Anti-interference optothermal elastic spectroscopy gas detection device and method

Abstract

An anti-interference photo-thermoelastic spectroscopy gas detection device and method are disclosed. In the anti-interference photo-thermoelastic spectroscopy gas detection device, a laser source is used to emit a laser beam matching the absorption characteristics of the gas to be measured; an optical switch is connected to the laser source and is used to switch the laser beam to a detection optical path or a background optical path; a gas cell contains the gas to be measured, and laser collimation modules are arranged at both ends of the gas cell to form the detection optical path; a reference cell contains background gas, and laser collimation modules are arranged at both ends of the reference cell to form the background optical path; a laser focusing module is arranged at the end of the detection optical path and the background optical path to focus the beams from the detection optical path and the background optical path, and a quartz tuning fork generates a photo-thermal signal based on the beams; a signal processing module is used to analyze and process the photo-thermal signal and calculate the concentration of the gas to be measured.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to an anti-interference photo-thermoelastic spectroscopic gas detection device and method. Background Art

[0002] Photo-thermoelastic spectroscopy (LITES) combines quartz-enhanced photoacoustic spectroscopy and tunable diode laser absorption spectroscopy, and is a highly sensitive gas detection method. Its advantages of in-situ, real-time, non-contact detection and high sensitivity make it have significant potential in various trace gas detection applications. However, the signal stability of existing LITES systems still faces challenges in complex environments. Environmental factors (such as temperature and humidity fluctuations) and oxidation of the quartz tuning fork (QTF) electrodes can cause resonance parameter drift, and the presence of background thermal response further affects its demodulation accuracy. Although differential methods or phase-sensitive detection techniques have been attempted to alleviate some interferences, as described in CN118310971A, the problem of signal distortion still has not been effectively solved in application scenarios with multiple interferences such as resonance parameter drift. Therefore, there is an urgent need for a LITES gas detection technical solution that can comprehensively cope with various interferences and improve detection accuracy.

[0003] The information disclosed in the background art section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] In view of the deficiencies or defects of the existing technology, an anti-interference photo-thermoelastic spectroscopic gas detection device and method are provided to solve the problem of insufficient gas detection accuracy in the existing technology in complex environments. Through a dual-path time-division multiplexing design and a signal demodulation method based on harmonic sideband analysis, the present invention realizes high-precision, non-contact gas detection and effectively suppresses multiple interferences such as resonance parameter drift and background thermal response.

[0005] The object of the present invention is achieved by the following technical solutions.

[0006] An anti-interference photo-thermoelastic spectroscopic gas detection device includes

[0007] a laser source for emitting a laser beam matching the absorption characteristics of the gas to be detected;

[0008] an optical switch connected to the laser source for switching the laser beam to the detection optical path or the background optical path;

[0009] a gas cell with the gas to be detected inside, and laser collimation modules are provided at both ends of the gas cell to form the detection optical path;

[0010] A reference cell with background gas inside, and laser collimation modules are provided at both ends of the reference cell to form the background optical path;

[0011] A laser focusing module is provided at the end of the detection optical path and the background optical path to focus the beams from the detection optical path and the background optical path,

[0012] A quartz tuning fork that generates a photo-thermal signal based on the beam;

[0013] A signal processing module for analyzing and processing the photo-thermal signal and calculating the concentration of the gas to be measured.

[0014] In the anti-interference photo-thermoelastic spectroscopy gas detection device, the laser beam irradiates a predetermined position of the quartz tuning fork after passing through the gas cell or the reference cell.

[0015] In the anti-interference photo-thermoelastic spectroscopy gas detection device, the detection optical path and the background optical path alternately irradiate the quartz tuning fork in a time-division multiplexing manner through an optical switch.

[0016] In the anti-interference photo-thermoelastic spectroscopy gas detection device, the signal processing module analyzes the harmonic sidebands of the photo-thermal signal, estimates the QTF parameters in real time and corrects the signal distortion, and calculates the concentration of the gas to be measured.

[0017] In the anti-interference photo-thermoelastic spectroscopy gas detection device, the laser source includes a laser, a laser control module and a laser modulation module to emit modulated laser light matching the absorption characteristics of the gas to be measured.

