甲烷是瓦斯的主要成分和温室气体之一,检测甲烷浓度对于工业生产安全和人员的生命健康保障均具有重要意义。本文设计了一种用于甲烷检测的共轴石英音叉增强光声光谱系统,利用石英音叉较高的品质因数克服了传统光声光谱技术中麦克风易受环境噪声干扰的缺点。设计了小型化气室,其体积仅为3 cm×2 cm×1 cm,简化了检测系统的结构。结合波长调制技术,分析了二次谐波信号幅值与调制深度的关系,实验得到的最佳调制电压幅度为0.175 V,对应的调制深度为0.169 cm -1。对甲烷浓度(体积分数为5×10 -4~5×10 -3)和二次谐波信号幅值进行拟合,线性度为0.99791;采用Allan方差分析了系统的稳定性,当平均时间为5 s时,系统的检测下限为4.337×10 -5。基于小体积光声池的光声光谱气体传感器具有体积小、质量轻、成本低的优点,更适合于便携式传感应用。

Methane (CH₄) is the main component of mine gas and one of greenhouse gases, and the measurement of CH₄ concentration is of great significance for industrial production safety and human health security. In this paper, an on-beam quartz tuning fork enhanced photoacoustic spectroscopic system for CH₄ detection was proposed, and a quartz tuning fork with a high quality factor was used to overcome the shortcomings of the traditional photoacoustic spectroscopy where microphones were susceptible to environmental noise. Furthermore, a miniaturized gas chamber with a volume of only 3 cm×2 cm×1 cm was developed, which simplified the structure of the detection system. Combining the wavelength modulation technology, we analyzed the relationship between the amplitude of second harmonic (2f) signal and the modulation depth. The experimental results demonstrate that the amplitude of optimal modulation signal was 0.175 V and the corresponding modulation depth was 0.169 cm ^-1. In addition, the CH₄ volume fraction in the range of 5×10 ^-4-5×10 ^-3 and the 2f signal amplitude were fitted and their linearity was found to be 0.99791. Besides, the stability of the system was analyzed based on Allan variance. When the average time was 5 s, the 1σ lower detection limit of the system was 4.337×10 ^-5. In summary, the photoacoustic spectroscopic gas sensor based on a small-volume photoacoustic gas cell has the advantages of small size, light weight and low cost, which is more suitable for portable sensing applications.