Simulation and Experimental Study of Quartz-Enhanced Photoacoustic Spectroscopy Technique for Human Exhale Breath Gas Sensing

This article presents the simulation and experimental study of quartz-enhanced photoacoustic spectroscopy (QEPAS) technical. This technique has gained interest in the area of gas sensing in the recent few years due to its highly selective and sensitive measurements offered by the quartz tuning fork (QTF). The experimental study is conducted using a quantum cascade laser (QCL) source operating in $8 \mu \mathrm{~m}$ for measuring acetone $\left(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\right)$, ammonia $\left(\mathrm{NH}_{3}\right)$, and methane $\left(\mathrm{CH}_{4}\right)$ in low and high concentrations. The voltage produced for different concentrations of gases by the QTF due to the piezoelectric effect is experimentally obtained and recorded. The Opto-acoustic module consisting of the QTF and the pressure generation by the gas molecules is modelled and designed using the COMSOL Multiphysics software. The photoacoustic pressure generated by gas induces potential in the quartz material and causes the prongs to displace symmetrically. The prong displacement and the potential generated for different concentrations are captured and presented. The proposed system offers ultralow sensitivity in the parts-per-billion (ppb) order, which makes it an ideal candidate for human exhale breath (HEB) gas analysis for non-invasive disease diagnosis.