An interference gas suppression device based on differential photoacoustic cell sound pressure reverse distribution

Abstract

This invention discloses an interference gas suppression device based on the reverse sound pressure distribution of a differential photoacoustic cell. A function generator produces a modulation signal and a reference signal with the same frequency and phase. A laser driving module outputs a driving current according to the modulation signal. First and second lasers generate a first modulated laser with wavelengths covering the absorption spectra of the target and interference gases, and a second modulated laser with wavelengths covering the absorption spectra of the interference gas, based on the driving current. The differential photoacoustic cell receives and performs acoustic enhancement, electrical signal conversion, and differential processing on the photoacoustic signal generated after the interaction between the modulated laser and the gas to be tested, based on the reverse sound pressure distribution characteristics, and outputs a differential photoacoustic signal. A lock-in amplifier performs phase-sensitive detection and low-noise amplification on the differential photoacoustic signal based on the reference signal, and outputs an amplitude signal related to the concentration of the target gas. Thus, a device that can suppress interference gases under the condition that the absorption lines of the target gas and the interference gas are highly coincident is provided.

Description

Technical Field

[0001] This invention belongs to the field of photoacoustic spectroscopy gas detection technology, specifically relating to an interference gas suppression device based on the reverse distribution of sound pressure in a differential photoacoustic cell. Background Technology

[0002] Photoacoustic spectroscopy gas sensing technology is a rapidly developing indirect absorption spectroscopy technique in recent years. Its basic principle lies in converting the absorption of modulated light radiation by gas molecules into a detectable acoustic signal. When a modulated laser of a specific wavelength is incident on a gas sample, the gas molecules absorb the light energy and transition from the ground state to an excited state. Subsequently, nonradiative relaxation occurs through intermolecular collisions, converting the absorbed light energy into heat energy, causing periodic changes in the gas temperature. These periodic temperature changes further lead to periodic expansion and contraction of the gas volume, thereby exciting acoustic signals within a closed or semi-closed acoustic cavity. These acoustic waves are detected using acoustic sensing elements such as a photoacoustic cell, tuning fork quartz crystal oscillator, or cantilever beam. After demodulation and analysis by a signal processing unit, the concentration and related physicochemical information of the gas sample can be obtained. Photoacoustic spectroscopy gas sensing technology has advantages such as zero background signal, detection sensitivity proportional to excitation light power, compact system structure, fast response speed, and low cost, and has been widely used in environmental monitoring, industrial process control, biomedical detection, and online analysis of trace gases.

[0003] In microphone-based photoacoustic spectroscopy gas detection systems, the photoacoustic cell is the core component for achieving photoacoustic conversion and acoustic resonance enhancement. Differential photoacoustic cell structures are widely used in photoacoustic spectroscopy detection systems to improve the signal-to-noise ratio and suppress interference from environmental noise and light source fluctuations. However, in actual gas detection processes, especially in multi-component mixed gas or complex background gas environments, the target gas and interfering gases often exhibit overlapping or adjacent absorption spectra. Under these conditions, the interfering gas will also generate a photoacoustic response signal at the excitation wavelength of the target gas. Since traditional differential photoacoustic detection methods mainly rely on the symmetrical response of two resonant cavities to the same excitation light, their differential processing can only effectively suppress background noise, but it is difficult to distinguish photoacoustic signals caused by absorption by different gases. Therefore, it cannot fundamentally eliminate the influence of interfering gases on the detection results, limiting the application of photoacoustic spectroscopy in highly selective gas detection.

[0004] In existing technologies, differential photoacoustic cells are typically used as a single acoustic system. Technological improvements primarily focus on increasing the effective absorption path of the gas, introducing multi-channel detection methods, or optimizing signal processing to enhance photoacoustic signal intensity and detection sensitivity. For example, in a multi-component gas detection device for hydrogen production, a frequency-modulated laser is combined with a near-concentric cavity to increase the gas absorption path. This, along with a differential resonant photoacoustic cell and a lock-in amplifier to reduce noise levels, improves the detection sensitivity of photoacoustic spectroscopy and acoustic resonance frequency tracking, enabling joint detection of multiple gas components. This approach offers advantages in improving detection sensitivity by enhancing gas absorption and suppressing system noise. However, the differential photoacoustic cell is mainly used to reduce noise levels and improve the signal-to-noise ratio; the differential processing still relies on photoacoustic signals obtained under symmetrical acoustic response conditions. In such detection scenarios, interfering gases also generate significant photoacoustic response signals at the excitation wavelength of the target gas. Simply increasing the absorption path or improving system sensitivity often amplifies the photoacoustic signal of the interfering gas, making it difficult to effectively eliminate its influence.

