Multi-component gas remote detection device and detection method based on photoacoustic spectroscopy

Abstract

The embodiment of the invention discloses a multi-component gas remote detection device and detection method based on photoacoustic spectroscopy. The device comprises a laser generation assembly used for providing a detection laser beam; the diffusion type gas absorption cell is used for being arranged on a remote to-be-detected gas site, and the two ends of the diffusion type gas absorption cell are connected with a first long-range optical fiber and a second long-range optical fiber respectively; the laser generation assembly is connected with the first long-range optical fiber so as to emit a detection laser beam into the diffusion type gas absorption cell, and the detection laser beam is emitted from the second long-range optical fiber after being absorbed by the to-be-detected gas; the photoacoustic detection assembly is used for generating and detecting a photoacoustic signal generated by excitation of the detection laser beam; the photoacoustic detection assembly is connected with the second long-range optical fiber, and a detection laser beam emitted from the second long-range optical fiber enters the photoacoustic detection assembly; the data processing assembly is arranged to be connected with the photoacoustic detection assembly and used for processing the photoacoustic signals collected by the photoacoustic detection assembly and obtaining the gas composition of the to-be-detected gas through inversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas detection, and particularly relates to a multi-component gas remote detection device and a detection method based on photoacoustic spectroscopy. Background Art

[0002] The theoretical basis of the photoacoustic spectroscopy gas detection technology is the photoacoustic effect: target gas molecules in a closed container absorb a modulated periodic laser signal (the emission wavelength of this laser corresponds to the characteristic absorption peak of the gas to be detected), causing a periodic change in temperature in the closed space, and then resulting in a periodic change in the pressure in the closed space, that is, generating an acoustic wave signal. The intensity of this acoustic wave signal is related to the concentration of the target gas. Therefore, the gas concentration can be inversely calculated by detecting the intensity of the acoustic wave signal.

[0003] Currently, for the multi-component gas detection based on photoacoustic spectroscopy technology, the main solutions include using a broadband light source (the spectral line width range of the broadband light source is relatively wide, and it can emit continuous light radiation in a relatively wide wavelength range) combined with multiple filters with different central wavelengths; using multiple lasers in combination, with the wavelength of each laser corresponding to the characteristic absorption peak of a gas to be detected; a single laser, by adjusting its wavelength to cover the absorption peaks of multiple gases.

[0004] For remote monitoring, the current solution is to use an all-fiber optical probe, integrating the gas absorption cell to be detected and the acoustic detection module on one probe, and realizing remote monitoring through a long-range optical fiber. This remote detection has at least the following technical problems:

[0005] In the existing remote detection device, the acoustic detection module is placed at the detection site. However, the photoacoustic spectroscopy technology has extremely high sensitivity, and the acoustic detection module is extremely vulnerable to external environmental noise and vibration, resulting in a large deviation in the detection result;

[0006] In order to achieve high-sensitivity detection, a resonant structure is usually used for the photoacoustic cell. When detecting the gas concentration, the modulation frequency of the laser corresponds to the resonant frequency of this resonant photoacoustic cell; the resonant frequency of the photoacoustic cell is related to the gas flow rate and gas characteristics. Therefore, when an unknown concentration of the gas to be detected is introduced into the photoacoustic cell for testing, the resonant frequency of the photoacoustic cell will shift, resulting in the introduction of test errors;

[0007] The resonant frequency of the photoacoustic cell is related to temperature. When it works at the test site, its performance is affected by the temperature of the working site, and the detection result is inaccurate. Summary of the Invention

[0008] In view of this, on the one hand, some embodiments disclose a multi-component gas remote detection device based on photoacoustic spectroscopy, including:

[0009] A laser generating assembly for providing a detection laser beam for detecting a gas to be measured;

[0010] A diffusion-type gas absorption cell, which is to be arranged at the site of the remote gas to be measured and is set such that the gas to be measured can freely enter the diffusion-type gas absorption cell; both ends of the diffusion-type gas absorption cell are respectively connected with a first long-range optical fiber and a second long-range optical fiber; wherein, the laser generating assembly is arranged to be connected with the first long-range optical fiber to inject the detection laser beam into the diffusion-type gas absorption cell, and after being absorbed by the gas to be measured, it exits from the second long-range optical fiber;

[0011] A photoacoustic detection assembly for generating and detecting a photoacoustic signal generated by exciting the detection laser beam; the photoacoustic detection assembly is arranged to be connected with the second long-range optical fiber, and the detection laser beam exiting from the second long-range optical fiber enters the photoacoustic detection assembly;

[0012] A data processing assembly, which is arranged to be connected with the photoacoustic detection assembly, for processing the photoacoustic signal collected by the photoacoustic detection assembly and inversely obtaining the gas composition of the gas to be measured.

