Photoacoustic spectrophone and gas detection device

Abstract

The invention relates to the field of gas sensing, and discloses a photoacoustic spectrophone and a gas detection device.The photoacoustic spectrophone comprises an acoustic resonant cavity and a quartz tuning fork, and the acoustic resonant cavity is arranged on one side of the quartz tuning fork; the acoustic resonant cavity is used for guiding a laser beam to sequentially pass through the acoustic resonant cavity and the quartz tuning fork and resonating and amplifying an excited acoustic signal; the sectional area of the acoustic resonant cavity close to the quartz tuning fork is smaller than that of the acoustic resonant cavity away from the quartz tuning fork Compared with the prior art, the sectional area of the acoustic resonant cavity is greatly changed, high acoustic impedance is brought, surrounding environment noise is restrained, meanwhile, the sound pressure and the signal-to-noise ratio are improved, the gas detection precision is improved, the light collimation space is opened, the requirement for the light beam contour quality is lowered, the photoacoustic spectrum sound detector can be matched with more light sources, and the detection efficiency is improved. And the application flexibility and practicability are enhanced. In addition, the acoustic resonant cavity is higher in structural parameter adjustability, the resonant frequency and bandwidth can be adjusted, and the quality factor and the stability of the system are improved.

Description

Technical Field

[0001] The invention relates to the field of gas sensing, in particular to a photoacoustic spectrum detector and a gas detection device. Background Art

[0002] Quartz enhanced photoacoustic spectroscopy is a photoacoustic spectroscopy technique that has attracted much attention in recent years. It uses a quartz tuning fork as a converter of sound waves to convert sound wave signals into electrical signals, thereby achieving high-sensitivity detection of substances. In order to further improve the detection sensitivity of this technology, researchers enhance the intensity of sound waves by matching the resonance of the acoustic resonator and the tuning fork. At present, the coaxially configured acoustic resonator is widely used due to its excellent effect. This configuration consists of a pair of thin tubes with consistent parameters, which are installed on both sides of the tuning fork.

[0003] However, according to the research in the literature [Applied Physics B, 2012, 108: 361-367], it is found that in a coaxial configuration, the capillary at the entrance of the laser beam plays a dominant role in amplifying the sound wave, while the capillary at the exit plays a smaller role. Based on this finding, if the device is simplified and the capillary at the exit of the beam is omitted, the requirements for the beam quality of the device can be effectively reduced. However, despite this, the photoacoustic signal in the prior art is still lost. Due to the influence of external environmental noise, the accuracy of gas detection is still not high enough, and the requirements for the beam profile quality are still too high. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to improve the accuracy of gas detection and further reduce the requirements for the quality of the beam profile. In order to solve the above technical problems, the present invention provides a photoacoustic spectrometer, comprising an acoustic resonant cavity and a quartz tuning fork, wherein the acoustic resonant cavity is arranged on one side of the quartz tuning fork, and the axis of the acoustic resonant cavity is perpendicular to the axis of the quartz tuning fork; the acoustic resonant cavity is used to guide a laser beam to pass through the acoustic resonant cavity and the quartz tuning fork in sequence and resonately amplify the acoustic wave signal generated by the laser beam exciting the gas to be measured;

[0005] The acoustic resonance cavity is a truncated cone structure with a through-hole in the middle, and the side of the acoustic resonance cavity close to the quartz tuning fork is defined as a first side, and the side of the acoustic resonance cavity away from the quartz tuning fork is defined as a second side, and the inner radius of the cross-section of the first side is smaller than the inner radius of the cross-section of the second side.

[0006] Preferably, the quartz tuning fork comprises a first vibration arm and a second vibration arm, the first vibration arm is connected to a first pin, the second vibration arm is connected to a second pin, the first pin is electrically connected to a vibration generator, and the second pin is electrically connected to a signal processing module.

[0007] Preferably, a vibration arm gap is provided between the first vibration arm and the second vibration arm, and the width of the vibration arm gap is 300 μm.

