Absorption cell based on Faraday rotation spectrum of alternating current magnetic field and gas detection device

Abstract

The invention discloses an absorption cell based on an alternating current magnetic field Faraday rotation spectrum and a gas detection device, the absorption cell comprises an absorption cell cavity, gas to be detected is introduced into the absorption cell cavity, an optical signal of a wave band corresponding to a gas molecule or free radical absorption spectral line of the gas to be detected is received, a coil is wound on the absorption cell cavity, and the coil is wound on the absorption cell cavity. The coil is used for generating an alternating current magnetic field to induce gas molecules or free radicals in the cavity of the absorption cell to generate a Faraday effect, and heat generated by the coil is used for heat tracing temperature control of the cavity of the absorption cell; the device has the advantages that heat tracing temperature control is realized while the detection sensitivity of the gas to be detected is improved.

Description

Technical Field

[0001] The present invention relates to the field of gas detection, and particularly to an absorption cell and a gas detection device based on Faraday rotation spectroscopy of an alternating magnetic field. Background Art

[0002] In the detection of gas pollutants emitted from stationary sources or mobile sources, spectral overlap is a key factor affecting the accuracy of gas detection. For example, in the pollutants emitted from stationary source flue gas or mobile source tail gas, the characteristic absorption spectral line of NO molecules is located in the fundamental absorption region of the mid-infrared band, and the absorption intensity is relatively strong. However, the characteristic absorption spectral lines of other components in the pollutants also have absorption in this region, which will cause spectral overlap. For example, the interference of water vapor (H2O) and carbon dioxide (CO2) will make it difficult for some traditional optical detection methods, such as TDLAS, FTIR, NDIR, DOAS, and PAS, to effectively distinguish the target signal from the background noise. As paramagnetic molecules or free radicals, NO, NO2, and OH will have Zeeman splitting and energy level transitions in an axial magnetic field, resulting in the rotation of the polarization plane of linearly polarized light. While water vapor (H2O) and carbon dioxide (CO2) are diamagnetic molecules and do not have the Faraday rotation effect. Therefore, the Faraday rotation spectroscopy detection method can more accurately detect gas molecules or free radicals such as NO, NO2, and OH in the presence of coexisting water vapor (H2O) and carbon dioxide (CO2). Chinese Patent Publication No. CN115931730A discloses a gas cell and a gas sensing device based on Faraday magneto-optical rotation spectroscopy, which uses a permanent magnet ring array arranged non-equidistantly to generate a static magnetic field, fabricates a permanent magnet absorption cell, and generates a Faraday rotation spectroscopy signal by modulating the laser wavelength. The static magnetic field generated by this patent application does not generate heat and can operate with low power consumption.

[0003] However, under increasingly strict emission regulations, the sensitivity requirements for gas detection devices for pollutants emitted from stationary sources or mobile sources are getting higher and higher. The stable magnetic field modulation Faraday rotation spectroscopy in the above patent literature needs to modulate the laser wavelength to achieve Zeeman splitting, and its detection sensitivity is limited by the inherent limitations of standard wavelength modulation spectroscopy, such as optical interference. In addition, in the detection of gas pollutants emitted from stationary sources or mobile sources, the gas to be measured belongs to high-temperature and high-humidity gas, and the measurement absorption cell in the detection device needs to be heated and temperature-controlled to inhibit the condensation of water vapor into liquid to contaminate the inner wall and window of the absorption cell. Especially in the detection of NO, constant-temperature heating is required, which can effectively prevent chemical reactions caused by temperature fluctuations (such as the conversion of NO and NO2) to ensure the accuracy of measurement. Therefore, this device requires an additional heating and temperature control device, which increases the complexity of the system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the detection sensitivity of the gas to be measured while realizing heating and temperature control.