[0013] Furthermore, for the multi-component gas remote detection device based on photoacoustic spectroscopy disclosed in some embodiments, the laser generating assembly includes:

[0014] A laser device assembly including a plurality of fiber output lasers with different wavelength modulation ranges for outputting a plurality of laser beams with different wavelengths;

[0015] A laser control module, which is arranged to be connected with the laser device assembly for controlling the laser device assembly to generate a plurality of laser beams with different wavelengths;

[0016] An optical fiber combiner, which is arranged to be connected with the output optical fiber of the laser device assembly for combining a plurality of laser beams with different wavelengths into a detection laser beam.

[0017] For the multi-component gas remote detection device based on photoacoustic spectroscopy disclosed in some embodiments, the diffusion-type gas absorption cell is a tubular structure with a hollowed-out tube wall, and both ends of the tubular structure are respectively provided with a laser inlet and a laser outlet, which are respectively connected with the first long-range optical fiber and the second long-range optical fiber.

[0018] For the multi-component gas remote detection device based on photoacoustic spectroscopy disclosed in some embodiments, the photoacoustic detection assembly includes a photoacoustic cell and a microphone arranged in the photoacoustic cell, and a gas with a constant concentration is arranged in the photoacoustic cell.

[0019] On the other hand, some embodiments disclose a multi-component gas remote detection method based on photoacoustic spectroscopy, which is implemented by the multi-component gas remote detection device disclosed in the embodiments of the present application. The method specifically includes:

[0020] Using the laser generating assembly to generate a detection laser beam;

[0021] The detection laser beam is incident into the diffusion gas absorption cell through the first long-range optical fiber and exits through the second long-range optical fiber;

[0022] The detection laser beam exiting from the second long-range optical fiber enters the photoacoustic detection component, and the gas to be measured in the photoacoustic detection component generates a photoacoustic signal based on the photoacoustic effect under the action of the detection laser beam;

[0023] The data processing component receives and processes the photoacoustic signal, and inversely calculates the gas composition of the gas to be measured.

[0024] Furthermore, for the multi-component gas remote detection method based on photoacoustic spectroscopy disclosed in some embodiments, the inversely calculated gas composition of the gas to be measured includes:

[0025] Convert the photoacoustic signal into an electrical signal;

[0026] Process the electrical signal to inversely calculate the power of the detection laser beam entering the photoacoustic detection component;

[0027] Inversely calculate the gas composition of the gas to be measured in the diffusion gas absorption cell according to the power of the detection laser beam.

[0028] For the multi-component gas remote detection method based on photoacoustic spectroscopy disclosed in some embodiments, the calculation formula for the power of the detection laser beam entering the photoacoustic detection component is:

[0029]

[0030] where, I T is the power of the detection laser beam entering the photoacoustic detection component, λ is the wavelength of the laser beam, P is the amplitude of the photoacoustic signal detected by the microphone, s m is the microphone sensitivity, C1 is the constant gas concentration in the photoacoustic cell, α is the gas absorption coefficient in the photoacoustic cell, and F is the photoacoustic cell constant.

[0031] For the multi-component gas remote detection method based on photoacoustic spectroscopy disclosed in some embodiments, the calculation formula for the gas concentration of the gas to be measured is:

[0032]

[0033] where, C0 is the gas concentration to be measured, I0 is the optical power of light with a certain wavelength incident into the diffusion gas absorption cell through the long-range optical fiber, I T is the power of the detection laser beam entering the photoacoustic detection component, α is the absorption coefficient of the gas to be measured in the diffusion gas absorption cell, and L is the optical path of the detection laser beam in the gas to be measured for absorbing light, which is equal to the length of the diffusion gas absorption cell.

[0034] In some embodiments of the multi-component gas remote detection method based on photoacoustic spectroscopy, the laser generating component is configured to output only one laser beam of a set wavelength at the same time.

[0035] The multi-component gas remote detection device and detection method based on photoacoustic spectroscopy disclosed in the embodiment of the present invention use a microphone as a detector, which is non-selective to the laser wavelength, is not affected by stray light and external ambient light, and has high detection sensitivity; the photoacoustic detection component and the gas absorption component are separated from each other, so that the photoacoustic detection component can be kept away from the test space with a changeable environment, and the interference of external environmental noise, vibration, etc. on the acoustic detection module is prevented, and the detection sensitivity and stability are high; there is only one diffusion gas absorption pool in the test space, which is not subject to electromagnetic interference and can work in a strong electromagnetic interference environment; the gas to be tested with a known concentration is sealed in the photoacoustic detection component, and the gas composition in it remains unchanged during the entire detection process, avoiding the change of the photoacoustic pool resonance frequency caused by the change of gas characteristics, and the detection accuracy is high; the low loss characteristics of optical fiber are used to realize remote monitoring, and compared with the free space optical path, the optical fiber optical path has good stability and is not affected by vibration; the multi-component gas of known concentration can be sealed in the sealed photoacoustic pool at the same time, and multi-gas detection can be realized. The multi-component gas remote detection device and detection method based on photoacoustic spectroscopy have good application prospects in the field of gas remote detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the composition of a remote detection device disclosed in some embodiments;

