A humidity self-calibrating mixed gas analysis device and method

Abstract

The application provides a humidity self-calibration gas analysis device and method, comprising: a tuning fork and a micro-wire; two ends of the micro-wire are bridged on two vibrating arms at the opening of the tuning fork; after the device is placed in a to-be-measured environment, a conductance spectrum corresponding to a resonance frequency of the tuning fork is used to determine the humidity of the to-be-measured environment, and a photoacoustic spectrum signal generated by the tuning fork under the action of an optical signal is used to determine the concentration of a to-be-measured gas in the to-be-measured environment; when the device is used to monitor the concentration of the to-be-measured gas in the to-be-measured environment, a first photoacoustic spectrum signal value measured by the tuning fork under different humidities when the concentration of the to-be-measured gas is a preset value is obtained in advance; then, the device measures a corresponding humidity value and a second photoacoustic spectrum signal value of the to-be-measured gas according to requirements, compares the second photoacoustic spectrum signal value with the first photoacoustic spectrum signal value corresponding to the humidity value, and determines whether the concentration of the to-be-measured gas changes. The application can perform humidity self-calibration and realize accurate analysis of the concentration of the to-be-measured gas.

Description

Technical Field

[0001] This invention belongs to the field of gas sensing, and more specifically, relates to a humidity self-calibrating mixed gas analysis device and method. Background Technology

[0002] The 32768Hz quartz tuning fork is a mass-produced crystal oscillator with a resonant frequency of 32768Hz, commonly used as a timing element in mobile phones and clocks. Due to the low internal mechanical losses of quartz, the Q-factor of a quartz tuning fork is as high as approximately 100,000 in a vacuum and approximately 10,000 in atmospheric conditions. After removing its metal casing, the quartz tuning fork is exposed and used as a piezoelectric sensor. To date, the quartz tuning fork has been used as a sensor in many scientific fields. It can be used in micro-force sensing, electric field analysis, atomic force microscopy, dynamic mechanical analysis, thermal microscopy, photodetectors, and acoustic detectors. Compared to other mechanical resonators (such as cantilever beam and string resonators), the quartz tuning fork has a simpler structure, and its resonant behavior can be directly read from its own piezoelectric effect without the need for additional readout devices.

[0003] Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a photoacoustic technique based on quartz tuning forks, offering a compact and highly sensitive method for trace gas detection. In QEPAS, the quartz tuning fork is used as an acoustic sensor; sound waves applied to the vibrating arm of the tuning fork are converted into electrical signals via the piezoelectric effect. Because the quartz tuning fork only responds to vibrations at a frequency of 32768 Hz, the sensor exhibits excellent resistance to environmental noise and high sensitivity. Quartz tuning fork gas sensors have been applied in atmospheric environmental monitoring, petroleum gas monitoring, human medical diagnosis, and fire early warning. However, like most laser spectral sensors, current quartz tuning fork gas sensors are susceptible to water vapor interference in the infrared region. In practical gas monitoring, researchers must measure water vapor concentration to calibrate sensor performance. Furthermore, the narrow frequency response bandwidth of existing tuning forks necessitates high stability of the excitation modulation optical signal, leading to higher equipment costs.

[0004] In summary, current quartz-enhanced photoacoustic spectroscopy gas sensors suffer from strong interference from water molecules in the infrared region, and the tuning fork frequency response bandwidth is narrow. This leads to inaccurate detection of target gas concentration in existing quartz-enhanced photoacoustic spectroscopy, unreliable gas analysis results, and high equipment requirements and costs. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a humidity self-calibrating mixed gas analysis device and method, which aims to solve the problems of inaccurate target gas concentration detection, resulting in unreliable gas analysis results, as well as complex equipment and high cost.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a humidity self-calibrating gas analysis device, comprising: a tuning fork and microfilaments;

[0007] The two ends of the microfilament are bridged to the two arms at the opening of the tuning fork; the microfilament is sensitive to water molecules, storing water molecules when the humidity of its environment increases and releasing water molecules when the humidity of its environment decreases; the elastic modulus of the microfilament is inversely correlated with the water molecule content inside it.

