A low-temperature hydrogen sensor based on acoustic metamaterials

Abstract

The application discloses a low-temperature hydrogen sensor based on acoustic metamaterials, which is a tubular structure composed of two parts of phononic crystals, interface states are formed on the butt joint interface of the two parts of phononic crystals, and the detection of hydrogen concentration is realized by utilizing the relationship between the frequency of the interface states and the acoustic characteristics of the gas medium in the tube. The low-temperature hydrogen sensor provided by the application uses acoustic interface states as the basic principle of the sensor, can avoid the shortcoming that the performance of the traditional hydrogen sensor is reduced with the reduction of temperature, and thus realizes low-temperature hydrogen sensing. The frequency of the interface states is determined by the acoustic characteristics of the gas medium in the tube, and the acoustic characteristics of hydrogen are quite different from those of air, so when hydrogen is mixed into air, the interface states will be shifted, and thus the hydrogen concentration can be detected by measuring the frequency and the sound pressure at the interface. The application does not need sensitive materials to absorb hydrogen in principle, and thus can be used at extremely low temperature.

Description

Technical Field

[0001] The invention relates to a low-temperature hydrogen sensor based on acoustic metamaterials, belonging to hydrogen sensing technology. Background Art

[0002] Compared to fossil fuels, hydrogen energy is clean and renewable, offering promising applications in fuel cells and hydrogen-powered vehicles. However, due to its colorless, odorless, flammable, and explosive properties, hydrogen requires highly sensitive sensors for monitoring. Research on hydrogen sensors has yielded significant results, with known types including electrochemical, semiconductor, catalytic, thermal conductivity, optical, and acoustic. These sensors operate on different principles, but most require a sensitive material to react with hydrogen to adsorb hydrogen. However, repeated hydrogen adsorption can easily damage the sensitive material, shortening the sensor's lifespan. Furthermore, because high temperatures enhance the reaction between hydrogen and the sensitive material, hydrogen sensors with heating elements are significantly more sensitive than those operating at room temperature. However, heating not only consumes significant power but also poses an explosion risk. Therefore, room-temperature hydrogen sensors face the challenge of further improving their sensitivity. When temperatures drop below freezing, the sensitivity of hydrogen sensors based on these materials decreases significantly, making them unsuitable for low-temperature applications. Summary of the Invention

[0003] Purpose of the invention: To overcome the shortcomings of the existing technology, the present invention provides a low-temperature hydrogen sensor based on acoustic metamaterials. Compared with traditional hydrogen sensors, this sensor utilizes the acoustic properties of the gas medium in the waveguide in principle, does not require sensitive materials to adsorb hydrogen, and can overcome the limitations of traditional hydrogen sensors on low-temperature working environments.

[0004] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0005] A low-temperature hydrogen sensor based on acoustic metamaterials. The acoustic metamaterial is a tubular structure composed of two parts of phononic crystals. An interface state is formed at the docking interface of the two parts of the phononic crystals. The relationship between the frequency of the interface state and the acoustic properties of the gas medium in the tube is used to detect the hydrogen concentration.

[0006] Preferably, the two parts of phononic crystals are respectively called phononic crystals PC L and phononic crystal PC R , phononic crystal PC L and phononic crystal PC R The radius is r A Cylindrical waveguide W A and radius r B Cylindrical waveguide W BPeriodically alternating arrangement constitutes phononic crystal PC L The single cell and the phononic crystal PC R The individual cells have the same total length. The cylindrical waveguide W in the individual cells A The ratio of the total length of a single cell is called the cell ratio; adjusting the phononic crystal PC L Cell ratio and phononic crystal PC R The cell ratio of the phononic crystal PC L and phononic crystal PC R At least one band gap in the band structure has different topological properties.

[0007] Specifically, a phononic crystal PC is designed. The phononic crystal PC is composed of a radius r A Cylindrical waveguide W A and radius r B Cylindrical waveguide W B The phononic crystal PC is composed of a periodic alternating arrangement, and the single cell of the phononic crystal PC and the phononic crystal PC L A single cell, forming a phononic crystal PC R The individual cells of the phononic crystal PC have the same total length; the cell ratio of the phononic crystal PC is continuously adjusted, and each band gap of the phononic crystal PC will change continuously; the cell ratio of the phononic crystal PC is continuously adjusted until at least one band gap of the phononic crystal PC undergoes a transition from open to closed and then to open. The cell ratio of the phononic crystal PC when the band gap is closed is called the topological critical point; the phononic crystal PC is set to L Cell ratio and phononic crystal PC R The cell ratios are located on both sides of the topological critical point of the phononic crystal, namely the phononic crystal PC L Cell ratio and phononic crystal PC R The cell ratio of , one of which is smaller than the topological critical point and the other is larger than the topological critical point, can realize the phononic crystal PC L and phononic crystal PC R At least one band gap in the band structure has different topological properties.