[0005] The present invention solves the above technical problems by the following technical means: An absorption cell based on the Faraday rotation spectrum of an alternating magnetic field, including an absorption cell cavity. The absorption cell cavity is filled with the gas to be measured and receives an optical signal in a wavelength band corresponding to the absorption spectrum of the gas molecules or free radicals of the gas to be measured. A coil is wound around the absorption cell cavity. The coil is used to generate an alternating magnetic field to induce the Faraday effect in the gas molecules or free radicals in the absorption cell cavity. At the same time, the heat generated by the coil is used for heat tracing and temperature control of the absorption cell cavity.

[0006] Further, the absorption cell further includes two gas nozzles and two window plates. The two gas nozzles are installed on the absorption cell cavity. One gas nozzle is for the inflow of the gas to be measured, and the other gas nozzle is for the outflow of the gas to be measured. The two window plates are respectively installed on the two side sections of the absorption cell cavity and have a preset inclination angle to allow the light beam to pass through without generating interference.

[0007] Further, the absorption cell further includes two temperature sensors, which are respectively installed at the inlet and outlet of the gas to be measured in the absorption cell cavity.

[0008] Further, the method for heat tracing and temperature control is as follows:

[0009] S1. Collect the gas temperatures at the inlet and outlet of the gas to be measured in the absorption cell cavity.

[0010] S2. Compare the temperatures at the two locations. If they are different, go to S3; if they are the same, calculate the concentration of the gas to be measured.

[0011] S3. According to the fitting relationship between the absorption cell temperature and the effective current value, adjust the effective current value applied to the coil, so as to adjust the gas temperature at the outlet of the gas to be measured in the absorption cell cavity, and return to S1. Loop through S1 to S3 until the gas temperatures at the inlet and outlet of the gas to be measured in the absorption cell cavity are the same.

[0012] Even further, the calculation process of the concentration of the gas to be measured is as follows:

[0013] According to the fitting relationship between the peak-to-peak value of the spectral signal output from the absorption cell cavity and the effective current value of the coil, calculate the change ΔS in the peak-to-peak value of the spectral signal caused by the change in the effective current value. Collect the current peak-to-peak value S0 of the spectral signal, and use the formula S = S0 - ΔS to obtain the corrected peak-to-peak value S of the spectral signal. According to the calibration relationship between the concentration of the gas to be measured and the peak-to-peak value of the spectral signal, calculate the concentration of the gas to be measured.

[0014] The present invention also provides a gas detection device using the absorption cell based on the AC magnetic field Faraday rotation spectroscopy as described above, which includes a coil driving module, a laser control module, a light source, a polarizer, an analyzer, a detector, a signal acquisition module, an MCU control and data processing module, a gas pump, and a temperature control module. The input end of the laser control module receives the signal from the MCU control and data processing module, and the output end of the laser control module is connected to the light source through a signal line. A polarizer, an absorption cell, an analyzer, and a detector are sequentially arranged on the optical path behind the light source; the signal acquisition module is connected to the detector through a signal line, and the MCU control and data processing module is respectively connected to the signal acquisition module, the coil driving module, and the laser control module through signal lines; the temperature control module is connected to the coil driving module, and the coil driving module is connected to the coil; the gas pump is installed at the inlet of the gas to be measured in the absorption cell cavity.

[0015] Further, the coil driving module includes a capacitor and a power amplifier module; the capacitor is connected in series with the coil in the absorption cell, and the power amplifier module serves as the power supply for the coil and the capacitor, and drives the coil by amplifying the amplitude of the input signal; the power amplifier module is respectively connected to the temperature control module and the MCU control and data processing module through signal lines; the amplification factor signal of the power amplifier module is the control signal of the effective current value output by the temperature control module.

[0016] Further, the input signal of the laser control module is a 10 Hz sawtooth wave signal generated by the MCU control and data processing module.

[0017] Further, the light source is a QCL laser, and the QCL laser generates an optical signal in a wavelength band corresponding to the absorption spectrum line of the gas molecules or free radicals of the gas to be measured.

[0018] Further, the included angle between the polarization axes of the polarizer and the analyzer is in the range of 90°±10° and not equal to 90°.

