Fourier photoacoustic gas detection device and method

Abstract

The application discloses a Fourier photoacoustic gas detection device and method, and belongs to the technical field of gas detection. In view of the limited anti-interference ability of a sound signal and the low detection sensitivity of an existing Fourier transform photoacoustic spectrum, a Fourier photoacoustic gas detection device is designed. A supercontinuum broadband light source is used as an excitation light source of a photoacoustic effect, the broadband light source is subjected to unified intensity modulation through an intensity modulation assembly and phase modulation through an interferometer assembly. After the broadband interference light emitted through double modulation interacts with gas molecules, wide-spectrum mixed sound waves are generated, a quartz tuning fork sound measurement assembly extracts resonance components and converts the resonance components into electrical signals. The generated electrical signals are sequentially subjected to processing through a signal amplification assembly, a phase-sensitive demodulation assembly and a Fourier transform assembly, and the processed signals are used for component discrimination and concentration inversion of a target gas.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically relating to a Fourier photoacoustic gas detection device and method. Background Technology

[0002] Fourier transform spectroscopy, with its high resolution, wide spectral range, and parallel multiplexing capabilities, meets the needs of broadband gas detection and simultaneous multi-gas detection, making it an ideal method for material analysis. Although this technology is relatively mature, some challenges remain. Commercial photodetectors, as the core component of Fourier transform spectroscopy, suffer from limitations such as narrow spectral response range, low power tolerance, and the need for cooling, severely impacting its performance. Meanwhile, as a direct absorption spectroscopy technique, Fourier transform spectroscopy's sensitivity is limited by the light absorption path length and requires extracting weak absorption signals from strong background light, resulting in relatively poor sensitivity. Photoacoustic spectroscopy, as a technique without background interference and wavelength selectivity, has been widely applied in trace gas detection fields due to its high sensitivity, fast response, and large dynamic range, such as in air pollution detection, factory emission monitoring, and medical disease diagnosis. Its basic principle is to use acoustic transducers such as microphones 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 simultaneous detection of multiple gases, and can operate in a wide wavelength range from ultraviolet to terahertz without the need to replace the detector.

[0003] However, traditional Fourier transform photoacoustic spectroscopy mostly relies on non-resonant photoacoustic modules (such as non-resonant photoacoustic cells or cantilever beams) for acoustic signal detection. These non-resonant acoustic detection modules typically have a broad and flat response to low-frequency sound waves, lacking frequency selectivity. This makes it difficult to effectively distinguish between target signals and environmental noise when picking up signals, thus reducing the system's signal-to-noise ratio (SNR). Furthermore, the non-selective acoustic response is easily interfered with by environmental noise when processing weak signals, affecting detection sensitivity and accuracy. Secondly, traditional resonant Fourier transform photoacoustic spectroscopy utilizes the selective response of resonant photoacoustic cell detection modules to specific frequency sound waves. This amplifies the target signal through resonance and shields against external noise interference, significantly improving the system's SNR and detection sensitivity. However, existing resonant photoacoustic cells typically have low resonant frequencies and quality factors of only tens, resulting in limited anti-interference capabilities under environmental noise, restricting their adaptability in complex environments. Summary of the Invention

[0004] To address the limitations of existing Fourier transform photoacoustic spectroscopy in resisting interference with sound signals and its low detection sensitivity, this 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 enhanced, providing a novel solution for broadband, high-resolution gas detection.

[0005] This invention uses a supercontinuum broadband light source as the excitation source. Under the action of an intensity modulation component, the broadband light source is intensity modulated, thereby achieving unified modulation of all wavelength components of the broadband light source. This ensures that the mixed photoacoustic signals generated over a wide spectral range are resonantly collected by the quartz tuning fork. Compared to Fourier transform photoacoustic spectroscopy gas detection devices based on photoacoustic cells, this invention uses a quartz tuning fork, which operates in the several kHz range, possesses sharp resonant acoustic characteristics, and has strong resistance to environmental noise interference, to detect sound waves, thus improving the sensitivity of the sensing system. This invention, by improving the structure and detection method of Fourier transform photoacoustic spectroscopy, achieves resonant detection of Fourier transform photoacoustic spectra. Through acoustic and electrical two-stage filtering, the detection sensitivity of the system is improved, and the dynamic range of the system is increased.