[0008] Preferably, the phononic crystal PC is formed L The cell consists of two segments of length l AL / 2 cylindrical waveguide W A and a segment of length l BL Cylindrical waveguide W B , cylindrical waveguide W B Sandwiched between two cylindrical waveguides W A The total length of a single cell is l = l AL +l BL , phononic crystal PC LThe ratio of the cell of the phononic crystal PC The phononic crystal PC R The cell comprises two cylindrical waveguides W AR with a length of l A / 2 and a cylindrical waveguide W BR with a length of l B The cylindrical waveguide W B is sandwiched between the two cylindrical waveguides W A The total length of the single cell is l = l AR + l BR The ratio of the cell of the phononic crystal PC R is denoted as In the design of the phononic crystal PC, a similar structure is adopted, i.e. the cell of the phononic crystal PC comprises two cylindrical waveguides W A with a length of l A / 2 and a cylindrical waveguide W B with a length of l B The cylindrical waveguide W B is sandwiched between the two cylindrical waveguides W A The total length of the single cell is l = l A + l B The ratio of the cell of the phononic crystal PC is denoted as

[0009] Preferably, the number of the cells of the phononic crystal PC L and the phononic crystal PC R is equal and is more than three. In the design of the phononic crystal PC, a similar structure is adopted, i.e. the number of the cells of the phononic crystal PC L , the phononic crystal PC R and the phononic crystal PC is equal and is more than three.

[0010] Preferably, the two parts of the phononic crystal are respectively denoted as the phononic crystal PC L and the phononic crystal PC R An interface state is formed on the interface of the two parts of the phononic crystal, and the frequency of the interface state is determined according to the equation X L + X R = 0, wherein X L and X R are the acoustic reactance of the phononic crystal PC L and the phononic crystal PC R respectively; according to the physical relationship between the interface state frequency and the sound velocity of the gas, the physical relationship between the sound velocity of the gas and the gas component, and the physical relationship between the gas component and the hydrogen concentration, a mathematical relationship between the interface state frequency and the hydrogen concentration is determined.

[0011] Preferably, the frequency offset of the interface state is Δf IThe relationship with the hydrogen concentration δ is The interface state frequency offset Δf I is approximately proportional to the hydrogen concentration δ, wherein f I is the interface state frequency of the background gas, i.e. the gas mixed with hydrogen, such as the case of mixing hydrogen in air, and the concentration of hydrogen in air needs to be detected.

[0012] Advantages: the low-temperature hydrogen sensor based on acoustic metamaterials provided by the application utilizes the relationship between the interface state frequency and the acoustic characteristics of the gas medium in the waveguide to detect the hydrogen concentration, and does not need a sensitive material to adsorb hydrogen, thus having the following advantages: first, the low-temperature hydrogen sensor has a quite wide working temperature range and performs well even at an extremely low temperature of -34℃; second, the sensitivity of the low-temperature hydrogen sensor will not decrease due to the presence of oxygen in air; in addition, since the response and recovery processes are physical processes, the low-temperature hydrogen sensor has excellent linearity, fast dynamic response and good repeatability; finally, the low-temperature hydrogen sensor can be free from mechanical damage caused by repeated adsorption of hydrogen, thus having a long service life. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a structural schematic diagram of the application;

[0014] Fig. 2(a) is the band structure of the phononic crystal PC L in the embodiment;

[0015] Fig. 2(b) is the band structure of the phononic crystal PC R in the embodiment;

[0016] Fig. 2(c) is the band structure of the phononic crystal with different cell ratios in the embodiment;

[0017] Figure 3 is an experimental system adopting the structure of the embodiment, and the figure includes: 1-gas source, 2-gas mixing instrument, 3-refrigerator, 4-thermometer, 5-loudspeaker as an audio signal playing device, 6-low-temperature hydrogen sensor, 7-microphone as an audio signal receiving device, and 8-data acquisition device with a signal generator;

