Sound detector for photoacoustic spectrum gas measurement and detection equipment

Abstract

The invention relates to the technical field of photoelectric detection and sensors, and discloses a sound detector for photoacoustic spectrometry gas measurement and detection equipment. The sound detector comprises a base, two vibration arms and two open grooves. Two pins are arranged below the base and are respectively connected with a vibration generating device and a signal demodulation device; the two vibration arms are fixed above the base and are in contact with gas to be detected, a vibration arm gap is arranged between the two vibration arms, and the vibration arm gap is used for allowing a laser beam emitted by the laser to pass through; the grooves are cylindrical grooves or spherical grooves, and the two grooves are correspondingly formed in the outer sides of the two vibration arms, or the two grooves are formed in the two sides of the base respectively. The detection equipment comprises a sound detector, a laser, a vibration generation device and a signal demodulation device. Two vibration arms of the sound detector are arranged in gas to be detected, a laser beam emitted by the laser device penetrates through a vibration arm gap between the two vibration arms to generate a photoacoustic effect, and the vibration generation device is electrically connected with two pins of the decibel sound detector of the signal demodulation device.

Description

Technical Field

[0001] The present application relates to photoelectric detection and sensors, and in particular to a sound detector and detection equipment for photoacoustic spectroscopy gas measurement. Background Art

[0002] Trace gases refer to a class of gases with extremely low concentrations in the atmosphere or other gas mixtures. PAS (Photoacoustic Spectroscopy) is a trace gas detection method based on the photoacoustic effect. It inverts material information by measuring the acoustic wave signals generated by gas molecules after absorbing laser energy. It is widely used in environmental monitoring, industrial safety and other fields.

[0003] The core mechanism of PAS is that after gas molecules absorb modulated laser light, they convert energy into local heat energy through non-radiative relaxation, triggering periodic thermal expansion and exciting sound waves. The sound pressure amplitude P can be expressed as: Where α is the molecular absorption coefficient, P laser is the laser power, Q is the sensor quality factor, f relax =1 / (2πτ) is the relaxation frequency of gas molecules (τ is the relaxation time).

[0004] In QEPAS (Quartz-Enhanced Photoacoustic Spectroscopy) technology, a quartz crystal oscillator serves as the core transducer element of the acoustic detector, converting acoustic signals into electrical signals through the piezoelectric effect. When a laser beam passes through the quartz crystal oscillator, it stimulates the photoacoustic effect of molecules in the gas being measured, causing the gas to generate an acoustic signal. This acoustic signal then drives the acoustic detector to vibrate, generating an electrical signal. The intensity of the acoustic signal generated by the gas being measured is correlated with its concentration, so the concentration of the gas being measured can be determined by analyzing the electrical signal.

[0005] The detection sensitivity of the sound detector is affected by the relaxation frequency of the gas molecules f relax , quartz tuning fork resonant frequency f q , laser modulation frequency f mod The strict constraints of the three-frequency matching relationship: when f q ≈f relax And f mod =f q / 2, the acoustic wave energy accumulation efficiency and signal-to-noise ratio reach the optimal level.

[0006] However, due to its inherent structural limitations, traditional commercial quartz crystal oscillators have a problem of fixed resonant frequency. The high-frequency characteristics of traditional commercial quartz crystal oscillators deviate significantly from low relaxation rate gases such as SF6 (sulfur hexafluoride) and NH3 (ammonia), resulting in a large difference between the resonant frequency of the quartz crystal oscillator and the relaxation frequency of the gas molecules of the low-frequency gas to be measured. At the same time, according to the following formula (S is the signal intensity, Δf = f q / Q is the tuning fork bandwidth): It can be seen that the signal strength S is directly related to the vibration amplitude A of the tuning fork arm 21. It can be seen that the frequency matching of the low-frequency characteristics of the quartz crystal oscillator and the strength of the vibration amplitude jointly affect the detection sensitivity of trace gases, and the two together constitute the core limiting factors of sensitivity.

[0007] Therefore, how to reduce the frequency of the quartz crystal oscillator structure in the sound detector and increase the vibration amplitude of the quartz crystal oscillator structure has become the research and development focus in the industry. Summary of the Invention

[0008] The technical problem to be solved by the invention is: how to reduce the frequency of the quartz crystal oscillator structure in the sound detector and increase the vibration amplitude of the quartz crystal oscillator structure.

[0009] In order to solve the above technical problems, the present application provides a sound detector and detection equipment for photoacoustic spectroscopy gas measurement.

[0010] In a first aspect of the present application, a sound detector for photoacoustic spectroscopy gas measurement is provided, comprising: a base, two pins are provided at the bottom of the base, the two pins are respectively connected to a vibration generating device and a signal demodulation device; two vibration arms, the two vibration arms are respectively fixed on the top of the base, the two vibration arms are used to contact the gas to be measured, and a vibration arm gap is provided between the two vibration arms, the vibration arm gap is used for allowing a laser beam emitted by a laser to pass through, and the base and the two vibration arms are both made of quartz material; two slots, the slots are cylindrical slots or spherical slots, the two slots are correspondingly arranged on the outsides of the two vibration arms, or the two slots are arranged on both sides of the base.

