A trace methane concentration detection system and method based on second-order singular points

Abstract

The present application relates to the field of gas concentration detection, and specifically provides a trace methane concentration detection system and method based on second-order singular point, the system comprising a double clamped beam resonant structure, a data acquisition and processing unit and a display module. The method comprises the following steps: coupling strength calculation value determination; system structure adjustment; working point calibration; frequency splitting-concentration relationship calibration; actual detection. The trace methane concentration detection system and method based on second-order singular point can preferentially identify methane molecules in a multi-component mixed gas, and then convert and amplify the small change in methane concentration into an easily observable system eigenfrequency shift through the characteristic of the quadratic root of the parameter change of the second-order singular point system and external small disturbance, so as to realize selective and high-sensitivity detection of weak methane concentration changes.

Description

Technical Field

[0001] This invention relates to the field of gas concentration detection, and specifically to a trace methane concentration detection system and method based on second-order singularities. Background Technology

[0002] Methane is an important energy gas, widely present in various aspects of daily life, including natural gas extraction and transportation, coal mine ventilation, landfills, wastewater treatment, agriculture, and urban gas pipelines. Methane leaks can cause not only safety accidents such as poisoning, fires, and explosions, but also energy losses. Therefore, achieving accurate, stable, and highly sensitive detection of methane concentrations, especially trace amounts, has significant engineering application value and environmental implications.

[0003] Currently, methane concentration detection has developed into several technical approaches, mainly including catalytic combustion, infrared absorption or laser spectroscopy, semiconductor metal oxide, and electrochemical methods. Catalytic combustion typically utilizes the temperature or resistance changes caused by the exothermic oxidation of methane on the surface of a catalytic element to achieve concentration detection; infrared absorption or laser spectroscopy relies on the absorption characteristics of methane molecules in characteristic absorption bands, measuring the attenuation of light intensity to invert the methane concentration; semiconductor metal oxide methods mainly utilize the interaction between methane and adsorbed oxygen on the surface of a sensitive material, causing changes in the material's conductivity, thereby achieving detection; electrochemical methods rely on changes in current, charge, and other signals generated by electrode interface reactions for measurement. These methods have been widely applied in industrial safety monitoring, environmental monitoring, and gas leak early warning systems.

[0004] However, existing methane detection methods still have significant limitations in trace detection and complex environmental applications. First, in trace methane detection scenarios, the output signal of traditional detection methods typically exhibits an approximately linear relationship with methane concentration. When the methane concentration is low, the signal variation is limited and easily affected by instrument noise, baseline drift, and environmental disturbances, resulting in limited detection limits and resolution, making it difficult to promptly identify subtle concentration changes. Second, methane molecules are chemically relatively stable, with relatively low reactivity at room temperature. This means that some detection methods relying on surface reactions or electrochemical processes often suffer from weak responses, high operating temperatures, or insufficient long-term stability in low-concentration methane detection. For example, catalytic combustion and some semiconductor metal oxide methane sensors typically require high operating temperatures, and their sensitive elements are prone to catalyst poisoning, activity decay, and material aging during long-term use, leading to zero-point drift, decreased sensitivity, and increased maintenance costs. Furthermore, trace methane detection is typically not performed in an ideal single-gas environment. In practical applications, the target environment often contains multiple background components, including water vapor, carbon dioxide, carbon monoxide, other low-molecular-weight hydrocarbons, and volatile organic compounds. These non-target gases may simultaneously interact with methane on the surface of sensitive materials, resulting in adsorption competition, cross-sensitivity, or non-specific responses. They may also cause coupling interference to the detection baseline and output signal by altering local temperature, humidity, pressure, and thermophysical parameters of the medium. Therefore, effectively identifying methane molecules in complex background gas compositions and accurately extracting their concentration information is one of the key problems that urgently needs to be solved in the field of trace methane detection. In addition, while some high-precision methane detection technologies have advantages in sensitivity or selectivity, they usually require complex optical systems, precision modulation and demodulation circuits, temperature and humidity compensation units, or subsequent algorithm processing modules. This results in a large overall device size, complex structure, and high cost, which is not conducive to building compact, low-maintenance, and easily integrated long-term online monitoring equipment.