[0018] In the anti-interference photo-thermoelastic spectroscopy gas detection device, laser focusing modules are respectively provided in the detection optical path and the background optical path to focus the beams.

[0019] In the anti-interference photo-thermoelastic spectroscopy gas detection device, the beam of the detection optical path irradiates the front surface of the quartz tuning fork, and the beam of the background optical path irradiates the symmetric position on the back surface of the quartz tuning fork after passing through the reference cell.

[0020] The detection method of the anti-interference photo-thermoelastic spectroscopy gas detection device includes,

[0021] Obtaining the frequency response characteristics of the quartz tuning fork by sweeping the frequency, extracting the initial resonance parameters, including the resonance frequency and the quality factor, switching the optical switch to the detection optical path, filling the gas cell with different concentrations of the gas to be measured including zero concentration, obtaining the initial background response N0 and the response S0 of the gas to be measured, performing harmonic sideband signal processing on the initial background response N0 and the response S0 of the gas to be measured, and establishing an amplitude-concentration calibration relationship;

[0022] Switching the optical switch to the background optical path and obtaining the background photo-thermal response N in real time r, in combination with the initial background response N0, inversely calculate the real-time resonance parameters of the QTF based on the mathematical relationship;

[0023] Switch the optical switch to the detection optical path, and obtain the photo-thermal response S of the gas to be measured in real time r , for the background response N obtained in real time r and the response S of the gas to be measured r Perform harmonic sideband signal processing, and calculate the concentration of the gas to be measured according to the amplitude-concentration calibration relationship.

[0024] In the method described above, the harmonic sideband signal processing includes

[0025] Perform Fourier analysis on the gas and background photo-thermal signals to obtain the amplitudes and phases of the harmonic sideband components;

[0026] Based on the resonance parameters, construct an inverse transfer function that is reciprocal to the QTF resonance transfer function, which is used to perform frequency-domain correction on the harmonic sideband components of the gas photo-thermal signal and the background photo-thermal signal, and correct their amplitude and phase distortions;

[0027] Differentiate the corrected gas and background photo-thermal frequency-domain signals and use the inverse Fourier transform to reconstruct the time-domain signal.

[0028] In the method described above, inversely calculating the real-time resonance parameters of the QTF based on the mathematical relationship includes

[0029] Input the amplitude of the harmonic sideband component of the background signal into the QTF equivalent resonance model, and combine the frequency sweep to obtain the initial resonance parameters, list the equations and solve for the real-time resonance parameters.

[0030] Compared with the prior art, the beneficial effects brought by the present invention are:

[0031] The present invention realizes non-contact and high-sensitivity detection of the gas to be measured, and at the same time has strong resistance to interference such as resonance parameter drift and background thermal response. By utilizing the dynamic fingerprint information of the resonator parameters contained in the harmonic sidebands, it is possible to monitor and correct the changes of the QTF resonance parameters in real time, solve the problem that the LITES technology is interfered by resonance parameter drift and background thermal response in complex environments, and significantly improve the detection accuracy and long-term stability. This method can realize real-time parameter estimation and signal correction without additional complex hardware, is simple and efficient to operate, and provides a high-precision and practical technical solution for gas monitoring.

[0032] The above description is only an overview of the technical solution of the present invention. In order to make the technical means of the present invention clearer and clearer, to the extent that those skilled in the art can implement it according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following will be illustrated by specific embodiments of the present invention. Description of the Drawings

[0033] By reading the detailed description in the following preferred specific embodiments, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The accompanying drawings of the specification are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Obviously, the following described drawings are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0034] In the drawings:

[0035] Figure 1 is a schematic diagram of an anti-interference photo-thermoelastic spectroscopic gas detection device according to an embodiment of the present invention;

[0036] Figure 2 is a flowchart of an anti-interference photo-thermoelastic spectroscopic gas detection method proposed by the present invention;

[0037] Figure 3 is an amplitude-frequency scan curve of a quartz tuning fork used in an embodiment of the present invention;

[0038] Figure 4 is a relationship curve between the signal amplitude and concentration of C2H2 established in Example 1 of the present invention;

