Optimization of resonator radial dimensions for quartz enhanced photoacoustic spectroscopy systems

A finite element model for QEPAS systems has been developed that can apply to both on-axis and off-axis systems. The model includes the viscous and thermal loss on the acoustic resonator sidewalls, and these factors are found to significantly affect the signal to noise ratio. The model results are compared to experimental data and it is found that the model correctly predicts the optimal radial dimensions for resonator tubes of a given length. The model is applied to examine the dependence of signal-to-noise ratio on resonator diameter and sidewall thickness. The model is also applied to off-axis systems.