[0008] Preferably, the laser beam is coaxial with the acoustic resonant cavity, and the beam waist radius of the laser beam is smaller than the vibration arm gap.

[0009] Preferably, the quartz tuning fork adopts a cylindrical crystal oscillator with a resonance frequency of 32.768 kHz.

[0010] Preferably, the inner radius of the cross section of the first side is in a range of 0.2 mm to 0.3 mm, and the length of the acoustic resonance cavity is in a range of 4 mm to 5 mm.

[0011] Preferably, the inner radius of the cross section of the second side is in a range of 0.2 mm to 1.5 mm.

[0012] Preferably, the distance between the central axis of the acoustic resonance cavity and the top of the quartz tuning fork ranges from 0 mm to 3 mm, and the horizontal distance between the first side and the quartz tuning fork ranges from 0 mm to 0.08 mm.

[0013] Preferably, the inner wall of the acoustic resonance cavity and the surface of the quartz tuning fork are both set as hard sound field boundaries.

[0014] Preferably, the acoustic resonance cavity is made of stainless steel.

[0015] The present invention also provides a gas detection device, including a photoacoustic spectrometer, wherein the vibrating arm of a quartz tuning fork in the photoacoustic spectrometer is arranged in the gas to be detected, and includes a laser and a signal demodulation device, wherein the laser is used to generate a laser beam to the photoacoustic spectrometer to stimulate the photoacoustic effect of molecules in the gas to be detected; and the signal demodulation device is electrically connected to the photoacoustic spectrometer to demodulate the electrical signal generated by the quartz tuning fork.

[0016] Preferably, the signal demodulation device includes a preamplifier and a phase-locked amplifier, the preamplifier is electrically connected to the quartz tuning fork and the phase-locked amplifier respectively, the preamplifier is used to perform trans-impedance amplification on the electrical signal generated by the quartz tuning fork to obtain a photoacoustic signal, and the phase-locked amplifier is used to demodulate the photoacoustic signal output by the preamplifier to obtain concentration information of the gas to be measured.

[0017] Preferably, it also includes a function generator, an adder, a laser driver, a fiber collimating lens and a computer device; the modulation signal output end of the function generator is connected to the adder, the laser driver and the laser in sequence; the synchronization signal output end of the function generator is connected to the signal demodulation device; and the computer device is also respectively connected to the output end of the signal demodulation device and the input end of the function generator.

[0018] Preferably, the phase-locked amplifier is connected to the synchronization signal output terminal of the function generator and the input terminal of the computer device, and the phase-locked amplifier uses the reference signal of the function generator to perform demodulation and inputs the demodulated signal to the computer device.

[0019] Preferably, the emission center wavelength of the laser corresponds to the target absorption line of the gas to be measured.

[0020] Compared with the prior art, the photoacoustic spectrometer and gas detection device provided in the embodiments of the present invention have the following beneficial effects:

[0021] In the present invention, the cross-sectional area of ​​the acoustic resonant cavity from the side away from the quartz tuning fork to the side close to the quartz tuning fork has a large change, thereby bringing a higher acoustic impedance, making it difficult for the ambient noise around the spectrometer to enter the resonant cavity, thereby suppressing the ambient noise around, and at the same time, the conical structural design of the acoustic resonant cavity improves the sound pressure intensity of the sound wave of the same frequency as the quartz tuning fork, thereby further improving the signal-to-noise ratio, and finally achieving the improvement of gas detection accuracy; in addition, since the cross-sectional area of ​​the acoustic resonant cavity away from the side of the quartz tuning fork is large, the light collimation space is opened, and the requirements for the quality of the laser beam profile are further reduced, so that the photoacoustic spectrometer can match and use more light sources, and enhance the flexibility and practicality of its application. This is very important in the photoacoustic detection system based on incoherent light sources, mid-infrared light sources and THz sources, because any contact between the excitation light and the resonant cavity may introduce photothermal background noise, reducing the detection signal-to-noise ratio. In addition, the conical acoustic resonant cavity, due to the relatively large number of adjustable structural parameters, is conducive to adjusting the resonant frequency and bandwidth, and improving the quality factor and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is an isometric view of the photoacoustic spectrometer of the present invention;