[0005] Therefore, although existing technologies have made some progress in improving the sensitivity of photoacoustic spectroscopy detection by using differential photoacoustic cell structures and increasing absorption paths, there is still a lack of photoacoustic spectroscopy gas detection methods and devices that can suppress or remove the influence of interfering gases from the acoustic mechanism level when the absorption lines of the target gas and the interfering gas are highly overlapping. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides an interference gas suppression device based on the reverse distribution of sound pressure in a differential photoacoustic cell.

[0007] The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides an interference gas suppression device based on the reverse distribution of sound pressure in a differential photoacoustic cell. The interference gas suppression device includes a first laser, a second laser, a differential photoacoustic cell, a function generator, a laser driving module, and a lock-in amplifier. The function generator is used to generate a modulation signal and a reference signal that are in phase and at the same frequency. The laser driving module is used to output a driving current according to the modulation signal; The first laser and the second laser are used to generate modulated lasers of different wavelengths based on the driving current; wherein, the wavelength of the first modulated laser output by the first laser covers the absorption spectral lines of the target gas and the interfering gas, and the wavelength of the second modulated laser output by the second laser covers the absorption spectral lines of the interfering gas. The differential photoacoustic cell is used to receive the modulated laser and the gas to be tested, and to perform acoustic enhancement, electrical signal conversion and differential processing on the photoacoustic signal generated after the interaction between the modulated laser and the gas to be tested through the reverse sound pressure distribution characteristics, and output a differential photoacoustic signal. The lock-in amplifier is used to perform phase-sensitive detection and low-noise amplification of the differential photoacoustic signal based on the reference signal, and output an amplitude signal related to the concentration of the target gas.

[0008] The present invention provides an interference gas suppression device based on the reverse distribution of acoustic pressure in a differential photoacoustic cell. The wavelength of the first modulated laser output by the first laser covers the absorption spectrum of both the target gas and the interference gas, and the wavelength of the second modulated laser output by the second laser covers the absorption spectrum of the interference gas. The acoustic pressure distribution excited by the two modulated lasers in the differential photoacoustic cell exhibits reverse characteristics in the overall acoustic mode. By performing differential processing on the two photoacoustic signals, the photoacoustic signals of the interference gas are effectively canceled, thereby highlighting the effective detection signal of the target gas.

[0009] This invention fully utilizes the overall acoustic characteristics of the differential photoacoustic cell without altering its basic structural form or relying on additional microphones or complex optical path designs. It has the advantages of simple structure, clear implementation method, and strong system compatibility. It can significantly improve the selectivity and measurement accuracy of photoacoustic gas detection under conditions of high overlap of absorption spectral lines, and is suitable for high-sensitivity gas detection applications in complex gas environments.

[0010] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of an interference gas suppression device based on the reverse distribution of sound pressure in a differential photoacoustic cell, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the photoacoustic cell provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the acoustic modal simulation cloud map formed in the differential photoacoustic cell when the first modulated laser passes through the first resonant cavity, according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the acoustic modal simulation cloud map formed in the differential photoacoustic cell when the second modulated laser passes through the second resonant cavity, according to an embodiment of the present invention. Figure 5 This is a comparison of the absorption cross sections of propofol and acetone in the 220-320 nm wavelength band. Figure 6 This is a schematic diagram of the sound pressure signal obtained by the first microphone under simulation conditions; Figure 7This is a schematic diagram of the sound pressure signal obtained by the second microphone under simulation conditions; Figure 8 This is a schematic diagram of the differential photoacoustic signal obtained from the simulation; Figure 9 This is a schematic diagram of the differential photoacoustic signal response under different concentrations of acetone interference conditions against a measured background of 20 ppb propofol. Figure 10 This is a graph showing the linear relationship between propofol concentration and photoacoustic signal amplitude.

