QEPAS detection system based on resonance tube coaxial coupling configuration

Abstract

The invention relates to a QEPAS detection system based on resonance tube coaxial coupling configuration. The QEPAS detection system comprises a laser signal emission unit, a photoacoustic detection unit and an electric signal acquisition unit which are connected in sequence, the photoacoustic detection unit comprises an air inlet, an air outlet, a resonant cavity, a reflecting mirror and a quartz tuning fork; wherein the centers of the resonant cavities, the reflectors and the quartz tuning fork are located on an optical transmission path, the resonant cavities are arranged at the center of the photoacoustic detection unit and distributed on the two sides of the quartz tuning fork, and the reflectors are oppositely installed at the two ends of the resonant cavities; the quartz tuning fork is mounted at the gap of the resonant cavity; the exhaust port and the gas inlet are formed in the two sides of the resonant cavity respectively, background gas and target gas enter the photoacoustic detection unit from the gas inlet, and after detection is completed, mixed gas is exhausted out of the photoacoustic detection unit from the exhaust port. Compared with the prior art, the resonance characteristic of the resonance tube is utilized to enhance the photoacoustic signal, the coaxial structure optimizes the acoustic environment, and efficient and accurate detection of trace gas can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of trace gas detection, and in particular to a QEPAS detection system based on a coaxial coupling configuration of resonance tubes. Background Technique

[0002] Quartz-enhanced photoacoustic spectroscopy (QEPAS) technology is a new trace gas detection technology based on the photoacoustic effect, which mainly uses a quartz tuning fork (QTF) to enhance photoacoustic signal detection. The principle is that when gas molecules absorb a modulated laser of a specific wavelength, they will convert the absorbed light energy into heat energy through a non-radiative relaxation process, causing the temperature of the surrounding gas to rise and generating a periodic pressure change, that is, a photoacoustic signal. This photoacoustic signal acts on the quartz tuning fork. Due to the high Q value (quality factor) of the quartz tuning fork, a resonance response will be generated. And due to the piezoelectric effect of quartz, this vibration will be converted into an electrical signal, and the electrical signal is measured by an electrical detection system to achieve the detection of the gas. Compared with traditional photoacoustic spectroscopy technology, QEPAS has many advantages such as strong detection sensitivity, small volume, and extremely high quality factor. As an advanced technology in the field of trace gas detection, it plays an important role in the early warning of oil-filled equipment failures, atmospheric environment monitoring, long-distance detection of explosives, etc. In-depth research on QEPAS technology helps to further explore its potential in the early warning of oil-filled equipment failures. By accurately monitoring the gas components inside the equipment, it is possible to detect problems in the budding stage of the failure, greatly reducing the risk of production interruption caused by sudden equipment failures, ensuring the stable operation of industrial production, and reducing the high costs generated by equipment maintenance and replacement. In addition, the development of QEPAS technology can also drive the innovation and upgrading of related industries, promote technological innovation in industries such as sensor manufacturing and optical instruments, create more economic growth points, and promote scientific and technological progress and social development.

[0003] As disclosed in the Chinese patent application CN202010851747.3, by vertically arranging it directly above the absorption cavity to form a T-shaped structure with the absorption cavity, the resonance cavity is decoupled from the absorption cavity. The solution of separating the quartz tuning fork from the absorption cavity requires maintaining the modulation frequency of the laser, the eigenfrequency of the photoacoustic resonator, and the resonance frequency of the quartz tuning fork to be consistent with the absorption peak of the trace gas to be measured in order to achieve accurate measurement. And the eigenfrequency of the resonator is related to the cavity sizes of the resonance cavity and the absorption cavity. When the system parameters are fixed, it can only measure gases with specific absorption frequencies and is difficult to quickly adjust according to the absorption characteristics of the target gas.