[0008] After the device is placed in the environment to be tested, the conductivity spectrum corresponding to the resonance frequency of the tuning fork is used to determine the water molecule concentration, i.e., humidity, of the environment to be tested. The photoacoustic spectrum signal generated by the tuning fork under the action of the light signal is used to determine the concentration of the gas to be tested in the environment to be tested.

[0009] When the device is used to monitor the concentration of the gas to be tested in the environment, it first obtains the first photoacoustic spectral signal value obtained by tuning fork measurement under different humidity levels when the concentration of the gas to be tested is a preset value. Then, the device measures the conductivity spectrum of the tuning fork as required to obtain the corresponding humidity value. Next, it measures the second photoacoustic spectral signal value of the gas to be tested by tuning fork. The second photoacoustic spectral signal value is compared with the first photoacoustic spectral signal value corresponding to the humidity value. If the second photoacoustic spectral signal value is relatively smaller, it indicates that the concentration of the gas to be tested has decreased compared with the preset value. If the second photoacoustic spectral signal value is relatively larger, it indicates that the concentration of the gas to be tested has increased compared with the preset value. Otherwise, it indicates that the concentration of the gas to be tested has not changed.

[0010] In one possible example, the microfilaments are spider silk, silkworm silk, or animal hair.

[0011] In one possible example, the device can also be used to monitor the humidity of the environment under test.

[0012] In one possible example, if the humidity of the environment to be measured and the concentration of the gas to be measured need to be maintained at preset humidity and preset gas concentration;

[0013] When the device is used to monitor the concentration and humidity of the gas to be measured in the environment under test, if the measured humidity changes compared to the preset humidity, the humidity of the environment under test is adjusted to reach the preset humidity; if the measured second photoacoustic spectral signal value of the gas to be measured at the current humidity changes compared to the first photoacoustic spectral signal value of the preset gas concentration at the current humidity, the concentration of the gas to be measured in the environment under test is adjusted to reach the preset gas concentration.

[0014] In one possible example, the device has a higher frequency response bandwidth to photoacoustic spectral signals compared to a tuning fork without bridging microfilaments, thus reducing the device's requirements for the frequency stability of the input optical signal.

[0015] Secondly, the present invention provides a humidity self-calibrating gas analysis method, comprising the following steps:

[0016] The two ends of the microfilament are bridged to the two arms at the opening of the tuning fork; the microfilament is sensitive to water molecules, storing water molecules when the humidity of its environment increases and releasing water molecules when the humidity of its environment decreases; the elastic modulus of the microfilament is inversely correlated with the water molecule content inside it.

[0017] The tuning fork is placed in the test environment, and the water molecule concentration, i.e. humidity, of the test environment is determined by the conductivity spectrum corresponding to the resonance frequency of the tuning fork. The concentration of the gas to be tested in the test environment is determined by the photoacoustic spectrum signal generated by the tuning fork under the action of light signal.

[0018] First, the first photoacoustic spectral signal value of the gas to be tested is obtained by measuring with a tuning fork at different humidity levels when the concentration of the gas to be tested is at a preset value. Then, the corresponding humidity value and the second photoacoustic spectral signal value of the gas to be tested are obtained by measuring with a tuning fork as required. The second photoacoustic spectral signal value is compared with the first photoacoustic spectral signal value corresponding to the humidity value. If it is relatively smaller, it indicates that the concentration of the gas to be tested has decreased compared with the preset value. If it is relatively larger, it indicates that the concentration of the gas to be tested has increased compared with the preset value. Otherwise, it indicates that the concentration of the gas to be tested has not changed.

[0019] In one possible example, the microfilaments are spider silk, silkworm silk, or animal hair.

[0020] In one possible example, the tuning fork can also be used to monitor the humidity of the environment under test.

[0021] In one possible example, if the humidity of the environment to be measured and the concentration of the gas to be measured need to be maintained at preset humidity and preset gas concentration;

[0022] If the humidity measured by the tuning fork changes compared to the preset humidity, adjust the humidity of the environment to be measured to reach the preset humidity.

[0023] If the second photoacoustic spectral signal value of the gas under the current humidity obtained by the tuning fork measurement changes compared with the first photoacoustic spectral signal value of the preset gas concentration under the current humidity value, then the concentration of the gas under test in the test environment is adjusted to reach the preset gas concentration.