[0012] Reference numerals: 1. First buffer cavity; 2. Second buffer cavity; 3. First resonant cavity; 4. Second resonant cavity; 5. Entrance window; 6. Exit window; 7. Air inlet; 8. Air outlet; 9. First modulated laser; 10. Second modulated laser; 11. First microphone; 12. Second microphone. Detailed Implementation

[0013] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0014] To address the problem in existing technologies where the absorption lines of the target gas and interfering gas highly overlap, making it difficult to mitigate the influence of interfering gases at the acoustic mechanism level, this invention provides an interfering gas suppression device based on differential photoacoustic cell sound pressure reverse suppression or removal distribution. (See also...) Figure 1 , Figure 1 This is a schematic diagram of an interference gas suppression device based on the reverse distribution of sound pressure in a differential photoacoustic cell, provided by an embodiment of the present invention. The interference gas suppression device includes a first laser, a second laser, a differential photoacoustic cell, a function generator, a laser driving module, and a lock-in amplifier. A function generator is used to generate modulated signals and reference signals that are in phase and at the same frequency. A laser driver module is used to output a drive current based on a modulation signal; A first laser and a second laser are used to generate modulated lasers of different wavelengths based on a driving current; wherein, the wavelength of the first modulated laser output by the first laser covers the absorption spectral lines of both the target gas and the interfering gas, and the wavelength of the second modulated laser output by the second laser covers the absorption spectral lines of the interfering gas. The differential photoacoustic cell is used to receive modulated laser and gas under test, and to perform acoustic enhancement, electrical signal conversion and differential processing on the photoacoustic signal generated after the interaction between the modulated laser and the gas under test through the reverse sound pressure distribution characteristics, and output a differential photoacoustic signal. A lock-in amplifier is used to perform phase-sensitive detection and low-noise amplification of differential photoacoustic signals based on a reference signal, and outputs an amplitude signal related to the target gas concentration.

[0015] In this embodiment of the invention, a differential photoacoustic cell is used as the core gas sensing unit, and combined with multi-source excitation and synchronous signal demodulation, to achieve highly selective detection of the target concentration in the gas to be tested.

[0016] In this embodiment of the invention, a first laser, namely laser a, and a second laser, namely laser b, are used to generate modulated lasers of different wavelengths based on a driving current; wherein, the wavelength of the first modulated laser output by the first laser covers the absorption spectrum of the target gas and the interfering gas, and the wavelength of the second modulated laser output by the second laser covers the absorption spectrum of the interfering gas.

[0017] The function generator is used to generate a modulation signal and a reference signal that are in phase and frequency, and outputs them to the laser driver module and the lock-in amplifier, respectively, to achieve synchronous control of laser modulation and signal demodulation.

[0018] The laser driver module outputs a drive current based on the modulation signal output by the function generator to modulate the current of the first and second lasers, so that the lasers operate stably at a predetermined modulation frequency.

[0019] In this embodiment of the invention, the differential photoacoustic cell includes a photoacoustic cell and a differential signal processing circuit; The photoacoustic cell is used to receive modulated laser and gas under test, and to perform acoustic enhancement and electrical signal conversion on the photoacoustic signal generated after the interaction between the modulated laser and the gas under test through the reverse sound pressure distribution characteristics, and output two acoustic signals. The differential signal processing circuit is used to perform differential processing on two acoustic signals and output a differential photoacoustic signal.

[0020] By performing differential processing inside the differential photoacoustic cell, common-mode noise and photoacoustic signals generated by interfering gases can be effectively suppressed before signal output, thereby improving the overall signal-to-noise ratio and detection stability of the system.

[0021] The lock-in amplifier uses a reference signal that is in phase and frequency with the output modulation signal of the function generator to perform phase-sensitive detection and low-noise amplification on the differential photoacoustic signal, thereby extracting the effective photoacoustic response related to the target gas concentration. It outputs the amplitude signal related to the target gas concentration to an external data processing device for data storage, display, analysis, concentration inversion and other operations. The external data processing device can be a computer or other processor.

[0022] In this embodiment of the invention, the interfering gas suppression device further includes a flow controller and a pressure controller; A flow controller is used to regulate the flow rate of the gas to be measured entering the differential photoacoustic cell; The pressure controller is used to regulate the pressure of the gas to be measured entering the differential photoacoustic cell.

[0023] In this embodiment of the invention, a flow controller is connected between the gas to be measured and the inlet of the differential photoacoustic cell structure to precisely control the volumetric flow rate or mass flow rate of the gas to be measured. Within the controlled flow rate range, the gas inside the resonant cavity can be fully replaced.

[0024] In this embodiment of the invention, a pressure controller is connected between the flow controller and the outlet of the differential photoacoustic cell structure to stabilize the internal working pressure of the photoacoustic cell at a preset value.