[0018] Figure 4 is the frequency spectrum obtained by simulation and experimental measurement of the low-temperature hydrogen sensor at the interface in the embodiment;

[0019] Figure 5 is the sound velocity of hydrogen and air at different temperatures;

[0020] Figure 6 is the interface state corresponding to different hydrogen concentrations at room temperature (21℃) measured by experiment;

[0021] Figure 7 Frequency shifts in air for theoretical calculations, simulations and experimental measurements are compared for room temperature (21 °C) and cryogenic temperature (-34 °C);

[0022] Figure 8(a) shows the relative frequency shift versus hydrogen concentration in air for experimental measurements at 21 °C and -34 °C;

[0023] Figure 8(b) shows the relative frequency shift versus hydrogen concentration in air for experimental measurements with different sizes of cryogenic hydrogen sensors;

[0024] Figure 9 Dynamic response of the interface state frequency to different concentrations of hydrogen;

[0025] Figure 10(a) shows the acoustic pressure change corresponding to different concentrations of hydrogen in air for experimental measurements at 21 °C;

[0026] Figure 10(b) shows the acoustic pressure change corresponding to different concentrations of hydrogen in air for experimental measurements at -34 °C;

[0027] Figure 11 Dynamic response of the acoustic pressure amplitude to different concentrations of hydrogen;

[0028] Figure 12 Sound velocity of hydrogen and argon at different temperatures;

[0029] Figure 13(a) shows frequency shifts in argon for theoretical calculations, simulations and experimental measurements, comparing room temperature (21 °C) and cryogenic temperature (-34 °C);

[0030] Figure 13(b) shows frequency shifts at room temperature for theoretical calculations, simulations and experimental measurements, comparing air and argon as background;

[0031] Figure 14 Relative frequency shift versus hydrogen concentration in argon for 21 °C and -34 °C;

[0032] Figure 15(a) shows the acoustic pressure change corresponding to different concentrations of hydrogen in argon for experimental measurements at 21 °C;

[0033] Figure 15(b) shows the acoustic pressure change corresponding to different concentrations of hydrogen in argon for experimental measurements at -34 °C. DETAILED DESCRIPTION

[0034] The application will be described in more detail with reference to the drawings and specific embodiments.

[0035] The application discloses a low-temperature hydrogen sensor based on acoustic metamaterials, which is a tubular structure composed of two parts of phononic crystals, interface states are formed on the joint interface of the two parts of phononic crystals, and the detection of hydrogen concentration is realized by utilizing the relationship between the frequency of the interface states and the acoustic characteristics of the gas medium in the tube.

[0036] As shown in Figure 1 , the low-temperature hydrogen sensor based on acoustic metamaterials is a tubular structure composed of two parts of phononic crystals, the two parts of phononic crystals are called phononic crystal PC L and phononic crystal PC R , the phononic crystal PC L and the phononic crystal PC R are both composed of a cylindrical waveguide W A with a radius of r A and a cylindrical waveguide W B with a radius of r B periodically arranged alternately; the total length of the single cell constituting the phononic crystal PC L and the single cell constituting the phononic crystal PC R is l, and the ratio of the cylindrical waveguide W A in the single cell to the total length of the single cell is called the cell ratio. Meanwhile, a phononic crystal PC with a similar structure is designed, the phononic crystal PC is composed of a cylindrical waveguide W A with a radius of r A and a cylindrical waveguide W B with a radius of r B periodically arranged alternately, and the single cell constituting the phononic crystal PC and the single cell constituting the phononic crystal PC L and the single cell constituting the phononic crystal PC R have the same total length. In this example, the number of the single cells constituting the phononic crystal PC L , the phononic crystal PC R and the phononic crystal PC is three.