[0037] Figure 2 Schematic diagram of the structure of the diffusion type gas absorption cell disclosed in some embodiments;

[0038] Figure 3 A flow chart of a remote detection method disclosed in some embodiments.

[0039] Reference numerals

[0040] 1 Laser generating assembly 2 First long-distance optical fiber

[0041] 3 Diffusion gas absorption cell 4 Second long-distance optical fiber

[0042] 5 Photoacoustic detection component 6 Data processing component

[0043] 31 incident optical collimator 32 first end cap

[0044] 33 Gas diffusion hole 34 Tube wall body

[0045] 35 second end cap 36 output optical collimator DETAILED DESCRIPTION

[0046] As used herein, the term "embodiment" refers to any embodiment described as "exemplary," and such an embodiment need not be construed as superior or better than other embodiments. For performance index tests in the embodiments of the present invention, unless otherwise specified, conventional test methods in the art are used. It should be understood that the terms described in the embodiments of the present invention are merely used to describe specific embodiments and are not intended to limit the content disclosed in the embodiments of the present invention.

[0047] Unless otherwise specified, the technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments of the present invention belong; other test methods and technical means not specifically noted in the embodiments of the present invention refer to the experimental methods and technical means commonly used by those of ordinary skill in the art.

[0048] The terms "substantially" and "about" as used herein are used to describe minor fluctuations. For example, they may refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. Numerical data presented or represented herein in a range format are used only for convenience and brevity and should therefore be flexibly interpreted to include not only the explicitly listed values that are the bounds of the range, but also all individual values or subranges included within the range. For example, the numerical range of "1 to 5%" should be interpreted to include not only the explicitly listed values from 1% to 5%, but also individual values and subranges within the indicated range. Thus, within this numerical range, individual values such as 2%, 3.5%, and 4% are included, as well as subranges such as 1% to 3%, 2% to 4%, and 3% to 5%, etc. This principle also applies to ranges that list only one numerical value. In addition, such an interpretation applies regardless of the width of the range or the characteristics described.

[0049] In this document, including in the claims, conjunctions such as "comprising," "including," "carrying," "having," "containing," "involving," "accommodating," etc. are understood to be open-ended, i.e., meaning "including but not limited to." Only the conjunctions "consisting of" and "composed of" are closed conjunctions.

[0050] To better illustrate the content of the present invention, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that the present invention can be implemented without some specific details. In the embodiments, some methods, means, instruments, devices, etc. well-known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0051] On the premise of no conflict, the technical features disclosed in the embodiments of the present invention can be arbitrarily combined, and the obtained technical solutions belong to the content disclosed in the embodiments of the present invention.

[0052] In some embodiments, such as Figure 1 shown, the multi-component gas remote detection device based on photoacoustic spectroscopy includes:

[0053] A laser generating component 1 for providing a detection laser beam for detecting a gas to be measured; generally, the detection laser beam generated by the laser generator contains laser light with characteristic wavelengths corresponding to the absorption peaks of the gas to be measured;

[0054] A diffusion-type gas absorption cell 3 for being arranged at the site of the remote gas to be measured and set such that the gas to be measured can freely enter the diffusion-type gas absorption cell; both ends of the diffusion-type gas absorption cell 3 are respectively connected with a first long-range optical fiber 2 and a second long-range optical fiber 4; wherein, the laser generating component 1 is arranged to be connected with the first long-range optical fiber 2 to inject the detection laser beam into the diffusion-type gas absorption cell, and the detection laser beam is absorbed by the gas to be measured during the process of passing through the gas absorption cell and finally exits from the second long-range optical fiber 4; usually, the gas absorption cell is remotely arranged at the detection site, and the gas to be measured at the detection site can freely and unrestrictedly enter the absorption cell, so that the gas to be measured in the absorption cell is maintained in the same state as the gas to be measured at the detection site;

[0055] A photoacoustic detection component 5 for generating and detecting a photoacoustic signal excited by the detection laser beam; the photoacoustic detection component 5 is arranged to be connected with the second long-range optical fiber 4 to allow the detection laser beam exiting from the second long-range optical fiber 4 to enter the photoacoustic detection component 5;

[0056] A data processing component 6 arranged to be connected with the photoacoustic detection component 5 for processing the photoacoustic signal collected by the photoacoustic detection component 5 and inversely obtaining the gas composition of the gas to be measured.