[0011] In one embodiment, the diameter of any slot is 0.1 mm to 0.35 mm.

[0012] In one embodiment, the vertical distance between the center of any slot and the bottom of the corresponding vibration arm is -1 mm to 3.5 mm; when the vertical distance is negative, the two slots are arranged on both sides of the base, and when the vertical distance is positive, the two slots are arranged on the outside of the two vibration arms.

[0013] In one embodiment, the width of the vibration arm is 600 microns, the thickness of the vibration arm is 300 microns, and the vibration arm gap is 300 microns.

[0014] In one embodiment, the diameters of the two slots are both 0.25 mm, and the vertical distances between the centers of the two slots and the bottoms of the corresponding vibration arms are both 0.1 mm.

[0015] In a second aspect of the present application, a detection device for photoacoustic spectroscopy gas measurement is provided, comprising: the acoustic detector provided in the first aspect of the present application, wherein the two vibrating arms of the acoustic detector are placed in the gas to be measured; a laser, wherein the laser beam emitted by the laser passes through the gap between the two vibrating arms to stimulate the photoacoustic effect of the molecules in the gas to be measured; a vibration generating device, wherein the vibration generating device is electrically connected to one of the pins of the acoustic detector, and the vibration generating device is used to provide a resonant signal to the acoustic detector; and a signal demodulation device, wherein the signal demodulation device is electrically connected to another pin of the acoustic detector, and the signal demodulation device is used to demodulate the electrical signal generated by the photoacoustic effect of the acoustic detector to obtain concentration information of the gas to be measured.

[0016] In one embodiment, the signal demodulation device includes a preamplifier and a phase-locked amplifier. The preamplifier is electrically connected to another pin of the acoustic detector, and the preamplifier is electrically connected to the phase-locked amplifier. The preamplifier is used to perform trans-impedance amplification on the electrical signal generated by the acoustic detector to obtain a photoacoustic signal. 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] In one embodiment, the detection device further 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 laser driver is used to drive the laser to emit a laser beam, and the fiber collimating lens is used to shape the laser beam emitted by the laser; the computer device is respectively connected to the output end of the signal demodulation device and the input end of the function generator; a phase-locked amplifier is connected to the synchronization signal output end of the function generator and the input end of the computer device, the phase-locked amplifier uses the reference signal of the function generator to perform demodulation, and inputs the demodulated signal into the computer device, so that the computer device calculates the concentration information of the gas to be measured.

[0018] The third aspect of the present application provides a detection method for photoacoustic spectroscopy gas measurement, which is applied to the detection equipment provided in the second aspect of the present application. The detection method includes: selecting a target absorption line corresponding to the gas to be measured; controlling the driving current of the laser driver so that the wavelength of the laser sweeps across the target absorption line to stimulate the photoacoustic effect of the gas to be measured; collecting the acoustic wave signal generated by the de-excitation of the gas to be measured through a sound detector, and converting the acoustic wave signal into an electrical signal; processing the electrical signal in turn through a preamplifier and a phase-locked amplifier, and then transmitting it to a computer device; after calculation by software on the computer device, the concentration information of the gas to be measured is displayed on a monitor connected to the computer device.

[0019] In one embodiment, the step of controlling the driving current of the laser driver includes: generating a modulation signal with a frequency half of the resonant frequency of the acoustic detector through a function generator, and superimposing the modulation signal on the driving current of the laser driver, so that the wavelength of the laser is modulated at the frequency of the modulation signal; when the laser wavelength sweeps across the target absorption line, the frequency of the acoustic wave signal generated by the photoacoustic effect matches the resonant frequency of the acoustic detector, and the phase-locked amplifier locks and amplifies the electrical signal generated by the acoustic detector due to resonance, and extracts the signal component consistent with the resonant frequency of the acoustic detector to enhance the detection sensitivity.

[0020] In one embodiment, the detection method may further include: passing a standard gas of known concentration into the detection equipment; executing the steps before displaying the concentration information of the gas to be measured on a display connected to the computer device; recording the correspondence between the standard gas concentration and the output signal of the phase-locked amplifier, and establishing a calibration curve; when measuring a gas of unknown concentration, converting the processed electrical signal into a concentration value through the calibration curve, and displaying the concentration value on the display.

[0021] Compared with the prior art, the acoustic detector, detection device, and detection method for photoacoustic spectroscopy gas measurement in the embodiment of the present application have the following advantages:

[0022] During testing, a laser beam can be incident from one side of the acoustic detector, pass through the gap between the vibrating arms, and exit from the other end of the acoustic detector. During this process, the laser beam excites the photoacoustic effect of the molecules in the gas being measured, causing the gas to generate an acoustic wave signal. This acoustic wave signal then drives the acoustic detector to vibrate, forming an electrical signal. The intensity of the acoustic wave signal generated by the gas being measured is related to the concentration of the gas being measured. Therefore, by analyzing the electrical signal, the concentration information of the gas being measured can be obtained.