[0037] In this example, the cell constituting the phononic crystal PC L includes two cylindrical waveguides W A with a length of l AL / 2 and one cylindrical waveguide W B with a length of l BL , the cylindrical waveguide W B is clamped between the two cylindrical waveguides W A , the total length of the single cell is l = l AL +l BL , and the cell ratio of the phononic crystal PC L is The cell constituting the phononic crystal PC R includes two cylindrical waveguides W AR with a length of l A / 2 and a cylindrical waveguide W BR with a length of l B , the cylindrical waveguide W B is sandwiched between the two cylindrical waveguides W A , and the total length of the single cell is l = l AR +l BR , and the cell ratio of the phononic crystal PC R is denoted as The cell constituting the phononic crystal PC includes two cylindrical waveguides W A with a length of l A / 2 and a cylindrical waveguide W B with a length of l B , the cylindrical waveguide W B is sandwiched between the two cylindrical waveguides W A , and the total length of the single cell is l = l A +l B , and the cell ratio of the phononic crystal PC is denoted as

[0038] In this example, the cell ratio is designed as l = 5.95 cm. If the cell ratio of the phononic crystal PC is continuously adjusted, each band gap of the phononic crystal PC will continuously change; the cell ratio of the phononic crystal PC is continuously adjusted until at least one band gap of the phononic crystal PC experiences a transition from opening to closing and then to opening, and the cell ratio of the phononic crystal PC when the band gap is closed is called a topological critical point; the cell ratio of the phononic crystal PC L and the cell ratio of the phononic crystal PC R are located on the two sides of the topological critical point of the phononic crystal, i.e., the cell ratio of the phononic crystal PC L and the cell ratio of the phononic crystal PC R , one of which is less than the topological critical point and the other of which is greater than the topological critical point, so that at least one band gap in the energy band structure of the phononic crystal PC L and the phononic crystal PC R has different topological properties.

[0039] In this example, the determined topological critical point is 0.50, the cell ratio of the phononic crystal PC L is designed as 0.35, and the cell ratio of the phononic crystal PC R is designed as 0.76; accordingly, l AL = 2.10 cm, l BL = 3.85 cm, and the energy band structure of the phononic crystal PC L is shown in FIG. 2(a); lAR =4.55cm, l BR =1.40cm, phononic crystal PC R The band structure of is shown in Figure 2(b).

[0040] The topological properties of any band gap in the band structure are determined by the sum of the Zak phases of the bands below it. As shown in Figure 2(c), when the cell ratio is from 0.35 (PC L ) changes continuously to 0.76(PC R ), the first band gap is not closed, so the Zak phase of the first energy band does not change. In this case, the phononic crystal PC L and phononic crystal PC R The first energy band has the same Zak phase. Since the topological properties of the first band gap are determined by the Zak phase of the first energy band, the phononic crystal PC L and phononic crystal PC R The first band gap has the same topological properties; when the cell ratio is from 0.35 (PC L ) changes continuously to 0.76(PC R ), the second band gap undergoes a transition from open to closed and then to open, so the Zak phase of the second energy band changes. Figure 2(a) and 2(b) The phononic crystal PC shown L and phononic crystal PC R The spatial distribution of the eigenmodes at the bottom and top of the second energy band (both expressed in W A As the origin), we can judge that the Zak phases of their second energy bands are π and 0 respectively. Since the topological properties of the second band gap are determined by the sum of the Zak phases of the first and second energy bands, the phononic crystal PC L and phononic crystal PC R The second band gap has different topological properties; therefore, the second band gap in the phononic crystal PC L and phononic crystal PC R An interface state will appear on the docking surface.

[0041] like Figure 3The experimental system using the low-temperature hydrogen sensor is shown. The low-temperature hydrogen sensor 6 is arranged in the low-temperature environment provided by the refrigerator 3, the thermometer 4 monitors the temperature in the refrigerator in real time, the gas to be measured is stored in the gas source 1, is connected to the gas inlet of the low-temperature hydrogen sensor 6 through the gas distribution instrument 2, and is finally discharged from the gas outlet of the low-temperature hydrogen sensor 6. The microphone 7 and the loudspeaker 5 are oppositely arranged at the two ends of the interface of the two parts of the phononic crystal. A broadband white noise signal of 1000-7000 Hz is used to drive the loudspeaker 5, the sound wave emitted by the loudspeaker 5 enters the low-temperature hydrogen sensor 6 through the conical horn, and is received by the microphone 7 after passing through the low-temperature hydrogen sensor 6 and reaching the other end of the interface. The sound pressure signal collected by the microphone 7 is subjected to Fourier transform, and the sound pressure spectrum is obtained.