[0025] By working in tandem with the flow controller and the pressure controller, the impact of gas flow and pressure fluctuations on the photoacoustic signal is reduced, thereby further improving the repeatability and reliability of the detection results.

[0026] In this embodiment of the invention, the interfering gas suppression device may further include an exhaust gas treatment module for rendering the tested gas harmless after detection.

[0027] See Figure 2 , Figure 2 This is a schematic diagram of the structure of the photoacoustic cell provided in an embodiment of the present invention. The photoacoustic cell includes a first buffer cavity 1, a second buffer cavity 2, a first resonant cavity 3, a second resonant cavity 4, an entrance window 5, an exit window 6, an air inlet 7, an air outlet 8, a first microphone 11, and a second microphone 12. The first resonant cavity 3 and the second resonant cavity 4 are arranged in parallel; the first buffer cavity 1 is connected to the first end of the first resonant cavity 3 and the second resonant cavity 4, and the second buffer cavity 2 is connected to the second end of the first resonant cavity 3 and the second resonant cavity 4, wherein the first end and the second end are arranged opposite to each other. The entrance window 5 is located on the side of the first buffer cavity 1 away from the first resonant cavity 3 and the second resonant cavity 4; the exit window 6 is located on the side of the second buffer cavity 2 away from the first resonant cavity 3 and the second resonant cavity 4. The first buffer chamber 1 is provided with an air inlet 7; the second buffer chamber 2 is provided with an air outlet 8; The first microphone 11 is located at the sound pressure level antagonism of the first resonant cavity 3; the second microphone 12 is located at the sound pressure level antagonism of the second resonant cavity 4. The first microphone 11 is used to collect acoustic signals in the first resonant cavity 3, and the second microphone 12 is used to collect acoustic signals in the second resonant cavity 4.

[0028] In this embodiment of the invention, the first laser outputs a first modulated laser 9 which is incident on the first resonant cavity 3, and the second laser outputs a second modulated laser 10 which is incident on the second resonant cavity 4. The gas to be tested enters the differential photoacoustic cell through the air inlet 7. The non-inverting input terminal of the differential amplifier circuit is connected to the first microphone 11, the inverting input terminal of the differential amplifier circuit is connected to the second microphone 12, the output terminal of the differential amplifier circuit is connected to the input terminal of the lock-in amplifier, the first output terminal of the function generator is connected to the reference input terminal of the lock-in amplifier, the second output terminal of the function generator is connected to the input terminal of the laser driving module, and the output terminal of the laser driving module is connected to the first laser and the second laser respectively.

[0029] In this embodiment of the invention, the first resonant cavity 3 and the second resonant cavity 4 have the same structural parameters and are used for acoustic excitation of two modulated laser beams, respectively. For example, the length of the first resonant cavity 3 and the second resonant cavity 4 are both 35 mm, and the inner diameter is 4 mm. A first buffer cavity 1 and a second buffer cavity 2 are respectively provided at both ends of the first resonant cavity 3 and the second resonant cavity 4 to reduce background noise caused by gas flow and external disturbances. The length of the first buffer cavity 1 and the second buffer cavity 2 are both 8 mm, and the inner diameter is 12 mm. The entrance window 5 and the exit window 6 are both optical-grade windows. The entrance window 5 is located on the side of the first buffer cavity 1 away from the first resonant cavity 3 and the second resonant cavity 4; the exit window 6 is located on the side of the second buffer cavity 2 away from the first resonant cavity 3 and the second resonant cavity 4, and is used for the incident and exit of the modulated laser. A first microphone 11 and a second microphone 12 are respectively installed inside the first resonant cavity 3 and the second resonant cavity 4. Both microphones are arranged at the sound pressure antinode positions of the corresponding resonant cavities to obtain the maximum acoustic response signal. The first modulated laser 9 and the second modulated laser 10 are respectively incident on different resonant tubes in the differential photoacoustic cell. The first modulated laser 9 has a center wavelength of 275 nm and is used to cover the absorption spectrum of the target gas and interfering gases, such as propofol and interfering gases, such as acetone; the second modulated laser 10 has a center wavelength of 295 nm and only covers the absorption spectrum of interfering gases, such as acetone.