[0019] The advantages of the present invention are as follows:

[0020] (1) Aiming at the spectral overlap problem in the existing optical detection methods, the present invention proposes an AC magnetic field modulation Faraday rotation spectroscopy detection scheme, which avoids the spectral overlap interference of diamagnetic molecules on the detection of paramagnetic molecules in the axial magnetic field from the technical level, and realizes the accurate detection of paramagnetic gas molecules or free radicals in the background of coexisting diamagnetic molecules.

[0021] (2) In view of the detection sensitivity problem of the prior art, the present invention proposes an alternating current magnetic field modulation Faraday rotation spectroscopy detection scheme. A coil is wound around the absorption cell cavity. The coil is used to generate an alternating current magnetic field to induce the Faraday effect in gas molecules or free radicals in the absorption cell cavity. Thus, the alternating current magnetic field modulation spectroscopy directly realizes Zeeman splitting through the magnetic field frequency, effectively avoiding the inherent limitations of the wavelength modulation spectroscopy in the prior art, opening up a new path for constructing a highly sensitive gas detection device, and achieving highly sensitive detection of ultra-low emission gas pollutants from fixed sources or mobile sources. In addition, the present invention uses the heat generated during the alternating current magnetic field modulation to directly control the temperature and heat the absorption cell, suppressing water vapor condensation, ensuring the stability of the optical detection system, and reducing the complexity of the system.

[0022] (3) Based on the reading of the temperature sensor at the gas inlet of the absorption cell, the present invention determines the magnitude of the effective current of the coil, and further controls the heat generation rate of the coil to make the readings of the two temperature sensors the same, realizing the temperature control and heating of the absorption cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0024] Figure 2 It is a schematic structural diagram of an absorption cell in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of a coil driving module in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the temperature control and heating and gas concentration calculation process in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0027] Figure 5 It is the temperature measurement result of the absorption cell at different effective currents in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0028] Figure 6 It is a fitting relationship diagram between the temperature of the absorption cell and the square of the effective current value in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0029] Figure 7 It is the spectrogram corresponding to different effective current values of NO gas with the same concentration in a gas detection device based on alternating current magnetic field Faraday rotation spectroscopy disclosed in an embodiment of the present invention;

[0030] Figure 8 The fitting relationship diagram between the peak-to-peak value of the signal and different effective current values for NO gas with the same concentration in the gas detection device based on the AC magnetic field Faraday rotation spectrum disclosed in the embodiments of the present invention. Detailed implementation manners

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0032] As Figure 1 shown, the embodiments of the present invention provide a gas detection device based on the AC magnetic field Faraday rotation spectrum. The gas detection device will be described in detail below, and the absorption cell will be described together when introducing the gas detection device. The gas detection device includes an absorption cell 1, a coil driving module 2, a laser control module 3, a light source 4, a polarizer 5, an analyzer 6, a detector 7, a signal acquisition module 8, an MCU control and data processing module 9, a gas pump 10, a first temperature sensor 11, a second temperature sensor 12, and a temperature control module 13. All signal lines in the gas detection device are connected using coaxial cables; the power lines are connected using flexible wires; the gas paths are connected using a combination of high-temperature resistant hoses and quick connectors.

[0033] As Figure 2 shown, the absorption cell includes an absorption cell cavity 101, two gas nozzles 102, a coil 103, and a window pane 104; the absorption cell cavity 101 is a quartz tube with an outer diameter of 12 mm and a length of 25 cm for accommodating the gas to be measured; the two gas nozzles 102 are quartz tubes with an outer diameter of 5 mm and a length of 3.5 cm, which are connected to the absorption cell cavity 3 cm away from the cross-sections on both sides of the absorption cell by flame welding for the gas to be measured in the cavity to exchange with the external environment. One gas nozzle 102 is for gas inflow, and the other gas nozzle 102 is for gas outflow; the window pane 104 is a flat disc made of calcium fluoride with a diameter of 12 mm, which is pasted on the cross-sections on both sides of the absorption cell cavity by adhesive bonding and has a certain inclination angle for the light beam to pass through without generating interference. This inclination angle is not particularly limited and can be selected according to needs within an angle of 5° in actual applications to ensure no interference.

