Photoacoustic cell signal enhancement detection system and method

Abstract

The invention discloses a photoacoustic cell signal enhancement detection system and method, comprising: a main control unit, a modulation unit for emitting laser, an optical microphone with a photoacoustic enhancement structure and a photoacoustic cell for collecting photoacoustic signals; the main control unit is respectively connected to the modulation unit and the optical microphone, and the photoacoustic cell is respectively connected to the optical microphone and the modulation unit; the invention effectively improves the sensitivity of the optical microphone by adopting a secondary resonance cavity to amplify the acoustic signal, and at the same time detects the change of the light intensity signal related to the displacement at the detector, the system passively detects the membrane displacement with a sub-angstrom resolution, and very accurately detects and measures this very small change through optical and electronic processing, obtains the real source signal losslessly, and effectively improves the detection accuracy.

Description

Technical Field

[0001] The invention relates to the field of gas detection, and in particular to a photoacoustic cell signal enhancement detection system and method. Background Art

[0002] SF6 electrical equipment (gas insulated switchgear GIS, gas insulated transformer GIT, long-distance gas insulated pipeline GIL, gas insulated circuit breaker GCB, cable GIC, etc.) is widely used in the field of power transmission and distribution equipment due to its good insulation and arc extinguishing medium characteristics, and has outstanding advantages such as small footprint, safe and reliable operation, and long maintenance cycle. The working voltage covers all levels from 35kV to 1200kV. At present, SF6 electrical equipment has an absolute advantage and there is a trend to expand its application scope. SF6 electrical equipment is a basic component of the power system, and its working condition is directly related to the safe and economical operation of the power system.

[0003] At present, the online detection of decomposition products in sulfur hexafluoride gas-insulated equipment is a hot topic and a difficult point in research. Spectral analysis methods are also widely used in the detection of sulfur hexafluoride decomposition products due to their high detection sensitivity and excellent anti-cross-interference performance. Commonly used detection methods include differential absorption spectroscopy (DOAS), non-dispersive infrared spectroscopy (NDIR), tunable semiconductor absorption spectroscopy (TDLAS) system, laser cavity ring-down spectroscopy (CRDS), photoacoustic spectroscopy (PAS), etc.

[0004] Among them, photoacoustic spectroscopy trace gas detection technology (PAS) has been increasingly used in trace gas detection applications in power systems due to its high sensitivity, good signal-to-noise ratio, low detection limit, fast response time, and easy online calibration.

[0005] Photoacoustic spectroscopy trace gas detection technology is based on the principle of photoacoustic effect to detect the concentration of absorbed gas. In a closed container, when a light beam of a specific infrared band irradiates a group of gas molecules, the gas molecules choose to absorb the light energy of a part of the band. After absorbing the incident light, the gas molecules in the photoacoustic cell are excited from a low energy state to a high energy state, and then return to a low energy state in the form of spontaneous radiation transition and non-radiative transition. In the process of non-radiative transition, its energy is converted into the translational kinetic energy and rotational kinetic energy of the gas molecules, which increases the temperature of the gas. When the gas volume remains unchanged, the temperature increases and the pressure increases. If the intensity or wavelength of the incident light is modulated, the temperature of the absorbed gas will change at the same frequency, resulting in periodic changes in the gas pressure. If the modulation frequency is within the acoustic frequency range, the periodic change in gas pressure will generate a photoacoustic signal. By detecting the photoacoustic signal with a microphone, information on the gas concentration can be obtained.

[0006] Among them, the photoacoustic cell is the key to the detection system. Generally, the switching frequency of the light source is set to be consistent with the resonant frequency of the photoacoustic cell, so that the sound signal can resonate to enhance the intensity of the sound signal, thereby achieving ultimately higher detection performance.

[0007] In the prior art, capacitive acoustic sensors are the most common, and the sensor has a built-in capacitive electret microphone that is sensitive to sound. Sound waves cause the electret film in the microphone to vibrate, resulting in changes in capacitance, and generating a small voltage that changes accordingly. This voltage is converted into a stronger voltage signal after passing through a preamplifier, and is received by a data acquisition device after A / D conversion, and is transmitted to a digital processing system for processing. Among them, MEMS (micro-electromechanical system) acoustic sensors are commonly used. MEMS (micro-electromechanical system) acoustic sensors are miniature microphones and ultrasonic sensors manufactured based on MEMS technology. Simply put, a capacitor is integrated on a micro silicon chip. Its essence is still a capacitive acoustic sensor, and its advantages are small size and low batch manufacturing cost.

