Fourier photoacoustic gas detection device and method

Abstract

The invention discloses a Fourier photoacoustic gas detection device and method, and belongs to the technical field of gas detection. In order to solve the problems that the anti-interference capability of an existing Fourier transform photoacoustic spectrum on a sound signal is limited and the detection sensitivity is low, the Fourier photoacoustic gas detection device is designed, and a super-continuum spectrum broadband light source is used as an excitation light source of a photoacoustic effect; uniform intensity modulation of wide-spectrum light is achieved through the intensity modulation assembly, and phase modulation is achieved through the interferometer assembly. The broadband interference light emitted through double modulation acts with gas molecules to generate wide-spectrum mixed sound waves, and the quartz tuning fork sound measurement assembly extracts resonance components in the wide-spectrum mixed sound waves and converts the resonance components into electrical signals; the generated electrical signal is processed by the signal amplification assembly, the phase-sensitive demodulation assembly and the Fourier transform assembly in sequence, and component discrimination and concentration inversion of the target gas are realized by the processed signal.

Description

Technical Field

[0001] The invention belongs to the technical field of gas detection, and in particular relates to a Fourier photoacoustic gas detection device and method. Background Art

[0002] Fourier transform spectroscopy has the characteristics of high resolution, wide spectral range, and parallel multiplexing. It can meet the needs of broadband gas detection and synchronous multi-gas detection, and is an ideal method for material analysis. Although the technology is relatively mature, it still has some challenges. As the core component of Fourier transform spectroscopy technology, commercial photodetectors have limitations such as narrow spectral response range, low power tolerance, and the need for refrigeration, which seriously affect the performance of Fourier transform spectroscopy. At the same time, as a direct absorption spectroscopy technology, Fourier transform spectroscopy is limited in sensitivity by the length of the light absorption path, and needs to extract weak absorption signals from strong background light, making its sensitivity poor. As a technology without background interference and wavelength selectivity, photoacoustic spectroscopy has been widely used in the field of trace gas detection due to its advantages such as high sensitivity, fast response, and large dynamic range, such as atmospheric pollution detection, factory emission monitoring, and medical disease diagnosis. Its basic principle is to use microphones and other acoustic-electric devices as acoustic transducers to detect sound waves induced by the photoacoustic effect. Therefore, Fourier transform photoacoustic spectroscopy can achieve background-free broadband gas detection and multi-gas synchronous detection, and can work in a wide wavelength range from ultraviolet to terahertz without changing the detector.

[0003] However, most traditional Fourier transform photoacoustic spectroscopy relies on non-resonant photoacoustic modules (such as non-resonant photoacoustic cells or cantilever beams) to detect acoustic signals. This type of non-resonant acoustic detection module usually responds to low-frequency sound waves in a wide and flat manner and lacks frequency selectivity, which makes it impossible to effectively distinguish between target signals and environmental noise when picking up signals, thereby reducing the signal-to-noise ratio of the system. In addition, the non-selective acoustic response is easily interfered by environmental noise when processing weak signals, thereby affecting the sensitivity and accuracy of detection. Secondly, the traditional resonant Fourier transform photoacoustic spectroscopy uses the selective response of the resonant photoacoustic cell detection module to sound waves of a specific frequency, amplifies the target signal through resonance and shields external noise interference, greatly improving the signal-to-noise ratio and detection sensitivity of the system. At the same time, the resonant frequency of the existing resonant photoacoustic cell is usually low, and the quality factor is only a few dozen, resulting in its limited anti-interference ability under environmental noise interference, restricting its adaptability in complex environments. Summary of the invention

[0004] In view of the limited anti-interference ability of existing Fourier transform photoacoustic spectroscopy for sound signals and the low detection sensitivity, the present invention provides a Fourier transform photoacoustic gas detection device and method. By improving the structure and detection method of Fourier transform photoacoustic spectroscopy, the signal-to-noise ratio and detection sensitivity are improved, providing a new solution for broadband and high-resolution gas detection.