[0039] Figure 5 is a schematic diagram of the concentration inversion accuracy of C2H2 in the tuning fork oxidation test experiment of Example 1 of the present invention;

[0040] Figure 6 is a schematic diagram of the comparison of signal waveforms detected by the traditional method and the method proposed by the present invention for 1000 μL / L C2H2 in the tuning fork oxidation test experiment of Example 1 of the present invention;

[0041] Figure 7 is a schematic diagram of the suppression degree of background noise in the tuning fork oxidation test experiment of Example 1 of the present invention;

[0042] Figure 8 is a schematic diagram of the influence of humidity change on resonance parameters and the ability of the detection method to resist humidity change in Example 2 of the present invention.

[0043] The following further explains the present invention in conjunction with the accompanying drawings and embodiments. Detailed Embodiments

[0044] Specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0045] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different terms to refer to the same component. The specification and claims do not use the difference in terms as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. As used throughout the specification and claims, the term "comprising" or "including" is an open-ended term and should be interpreted as "including but not limited to". The following description is a preferred embodiment for implementing the present invention, but the description is for the purpose of the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be defined by the appended claims.

[0046] For ease of understanding of the embodiments of the present invention, the following will further explain with several specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0047] For better understanding, as Figures 1 to 8 shown, an anti-interference photo-thermoelastic spectroscopic gas detection device includes,

[0048] a laser source 1 for emitting a laser beam matching the absorption characteristics of the gas to be measured; the chemical bonds in the molecules of the gas to be measured undergo specific vibrations, so they will absorb light of a specific wavelength, so a laser matching this absorption characteristic is emitted.

[0049] an optical switch 4 connected to the laser source 1 for switching the laser beam to the detection optical path or the background optical path;

[0050] a gas cell 6 containing the gas to be measured, and laser collimation modules 5 are provided at both ends of the gas cell 6 to form the detection optical path;

[0051] a reference cell 7 containing a background gas, and laser collimation modules 5 are provided at both ends of the reference cell 7 to form the background optical path;

[0052] a laser focusing module 8 provided at the ends of the detection optical path and the background optical path to focus the beams from the detection optical path and the background optical path;

[0053] a quartz tuning fork 9 generating a photo-thermal signal based on the beam;

[0054] A signal processing module for analyzing and processing optothermal signals and calculating the concentration of the gas to be measured. By analyzing the optothermal signals, the inverse QTF resonance parameters are retrieved, based on which the frequency-domain correction and time-domain reconstruction of the second harmonic sidebands of the optothermal signals are performed, and then the amplitudes are extracted and combined with the pre-established amplitude-concentration relationship to calculate the gas concentration.

[0055] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, the laser beam irradiates a predetermined position of the quartz tuning fork 9 after passing through the gas cell 6 or the reference cell 7.

[0056] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, the detection optical path and the background optical path alternately irradiate the quartz tuning fork 9 in a time-division multiplexing manner through the optical switch 4.

[0057] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, the signal processing module analyzes the harmonic sidebands of the optothermal signals, estimates the QTF parameters in real time and corrects the signal distortion, and calculates the concentration of the gas to be measured. The QTF parameters include the resonance frequency and the quality factor, and correcting the signal distortion means the amplitude and phase distortion of the sideband components introduced by the resonator resonance effect.

[0058] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, the laser source 1 includes a laser, a laser control module 2 and a laser modulation module 3 to emit modulated laser light matching the absorption characteristics of the gas to be measured.

[0059] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, laser focusing modules 8 are respectively provided in the detection optical path and the background optical path to focus the light beam.

[0060] In a preferred embodiment of the anti-interference optothermal elastic spectroscopy gas detection device, the light beam of the detection optical path irradiates the front of the quartz tuning fork 9, and the light beam of the background optical path irradiates the symmetric position on the back of the quartz tuning fork 9 after passing through the reference cell 7.