[0004] In existing QEPAS technologies such as Chinese Patent Applications CN201510292635.8 and CN201610053998.0, the detection of pressure vibration signals by a quartz tuning fork is achieved by setting micropores on the resonant cavity. The single-tube acoustic resonant cavity is perpendicular to the side of the tuning-fork quartz crystal oscillator arm, and its waist is located within the gap of the arm. Acoustic wave coupling is achieved through the square hole in the waist. The photoacoustic signal is weak, the detection sensitivity is limited, and there are problems such as being vulnerable to external environmental noise interference and insufficient detection ability for complex samples. Summary of the Invention

[0005] The object of the present invention is to overcome the technical problems of the above-mentioned traditional QEPAS technology, such as being vulnerable to external environmental noise interference, weak photoacoustic signal, limited detection sensitivity, and insufficient detection ability for complex samples, and to provide a QEPAS detection system based on a coaxial coupling configuration of a resonance tube.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A QEPAS detection system based on a coaxial coupling configuration of a resonance tube includes a laser signal emitting unit, a photoacoustic detection unit, and an electrical signal acquisition unit that are connected in sequence.

[0008] The photoacoustic detection unit includes: an air inlet, an air outlet, a resonant cavity, a mirror, and a quartz tuning fork; wherein, the centers of the resonant cavity, the mirror, and the quartz tuning fork are located on the optical transmission path of the laser signal emitting unit; the quartz tuning fork is installed at the center of the photoacoustic detection unit, and resonant cavities are respectively arranged on both sides of the quartz tuning fork; the mirrors are oppositely installed at both ends of the resonant cavity; the quartz tuning fork is located at the gap between the two side resonant cavities and is electrically connected to the electrical signal acquisition unit;

[0009] The air outlet and the air inlet are respectively arranged on both sides of the resonant cavity. Background gas and target gas enter the photoacoustic detection unit from the air inlet, and the mixed gas is discharged from the air outlet of the photoacoustic detection unit after the detection is completed.

[0010] As a preferred technical solution, the laser signal emitting unit includes a laser, an optical modulator, a power amplifier, a filter, an optical isolator, and a collimator that are connected in sequence through an optical fiber; the optical centers of the components of the laser signal emitting unit are on the same horizontal line, and the photoacoustic detection unit is opposite to the collimator.

[0011] As a preferred technical solution, the optical modulator is an acousto-optic modulator, which modulates the frequency, intensity, and phase parameters of the laser output by the laser according to the absorption characteristics of the target gas to generate a periodic optical signal.

[0012] As a preferred technical solution, the filter is a band-pass filter, which is used to screen the optical signal of the wavelength absorbed by the target gas.

[0013] As a preferred technical solution, the collimator is a double-lens collimator, which adopts a combination of lenses with positive and negative focal lengths. When light passes through the first lens, it is focused and diverges at the second lens, so that the light forms a focal point on the focal plane between the two lenses, collimates the divergent light into a parallel light beam, and makes the light accurately irradiate the target gas.

[0014] As a preferred technical solution, the opposite surface of the mirror is concave. By adjusting the curvature and position of the mirror, the laser is converged to form a multiple reflection path of the optical signal in the resonant cavity.

[0015] As a preferred technical solution, the quartz tuning fork is a quartz tuning fork with a micro-nano structured surface.

[0016] As a preferred technical solution, the electrical signal acquisition unit includes, in sequence and connected by data: a transimpedance amplifier, a lock-in amplifier, and a computer;

[0017] The transimpedance amplifier converts the current signal generated by the quartz tuning fork into a voltage signal and amplifies the voltage signal.

[0018] The lock-in amplifier receives the signal from the transimpedance amplifier and performs a comparison operation with the reference signal to extract the signal component with the same frequency and phase as the reference signal.

[0019] The computer calculates and analyzes the data of the target gas based on the acquired electrical signal.

[0020] As a preferred technical solution, the detection system further includes a laser driver, which is respectively signal-connected to the laser in the laser signal transmitting unit and the computer, and is used to adjust the power and wavelength parameters of the laser.