[0006] To achieve the above objectives, the present invention employs the following technical solutions:

[0007] A Fourier photoacoustic gas detection device, comprising a broadband light source, an intensity modulation component, an interferometer component, a broadband interference beam, a quartz tuning fork acoustic 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 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 frequency of the light source intensity changes is equal to the resonant frequency of the quartz tuning fork.

[0010] The output of the interferometer assembly is broadband interference light, which is connected to the quartz tuning fork acoustic measurement assembly. The interferometer assembly performs phase modulation on the broadband light source and obtains an intensity interferogram in the time domain through a Michelson interferometer, and then outputs broadband interference light.

[0011] The quartz tuning fork acoustic measurement component uses a quartz tuning fork to enhance the resonance components in the mixed acoustic signal generated in a broadband spectral range. At the same time, it converts the sound signal into an electric current signal through the piezoelectric effect and amplifies it. Its output terminal is connected to the input terminal of the signal amplification component.

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

[0013] The output of the phase-sensitive demodulation component is connected to the Fourier transform component. The Fourier transform spectral component performs Fourier transform processing on the acquired mixed photoacoustic spectrum over a wide spectral range to extract photoacoustic spectra of different wavelengths.

[0014] Specifically, the amplitude of the photoacoustic signal after Fourier transform is linearly related to the gas concentration. The higher 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. The type of gas is obtained by comparing it with the shape and wavelength position of the standard absorption spectrum.

[0015] Furthermore, the broadband light source is a supercontinuum broadband light source, and the intensity modulation component includes a modulator (which may be an optical chopper, an acousto-optic modulator, an internal electrical modulator, 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 to drive the modulator. In order to ensure 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, in which the intensity-modulated supercontinuum broadband light source is collimated and incident on the Michelson interferometer to perform phase modulation on the supercontinuum broadband light source, thereby obtaining broadband interference light with intensity variation in the time domain.

[0017] Furthermore, the quartz tuning fork acoustic measurement component includes a quartz tuning fork (using a custom-made quartz tuning fork), dual micro acoustic resonators, and a gas chamber assembly. The quartz tuning fork is used to resonate and detect the mixed acoustic signal generated by broadband interference light. The dual micro acoustic resonators are used to form a standing wave field to enhance the amplitude of the acoustic wave. The gas chamber assembly is used to contain the gas to be measured. The quartz tuning fork and dual micro acoustic resonators are used to achieve resonant enhancement detection of the acoustic wave signal. The broadband interference light, after intensity modulation by the modulator and phase modulation by the Michelson interferometer, is collimated and incident through the gap between the two arms of the dual micro acoustic resonators and the quartz tuning fork, in order 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 amplification component is a preamplifier, the input terminal of which is connected to the pin output of the quartz tuning fork. 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 lock-in amplifier, the input of which is connected to the output of the preamplifier, and the demodulation frequency is the resonant frequency of the quartz tuning fork, thus obtaining a mixed photoacoustic signal for use in a wide spectral range.

[0020] Furthermore, the Fourier transform component includes an analog-to-digital converter and a Fourier transform electronic unit. The input terminal of the analog-to-digital converter is connected to the output terminal of the lock-in amplifier, converting the analog signal output by the lock-in amplifier into an electronic signal. The Fourier transform electronic unit is used to perform Fourier transform on the photoacoustic signal to extract mixed photoacoustic signals over a wide spectral range.

[0021] Furthermore, the quartz tuning fork acoustic measurement component has a full-spectrum response capability.

[0022] A Fourier transform 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 acoustic assembly;

[0024] Step 2: Connect the supercontinuum broadband light source to the modulator and perform intensity modulation on 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. The phase of the supercontinuum broadband light source is modulated, and broadband interference light with regular intensity changes in the time domain is obtained by scanning the moving mirror in the interferometer.

[0026] Step 4: The broadband interference light is collimated and incident through the dual micro acoustic resonator and the gap between the two arms of the quartz tuning fork, and interacts with the gas molecules therein to generate mixed sound waves through the photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork, the resonant component in the mixed sound waves is detected by the quartz tuning fork and an electrical signal is output from its pins.

