas to be tested from the inlet valve 81. Observe the displacement D of the interference fringes at the scale, and obtain the change in the thickness of the air layer according to formula 1:

[0050] ΔH=Dλ / 2L Formula 1;

[0051] Where ΔH is the change in the thickness of the air layer, D is the displacement of the interference fringes at the observation scale, λ is the wavelength of the light source, and L is the distance between two adjacent bright or dark fringes;

[0052] S3. According to the change in the thickness of the air layer ΔH, that is, the change in the thickness of the palladium film 30, the corresponding hydrogen concentration is found in the fitting curve.

[0053] By adjusting the thickness and / or position of the gasket, the angle between the substrate and the bottom plate 11 can be adjusted. The smaller the angle, the greater the displacement of the interference fringes at the observation scale under the same hydrogen concentration, that is, the same change in the thickness of the air layer, which means that the observability and precision are higher.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for hydrogen tracking detection using a thin film interference type hydrogen sensor, characterized in that: The thin film interference type hydrogen sensor comprises a container with a cavity and an opening on the upper surface, a substrate placed on the lower surface in the cavity, a gasket arranged between a point on the edge of the substrate and the lower surface, a glass plate closing the opening, and a light source penetrating into the cavity through the glass plate, wherein the glass plate is parallel to the lower surface, an air layer is present between the substrate and the glass plate, a palladium film is provided on the surface of one side of the substrate close to the glass plate, a valve leading to the air layer is provided in the container, and the incident light of the light source is perpendicular to the glass plate; The method comprises the following steps: 1) The light source is incident vertically, and the air layer shows the first interference fringe, and an observation scale is determined in the field of view; 2) introducing the gas to be tested, the thickness of the palladium film changes with the change of the hydrogen concentration in the gas, the thickness of the air layer also changes accordingly, and the first interference fringes change into second interference fringes; 3) Observe the displacement of interference fringes at the scale position to determine the change in hydrogen concentration in the gas to be measured. Relative to the initial position, if the displacement of interference fringes increases, the hydrogen concentration increases, and if the displacement decreases, the hydrogen concentration decreases; Calculate the hydrogen concentration in the gas to be tested based on the displacement of the interference fringes: The calculation method includes the following steps: introduce a number of gases with standard hydrogen concentrations to obtain the change in palladium film thickness at the corresponding standard concentration, fit a standard curve of the relationship between the change in palladium film thickness and hydrogen concentration, and then bring the change in air layer thickness obtained during the test process into the standard curve to obtain the corresponding hydrogen concentration; compare and obtain the displacement of the first interference fringes and the second interference fringes at the observation scale, and obtain the change in air layer thickness according to Formula 1: ΔH=Dλ / 2L Formula 1; Among them, ΔH is the change in the thickness of the air layer, D is the displacement of the interference fringes at the observation scale, λ is the wavelength of the light source, and L is the distance between two adjacent bright fringes or dark fringes.

2. The method according to claim 1, characterized in that: By adjusting the thickness and / or position of the gasket, the angle between the substrate and the lower surface is adjusted. The smaller the angle, the higher the precision. Finally, the precision of the thin film interference type hydrogen sensor is adjusted.

3. The method according to claim 1, characterized in that: The palladium film has a thickness of 10nm to 1000nm, and a thickness non-uniformity of less than 1%.

4. The method according to claim 1, characterized in that: The substrate is a solid substrate with uniform thickness and polished on one side or both sides. The substrate material is glass, metal, silicon wafer, ceramic or crystal. The palladium film is coated on the surface of the substrate by sputtering, evaporation or pulse laser deposition process.

5. The method according to claim 1, characterized in that: The light source is monochromatic light and is a surface light source.

6. The method according to claim 1, characterized in that: The contact surface between the glass plate and the container is provided with vacuum sealing grease.

7. The method according to claim 1, characterized in that: The spacer is used to ensure that the angle between the substrate and the lower surface is greater than 0° and less than 2°.

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