[0021] As a preferred technical solution, the detection system further includes a background gas controller and a target gas controller that deliver the corresponding gas to the photoacoustic detection unit through a gas pipeline;

[0022] The background gas controller is used to adjust the flow rate and pressure parameters of the background gas to create a controlled gas environment for the detection system;

[0023] The target gas controller is used to control the flow rate, concentration, and pressure of the target gas, and deliver the target gas to the photoacoustic detection unit at a stable flow rate to ensure a stable photoacoustic effect between gas molecules and the laser during the detection process.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The resonance tube proposed in this application consists of a resonant cavity and a mirror. Two resonant cavities are arranged at both ends of the quartz tuning fork, and the quartz tuning fork is installed at the gap of the resonant cavity. The photoacoustic signal generated in the resonant cavity directly acts on the quartz tuning fork, with a more direct coupling method. Moreover, the mirror is used to enhance the interaction between light and gas to generate a stronger photoacoustic signal. The photoacoustic signal is reflected and superimposed multiple times in the tube, greatly amplifying the originally weak signal, so that trace gases with lower concentrations can be detected, significantly improving the detection sensitivity.

[0026] 2) In terms of light propagation, in this application, the mirrors are relatively installed at both ends of the resonant cavity, enabling the laser to be reflected multiple times in the resonant cavity, greatly extending the optical path and increasing the interaction opportunity between the laser and gas molecules. At the same time, the concave reflection converges the laser, enhancing the light intensity in a specific area and improving the absorption efficiency of gas molecules for laser energy. And the structure of the resonance tube can accurately plan the light propagation path, making the photoacoustic signal propagate along a specific path and effectively act on the quartz tuning fork, reducing the energy loss and interference during the propagation of the acoustic signal, making the interaction between the sample gas and the laser more sufficient. Even in the face of complex samples, the type and concentration of the gas therein can be accurately determined, realizing the efficient and accurate detection of trace gases.

[0027] 3) In terms of sound propagation, in this application, the resonant cavity has the ability to select and enhance photoacoustic signals of specific frequencies. The photoacoustic signals matching the natural frequency of the resonant cavity are reflected and superimposed multiple times in the cavity and thus enhanced, while other frequency signals are suppressed, reducing the background noise interference. The coaxial structure adopted optimizes the acoustic environment and effectively reduces the interference of external environmental noise on the detection process. By accurately planning the sound propagation path, the influence of stray sound waves on the detection components is reduced, enhancing the selectivity of the system for the target photoacoustic signal. Brief Description of the Drawings

[0028] Figure 1 Schematic diagram of the QEPAS detection system based on the coaxial coupling configuration of a micro-resonance tube provided by an embodiment of the present invention

[0029] Figure 2 Photoacoustic signal data curve graph of the existing detection scheme using a single-tube acoustic resonator;

[0030] Figure 3 Photoacoustic signal data curve graph of the QEPAS detection system based on the coaxial coupling configuration of a micro-resonance tube of the present invention;

[0031] As shown in the figure: 1. Laser; 2. Optical modulator; 3. Power amplifier; 4. Filter; 5. Optical isolator; 6. Collimator; 7. Photoacoustic detection unit; 8. Transimpedance amplifier; 9. Phase-locked amplifier; 10. Computer; 11. Laser driver; 12. Background gas controller; 13. Target gas controller; 14. Inlet; 15. Outlet; 16. Resonant cavity; 17. Mirror; 18. Quartz tuning fork. Detailed implementation mode

[0032] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives the detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Embodiment 1

[0034] As Figure 1 shown, the QEPAS detection system based on the coaxial coupling configuration of a micro-resonant tube provided by the present invention includes: a laser 1, an optical modulator 2, a power amplifier 3, a filter 4, an optical isolator 5, a collimator 6, a photoacoustic detection unit 7, a transimpedance amplifier 8, a phase-locked amplifier 9, a computer 10, and a laser driver 11.