[0024] In one possible example, the microfilament is used to increase the frequency response bandwidth of the tuning fork to photoacoustic spectral signals and reduce its frequency stability requirements for the input optical signal.

[0025] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0026] This invention provides a humidity-self-calibrated mixed gas analysis device and method, proposing a novel approach to analyzing mixed gases. A spider silk bridging the two arms of a tuning fork enhanced with photoacoustic spectroscopy and conductivity spectroscopy forms a conductivity spectral channel. A laser beam enters through the gap between the two arms, passes through the quartz tuning fork, and is excited to form a photoacoustic spectral channel. This invention can distinguish changes in humidity and the concentration of the analyte gas under preset conditions.

[0027] This invention provides a humidity-self-calibrated mixed gas analysis device and method. The tuning fork modified with microfilaments has a frequency response curve bandwidth that is 67% higher than that of existing technologies. This reduces the stability requirements of the laser modulation frequency in spectroscopic techniques, improves the tolerance of the equipment, and reduces equipment costs. This invention uses the same tuning fork to measure both conductivity and spectral spectra, simplifying the device structure, reducing costs, and providing superior functionality compared to existing technologies.

[0028] This invention provides a humidity-self-calibrated mixed gas analysis device and method that eliminates the interference of water molecules on gas detection in the infrared region. The concentration of water molecules is detected through a conductivity spectral channel, and the concentration of the target gas is detected through a photoacoustic spectral channel. The combined use of these two channels solves the problem of water molecule interference in infrared gas detection, enabling the analysis of two-component mixed gases.

[0029] This invention provides a humidity-self-calibrated mixed gas analysis device and method. Based on a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy technique using a microfilament-modified tuning fork, it enables the analysis of the concentrations of two components using a single laser. By changing the microfilament material and the laser wavelength, it is possible to detect various other two-component mixed gases, effectively improving the detection capability of the quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy signal. The tuning fork provided by this invention can operate simultaneously under multi-modal driving conditions; that is, the microfilament-modified tuning fork can be used for photoacoustic spectroscopy detection. Attached Figure Description

[0030] Figure 1 A three-dimensional model of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork provided in an embodiment of the present invention.

[0031] Figure 2 Frequency response curves of a quartz-enhanced photoacoustic spectrum-conductivity spectrum coupled tuning fork and a bare tuning fork, as provided in the embodiments of the present invention.

[0032] Figure 3 The resonance curves of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork under different humidity conditions are provided for embodiments of the present invention.

[0033] Figure 4 The resonance frequency diagram obtained at different relative humidities in the quartz enhanced conductivity spectrum provided in the embodiments of the present invention.

[0034] Figure 5 The photoacoustic signal amplitude diagram of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork with a carbon dioxide concentration of 5% at different humidity levels is provided in an embodiment of the present invention.

[0035] Figure 6 The resonance frequency diagrams obtained in the quartz-enhanced photoacoustic spectrum provided in the embodiments of the present invention are for carbon dioxide with a concentration of 5% at different relative humidities.

[0036] Figure 7 The resonance curves of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork at different carbon dioxide concentrations are provided for embodiments of the present invention.

[0037] Figure 8 The resonance frequency diagram obtained in the quartz enhanced conductivity spectrum provided in the embodiment of the present invention is a diagram of the resonance frequency obtained at different carbon dioxide concentrations.

[0038] Figure 9 The photoacoustic signal amplitude diagram of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork at 65% RH with different concentrations of carbon dioxide is provided in an embodiment of the present invention.

[0039] Figure 10 The resonance frequency diagrams obtained at different carbon dioxide concentrations under 65% RH in the quartz-enhanced photoacoustic spectrum provided in the embodiments of the present invention are shown.

[0040] Figure 11 This is a schematic diagram of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupled tuning fork spider silk provided in an embodiment of the present invention.

[0041] Figure 12 This is a system diagram of a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupling technique for mixed gas analysis provided in an embodiment of the present invention.