[0005] In recent years, mass-sensitive detection methods based on resonant structure frequency shifts have provided new research ideas for gas detection in complex background gas environments. These methods typically introduce a specific adsorption coating on the surface of the resonant structure that recognizes the target gas. When target gas molecules are adsorbed by the coating, the equivalent mass of the resonant structure changes, causing a shift in the resonant frequency. For methane detection, adding a functional coating with specific methane adsorption capabilities to the surface of the resonant structure could potentially preferentially identify methane molecules under complex background gas conditions and convert methane adsorption behavior into a measurable frequency change signal, thus providing a new technical path to improve the selectivity of methane detection. However, under trace methane conditions, the additional mass change caused by the specific adsorption coating is usually small, resulting in a weak resonant frequency shift. The detection signal is easily limited by structural noise, environmental disturbances, and readout resolution, still failing to meet the demand for high-sensitivity detection in low-concentration scenarios. Therefore, how to further amplify the small frequency changes caused by methane adsorption while maintaining the specific recognition capability of methane remains an important problem that related technologies still need to solve. Summary of the Invention

[0006] This invention addresses the aforementioned problems by providing a trace methane concentration detection system and method based on second-order singularities. By adding a functional coating to the surface of the structure, it enables preferential identification of methane molecules in multi-component mixed gases. Furthermore, by leveraging the quadratic root-like property of parameter changes in the second-order singularity system to external perturbations, minute changes in methane concentration are transformed and amplified into easily observable intrinsic frequency shifts of the system, thereby achieving selective and highly sensitive detection of subtle changes in methane concentration.

[0007] This invention provides a trace methane concentration detection system and method based on second-order singularities, comprising:

[0008] A double-fixed beam resonant structure includes a reference beam, a sensitive beam, and a coupling structure placed between the two;

[0009] The data acquisition and processing unit is used to acquire the spectral response diagram of the double-fixed beam resonant structure and process the resonant peak position data in the spectral response diagram to calculate the methane concentration in the gas.

[0010] The display module, connected to the data acquisition and processing unit, is used to display the calculated gas concentration and output analog and digital signals.

[0011] Among them, the reference beam serves as a frequency reference and stability benchmark, the upper surface of the sensitive beam is uniformly covered with a functional coating for recognizing and adsorbing methane molecules, and the coupling structure is used to realize and adjust the dissipative coupling characterized by the pure imaginary coupling constant.

[0012] The data acquisition and processing unit includes:

[0013] The coupling strength calculation module is used to calculate the theoretical value of coupling strength based on the resonant frequencies of the sensitive beam and the reference beam, as well as the singularity requirements.

[0014] The spectrum acquisition module, including a vibration sensor and a spectrum analyzer, is used to acquire the spectrum response diagram of a double-fixed beam resonant structure.

[0015] The spectrum analysis module determines the two resonant frequency values ​​corresponding to the double-fixed beam resonant structure under singular point state based on the position of the resonant peak in the spectrum response diagram.

[0016] The function relationship module is used to determine the functional relationship between the difference between two resonant frequency values ​​and the gas concentration.

[0017] The gas concentration calculation module is used to calculate the methane concentration in a gas.

[0018] The trace methane concentration detection system based on second-order singularities provided by the present invention may also have the following features: the reference beam has a predetermined geometric dimension, the width and thickness of the sensitive beam are consistent with those of the reference beam, and the length of the sensitive beam has a predetermined difference from the length of the reference beam.

[0019] This invention also provides a method for detecting trace methane concentration based on second-order singularities, using the above-described system, and comprising the following steps:

[0020] S1, the theoretical value of coupling strength is determined. A second-order non-Hermitian Hamiltonian is established based on the parameters of the double-fixed beam resonant structure, and the coupling strength corresponding to the singular point state is calculated to obtain the theoretical value of coupling strength.