[0042] As shown in Figure 4 The frequency spectrum obtained by simulation and experimental measurement of the low-temperature hydrogen sensor at the interface is shown. It can be seen that the interface state frequency is 5453 Hz. The interface state frequency of the low-temperature hydrogen sensor is determined by the following equation:

[0043] X L +X R =0 (1)

[0044] Wherein: X L and X R are the acoustic impedance of the phononic crystal PC L and the phononic crystal PC R . X L and X R can be obtained according to the impedance transfer theory. According to the impedance transfer theory, X L and X R are related to the frequency of the sound wave, the structural parameters and the sound velocity of the gas medium in the tube. The sound velocity c of the gas can be expressed as Where γ is the specific heat ratio of the gas, and P and ρ are the pressure and mass density of the gas, respectively. Therefore, when the structural parameters and the gas pressure of the low-temperature hydrogen sensor are constant, the interface state frequency depends on the acoustic characteristics of the gas, and the interface state shifts with the change of the gas component.

[0045] Considering that the gas is a mixed gas mixed with hydrogen gas with a concentration of δ in air, the density of the mixed gas is ρ = δρ h +(1-δ)ρ0, when the gas pressure P is constant, the sound velocity of the gas can be expressed as:

[0046]

[0047] Where δ is a small quantity. In the formula, it has been considered that hydrogen and air have the same γ. According to the impedance transfer formula, the shift amount Δf I of the interface state frequency caused by the mixed hydrogen is determined by the following formula:

[0048]

[0049] Where: f I is the interface state frequency of the background air, and Δc is the shift in the speed of sound caused by the mixing of hydrogen. From this, the theoretical formula for the interface state frequency shift can be obtained:

[0050]

[0051] It can be seen that the relative sensitivity of the low-temperature hydrogen sensor is a constant of 0.50 and has nothing to do with the size of the structure. The initial interface state frequency f in air I The larger the value, the greater the offset of the interface state frequency caused by the same hydrogen concentration, and the absolute sensitivity of the low-temperature hydrogen sensor The higher it is.

[0052] The speeds of sound of hydrogen and air at room temperature are c h =1280m / s and c0=330m / s, which are very different. Therefore, a small amount of hydrogen mixed into the air can cause a significant shift in the interface state.

[0053] According to the ideal gas equation of state, the speed of sound can be expressed as:

[0054]

[0055] Where: R is the gas constant, T is the temperature, and M is the molar mass of the gas. When the ambient temperature changes, the gas sound speed can be expressed as:

[0056]

[0057] Where: T0 is the initial temperature, ΔT is the temperature change, and ΔT is small compared to T0. The effect of temperature on the initial interface state frequency can be expressed as:

[0058]

[0059] It can be seen that the relative sensitivity of the low-temperature hydrogen sensor has nothing to do with temperature. Figure 5 The figure shows the sound speed of hydrogen and air at different temperatures. It can be seen that the sound speed of hydrogen and air changes very little with temperature. Therefore, the absolute sensitivity of the low-temperature hydrogen sensor is little affected by temperature.

[0060] like Figure 6 The frequency spectrum of the interface state at room temperature (21°C) corresponding to hydrogen concentrations of 0, 0.36%, 0.64%, and 0.88% is shown. It can be seen that when the hydrogen concentration increases, the interface state frequency shifts to high frequency. The frequency shift Δf of the interface state at room temperature (21°C) and low temperature (-34°C)I The relationship with hydrogen concentration is as follows Figure 7 As shown in the figure, it shows good linearity and the sensitivity at low temperature is only 11% lower than that at room temperature. This shows that our low-temperature hydrogen sensor can be used for hydrogen detection at extremely low temperatures.

[0061] As shown in Figure 8(a), the relative frequency shift Δf at 21°C and -34°C I / f I With the relationship of δ, we can see that Δf I / f I Proportional to δ, with a proportionality coefficient of 0.50, and independent of the operating temperature. The experimental results are consistent with formula (4). In addition, the relative sensitivity of the low-temperature hydrogen sensor is also independent of the structural parameters. We made a sensor with a size 0.8 times that of the original sensor, with a cross-sectional radius of r A =1.34cm and r B =0.84cm, unit length is l AL =1.68cm, l BL =3.08cm and l AR =3.64cm, l BR =1.12cm, the initial interface state frequency is 6853Hz. As shown in Figure 8(b), its relative sensitivity is still 0.50.

[0062] like Figure 9 Shown is the interface state frequency f I The dynamic response of each round of ventilation and deflation is 4 minutes. It can be seen that when hydrogen is introduced, f I The response occurs quickly, and after the hydrogen is evacuated, I Return to the original value.