[0023] Since the vibrating arm in the sound detector is a cantilever beam structure with one end fixed and the other end suspended, it conforms to the Euler-Bernoulli beam theory. Due to the sensitivity of the moment of inertia to the cross-sectional area, the provision of slots can reduce the moment of inertia, thereby reducing the resonant frequency of the sound detector. At the same time, the slots reduce the stiffness and damping of the connection between the two vibrating arms and the base, so the vibration amplitude of the sound detector can also be increased accordingly. The sound detector of the present application can simultaneously reduce the frequency and increase the vibration amplitude, thereby significantly improving the detection sensitivity of the sound detector by reducing the restrictive effect on the detection sensitivity from two aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a three-dimensional schematic diagram of a sound detector for photoacoustic spectroscopy gas measurement in an embodiment of the present application.

[0025] Figure 2 This is a schematic diagram of the main view of a sound detector for photoacoustic spectroscopy gas measurement in an embodiment of the present application.

[0026] Figure 3 This is a structural block diagram of a detection device for photoacoustic spectroscopy gas measurement in an embodiment of the present application.

[0027] Figure 4 This is a simulation verification relationship diagram for the frequency, maximum vibration amplitude, and the distance from the center of the slot to the bottom of the vibration arm in the embodiment of the present application.

[0028] Figure 5 This is a simulation verification relationship diagram for frequency, maximum vibration amplitude and slot diameter in the embodiment of the present application.

[0029] Figure 6 This is a comparison diagram of the acoustic detector used for photoacoustic spectroscopy gas measurement in an embodiment of the present application and other crystal oscillators with the same frequency but different structures.

[0030] Figure 7 This is a comparison diagram of the acoustic detector used for photoacoustic spectroscopy gas measurement in an embodiment of the present application and other crystal oscillators with the same structure but different frequencies.

[0031] Figure 8 This is a flow chart of a detection method for photoacoustic spectroscopy gas measurement in an embodiment of the present application.

[0032] Reference numerals:

[0033] 1. Laser beam, 10. Detection equipment, 11. Vibration generator, 12. Sound detector, 13. Signal demodulation device, 131. Preamplifier, 132. Lock-in amplifier, 14. Laser, 15. Function generator, 16. Adder, 17. Laser driver, 18. Fiber collimating lens, 19. Computer equipment, 20. Base, 21. Vibration arm, 22. Vibration arm gap, 23. Pin, 24. Slot. DETAILED DESCRIPTION

[0034] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] In the description of this application, it should be understood that the term "two sides" used in this application refers to the left and right directions in the drawings, "width" refers to the left and right dimensions in the drawings of this application, and "thickness" refers to the dimension extending into the paper in the drawings of this application.

[0036] Among the gas concentration measurement methods, PAS (Photoacoustic Spectroscopy) is a trace gas detection method based on the photoacoustic effect, which can effectively detect the gas concentration of trace gases.

[0037] Specifically, when the laser beam passes through the quartz crystal oscillator, it excites the photoacoustic effect of the molecules in the gas to be measured, and the gas to be measured generates an acoustic wave signal, which then drives the acoustic detector to vibrate to form an electrical signal. The intensity of the acoustic wave signal generated by the gas to be measured is related to the concentration of the gas to be measured. Therefore, by analyzing the electrical signal, the concentration information of the gas to be measured can be obtained.

[0038] However, the inventors discovered that existing sound detectors, based on a quartz crystal oscillator as their primary structure, have limited overall structure and are difficult to increase in vibration frequency. Because the sound detector primarily relies on resonance between the gas and the oscillator to transmit gas vibrations to the sound detector, if the quartz crystal oscillator's vibration frequency is insufficient, it will have difficulty resonating with high-frequency gas molecules (such as sulfur hexafluoride and ammonia), resulting in low transmission efficiency and poor measurement sensitivity.

[0039] Based on this, Figure 1 and Figure 2 As shown, a sound detector 12 for photoacoustic spectroscopy gas measurement in a preferred embodiment of the present application may include: a base 20, two vibrating arms 21 and two slots 24. Two pins 23 are provided below the base 20, and the two pins 23 are respectively connected to the vibration generating device 11 and the signal demodulating device 13. The two vibrating arms 21 are respectively fixed on the top of the base 20, and the two vibrating arms 21 are used to contact the gas to be measured. A vibrating arm gap 22 is provided between the two vibrating arms 21, and the vibrating arm gap 22 is used for the laser beam 1 emitted by the laser 14 to pass through. The base and the two vibrating arms are both made of quartz. The slot 24 is a cylindrical slot 24 or a spherical slot 24. The two slots 24 are correspondingly provided on the outside of the two vibrating arms 21, or the two slots 24 are provided on both sides of the base 20.