[0021] S2, System structure adjustment, placing the double-fixed beam resonant structure into a sealed space with reserved gas inlet, outlet and data transmission channels;

[0022] S3, Operating point calibration: Connect to the data acquisition and processing unit, adjust the actual value of coupling strength with reference to the theoretical value of coupling strength until the system reaches the second-order singularity, and record the various parameters of the system at this time as EP operating point calibration parameters;

[0023] S4, Frequency splitting-concentration relationship calibration: Keep the EP operating point calibration parameters unchanged, and sequentially introduce several gases with known methane concentrations into a closed space. Perform frequency sweeping and spectrum analysis on the double-fixed beam resonant structure under the condition of introducing each gas concentration. Based on the analysis results, establish the functional relationship between the resonant frequency difference of the double-fixed beam resonant structure and the gas concentration.

[0024] S5, actual testing, including:

[0025] S5-1, introduces the gas in the environment to be tested into a closed space;

[0026] S5-2, The frequency sweep excitation of the double-fixed beam resonant structure is performed, and the frequency domain response diagram of the double-fixed beam resonant structure is collected by vibration sensor and spectrum analyzer.

[0027] S5-3. Based on the position of the resonance peak in the spectrum response diagram, determine the two resonant frequency values ​​corresponding to the system, calculate the difference between the two resonant frequencies to obtain the frequency split, substitute the frequency split into the function relationship, and calculate the methane concentration in the current gas.

[0028] S5-4 The display module displays the calculation results and outputs analog and digital signals.

[0029] The trace methane concentration detection method based on second-order singularity provided by the present invention may also have the following features: In step S1, the calculation process of the theoretical value of coupling strength includes: solving for the eigenvalues ​​of the second-order non-Hermi Hamiltonian H to obtain the two eigenfrequencys of the system and the corresponding two eigenvectors. When the eigenvalues ​​are degenerate and the two eigenvectors coincide, the system reaches a singularity. The coupling strength at this time is calculated, that is, the theoretical value of coupling strength.

[0030] The trace methane concentration detection method based on second-order singularity provided by the present invention may also have the following features: the specific process of step S3 is as follows: the actual value of coupling strength is finely adjusted according to the theoretical value of coupling strength. When the two resonance peaks in the frequency domain response graph measured by the spectrum analyzer gradually approach each other on the spectrum until they just overlap, it is determined that the system has reached the second-order singularity. At this time, the system is in the singularity state, and the various parameters of the system in this state are recorded as EP operating point calibration parameters.

[0031] The trace methane concentration detection method based on second-order singularity provided by the present invention may also have the following feature: in step S3, the EP operating point calibration parameters include the resonant frequency and actual value of the coupling strength of the double-fixed beam resonant structure when the system is in the singularity operating state.

[0032] The trace methane concentration detection method based on second-order singularities provided by this invention may also have the following features: In step S4, the spectrum analysis includes: using a vibration sensor and a spectrum analyzer to acquire the frequency domain response diagram of the system, obtaining the two resonant frequency values ​​corresponding to the system at the corresponding concentration, calculating the difference between the two resonant frequency values ​​to obtain the frequency split; the functional relationship is derived based on the frequency split, the concentration value of the known concentration gas used for calibration, and the EP operating point calibration parameters, and is used to invert the methane concentration in the gas.

[0033] Compared with existing catalytic combustion, infrared absorption, and semiconductor metal oxide detection methods, the trace methane concentration detection system and method based on second-order singularities of the present invention have the following effects and benefits:

[0034] 1) The structure is relatively compact, which facilitates miniaturization and integration: The detection system of the present invention is mainly composed of a double-fixed beam resonant structure, a data acquisition and processing unit and a display module. The overall structure is more compact than optical air cells, long optical path detection systems and other solutions. It is easy to achieve miniaturization and integrated packaging by using micromachining, microelectromechanical systems technology or other micro-nano manufacturing methods, which is suitable for expansion into portable, online and array detection.

