Chen Xiang, Liu Hao, Hu Mai, Yao Lu, Xu Zhenyu, Deng Hao, Kan Ruifeng
Jinlin Institute of Technology, Nanjing 211169, China.
Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China.
Sensors (Basel). 2022 May 26;22(11):4030. doi: 10.3390/s22114030.
To achieve multi-gas measurements of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors under a frequency-division multiplexing mode with a narrow modulation frequency interval, we report a frequency-domain detection method. A CH absorption line at 1653.72 nm and a CO absorption line at 2004.02 nm were investigated in this experiment. A modulation frequency interval of as narrow as 0.6 Hz for CH and CO detection was achieved. Frequency-domain 2 signals were obtained with a resolution of 0.125 Hz using a real-time frequency analyzer. With the multiple linear regressions of the frequency-domain 2 signals of various gas mixtures, small deviations within 2.5% and good linear relationships for gas detection were observed under the frequency-division multiplexing mode. Detection limits of 0.6 ppm for CH and 2.9 ppm for CO were simultaneously obtained. With the 0.6-Hz interval, the amplitudes of QEPAS signals will increase substantially since the modulation frequencies are closer to the resonant frequency of a QTF. Furthermore, the frequency-domain detection method with a narrow interval can realize precise gas measurements of more species with more lasers operating under the frequency-division multiplexing mode. Additionally, this method, with a narrow interval of modulation frequencies, can also realize frequency-division multiplexing detection for QEPAS sensors under low pressure despite the ultra-narrow bandwidth of the QTF.
为了在窄调制频率间隔的频分复用模式下实现石英增强光声光谱（QEPAS）传感器的多气体测量，我们报告了一种频域检测方法。本实验研究了1653.72 nm处的CH吸收线和2004.02 nm处的CO吸收线。实现了用于CH和CO检测的低至0.6 Hz的调制频率间隔。使用实时频率分析仪以0.125 Hz的分辨率获得了频域2信号。通过对各种气体混合物的频域2信号进行多元线性回归，在频分复用模式下观察到气体检测的偏差在2.5%以内且具有良好的线性关系。同时获得了CH的检测限为0.6 ppm和CO的检测限为2.9 ppm。在0.6 Hz的间隔下，由于调制频率更接近石英晶体谐振器（QTF）的谐振频率，QEPAS信号的幅度将大幅增加。此外，具有窄间隔的频域检测方法可以在频分复用模式下通过更多激光器实现对更多种类气体的精确测量。此外，这种调制频率间隔窄的方法，尽管QTF的带宽超窄，也能在低压下实现QEPAS传感器的频分复用检测。