[0040] Using the above solution, the quartz crystal oscillator is made into two vibration arms 21 and a base 20, and the two vibration arms 21 are made into a cantilever structure, making it easier for the two vibration arms 21 to vibrate. And because the moment of inertia is sensitive to the cross-sectional area, the provision of the slots 24 can reduce the moment of inertia, thereby reducing the resonant frequency of the acoustic detector 12. At the same time, because the slots 24 reduce the stiffness and damping of the connection between the two vibration arms 21 and the base, the vibration amplitude of the acoustic detector 12 can also be increased accordingly. Through this design, frequency tuning, amplitude enhancement and stress optimization can be achieved simultaneously by adjusting the size and height of the slots 24, so that the frequency-adjustable photoacoustic spectrometer 12 can adapt to the measurement of gas molecules with different relaxation frequencies, thereby broadening the application range of the QEPAS technology. In particular, for gases with low relaxation rates, the detection sensitivity is significantly improved, overcoming the limitations of traditional QEPAS systems in measuring these gases.

[0041] Moreover, since the shape of the slot 24 can be cylindrical or spherical, the cross-sectional change of the vibrating arm 21 is more gentle. On the basis of reducing the moment of inertia of the vibrating arm 21, it can effectively reduce stress concentration and reduce the possibility of mechanical damage to the vibrating arm 21 during vibration.

[0042] The sound pressure amplitude P can be expressed as:

[0043]

[0044] Where α is the molecular absorption coefficient, P laser is the laser power, Q is the sensor quality factor, f relax =1 / (2πτ) is the relaxation frequency of gas molecules (τ is the relaxation time). A high relaxation frequency means that the time it takes for gas molecules to recover from a non-equilibrium state to an equilibrium state through collisions, energy exchange, etc. is shorter.

[0045] According to the inventor's calculation, the detection sensitivity of the acoustic detector 12 is affected by the gas molecule relaxation frequency f relax , quartz tuning fork resonant frequency f q , laser modulation frequency f mod The strict constraints of the three-frequency matching relationship: when f q ≈f relax And f mod =f q / 2, the acoustic wave energy accumulation efficiency and signal-to-noise ratio reach the optimal level, that is, the detection is most sensitive.

[0046] However, detection sensitivity not only depends on frequency matching, but is also directly related to the vibration amplitude A of the tuning fork arm 21. The two together constitute the core limiting factors of sensitivity:

[0047]

[0048] In formula 2, S is the signal strength, Δf=f q / Q is the bandwidth of the tuning fork. q Deviation f relax , the acoustic wave energy accumulation time is shortened, resulting in signal attenuation; at the same time, the amplitude A of the vibration arm 21 is affected by mechanical damping and Q value (A∝Q·P).

[0049] Therefore, the connection between the rigidly fixed arm 21 and the base in the prior art produces significant mechanical damping, and the vibration energy is dissipated through the base 20, resulting in amplitude attenuation. However, the structure of the slot 24 in the present application weakens the rigidity of the connection between the arm 21 and the base, thereby reducing the mechanical damping during vibration, reducing energy dissipation, and increasing the amplitude.

[0050] The two vibration arms 21 have the same structure, the length of the vibration arm 21 is L, the width of the vibration arm 21 is H, and the thickness of the vibration arm 21 is B; the outer side of the two vibration arms 21 is provided with a slot 24, the diameter of the slot 24 is d, the radius is r = d / 2, and the distance between the center of the slot 24 and the bottom of the vibration arm 21 is h; suppose the Young's modulus of the material of the quartz crystal oscillator in this application is E and the density is ρ.

[0051] Then the formula for the moment of inertia of the cross section of the vibrating arm 21 (i.e., Formula 3) can be expressed as:

[0052]

[0053] In formula 3, I rect represents the moment of inertia of the original rectangular cross section of the boom 21 .

[0054] According to the parallel axis theorem, the moment of inertia of the 24-way slot about the neutral axis is:

[0055]

[0056] In formula 4, I semi It represents the moment of inertia of slot 24 about the neutral axis. The meaning of other letters can be found in the previous formulas.

[0057] Furthermore, the correction formula for the moment of inertia of the swing arm 21 caused by the slot 24 can be:

[0058]

[0059] In formula 5, I net It represents the effective moment of inertia of the swing arm 21 after the slot 24 is opened.

[0060] From Formula 3, Formula 4, and Formula 5, it can be obtained that the correction formula for the cross section of the vibrating arm 21 due to the slot 24 is:

[0061]

[0062] In formula 6, A net It represents the effective area of ​​the cross section of the vibration arm 21 after the slot 24 is provided.

[0063] Furthermore, the resonant frequency f of the quartz crystal oscillator is related to I eff (effective moment of inertia), A net (Effective area) satisfies the following relationship:

[0064]

[0065] In formula 7, I net (i.e. I eff) represents the effective moment of inertia of arm 21 after slot 24 is formed, and L represents the effective length of arm 21, i.e., the actual length of the vibrating portion. When the moment of inertia of the cross-section of arm 21 decreases, the natural frequency of the quartz crystal oscillator, including arm 21 and the base, decreases, and vice versa.