[0035] 2) It helps to suppress the impact of environmental disturbances on the accuracy of results: The detection system of this invention adopts a dual-fixed-beam resonant structure, in which one beam serves as a reference beam and the other as a sensitive beam coated with a functional layer. Factors such as ambient temperature fluctuations, substrate vibration, device aging, and some non-specific background adsorption typically have similar effects on both beams, while the additional mass change caused by methane-specific adsorption mainly affects the sensitive beam. This controllable design helps to offset the influence of environmental factors and improves the stability and reliability of detection results under complex environments.

[0036] 3) Excellent selective recognition capability for methane: In the detection system of this invention, a functional coating with specific adsorption properties for methane is introduced onto the surface of the sensitive beam. This allows target methane molecules to preferentially recognize and adsorb onto the functional coating, thereby enhancing the system's response capability to methane from the source. Compared with detection methods that rely solely on changes in overall physical properties caused by the medium, this invention can more effectively distinguish methane from other non-target gases in complex background gas environments, improving the selectivity and accuracy of methane detection.

[0037] 4) High sensitivity for trace methane detection: The detection method of this invention utilizes the nonlinear amplification characteristic of the system's eigenvalues ​​near the second-order singularity to small perturbations, transforming the weak mass change caused by methane molecule adsorption into a more significant frequency splitting signal. Compared to traditional linear response detection methods, this invention can improve the system's ability to resolve weak concentration changes under low-concentration, especially trace methane detection conditions, which is beneficial for lowering the detection limit and improving detection sensitivity.

[0038] 5) Clear output characteristics and relatively simple data processing: The detection method of this invention uses the system's resonant frequency and its splitting quantity as the main detection characteristics, and the output physical quantity is clear. The results can be obtained through peak search by a spectrum analyzer or spectral line fitting. Compared with detection methods that require complex pattern recognition, multi-dimensional feature extraction, or large-scale algorithm compensation, this invention has lower dependence on back-end data processing and signal interpretation, which is conducive to achieving rapid detection and real-time output.

[0039] 6) Long system lifespan without relying on catalytic combustion or electrochemical consumption processes: The detection mechanism of this invention is mainly based on the specific adsorption of methane molecules and the frequency readout of the double-fixed beam resonant structure. It does not rely on the continuous reaction of catalysts or the consumption of electrode electrolytes, thus avoiding the problems of catalyst poisoning, electrode aging, and electrolyte failure that exist in traditional catalytic combustion or partially electrochemical sensors. This helps to extend the system lifespan and reduce the maintenance frequency. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the detection system in an embodiment of the present invention;

[0041] Figure 2 This is a flowchart of the detection method in an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram of the detection system in an embodiment of the present invention.

[0043] In the diagram: 100. System; 1. Double-fixed beam resonant structure; 11. Reference beam; 12. Coupled structure; 13. Sensitive beam; 2. Data acquisition and processing unit; 21. Coupling strength calculation module; 22. Spectrum acquisition module; 23. Spectrum analysis module; 24. Functional relationship module; 25. Gas concentration calculation module; 3. Display module. Detailed Implementation

[0044] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0045] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following embodiments are described in detail with reference to the accompanying drawings.

[0046] Figure 1 This is a schematic diagram of the detection system 100 in an embodiment of the present invention.

[0047] like Figure 1 As shown: This embodiment provides a trace methane concentration detection system 100 based on second-order singularities, including a double-fixed beam resonant structure 1, a data acquisition and processing unit 2, and a display module 3.

[0048] The double-fixed beam resonant structure 1 includes a reference beam 11, a sensitive beam 13, and a coupling structure 12 disposed between the two.

[0049] Reference beam 11 serves as a frequency reference and stability benchmark, and its geometric dimensions are predetermined.

[0050] The width and thickness of the sensitive beam 13 are the same as those of the reference beam 11. The length can be preset according to actual detection requirements, but its length should be less than that of the reference beam 11. The upper surface is uniformly covered with a functional coating for identifying and adsorbing methane molecules.

