研究目的
To realize the remote detection of dangerous goods at an airport by exploring a new technical prototype based on photoacoustic spectroscopy telemetry for dangerous goods, specifically detecting trace acetylene gas.
研究成果
The study successfully demonstrated a novel photoacoustic spectroscopy telemetry method for detecting trace acetylene gas at a distance of 6 m using a QTF, with results consistent with standard absorption coefficients. It provides a foundation for remote detection of dangerous goods, with plans for future quantitative analysis.
研究不足
The acetylene used contained trace impurities, and the method is currently qualitative; future work is needed for quantitative analysis. The system's sensitivity and range may be limited by noise and optical path adjustments.
1：Experimental Design and Method Selection:
The system uses a laser as an excitation source modulated by an electro-optic modulator to match the resonance frequency of a quartz tuning fork (QTF). Laser light scattered from the detected object is collected by an astronomical telescope at 6 m distance, and the QTF's vibration generates a voltage signal due to piezoelectric effects, which is amplified and processed to perform photoacoustic spectroscopy.
2：Sample Selection and Data Sources:
Acetylene gas produced from calcium carbide was used, containing trace impurities like hydrogen sulfide and phosphine, but these do not absorb at 1532 nm.
3：List of Experimental Equipment and Materials:
Includes a 1532-nm CW-DFB fiber-coupled diode laser (12 mW power), electro-optic modulator, astronomical telescope, QTF, preamplifier circuit, band-pass filter, phase-locked amplifier, computer, alignment jig, and colorimetric ware.
4：Experimental Procedures and Operational Workflow:
The laser wavelength is tuned by changing temperature, modulated light is absorbed by acetylene, scattered light is collected by the telescope, and the QTF's voltage signal is measured and analyzed.
5：Data Analysis Methods:
Signal-to-noise ratio (SNR) is calculated using SNR = 20 log(Vs/Vn), and minimum detectable concentration is derived from Smin = C/SNR; data is processed with a phase-locked amplifier and computer.
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diode laser
CW-DFB, fiber-coupled
Huaying
Used as the excitation source for photoacoustic spectroscopy.
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electro-optic modulator
SOFN Instruments Co.
Modulates the frequency of the light intensity to match the resonance frequency of the QTF.
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astronomical telescope
Collects laser light scattered on the surface of the detected object at a distance.
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quartz tuning fork
commercial quartz crystal oscillator
Acts as a light sound detector; vibrations generate a voltage signal due to piezoelectric effects.
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preamplifier circuit
Amplifies the weak voltage signal from the QTF.
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band-pass filter
Reduces noise by filtering frequencies outside the central band.
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phase-locked amplifier
Processes the amplified signal for analysis.
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computer
Used for data processing and analysis.
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alignment jig
Adjusts the optical path for the laser and telescope.
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