Quartz-Enhanced Photoacoustic Spectroscopy Sensor with a Small-Gap Quartz Tuning Fork

Abstract

A highly sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a custom quartz tuning fork (QTF) with a small-gap of 200 μm was demonstrated. With the help of the finite element modeling (FEM) simulation software COMSOL, the change tendency of the QEPAS signal under the influence of the laser beam vertical position and the length of the micro-resonator (mR) were calculated theoretically. Water vapor (H2O) was selected as the target analyte. The experimental results agreed well with those of the simulation, which verified the correctness of the theoretical model. An 11-fold signal enhancement was achieved with the addition of an mR with an optimal length of 5 mm in comparison to the bare QTF. Finally, the H2O-QEPAS sensor, which was based on a small-gap QTF, achieved a minimum detection limit (MDL) of 1.3 ppm, indicating an improvement of the sensor performance when compared to the standard QTF that has a gap of 300 μm.

Review of Recent Advances in QEPAS-Based Trace Gas Sensing

“…The schematic of the laser beam, a QTF, and the generated acoustic wave is shown in Figure 8. The first custom QTF with a small gap of 200 µm used in the QEPAS sensor was reported by Ma [75]. Using the COMSOL software, a finite element modeling (FEM) was constructed, and the displacement of QTF with different micro-resonators (mR) was calculated theoretically.…”

Dual Path Lock-In System for Elimination of Residual Amplitude Modulation and SNR Enhancement in Photoacoustic Spectroscopy

“…It is very simple and effective in practical applications. The dual path lock-in technique can be applied not only in the photoacoustic spectroscopy based on PAS cells, but also to quartz-enhanced photoacoustic spectroscopy [22] and cantilever-enhanced photoacoustic spectroscopy [23].…”

Quartz Enhanced Photoacoustic Spectroscopy Based on a Custom Quartz Tuning Fork

“…These resonators were demonstrated to work at the first overtone frequency and making possible dual gas sensing by exciting both fundamental and overtone flexural modes [13]. Another choice is to reduce the gap between the prongs to benefit more from the acoustic pressure actuating the QTF [14], despite the induced elevation of the background noise due to higher residual illumination of the QTF’s prongs. This approach could be considered in the MIR thanks to the use of background noise suppression techniques such as the electrical modulation cancellation method [15] or phase quadrature measurements, which we recently introduced [16].…”