[0030] It should be understood that the dimensional parameters of the first and second resonant cavities and the first and second buffer cavities described above are merely illustrative examples of embodiments of the present invention and are not intended to limit the present invention. Without departing from the technical solution and beneficial effects of the present invention, the relevant dimensional parameters can be appropriately adjusted according to actual application requirements.

[0031] In this embodiment of the invention, the acoustic modal characteristics of the differential photoacoustic cell are as follows: Figure 3 As shown, Figure 3This is a schematic diagram of the acoustic mode simulation cloud map formed in the differential photoacoustic cell when the first modulated laser 9 passes through the first resonant cavity 3, according to an embodiment of the present invention. When the first modulated laser 9 passes through the first resonant cavity 3, a specific acoustic mode is formed in the differential photoacoustic cell, and its sound pressure distribution exhibits first-order longitudinal standing wave characteristics. Figure 4 As shown, Figure 4 This is a schematic diagram of the acoustic mode simulation cloud diagram formed in the differential photoacoustic cell when the second modulated laser 10 passes through the second resonant cavity 4, according to an embodiment of the present invention. When the second modulated laser 10 passes through the second resonant cavity 4 at the same modulation frequency, the acoustic mode formed in the differential photoacoustic cell is similar to... Figure 3 The sound pressure distribution shown is inversely related in overall phase, meaning the sound pressure distribution directions are opposite under the two operating conditions. This acoustic characteristic is an inherent property of the differential photoacoustic cell structure at a specific modulation frequency. In this embodiment of the invention, the resonant frequency of the differential photoacoustic cell is 4110 Hz, and both the first modulation laser 9 and the second modulation laser 10 are modulated at this resonant frequency.

[0032] In the interference gas suppression device based on the reverse sound pressure distribution of the differential photoacoustic cell provided by the present invention, the wavelength of the first modulated laser 9 output by the first laser covers the absorption spectrum of the target gas and the interference gas, and the wavelength of the second modulated laser 10 output by the second laser covers the absorption spectrum of the interference gas. The sound pressure distribution excited by the two modulated lasers in the differential photoacoustic cell exhibits reverse characteristics in the overall acoustic mode. By performing differential processing on the two photoacoustic signals, the photoacoustic signals of the interference gas are effectively canceled, thereby highlighting the effective detection signal of the target gas.

[0033] This invention fully utilizes the overall acoustic characteristics of the differential photoacoustic cell without altering its basic structural form or relying on additional microphones or complex optical path designs. It has the advantages of simple structure, clear implementation method, and strong system compatibility. It can significantly improve the selectivity and measurement accuracy of photoacoustic gas detection under conditions of high overlap of absorption spectral lines, and is suitable for high-sensitivity gas detection applications in complex gas environments.

[0034] The following simulation experiment was conducted using an interference gas suppression device based on the reverse sound pressure distribution of a differential photoacoustic cell, as provided in this embodiment of the invention: Taking acetone as the interfering gas and propofol as the target gas as an example, see [link to relevant documentation]. Figure 5 , Figure 5 This is a comparison of the absorption cross sections of propofol and acetone in the 220-320 nm wavelength range. Figure 5When the intensity is magnified 100 times, it can be seen that the absorption spectra of propofol and acetone overlap significantly in the 275nm band, while in the 295nm band, only acetone shows significant absorption, and propofol shows almost no absorption. Based on the above spectral characteristics, in this embodiment of the invention, the first modulated laser 9 (275 nm) is used to simultaneously excite the photoacoustic signals of propofol and acetone, and the second modulated laser 10 (295 nm) is used to excite the photoacoustic signal of acetone alone.