[0008] However, due to the limitations of materials and manufacturing processes, the improvement of key parameters of traditional condenser microphones has reached its limit, making it difficult to improve detection sensitivity. Photoacoustic spectroscopy trace gas detection technology converts optical energy into acoustic energy. The photoacoustic signal is very weak. The improvement of detection sensitivity of photoacoustic spectroscopy detection technology is very dependent on the sensitivity of the acoustic sensor. Currently, the detection sensitivity is limited by the sensitivity of the microphone. Summary of the invention

[0009] The purpose of the present invention is to provide a photoacoustic pool signal enhancement detection system and method to solve the above-mentioned problems; the present invention solves the problem of low detection sensitivity and accuracy of optical microphones; and solves the problem of inaccurate detection results.

[0010] The technical solution adopted by the present invention is as follows:

[0011] A photoacoustic cell signal enhancement detection system comprises: a main control unit, a modulation unit for emitting laser, an optical microphone with a photoacoustic enhancement structure and a photoacoustic cell for collecting photoacoustic signals; the main control unit is respectively connected to the modulation unit and the optical microphone, and the photoacoustic cell is respectively connected to the optical microphone and the modulation unit; the main control unit controls the modulation unit and the optical microphone to emit laser and control the laser frequency; the photoacoustic cell is used to contain a gas to be detected, and receives the laser emitted by the modulation unit and amplifies it, and then transmits the amplified information to the optical microphone for collection.

[0012] Furthermore, the optical microphone includes: a detection unit, a beam splitter, a beam combiner, a circulator, a collimator, an enhancement cavity, an optical reflective diaphragm and an acoustic energy absorbing diaphragm; the beam splitter and the beam combiner are respectively connected to the detection unit and the circulator, one end of the collimator is connected to the circulator, and the other end is located in the enhancement cavity and connected to the optical reflective diaphragm, the acoustic energy absorbing diaphragm is located in the enhancement cavity, and forms a signal amplification cavity between the acoustic energy absorbing diaphragm and the optical reflective diaphragm; the surface area of ​​the acoustic energy absorbing diaphragm is much larger than the surface area of ​​the optical reflective diaphragm.

[0013] Furthermore, the detection unit includes a detector and a laser, the detector is connected to the beam combiner, and the laser is connected to the beam splitter.

[0014] Furthermore, the photoacoustic pool includes: a photoacoustic resonance cavity, a sealed lens, an air inlet and an air outlet for air intake and exhaust, a fastener for fixing the optical microphone structure, a reference gas chamber filled with the measured gas and a measured gas cavity; the measured gas cavity body is connected to the optical microphone, and the two ends of the measured gas cavity body are respectively connected to the photoacoustic resonance cavity, and the photoacoustic resonance cavities at both ends are respectively connected to the sealed lenses, wherein the sealed lens connected to the photoacoustic resonance cavity at one end is connected to the reference gas chamber, and the sealed lens connected to the photoacoustic resonance cavity at the other end is connected to the cavity, and the air inlet and the air outlet are respectively located at the two ends of the side of the photoacoustic pool.

[0015] Furthermore, the modulation unit includes a gas absorption laser and a photodetector; the gas absorption laser emits laser light to the gas cavity to be measured.

[0016] A photoacoustic cell signal enhancement detection method includes a signal amplification step and a detection step, wherein the signal amplification step amplifies the vibration signal so that the optical microphone can more easily receive the vibration signal and perform further detection;

[0017] The signal amplification step includes: the main control unit controls the modulation unit so that the gas absorption laser emits a laser that can be absorbed by the measured gas; the laser passes through the sealed lens and reaches the photoacoustic resonance cavity; part of the laser is absorbed by the measured gas, and part of the laser passes through the gas reference absorption cell and then shoots to the photodetector; the measured gas resonates in the photoacoustic resonance cavity; the acoustic energy absorption diaphragm receives the vibration signal in the acoustic resonance cavity, and transmits the vibration signal to the inside of the signal amplification cavity, and is transmitted to the optical reflection diaphragm through the gas in the signal amplification cavity and amplified;

[0018] The detection steps include: the main control unit controls the laser to emit a laser with constant power; after passing through the beam splitter, it is divided into two beams, one of which is emitted to the detector through the beam combiner, and the other is guided to the collimator after passing through the circulator; finally, it is combined with the light source separated by the beam splitter into one beam and irradiated to the detector; the light intensity signal at the detector generates an electrical signal change as the reflective film changes; the gas concentration can be inverted according to the amplitude of the electrical signal change.