[0035] The positions of the above-mentioned units are set as follows: the laser 1, the optical modulator 2, the power amplifier 3, the filter 4, the optical isolator 5, and the collimator 6 are connected in sequence through optical fibers, and the optical centers of each unit are on the same horizontal line; the photoacoustic detection unit 7 is opposite to the collimator 6; the transimpedance amplifier 8, the phase-locked amplifier 9, and the computer 10 are connected in sequence through data lines; the computer 10 is also connected to the laser driver 11. The specific settings of each unit are as follows:

[0036] The laser 1 generates laser light of a specific wavelength as an excitation source to excite a gas sample to generate a photoacoustic signal.

[0037] In this embodiment, the laser 1 is preferably a distributed feedback (DFB) laser, which has the advantages of narrow linewidth, high stability, and tunability, and can provide a high-quality, stable, and flexible laser source for the QEPAS detection system, which helps to improve the overall performance and applicability of the system.

[0038] The optical modulator 2 modulates the laser light output by the laser 1 to generate a periodic optical signal; precisely modulates the laser parameters, improves the absorption efficiency of the gas to the laser energy, and enhances the intensity of the photoacoustic signal.

[0039] In this embodiment, the optical modulator 2, preferably an acousto-optic modulator (AOM), can effectively modulate the laser beam with high precision, in a high frequency range, and with low loss in the QEPAS detection system by utilizing the acousto-optic effect and the Bragg diffraction principle, which helps improve the performance and detection ability of the system.

[0040] The power amplifier 3 amplifies the power of the modulated laser signal to enhance the energy of the laser and increase the intensity of the photoacoustic signal generated by the photoacoustic effect, thereby improving the detection performance of the entire system.

[0041] In this embodiment, the power amplifier 3 is preferably a broadband high-power solid-state power amplifier, which has high gain and high output power, can enhance the interaction between the laser and the gas, improve the detection sensitivity, the broadband characteristic is suitable for different gas detections, the high linearity ensures accurate results, the low noise helps detect weak signals, and it has high stability and reliability, which can reduce system failures.

[0042] The optical filter 4 is used to screen the optical signal with the wavelength most suitable for the absorption of the target gas, improving the pertinence and accuracy of the detection.

[0043] In this embodiment, the optical filter 4 is preferably a band-pass filter, which can work stably in a complex temperature environment, can accurately select the target wavelength range, can customize the center wavelength and bandwidth, while achieving high-precision gas detection, and achieving the purpose of enhancing the intensity of the target wavelength light, increasing the intensity of the photoacoustic signal, and lowering the detection limit.

[0044] The optical isolator 5 only allows light to transmit in one direction, avoiding optical feedback caused by reflected light, reducing interference, and ensuring the stability of the entire system and the accuracy of the detection.

[0045] In this embodiment, the optical isolator 5 is preferably a single-stage isolator of MolTech, which can achieve a high isolation degree, can effectively prevent the reverse light from passing through, and avoid the adverse effects of the reflected light on the light source and the optical path system, such as reducing the influence of the reflected light on the spectral output power stability of the laser, thereby ensuring the stability and reliability of the system.

[0046] The collimator 6 turns the divergent light into a parallel light beam, improving the directivity and focusing of the light, enabling the light to irradiate the target gas more accurately, increasing the interaction efficiency between the light and the gas, and enhancing the performance of the entire detection system.

[0047] In this embodiment, the collimator 6, preferably a double-lens collimator, adopts a combination of lenses with positive and negative focal lengths. When light passes through the first lens, it is focused, and then diverges at the second lens, causing the light to form a focal point on the focal plane between the two lenses. Thus, a better collimation effect can be obtained, and the light emitted by the laser in the QEPAS system can be more accurately collimated into a parallel beam, reducing the influence of beam divergence on the detection accuracy of the system.