[0034] The coil (103) is 1.5 mm 2Oxygen-free copper-clad wire is tightly wound between the two air nozzles of the absorption cell cavity 101 in 4 layers with a total of 480 turns to generate an AC magnetic field to induce the Faraday effect of the paramagnetic molecules in the cavity. At the same time, the heat generated by the coil 103 is used to heat and control the temperature of the absorption cell 1.

[0035] like Figure 3 As shown, the coil drive module 2 includes a 16uF capacitor ( Figure 3 C) and a power amplifier module with an output power of 2000W ( Figure 3 U in); the capacitor is connected in series with the coil 103 in the absorption tank 1 to form an RCL circuit that can generate an AC magnetic field; the power amplifier module serves as the power supply of the RCL circuit, and drives the coil 103 by amplifying the input signal amplitude; the capacitor, the power amplifier module, and the coil 103 are connected to each other by power lines.

[0036] The power amplifier module is connected to the MCU control and data processing module 9 and the temperature control module 13 signal lines respectively; the input signal of the power amplifier module is the 746Hz sine wave signal generated by the MCU control and data processing module 9; the amplification factor signal of the power amplifier module is the control signal of the effective value of the output current of the temperature control module 13.

[0037] The temperature control module 13 is connected to two temperature sensors, namely the first temperature sensor 11 and the second temperature sensor 12, through signal lines respectively; the first temperature sensor 11 is installed at the gas inlet of the absorption tank 1 to detect the inlet gas temperature of the absorption tank 1, and the second temperature sensor 12 is installed at the gas outlet of the absorption tank 1 to detect the outlet gas temperature of the absorption tank 1; the temperature control module 13 analyzes the data collected by the two temperature sensors, and determines the effective value of the current of the coil 103 based on the reading of the first temperature sensor 11, and then controls the heat generation rate of the coil 103 so that the readings of the first temperature sensor 11 and the second temperature sensor 12 are the same, thereby realizing the heating temperature control of the absorption tank. The detailed process of the heating temperature control is introduced in detail in the principle process part later.

[0038] The air pump 10 is a brushless DC vacuum pump, which controls the gas to be measured to flow into the absorption cell 1 from one air nozzle 102 and to flow out of the absorption cell 1 from another air nozzle 102 .

[0039] The laser control module 3 is connected to the light source 4 through a signal line; the input signal of the laser control module 3 is a 10 Hz sawtooth wave signal generated by the MCU control and data processing module 9; the light source 4 is a laser that can generate a wavelength band corresponding to the absorption spectral lines of gas molecules or free radicals such as NO, NO2, OH, etc., such as a QCL laser. On the optical path behind the light source 4, a polarizer 5, an absorption cell 1, an analyzer 6, and a detector 7 are sequentially arranged. After the laser beam passes through the polarizer 5 and becomes linearly polarized light, it interacts with the paramagnetic molecules in the absorption cell 1 and then passes through the analyzer 6 and is received by the detector 7.

[0040] The polarization axes of the polarizer 5 and the analyzer 6 are nearly perpendicular, but not equal to 90°; the included angle between the polarization axes of the polarizer 5 and the analyzer 6 is usually within 90° ± 10°; the specific value is the deflection angle corresponding to the maximum signal-to-noise ratio obtained by the device.

[0041] The detector 7 is a thermoelectrically cooled mercury cadmium telluride photodetector, which converts the received light intensity signal into an electrical signal, that is, the Faraday rotation spectroscopy signal.

[0042] The signal acquisition module 8 is connected to the detector 7 through a signal line to acquire the Faraday rotation spectroscopy signal output by it.