[0019] Furthermore, the method for the measured gas to form resonance in the photoacoustic resonance cavity is that the measured gas generates thermal motion after absorbing part of the laser energy, forms vibration under the periodic driving of the modulation unit, and forms resonance in the photoacoustic resonance cavity.

[0020] Furthermore, the method of combining the light source separated by the beam splitter into one beam and illuminating the detector is as follows: one of the laser beams becomes parallel light after passing through a collimator and is emitted toward an optical reflective film, and then is reflected by the optical reflective film and then emitted back toward the collimator, and passes through an optical fiber guide circulator, and then passes through a circulator to guide the collimator, and is combined with the light source separated by the beam splitter into one beam and illuminating the detector.

[0021] Furthermore, the vibration signal amplification method is: through the structure that the surface area of ​​the acoustic energy absorption diaphragm is much larger than the surface area of ​​the optical reflection diaphragm, the optical reflection film will multiply the vibration signal at the diaphragm.

[0022] Furthermore, it also includes a resonant frequency self-calibration method, including: the display and main control unit sends a control signal to control the buzzer to change the frequency from low to high in sequence, record the change amplitude of the electrical signal at each frequency, and record the intensity change curve, the point with the strongest intensity is the resonant frequency point of the photoacoustic pool; the modulation unit drives the gas absorption laser, changes its set temperature and driving current, so that the central wavelength of the laser emitted by the laser changes around the central absorption wavelength of the measured gas, and observes the absorption ratio change through the detector, and uses the digital processing algorithm to calculate the optimal control temperature and control current of the gas absorption laser to achieve the purpose of automatic correction.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. The optical microphone of the present invention effectively improves the sensitivity of the optical microphone by amplifying the acoustic signal through a secondary resonance cavity formed by an enhancement cavity and a signal amplification cavity.

[0025] 2. The present invention can detect and measure this very small change very accurately through optical and electronic processing, obtain the real source signal losslessly, and effectively improve the accuracy of detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0027] Figure 1 It is a structural diagram of the photoacoustic cell signal enhancement detection system.

[0028] Figure 2 This is a diagram of the structure of an optical microphone.

[0029] Figure 3 It is a signal amplification flow chart of the photoacoustic cell signal enhancement detection method.

[0030] Figure 4 It is a detection flow chart of the photoacoustic cell signal enhancement detection method.

[0031] Among them, 1-main control unit; 2-modulation unit; 3-optical microphone; 4-photoacoustic cell; 21-gas absorption laser; 22-photodetector; 31-detection unit; 32-beam splitter; 33-beam combiner; 34-circulator; 35-collimator; 36-enhancement cavity; 37-optical reflection diaphragm; 38-acoustic energy absorption diaphragm; 39-signal amplification cavity; 311-detector; 312-laser; 41-photoacoustic resonance cavity; 42-sealed lens; 43-air inlet; 44-air outlet; 45-fastener; 46-reference gas chamber; 47-buzzer; 48-measured gas cavity; 49-cavity. DETAILED DESCRIPTION

[0032] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0033] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other alternative features that are equivalent or have similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0034] Example 1

[0035] A photoacoustic cell 4 signal enhancement detection system, such as Figure 1 and Figure 2 As shown, it includes: a main control unit 1, a modulation unit 2 for emitting laser, an optical microphone 3 with a photoacoustic enhancement structure and a photoacoustic pool 4 for collecting photoacoustic signals; the main control unit 1 is respectively connected to the modulation unit 2 and the optical microphone 3, and the photoacoustic pool 4 is respectively connected to the optical microphone 3 and the modulation unit 2.

[0036] The modulation unit 2 includes a gas absorption laser 21 and a photodetector 22 ; the gas absorption laser 21 emits laser light to the gas cavity 48 to be measured.