[0051] The coupling structure 12 is an externally controlled circuit used to achieve dissipative coupling, characterized by a pure imaginary coupling constant required by the system in singular state, thus providing non-Hermitianness to the system. Specifically, in the coupling structure 12, one part of the circuit measures the displacement response of the reference beam 11 and generates a corresponding excitation in the sensitive beam 13, while another part of the circuit measures the displacement response of the sensitive beam 13 and generates a corresponding excitation in the reference beam 11. Both parts of the circuit have a 90° phase shift with the signal, thereby achieving virtual coupling of mutual feedback and excitation.

[0052] Data acquisition and processing unit 2 is used to acquire the spectral response diagram of the double-fixed beam resonant structure 1 and process the resonant peak position data in the spectral response diagram to calculate the methane concentration in the gas. Data acquisition and processing unit 2 includes a coupling strength calculation module 21, a spectrum acquisition module 22, a spectrum analysis module 23, a function relationship module 24, and a gas concentration calculation module 25.

[0053] The coupling strength calculation module 21 is used to calculate the theoretical value of coupling strength; the spectrum acquisition module 22 includes a vibration sensor and a spectrum analyzer, used to acquire the spectrum response diagram of the double-fixed beam resonant structure 1; the spectrum analysis module 23 determines the two resonant frequency values ​​corresponding to the double-fixed beam resonant structure 1 under the singular point state based on the position of the resonant peak in the spectrum response diagram; the function relationship module 24 is used to determine the functional relationship between the difference between the two resonant frequency values ​​and the gas concentration; and the gas concentration calculation module 25 is used to calculate the methane concentration in the gas.

[0054] Display module 3 is connected to data acquisition and processing unit 2 and is used to display the calculation results of methane gas concentration and output analog and digital signals.

[0055] Figure 2 This is a flowchart of the detection method in an embodiment of the present invention.

[0056] This embodiment also provides a method for detecting trace methane concentration based on second-order singularities, using the aforementioned system 100, such as... Figure 2 As shown: This includes the following steps S1-S5.

[0057] S1, the theoretical value of coupling strength is determined. The coupling strength corresponding to the singular point state is calculated based on the second-order non-Hermi Hamiltonian of the double-fixed beam resonant structure 1, and the theoretical value of coupling strength is obtained.

[0058] Specifically, the theoretical value of the coupling strength is output by the coupling strength calculation module 21, and its calculation process includes:

[0059] The double-fixed beam system 100 can be represented by a second-order non-Hermi-Hamiltonian. This represents the overall energy structure and interaction modes of system 100:

[0060] ,

[0061] In the formula, and These are the resonant frequencies of the sensitive beam 13 and the reference beam 11, respectively. It is the equivalent loss rate of sensitive beam 13 and reference beam 11. Let represent the coupling strength between sensitive beam 13 and reference beam 11, where i is the imaginary unit. For ease of representation and calculation, let . , For such a second-order non-Hermi Hamiltonian Solving for the eigenvalues, we obtain the two eigenfrequency of system 100 as follows:

[0062]

[0063] The corresponding eigenvectors are .when When the real parts of the two eigenvalues ​​are the same and the imaginary parts bifurcate, it is an anti-PT symmetric phase; when When, we obtain two eigenvalues ​​with identical real bifurcation and imaginary parts, which is an anti-PT symmetric broken phase; when When the eigenvalues ​​become degenerate and the eigenvectors coincide, this is the singularity of the system at point 100. At this point, the resonant peak frequency in the frequency domain response is... (loss It only affects the width of the resonance peak, not the frequency corresponding to the peak value. The coupling strength at this point is then calculated. That is, the theoretical value of the coupling strength.

[0064] S2, System 100 structural adjustment: The double-fixed beam resonant structure 1 is placed in a sealed space with reserved gas inlet, outlet and data transmission channels, so that gas containing methane can be sampled and filled into the sealed space later.

[0065] S3, Operating point calibration, connected to data acquisition and processing unit 2, fine-tuning the actual value of coupling strength with reference to the theoretical value of coupling strength, when the two resonance peaks in the frequency domain response graph measured by the spectrum acquisition module 22 gradually approach each other on the spectrum until they just overlap, it is determined that the system 100 has reached the second-order singular point. At this time, the system 100 is in the singular point state, and the various parameters of the system 100 at this time are recorded as EP operating point calibration parameters.