[0063] When the interface state shifts with the introduction of hydrogen, the initial interface state frequency f I The sound pressure at the location also decreases. Figure 6 As shown. Since sound pressure is easier to measure directly, the change of hydrogen content in the environment can be monitored by measuring the sound pressure amplitude. We use the frequency f I The sine signal is used to drive the speaker, and the sound pressure signal collected by the microphone is Fourier transformed to obtain f I The sound pressure amplitude at . Figure 10(a) and 10(b) The values ​​shown are at 21°C and -34°C. I The relationship between the sound pressure amplitude and the hydrogen concentration at , we can see that they are similar. Figure 11For the dynamic response of the sound pressure amplitude, it can be seen that the sound pressure amplitude has a fast response, and the sound pressure amplitude returns to the original value after the hydrogen is exhausted. The response and recovery of the low-temperature hydrogen sensor are determined by the diffusion of the gas, which belongs to a physical process. Therefore, the low-temperature hydrogen sensor has a fast response to hydrogen, and can still recover to the original state after multiple rounds of gas release cycles, avoiding the baseline shift problem of the sensor based on chemical adsorption.

[0064] Since hydrogen can react with oxygen in air at room temperature on the surface of a metal catalyst, the sensitivity of a hydrogen sensor using a metal catalyst as a sensitive material in air is much lower than that in other background gases (such as argon, nitrogen). We used the hydrogen sensor of the present application to detect hydrogen in an argon background. Unlike hydrogen and air, argon is a monatomic molecular gas, and therefore has a different γ from hydrogen and air. Therefore, the sound velocity of the mixed gas of hydrogen and argon can be expressed as:

[0065] c≈c0(1+0.37δ) (8)Therefore, the relative frequency shift in the argon background is:

[0066]

[0067] It can be seen that the relative sensitivity in the argon background is 0.37, which is lower than the relative sensitivity 0.50 in the air background. Since the sound velocity of argon is lower than that of air, the initial interface state frequency of argon is also lower than that of air, so the absolute sensitivity in the argon background is also lower than that in the air background.

[0068] As shown in Figure 12 , the sound velocity of hydrogen is much higher than that of argon in a wide temperature range. As shown in Fig. 13(a), the absolute sensitivity at room temperature and low temperature in the argon background also differs not much. Fig. 13(b) compares the experimental results in the air and argon backgrounds, and it can be seen that the sensitivity in the air background is 62% higher than that in the argon background. As shown in Figure 14 , the relative sensitivity of the low-temperature hydrogen sensor in the argon background is 0.37, which is independent of temperature. As shown in Fig. 15(a) and Fig. 15(b), the sound pressure amplitude at f I is plotted against the hydrogen concentration in the argon background at 21℃ and -34℃, respectively, which is similar to the results in the air background.

[0069] The low-temperature hydrogen sensor does not need a sensitive material to adsorb hydrogen, and thus has the following advantages: first, the low-temperature hydrogen sensor has a relatively wide working temperature range and performs well even at an extremely low temperature of -34℃; second, the sensitivity of the low-temperature hydrogen sensor does not decrease due to the presence of oxygen in the air; third, since the response and recovery processes are physical processes, the low-temperature hydrogen sensor has a fast dynamic response and good repeatability; and finally, the low-temperature hydrogen sensor is immune to mechanical damage caused by repeated adsorption of hydrogen, and thus has a long service life.

[0070] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the above examples do not limit the present application in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present application.

Claims

1. An acoustic metamaterial-based low-temperature hydrogen sensor, characterized by: The acoustic metamaterial is a tubular structure composed of two parts of phononic crystals. An interface state is formed at the interface of the two parts of the phononic crystals. The relationship between the frequency of the interface state and the acoustic properties of the gas medium in the tube is used to detect the hydrogen concentration. The two parts of the phononic crystals are respectively called phononic crystal PC L and phononic crystal PC R , phononic crystal PC L and phononic crystal PC R The radius is Cylindrical waveguide W A and the radius is Cylindrical waveguide W B Periodically alternating arrangement constitutes phononic crystal PC L The single cell and the phononic crystal PC R The individual cells have the same total length. The cylindrical waveguide W in the individual cells A The ratio of the total length of a single cell is called the cell ratio; adjusting the phononic crystal PC L Cell ratio and phononic crystal PC R The cell ratio makes the phononic crystal PC L and phononic crystal PC R At least one band gap in the band structure has different topological properties.