[0037] The photoacoustic pool 4 includes: a photoacoustic resonance cavity 41, a sealing lens 42, an air inlet 43 and an air outlet 44 for air intake and exhaust, a fastener 45 for fixing the structure of the optical microphone 3, a reference gas chamber 46 filled with the measured gas, and a measured gas cavity 48; the measured gas cavity 48 is connected to the optical microphone 3, and the two ends of the measured gas cavity 48 are respectively connected to the photoacoustic resonance cavity 41, and the photoacoustic resonance cavities at both ends are respectively connected to the sealing lens 42, the sealed lens 42 connected to the photoacoustic resonance cavity at one end is connected to the reference gas chamber 46, and the sealed lens 42 connected to the photoacoustic resonance cavity at the other end is connected to the cavity 49, and the gas inlet and outlet are respectively located at the two symmetrical ends of the photoacoustic pool 4.

[0038] The main control unit 1 controls the modulation unit 2, so that the gas absorption laser 21 emits a laser that can be absorbed by the gas to be measured. The laser passes through the cavity 49 and the sealed lens 42 and reaches the photoacoustic resonance cavity 41. Part of the laser is absorbed by the gas to be measured, and part of the laser passes through the gas reference chamber 46 and is emitted to the photodetector 22. After the gas to be measured absorbs part of the laser energy, it generates thermal motion, forms vibration under the periodic drive of the modulation unit 2, and forms resonance in the photoacoustic resonance cavity 41.

[0039] In this embodiment, the reference gas chamber 46 and the photodetector 22 are used to calibrate the resonance frequency shift. The cavity 49 is a passage for the laser to pass through and reach the sealed lens, and can also be used as a space for placing a fixed structure for fixing equipment such as a laser.

[0040] The optical microphone 3 includes: a detection unit 31, a beam splitter 32, a beam combiner 33, a circulator 34, a collimator 35, and an enhanced cavity 36; an optical reflective diaphragm 37 and an acoustic energy absorbing diaphragm 38; the beam splitter 32 and the beam combiner 33 are respectively connected to the detection unit 31 and the circulator 34, one end of the collimator 35 is connected to the circulator 34, and the other end is located in the enhanced cavity 36 and connected to the optical reflective diaphragm 37, the acoustic energy absorbing diaphragm 38 is located in the enhanced cavity 36, and forms a cavity structure with the optical reflective diaphragm 37.

[0041] The detection unit 31 includes a detector 311 and a laser 312 . The detector 311 is connected to the beam combiner 33 , and the laser 312 is connected to the beam splitter 32 .

[0042] The acoustic energy absorbing diaphragm 38 receives the vibration signal in the acoustic resonance cavity, and transmits the vibration signal to the inside of the signal amplifying cavity 39, and transmits the vibration signal to the optical reflecting diaphragm 37 through the gas inside the signal amplifying cavity 39; the signal amplifying cavity 39 is located between the acoustic energy absorbing diaphragm 38 and the optical reflecting diaphragm 37, and the surface area of ​​the acoustic energy absorbing diaphragm 38 is much larger than the surface area of ​​the optical reflecting diaphragm 37. The optical reflecting diaphragm 37 will multiply the vibration signal at the acoustic energy absorbing diaphragm 38, and the amplification ratio is less than the surface area ratio. The amplified vibration signal can be more easily received by the optical microphone 3 and further detected.

[0043] Specifically, the main control unit 1 controls the laser 312 in the detection unit 31 to emit a laser with constant power. The laser is divided into two beams after passing through the beam splitter 32, namely, a first sub-laser beam and a second sub-laser beam. The first sub-laser beam passes through the beam combiner 33 and is combined with the second sub-laser beam returned by the circulator 34 into a laser beam and then emitted to the detector 311; the second sub-laser beam passes through the circulator 34 and is guided to the collimator 35, and becomes parallel light after passing through the collimator 35 and is emitted to the optical reflective film 37, and is reflected by the optical reflective film 37 and then emitted back to the collimator 35, and is guided to the circulator 34 through the optical fiber, and then is guided to the beam combiner 33 through the circulator 34, and is combined with the first sub-laser beam separated by the beam splitter 32 into a beam to illuminate the detector 311; the two beams introduced by the beam combiner 33 have the same frequency but different phases. When the optical reflective film is slightly displaced, the phase difference changes, and then an interference effect is generated, and the interference effect is related to the phase difference. The light intensity signal at the detector 311 causes the electric signal to change following the change of the reflective film; the amplitude of the electric signal change is related to the concentration of the gas being measured, and the gas concentration can be inverted based on the amplitude of the electric signal change.