[0061] The detection method of the anti-interference optothermal elastic spectroscopy gas detection device includes

[0062] Obtaining the frequency response characteristics of the quartz tuning fork 9 by frequency sweeping, extracting the initial resonance parameters, which include the resonance frequency and the quality factor, switching the optical switch 4 to the detection optical path, filling different concentrations of the gas to be measured including zero concentration in the gas cell 6, obtaining the initial background response N0 and the response S0 of the gas to be measured, both of which are optothermal signals, performing harmonic sideband signal processing on the initial background response N0 and the response S0 of the gas to be measured, and establishing an amplitude-concentration calibration relationship;

[0063] Switching the optical switch 4 to the background optical path and obtaining the background optothermal response N in real time r, in combination with the initial background response N0, inversely calculate the real-time resonance parameters of the QTF based on the mathematical relationship;

[0064] Switch the optical switch 4 to the detection optical path, and obtain the photo-thermal response S of the gas to be measured in real time r , for the background response N obtained in real time r and the response S of the gas to be measured r Perform harmonic sideband signal processing, and calculate the concentration of the gas to be measured according to the amplitude-concentration calibration relationship.

[0065] In a preferred embodiment of the method described above, the harmonic sideband signal processing includes

[0066] Perform Fourier analysis on the gas and background photo-thermal signals to obtain the amplitude and phase of the harmonic sideband components;

[0067] Based on the resonance parameters, construct an inverse transfer function that is reciprocal to the QTF resonance transfer function, which is used to perform frequency-domain correction on the harmonic sideband components of the gas photo-thermal signal and the background photo-thermal signal, and correct their amplitude and phase distortions;

[0068] Differentiate the corrected gas and background photo-thermal frequency-domain signals and then use the inverse Fourier transform to reconstruct the time-domain signal.

[0069] In a preferred embodiment of the method described above, inversely calculating the real-time resonance parameters of the QTF based on the mathematical relationship includes

[0070] Input the amplitude of the harmonic sideband component of the background signal into the QTF equivalent resonance model, and combine frequency sweeping to obtain the initial resonance parameters, write a system of equations and solve for the real-time resonance parameters. Model the QTF as an equivalent RLC resonance circuit, and the form of its transfer function can be seen in the embodiment. Given the resonance parameters (resonance frequency and quality factor) of the QTF, the specific transfer function can be determined, which shows a second-order band-pass characteristic.

[0071] In one embodiment, the laser beam is time-division switched by the optical switch 4 to the gas cell 6 containing the gas to be measured and the reference cell 7 containing the background gas, and alternately irradiates the quartz tuning fork 9 (Quartz tuning fork, QTF) to generate photo-thermal signals. Combined with an optimized signal processing module, the detection accuracy is effectively improved. The detection method is based on harmonic sideband analysis, uses the background signal to estimate the QTF resonance parameters in real time, constructs an inverse transfer function to correct the frequency-domain distortion of the signal, and realizes high-precision gas concentration calculation through time-domain signal reconstruction. This scheme significantly suppresses the resonance parameter drift and the interference of the background thermal response, and greatly reduces the concentration detection error of the gas to be measured, providing a reliable technical solution for high-precision gas detection in complex environments.

[0072] In one embodiment, in the harmonic sideband signal processing, the inverse transfer function is generated by taking the reciprocal of the QTF resonance transfer function constructed based on resonance parameters, and is used to correct the amplitude distortion and phase distortion of the harmonic sidebands.

[0073] The reconstructed time-domain signal is obtained by taking the difference between the corrected frequency-domain signals of the gas and background photothermal signals and then performing an inverse Fourier transform. The harmonic sideband is preferably the second harmonic sideband to obtain the maximum signal-to-noise ratio. In one embodiment, the predetermined position is the central position of the quartz tuning fork 9.

[0074] In one embodiment, the signal processing module includes a signal collection and amplification circuit 10 and a host computer 11.

[0075] Embodiment 1:

[0076] Device:

[0077] As Figure 1 shown is a light-induced thermoelastic spectroscopy gas detection device with anti-interference provided by the present invention, which is used to detect the gas to be measured C2H2, and its selected infrared absorption peak is 1530.371 nm. The device mainly includes a laser source 1, an optical switch 4, a gas cell 6, a reference cell 7, a quartz tuning fork 9 (QTF), and a signal processing module, etc., and the specific configuration is as described below.