[0043] The MCU control and data processing module 9 is respectively connected to the signal acquisition module 8, the coil drive module 2, and the laser control module 3 through signal lines. The MCU control and data processing module 9 uses a 746 Hz sine signal as a reference signal to analyze the signal acquired by the signal acquisition module 8 and calculate the peak-to-peak value S of the corrected signal; then, according to the calibrated parameters, calculate the concentration of the gas to be measured. The principle process of the trace heating temperature control and the concentration of the gas to be measured will be introduced in detail below. As Figure 4 shown, the specific process is as follows:

[0044] S1. Collect the gas temperatures at the inlet and outlet of the gas to be measured in the absorption cell cavity.

[0045] S2. Compare the two temperatures. If they are different, go to S3; if they are the same, go to S4.

[0046] S3. According to the fitting relationship between the absorption cell temperature and the effective current value, adjust the effective current value applied to the coil, so as to adjust the gas temperature at the outlet of the gas to be measured in the absorption cell cavity, return to S1, and loop through S1 to S3 until the gas temperatures at the inlet and outlet of the gas to be measured in the absorption cell cavity are the same.

[0047] S4. According to the fitting relationship between the peak-to-peak value of the spectral signal output from the absorption cell cavity and the effective current value of the coil, calculate the change ΔS in the peak-to-peak value of the spectral signal caused by the change in the effective current value. Collect the current peak-to-peak value S0 of the spectral signal, and use the formula S = S0 - ΔS to obtain the corrected peak-to-peak value S of the spectral signal. According to the calibration relationship between the concentration of the gas to be measured and the peak-to-peak value of the spectral signal, calculate the concentration of the gas to be measured.

[0048] According to Figure 5 It can be seen that for different effective current values, when reaching the thermal equilibrium state, the temperature of the absorption cell is a constant value; therefore, the temperature control of the absorption cell can be achieved by adjusting the effective current value.

[0049] Assume that the temperature of the gas to be measured is T, and the peak-to-peak value of the signal before correction is S0.

[0050] According to Figure 6 the fitting expression of the temperature of the absorption cell in [reference] and the square of the effective current value, the effective current value I can be calculated

[0051]

[0052] Figure 7 is the spectral diagram corresponding to the same concentration of NO gas at different effective current values. Figure 8 For the same concentration of NO gas, the fitting relationship diagram between the peak-to-peak value of the signal and different effective current values. According to Figure 8 the fitting formula in [reference], it can be seen that for every 1A increase in the effective current value, the peak-to-peak value of the corresponding signal will increase by 139.045 mV. That is

[0053] ΔS = 139.045·I (2)

[0054] That is, the corrected peak-to-peak value S of the signal is

[0055] S = S0 - ΔS (3)

[0056] Then, according to the calibration relationship between the concentration of the gas to be measured and the peak-to-peak value of the signal, the concentration of the gas to be measured can be calculated. The calibration relationship between the concentration of the gas to be measured and the peak-to-peak value of the signal is pre-given.

[0057] Through the above technical solutions, the present invention provides an absorption cell and a gas detection device based on the Faraday rotation spectrum of an alternating magnetic field. In the detection of gas pollutants emitted from fixed sources or mobile sources, the interference of diamagnetic molecules such as water vapor (H2O) and carbon dioxide (CO2) is suppressed by the action of an axial magnetic field, avoiding the phenomenon of spectral overlap at the technical level. Moreover, the Zeeman splitting is directly modulated by the frequency of the alternating magnetic field, effectively circumventing the inherent limitations of wavelength modulation spectroscopy and achieving high-sensitivity detection of paramagnetic gas molecules (such as NO, NO2) or free radicals (OH). At the same time, the heat generated during the modulation of the alternating magnetic field is used to directly control the temperature and heat the absorption cell, suppressing the condensation of water vapor, ensuring the stability of the optical detection system, and reducing the complexity of the system.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An absorption cell based on Faraday rotation spectroscopy of an alternating magnetic field, characterized in that It includes an absorption cell cavity. The absorption cell cavity is introduced with a gas to be measured and receives an optical signal in a wavelength band corresponding to the absorption spectrum line of the gas molecules or free radicals of the gas to be measured. A coil is wound around the absorption cell cavity. The coil is used to generate an alternating magnetic field to induce the Faraday effect in the gas molecules or free radicals in the absorption cell cavity. At the same time, the heat generated by the coil is used for heat tracing and temperature control of the absorption cell cavity.