[0044] The inversion method is to measure the corresponding relationship between the amplitude of the electrical signal change and the known concentration of the gas, and record multiple sets of calibration data. When the unknown concentration gas is introduced again, the recorded calibration data is checked back and the gas concentration is checked linearly.

[0045] Therefore, by amplifying the vibration signal, the optical microphone 3 can more easily receive the vibration signal information, thereby effectively improving the sensitivity of the optical microphone 3.

[0046] Example 2

[0047] A method for enhancing the detection of a photoacoustic cell 4 signal includes a signal amplification step and a detection step. The signal amplification step amplifies the vibration signal so that the optical microphone 3 can more easily receive the vibration signal and perform further detection.

[0048] Signal amplification steps, such as Figure 2 Shown include:

[0049] S11: the main control unit 1 controls the modulation unit 2 so that the gas absorption laser 21 emits laser light that can be absorbed by the gas to be measured.

[0050] S12: The laser passes through the sealing lens 42 and reaches the photoacoustic resonance cavity 41.

[0051] S13: Part of the laser light is absorbed by the gas being measured, and part of the laser light passes through the gas reference absorption cell and then is emitted to the photodetector 22 .

[0052] S14: The gas to be measured forms resonance in the photoacoustic resonance cavity 41 .

[0053] In the above steps, the method for the measured gas to form resonance in the photoacoustic resonance cavity 41 is: the measured gas generates thermal motion after absorbing part of the laser energy, forms vibration under the periodic driving of the modulation unit 2, and forms resonance in the photoacoustic resonance cavity 41.

[0054] S15: The acoustic energy absorbing diaphragm 38 receives the vibration signal in the acoustic resonance cavity, and transmits the vibration signal to the inside of the signal amplifying cavity 39, and is transmitted to the optical reflecting diaphragm 37 via the gas inside the amplifying cavity and amplified.

[0055] In the above steps, the method of amplifying the vibration signal is as follows: the surface area of ​​the acoustic energy absorbing diaphragm 38 is much larger than the surface area of ​​the optical reflecting diaphragm 37, and the optical reflecting film will multiply the vibration signal at the diaphragm.

[0056] The amplified vibration signal can be more easily collected and identified by the optical microphone 3, which is beneficial to the subsequent detection steps.

[0057] Testing steps, such as Figure 3 Shown include:

[0058] S21: The main control unit 1 controls the laser 312 to emit a laser with constant power.

[0059] S22: After passing through the beam splitter 32, it is divided into two beams, one of which passes through the beam combiner 33 and is combined with the laser returned by the circulator 34 into one laser beam and then emitted to the detector 311, and the other beam passes through the circulator 34 and is directed to the collimator 35.

[0060] In the above steps, the laser is divided into two beams by the beam splitter 32, namely the first sub-laser beam and the second sub-laser beam. The first sub-laser beam is combined into one laser beam by the beam combiner 33 and the second sub-laser beam returned by the circulator 34 and then emitted to the detector 311. The second sub-laser beam passes through the circulator 34 and then is directed to the collimator 35.

[0061] S23: Finally, the two light beams split by the beam splitter 32 are combined into one beam and directed toward the detector 311 .

[0062] In the above steps, the method for combining the light source separated by the beam splitter 32 into a beam and irradiating the detector 311 is as follows: the second sub-laser beam becomes parallel light after passing through the collimator 35 and is irradiated toward the optical reflective film, and after being reflected by the optical reflective film, it is directed back toward the collimator 35, and passes through the optical fiber guide circulator 34, and then passes through the circulator 34 to the beam combiner 33, and is combined with the first sub-laser beam separated by the beam splitter 32 into a beam and irradiated toward the detector 311.

[0063] S24: The light intensity signal at the detector 311 generates an electrical signal change following the change of the optical reflective film 37 .

[0064] In the above steps, the two beams of light introduced by the beam combiner 33 have the same frequency but different phases. When the optical reflective film 37 is slightly displaced, the phase difference changes, and then an interference effect is generated. The interference effect is related to the phase difference, which causes the light intensity signal at the detector 311 to produce an electrical signal change following the change of the optical reflective film 37.

[0065] S25: The gas concentration can be inverted according to the amplitude of the electrical signal change.

[0066] In the above steps, the inversion method is to measure the corresponding relationship between the amplitude of the electrical signal change and the known concentration of the gas, and record multiple sets of calibration data. When the unknown concentration gas is introduced again, the recorded calibration data is checked and the gas concentration is checked linearly.