[0078] The laser source 1 uses a continuous-wave distributed feedback laser, which emits a modulated laser with a center wavelength of 1530 nm and an output power of 10 mW to match the absorption characteristics of the gas to be measured. The laser modulation module 3 consists of an arbitrary waveform generator and an adder. The arbitrary waveform generator generates a sawtooth wave with a frequency of 0.2 Hz and a sine wave with a frequency half of the QTF resonance frequency. After being superimposed by the adder, a modulation signal is formed for second harmonic detection. The laser control module includes a laser diode controller and a laser temperature controller. The laser diode controller receives the modulation signal to control the laser output, and the laser temperature controller precisely adjusts the output center wavelength of the laser to align it with the absorption peak of C2H2 at 1530.371 nm. The optical switch 4 is connected to the laser source 1 to switch the laser beam to the detection optical path or the background optical path in a time-sharing manner. In the detection optical path, the laser beam passes through the gas cell 6 containing the gas to be measured C2H2 after being collimated by the laser collimation module 5, generating specific absorption. After exiting, it is focused by the laser focusing module 8 onto the front of the QTF. In the background optical path, the laser beam passes through the reference cell 7 containing the background gas (air), and the remaining configuration is the same as that of the gas cell 6. After exiting, it is focused onto the symmetric position on the back of the QTF to provide a background signal. The QTF is a large-sized quartz tuning fork 9, which is arranged at the end of the detection optical path and the background optical path, receives the two beams of light and generates a photo-thermal signal. The photo-thermal signal generated by the QTF is amplified by the signal collection and amplification circuit 10 and then output to the signal processing module. The signal processing module consists of a host computer 11, which is built-in with a harmonic sideband signal processing program to process the photo-thermal signal and invert the concentration of the gas to be measured. To verify the performance of the device, experiments are carried out using standard gas with a C2H2 concentration of 1000 μL / L, with air as the background gas, and the concentration is precisely controlled by a mass flow meter.

[0079] Method:

[0080] The anti-interference photo-thermoelastic spectroscopy gas detection method proposed by the present invention is applied to the above device, and its process is as Figure 2 shown. This method includes a calibration stage and a real-time detection stage, and the specific steps are as follows:

[0081] Calibration stage: First, the initial resonance parameters ω0 (0) and Q (0) of the QTF are obtained by frequency sweeping. In this embodiment, the initial resonance frequency ω0 (0) of the QTF is 10939.96 Hz, and the quality factor Q (0) is 14540.3, as Figure 4 shown. The QTF can be modeled as an equivalent RLC resonance circuit to lay the foundation for subsequent processing. Its transfer function H(s) is:

[0082]

[0083] Among them, ω0 is the resonant angular frequency, Q is the quality factor, and s is the Laplace transform result of the optothermal signal. This transfer function has a second-order band-pass characteristic. Subsequently, the optical switch 4 is switched to the background optical path, and different concentrations of the gas to be measured, C2H2, are filled into the reference cell 7 in sequence. The QTF receives the beam in the background optical path and generates an optothermal signal, and the initial background response and the response of the gas to be measured are obtained respectively. The initial background response and the response of the gas to be measured are processed for harmonic sideband signals, and the calibration relationship between the signal amplitude and the gas concentration is established. The result is as Figure 4 shown, and at the same time, the harmonic sideband amplitude A (0) of the background signal (by fast Fourier transform) is recorded as the baseline required for the inversion of the resonant parameters.

[0084] Real-time detection stage: First, the optical switch 4 is switched to the background optical path, and the reference cell 7 is filled with the background gas (air). The QTF receives the beam in the background optical path to obtain the background optothermal response during real-time detection. Then, the sideband amplitude A' of the sideband background thermal response signal is obtained through fast Fourier transform, and its mathematical relationship with A (0) satisfies:

[0085]

[0086] where α i is the proportion of a certain sideband component in the total sideband amplitude (satisfying ), k' is the global amplitude scaling factor, reflecting the global changes such as the power of the excitation source, δ is the Dirac function, j is the imaginary unit, ω n is the laser modulation angular frequency, ω s is the wavelength scanning angular frequency, ω0 is the resonant angular frequency of the quartz tuning fork (QTF), and the one without a subscript is the angular frequency variable. Q’ and ω0’ are the resonant parameters during real-time detection. By analyzing multiple sideband components (N>3), an overdetermined system of equations is constructed:

[0087]

[0088] and the nonlinear least squares method is used for optimization to solve for ω0', Q' and k'. β represents the parameter vector to be optimized, and ε represents the error. In this way, the real-time inversion of the resonant parameters is achieved.