[0057] In the multi-component gas remote detection device based on photoacoustic spectroscopy disclosed in some embodiments, the laser generating component includes: a laser device component including a plurality of fiber output lasers with different wavelength modulation ranges for outputting a plurality of laser beams with different wavelengths; a laser control module arranged to be connected with the laser device component for controlling the laser device component to generate a plurality of laser beams with different wavelengths; an optical fiber combiner arranged to be connected with the output optical fiber of the laser device component for combining the plurality of laser beams with different wavelengths into a detection laser beam.

[0058] Generally, the laser assembly consists of multiple fiber output lasers with different wavelength modulation ranges. The laser output fiber is connected to a fiber combiner, which combines the light of multiple wavelengths into a single beam as the detection laser beam. This laser group can emit laser light corresponding to the absorption peaks of the gas components to be measured, that is, the output laser wavelength of the laser corresponds to the characteristic absorption peaks of the gas molecules to be measured. The laser control module includes a temperature and current adjustment device, a signal generator, etc.; by using the temperature control device and current adjustment device of the laser control module, the output wavelength of the laser can be controlled to make the output laser wavelength match the peak wavelength of the absorption peak of the gas to be measured; generally, at the same time, the laser control module only controls one laser to work, and the other lasers do not work, ensuring that only the laser output by one laser can enter the photoacoustic cell at the same time.

[0059] The fiber combiner is connected to the diffusion gas absorption cell by a first long-range fiber, and a second long-range fiber is connected between the diffusion gas absorption cell and the sealed photoacoustic cell. The laser beam emitted by the laser assembly enters the fiber combiner from one end along the fiber. After being combined by the fiber combiner, the laser beam enters the diffusion gas absorption cell through the first long-range fiber. After a part of the power is absorbed by the gas to be measured, the laser beam exits from the output fiber at the other end of the diffusion gas absorption cell. The laser beam exiting from the output fiber enters the sealed photoacoustic cell through the second long-range fiber, and a photoacoustic signal is generated by the photoacoustic effect.

[0060] In some embodiments, the multi-component gas remote detection device based on photoacoustic spectroscopy disclosed, the diffusion gas absorption cell is a tubular structure with a hollowed-out tube wall. Laser inlets and laser outlets are respectively provided at both ends of the tubular structure, and are respectively connected to the first long-range fiber and the second long-range fiber. In some embodiments, the diffusion gas absorption cell uses a hollow stainless steel tube with a hollowed-out tube wall. The hollowed-out structure of the tube wall and the hollow structure of the steel tube can be optimized according to the actual site to adapt to different detection spaces, while ensuring that the gas to be measured can freely enter the gas absorption cell.

[0061] In some embodiments, such as Figure 2As shown, the diffusion-type gas absorption cell 3 uses a stainless steel tube with a hollowed-out tube wall. The interior of the gas absorption cell is hollow and is used to generate the gas laser absorption effect. A plurality of uniformly arranged gas diffusion holes 33 are provided on the tube wall body 34 of the diffusion-type gas absorption cell 3. At the left and right ends of the tube wall body 34, a first end cap 32 and a second end cap 35 are provided; among them, the first end cap 32 is provided with a laser inlet, and an incident optical collimator 31 is installed therein. The incident optical collimator 31 is arranged to be connected to the first long-range optical fiber 2; the second end cap 36 is provided with a laser outlet, and an exit optical collimator 36 is installed therein. The exit optical collimator 36 is further arranged to be connected to the second long-range optical fiber 4; generally, the center lines of the two collimators are accurately set to ensure strict parallelism with the central axis of the inner cavity of the gas diffusion cell; the main functions of the incident optical collimator 31 and the exit optical collimator 36 are to efficiently convert the divergent light beam into a parallel light beam, effectively reduce the loss of the optical signal during transmission, and achieve precise control of the propagation direction of the light beam; usually, the overall size and contour of the diffusion-type gas absorption cell 3 can be optimized according to the actual detection site to adapt to different detection spaces and ensure that the gas to be measured can fully enter the gas cell.