2. The low-temperature hydrogen sensor based on acoustic metamaterials according to claim 1, characterized in that: The phononic crystal PC is designed, and the phononic crystal PC is composed of the cylindrical waveguide W with a radius of A and the cylindrical waveguide W with a radius of B periodically and alternately arranged, and the single cell of the phononic crystal PC and the single cell of the phononic crystal PC L and the single cell of the phononic crystal PC R have the same total length; the cell ratio of the phononic crystal PC is continuously adjusted, and each band gap of the phononic crystal PC is continuously changed; The cell ratio of the phononic crystal PC is continuously adjusted until at least one band gap of the phononic crystal PC experiences a transition from opening to closing and then to opening, and the cell ratio of the phononic crystal PC when the band gap is closed is referred to as a topological critical point; the cell ratio of the phononic crystal PC L and the cell ratio of the phononic crystal PC R are respectively located on both sides of the topological critical point of the phononic crystal, that is, the cell ratio of the phononic crystal PC L and the cell ratio of the phononic crystal PC R , one of which is less than the topological critical point, and the other is greater than the topological critical point, that is, the phononic crystal PC L and the phononic crystal PC R have different topological properties in at least one band gap of the band structure.

3. The low-temperature hydrogen sensor based on acoustic metamaterial according to claim 1 or 2, characterized in that: The cell constituting the phononic crystal PC L includes two segments of cylindrical waveguide W with length A and one segment of cylindrical waveguide W with length B , the cylindrical waveguide W B is sandwiched between the two segments of cylindrical waveguide W A , the total length of the single cell is , the cell of the phononic crystal PC L is denoted as ; A cell constituting a phononic crystal PC R includes two segments of a cylindrical waveguide W having a length of A and a segment of a cylindrical waveguide W having a length of B , the cylindrical waveguide W B is sandwiched between the two segments of the cylindrical waveguide W A , the total length of the single cell is , and the cell constituting the phononic crystal PC R is denoted by .

4. The low-temperature hydrogen sensor based on acoustic metamaterial according to claim 2, characterized in that: The cell constituting the phononic crystal PC L includes two segments of cylindrical waveguide W with length A and one segment of cylindrical waveguide W with length B , the cylindrical waveguide W B is sandwiched between the two segments of cylindrical waveguide W A , the total length of the single cell is , the cell of the phononic crystal PC L is denoted as ; The cell constituting the phononic crystal PC R includes two segments of cylindrical waveguide W with length A and one segment of cylindrical waveguide W with length B , the cylindrical waveguide W B is sandwiched between the two segments of cylindrical waveguide W A , the total length of the single cell is , the cell of the phononic crystal PC R is denoted as ; The cell that constitutes the phononic crystal PC consists of two segments of length Cylindrical waveguide W A and a long Cylindrical waveguide W B , cylindrical waveguide W B Sandwiched between two cylindrical waveguides W A The total length of a single cell is , the cell ratio of the phononic crystal PC is recorded as .

5. The low-temperature hydrogen sensor based on acoustic metamaterials according to claim 1, 2 or 4, characterized in that: The number of cells constituting the phononic crystal PC L and the phononic crystal PC R is equal and is three or more.

6. The low-temperature hydrogen sensor based on acoustic metamaterials according to claim 2 or 4, characterized in that: The phononic crystal PC L The phononic crystal PC R The sum of the number of the and cells is equal to the number of the phononic crystal PC and is three or more.

7. The low-temperature hydrogen sensor based on acoustic metamaterials of claim 1, wherein: The two-part phononic crystal is respectively referred to as phononic crystal PC L and phononic crystal PC R , interface states are formed on the butt joint interface of the two-part phononic crystal, and the interface state frequency is determined according to equation , wherein and are respectively the acoustic impedance of phononic crystal PC L and phononic crystal PC R ; according to the physical relationship between the interface state frequency and the gas sound speed, the physical relationship between the gas sound speed and the gas component, and the physical relationship between the gas component and the hydrogen concentration, a mathematical relationship between the interface state frequency and the hydrogen concentration is determined.

8. The low-temperature hydrogen sensor based on acoustic metamaterials according to claim 7, characterized in that: interface state frequency offset with hydrogen concentration is where is the interface state frequency of the background gas.

9. The low-temperature hydrogen sensor based on acoustic metamaterials according to claim 8, characterized in that: the background gas is air.

Images