[0066] Specifically, the EP operating point calibration parameters include the actual values ​​of the resonant frequency and coupling strength of the double-fixed beam resonant structure 1 in the singular point state.

[0067] S4, Frequency splitting-concentration relationship calibration: Keeping the EP operating point calibration parameters unchanged, several gases with known methane concentrations are sequentially introduced into the sealed space. Frequency sweeping and spectrum analysis are performed on the double-fixed beam resonant structure 1 under the condition of introducing each gas concentration. Based on the analysis results, a functional relationship between the resonant frequency difference of the double-fixed beam resonant structure 1 and the gas concentration is established.

[0068] The spectrum analysis includes: using the vibration sensor and spectrum analyzer in the spectrum acquisition module 22 to acquire the frequency domain response diagram of the system 100, obtaining the two resonant frequency values ​​of the system 100 at the corresponding concentration, and calculating the difference between the two resonant frequency values ​​to obtain the frequency split.

[0069] The functional relationship is derived based on the frequency split, the known gas concentration value used for calibration, and the EP operating point calibration parameters, and is used to invert the methane concentration in the gas. Functional relationship module 24 outputs the functional relationship.

[0070] Figure 3 This is a schematic diagram of the detection system 100 in an embodiment of the present invention.

[0071] like Figure 3 As shown: When system 100 is placed in an environment containing methane, the functional coating on the sensitive beam 13 will recognize and adsorb methane molecules. Under singularity operating conditions, slight changes in gas concentration will affect the frequency of the sensitive beam 13. A small perturbation was introduced The perturbated system's 100 Hamiltonian can be written as:

[0072]

[0073] For this Hamiltonian, near the singular point, we have Then the 100 eigenvalues ​​of the system can be written as:

[0074]

[0075] when At that time, discard higher-order small quantities Rewrite the above formula as:

[0076]

[0077] but

[0078] That is, in the vicinity of system 100 at this singular point state, the eigenvalues ​​of system 100 will be similar to... Splitting in a square root relationship (i.e.) This embodiment amplifies the weak perturbations caused by the adsorption of trace methane molecules into easily distinguishable frequency splitting or shifting signals, thereby achieving highly selective and sensitive detection of trace methane concentrations. Compared to traditional linear detection mechanisms, it can achieve more significant amplification of characteristic quantities for weak perturbations.

[0079] S5, actual testing, including:

[0080] S5-1, introduces the gas in the environment to be tested into a closed space;

[0081] S5-2, the double-fixed beam resonant structure 1 is subjected to frequency sweep excitation, and the spectrum acquisition module 22 acquires the frequency domain response diagram of the double-fixed beam resonant structure 1.

[0082] S5-3. Based on the position of the resonance peak in the spectrum response diagram, determine the two resonant frequency values ​​corresponding to system 100 at the resonant peak position, calculate the difference between the two resonant frequencies to obtain the frequency split, substitute the frequency split into the function relationship, and calculate the methane concentration in the current gas.

[0083] Specifically, the spectrum analysis module 23 determines the two resonant frequency values ​​corresponding to the system 100 at the resonant peak position based on the spectrum response diagram acquired by the spectrum acquisition module 22, and outputs the difference between the two resonant frequency values, i.e., the frequency split. The gas concentration calculation module 25 substitutes the frequency split into the function relationship output by the function relationship module 24 to calculate the current methane concentration in the gas.

[0084] S5-4, the display module 3 displays the calculation results and outputs analog and digital signals as needed to realize alarm, linkage control or data upload.

[0085] The role and effect of the embodiments

[0086] The trace methane concentration detection system 100 and method based on second-order singularities in this embodiment have the following functions and effects:

[0087] 1) The structure is relatively compact, which is conducive to miniaturization and integration: The detection system 100 in this embodiment is mainly composed of a double-fixed beam resonant structure 1, a data acquisition and processing unit 2 and a display module 3. The overall structure is more compact than optical air cell, long optical path detection system 100 and other solutions. It is easy to achieve miniaturization and integrated packaging by using micromachining, microelectromechanical system 100 process or other micro-nano manufacturing methods. It is suitable for expansion to portable, online and array detection.