[0062] In some embodiments, a multi-component gas remote detection device based on photoacoustic spectroscopy is disclosed. The photoacoustic detection component includes a photoacoustic cell and a microphone disposed in the photoacoustic cell. A gas with a constant concentration is disposed in the photoacoustic cell. Generally, the photoacoustic cell has a closed space, and a gas with a known concentration and type is disposed in the closed space; the gas with a known concentration and type undergoes a photoacoustic phenomenon under the action of a laser in the closed photoacoustic cell, and the generated sound wave is collected by a microphone embedded in the closed photoacoustic cell. The microphone collects the photoacoustic signal generated by the gas in the closed photoacoustic cell absorbing light energy and converts the photoacoustic signal into an electrical signal. Usually, the gas disposed in the photoacoustic cell has a known concentration and a known type, and can be set according to the gas composition to be detected at the measurement site and sealed in the photoacoustic cell in advance to keep its concentration constant; generally, other types of gases disposed in the photoacoustic cell should at least include all the gases in the gas to be measured so as to be able to detect all the gases to be measured present at the detection site.

[0063] Generally, the data processing module includes devices such as a preamplifier, a lock-in amplifier, a data acquisition card, and an information processor. The electrical signal obtained by the microphone enters the data processing module through a transmission line for data processing. The specific data processing process includes: the electrical signal is amplified by the preamplifier, and then enters the lock-in amplifier through the transmission line. The lock-in amplifier is used to demodulate the received signal to extract the photoacoustic signal component that matches the modulation frequency of the initial laser (i.e., the detection laser beam); the signal after lock-in amplification enters the data acquisition card to realize the analog-to-digital conversion of the signal; after the conversion is completed, these digital signals are input into an information processor (such as a computer), and the digital signals are processed using a set program (such as computer software), and then the photoacoustic amplitude in the photoacoustic cell can be inversely obtained. Further, by using the obtained photoacoustic amplitude and combining the working principle of photoacoustic spectroscopy, the optical power transmitted from the diffusion-type gas absorption cell can be calculated, and then using Lambert-Beer's law, the concentration of the gas to be measured can be inversely obtained.

[0064] Some embodiments disclose a multi-component gas remote detection method based on photoacoustic spectroscopy, which is implemented by the multi-component gas remote detection device disclosed in the embodiments of the present application, as Figure 3 shown. The method specifically includes:

[0065] S1. Using a laser generating component to generate a detection laser beam; generally, the detection laser beam includes a laser with a characteristic wavelength corresponding to the absorption peak of the gas to be measured;

[0066] S2. The detection laser beam enters the diffusion-type gas absorption cell through the first long-range optical fiber, and after being absorbed by the gas to be measured in the absorption cell, it exits through the second long-range optical fiber;

[0067] S3. The detection laser beam exiting from the second long-range optical fiber enters the photoacoustic detection component, and the detection laser beam generates a photoacoustic signal based on the photoacoustic effect under the action of the gas to be measured in the photoacoustic detection component;

[0068] S4. The data processing component receives and processes the photoacoustic signal, and inversely obtains the gas composition of the gas to be measured.

[0069] In some embodiments, inversely obtaining the gas composition of the gas to be measured includes: converting the photoacoustic signal into an electrical signal; processing the electrical signal to inversely obtain the power of the detection laser beam entering the photoacoustic detection component; and inversely obtaining the gas composition of the gas to be measured in the diffusion-type gas absorption cell according to the power of the detection laser beam.

[0070] In some embodiments, the calculation formula for the power of the detection laser beam entering the photoacoustic detection component is:

[0071]

[0072] where, I Tis the power of the detection laser beam entering the photoacoustic detection component, λ is the wavelength of the laser beam, P is the amplitude of the photoacoustic signal detected by the microphone, and s m is the microphone sensitivity, C1 is the constant gas concentration in the photoacoustic cell, α is the gas absorption coefficient in the photoacoustic cell, and F is the photoacoustic cell constant.

[0073] For the multi-component gas remote detection method based on photoacoustic spectroscopy disclosed in some embodiments, the calculation formula for the gas concentration of the gas to be measured is:

[0074]

[0075] where C0 is the concentration of the gas to be measured, I0 is the power of the detection laser beam incident on the diffusion-type gas absorption cell, and I T is the power of the detection laser beam entering the photoacoustic detection component, α is the absorption coefficient of the gas to be measured in the diffusion-type gas absorption cell, L is the optical path of the detection laser beam in the light-absorbing gas of the gas to be measured, which is equal to the length of the diffusion-type gas absorption cell. Usually, the detection laser beam incident on the diffusion-type gas absorption cell has a certain characteristic wavelength and can be absorbed by a certain specific gas in the gas to be measured. The power incident on the gas absorption cell is I0, and the power becomes I T after absorption by the gas in the absorption cell, and then enters the photoacoustic detection component to realize the detection of the specific gas.

[0076] For the multi-component gas remote detection method based on photoacoustic spectroscopy disclosed in some embodiments, the laser generating component is configured in a time-division multiplexing mode, and only outputs a laser with a set wavelength at the same time, and outputs lasers with different wavelengths at different times. During the detection process, laser beams with different wavelengths can be generated at different times to realize the detection of different gases at different times. Usually, laser beams with different wavelengths are continuously generated at intervals in different time periods during the detection process to realize the continuous detection of multiple gases.