2. The absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 1, characterized in that, It also includes two gas nozzles and two window plates. The two gas nozzles are installed on the absorption cell cavity. One gas nozzle is used for the inflow of the gas to be measured, and the other gas nozzle is used for the outflow of the gas to be measured. The two window plates are respectively installed on the two side sections of the absorption cell cavity and have a preset inclination angle.

3. The absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 1, characterized in that, It also includes two temperature sensors, which are respectively installed at the gas inlet to be measured and the gas outlet to be measured of the absorption cell cavity.

4. The absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 1, wherein The method for heat tracing and temperature control is as follows: S1. Collect the gas temperatures at the gas inlet to be measured and the gas outlet to be measured of the absorption cell cavity. S2. Compare the temperatures at the two locations. If they are different, go to S3; if they are the same, calculate the concentration of the gas to be measured. S3. According to the fitting relationship between the absorption cell temperature and the effective current value, adjust the effective current value applied to the coil, so as to adjust the gas temperature at the gas outlet to be measured of the absorption cell cavity, and return to S1. Loop through S1 to S3 until the gas temperatures at the gas inlet to be measured and the gas outlet to be measured of the absorption cell cavity are the same.

5. The absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 4, characterized in that, The calculation process of the concentration of the gas to be measured is as follows: According to the fitting relationship between the peak-to-peak value of the spectral signal output by the absorption cell cavity and the effective current value of the coil, calculate the change ΔS in the peak-to-peak value of the spectral signal caused by the change in the effective current value. Collect the current peak-to-peak value S0 of the spectral signal, and use the formula S = S0 - ΔS to obtain the corrected peak-to-peak value S of the spectral signal. According to the calibration relationship between the concentration of the gas to be measured and the peak-to-peak value of the spectral signal, calculate the concentration of the gas to be measured.

6. The gas detection device using the absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to any one of claims 1-5, characterized in that, It includes a coil driving module, a laser control module, a light source, a polarizer, an analyzer, a detector, a signal acquisition module, an MCU control and data processing module, an air pump, and a temperature control module. The input end of the laser control module receives the signal from the MCU control and data processing module. The output end of the laser control module is connected to the light source through a signal line. A polarizer, an absorption cell, an analyzer, and a detector are sequentially arranged on the optical path behind the light source. The signal acquisition module is connected to the detector through a signal line. The MCU control and data processing module is respectively connected to the signal acquisition module, the coil driving module, and the laser control module through signal lines. The temperature control module is connected to the coil driving module, and the coil driving module is connected to the coil. The air pump is installed at the gas inlet to be measured of the absorption cell cavity.

7. The gas detection device for the absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 6, wherein The coil driving module includes a capacitor and a power amplifier module. The capacitor is connected in series with the coil in the absorption cell. The power amplifier module serves as the power supply for the coil and the capacitor, and drives the coil by amplifying the amplitude of the input signal. The power amplifier module is respectively connected to the temperature control module and the MCU control and data processing module through signal lines. The amplification factor signal of the power amplifier module is the control signal of the effective current value output by the temperature control module.

8. The gas detection device of the absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 6, wherein The input signal of the laser control module is a 10 Hz sawtooth wave signal generated by the MCU control and data processing module.

9. The gas detection device of the absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 6, wherein, The light source is a QCL laser, and the QCL laser generates an optical signal in a band corresponding to the absorption spectrum line of the gas molecules or free radicals of the gas to be measured.

10. The gas detection device for the absorption cell based on the Faraday rotation spectrum of an alternating magnetic field according to claim 6, characterized in that, The included angle between the polarization axes of the polarizer and the analyzer is within the range of 90° ± 10° and not equal to 90°.

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