[0066] In summary, the simplified formula for the resonant frequency f of the quartz crystal oscillator can be:

[0067]

[0068] The vibration amplitude A of the quartz crystal is related to the quality factor Q, the driving force F, and the damping coefficient c, and the relevant formula is:

[0069]

[0070] Where, ω=2πf, quality factor Effective mass m eff ∝ρA net L, stiffness The symbol ∝ means proportional to.

[0071] The simplified formula for the quartz crystal vibration amplitude A can be:

[0072]

[0073] After integration, we can get:

[0074]

[0075] It can be seen from Formula 11 that as the diameter d of the slot 24 increases, the signal strength S increases; and as the distance h between the center of the slot 24 and the bottom of the vibration arm 21 decreases, the signal strength S increases.

[0076] Therefore, in any embodiment of the present application, the diameter of any slot 24 can be 0.1 mm to 0.35 mm.

[0077] The specific diameter of the slot 24 can be adjusted according to the actual size of the acoustic detector 12 , and the present application does not impose any limitation in this embodiment.

[0078] Moreover, in another embodiment of the present application, the vertical distance between the center of any slot 24 and the bottom of the corresponding vibration arm 21 can be -1 mm to 3.5 mm; wherein, when the vertical distance is negative, the two slots 24 are respectively arranged on both sides of the base 20, and when the vertical distance is positive, the two slots 24 are correspondingly arranged on the outer sides of the two vibration arms 21.

[0079] In summary, when the diameter d of the slot 24 increases, the frequency of the quartz crystal oscillator decreases significantly due to the sensitivity of the moment of inertia to the diameter d. At the same time, due to the reduction of stiffness and damping, the vibration amplitude of the quartz crystal oscillator arm 21 increases, such as Figure 5 shown.

[0080] When the absolute value of the distance h between the center of the slot 24 and the bottom of the vibrating arm 21 decreases, the closer it is to the root of the vibrating arm 21, the more significant the moment of inertia correction is, the frequency of the quartz crystal oscillator decreases significantly, and the vibration amplitude of the vibrating arm 21 increases. Figure 4 As shown, in a possible example, h = 0.1 mm, the stress distribution is optimal, the damping is minimum, and the vibration amplitude of the quartz crystal oscillator reaches a peak value.

[0081] Further, such as Figures 4 and 5 As shown, finite element simulation can be performed through simulation software to assist in analyzing the diameter of the slot 24 of the quartz crystal oscillator and the distance between the center of the circle and the bottom of the vibration arm 21. By performing parametric scanning on the diameter of the slot 24 and the distance between the center of the circle and the bottom of the vibration arm 21 from 0.1mm to 0.35mm and -1mm to 3.5mm respectively, the low-order resonant frequency of the quartz crystal oscillator under different sizes of the slot 24 is simulated, and it is finally obtained that when the slot 24 is close to the root of the vibration arm 21 and the size becomes larger, its low-order resonant frequency is significantly reduced and the vibration amplitude is significantly enhanced.

[0082] The slots 24 of the quartz crystal oscillator can control the low-order resonant frequency range of the quartz crystal oscillator from 27 kHz to 35 kHz, so that the sound detector 12 can match more light sources.

[0083] As a further preferred solution, the diameters of the two slots 24 can be selected to be 0.25 mm, and the vertical distances between the centers of the two slots 24 and the bottoms of the corresponding vibration arms 21 can be selected to be 0.1 mm, so that the quartz crystal oscillator frequency f in the sound detector of this application can be achieved to be 29.664 kHz.

[0084] The quartz crystal oscillator of this embodiment is compared with the crystal oscillator (29kHz) with the same frequency but different structure. Figure 6 As shown in FIG, the normalized intensity of the piezoelectric signal obtained by the finite element analysis method when detecting molecules with the same relaxation time is significantly higher than that of a quartz crystal oscillator with the same frequency but a different structure.

[0085] The quartz crystal oscillator of this embodiment is compared with the crystal oscillator (34kHz) with the same structure but different frequency. Figure 7 As shown in FIG, the normalized intensity of the piezoelectric signal obtained by the finite element analysis method when detecting molecules with the same relaxation time is significantly higher than that of a quartz crystal oscillator with the same structure but a different frequency.

[0086] In a preferred embodiment of the present application, the width of the vibration arm 21 is 600 microns, the thickness of the vibration arm 21 is 300 microns, and the vibration arm gap 22 is 300 microns.

[0087] Correspondingly, such as Figure 3 As shown, the present application also provides a detection device 10 for photoacoustic spectroscopy gas measurement. The detection device 10 may include: a sound detector 12 , a laser 14 , a vibration generating device 11 and a signal demodulation device 13 .

[0088] The two vibrating arms 21 of the acoustic detector 12 are placed in the gas to be measured. The laser beam 1 emitted by the laser 14 passes through the gap 22 between the two vibrating arms 21 to stimulate the photoacoustic effect of the molecules in the gas to be measured. The vibration generating device 11 is electrically connected to one of the pins 23 of the acoustic detector 12, and the vibration generating device 11 is used to provide a resonant signal to the acoustic detector 12. The signal demodulation device 13 is electrically connected to the other pin 23 of the acoustic detector 12, and the signal demodulation device 13 is used to demodulate the electrical signal generated by the photoacoustic effect of the acoustic detector 12 to obtain the concentration information of the gas to be measured.