[0048] The photoacoustic detection unit 7 includes: an air inlet 14, an air outlet 15, a resonant cavity 16, a mirror 17, and a quartz tuning fork 18. The positions of the above-mentioned units are set as follows: the air inlet 14 is arranged on the left side of the photoacoustic detection unit 7; the air outlet 15 is symmetrically arranged with the air inlet 14 on the right side of the photoacoustic detection unit 7; the resonant cavity 16 is arranged at the center of the photoacoustic detection unit 7 and distributed on both sides of the quartz tuning fork 18; the mirrors 17 are relatively installed at both ends of the resonant cavity 16; the quartz tuning fork 18 is installed at the gap of the resonant cavity 16.

[0049] Among them, the centers of the resonant cavity 16, the mirror 17, and the quartz tuning fork 18 are on the optical transmission path. The air inlet 14 is used to allow background gas and target gas to enter the photoacoustic detection unit from the air inlet 14; the air outlet 15 is used to allow the mixed gas after detection to be discharged from the photoacoustic detection unit through the air outlet 15.

[0050] In this embodiment, the air inlet 14 is preferably a circular air inlet with an inner diameter of 4 - 6 mm; the air outlet 15 is preferably symmetrically arranged in the photoacoustic detection unit with the same size as the air inlet 14.

[0051] The resonant cavity 16 optimizes the interaction between the laser and gas molecules, enabling the laser to better interact with gas molecules in the cavity, improving the absorption efficiency of gas molecules for laser energy, allowing gas molecules to more efficiently convert the absorbed light energy into heat energy, and then generating photoacoustic signals. By selecting the resonant frequency, the photoacoustic signals of specific frequencies are enhanced, while signals and noises of other frequencies are suppressed. This helps reduce the background noise of the system, enabling the system to more accurately focus on the photoacoustic signals generated by the target gas, thereby improving the detection accuracy and reliability, and ultimately significantly enhancing the overall performance of the system.

[0052] In this embodiment, the resonant cavity 16 is preferably a cylindrical resonant cavity with an inner diameter of about 5 - 10 mm and a length of about 30 - 50 mm, and is installed on the optical transmission path of the photoacoustic detection unit.

[0053] The mirror 17 converges the laser by adjusting the curvature and position of the mirror, causing the optical signal to form a multiple reflection path in a specific area and extending the optical path of the laser in this area.

[0054] In this embodiment, the mirror 17, preferably a mirror with a concave opposite surface, is installed in the resonant cavity 16, which can achieve the focusing of the reflected light beam, maximize the utilization of the optical signal, and ensure the reliability of the detection result.

[0055] The quartz tuning fork 18, as an acoustic wave transducer, after the gas molecules absorb the laser energy and generate a photoacoustic signal, converts the pressure change caused by the photoacoustic signal into mechanical vibration, and based on the piezoelectric effect, converts the mechanical vibration into an electrical signal, accurately extracting the information of the target gas from the weak photoacoustic signal.

[0056] In this embodiment, the quartz tuning fork 18 is preferably a quartz tuning fork with a micro-nano structured surface. The micro-nano structure can be a periodic nano-column array, and its size and spacing can be optimized according to the frequency of the photoacoustic signal. When the photoacoustic signal acts on the nano-column array, it will cause local stress changes, which can more effectively drive the tuning fork to vibrate, thereby improving the signal conversion efficiency; because the micro-nano structure can enhance signal coupling, the quartz tuning fork is more sensitive to weak photoacoustic signals. When detecting low-concentration target gases, weak photoacoustic signals can also be detected more effectively.