[0023] Figure 2 is a front view of the photoacoustic spectrometer of the present invention;

[0024] Figure 3 is a top view of the photoacoustic spectrometer of the present invention;

[0025] Figure 4 is a structural block diagram of a gas detection device of the present invention;

[0026] Figure 5 The relationship between the sound pressure and the radius and length of the conical resonant cavity in the simulation verification of the photoacoustic spectrometer of the present invention;

[0027] Figure 6The sound pressure comparison between the acoustic resonant cavity of the present invention and the traditional cylindrical acoustic resonant cavity (the traditional cylindrical acoustic resonant cavity is a point when the length is 4.6mm and the radius is 0.2mm, in order to compare with the sound pressure when the conical acoustic resonant cavity is assembled, the dotted line is extended).

[0028] In the figure: 1. Photoacoustic spectrometer; 11. Acoustic resonant cavity; 12. Quartz tuning fork; 121. First pin; 122. Second pin; 13. Laser beam; 2. Computer equipment; 3. Function generator; 4. Adder; 5. Laser driver; 6. Laser; 7. Fiber collimating lens; 8. Preamplifier; 9. Lock-in amplifier. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0030] like Figures 1 to 3 As shown, a preferred embodiment of the present invention provides a photoacoustic spectrometer, comprising an acoustic resonant cavity 11 and a quartz tuning fork 12, wherein the acoustic resonant cavity 11 is disposed on one side of the quartz tuning fork 12, and the axis of the acoustic resonant cavity 11 is perpendicular to the axis of the quartz tuning fork 12; the acoustic resonant cavity 11 is used to guide a laser beam 13 to sequentially pass through the acoustic resonant cavity 11 and the quartz tuning fork 12 and resonantly amplify the acoustic wave signal generated by the laser beam 13 exciting the gas to be measured;

[0031] The acoustic resonance cavity 11 is a truncated cone structure with a through-hole arrangement in the middle. The side of the acoustic resonance cavity 11 close to the quartz tuning fork 12 is defined as the first side, and the side of the acoustic resonance cavity 11 away from the quartz tuning fork 12 is defined as the second side. The inner radius of the cross-section of the first side is smaller than the inner radius of the cross-section of the second side.

[0032] Specifically, the principle of the photoacoustic spectrometer 1 for testing gas concentration is as follows: the acoustic resonance cavity 11 is set on one side of the quartz tuning fork 12, and the resonance frequency of the acoustic resonance cavity 11 is made the same as the resonance frequency of the quartz tuning fork 12. When testing, the laser light beam 13 is incident from the side of the acoustic resonance cavity 11 away from the quartz tuning fork 12, passes through the cavity in the acoustic resonance cavity 11, and is emitted from the other end of the acoustic resonance cavity 11, and finally passes through the quartz tuning fork 12. During this process, the laser light beam 13 excites the photoacoustic effect of the molecules in the gas to be tested, and the gas to be tested generates a sound wave signal, which then drives the quartz tuning fork 12 to vibrate to form an electrical signal. The intensity of the sound wave signal generated by the gas to be tested is related to the concentration of the gas to be tested. Therefore, the concentration information of the gas to be tested can be obtained by analyzing the electrical signal. In the existing technology, the surrounding environmental noise is not processed, the signal-to-noise ratio is low, resulting in low gas detection accuracy. On the other hand, the collimation requirements and profile quality requirements of the laser beam 13 are also high in order to obtain a relatively good sound wave signal.

