Photoacoustic spectroscopy sensing based on an annular quartz tuning fork

This paper reports for the first time the construction of a gas sensing system using a self-developed annular quartz tuning fork (QTF). This annular QTF breaks through the limitations of conventional standard QTFs and features three core advantages: (1) Compared to the standard single‑ended QTF, the closed annular structure exhibits higher induced stress and an enhanced surface charge under the same lateral deformation excitation; (2) The annular structure of the QTF can collect and utilize the four-directional photoacoustic energy on the acoustic excitation surface, notably boosting the acoustic-mechanical-electric coupling efficiency; (3) The large central hollow area is compatible with more excitation methods and acoustic resonator enhancement strategies, which can significantly improve the system performance. Experimental results demonstrate that in the quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing system, the 2 f peak intensity and signal-to-noise ratio (SNR) of the annular QTF reach 3.57 and 3.15 times those of the standard QTF, respectively. An ellipsoidal acoustic resonator (EAR) adapted to its unique structure was designed via finite element analysis (FEA). When integrated with the EAR, the SNR of the QEPAS system is improved by a factor of 21.43 compared with the system without the EAR. The detection performance of the annular QTF was further validated in the light-induced thermoelastic spectroscopy (LITES) sensing system. The annular QTF demonstrates superior performance, with its 2 f peak intensity and SNR measuring 4.16 and 3.62 times higher than those of the standard QTF, respectively. This study breaks the conventional design paradigm of QTFs and provides a novel approach for QEPAS.