[0077] In some embodiments, the multi-component gas remote detection method based on photoacoustic spectroscopy includes the steps of:

[0078] S1. Use a distributed laser component to generate a laser beam. After being combined by an optical fiber combiner, it is incident into a diffusion-type gas absorption cell along a long-range optical fiber. After the detection laser beam is absorbed by the gas to be measured, it exits from the output optical fiber at the other end of the diffusion-type gas absorption cell;

[0079] S2. The detection laser beam exiting from the output optical fiber enters a sealed photoacoustic cell through the long-range optical fiber, and a photoacoustic signal is generated based on the photoacoustic effect between the laser beam and the gas to be measured;

[0080] S3. Use a microphone to collect the photoacoustic signal in the sealed photoacoustic cell and convert it into an electrical signal;

[0081] S4. Analyze the obtained electrical signal and invert to obtain the power of the detected laser beam after transmission.

[0082] S5. Utilize the Lambert-Beer law, and based on the power of the detected laser beam after transmission obtained, invert to obtain the gas concentration in the diffusion-type gas absorption cell.

[0083] Generally, in step S1, the diffusion-type gas absorption cell is placed in the space of the gas to be measured. There are multiple gas diffusion holes on the surface of the diffusion-type gas absorption cell to ensure that the gas in the space to be measured can enter the interior of the diffusion-type gas absorption cell through diffusion. Long-range optical fibers are connected to both ends of the diffusion-type gas absorption cell. The distributed laser assembly is composed of multiple fiber output lasers with different wavelength modulation ranges. The laser output fiber of the laser is connected to the fiber combiner to combine the lasers of multiple wavelengths into one beam as the detection laser beam for detecting gas components. Usually, the laser assembly can emit lasers targeting the absorption peaks of specific gas components. According to the Lambert-Beer law, by detecting the power of the laser beam corresponding before and after passing through these specific gas components, the concentration of each gas component can be deduced. Usually, the fiber combiner is responsible for combining the lasers output by multiple lasers into one fiber through multiple optical fibers to form a detection laser beam. In addition, a single laser can emit a laser with a specific wavelength targeting the absorption peak of a certain specific gas component, and multiple lasers can control the emission of multiple laser beams with specific wavelengths targeting the absorption peaks of multiple specific gas components. By detecting the photoacoustic signals generated by different component gases, the concentration of each component can be inverted. The laser control module uses a time-division multiplexing mode to control multiple lasers in a time-division manner to ensure that only the laser output by one laser can enter the photoacoustic cell at the same moment, that is, into the detection laser beam in the gas absorption cell and the photoacoustic cell, and only one wavelength of laser is included at the same time. The long-range optical fiber has extremely low loss and can be used to achieve remote and accurate detection.

[0084] Generally, in step S2, the sealed photoacoustic cell is filled with a multi-component gas to be measured with a constant concentration. The detection laser beam transmitted from the diffusion-type gas absorption cell enters the sealed photoacoustic cell along the long-range optical fiber. After the laser beam containing the periodically modulated laser in the sealed photoacoustic cell is absorbed by the gas molecules to be measured, the gas molecules will jump from the ground state to the excited state, and then gradually release energy through a non-radiative relaxation process, resulting in a periodic change in the local temperature, and further causing a periodic change in the pressure of the sealed space in the sealed photoacoustic cell, that is, generating an acoustic wave signal.

[0085] Generally, in step S3, use a microphone to collect the photoacoustic signal generated by the gas in the sealed photoacoustic cell absorbing light energy and convert the photoacoustic signal into an electrical signal.

[0086] Generally, in step S4, the obtained electrical signal enters the data processing module through the transmission line. The specific processing process of the data processing module is as follows: the electrical signal is amplified by the preamplifier and then enters the lock-in amplifier through the transmission line. The lock-in amplifier is used to demodulate the received signal to extract the photoacoustic signal component that matches the initial optical modulation frequency. When the laser beam passes through the gas to be measured, specific gas molecules will absorb the laser that matches their absorption wavelength. Combining with the Lambert-Beer law, by measuring the change in the laser power after absorption, the concentration of the gas can be determined. This method has high precision and high sensitivity. Especially when using a tunable laser, it can quickly tune the laser wavelength within a specific narrow wavelength range to precisely match the absorption peak of the gas to be measured, thereby achieving accurate concentration measurement, and is particularly suitable for detecting low-concentration gases.