[0033] In the present embodiment, firstly, the cross-sectional area of ​​the acoustic resonant cavity 11 away from the quartz tuning fork 12 is larger, thereby reducing the difficulty of laser collimation, and the laser can be better incident into the acoustic resonant cavity 11. The acoustic resonant cavity 11 can also guide the laser beam 13, and at the same time, the quality requirements for the outer contour of the laser beam 13 are also reduced, so that the photoacoustic spectrometer 1 can match more light sources.

[0034] Secondly, the low-frequency resonance frequency of the acoustic resonance cavity 11 is controlled to be 32.7kHz. The conical acoustic resonance cavity 11 can enhance the sound pressure near the vibrating arm of the quartz tuning fork 12 and suppress environmental noise, thereby improving the signal-to-noise ratio of the quartz tuning fork 12 to detect the acoustic wave signal near its vibrating arm, thereby improving the gas detection accuracy. The specific principle is as follows:

[0035] Use the scalar wave equation to describe the propagation of sound waves in one-dimensional space and time:

[0036]

[0037] Where t represents time, x represents the spatial coordinate, c represents the speed of sound, and p represents pressure.

[0038] In acoustics, three different impedance concepts are commonly used: acoustic impedance, specific impedance, and mechanical impedance. ac Defined as the average pressure p on the boundary av The ratio of the volume flow rate Q across the boundary,

[0039]

[0040] Specific impedance Z spIt is defined as the ratio of the pressure p at a point to the particle velocity u = |u|,

[0041]

[0042] From the relationship between the pressure at each point and the particle velocity, different wave types can be defined by their respective characteristic specific acoustic impedance. The characteristic (specific acoustic) impedance of a lossless plane traveling wave is given by the known quantity Z 0 =c s ρ 0 Finally, the mechanical impedance Z mech It is defined as the ratio of the force F on the boundary to the particle velocity:

[0043]

[0044] For a constant surface area S, the relationship between these three impedance concepts is as follows:

[0045] Z mech =SZ sp =S 2 Z ac ;

[0046] The acoustic impedance Z is defined as the ratio of the sound pressure p to the volume flow Q:

[0047] In one-dimensional flow, the volume flow rate Q can be expressed as the product of the speed of sound v and the cross-sectional area A:

[0048] Q = A·v;

[0049] From the above formula, we can get the acoustic impedance:

[0050] The relationship between the sound velocity c and the acoustic impedance Z can be expressed by the following formula: Z = ρc, where ρ is the medium density.

[0051] Combining the above formula, the relationship between sound pressure and cross-sectional area can be obtained: p = Z·Q = Z·A·v, and substituting into the acoustic impedance formula: p = (ρc)·(A·v), it is shown that the sound pressure p is proportional to the product of the cross-sectional area A and the sound velocity v. In the conical acoustic resonant cavity 11 of the present embodiment, when the cross-sectional area A decreases, although the sound velocity v may remain unchanged, the sound pressure p will increase, because the acoustic impedance Z increases with the decrease in cross-sectional area, resulting in the need for higher sound pressure to maintain the same volume flow, thereby improving the signal-to-noise ratio near the vibrating arm of the quartz tuning fork 12, and ultimately improving the accuracy of gas detection.

[0052] In some embodiments, the quartz tuning fork 12 includes a first arm and a second arm, the first arm is connected to a first pin 121, the second arm is connected to a second pin 122, the first pin 121 is electrically connected to a vibration generator, and the second pin 122 is electrically connected to a signal processing module.

[0053] Specifically, when the laser beam 13 passes through the gas to be measured, it will excite the molecules in the gas to be measured to generate sound wave signals. After these sound wave signals are resonated and enhanced in the acoustic resonance cavity 11, they will drive the first arm and the second arm of the quartz tuning fork 12 to vibrate, and the electrical signal generated by the vibration will be transmitted to the signal processing module through the second pin 122 for subsequent processing. The vibration generator and the signal processing module are both used to measure the crystal oscillator frequency of the quartz tuning fork 12. In a specific embodiment, the signal processing module includes a signal demodulation device and a subsequent series of analysis devices, which are described in detail in the subsequent gas detection device.