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

[0028] Step 6: Perform analog-to-digital conversion on the demodulated signal from the lock-in amplifier, then perform Fourier transform on the signal to obtain the spectrum in the frequency domain, analyze the signal, and infer the type and concentration of the gas.

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

[0030] This invention provides a Fourier photoacoustic gas detection device and method, employing a quartz tuning fork as an acoustic transducer to achieve resonant detection of mixed photoacoustic spectra across a broad spectral range. A supercontinuum broadband light source is uniformly modulated by an intensity modulation component, ensuring that the sound waves generated by each wavelength component of the broadband light source during the photoacoustic effect are equal to the resonant frequency of the quartz tuning fork. A Michelson interferometer is used to phase-modulate the broadband light source and convert it into broadband interference light. Therefore, after the intensity- and phase-modulated broadband interference light interacts with gas molecules, a mixed sound wave across a broad spectral range is generated due to the photoacoustic effect. The acoustic component resonating with the quartz tuning fork is acoustically amplified, effectively increasing the amplitude of the photoacoustic signal in addition to acoustically filtering environmental noise, thereby improving the system's sensitivity. Simultaneously, a signal amplification component amplifies the signal output from the quartz tuning fork and further uses a lock-in amplifier for phase-sensitive demodulation. This process reduces noise levels and improves the system's signal-to-noise ratio. Then, the Fourier transform component converts the photoacoustic signal output from the lock-in amplifier into a digital signal, and further performs Fourier transform processing to finally obtain a frequency-domain photoacoustic signal characterizing the concentration and type of the gas to be measured. This resonant detection and Fourier transform approach enables broadband gas detection and simultaneous detection of multiple gases, improving the system's applicability. In summary, this invention has significant scientific and engineering application value. Attached Figure Description

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

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

[0033] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0034] This 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, a broadband interference light 5, a gas chamber assembly 6, a dual micro acoustic resonator 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.

[0035] The supercontinuum broadband light source 1 undergoes uniform intensity modulation of all wavelength components of the light source 1 via modulator 2. By changing the frequency of function generator 3, the frequency of the periodic change in broadband light intensity is altered, ensuring that the frequencies of all wavelength components of the broadband light source 1 are equal to the resonant frequencies of the quartz tuning fork 8. The intensity-modulated broadband light then enters the Michelson interferometer 4, where phase modulation and interference are performed, outputting broadband interference light 5. This broadband interference light 5 then enters the gas chamber assembly 6 and is collimated through the gap between the dual micro acoustic resonator 7 and the vibrating arm of the quartz tuning fork 8, as shown in the image. Figure 2 As shown, after the gas molecules near the vibrating arm of the quartz tuning fork 8 interact with the broadband interference light 5, they release sound waves 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 lock-in 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 transform photoacoustic gas detection method, the specific implementation process of which is as follows:

[0037] Step 1: Fill the gas sample to be tested into the gas chamber assembly 6 of the quartz tuning fork acoustic 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 resonant 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 to obtain an interferogram 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 gas molecules to generate mixed sound waves across a wide spectral range, which are then extracted by the quartz tuning fork 8. To achieve effective detection and minimize detection noise, the broadband interference light 5 needs to be collimated through the gap between the two arms of the dual micro-acoustic resonators 7 and the quartz tuning fork 8. Figure 2 As shown.

[0040] Step 4: Use lock-in amplifier 10 to perform a harmonic demodulation on the output of preamplifier 9. The demodulation frequency is the resonant frequency of quartz tuning fork 8.

[0041] Step 5: The output of the lock-in amplifier 10 is sequentially fed into the analog-to-digital converter 11 and the Fourier transform electronic unit 12 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 measured with the signal generated by the calibrated concentration, the concentration of the gas to be measured can be calculated. The type of gas is obtained by comparing the position of the spectral wavelength and the shape of the standard absorption spectrum.

[0043] In this invention, modulator 2 applies intensity modulation to all wavelength components of the supercontinuum broadband light source 1, necessary for generating photoacoustic signals, thereby producing mixed sound waves across a wide spectral range. The acoustic components in the mixed sound waves that resonate with the quartz tuning fork 8 will accumulate resonantly due to the high Q value of the quartz tuning fork 8, thus improving detection sensitivity compared to non-resonant methods.