[0005] The present invention uses a supercontinuum broadband light source as an excitation light source, and modulates the intensity of the broadband light source under the action of an intensity modulation component, thereby achieving uniform modulation of all wavelength light components of the broadband light source, so that the mixed photoacoustic signals generated within a wide spectral range are all resonantly collected by a quartz tuning fork. Compared with the Fourier transform photoacoustic spectroscopy gas detection device based on a photoacoustic cell, a quartz tuning fork that works within a few kHz range, has sharp resonant acoustic characteristics, and has strong resistance to environmental noise interference is used to detect sound waves to improve the sensitivity of the sensing system. The present invention completes the resonant detection of the Fourier transform photoacoustic spectroscopy by improving the structure and detection method of the Fourier transform photoacoustic spectroscopy, and improves the detection sensitivity of the system and increases the dynamic range of the system through acoustic and electrical two-stage filtering.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A Fourier photoacoustic gas detection device, comprising a broadband light source, an intensity modulation component, an interferometer component, broadband interference light, a quartz tuning fork sound measurement component, a signal amplification component, a phase-sensitive demodulation component and a Fourier transform component; wherein:

[0008] The output end of the broadband light source is connected to the input end of the intensity modulation component;

[0009] The output end of the intensity modulation component is connected to the interferometer component; the intensity modulation component is used to modulate the intensity of the broadband light source so that the periodic change frequency of the intensity of the light source is equal to the resonance frequency of the quartz tuning fork;

[0010] The output end of the interferometer component outputs broadband interference light, and the broadband interference light is connected to the quartz tuning fork sound measuring component; the interferometer component phase modulates the broadband light source through a Michelson interferometer and obtains an intensity interference pattern in the time domain, and outputs broadband interference light;

[0011] The quartz tuning fork sound measuring component uses a quartz tuning fork to resonate and enhance the resonant components in the mixed sound signal generated within a broadband spectrum range, and at the same time converts the sound signal into a current signal through the piezoelectric effect and amplifies it, and its output end is connected to the input end of the signal amplification component;

[0012] The output end of the signal amplification component is connected to the input end of the phase-sensitive demodulation component, the amplified signal is subjected to phase-sensitive detection, the resonant frequency component is further extracted from the electrical level, and it is amplified again;

[0013] The output end of the phase-sensitive demodulation component is connected to the Fourier transform component, and the Fourier transform spectrum component performs Fourier transform processing on the collected mixed photoacoustic spectrum within a wide spectrum range to extract photoacoustic spectra of different light wavelengths.

[0014] Specifically, the amplitude of the photoacoustic signal after Fourier transformation is linearly related to the gas concentration. The greater the gas concentration, the greater the signal amplitude. By comparing the signal generated by the gas to be measured with the signal generated by the calibrated concentration, the concentration of the gas to be measured can be calculated, and the type of gas can be obtained by comparing with the shape and wavelength position of the standard absorption spectrum.

[0015] Furthermore, the broadband light source is a supercontinuum broadband light source, the intensity modulation component includes a modulator (which may be an optical chopper, an acousto-optic modulator, an internal electrical modulation, etc.) and a function generator, the supercontinuum broadband light source is connected to the modulator, and the function generator is used to provide a radio frequency signal for driving the modulator. In order to satisfy the requirement of resonant detection of all wavelength components of the supercontinuum broadband light source, the frequency of the radio frequency signal output by the function generator is aligned with the resonant frequency of the quartz tuning fork.

[0016] Furthermore, the interferometer component is a Michelson interferometer, and the intensity-modulated supercontinuum broadband light source is collimated and incident on the Michelson interferometer, which is used to phase modulate the supercontinuum broadband light source to obtain broadband interference light with intensity variation in the time domain.

[0017] Furthermore, the quartz tuning fork sound measuring component includes a quartz tuning fork (customized quartz tuning fork), a dual micro-acoustic resonant cavity and an air chamber component. The quartz tuning fork is used to resonate and detect the mixed sound signal generated by broadband interference light. The dual micro-acoustic resonant cavity is used to form a standing wave field to increase the amplitude of the sound wave. The air chamber component is used to accommodate the gas to be measured. The quartz tuning fork and the dual micro-acoustic resonant cavity are used to realize resonance enhanced detection of the sound wave signal. The broadband interference light after modulator intensity modulation and Michelson interferometer phase modulation is collimated and incident through the dual micro-acoustic resonant cavity and the gap between the two arms of the quartz tuning fork, which is used to maximize the photoacoustic signal and minimize thermal noise, while controlling parameters such as pressure and temperature during the absorption process.

[0018] Furthermore, the signal amplifying component is a preamplifier, the input end of the preamplifier is connected to the pin output of the quartz tuning fork, and the current signal output by the quartz tuning fork is converted into a voltage signal and amplified.