[0042] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is a computer device; 2 is a function signal generator; 3 is an adder; 4 is a laser driver; 5 is a semiconductor laser; 6 is an optical fiber assembly-focuser; 7 is a transparent gas cell; 8 is a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork; 8.1 is a tuning fork base; 8.2 is a tuning fork vibrating arm; 8.3 is a tuning fork pin; 8.4 is a microfilament; 9 is a preamplifier; and 10 is a lock-in amplifier. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0044] In this article, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this article indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0045] It is understood that the device provided by this invention employs a tuning fork and microfilaments; the tuning fork can be selected as needed, for example, a quartz tuning fork commonly used by those skilled in the art. Similarly, the microfilaments can also be selected as needed, such as spider silk, silkworm silk, or animal hair.

[0046] To illustrate this more clearly, the following examples use a quartz tuning fork and spider silk as illustrations.

[0047] It should be noted that the conductivity spectroscopy technique based on quartz tuning forks exhibits highly sensitive gas sensing capabilities. An elastic microfilament can span the arm of the quartz tuning fork, forming a resonant system with it. If the microfilament reacts with a specific gas, the change in its elastic modulus or mass will couple with the quartz tuning fork. Since the quartz tuning fork is an extremely sensitive mechanical resonator, the resonant frequency or Q-factor change of the quartz tuning fork can be determined by the conductivity spectrum of the microfilament and the microfilament.

[0048] As those skilled in the art will understand, spider silk is a humidity-sensitive material because it is highly sensitive to water molecules. When the environment changes from dry to humid, the structure of spider silk adapts to a jointed form to store water molecules. Under high humidity, unrestricted spider silk shrinks by up to 50%, while restricted silk generates stresses exceeding 50 MPa. Furthermore, the shrinkage stress generated by spider silk is transient, thus reversible and reusable. Here, we obtained spider silk from the spindle-shaped silk glands of the orange baboon spider.

[0049] The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork provided by the present invention includes: two rectangular tuning fork arms, a tuning fork base and two tuning fork pins; a spider silk is connected to two arms on one side of the quartz tuning fork at a predetermined distance from the tuning fork opening;

[0050] When the detection device is operational, it first excites the quartz tuning fork using a series of sinusoidal signals of different frequencies, recording the output corresponding to the resonant amplitude at each frequency. The Lorentz function is used to fit the resonance curve to obtain the resonant frequency. Then, a laser is incident through the gap between the two rectangular tuning fork arms, passing through the quartz tuning fork, and generating an electrical signal from the tuning fork pins under the action of the photoacoustic effect; this electrical signal corresponds to the photoacoustic spectrum signal of the incident laser.

[0051] In a second aspect, the present invention provides a gas detection device including the quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy combined technology given in the first aspect above, and further includes: a semiconductor laser, a focuser, and a signal demodulation device;

[0052] The semiconductor laser is used to project laser light onto the gas to be detected;

[0053] The focuser is used to focus the laser light passing through the gas to be tested onto the quartz-enhanced photoacoustic spectral signal detection device.

[0054] The quartz-enhanced photoacoustic spectral signal detection device is used to output a corresponding electrical signal under the action of the laser.

[0055] The signal demodulation device is used to demodulate the electrical signal to obtain the concentration information of the gas to be measured.

[0056] In an optional example, the signal demodulation device includes a preamplifier and a lock-in amplifier;

[0057] The preamplifier is used to amplify the electrical signal output by the quartz-enhanced photoacoustic spectral signal detection device through transimpedance amplification to obtain the corresponding quartz-enhanced photoacoustic spectral signal.

[0058] The lock-in amplifier is used to demodulate the quartz-enhanced photoacoustic spectral signal to obtain the concentration information of the gas to be measured.

[0059] In an optional example, the device further includes: a transparent air chamber;

[0060] The transparent gas chamber is used to hold the gas to be tested.

[0061] It is understood that the device provided by this invention can analyze the concentration of a gas to be measured, which can be any gas whose concentration can be measured by a tuning fork based on photoacoustic spectral signals. The following embodiments use carbon dioxide (CO2) as an example to illustrate the concept.

[0062] The quartz tuning fork has two arms. This invention bridges the two arms with a spider silk to form a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupled tuning fork, used for conductivity spectroscopy to detect humidity. A laser is incident through the gap between the two arms and excited in the vicinity of the spider silk, used for photoacoustic spectroscopy to detect carbon dioxide. Humidity can be detected by conductivity spectroscopy, and the concentration of carbon dioxide under humidity conditions can be detected by photoacoustic spectroscopy.