[0088] 2) It helps to suppress the impact of environmental disturbances on detection accuracy: The detection system 100 in this embodiment adopts a dual-fixed-beam resonant structure 1, in which one beam serves as a reference beam 11 and the other beam serves as a sensitive beam 13 coated with a specific adsorption layer. Factors such as ambient temperature fluctuations, substrate vibration, device aging, and some non-specific background adsorption usually have similar effects on the two beams, while the additional mass change caused by methane specific adsorption mainly affects the sensitive beam 13. The comparative design of the detection system 100 helps to reduce the influence of environmental factors and improve the stability and reliability of detection results under complex environments.

[0089] 3) Excellent selective recognition capability for methane: In the detection system 100 of this embodiment, a functional coating with specific adsorption properties for methane is introduced on the surface of the sensitive beam 13, enabling target methane molecules to preferentially recognize and adsorb onto the functional coating, thereby enhancing the system 100's response capability to methane from the source. Compared with detection methods that rely solely on changes in overall physical properties caused by the medium, this invention can more effectively distinguish methane from other non-target gases in complex background gas environments, improving the selectivity and accuracy of methane detection.

[0090] 4) High sensitivity for trace methane detection: The detection method in this embodiment utilizes the nonlinear amplification characteristic of the system's eigenvalues ​​near the second-order singularity to small perturbations, converting the weak mass change caused by methane molecule adsorption into a more significant frequency splitting signal. Compared to traditional linear response detection methods, this invention can improve the system's ability to resolve weak concentration changes under low-concentration, especially trace methane detection conditions, which is beneficial for lowering the detection limit and improving detection sensitivity.

[0091] 5) Clear output features and relatively simple data processing: The detection method in this embodiment uses the resonant frequency and splitting amount of system 100 as the main detection features. The output physical quantity is clear, and the result can be obtained through peak search of a spectrum analyzer or spectral line fitting. Compared with detection methods that require complex pattern recognition, multi-dimensional feature extraction, or large-scale algorithm compensation, this invention has lower dependence on back-end data processing and signal interpretation, which is conducive to achieving rapid detection and real-time output.

[0092] 6) The system 100 has a long service life because it does not rely on catalytic combustion or electrochemical consumption processes: The detection mechanism of this embodiment is mainly based on the specific adsorption of methane molecules and the frequency readout of the double-fixed beam resonant structure 1. It does not rely on the continuous reaction of catalysts or the consumption of electrode electrolytes, thus avoiding the problems of catalyst poisoning, electrode aging and electrolyte failure that exist in traditional catalytic combustion or partially electrochemical sensors. This helps to extend the service life of the system 100 and reduce the maintenance frequency.

[0093] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A trace methane concentration detection system based on second-order singularities, characterized in that, include: A double-fixed beam resonant structure includes a reference beam, a sensitive beam, and a coupling structure placed between the two; The data acquisition and processing unit is used to acquire the spectral response diagram of the double-fixed beam resonant structure and process the resonant peak position data in the spectral response diagram to calculate the methane concentration in the gas. The display module, connected to the data acquisition and processing unit, is used to display the calculation results of gas concentration and output analog and digital signals. The reference beam serves as a frequency reference and stability benchmark, the upper surface of the sensitive beam is uniformly covered with a functional coating for recognizing and adsorbing methane molecules, and the coupling structure is used to achieve dissipative coupling characterized by a pure imaginary coupling constant. The data acquisition and processing unit includes: The coupling strength calculation module is used to calculate the theoretical value of the coupling strength. The spectrum acquisition module, including a vibration sensor and a spectrum analyzer, is used to acquire the spectrum response diagram of the double-fixed beam resonant structure. The spectrum analysis module determines the two resonant frequency values ​​corresponding to the double-fixed beam resonant structure under the singular point state based on the resonant peak position in the spectrum response diagram. The function relationship module is used to determine the functional relationship between the difference between two resonant frequency values ​​and the gas concentration; The gas concentration calculation module is used to calculate the methane concentration in a gas.