[0019] Furthermore, the phase-sensitive demodulation component is a phase-locked amplifier, the input end of the phase-locked amplifier is connected to the output end of the preamplifier, the demodulation frequency is the resonance frequency of the quartz tuning fork, and a mixed photoacoustic signal for a wide spectral range is obtained.

[0020] Furthermore, the Fourier transform component includes an analog-to-digital converter and a Fourier transform electronic unit. The input end of the analog-to-digital converter is connected to the output end of the phase-locked amplifier to convert the analog signal output by the phase-locked amplifier into an electronic signal. The Fourier transform electronic unit is used to perform Fourier transform on the photoacoustic signal to achieve extraction of mixed photoacoustic signals within a wide spectral range.

[0021] Furthermore, the quartz tuning fork photodetector assembly has full spectrum response capability.

[0022] A Fourier photoacoustic gas detection method, the method comprising the following steps:

[0023] Step 1: Fill the gas sample to be tested into the gas chamber of the quartz tuning fork sound measuring component;

[0024] Step 2: The supercontinuum broadband light source is connected to the modulator to perform intensity modulation of all wavelength components of the supercontinuum broadband light source at a uniform frequency;

[0025] Step 3: The intensity-modulated supercontinuum broadband light source is incident on the Michelson interferometer to perform phase modulation on the supercontinuum broadband light source. By scanning the moving mirror in the interferometer, broadband interference light with regular intensity changes in the time domain is obtained.

[0026] Step 4: The broadband interference light is collimated and incident through the double micro-acoustic resonant cavity and the gap between the two arms of the quartz tuning fork, and interacts with the gas molecules therein, generating a mixed sound wave through the photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork, the resonant component in the mixed sound wave is detected by the quartz tuning fork and an electrical signal is output from its pin;

[0027] Step 5: Amplify the mixed sound wave through a preamplifier, and then demodulate the amplified electrical signal through a lock-in amplifier;

[0028] Step 6: Perform analog-to-digital conversion on the signal demodulated by the phase-locked amplifier, and then perform Fourier transform on the signal to obtain a spectrum in the frequency domain. Analyze the signal to invert the type and concentration of the gas.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The present invention provides a Fourier photoacoustic gas detection device and method, which uses a quartz tuning fork as an acoustic transducer to realize resonant detection of a mixed photoacoustic spectrum within a wide spectral range. The supercontinuum broadband light source is uniformly modulated by an intensity modulation component, so that the sound wave generated by each wavelength component of the broadband light source during the photoacoustic effect is equal to the resonant frequency of the quartz tuning fork. The broadband light source is phase modulated and converted into broadband interference light by a Michelson interferometer. Therefore, after the broadband interference light after intensity modulation and phase modulation interacts with gas molecules, a mixed sound wave within a wide spectral range will be generated due to the photoacoustic effect, wherein the acoustic component resonating with the quartz tuning fork will be acoustically enhanced, and on the basis of acoustic filtering of environmental noise, the amplitude of the photoacoustic signal can be effectively improved, thereby improving the sensitivity of the system. At the same time, the signal amplification component amplifies the signal output by the quartz tuning fork, and further uses a phase-locked amplifier for phase-sensitive demodulation. In this process, the noise level is reduced and the system signal-to-noise ratio is improved. Then, the Fourier transform component converts the photoacoustic signal output by the phase-locked amplifier into a digital signal, and further performs Fourier transform processing, and finally obtains a frequency domain photoacoustic signal that characterizes the concentration and type of the gas to be measured. Such resonant detection and Fourier transform methods realize broadband gas detection and multi-gas synchronous detection, and improve the scope of application of the system. In summary, the present invention has important scientific and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a Fourier photoacoustic gas detection device provided by the present invention; wherein: a supercontinuum broadband light source-1, a modulator-2, a function generator-3, a Michelson interferometer-4, a broadband interference light-5, a gas chamber component-6, a double micro-acoustic resonant cavity-7, a quartz tuning fork-8, a preamplifier-9, a lock-in amplifier-10, an analog-to-digital converter-11, and a Fourier transform electronic unit-12;

[0032] Figure 2 This is a schematic diagram of the broadband interference light collimated incident on the quartz tuning fork of the present invention. DETAILED DESCRIPTION

[0033] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0034] The present invention provides a Fourier photoacoustic gas detection device, such as Figure 1As shown, it includes a supercontinuum broadband light source 1, a modulator 2, a function generator 3, a Michelson interferometer 4, broadband interference light 5, an air chamber assembly 6, a double micro-acoustic resonant cavity 7, a quartz tuning fork 8, a preamplifier 9, a phase-locked amplifier 10, an analog-to-digital converter 11, and a Fourier transform electronic unit 12.