[0054] In some embodiments, the quartz tuning fork 12 uses a cylindrical crystal oscillator with a resonance frequency of 32.768kHz. Furthermore, a vibration arm gap is provided between the first vibration arm and the second vibration arm, and the width of the vibration arm gap is 300μm. Furthermore, the laser beam 13 is coaxial with the acoustic resonant cavity 11, and the waist radius of the laser beam 13 is smaller than the vibration arm gap.

[0055] Specifically, the quartz tuning fork 12 adopts a strongly resonant quartz tuning fork 12 of standard size. In a specific embodiment, the width, thickness and arm gap of the quartz tuning fork 12 are 600μm, 330μm and 300μm respectively. After passing through the acoustic resonant cavity 11, the laser beam 13 will continue to pass through the arm gap of the quartz tuning fork 12. In order to ensure that the laser beam 13 can smoothly pass through the arm gap, the laser beam 13 is coaxial with the acoustic resonant cavity 11. The axis of the acoustic resonant cavity 11 also needs to intersect perpendicularly with the central axis of the arm gap of the quartz tuning fork 12, and the length of the widest part of the laser beam 13 must also be smaller than the arm gap, that is, the waist radius of the laser beam 13 must be smaller than the arm gap, so as to facilitate the laser beam 13 to smoothly pass through the quartz tuning fork 12.

[0056] In some embodiments, the inner radius of the cross-section of the first side ranges from 0.2 mm to 0.3 mm, and the length of the acoustic resonance cavity 11 ranges from 4 mm to 5 mm; further, the inner radius of the cross-section of the second side ranges from 0.2 mm to 1.5 mm, the distance between the central axis of the acoustic resonance cavity 11 and the top of the quartz tuning fork 12 ranges from 0 mm to 3 mm, and the horizontal distance between the first side and the quartz tuning fork 12 ranges from 0 mm to 0.08 mm; further, the inner wall of the acoustic resonance cavity 11 and the surface of the quartz tuning fork 12 are both set as hard sound field boundaries.

[0057] Specifically, in a specific embodiment, the inner radius of the first side of the acoustic resonant cavity 11 is 0.2 mm, the inner radius of the second side of the acoustic resonant cavity 11 is 0.95 mm, and the length of the acoustic resonant cavity 11 is 4.6 mm; and the inner wall of the acoustic resonant cavity 11 and the surface of the quartz tuning fork 12 are both set as hard sound field boundaries, so that the sound waves can be fully reflected. Since the sound waves generated by the photoacoustic spectroscopy are distributed in a cylindrical shape around the laser beam 13, and the cylinder of the sound wave and the cylinder of the beam are coaxial, the sound waves generated by the laser beam 13 can be set as a cylindrical sound source, and the intensity of the sound source is kept unchanged. In the current technology, the optimal radius of the cylindrical acoustic resonant cavity 11 is 0.2 mm, so the inner radius of the first side acoustic resonant cavity 11 is set to 0.2 mm, and the size of the inner radius of the second side of the acoustic resonant cavity 11 is changed. By changing the size of the inner radius of the second side, the signal-to-noise ratio is reduced and the gas detection accuracy is improved.

[0058] Further, such as Figure 5 and Figure 6 As shown, finite element simulation can be performed through simulation software to assist in analyzing the size of the inner radius of the second side. By performing a parametric scan of the inner radius of the second side of the acoustic resonance cavity 11 from 0.2 mm to 1.5 mm, the response of the acoustic resonance cavity 11 to the sound source at different sizes of the inner radius of the second side is simulated, and the sound pressure at a point in the middle of the tuning fork arm is detected, thereby comparing the amplification effect of the acoustic resonance cavity 11 on the sound waves at different sizes, and finally obtaining the optimal size of the inner radius of the second side as 0.95 mm. Under this size condition, the sound pressure is significantly improved, the signal-to-noise ratio is improved, and ultimately the accuracy of gas detection is improved.

