We report on a comparison between two quartz tuning forks (QTFs) employed for quartz-enhanced photoacoustic spectroscopy (QEPAS) having quadrupole and octupole electrode pattern configurations. With respect to the quadrupole, the implementation of the octupole pattern suppresses the fundamental mode and reduces by a factor of ~ 4.4 the electrical resistance for the first overtone mode with negligible variations of the related Q-factors. Both QTFs operating at the first overtone mode were implemented in a QEPAS sensor and the results showed that the octupole configuration provides a ~2.3 signal enhancement factor.
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.
We report on the development of a gas sensor system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) for the detection of trace levels of ethylene using a quantum cascade laser operating at ~ 10.3 μm. To realize a compact sensor architecture, a dedicated acoustic detection module was designed and implemented. The module includes a QEPAS spectrophone, composed of a quartz tuning fork, a micro-resonator tube and a low-noise pre-amplifier chip for the signal readout. The volume of the ADM is ~30 cm<sup>3</sup>. A minimum detection limit of 30 part-per-billion in concentration was obtained with a data acquisition time of 10 s.