[0067] In this embodiment, the photoacoustic pool 4 is affected by temperature changes and structural creep, and its resonant frequency will change during use. The system has a built-in frequency self-calibration system to calibrate its frequency offset. The specific implementation method is as follows: the main control unit 1 sends a control signal to control the buzzer 47 to change the frequency from low to high in sequence, record the change amplitude of the electrical signal at each frequency, and record the intensity change curve. The point with the strongest intensity is the resonant frequency of the photoacoustic pool 4; the gas absorption laser 21 is affected by temperature changes and changes in the device itself, and its central wavelength will change. The change in the central wavelength will affect the gas absorption intensity, and then affect the accuracy of the measurement system.

[0068] This embodiment sets a reference gas chamber 46 filled with the gas to be measured, and a photodetector 22. When the main control unit 1 determines through measurement that wavelength calibration is required, it will control the modulation unit 2 to drive the gas absorption laser 21, change the set temperature and driving current of the modulation unit 2, so that the central wavelength of the laser emitted by the gas absorption laser 21 changes around the central absorption wavelength of the gas to be measured, and observe the absorption ratio change through the photodetector 22, and calculate the optimal control temperature and control current of the gas absorption laser 21 with the help of a digital processing algorithm to achieve the purpose of automatic correction; the digital processing algorithm is a general TDLAS (tunable diode laser absorption spectroscopy) calculation method; the change of the laser center wavelength around the central absorption wavelength of the gas to be measured is specifically: the temperature is set to a constant value so that the laser center wavelength is near the absorption peak, and the laser is driven by a sawtooth current so that the laser wavelength scans the entire absorption peak.

[0069] The present invention effectively improves the sensitivity of the optical microphone 3 that amplifies the acoustic signal by using a secondary resonance cavity formed by an enhancement cavity and a signal amplification cavity. At the same time, the light intensity signal change related to the displacement is detected by the detector 311. The system passively detects the membrane displacement with sub-angstrom resolution, and very accurately detects and measures this very small change through optical and electronic processing, thereby obtaining a real source signal without loss, and effectively improving the accuracy of detection.

[0070] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A photoacoustic cell signal enhancement detection system, characterized in that: include: A main control unit (1), a modulation unit (2) for emitting laser light, an optical microphone (3) having a photoacoustic enhancement structure, and a photoacoustic cell (4) for collecting photoacoustic signals; the main control unit (1) is connected to the modulation unit (2) and the optical microphone (3), respectively, and the photoacoustic cell (4) is connected to the optical microphone (3) and the modulation unit (2), respectively; the main control unit (1) controls the modulation unit (2) and the optical microphone (3) to emit laser light and control the laser frequency; the photoacoustic cell (4) is used to contain a gas to be measured, and receives the laser light emitted by the modulation unit (2) and amplifies it, and then transmits the amplified information to the optical microphone (3) for collection; The optical microphone (3) comprises: a detection unit (31), a beam splitter (32), a beam combiner (33), a circulator (34), a collimator (35), an enhanced cavity (36), an optical reflective diaphragm (37) and an acoustic energy absorbing diaphragm (38); the beam splitter (32) and the beam combiner (33) are respectively connected to the detection unit (31) and the circulator (34); one end of the collimator (35) is connected to the circulator (34) and the other end is located in the enhanced cavity (36) and connected to the optical reflective diaphragm (37); the acoustic energy absorbing diaphragm (38) is located in the enhanced cavity (36) and forms a signal amplification cavity (39) with the optical reflective diaphragm (37); the surface area of ​​the acoustic energy absorbing diaphragm (38) is much larger than the surface area of ​​the optical reflective diaphragm (37).

2. The photoacoustic cell signal enhancement detection system according to claim 1, characterized in that: The detection unit (31) comprises a detector (311) and a laser (312); the detector (311) is connected to a beam combiner (33), and the laser (312) is connected to a beam splitter (32).