[0087] In the photoacoustic cell, in the first-order longitudinal normal mode, the microphone can obtain the maximum photoacoustic amplitude. At this time, the relationship between the photoacoustic amplitude and the gas concentration can be expressed by the following formula:

[0088] P = I T (λ)s m C1Fα

[0089] Therefore, the calculation formula for the power of the transmitted detection laser beam is:

[0090]

[0091] Among them, P is the amplitude of the photoacoustic signal detected by the microphone, s m is the microphone sensitivity. C1 is the constant gas concentration in the photoacoustic cell, I T is the power of the detection laser beam incident into the photoacoustic cell, α is the gas absorption coefficient in the photoacoustic cell, λ is the light wavelength, F is the photoacoustic cell constant, F is independent of factors such as the gas absorption coefficient and light power, and is related to factors such as the volume, resonance frequency, and quality factor of the photoacoustic cell, representing the ability of the photoacoustic system to convert the light energy absorbed by the gas into sound energy; for a certain closed photoacoustic cell, s m , C1, F, α are all regarded as constants;

[0092] In the first-order longitudinal normal mode, the cell constant F can be expressed as:

[0093]

[0094] Among them, Q 100 is the quality factor of the first-order longitudinal normal mode, γ is the ratio of the specific heat capacity at constant pressure to the specific heat capacity at constant volume of the gas, L c is the corrected length of the photoacoustic cell resonance cavity, f 100 is the normal frequency in the first-order longitudinal normal mode, that is, the resonance frequency, V c is the volume of the photoacoustic cell resonance cavity.

[0095] In step S5, the Lambert-Beer law in the field of laser absorption:

[0096]

[0097] where I L and I0 are the optical power and the initial optical power at the optical path L, respectively, α is the gas absorption coefficient, and C0 is the concentration value of the gas to be measured;

[0098] Furthermore, according to the Lambert-Beer law, for a gas to be measured, the relationship between the incident optical power and the transmitted optical power in the diffusion-type gas absorption cell is obtained:

[0099]

[0100] Dividing both sides of the equation by I0 gives:

[0101]

[0102] Taking the logarithm of both sides of the equation gives:

[0103]

[0104] Dividing both sides of the equation by -αL gives the concentration of the gas to be measured:

[0105]

[0106] where I0 is the optical power of light with a certain wavelength entering the diffusion-type gas absorption cell through the long-range optical fiber, I T is the transmitted optical power of this wavelength obtained in step S4, α is the absorption coefficient of the gas to be measured corresponding to this wavelength in the diffusion-type gas absorption cell, C0 is the concentration of the gas to be measured, and L is the optical path of light in the gas absorption cell to be measured, approximately equal to the length of the diffusion-type gas absorption cell.

[0107] The multi-component gas remote detection device and detection method based on photoacoustic spectroscopy disclosed in the embodiments of the present invention use a microphone as a detector, which has no selectivity for laser wavelength, is not affected by stray light and external ambient light, and has high detection sensitivity; the photoacoustic detection component and the gas absorption component are separated from each other, so that the photoacoustic detection component can be far away from the space to be measured with variable environment, preventing interference caused by external environmental noise, vibration, etc. to the acoustic detection module, and having high detection sensitivity and stability; there is only one diffusion-type gas absorption cell in the space to be measured, which is not affected by electromagnetic interference and can work in a strong electromagnetic interference environment; the photoacoustic detection component is filled with a known concentration of the gas to be measured in a sealed manner, and the gas components therein remain unchanged during the whole detection process, avoiding the change of the resonance frequency of the photoacoustic cell caused by the change of gas characteristics, and having high detection accuracy; by using the low-loss characteristic of optical fiber, remote monitoring is realized. Compared with the free-space optical path, the optical fiber optical path has good stability and is not affected by vibration; multiple gases with known concentrations can be sealed in the sealed photoacoustic cell at the same time, and multi-gas detection can be realized. The multi-component gas remote detection device and detection method based on photoacoustic spectroscopy have good application prospects in the field of gas remote detection.

[0108] The technical solutions disclosed in the embodiments of the present invention and the technical details disclosed in the embodiments are only exemplary illustrations of the inventive concept of the present invention, and do not constitute a limitation on the technical solutions of the embodiments of the present invention. Any conventional changes, substitutions or combinations made to the technical details disclosed in the embodiments of the present invention have the same inventive concept as the present invention and are within the protection scope of the claims of the present invention.