[0057] The resonance tube of the present invention is composed of the resonant cavity 16 and the mirror 17, and has unique acoustic-optical propagation characteristics. In terms of light propagation, the mirror 17 is relatively installed at both ends of the resonant cavity 16, enabling the laser to be reflected multiple times within the resonant cavity 16, greatly extending the optical path and increasing the interaction opportunity between the laser and gas molecules; at the same time, the concave mirror 17 has a converging effect on the laser, enhancing the light intensity in a specific area and improving the absorption efficiency of gas molecules for laser energy. In terms of sound propagation, the resonant cavity 16 has the ability to select and enhance specific frequency photoacoustic signals. The photoacoustic signals matching the natural frequency of the resonant cavity 16 are reflected and superimposed multiple times within the cavity to be enhanced, while other frequency signals are suppressed, reducing background noise interference; and the structure of the resonance tube can accurately plan the sound propagation path, enabling the photoacoustic signal to propagate along a specific path and effectively act on the quartz tuning fork, reducing the energy loss and interference during the propagation of the sound signal, and ensuring the accuracy and stability of the detection system for detecting photoacoustic signals.

[0058] The transimpedance amplifier 8, after the quartz tuning fork converts the photoacoustic signal into a weak current signal in the nanoampere level, the transimpedance amplifier will convert this current signal into a voltage signal and amplify it, raising the originally weak electrical signal to an amplitude suitable for subsequent processing and analysis.

[0059] In this embodiment, the transimpedance amplifier 8, preferably a DPPCA-300 transimpedance amplifier, has high gain and wide bandwidth, can effectively amplify photoacoustic signals of different frequencies; has extremely low noise, reducing interference to weak signals; has a high input impedance and does not affect the operation of the quartz tuning fork; has excellent linearity, ensuring accurate measurement of gas concentration; has a wide input current range, adapting to different experimental conditions; and has precise bias current adjustment to ensure long-term stable operation of the system.

[0060] The lock-in amplifier 9 extracts the signal components with the same frequency and phase as the reference signal from complex signals, receives the signal from the transimpedance amplifier and compares and operates it with the reference signal, effectively suppressing noise and improving the signal-to-noise ratio of the system.

[0061] The computer 10 is connected to the lock-in amplifier 9, calculates and analyzes data such as the concentration and absorption spectrum of the target gas, and converts the collected electrical signals into meaningful gas information through specific algorithms and mathematical models, helping users intuitively understand various properties and states of the gas; is connected to the laser driver and controls and adjusts the operating parameters of the laser to achieve automatic control of the detection system.

[0062] The laser driver 11 adjusts parameters such as the power and wavelength of the laser according to different detection requirements, thereby optimizing the detection performance of the system and ensuring the efficient and accurate operation of the entire detection system.

[0063] In this application, by arranging two resonant cavities 16 at both ends of the quartz tuning fork 18, the ability of the quartz tuning fork 18 to detect pressure vibration signals is enhanced, and thus the detection sensitivity is improved. The resonant cavities 16 are distributed on both sides of the quartz tuning fork 18, and the quartz tuning fork 18 is installed at the gap of the resonant cavities 16. After the photoacoustic signal is generated in the resonant cavities 16, it directly acts on the quartz tuning fork 18, and the coupling method is more direct. Moreover, the mirror 17 is used to enhance the interaction between light and gas to generate a stronger photoacoustic signal.

[0064] The specific working process of the above QEPAS detection system based on the coaxial coupling configuration of the micro-resonant tube is as follows:

[0065] The laser 1 generates an original laser signal, which enters the optical modulator 2. The optical modulator 2 modulates the laser signal into parameters such as frequency, intensity, and phase that are most conducive to the absorption of the target gas (such as acetylene gas) according to the absorption characteristics of the target gas, so as to generate an effective photoacoustic effect subsequently. The modulated laser signal enters the power amplifier 3, and the power amplifier 3 amplifies its power to enhance the energy of the optical signal. After passing through the filter 4, the function of the filter 4 is to select the optical signal within the required specific wavelength range, filter out stray light, and ensure that the optical signal entering the system has high purity and pertinence. The optical isolator 5 prevents reflected light or reverse light from entering the system and ensures the unidirectional transmission of the optical signal. The collimator 6 collimates the processed optical signal into an approximately parallel beam with a very small divergence angle, enabling the optical signal to better enter the photoacoustic detection unit 7, improving the directivity and concentration of the optical signal, and reducing the loss of optical energy. At the same time, the gas to be detected enters the intake port 14 of the photoacoustic detection unit 7 and fills the resonant cavity inside the photoacoustic detection unit. After the collimated parallel beam enters the resonant cavity of the photoacoustic detection unit 7, when there is a target gas (taking acetylene gas as an example) therein, a part of the laser signal is absorbed by the acetylene gas. According to the photoacoustic effect principle, the acetylene gas molecules that absorb light energy generate periodic thermal expansion and contraction, thereby generating an acoustic wave signal. During this process, the mirror 17 inside the photoacoustic detection unit 7 can reflect part of the unabsorbed light back, enabling it to pass through the resonant cavity again and improving the utilization efficiency of light. The acoustic wave signal generated by the photoacoustic effect is detected by the quartz tuning fork 18 inside the photoacoustic detection unit 7, and the quartz tuning fork 18 converts the acoustic wave signal into an electrical signal. The electrical signal converted by the quartz tuning fork 18 first enters the transimpedance amplifier 8, and the transimpedance amplifier 8 amplifies the weak electrical signal to increase the amplitude of the signal. The electrical signal amplified by the transimpedance amplifier 8 enters the lock-in amplifier 9. The lock-in amplifier 9 uses the signal frequency output by the function generator that is the same as the resonance frequency of the photoacoustic cell as the lock reference frequency to demodulate the photoacoustic signal and extract the information related to the concentration of the target gas from the noise. The intensity of the photoacoustic signal is proportional to the concentration of the target gas. Through the demodulation of the lock-in amplifier 9, the information related to the concentration of the target gas is obtained. The computer 10 receives the signal processed by the lock-in amplifier 9, calculates and processes it, completes the analysis of the signal, and finally presents the detection result. The computer 10 sends a control signal to the laser driver 11 according to the detection result. After receiving the instruction from the computer, the laser driver 11 works in coordination with the output signal of the lock-in amplifier 9 to adjust the output of the laser 1 to achieve the dynamic adjustment of the optical signal, and then realize the closed-loop control of the entire system. Through continuous feedback and adjustment, the detection accuracy and stability of the system for the target gas can be improved, ensuring that the system can continuously and stably detect the information related to the target gas in the photoacoustic spectrum and achieve the precise monitoring of the gas.

[0066] In this embodiment, the solution proposed by the present invention is also experimentally compared with the existing solution of arranging a single-tube acoustic resonator perpendicular to the side surface of the tuning fork quartz crystal oscillator arm, and opening a waist hole at the position corresponding to the arm gap of the single-tube acoustic resonator to achieve acoustic wave coupling. As Figure 2 shown is the photoacoustic signal data curve of the prior art; as Figure 3 is the photoacoustic signal data curve of the present invention. The experimental results show that compared with the prior art solution, the detection sensitivity of the solution of the present invention is increased by about 8 times.

[0067] Embodiment 2

[0068] This embodiment provides another implementation manner of the QEPAS detection system based on the coaxial coupling configuration of the micro-resonant tube of the present invention. Its main part is the same as the QEPAS detection system described in the embodiment, except that in this embodiment, the system further includes a background gas controller 12 and a target gas controller 13 respectively connected to the air inlet of the photoacoustic detection unit 7 through gas pipelines, wherein:

[0069] The background gas controller 12 creates a precisely controlled gas environment for the system by adjusting the parameters of the flow rate and pressure of the background gas.

[0070] The target gas controller 13 precisely controls the flow rate, concentration and pressure of the target gas, and transports the target gas to the photoacoustic detection unit at a stable flow rate to ensure that during the detection process, gas molecules can generate a stable photoacoustic effect with the laser.

