We report on a comparison between the piezoelectric and interferometric readouts of vibrations in quartz tuning forks (QTFs) when employed as sound wave transducers in quartz-enhanced photoacoustic trace gas sensors. We demonstrate the possibility to properly design the QTF geometry to enhance interferometric readout signal with respect to the piezoelectric one and vice versa. When resonator tubes are acoustically coupled with the QTFs, signal-to-noise ratio enhancements are observed for both readout approaches. These results open the way to the implementation of optical readout of QTF vibrations in applications where external electromagnetic field could distort the piezoelectric signal.
In this work, we report on the measurement of methane (CH4) effective non-radiative relaxation rate in a mixture containing 1% of CH4 and 0.15% of water vapor in nitrogen, by using a set of custom quartz tuning forks (QTFs). The dependence of quartz-enhanced photoacoustic spectroscopy (QEPAS) peak signal and QTF quality factor as a function of operating pressure allowed the estimation of the radiation-to-sound conversion efficiency and, consequently, the calculation of the effective relaxation rate of the investigated gas mixture. We measured an effective relaxation rate of 3.2 ms·Torr, in good agreement with values reported in literature.
We report on the performance of new quartz tuning fork (QTF) designs optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). We investigated the impact on resonance properties of prong geometries differing from the standard rectangular one. We proposed a QTF with T-shaped prongs and a QTF with prongs having rectangular grooves carved on the surface. QTFs were implemented in a QEPAS sensor and performances were compared in terms of signalto-noise ratio (SNR). Then, QTFs were acoustically coupled with single- and dual-tube micro-resonator systems. A record x60 SNR enhancement factor with respect to the bare QTF was achieved with QTF having T-shaped prongs.