Claims

1. A multi-component gas remote detection device based on photoacoustic spectroscopy, characterized in that, Comprising: A laser generating component for providing a detection laser beam for detecting a gas to be measured; A diffusion gas absorption cell, configured to be disposed at the on-site location of the remotely located gas to be measured and set such that the gas to be measured can freely enter the diffusion gas absorption cell; both ends of the diffusion gas absorption cell are respectively connected with a first long-range optical fiber and a second long-range optical fiber; wherein, the laser generating component is connected to the first long-range optical fiber to inject the detection laser beam into the diffusion gas absorption cell, and after being absorbed by the gas to be measured, it exits from the second long-range optical fiber; A photoacoustic detection component for generating and detecting a photoacoustic signal excited by the detection laser beam; the photoacoustic detection component is connected to the second long-range optical fiber, and the detection laser beam exiting from the second long-range optical fiber enters the photoacoustic detection component; A data processing component, connected to the photoacoustic detection component, for processing the photoacoustic signal collected by the photoacoustic detection component and inversely obtaining the gas composition of the gas to be measured.

2. The multi-component gas remote detection device based on photoacoustic spectroscopy according to claim 1, characterized in that, The laser generating component includes: A laser component, including a plurality of fiber output lasers with different wavelength modulation ranges, for outputting a plurality of laser beams with different wavelengths; A laser control module, connected to the laser component, for controlling the laser component to generate a plurality of laser beams with different wavelengths; An optical fiber combiner, connected to the output optical fiber of the laser component, for combining a plurality of laser beams with different wavelengths into a detection laser beam.

3. The multi-component gas remote detection device based on photoacoustic spectroscopy according to claim 1, characterized in that, The diffusion gas absorption cell is a tubular structure with a hollowed-out tube wall, and both ends of the tubular structure are respectively provided with a laser inlet and a laser outlet, which are respectively connected to the first long-range optical fiber and the second long-range optical fiber.

4. The multi-component gas remote detection device based on photoacoustic spectroscopy according to claim 1, characterized in that, The photoacoustic detection component includes a photoacoustic cell and a microphone disposed in the photoacoustic cell, and a gas with a constant concentration is disposed in the photoacoustic cell.

5. A multi-component gas remote detection method based on photoacoustic spectroscopy, characterized in that, Implemented by the detection device according to any one of claims 1 to 4, specifically including: Using the laser generating component to generate a detection laser beam; The detection laser beam is injected into the diffusion gas absorption cell via the first long-range optical fiber, and after being absorbed by the gas to be measured, it exits via the second long-range optical fiber; The detection laser beam exiting from the second long-range optical fiber enters the photoacoustic detection component, and in the photoacoustic detection component, the gas to be measured generates a photoacoustic signal based on the photoacoustic effect under the action of the detection laser beam; The data processing component receives and processes the photoacoustic signal, and inversely obtains the gas composition of the gas to be measured.

6. The multi-component gas remote detection method based on photoacoustic spectroscopy according to claim 5, characterized in that Inversely obtaining the gas composition of the gas to be measured includes: Converting the photoacoustic signal into an electrical signal; Processing the electrical signal to inversely obtain the power of the detection laser beam entering the photoacoustic detection component; According to the power of the detection laser beam, inversely obtaining the gas composition of the gas to be measured in the diffusion gas absorption cell.

7. The multi-component gas remote detection method based on photoacoustic spectroscopy according to claim 6, characterized in that The calculation formula for the power of the detection laser beam entering the photoacoustic detection component is: Among them, I T is the power of the detection laser beam entering the photoacoustic detection component, λ is the laser beam wavelength, P is the amplitude of the photoacoustic signal detected by the microphone, s m is the microphone sensitivity, C1 is the constant gas concentration in the photoacoustic cell, α is the gas absorption coefficient in the photoacoustic cell, and F is the photoacoustic cell constant.

8. The multi-component gas remote detection method based on photoacoustic spectroscopy according to claim 6, characterized in that The calculation formula for the gas concentration of the gas to be measured is: Wherein, C0 is the concentration of the gas to be measured, I0 is the power of the detection laser beam incident on the diffusion gas absorption cell, I T is the power of the detection laser beam entering the photoacoustic detection component, α is the absorption coefficient of the gas to be measured in the diffusion gas absorption cell, and L is the optical path of the detection laser beam in the light-absorbing gas to be measured, which is equal to the length of the diffusion gas absorption cell.

9. The multi-component gas remote detection method based on photoacoustic spectroscopy according to claim 5, wherein The laser generating component is configured to output only one laser beam with a set wavelength at the same time.

10. The multi-component gas remote detection method based on photoacoustic spectroscopy according to claim 5, characterized in that, The cell constant F is expressed as: Among them, Q 100 is the quality factor of the first-order longitudinal normal mode, γ is the ratio of the molar heat capacity at constant pressure to the molar heat capacity at constant volume of the gas, and L c is the corrected length of the photoacoustic cell resonance cavity, f 100 is the normal frequency in the first-order longitudinal normal mode, that is, the resonance frequency, and V c is the volume of the photoacoustic cell resonance cavity.

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