Fluid property investigation by impedance characterization of quartz crystal resonators: Part II: Parasitic effects, viscoelastic fluids

Abstract

In the concluding part of this communication, we examine the influence of parasitic effects on the performance of thickness-shear mode (TSM) quartz crystal resonators (QCR). To achieve this, we characterized the increase in energy dissipation and associated loss in crystal performance due to mounting in a liquid-tight cell, a type of which is often necessary for fluid property investigation. The results show that while this approach may be satisfactory for most common fluids, alternative approaches may be required for device operation in highly lossy media. Subsequently, we report on a series of TSM QCR contacted by viscoelastic fluids (poly(dimethylsiloxane) (PDMS) melts). These were studied using frequency response analysis, at the fundamental and accessible harmonic modes. The results show, in agreement with theory presented earlier, that the effect of fluid elasticity is a reduction in the equivalent resistance relative to that of a purely Newtonian reservoir with identical density and viscosity equal to the zero-shear rate viscosity of the viscoelastic bulk. A similar effect is shown in relation to the inductance. The results also show a correlation between the mechanical response of the crystal as shown by its resonance frequency shift upon damping, and its impedance response, via the shift in the equivalent motional resistance.