[0059] In addition, in some other embodiments, the acoustic resonance cavity 11 is made of stainless steel.

[0060] like Figure 4 As shown, the present invention also provides a gas detection device, which uses the above-mentioned photoacoustic spectrometer 1, the vibrating arm of the quartz tuning fork 12 in the photoacoustic spectrometer 1 is set in the gas to be measured, including a laser 6 and a signal demodulator, the laser 6 is used to generate a laser beam 13 to the photoacoustic spectrometer 1 to stimulate the photoacoustic effect of the molecules in the gas to be measured; the signal demodulator is electrically connected to the photoacoustic spectrometer 1 to demodulate the electrical signal generated by the quartz tuning fork 12.

[0061] Furthermore, the signal demodulation device includes a preamplifier 8 and a phase-locked amplifier 9. The preamplifier 8 is electrically connected to the quartz tuning fork 12 and the phase-locked amplifier 9 respectively. The preamplifier 8 is used to perform trans-impedance amplification on the electrical signal generated by the quartz tuning fork 12 to obtain a photoacoustic signal. The phase-locked amplifier 9 is used to demodulate the photoacoustic signal output by the preamplifier 8 to obtain the concentration information of the gas to be measured.

[0062] Furthermore, the gas detection device also includes a function generator 3, an adder 4, a laser driver 5, a fiber collimating lens 7 and a computer device 2; the modulation signal output end of the function generator 3 is connected to the adder 4, the laser driver 5 and the laser 6 in sequence; the synchronization signal output end of the function generator 3 is connected to the signal demodulation device; the computer device 2 is also respectively connected to the output end of the signal demodulation device and the input end of the function generator 3.

[0063] The phase-locked amplifier 9 is connected to the synchronization signal output terminal of the function generator 3 and the input terminal of the computer device 2 . The phase-locked amplifier 9 uses the reference signal of the function generator 3 to perform demodulation and inputs the demodulated signal to the computer device 2 .

[0064] Specifically, the laser 6 is used to provide a high-energy laser beam 13 to excite the molecules in the gas to be measured; the fiber collimating lens 7 is used to shape the laser beam 13 and inject the shaped laser beam 13 into the photoacoustic spectrometer 1; the signal demodulation device is connected to the photoacoustic spectrometer 1 to demodulate the electrical signal to obtain the concentration information of the gas to be measured; the laser driver 5 can drive the laser 6; further, the preamplifier 8 can perform transimpedance amplification on the electrical signal output by the quartz tuning fork 12 to enhance the signal strength and obtain a clear photoacoustic signal; the phase-locked amplifier 9 is used to accurately demodulate the photoacoustic signal output by the preamplifier 8 to calculate and obtain the concentration information of the gas to be measured. In addition, the laser 6 emits at least mid-infrared light.

[0065] In the specific detection process, the whole gas detection device adopts harmonic detection technology. A general sine wave with a modulation frequency of the function generator 3 and a resonance frequency of the quartz tuning fork 12 is sent to the laser driver 5. The laser driver 5 can control the injection current and temperature of the laser 6. The laser beam 13 emitted by the laser 6 enters the photoacoustic spectrometer 1 after passing through the fiber collimating lens 7. The laser beam 13 first enters the acoustic resonant cavity 11, then passes through the arm gap of the quartz tuning fork 12, and finally exits. The laser beam 13 emitted by the laser 6 excites the gas to be measured to generate sound waves, and the sound waves drive the tuning fork to vibrate and then generate electrical signals and output to the preamplifier 8, and then sent to the phase-locked amplifier 9 for demodulation. The reference signal demodulated by the phase-locked amplifier 9 comes from the synchronization port of the function generator 3. The signal demodulated by the phase-locked amplifier 9 is sent to the computer device 2 with a data acquisition card to collect and record data. In addition, the measured concentration of the gas to be measured can also be displayed on the mobile computer in real time online, with high precision, strong portability, and online monitoring functions.

