Analysis of overtone flexural modes operation in quartz-enhanced photoacoustic spectroscopy

Abstract

Abstract:A detailed investigation of a set of custom quartz tuning forks (QTFs), operating in the fundamental and first overtone flexural modes is reported. Support losses are the dominant energy dissipation processes when the QTFs vibrate at the first overtone mode. These losses can be decreased by increasing the ratio between the prong length and its thickness. The QTFs were implemented in a quartz enhanced photoacoustic spectroscopy (QEPAS) based sensor operating in the near-IR spectral range and water vapor was selected as the gas target. QTF flexural modes having the highest quality factor exhibit the largest QEPAS signal, demonstrating that, by optimizing the QTF prongs sizes, overtone modes can provide a higher QEPAS sensor performance with respect to using the fundamental mode.

Synergetic Resonance Matching of a Microphone and a Photoacoustic Cell

“…The resonance mode was mainly in the radial and azimuthal direction, while the longitudinal mode had a negligible effect on the frequency response. These results provide guidance for those who develop photoacoustic spectroscopy using the ultrasound region and can be further applied to other ultrasound applications such as quartz-enhanced photoacoustic spectroscopy [26,27,28]. The method demonstrated here can be used to increase the signal-to-noise ratio and lower the detection limit of samples regardless of whether the sample is in open or closed form in all phases; liquid, solid, and gas.…”

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

“…For QTF#1 and QTF#3 higher quality factors were measured for the overtone mode, with respect to the fundamental mode [35]. Consequently, the QEPAS signal obtained operating in the first overtone mode is higher than that obtained using the fundamental mode for the QTF#1 (~ 5.3 times) and QTF#3 (~ 2.2 times), while for QTF#2 it is ~ 7.1 times lower.…”

“…Figure 2 depicts the results obtained when QTF#4 operated at the first overtone mode. We found that the scan was characterized by two peak values close to the antinode points of the vibration mode profile, corresponding to the maximum vibration amplitude [33,35]. The highest QEPAS peak signal was reached by positioning the laser beam focal spot close to the second antinode, 12 mm from the top of the prongs.…”

“…Consequently, the QEPAS signal obtained operating in the first overtone mode is higher than that obtained using the fundamental mode for the QTF#1 (~ 5.3 times) and QTF#3 (~ 2.2 times), while for QTF#2 it is ~ 7.1 times lower. For comparison, we tested QTF#4 in a QEPAS sensor similar to that reported in [35]. The exciting source was a single-mode DFB QCL emitting at 7.71 μm.…”

Damping Mechanisms of Piezoelectric Quartz Tuning Forks Employed in Photoacoustic Spectroscopy for Trace Gas Sensing

“…If the laser is modulated at one of frequencies of the in‐plane flexural resonance modes, non‐radiative relaxation processes generate sequential gas expansion, generating weak pressure waves (i.e., sound) that hit and bend QTF prongs. A QEPAS sensor performance depends on the selected QTF resonance quality factor Q , which is the ratio of the total input energy into the resonator to the energy dissipated within a vibration cycle . A high‐quality factor indicates a small resonance bandwidth and low dissipation losses.…”