[0089] Subsequently, the optical switch 4 is switched to the detection optical path, and the QTF receives the beam in the detection optical path to obtain the optothermal response of the gas to be measured, C2H2, during real-time detection. The harmonic sideband signal processing of the background optothermal response and the optothermal response of the gas to be measured during real-time detection includes the following specific steps: First, the Fourier transform is performed on the two optothermal signals to obtain the amplitude and phase of the harmonic sideband components; then, the inverse transfer function H is constructed using the real-time resonant parameters ω0' and Q' -¹(jω; ω0', Q') to perform frequency-domain correction on the amplitude and phase of the harmonic sideband components, where the corrected amplitude is the measured amplitude multiplied by H - ¹(jω; ω0', Q'), and the corrected phase is the measured phase plus arg(H - ¹(jω; ω0', Q')); finally, subtract the frequency-domain components of the corrected gas optothermal signal and the background optothermal signal to obtain the optothermal frequency-domain signal of the gas, and reconstruct the time-domain signal through inverse Fourier transform. The reconstructed time-domain signal is input into the host computer 11 for lock-in amplification processing to extract the second-harmonic amplitude, and calculate the concentration of the gas to be measured C2H2 according to the amplitude-concentration calibration relationship established in the calibration stage. It should be noted that the "harmonic sideband signal processing" in the real-time detection stage is the same as that in the calibration stage. The only difference is that the real-time resonant parameters ω0' and Q' obtained by inversion are used in the real-time detection stage, while the initial resonant parameters ω0 (0) and Q (0) .

[0090] Anti-interference performance test (tuning fork oxidation):

[0091] Expose the QTF to air for one month, and the oxidation of the surface electrode of the tuning fork causes the drift of the resonant parameters. After oxidation, the measured resonant frequency f0 drops from 10939.96 Hz to 10939.41 Hz, and the quality factor Q drops from 14540.3 to 13958.2. Analyze the background response sideband using this method, and the predicted values of f0 and Q are 10939.28 Hz and 14039.9 respectively, with errors of 0.0012% and 0.59% respectively. Detect the second-harmonic signals of different concentrations of C2H2 and invert their concentrations. Without correction (traditional method), the concentration error exceeds 60%; after correction, the error drops below 25%, and is below 10% at high concentrations (≥300 μL / L), as Figure 5 shown. Figure 6 Shows the comparison of the signal waveforms obtained by using the traditional method and the method of the present invention when detecting 1000 μL / L C2H2. Affected by the change of the QTF resonant parameters, the amplitude of the signal waveform measured by the traditional method is significantly reduced and obvious distortion appears. While the method of the present invention effectively overcomes the interference of the resonant parameter drift through harmonic sideband analysis and correction, and the obtained waveform is standard and the amplitude is stable. In addition, compare the background noise levels before and after correction, as Figure 7 shown, the method of the present invention improves the background noise suppression rate to more than 96%, significantly improving the signal-to-noise ratio.

[0092] Example 2:

[0093] Changes in environmental humidity can affect the adsorption of water molecules on the surface of the QTF, which can also lead to resonance parameter drift. In this embodiment, to further verify the anti-humidity interference performance of the device and method, another QTF was selected for the experiment, and its initial sweep frequency curve is as Figure 3 shown, and the other device configurations are the same as those in the foregoing Embodiment 1. At room temperature, a humidity control chamber was used to adjust the humidity level between 20% and 70%, and the specific test points were 20%, 40%, 55%, and 70%. After each humidity adjustment, the surface of the QTF was stabilized for 3 hours. The experimental results are as Figure 8 shown. As the humidity increases, both the resonance frequency and the quality factor of the QTF decrease. When detecting 1000 μL / L C2H2 under these conditions, the amplitude of the corrected signal remains stable, with a deviation of no more than 5%. In contrast, the uncorrected signal shows significant fluctuations with changes in humidity, reaching a maximum of 44%. This indicates that the device and method are robust to humidity interference.