[0066] When detecting trace gases, first select a target detection line that is close to the central wavelength of the light source. By controlling the driving current of the laser driver 5, the wavelength of the laser 6 is swept across the target absorption line. Specifically, the second harmonic detection technology is adopted, and the current of the laser 6 is modulated by the f / 2 signal frequency generated by the function generator 3, where f is the resonant frequency of the tuning fork used. After the gas to be measured is excited by the laser, the acoustic wave signal generated by the de-excitation is collected by the quartz tuning fork 12 and converted into a corresponding electrical signal. The electrical signal passes through the preamplifier 8 and the phase-locked amplifier 9 in turn, and then enters the system of the computer device 2 through the data acquisition card. After the data is calculated by the software, the gas concentration information is finally displayed on the screen with a human-computer interactive interface. When measuring a gas of unknown concentration, it should be calibrated in advance with a standard gas of known concentration, and the calibrated device can measure the gas.

[0067] In a more specific embodiment, the gas detection device based on the acoustic detector of the present invention works as follows: First, a 1.39 μm near-infrared fiber-coupled distributed feedback semiconductor laser 6 is used as an excitation source. Then a high-precision semiconductor laser 6 driver board is used to control the temperature and injection current of the semiconductor laser 6. The second harmonic wavelength modulation technology is used to improve the detection sensitivity of the enhanced spectroscopy technology of the quartz tuning fork 12. A signal generator is used to generate a triangle wave with a period of 400 s and a sine wave with a frequency of f0 / 2 (f0 is the resonant frequency of the spectroacoustic detector). The second harmonic wavelength modulation technology is used to reduce the background noise due to stray light and the influence of crosstalk from other gas absorption lines. The laser beam 13 is focused by a self-focusing lens through the acoustic resonant cavity 11 and then passes through the gap between the two arms of the quartz tuning fork 12. The focal length of the self-focusing lens is 11 mm, and the beam waist diameter of the laser is about 100 μm. The electrical signal output by the quartz tuning fork 12 is amplified by a 10 MΩ custom transimpedance preamplifier 8. The phase-locked amplifier 9 is used to demodulate the second harmonic signal. Finally, the entire system of the gas detection device is controlled and the concentration of the gas is calculated through the program on the computer device 2.

[0068] In some embodiments, the emission center wavelength of the laser 6 corresponds to the target absorption line of the gas to be measured.

[0069] In summary, the embodiment of the present invention provides a photoacoustic spectrometer 1 and a gas detection device, which adopt a truncated cone-shaped acoustic resonant cavity 11, and the cross-sectional area of ​​the acoustic resonant cavity 11 away from the quartz tuning fork 12 is larger, and the two ends of the acoustic resonant cavity 11 have a large cross-sectional area change, which brings a higher acoustic impedance, making it difficult for the environmental noise around the photoacoustic spectrometer 1 to enter the resonant cavity, and can better suppress the environmental noise, further improve the signal-to-noise ratio, so that the accuracy of gas detection is improved, and because the opening diameter of the second side is larger, the collimation space of the laser beam 13 is opened, which further reduces the requirements for the quality of the excitation beam profile, so that it can match more light sources, enhancing its application flexibility and practicality.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A photoacoustic spectrometer, comprising an acoustic resonance cavity and a quartz tuning fork, characterized in that: The acoustic resonant cavity is arranged on one side of the quartz tuning fork, and the axis of the acoustic resonant cavity is perpendicular to the axis of the quartz tuning fork; the acoustic resonant cavity is used to guide the laser beam to pass through the acoustic resonant cavity and the quartz tuning fork in sequence and resonately amplify the acoustic wave signal generated by the laser beam exciting the gas to be measured; The acoustic resonance cavity is a truncated cone structure with a through-hole in the middle, and the side of the acoustic resonance cavity close to the quartz tuning fork is defined as a first side, and the side of the acoustic resonance cavity away from the quartz tuning fork is defined as a second side, and the inner radius of the cross-section of the first side is smaller than the inner radius of the cross-section of the second side.