[0063] This invention is achieved through the following specific technical solution: The quartz tuning fork comprises two arms. The technical solution and gas detection device described in this invention are based on a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork, with a spider silk bridge connecting the two arms. A small amount of epoxy resin is used to attach a spider silk to the two arms of the quartz tuning fork, forming a spider silk bridge. The silk is approximately 846.6 micrometers long and approximately 6.4 micrometers in diameter. This method allows the spider silk to be bridged onto the quartz tuning fork, forming a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork. Its three-dimensional shape is shown below. Figure 1 As shown.

[0064] Under the same experimental conditions, we measured the frequency response curves of the quartz tuning fork before and after bridging with spider silk, as follows: Figure 2 As shown. A quartz tuning fork with only quartz-enhanced photoacoustic spectroscopy detection capability before being bridged with spider silk is called a bare tuning fork. A quartz tuning fork with both quartz-enhanced photoacoustic spectroscopy and quartz-enhanced conductivity spectroscopy detection capabilities after being bridged with spider silk is called a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy combined tuning fork. A series of sinusoidal signals of different frequencies were used to excite the quartz tuning fork, and the frequencies corresponding to the output and resonance amplitude of the quartz tuning fork were recorded. The horizontal axis represents the response frequency, and the vertical axis represents the normalized vibration amplitude corresponding to different vibration frequencies.

[0065] Depend on Figure 2 It can be seen that, Figure 2 The bandwidth of the response curve on the left is increased compared to the bandwidth of the response curve on the right. This shows that the frequency response bandwidth of the photoacoustic spectral signal of the spider silk-modified tuning fork provided by this invention is increased compared to the frequency response bandwidth of the bare tuning fork. Therefore, the frequency stability requirement of the laser signal for the tuning fork of this invention will be reduced, and the requirement for the frequency stability of the input optical signal can be relaxed.

[0066] Fitting the output signal of the tuning fork using the Lorentz function reveals that the frequency response curve of the quartz tuning fork is Lorentz-shaped. The resonant frequency of the tuning fork using quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy decreased from 32765.9 Hz to 32718.9 Hz, and the Q-factor decreased from 12000 to 7200. The definition of the Q-factor indicates a coupling phenomenon between the dynamic behavior of the spider silk and the dynamic behavior of the tuning fork itself during vibration. The changes in the resonant frequency and Q-factor of the tuning fork can be attributed to the change in the effective elastic modulus of the quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy-tuning fork caused by the spider silk.

[0067] The gas detection device of the present invention comprises the following parts: a function generator; an adder connected to the modulation signal output terminal of the function generator; a laser driver connected to the signal output terminal of the adder; a laser driven by the laser driver, the laser being used to emit at least excitation light; an optical fiber assembly disposed in the output optical path of the laser; the emitted laser acting on a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork after passing through a gas cell; a preamplifier connected to the pins of the tuning fork; and a lock-in amplifier connected to the output terminal of the preamplifier, the lock-in amplifier being connected to the synchronization signal output terminal of the function generator. Further, a computer device with a data acquisition card is included, the computer device being connected to both the output terminal of the lock-in amplifier and the input terminal of the function generator.

[0068] This invention conducts experimental research based on the aforementioned quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupled tuning fork sensor, first exploring the performance of the electrical spectrum under humidity changes. By changing the relative humidity inside a transparent container, Figure 3 The conductivity spectra of a tuning fork enhanced with photoacoustic spectroscopy-conductivity spectroscopy combined with quartz under different humidity levels (from ~15% RH to ~80% RH) are shown. It can be seen that the resonant frequency of the tuning fork decreases with increasing humidity. Figure 4 The figure shows the trend of the resonant frequency of the tuning fork as a function of relative humidity. The resonant frequency of the tuning fork using quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy gradually decreased from 32735.2 Hz at ~15% RH to 32716.9 Hz at ~80% RH. Figure 4 The points in the equation were fitted using a linear function, yielding a slope of -0.2966, an intercept of 32739.46, and a corresponding R-squared value of 0.99. (From...) Figure 4 It is evident that the conductivity spectrum signal of the quartz-enhanced photoacoustic spectroscopy-conductivity spectrum coupled tuning fork sensor has a good linear relationship with relative humidity, and humidity can be measured through the conductivity spectrum of the tuning fork.