[0035] Continuing with the example of acetone as the interfering gas and propofol as the target gas, see [link to example]. Figure 6 , Figure 6 This is a schematic diagram of the sound pressure signal obtained by the first microphone 11, i.e., microphone a, under simulation conditions. It includes three curves: the propofol sound pressure signal excited by the first modulated laser 9. ; Acetone acoustic pressure signal excited by the first modulated laser 9 ; Acetone acoustic pressure signal excited by the second modulated laser 10 See also Figure 7 , Figure 7 This is a schematic diagram of the sound pressure signal obtained by the second microphone 12, i.e., microphone b, under simulation conditions. It also contains the three signal components mentioned above, including the propofol sound pressure signal excited by the first modulated laser 9. ; Acetone acoustic pressure signal excited by the first modulated laser 9 ; Acetone acoustic pressure signal excited by the second modulated laser 10 Due to the inverse characteristics of sound pressure distribution, the acoustic responses excited by the interfering gas acetone in the two resonant tubes exhibit opposite phase trends. , After differential processing of the output electrical signals of the first microphone 11 and the second microphone 12, that is... , to obtain Figure 8 The differential photoacoustic signal shown is... Figure 8 This is a schematic diagram of the differential photoacoustic signal obtained from the simulation. It can be seen that the photoacoustic signal corresponding to the interfering gas acetone is effectively canceled out during the differential process, while the photoacoustic signal of the target gas propofol is preserved and significantly enhanced. See also... Figure 9 , Figure 9 This diagram illustrates the differential photoacoustic signal response under different concentrations of acetone interference against a measured background of 20 ppb propofol. It shows that the interference from acetone at 1 ppb, 2 ppb, and 3 ppb is minimal, indicating that the photoacoustic signal corresponding to the interfering gas acetone is effectively canceled out during the differential process. (See also...) Figure 10 , Figure 10 This is a graph showing the linear relationship between propofol concentration and photoacoustic signal amplitude, with the coefficient of determination for linear fitting results in the concentration range of 0-25 ppb. It reached 0.999.

[0036] The differential photoacoustic cell used in this invention is an integral structure with two resonant tubes having identical structural parameters and acoustic characteristics. At a specific modulation frequency, it exhibits the following characteristic: when the modulated laser passes through one of the resonant tubes, the sound pressure distribution within the differential photoacoustic cell shows an opposite relationship in the overall acoustic mode. Based on this acoustic characteristic, the interference gas suppression device constructed in this invention includes a first laser and a second laser, both operating in a modulation mode. The wavelength of the first modulated laser 9 covers the absorption lines of both the target gas and the interference gas, used to excite a mixed photoacoustic signal containing both gases; the wavelength of the second modulated laser 10 covers only the absorption lines of the interference gas, used to excite the interference gas alone to generate a photoacoustic signal. After optical collimation and coupling, the two laser beams are respectively incident on two different resonant tubes in the differential photoacoustic cell, causing them to excite sound waves at the same modulation frequency. Due to the overall acoustic structural characteristics of the differential photoacoustic cell, at this modulation frequency, the sound waves excited by the two laser beams in different resonant tubes show an opposite relationship in the sound pressure distribution. By arranging microphones in the differential photoacoustic cell and performing differential processing on the two photoacoustic signals, the photoacoustic signals generated by the interfering gas under the action of two modulated lasers can cancel each other out, while the target gas is only excited by the first modulated laser 9, and its corresponding photoacoustic signal is retained after differential processing, thereby achieving effective suppression of the interfering gas signal.

[0037] This invention does not rely on increasing the absorption optical path, raising laser power, or introducing additional complex acoustic structures. Instead, it fully utilizes the inherent reverse sound pressure distribution characteristics of the differential photoacoustic cell to suppress interfering gases from the perspective of photoacoustic signal generation and superposition mechanisms. This method has a simple structure, a clear implementation path, and is easily integrated with existing photoacoustic spectroscopy detection systems. It is particularly suitable for detection scenarios where the absorption spectra of the target gas and interfering gas highly overlap or are difficult to distinguish through wavelength selection. It can significantly improve the selectivity and measurement accuracy of photoacoustic spectroscopy detection in complex gas environments, expand the application capabilities of differential photoacoustic cells in multi-component gas detection, and has good engineering practical value and promising prospects for promotion.

[0038] Furthermore, the interference gas suppression device based on the reverse distribution of acoustic pressure in the differential photoacoustic cell provided in this embodiment of the invention has good versatility and can be applied to various combinations of target gas and interference gas. It is especially suitable for detection scenarios where the absorption spectra of the target gas and the absorption spectra of the interference gas partially overlap or are adjacent. Without changing the basic structure of the photoacoustic cell, the system can be adapted by selecting the laser wavelength. This invention can be integrated into photoacoustic spectroscopy detection systems such as medical respiratory gas detection, environmental monitoring, and industrial process analysis, and can improve detection selectivity and anti-interference ability while maintaining the simplicity and stability of the system structure.

[0039] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention.

[0040] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0041] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings and the disclosure in carrying out the claimed invention. In the description of the invention, the word "comprising" does not exclude other components or steps, "a" or "an" does not exclude a plurality, and "a plurality" means two or more, unless otherwise explicitly specified. Furthermore, while different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce good results.