[0089] The light beam emitted by the laser 14 passes through the gap 22 between the two vibration arms 21, so that the action area of ​​the laser and the gas to be measured is precisely positioned in the vibration sensitive area of ​​the sound detector 12. The sound waves generated by the photoacoustic effect can directly excite the vibration arm 21 to resonate, reducing energy loss.

[0090] The vibration generating device 11 provides an excitation signal consistent with its natural frequency to the sound detector 12, so that the sound detector 12 is in a resonant state in advance. When the sound wave frequency generated by the photoacoustic effect matches the resonant frequency, "resonance enhancement" is formed, further amplifying the sound wave signal, so that the signal-to-noise ratio is multiplied.

[0091] Because the vibration generator 11 and signal demodulator 13 are connected to two pins 23 of the acoustic detector 12, a differential "excitation-detection" structure is formed. The excitation pin 23 injects the resonant signal, while the detection pin 23 only picks up the weak electrical signal generated by the photoacoustic effect. This prevents the excitation signal from interfering with the detection terminal. This design also reduces common-mode noise such as ambient vibration and electromagnetic interference.

[0092] Not only that, in one embodiment, the signal demodulation device 13 includes a preamplifier 131 and a phase-locked amplifier 132. The preamplifier 131 is electrically connected to another pin 23 of the acoustic detector 12. The preamplifier 131 is electrically connected to the phase-locked amplifier 132. The preamplifier 131 is used to perform trans-impedance amplification on the electrical signal generated by the acoustic detector 12 to obtain a photoacoustic signal. The phase-locked amplifier 132 is used to demodulate the photoacoustic signal output by the preamplifier 131 to obtain the concentration information of the gas to be measured.

[0093] The electrical signal generated by the sound detector 12 when it is vibrated by the photoacoustic effect is essentially a picoampere current signal. The preamplifier 131 uses a transimpedance amplification circuit to linearly convert the current signal into a voltage signal (for example, 1pA current can be converted into 1mV voltage). The conversion gain is large, which can ensure that the signal is not distorted.

[0094] The phase-locked amplifier 132 uses the resonant signal (such as a 40kHz square wave) provided by the vibration generating device 11 as a reference signal to perform phase-sensitive detection on the photoacoustic signal output by the preamplifier 131. Only the components with the same frequency and phase as the reference signal are retained, and noise of other frequencies (such as power frequency interference and white noise) is filtered out.

[0095] In a further embodiment, the detection device 10 may further include a function generator 15, an adder 16, a laser driver 17, a fiber collimating lens 18, and a computer device 19. The modulation signal output of the function generator 15 is sequentially connected to the adder 16, the laser driver 17, and the laser 14. The laser driver 17 is used to drive the laser 14 to emit a laser beam 1, and the fiber collimating lens 18 is used to shape the laser beam 1 emitted by the laser 14. The computer device 19 is respectively connected to the output of the signal demodulation device 13 and the input of the function generator 15. The lock-in amplifier 132 is connected to the synchronization signal output of the function generator 15 and the input of the computer device 19. The lock-in amplifier 132 uses the reference signal of the function generator 15 to perform demodulation and inputs the demodulated signal to the computer device 19, so that the computer device 19 can calculate the concentration information of the gas to be measured.

[0096] Function generator 15 generates a low-frequency sawtooth wave (for wavelength scanning) and a high-frequency sine wave (for second harmonic modulation). These are superimposed by adder 16 and input to laser driver 17, achieving a combined "scanning + modulation" control. The sawtooth wave periodically sweeps the laser wavelength across the target absorption line, covering the entire absorption profile. The sine wave (with a frequency of half the resonant frequency of acoustic detector 12) causes high-frequency wavelength jitter during the scanning process, stimulating the second harmonic signal of the photoacoustic effect. Compared to single scanning techniques, detection sensitivity is increased several times.

[0097] Passing the Gaussian beam from laser 14 through a fiber collimating lens 18 compresses the divergence angle, concentrating the laser energy and significantly enhancing the efficiency of the photoacoustic effect. Furthermore, the collimated beam can precisely pass through the arm gap 22, preventing the laser from irradiating the surface of the arm 21 and generating additional thermal noise.

[0098] Function generator 15 provides a reference signal to lock-in amplifier 132 that is co-frequency and co-phase with the modulated signal, ensuring consistent phase reference during demodulation. For example, if ambient temperature changes cause the laser wavelength to drift, computer 19 can adjust the output frequency of function generator 15 in real time to ensure that the reference frequency of lock-in amplifier 132 consistently matches the frequency of the photoacoustic signal.

[0099] The computer device 19 regularly (e.g., every hour) controls the function generator 15 to output a standard frequency signal, drives the laser 14 to emit light of a known wavelength, and realizes system self-calibration in combination with a standard gas sample. The calibration process does not require manual intervention, forming a closed-loop control.