[0069] Figure 4The slope in the data is 0.2966, and the calculated detection sensitivity of the quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy-sensor for water molecules is 0.3% RH. We also measured the photoacoustic signal and noise at a carbon dioxide concentration of 5%, obtaining 25,723 count points and 152 count points, respectively, with a calculated detection signal-to-noise ratio (SNR) of 169, corresponding to a detection sensitivity of approximately 300 ppm for carbon dioxide.

[0070] In further experiments, we explored the performance of photoacoustic spectroscopy under varying humidity conditions. Figure 5 The photoacoustic spectra of a quartz-enhanced photoacoustic spectrum-conductivity spectrum coupled tuning fork at different humidity levels are shown. The carbon dioxide concentration was kept constant at 5%. The humidity was varied using a humidifier. Figure 6 Using relative humidity as the independent variable and keeping the carbon dioxide concentration constant, the amplitude of the photoacoustic signal was plotted. A linear function was used to fit the points, and an R-squared value of 0.99 was obtained. Figure 6 The fitted curve serves as a concentration calibration curve under different humidity levels with a fixed carbon dioxide concentration. From... Figure 6 As can be seen, the photoacoustic signal amplitude decreased from 25831.7 counts at ~33% RH to 18031.5 counts at ~80% RH. This linear decrease in photoacoustic spectral signal with increasing relative humidity differs from traditional quartz-enhanced photoacoustic spectral sensors.

[0071] After obtaining the relationship between the conductivity spectrum and photoacoustic spectrum and humidity, the performance of the sensor's electrical and photoacoustic spectra was measured under varying carbon dioxide concentrations. The photoacoustic signals of different carbon dioxide concentrations were measured at 65% RH by changing the carbon dioxide concentration inside a transparent container using a mass flow controller. Figure 7 The results show the changes in the conductivity spectrum of a tuning fork using quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy under different carbon dioxide concentrations, demonstrating that the resonant frequency of the tuning fork does not change with the carbon dioxide concentration. Figure 8 The relationship between resonant frequency and concentration is given by the function. As the carbon dioxide concentration changes from 3% to 7%, the resonant frequency remains constant, with a standard deviation less than 0.09. (Combined with...) Figure 7 and Figure 8 It can be seen that the humidity measurement by the tuning fork is not affected by the ambient gas, and the detection results are highly reliable. Figure 9 The photoacoustic spectra of carbon dioxide at different concentrations at 65% RH are shown. The photoacoustic spectral amplitudes as a function of carbon dioxide concentration are plotted on [the graph / plot]. Figure 10 In the middle, using a linear function fit, the slope was obtained as 5481.66, the intercept as -7450.05, and the R-squared value as approximately 0.99. Combined with... Figure 9 and Figure 10 It can be seen that when the humidity is constant, the measurement result of the gas to be tested has a good positive proportional relationship with its concentration.

[0072] Taking cortical cell culture as an example, the culture environment should be controlled at 65% relative humidity and 5% carbon dioxide. During the culture process, we maintain constant humidity and carbon dioxide concentration in the incubator by simultaneously detecting conductivity signals (resonance frequency) and photoacoustic signals. Table 1 shows the working process of the quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupling technology:

[0073] Table 1. Working Process of Quartz-Enhanced Photoacoustic Spectroscopy-Conductivity Spectroscopy Co-process Technology

[0074]

[0075] Firstly, through Figure 6 The carbon dioxide concentration at a preset concentration was calibrated under different humidity levels to obtain the first photoacoustic spectral signal value measured by a tuning fork at different humidity levels when the gas concentration was at the preset value. Then, the corresponding humidity value and the second photoacoustic spectral signal value of the gas were measured as required. The second photoacoustic spectral signal value was compared with the first photoacoustic spectral signal value for the corresponding humidity. If the second photoacoustic spectral signal value was lower, it indicated that the gas concentration had decreased compared to the preset value, and carbon dioxide needed to be increased; if it was higher, it indicated that the gas concentration had increased compared to the preset value, and carbon dioxide needed to be decreased; otherwise, the gas concentration remained unchanged. Additionally, if the humidity decreased, water vapor was added; if the humidity increased, water vapor was reduced; otherwise, the humidity remained unchanged.