2. The trace methane concentration detection system based on second-order singularities according to claim 1, characterized in that: in, The reference beam has predetermined geometric dimensions, the sensitive beam has the same width and thickness as the reference beam, and the length of the sensitive beam has a predetermined difference from the length of the reference beam.

3. A method for detecting trace methane concentration based on second-order singularities, comprising using the trace methane concentration detection system based on second-order singularities as described in claim 1 or 2, characterized in that, Includes the following steps: S1, The theoretical value of coupling strength is determined. A second-order non-Hermitian Hamiltonian is established based on the parameters of the double-fixed beam resonant structure, and the coupling strength corresponding to the singular point state is calculated to obtain the theoretical value of coupling strength. S2, System structure adjustment: The double-fixed beam resonant structure is placed in a sealed space with reserved gas inlet, outlet and data transmission channel; S3, Operating point calibration: Connect to the data acquisition and processing unit, adjust the actual value of coupling strength with reference to the theoretical value of coupling strength until the system reaches the second-order singularity, and record the various parameters of the system at this time as EP operating point calibration parameters; S4, Frequency splitting-concentration relationship calibration: Keeping the EP operating point calibration parameters unchanged, several gases with known methane concentrations are sequentially introduced into the sealed space. Frequency sweeping and spectrum analysis are performed on the double-fixed beam resonant structure under the condition of introducing each gas concentration. Based on the analysis results, a functional relationship between the resonant frequency difference of the double-fixed beam resonant structure and the gas concentration is established. S5, actual testing, including: S5-1, The gas of the environment to be tested is introduced into the sealed space; S5-2, The double-fixed beam resonant structure is subjected to frequency sweep excitation, and the vibration sensor and the spectrum analyzer acquire the frequency domain response diagram of the double-fixed beam resonant structure; S5-3. Based on the position of the resonance peak in the spectrum response diagram, determine the two resonant frequency values ​​corresponding to the system, calculate the difference between the two resonant frequencies to obtain the frequency split, substitute the frequency split into the function relationship, and calculate the methane concentration in the current gas. S5-4, the display module displays the calculation results and outputs analog digital signals.

4. The method for detecting trace methane concentration based on second-order singularities according to claim 3, characterized in that: In step S1, the calculation process of the theoretical value of the coupling strength includes: calculating the second-order non-Hermi Hamiltonian. Solving for the eigenvalues ​​yields the two eigenfrequencys of the system and the corresponding two eigenvectors. When the eigenvalues ​​become degenerate and the two eigenvectors coincide, the system reaches a singularity. The coupling strength at this point is calculated, which is the theoretical value of the coupling strength.

5. The method for detecting trace methane concentration based on second-order singularities according to claim 3, characterized in that: The specific process of step S3 is as follows: the actual value of the coupling strength is finely adjusted according to the theoretical value of the coupling strength. When the two resonance peaks in the frequency domain response graph measured by the spectrum analyzer gradually approach each other on the spectrum until they just overlap, it is determined that the system has reached the second-order singular point. At this time, the system is in the singular point state. The various parameters of the system in this state are recorded as EP operating point calibration parameters.

6. The method for detecting trace methane concentration based on second-order singularities according to claim 3, characterized in that: In step S3, the EP operating point calibration parameters include the actual values ​​of the resonant frequency and coupling strength of the double-fixed beam resonant structure when the system is in a singular operating state.

7. The method for detecting trace methane concentration based on second-order singularities according to claim 3, characterized in that: In step S4, the spectrum analysis includes: using the vibration sensor and the spectrum analyzer to acquire the frequency domain response diagram of the system, obtaining the two resonant frequency values ​​of the system at the corresponding concentration, and calculating the difference between the two resonant frequency values ​​to obtain the frequency splitting amount; The functional relationship is derived based on the frequency split and EP operating point calibration parameters, and is used to invert the methane concentration in the gas.

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