Abstract
A theoretical analysis and experimental investigation of the influence of gas pressure on resonance properties, namely, the quality factor and resonance frequency, of a T-shaped quartz tuning fork (QTF) is reported here. Two configurations are considered: a bare QTF, and a QTF coupled with a pair of resonator tubes (spectrophone). In both configurations, the effect of air on resonance frequency due to the additional inertia on prong motion and the influence of air damping on the quality factor, were analysed. By comparing the bare QTF and the spectrophone results, the effect of pressure on the acoustic coupling between the QTF and the tubes was theoretically modelled and then validated. The results show that acoustic coupling is strongly influenced by air pressure, leading to a shift of resonance frequency and a decrease in the quality factor up to 24%.
Highlights
A quartz tuning fork (QTF) is an acoustic resonator widely used as a clock oscillator due to its stability and precision [1]
The principle of detection in quartz-enhanced photo-acoustic spectroscopy (QEPAS) is based on the piezoelectric properties of a quartz crystal: acoustic waves photo-generated between the prongs hit and create oscillations at one of the in-plane resonance frequencies of the QTF; the mechanical stress generates a strain field; electric charges appear on the surface to be collected by electrodes and converted into a voltage or a current QEPAS signal [8]
We studied the resonance properties of a T-shaped QTF and how they are affected by acoustic coupling with a pair of resonator tubes in a spectrophone
Summary
A quartz tuning fork (QTF) is an acoustic resonator widely used as a clock oscillator due to its stability and precision [1]. A theoretical model was developed to predict the influence of air pressure both on the frequency and quality factor of the fundamental resonance mode of the QTF. Hao et al [11] developed a model to describe support losses as the effect of a shear force exerted from the vibrating beam on the QTF support, which excites elastic waves propagating into the support with a wavelength greater than the prong width w. With this assumption, the quality factor contribution Qsup related to support losses can be simplified as: Qsup. The experimental investigation proposed in the subsection aims to identify the most relevant mechanism of energy dissipation
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