[0076] The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork 8 described in this invention is illustrated in the following schematic diagram. Figure 11 As shown. The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupling tuning fork 8 consists of a tuning fork base 8.1, a rectangular tuning fork arm 8.2, tuning fork pins 8.3, and spider silk 8.4.

[0077] Specific embodiments of the gas detection device of the present invention are as follows: Figure 12As shown. Computer device 1 controls function generator 2 via serial communication. Function generator 2 generates the sweep signal required by preamplifier 9 and the modulation and scanning signals required by semiconductor laser 5. The sweep signal excites a tuning fork to generate a conductivity spectrum signal, which is output from tuning fork pin 8.3. The electrical signal is sent to preamplifier 9 for transimpedance amplification via tuning fork pin 8.3, and then enters lock-in amplifier 10 for demodulation. The synchronization signal of function generator 2 is connected to the reference channel of lock-in amplifier 10 for signal demodulation. Lock-in amplifier is connected to computer device 1 via serial port, transmitting the conductivity spectrum data of tuning fork to computer device 1 for display and storage. The modulation and scanning signals are added by adder 3, and the resulting drive signal is input to laser driver 4. Laser driver 4 controls the temperature and current of the laser chip. Semiconductor laser 5 driven by driver 4 emits laser light for photoacoustic spectroscopy. The laser emitted by semiconductor laser 5 is first focused by fiber optic assembly-focuser 6. The focused beam passes through transparent gas chamber 7 and irradiates the spiderweb neighborhood between the vibrating arm slots of quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork 8. The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork is located inside transparent gas chamber 7. The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy tuning fork 8 interacts with the laser, generating a photoacoustic spectral signal due to the photoacoustic effect, which is output from tuning fork pin 8.3. The photoacoustic spectral signal is sent to preamplifier 9 for transimpedance amplification via tuning fork pin 8.3, and then enters lock-in amplifier 10 for demodulation. The synchronization signal of function signal generator 2 is connected to the reference channel of lock-in amplifier 10 for signal demodulation. Lock-in amplifier is connected to computer device 1 via serial port, transmitting gas concentration data to computer device 1 for display and storage.

[0078] This invention relates to a quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupling technology and a gas detection device employing this technology. The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy coupling tuning fork of this invention features a newly designed spider silk bridge on the vibrating arm, forming a conductivity spectroscopy detection channel. The concentration of water molecules is detected through this conductivity spectroscopy channel, thus calibrating against interference from water molecules in infrared gas detection. The quartz-enhanced photoacoustic spectroscopy-conductivity spectroscopy technology based on this tuning fork can achieve the detection of various other two-component mixed gases by changing the microfilament material and the laser wavelength, effectively improving the detection capability of photoacoustic spectroscopy.

[0079] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A humidity-self-calibrating gas analysis device, characterized in that, include: Tuning fork and microfilaments; the microfilaments are spider silk; The two ends of the microfilament are bridged to the two arms of the tuning fork at the opening. Specifically, a spider silk is glued to the two arms of the quartz tuning fork using a small amount of epoxy resin, forming a channel for the electrical conductivity spectrum. A laser beam enters from the gap between the two arms, passes through the tuning fork, and is excited to form a photoacoustic spectrum channel. The microfilament is sensitive to water molecules. When the humidity of its environment increases, the microfilament stores water molecules; when the humidity of its environment decreases, the microfilament releases water molecules. The elastic modulus of the microfilament is inversely correlated with the water molecule content inside it. After the device is placed in the environment to be tested, the conductivity spectrum corresponding to the resonance frequency of the tuning fork is used to determine the water molecule concentration, i.e., humidity, of the environment to be tested. The photoacoustic spectrum signal generated by the tuning fork under the action of the light signal is used to determine the concentration of the gas to be tested in the environment to be tested. When the device is used to monitor the concentration of the gas to be measured in the environment, it first obtains the first photoacoustic spectral signal value obtained by tuning fork measurement under different humidity levels when the concentration of the gas to be measured is a preset value. Then, the device measures the conductivity spectrum of the tuning fork as required to obtain the corresponding humidity value. Next, it measures the second photoacoustic spectral signal value of the gas to be measured by tuning fork. The second photoacoustic spectral signal value is compared with the first photoacoustic spectral signal value corresponding to the humidity value. If the second photoacoustic spectral signal value is relatively smaller, it indicates that the concentration of the gas to be measured has decreased compared with the preset value. If the second photoacoustic spectral signal value is relatively larger, it indicates that the concentration of the gas to be measured has increased compared with the preset value. Otherwise, it indicates that the concentration of the gas to be measured has not changed. The device has a higher frequency response bandwidth for photoacoustic spectral signals compared to a tuning fork without bridging microfilaments, thus reducing the device's requirements for the frequency stability of the input optical signal.