[0100] Correspondingly, such as Figure 8 As shown, the present application also provides a detection method for photoacoustic spectroscopy gas measurement, which is applied to the detection device 10 in any embodiment of the present application. The detection method may include:

[0101] S101. Select a target absorption line corresponding to the gas to be measured.

[0102] S102 , controlling the driving current of the laser driver 17 so that the wavelength of the laser 14 sweeps across the target absorption line to stimulate the photoacoustic effect of the gas to be measured.

[0103] S103 , collecting the acoustic wave signal generated by the deexcitation of the gas to be measured through the acoustic detector 12 , and converting the acoustic wave signal into an electrical signal.

[0104] S104 , the electrical signal is processed by the preamplifier 131 and the lock-in amplifier 132 in sequence, and then transmitted to the computer device 19 .

[0105] S105 , after calculation by the software on the computer device 19 , the concentration information of the gas to be measured is displayed on a display connected to the computer device 19 .

[0106] In one embodiment, the step of controlling the driving current of laser driver 17 in step S102 may include generating a modulation signal having a frequency half the resonant frequency of acoustic detector 12 via function generator 15, and superimposing the modulation signal onto the driving current of laser driver 17, thereby modulating the wavelength of laser 14 at the frequency of the modulation signal. When the wavelength of laser 14 sweeps across the target absorption line, the frequency of the acoustic wave signal generated by the photoacoustic effect matches the resonant frequency of acoustic detector 12. Lock-in amplifier 132 locks in and amplifies the electrical signal generated by acoustic detector 12 due to resonance, extracting the signal component consistent with the resonant frequency of acoustic detector 12 to enhance detection sensitivity.

[0107] In another embodiment, the detection method may also include: passing a standard gas of known concentration into the detection device 10; executing the steps before displaying the concentration information of the gas to be measured on a display connected to the computer device 19; recording the correspondence between the standard gas concentration and the output signal of the phase-locked amplifier 132, and establishing a calibration curve; when measuring a gas of unknown concentration, converting the processed electrical signal into a concentration value through the calibration curve, and displaying the concentration value on the display.

[0108] It is understood that the detection method in this application includes all the technical features of the detection device 10, so the embodiments of the detection device 10 and its beneficial effects are applicable to the embodiments of the detection method in this application. Therefore, this application will not elaborate on the beneficial effects of the embodiments of the detection method.

[0109] The operating process of this application is as follows: a target absorption line of the gas to be measured is selected, a function generator 15 generates a modulated signal, which is driven by an adder 16 and a laser driver 17 to drive a laser 14. The emitted laser light is shaped by a fiber collimating lens 18 and then passes through the gap 22 between the arms, stimulating the photoacoustic effect in the gas. The two arms 21 of the acoustic detector 12 are vibrated by the acoustic wave in the gas, generating an electrical signal. This signal is amplified by a preamplifier 131 across impedance, and then demodulated by a lock-in amplifier 132 combined with the reference signal from the function generator 15. The demodulated signal is then transmitted to a computer, which calculates and displays the gas concentration.

[0110] In summary, the embodiments of the present application provide a sound detector 12, a detection device 10, and a detection method for photoacoustic spectroscopy gas measurement. Not only is a structure of the sound detector 12 proposed, but also a collaborative design of the sound detector 12, the laser 14, and the signal demodulation device 13 is provided to achieve high-precision detection of trace gases. Laser modulation and beam shaping improve the efficiency of the photoacoustic effect, the differential pin 23 and phase-locked amplification suppress noise, and computer closed-loop calibration ensures data accuracy. This solution has high detection sensitivity, fast response, and a compact size. It is suitable for scenarios such as environmental monitoring and industrial safety, providing a reliable technical solution for real-time gas detection.

[0111] The above-described contents are only preferred implementation methods of the present application. It should be noted that ordinary technicians in this technical field can make several improvements and substitutions without departing from the technical principles of the present application. These improvements and substitutions should also be regarded as the scope of protection of the present application.

Claims

1. A sound detector for photoacoustic spectroscopy gas measurement, characterized in that: include: A base (20), wherein two pins (23) are provided below the base (20), and the two pins (23) are respectively connected to the vibration generating device (11) and the signal demodulating device (13); Two vibration arms (21), the two vibration arms (21) are respectively fixed above the base (20), the two vibration arms (21) are used to contact the gas to be measured, a vibration arm gap (22) is provided between the two vibration arms (21), the vibration arm gap (22) is used to allow the laser beam (1) emitted by the laser (14) to pass through, and the base (20) and the two vibration arms (21) are all made of quartz material; Two slots (24), the slots (24) are cylindrical slots or spherical slots, the two slots (24) are correspondingly arranged on the outsides of the two vibration arms (21), or the two slots (24) are respectively arranged on both sides of the base (20).