[0035] The supercontinuum broadband light source 1 is used to uniformly modulate the intensity of all wavelength components of the supercontinuum broadband light source 1 through the modulator 2. By changing the frequency of the function generator 3, the frequency of the periodic change of the broadband light intensity is changed, so that the frequency of all wavelength components of the broadband light source 1 is equal to the resonance frequency of the quartz tuning fork 8. The broadband light after intensity modulation enters the Michelson interferometer 4, which performs phase modulation and interference on the broadband light and outputs broadband interference light 5. Then, the broadband interference light 5 enters the air chamber assembly 6, and is collimated to pass through the double micro-acoustic resonant cavity 7 and the gap between the vibration arms of the quartz tuning fork 8, as shown in FIG. Figure 2 As shown. After the gas molecules to be measured near the vibrating arm of the quartz tuning fork 8 interact with the broadband interference light 5, sound waves are released to the surroundings through thermal relaxation. Through the piezoelectric effect, the electrical signal output generated by the quartz tuning fork 8 is connected to the preamplifier 9, and then sent to the phase-locked amplifier 10 for demodulation. The demodulated signal is sent to the analog-to-digital converter 11 to be converted into a digital signal, and finally the digital signal is sent to the Fourier transform electronic unit 12 for Fourier transform.

[0036] A Fourier photoacoustic gas detection method, the specific implementation process is as follows:

[0037] Step 1: Fill the gas sample to be tested into the gas chamber component 6 of the quartz tuning fork sound measuring component; adjust the driving frequency of the function generator 3 and apply it to the modulator 2 to modulate the intensity of the broadband light source 1 so that the frequency of the broadband light intensity change is equal to the resonance frequency of the quartz tuning fork 8.

[0038] Step 2: Use a Michelson interferometer 4 to perform phase modulation and interference on the broadband light, obtain an interference pattern in the time domain, and output broadband interference light 5.

[0039] Step 3: Due to the photoacoustic effect, the modulated broadband interference light 5 interacts with the gas molecules to generate mixed sound waves in a wide spectral range, and the quartz tuning fork 8 extracts the resonant components. In order to achieve effective detection and minimize detection noise, the broadband interference light 5 needs to be collimated to pass through the gap between the dual micro-acoustic resonant cavity 7 and the two arms of the quartz tuning fork 8, such as Figure 2 shown.

[0040] Step 4: Use the phase-locked amplifier 10 to perform primary harmonic demodulation on the output of the preamplifier 9 , and the demodulation frequency is the resonance frequency of the quartz tuning fork 8 .

[0041] Step 5: The output of the lock-in amplifier 10 is sent to the analog-to-digital converter 11 and the Fourier transform electronic unit 12 in sequence for Fourier transform processing.

[0042] Step 6: The signal amplitude in the frequency domain is linearly related to the gas concentration. By comparing the signal generated by the gas to be tested with the signal generated by the calibration concentration, the concentration of the gas to be tested can be calculated. The type of gas can be obtained by comparing the spectral wavelength position and the shape of the standard absorption spectrum.

[0043] In the present invention, the modulator 2 applies the intensity modulation necessary for generating photoacoustic signals to all wavelength components of the supercontinuum broadband light source 1, thereby generating a mixed sound wave in a wide spectral range. The acoustic components in the mixed sound wave that resonate with the quartz tuning fork 8 will be resonantly accumulated due to the high Q value of the quartz tuning fork 8, which improves the detection sensitivity compared to the non-resonant method.

[0044] In the present invention, the broadband interference light 5 is collimated and incident on the quartz tuning fork 8, and generates mixed sound waves in a wide spectral range through the photoacoustic effect with the gas nearby.

[0045] In the present invention, broadband light is phase modulated and interfered by a Michelson interferometer 4 through step scanning to obtain broadband interference light 5 in the time domain, and the mixed photoacoustic signal generated by the broadband interference light 5 is used to realize single-frequency photoacoustic signal pickup through a Fourier transform scheme.