2. The apparatus according to claim 1, characterized in that, The microfilaments are silkworm silk or animal hair.

3. The apparatus according to claim 1, characterized in that, The device can also be used to monitor the humidity of the environment under test.

4. The apparatus according to claim 1 or 3, characterized in that, If the humidity and gas concentration of the environment to be measured need to be maintained at the preset humidity and gas concentration; When the device is used to monitor the concentration and humidity of the gas to be measured in the environment under test, if the measured humidity changes compared to the preset humidity, the humidity of the environment under test is adjusted to reach the preset humidity; if the measured second photoacoustic spectral signal value of the gas to be measured at the current humidity changes compared to the first photoacoustic spectral signal value of the preset gas concentration at the current humidity, the concentration of the gas to be measured in the environment under test is adjusted to reach the preset gas concentration.

5. A humidity self-calibrating gas analysis method, characterized in that, Includes the following steps: The two ends of a microfilament are bridged to the two arms of a tuning fork at the opening. The microfilament is spider silk. Specifically, a spider silk is glued to the two arms of a quartz tuning fork using a small amount of epoxy resin, forming a conductivity spectrum channel. A laser beam enters through the gap between the two arms, passes through the tuning fork, and is excited, forming a photoacoustic spectrum channel. The microfilament is sensitive to water molecules; when the humidity of its environment increases, the microfilament stores water molecules; when the humidity of its environment decreases, the microfilament releases water molecules. The elastic modulus of the microfilament is inversely correlated with its internal water molecule content. The tuning fork is placed in the test environment, and the water molecule concentration, i.e. humidity, of the test environment is determined by the conductivity spectrum corresponding to the resonance frequency of the tuning fork. The concentration of the gas to be tested in the test environment is determined by the photoacoustic spectrum signal generated by the tuning fork under the action of light signal. The first photoacoustic spectral signal value is obtained by measuring the tuning fork at different humidity levels when the concentration of the gas to be tested is a preset value. Then, the corresponding humidity value and the second photoacoustic spectral signal value of the gas to be tested are obtained by measuring the tuning fork as required. The second photoacoustic spectral signal value is compared with the first photoacoustic spectral signal value corresponding to the humidity value. If it is relatively smaller, it indicates that the concentration of the gas to be tested has decreased compared with the preset value. If it is relatively larger, it indicates that the concentration of the gas to be tested has increased compared with the preset value. Otherwise, it indicates that the concentration of the gas to be tested has not changed. The microfilament is used to improve the frequency response bandwidth of the tuning fork to the photoacoustic spectral signal and reduce its frequency stability requirements for the input optical signal.

6. The method according to claim 5, characterized in that, The microfilaments are silkworm silk or animal hair.

7. The method according to claim 5, characterized in that, The tuning fork can also be used to monitor the humidity of the environment under test.

8. The method according to claim 5 or 7, characterized in that, If the humidity and gas concentration of the environment to be measured need to be maintained at the preset humidity and gas concentration; If the humidity measured by the tuning fork changes compared to the preset humidity, adjust the humidity of the environment to be measured to reach the preset humidity. If the second photoacoustic spectral signal value of the gas under the current humidity obtained by the tuning fork measurement changes compared with the first photoacoustic spectral signal value of the preset gas concentration under the current humidity value, then the concentration of the gas under test in the test environment is adjusted to reach the preset gas concentration.

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