[0094] The laser source 1 of the present invention emits a laser beam that matches the light absorption characteristics of the gas, precisely exciting the gas molecules to be measured to produce selective absorption, thereby improving the detection sensitivity and specificity. The optical switch 4 realizes the time-division multiplexing switching of the detection optical path and the background optical path to eliminate common-mode interferences such as changes in environmental humidity and drift of QTF parameters, and extracts the real gas response signal by means of differential method. The gas cell 6 and the reference cell 7 are respectively filled with the gas to be measured and the background gas, and a collimation module is set to make the detection light path and the background light path symmetric and have the same transmission efficiency, ensuring the comparability of the two signals for differential. The laser focusing module 8 focuses the beam to a predetermined position (front / back) of the quartz tuning fork 9 to improve the light energy utilization rate and enhance the photo-thermal effect; symmetric illumination on the front and back makes the QTF background photo-thermal responses generated by the detection optical path and the background optical path consistent. The quartz tuning fork 9 serves as a photo-thermal signal sensor, and uses its high-Q value characteristic to amplify the weak photo-thermal signal, sweeps the frequency to obtain the initial QTF resonance parameters (resonance frequency, quality factor) to establish a QTF initial state model, providing a benchmark for subsequent real-time parameter estimation and ensuring the accuracy of signal correction. In the calibration stage, the amplitude-concentration calibration relationship is established to construct the basis for quantitative detection and achieve an accurate mapping from the photo-thermal signal to the gas concentration. The background photo-thermal response Nr is obtained in real time and the QTF real-time resonance parameters are inverted to dynamically track the changes in the QTF resonance parameters (caused by factors such as oxidation and humidity), eliminating measurement errors caused by device aging or environmental disturbances. An inverse transfer function is constructed for frequency-domain correction to correct the signal amplitude and phase distortion caused by changes in the QTF resonance characteristics, restoring the original photo-thermal signal form and improving the detection consistency. The harmonic sideband components are extracted by using the Fourier transform, and signal differential and reconstruction are performed to extract the second harmonic signal with high signal-to-noise ratio, suppressing noise interference and improving the detection accuracy. The second harmonic sideband is used as the main analysis object to obtain the maximum signal-to-noise ratio in the modulation spectrum, which is suitable for low-concentration gas detection and enhances the system robustness. Sweeping the frequency + testing the responses of different concentration gases to establish a standard signal database, providing a basis for subsequent concentration calculation and obtaining the QTF initial model parameters at the same time. In the real-time detection stage: background signal acquisition + parameter inversion + signal correction + concentration inversion implement a dynamic compensation mechanism to adapt to the drift of QTF parameters in a complex environment and ensure long-term stable and reliable detection. The overdetermined equations are solved by the nonlinear least squares method to accurately estimate the resonance frequency and quality factor of the current QTF, providing key parameters for constructing the inverse transfer function. Frequency-domain correction + differential + inverse Fourier transform are used to reconstruct the time-domain signal, effectively correcting the distortion of the photo-thermal signal, suppressing the background response, and improving the detection accuracy and resolution.The time-division multiplexing dual optical path structure effectively suppresses common-mode interference and improves detection stability. Even under the aging of QTF and humidity changes, it can still accurately identify the gas concentration. Harmonic sideband analysis + inverse transfer function correction realizes signal distortion compensation, restores the real optothermal signal, the second harmonic signal is more stable, the signal-to-noise ratio is higher, the detection accuracy is improved, the QTF real-time parameter inversion mechanism dynamically tracks the sensor state, and the adaptive compensation change can cope with practical problems such as QTF oxidation and electrode aging. The time-domain signal reconstruction improves the signal integrity and resolvability, and the lock-in amplification extracts the signal more accurately, facilitating concentration calculation. The systematic calibration and real-time detection process ensure the standardization and automation of the detection process, and are applicable to on-site rapid detection and long-term monitoring applications. Example 1: QTF oxidation experiment, simulating the device aging scenario in actual use, to verify the anti-interference ability of the system against resonant parameter drift. The results show that even when the QTF resonant frequency drops by 0.05% and the quality factor drops by 4%, the detection error can still be kept within 25%, which is better than the traditional method. Example 2: Humidity interference experiment, to verify the stability of the system under different humidity conditions. The results show that during the process of humidity rising from 20% to 70%, the amplitude fluctuation of the corrected C2H2 signal is less than 5%, which is significantly better than the uncorrected situation (the maximum deviation reaches 44%).

