Quartz–enhanced photoacoustic spectrophones exploiting custom tuning forks: a review

A detailed review on the design and realization of spectrophones exploiting custom quartz tuning forks (QTFs) aimed to applications of quartz-enhanced photoacoustic (QEPAS) trace-gas sensors is reported. A spectrophone consists of a custom QTF and a micro-resonator system based on a pair of tubes (dual-tube configuration) or a single-tube. The influence of the QTF and resonator tube geometry and sizes on the main spectrophone parameters determining the QEPAS performance, specifically the quality factor Q and the resonance frequency has been investigated. Results obtained previously are reviewed both when the QTF vibrates on the fundamental and the first overtone flexural modes. We also report new results obtained with a novel QTF design. Finally, we compare the QEPAS performance of all the different spectrophone configurations reported in terms of signal-to-noise ratio and provide relevant and useful conclusions from this analysis.