3. The photoacoustic cell signal enhancement detection system according to claim 1, characterized in that: The photoacoustic cell (4) comprises: a photoacoustic resonance cavity (41), a sealing lens (42), an air inlet (43) and an air outlet (44) for air intake and exhaust, a fastener (45) for fixing the structure of the optical microphone (3), a reference gas chamber (46) filled with a measured gas, and a measured gas cavity (48); the measured gas cavity (48) is connected to the optical microphone (3), and the two ends of the measured gas cavity (48) are respectively connected to the photoacoustic resonance cavity (41), and the photoacoustic resonance cavities (41) at both ends are respectively connected to the sealing lens (42), wherein the photoacoustic resonance cavity (41) at one end is connected to the sealing lens (42) and the reference gas chamber (46), and the photoacoustic resonance cavity (41) at the other end is connected to the sealing lens (42) and the cavity (49), and the air inlet (43) and the air outlet (44) are respectively located at the two ends of the side of the photoacoustic cell (4).

4. The photoacoustic cell signal enhancement detection system according to claim 1, characterized in that: The modulation unit (2) comprises a gas absorption laser (21) and a photodetector (22); the gas absorption laser (21) emits laser light to a gas cavity (48) to be measured.

5. A photoacoustic cell signal enhancement detection method, characterized in that: The method comprises a signal amplification step and a detection step, wherein the signal amplification step amplifies the vibration signal; The signal amplification step comprises: a main control unit (1) controls a modulation unit (2) so that a gas absorption laser (21) emits a laser that can be absorbed by the gas to be measured; the laser passes through a sealed lens (42) and reaches a photoacoustic resonance cavity (41); part of the laser is absorbed by the gas to be measured, and part of the laser passes through a gas reference absorption cell and is emitted to a photodetector (22); the gas to be measured resonates in the photoacoustic resonance cavity (41); an acoustic energy absorption diaphragm (38) receives a vibration signal in the acoustic resonance cavity, and transmits the vibration signal to the inside of a signal amplification cavity (39), and the vibration signal is transmitted to the optical reflection diaphragm (37) via the gas in the signal amplification cavity (39) and amplified; The detection steps include: the main control unit (1) controls the laser (312) to emit a laser with constant power; after passing through the beam splitter (32), the laser is divided into two beams, one of which passes through the beam combiner (33) and is emitted to the detector (311), and the other passes through the circulator (34) and is guided to the collimator (35); finally, the light source separated from the beam splitter (32) is combined into one beam and illuminates the detector (311); the light intensity signal at the detector (311) generates an electrical signal change following the change of the reflective film; and the gas concentration can be inverted according to the amplitude of the electrical signal change.

6. The photoacoustic cell signal enhancement detection method according to claim 5, characterized in that: The method for causing the measured gas to resonate in the photoacoustic resonance cavity (41) is as follows: the measured gas generates thermal motion after absorbing part of the laser energy, forms vibration under the periodic drive of the modulation unit (2), and forms resonance in the photoacoustic resonance cavity (41).

7. The photoacoustic cell signal enhancement detection method according to claim 5, characterized in that: The method for combining the light source separated from the beam splitter (32) into a beam and irradiating the detector (311) is as follows: one of the laser beams passes through a collimator (35) to become parallel light and irradiate the optical reflective film, then is reflected by the optical reflective film and irradiates the collimator (35) in the opposite direction, passes through an optical fiber guide circulator (34), then passes through the circulator (34) and is guided to the collimator (35), and is combined with the light source separated from the beam splitter (32) into a beam and irradiates the detector (311).

8. The photoacoustic cell signal enhancement detection method according to claim 7, characterized in that: The vibration signal amplification method comprises: using a structure in which the surface area of ​​the acoustic energy absorbing diaphragm (38) is much larger than the surface area of ​​the optical reflecting diaphragm (37), the optical reflecting diaphragm will multiply the vibration signal at the diaphragm.

9. The photoacoustic cell signal enhancement detection method according to claim 8, characterized in that: The invention also includes a resonance frequency self-calibration method, comprising: a display and main control unit (1) sends a control signal to control a buzzer (47) to change the frequency from low to high, record the change amplitude of the electric signal at each frequency, and record the intensity change curve, wherein the point with the strongest intensity is the resonance frequency point of the photoacoustic cell (4); a modulation unit (2) drives a gas absorption laser (21), changes its set temperature and driving current, so that the central wavelength of the laser emitted by the laser (312) changes around the central absorption wavelength of the measured gas, and observes the change of the absorption ratio through a detector (311), and calculates the optimal control temperature and control current of the gas absorption laser (21) with the help of a digital processing algorithm, so as to achieve the purpose of automatic correction.

Images