[0071] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A QEPAS detection system based on a resonant tube coaxial coupling configuration, comprising a laser signal emitting unit, a photoacoustic detection unit (7) and an electrical signal acquisition unit connected in sequence; It is characterized in that The photoacoustic detection unit (7) comprises: an air inlet (14), an air outlet (15), a resonant cavity (16), a reflector (17) and a quartz tuning fork (18); wherein the centers of the resonant cavity (16), the reflector (17) and the quartz tuning fork (18) are located on the optical transmission path of the laser signal emitting unit; the quartz tuning fork (18) is installed at the center of the photoacoustic detection unit (7), and the resonant cavity (16) is provided on both sides of the quartz tuning fork (18); the reflector (17) is relatively installed at the two ends of the resonant cavity (16); the quartz tuning fork (18) is located at the gap of the resonant cavity (16) and is electrically connected to the electrical signal acquisition unit; The exhaust port (15) and the air inlet (14) are respectively arranged on both sides of the resonant cavity (16); the background gas and the target gas enter the photoacoustic detection unit (7) from the air inlet (14); and after the detection is completed, the mixed gas is discharged from the photoacoustic detection unit (7) from the exhaust port (15).

2. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 1, characterized in that: The laser signal emitting unit comprises a laser (1), an optical modulator (2), a power amplifier (3), an optical filter (4), an optical isolator (5), and a collimator (6) which are sequentially connected via optical fibers; the optical centers of the components of the laser signal emitting unit are on the same horizontal line, and the photoacoustic detection unit (7) is opposite to the collimator (6).

3. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 2, characterized in that: The optical modulator (2) is an acousto-optic modulator, which modulates the frequency, intensity and phase parameters of the laser output by the laser (1) according to the absorption characteristics of the target gas to generate a periodic optical signal.

4. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 2, characterized in that: The optical filter (4) is a bandpass filter used to filter the optical signal of the wavelength absorbed by the target gas.

5. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 2, characterized in that: The collimator (6) is a double-lens collimator, which uses a lens combination with positive and negative focal lengths. When the light passes through the first lens, it is focused and diverged at the second lens, so that the light forms a focus on the focal plane between the two lenses, and the divergent light is collimated into a parallel beam, so that the light is accurately irradiated onto the target gas.

6. A QEPAS detection system based on a resonant tube coaxial coupling configuration according to claim 1, characterized in that: The opposite surface of the reflector (17) is a concave surface. By adjusting the curvature and position of the reflector, the laser light is converged so that the optical signal forms multiple reflection paths in the resonant cavity (16).

7. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 1, characterized in that: The quartz tuning fork (18) is a quartz tuning fork with a micro-nano structure surface.

8. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 1, characterized in that: The electrical signal acquisition unit comprises: a transimpedance amplifier (8), a lock-in amplifier (9) and a computer (10) which are sequentially connected in data; The transimpedance amplifier (8) converts the current signal generated by the quartz tuning fork (18) into a voltage signal and amplifies the voltage signal; The phase-locked amplifier (9) receives the signal from the transimpedance amplifier and compares it with the reference signal to extract a signal component with the same frequency and phase as the reference signal; The computer (10) calculates and analyzes the data of the target gas based on the collected electrical signals.

9. A QEPAS detection system based on a resonant tube coaxial coupling configuration according to claim 8, characterized in that: The detection system further comprises a laser driver (11), which is respectively connected to the laser signal emitting unit and the computer (10) by signals and is used to adjust the power and wavelength parameters of the laser emitted by the laser signal emitting unit.

10. A QEPAS detection system based on a resonance tube coaxial coupling configuration according to claim 1, characterized in that: The detection system also includes a background gas controller (12) and a target gas controller (13) for delivering corresponding gases to the photoacoustic detection unit (7) through a gas delivery pipe; The background gas controller (12) is used to adjust the flow rate and pressure parameters of the background gas to create a controlled gas environment for the detection system; The target gas controller (13) is used to control the flow rate, concentration and pressure of the target gas, and to deliver the target gas to the photoacoustic detection unit at a stable flow rate, so as to ensure that the gas molecules and the laser generate a stable photoacoustic effect during the detection process.

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