[0042] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An interference gas suppression device based on differential photoacoustic cell acoustic pressure counter-distribution, characterized in that, The interfering gas suppression device includes a first laser, a second laser, a differential photoacoustic cell, a function generator, a laser driver module, and a lock-in amplifier; The function generator is used to generate a modulation signal and a reference signal that are in phase and at the same frequency. The laser driving module is used to output a driving current according to the modulation signal; The first laser and the second laser are used to generate modulated lasers of different wavelengths based on the driving current; wherein, the wavelength of the first modulated laser output by the first laser covers the absorption spectral lines of the target gas and the interfering gas, and the wavelength of the second modulated laser output by the second laser covers the absorption spectral lines of the interfering gas. The differential photoacoustic cell is used to receive the modulated laser and the gas to be tested, and to perform acoustic enhancement, electrical signal conversion and differential processing on the photoacoustic signal generated after the interaction between the modulated laser and the gas to be tested through the reverse sound pressure distribution characteristics, and output a differential photoacoustic signal. The lock-in amplifier is used to perform phase-sensitive detection and low-noise amplification of the differential photoacoustic signal based on the reference signal, and output an amplitude signal related to the concentration of the target gas.

2. The interfering gas suppressing apparatus according to claim 1, characterized by, The differential photoacoustic cell includes a photoacoustic cell and a differential signal processing circuit; The photoacoustic cell is used to receive the modulated laser and the gas to be tested, and to perform acoustic enhancement and electrical signal conversion on the photoacoustic signal generated after the interaction between the modulated laser and the gas to be tested through the reverse sound pressure distribution characteristics, and output two acoustic signals. The differential signal processing circuit is used to perform differential processing on the two acoustic signals and output the differential photoacoustic signal.

3. The interfering gas suppressing apparatus according to claim 2, characterized by, The photoacoustic cell includes a first buffer cavity, a second buffer cavity, a first resonant cavity, a second resonant cavity, an entrance window, an exit window, an air inlet, an air outlet, a first microphone, and a second microphone. The first resonant cavity and the second resonant cavity are arranged in parallel; the first buffer cavity is connected to the first end of the first resonant cavity and the second resonant cavity, and the second buffer cavity is connected to the second end of the first resonant cavity and the second resonant cavity, wherein the first end and the second end are arranged opposite to each other; The entrance window is located on the side of the first buffer cavity away from the first resonant cavity and the second resonant cavity; the exit window is located on the side of the second buffer cavity away from the first resonant cavity and the second resonant cavity. The first buffer chamber is provided with the air inlet; the second buffer chamber is provided with the air outlet; The first microphone is located at the sound pressure level of the first resonant cavity; the second microphone is located at the sound pressure level of the second resonant cavity.

4. The interfering gas suppressing apparatus according to claim 3, characterized by The first laser outputs the first modulated laser, which is incident on the first resonant cavity. The second laser outputs the second modulated laser, which is incident on the second resonant cavity. The gas to be tested enters the differential photoacoustic cell through the air inlet. The non-inverting input of the differential amplifier circuit is connected to the first microphone, and the inverting input of the differential amplifier circuit is connected to the second microphone. The output of the differential amplifier circuit is connected to the input of the lock-in amplifier. The first output of the function generator is connected to the reference input of the lock-in amplifier, and the second output of the function generator is connected to the input of the laser driver module. The output of the laser driver module is connected to both the first laser and the second laser.

5. The interfering gas suppression device according to claim 3, characterized in that, The first resonant cavity and the second resonant cavity have the same structural parameters.

6. The interfering gas suppression device according to claim 3, characterized in that, Both the entrance window and the exit window are optical-grade windows.

7. The interfering gas suppression device according to claim 1, characterized in that, The interfering gas suppression device also includes a flow controller and a pressure controller; The flow controller is used to adjust the flow rate of the gas to be measured entering the differential photoacoustic cell; The pressure controller is used to adjust the pressure of the gas to be measured entering the differential photoacoustic cell.

8. The interfering gas suppression device according to claim 7, characterized in that, The flow controller is connected between the gas to be measured and the inlet of the differential photoacoustic cell structure; the pressure controller is connected between the flow controller and the outlet of the differential photoacoustic cell structure.

9. The interfering gas suppression device according to claim 1, characterized in that, The interfering gas suppression device may also include an exhaust gas treatment module for rendering the tested gas harmless after the detection is completed.

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