2. The photoacoustic spectrometer according to claim 1, characterized in that: The quartz tuning fork includes a first vibration arm and a second vibration arm, the first vibration arm is connected to a first pin, the second vibration arm is connected to a second pin, the first pin is electrically connected to a vibration generator, and the second pin is electrically connected to a signal processing module.

3. The photoacoustic spectrometer according to claim 2, characterized in that: A vibration arm gap is provided between the first vibration arm and the second vibration arm, and the width of the vibration arm gap is 300 μm.

4. The photoacoustic spectrometer according to claim 3, characterized in that: The laser beam is coaxial with the acoustic resonant cavity, and the beam waist radius of the laser beam is smaller than the vibration arm gap.

5. The photoacoustic spectrometer according to claim 1, characterized in that: The quartz tuning fork adopts a cylindrical crystal oscillator with a resonance frequency of 32.768 kHz.

6. The photoacoustic spectrometer according to claim 1, characterized in that: The inner radius of the cross section of the first side ranges from 0.2 mm to 0.3 mm, and the length of the acoustic resonance cavity ranges from 4 mm to 5 mm.

7. The photoacoustic spectrometer according to claim 6, characterized in that: The cross-sectional inner radius of the second side ranges from 0.2 mm to 1.5 mm.

8. The photoacoustic spectrometer according to claim 1, characterized in that: The distance between the central axis of the acoustic resonance cavity and the top of the quartz tuning fork ranges from 0 mm to 3 mm, and the horizontal distance between the first side and the quartz tuning fork ranges from 0 mm to 0.08 mm.

9. The photoacoustic spectrometer according to claim 1, characterized in that: The inner wall of the acoustic resonance cavity and the surface of the quartz tuning fork are both set as hard sound field boundaries.

10. The photoacoustic spectrometer according to claim 1, characterized in that: The acoustic resonance cavity is made of stainless steel.

11. A gas detection device, using the photoacoustic spectrometer according to any one of claims 1 to 10, wherein the vibrating arm of the quartz tuning fork in the photoacoustic spectrometer is arranged in the gas to be detected, characterized in that: It comprises a laser and a signal demodulation device. The laser is used to generate a laser beam to the photoacoustic spectrometer to stimulate the photoacoustic effect of molecules in the gas to be measured; the signal demodulation device is electrically connected to the photoacoustic spectrometer to demodulate the electrical signal generated by the quartz tuning fork.

12. The gas detection device according to claim 11, characterized in that: The signal demodulation device includes a preamplifier and a phase-locked amplifier, the preamplifier is electrically connected to the quartz tuning fork and the phase-locked amplifier respectively, the preamplifier is used to perform transimpedance amplification on the electrical signal generated by the quartz tuning fork to obtain a photoacoustic signal, and the phase-locked amplifier is used to demodulate the photoacoustic signal output by the preamplifier to obtain the concentration information of the gas to be measured.

13. The gas detection device according to claim 12, characterized in that: It also includes a function generator, an adder, a laser driver, a fiber collimating lens and a computer device; the modulation signal output end of the function generator is connected to the adder, the laser driver and the laser in sequence; the synchronization signal output end of the function generator is connected to the signal demodulation device; and the computer device is also respectively connected to the output end of the signal demodulation device and the input end of the function generator.

14. The gas detection device according to claim 13, characterized in that: The lock-in amplifier is connected to the synchronous signal output end of the function generator and the input end of the computer device. The lock-in amplifier uses the reference signal of the function generator to perform demodulation and inputs the demodulated signal to the computer device.

15. The gas detection device according to claim 11, characterized in that: The emission center wavelength of the laser corresponds to the target absorption line of the gas to be measured.

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