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

[0045] In this 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. The mixed photoacoustic signal generated by the broadband interference light 5 is then used to pick up the photoacoustic signal of single-frequency light through a Fourier transform scheme.

[0046] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A Fourier transform photoacoustic gas detection device, characterized in that: The device includes a broadband light source, an intensity modulation component, an interferometer component, a broadband interference beam, a quartz tuning fork acoustic 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 terminal of the intensity modulation component is connected to the interferometer component; The output end of the interferometer assembly is connected to the quartz tuning fork acoustic measurement assembly. The broadband interference light is connected to the quartz tuning fork acoustic measurement component; The output terminal of the quartz tuning fork acoustic measurement component is connected to the input terminal of the signal amplification component; The output terminal of the signal amplification component is connected to the input terminal of the phase-sensitive demodulation component; The output of the phase-sensitive demodulation component is connected to the Fourier transform component; The quartz tuning fork acoustic measurement assembly includes a quartz tuning fork (8), a dual micro acoustic resonator (7), and a gas chamber assembly (6). The quartz tuning fork (8) is used to resonate and detect the mixed acoustic signal generated by the broadband interference light (5). The dual micro acoustic resonator (7) is used to form a standing wave sound field. The gas chamber assembly (6) is used to contain the gas to be measured. Broadband interference light is collimated and incident through the gap between the two arms of the dual micro acoustic resonators and the quartz tuning fork, and interacts with the gas molecules therein to generate mixed sound waves through the photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork, the resonant component in the mixed sound waves is detected by the quartz tuning fork and an electrical signal is output from its pins.

2. The Fourier transform photoacoustic gas detection device according to claim 1, characterized in that: The broadband light source is a supercontinuum broadband light source (1). The intensity modulation component includes a modulator (2) and a function generator (3). The function generator (3) is used to provide a radio frequency signal to drive the modulator (2). The frequency of the radio frequency signal is tuned so that all wavelength components of the supercontinuum broadband light source (1) are resonantly detected.

3. The Fourier transform 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 the supercontinuum broadband light source (1) and obtain an intensity interferogram in the time domain, and output broadband interferometric light (5).

4. The Fourier transform photoacoustic gas detection device according to claim 3, characterized in that: The signal amplification component is a preamplifier (9), and the input terminal of the preamplifier (9) is connected to the pin output of the quartz tuning fork (8).

5. The Fourier transform photoacoustic gas detection device according to claim 4, characterized in that: The phase-sensitive demodulation component is a lock-in amplifier (10), and the input terminal of the lock-in amplifier (10) is connected to the output terminal of the preamplifier (9).

6. The Fourier transform photoacoustic gas detection device according to claim 5, characterized in that: The Fourier transform component includes an analog-to-digital converter (11) and a Fourier transform electronic unit (12) for performing analog-to-digital conversion and Fourier transform on the signal output by the lock-in amplifier (10).

7. The Fourier transform photoacoustic gas detection device according to claim 6, characterized in that: The quartz tuning fork acoustic measurement component has a full-spectrum response capability.

8. A Fourier transform photoacoustic gas detection method, characterized in that: The method is implemented based on a Fourier photoacoustic gas detection device according to any one of claims 1-7, and includes the following steps: Step 1: Fill the gas sample to be tested into the gas chamber assembly (6) of the quartz tuning fork acoustic assembly; Step 2: Connect 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 the Michelson interferometer (4) to perform phase modulation on the supercontinuum broadband light source (1). By scanning the moving mirror in the interferometer, broadband interference light (5) with regular intensity changes in the time domain is obtained. Step 4: The broadband interference light (5) is collimated and incident through the gap between the two arms of the dual micro acoustic resonator (7) and the quartz tuning fork (8), and interacts with the gas molecules therein to generate mixed sound waves through photoacoustic effect. Due to the piezoelectric effect of the quartz tuning fork (8), the resonant component in the mixed sound waves is detected by the quartz tuning fork (8) and outputs an electrical signal from its pin. Step 5: The mixed sound wave is amplified by a preamplifier (9), and then the amplified electrical signal is demodulated by a lock-in amplifier (10); Step 6: Perform analog-to-digital conversion on the demodulated signal from the lock-in amplifier (10), then perform Fourier transform on the signal to obtain the spectrum in the frequency domain, analyze the signal, and infer the type and concentration of the gas.

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