[0095] The foregoing description has been presented for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the form disclosed herein. Although several example aspects and embodiments have been discussed above, those skilled in the art will recognize some of their variations, modifications, alterations, additions, and subcombinations.

Claims

1. A detection method for a light-induced thermoelastic spectroscopy gas detection device based on anti-interference, characterized in that, The described detection method uses an anti-interference photoacoustic spectroscopy gas detection device, and the detection device includes: a laser source for emitting a laser beam matching the absorption characteristics of the gas to be measured; an optical switch connected to the laser source for switching the laser beam to the detection optical path or the background optical path; a gas cell with the gas to be measured inside, and laser collimation modules are provided at both ends of the gas cell to form a detection optical path; a reference cell with background gas inside, and laser collimation modules are provided at both ends of the reference cell to form a background optical path; a laser focusing module provided at the end of the detection optical path and the background optical path to focus the beams from the detection optical path and the background optical path; a quartz tuning fork that generates a photoacoustic signal based on the beam; a signal processing module for analyzing and processing the photoacoustic signal and calculating the concentration of the gas to be measured; The described detection method includes: The frequency response characteristics of the quartz tuning fork are obtained by sweeping the frequency, and the initial resonance parameters, including the resonance frequency and the quality factor, are extracted. The optical switch is switched to the detection optical path, and different concentrations of the gas to be measured, including zero concentration, are filled in the gas cell to obtain the initial background response N 0 and the response of the gas to be measured S 0, for the initial background response N 0 and the response of the gas to be measured S 0 is processed by the harmonic sideband signal to establish the amplitude-concentration calibration relationship; Switch the optical switch to the background optical path and obtain the background photothermal response in real time N r , combined with the initial background response N 0, invert the real-time resonance parameters of the QTF based on the mathematical relationship; Switch the optical switch to the detection optical path and obtain the optothermal response of the gas to be measured in real time S r , for the background response obtained in real time N r and the response of the gas to be measured S r perform harmonic sideband signal processing, and calculate the concentration of the gas to be measured according to the amplitude-concentration calibration relationship; The harmonic sideband signal processing includes: performing Fourier analysis on the gas and background photoacoustic signals to obtain the amplitudes and phases of the harmonic sideband components; constructing an inverse transfer function that is inversely related to the QTF resonance transfer function based on the resonance parameters for frequency-domain correction of the harmonic sideband components of the gas photoacoustic signal and the background photoacoustic signal to correct the amplitude and phase distortions; differencing the corrected gas and background photoacoustic frequency-domain signals and then using the inverse Fourier transform to reconstruct the time-domain signal.

2. The detection method according to claim 1, characterized in that, The laser source includes a laser, a laser control module, and a laser modulation module to emit a modulated laser matching the absorption characteristics of the gas to be measured.

3. The detection method according to claim 1, wherein, The beam of the detection optical path irradiates the front surface of the quartz tuning fork, and the beam of the background optical path irradiates the symmetric position on the back surface of the quartz tuning fork after passing through the reference cell.

4. The detection method according to claim 1, wherein Inverting the QTF real-time resonance parameters based on the mathematical relationship includes: inputting the amplitude of the harmonic sideband component of the background signal into the QTF equivalent resonance model, combining frequency sweeping to obtain the initial resonance parameters, writing a system of equations, and solving for the real-time resonance parameters.

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