2. The sound detector according to claim 1, wherein The diameter of any of the slots (24) is 0.1 mm to 0.35 mm.

3. The sound detector according to claim 1, wherein The vertical distance between the center of any one of the slots (24) and the bottom of the corresponding vibration arm (21) is -1 mm to 3.5 mm; wherein, when the vertical distance is negative, the two slots (24) are respectively arranged on both sides of the base (20); and when the vertical distance is positive, the two slots (24) are correspondingly arranged on the outsides of the two vibration arms (21).

4. The sound detector according to claim 1, wherein The width of the vibration arm (21) is 600 microns, the thickness of the vibration arm (21) is 300 microns, and the vibration arm gap (22) is 300 microns.

5. The sound detector according to claim 1, wherein The diameters of the two slots (24) are both 0.25 mm, and the vertical distances between the centers of the two slots (24) and the bottoms of the corresponding vibration arms (21) are both 0.1 mm.

6. A detection device for photoacoustic spectroscopy gas measurement, characterized in that: include: The sound detector (12) according to any one of claims 1 to 5, wherein the two vibration arms (21) of the sound detector (12) are placed in the gas to be measured; A laser (14), wherein a laser beam (1) emitted by the laser (14) passes through a vibration arm gap (22) between the two vibration arms (21) to stimulate the photoacoustic effect of molecules in the gas to be measured; a vibration generating device (11), the vibration generating device (11) being electrically connected to one of the pins (23) of the sound detector (12), the vibration generating device (11) being used to provide a resonance signal to the sound detector (12); A signal demodulation device (13) is electrically connected to another pin (23) of the sound detector (12), and the signal demodulation device (13) is used to demodulate the electrical signal generated by the sound detector (12) due to the photoacoustic effect to obtain the concentration information of the gas to be measured.

7. The detection device according to claim 6, characterized in that The signal demodulation device (13) includes a preamplifier (131) and a lock-in amplifier (132), wherein the preamplifier (131) is electrically connected to another pin (23) of the acoustic detector (12), and the preamplifier (131) is electrically connected to the lock-in amplifier (132), wherein the preamplifier (131) is used to perform transimpedance amplification on the electrical signal generated by the acoustic detector (12) to obtain a photoacoustic signal, and the lock-in amplifier (132) is used to demodulate the photoacoustic signal output by the preamplifier (131) to obtain the concentration information of the gas to be measured.

8. The detection device according to claim 7, characterized in that The detection device (10) further includes a function generator (15), an adder (16), a laser driver (17), a fiber collimating lens (18) and a computer device (19); The modulation signal output end of the function generator (15) is sequentially connected to the adder (16), the laser driver (17) and the laser (14), the laser driver (17) is used to drive the laser (14) to emit a laser beam (1), and the fiber collimating lens (18) is used to shape the laser beam (1) emitted by the laser (14); The computer device (19) is connected to the output end of the signal demodulation device (13) and the input end of the function generator (15) respectively; The lock-in amplifier (132) is connected to the synchronization signal output end of the function generator (15) and the input end of the computer device (19). The lock-in amplifier (132) uses the reference signal of the function generator (15) to perform demodulation and inputs the demodulated signal to the computer device (19), so that the computer device (19) calculates the concentration information of the gas to be measured.

9. A detection method for photoacoustic spectroscopy gas measurement, characterized in that: Applicable to the detection device (10) according to any one of claims 6 to 8, the detection method comprising: Select the target absorption line corresponding to the gas to be measured; controlling the driving current of the laser driver (17) so that the wavelength of the laser (14) sweeps across the target absorption line to stimulate the photoacoustic effect of the gas to be measured; Acquiring the acoustic wave signal generated by the deexcitation of the gas to be measured through a sound detector (12), and converting the acoustic wave signal into an electrical signal; The electrical signal is sequentially processed by a preamplifier (131) and a lock-in amplifier (132) and then transmitted to a computer device (19); After calculation by the software on the computer device (19), the concentration information of the gas to be measured is displayed on a display connected to the computer device (19).

10. The detection method according to claim 9, characterized in that: The step of controlling the driving current of the laser driver (17) comprises: A modulation signal having a frequency half the resonant frequency of the acoustic detector (12) is generated by a function generator (15), and the modulation signal is superimposed on the driving current of the laser driver (17), so that the wavelength of the laser (14) is modulated at the frequency of the modulation signal; When the wavelength of the laser (14) sweeps across the target absorption line, the frequency of the acoustic wave signal generated by the photoacoustic effect matches the resonant frequency of the acoustic detector (12), and the phase-locked amplifier (132) locks and amplifies the electrical signal generated by the acoustic detector (12) due to resonance, extracting the signal component consistent with the resonant frequency of the acoustic detector to enhance detection sensitivity.

11. The detection method according to claim 9, characterized in that: The detection method further comprises: Passing a standard gas of known concentration into the detection device (10); Executing the step in claim 9 before displaying the concentration information of the gas to be measured on a display connected to the computer device (19); Recording the corresponding relationship between the concentration of the standard gas and the output signal of the lock-in amplifier (132) to establish a calibration curve; When measuring a gas of unknown concentration, the processed electrical signal is converted into a concentration value through the calibration curve, and the concentration value is displayed on the display.

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