[0046] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A Fourier photoacoustic gas detection device, characterized in that: The device comprises a broadband light source, an intensity modulation component, an interferometer component, broadband interference light, a quartz tuning fork sound measurement component, a signal amplification component, a phase-sensitive demodulation component and a Fourier transform component; wherein: The output end of the broadband light source is connected to the input end of the intensity modulation component; The output end of the intensity modulation component is connected to the interferometer component; The output end of the interferometer component is connected to the quartz tuning fork sound measuring component; The broadband interference light is connected to the quartz tuning fork sound measuring component; The output end of the quartz tuning fork sound measuring component is connected to the input end of the signal amplifying component; The output end of the signal amplification component is connected to the input end of the phase-sensitive demodulation component; The output end of the phase-sensitive demodulation component is connected to the Fourier transform component.

2. A Fourier photoacoustic gas detection device according to claim 1, characterized in that: The broadband light source is a supercontinuum broadband light source (1), and the intensity modulation component comprises a modulator (2) and a function generator (3). The function generator (3) is used to provide a radio frequency signal for driving the modulator (2), and to tune the frequency of the radio frequency signal so as to complete resonance detection of all wavelength components of the supercontinuum broadband light source (1).

3. A Fourier photoacoustic gas detection device according to claim 2, characterized in that: The interferometer component is a Michelson interferometer (4), which is used to perform phase modulation on a supercontinuum broadband light source (1) and obtain an intensity interference pattern in the time domain, and output broadband interference light (5).

4. A Fourier photoacoustic gas detection device according to claim 3, characterized in that: The quartz tuning fork acoustic measurement component comprises a quartz tuning fork (8), a dual micro-acoustic resonant cavity (7) and an air chamber component (6); the quartz tuning fork (8) is used for resonantly detecting a mixed acoustic signal generated by broadband interference light (5); the dual micro-acoustic resonant cavity (7) is used for forming a standing wave acoustic field; and the air chamber component (6) is used for containing a gas to be measured.

5. A Fourier photoacoustic gas detection device according to claim 4, characterized in that: The signal amplification component is a preamplifier (9), and the input end of the preamplifier (9) is connected to the pin output of the quartz tuning fork (8).

6. A Fourier photoacoustic gas detection device according to claim 5, characterized in that: The phase-sensitive demodulation component is a lock-in amplifier (10), and the input end of the lock-in amplifier (10) is connected to the output end of the preamplifier (9).

7. A Fourier photoacoustic gas detection device according to claim 6, characterized in that: The Fourier transform component comprises an analog-to-digital converter (11) and a Fourier transform electronic unit (12), which are used to perform analog-to-digital conversion and Fourier transform on the signal output by the lock-in amplifier (10).

8. The Fourier photoacoustic gas detection device according to claim 6, characterized in that: The quartz tuning fork photodetector assembly has full spectrum response capability.

9. A Fourier photoacoustic gas detection method, characterized in that: The method comprises the following steps: Step 1: Filling the gas sample to be tested into the gas chamber component (6) of the quartz tuning fork sound measuring component; Step 2: connecting the supercontinuum broadband light source (1) to the modulator (2) to perform intensity modulation of all wavelength components of the supercontinuum broadband light source (1) at a uniform frequency; Step 3: The intensity-modulated supercontinuum broadband light source (1) is incident on a Michelson interferometer (4), and phase modulation is performed on the supercontinuum broadband light source (1). By scanning a moving mirror in the interferometer, a broadband interference light (5) with a regular intensity variation in the time domain is obtained; Step 4: The broadband interference light (5) is collimated and incident through the double micro-acoustic resonant cavity (7) and the gap between the two arms of the quartz tuning fork (8), and interacts with the gas molecules therein to generate a mixed sound wave through the photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork (8), the resonant component in the mixed sound wave is detected by the quartz tuning fork (8) and an electrical signal is output from its pin; Step 5: amplifying the mixed sound wave through a preamplifier (9), and then demodulating the amplified electrical signal through a lock-in amplifier (10); Step 6: Perform analog-to-digital conversion on the demodulated signal of the lock-in amplifier (10), then perform Fourier transform on the signal to obtain a spectrum in the frequency domain, analyze the signal, and invert the type and concentration of the gas.

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