Parallel Plate Resonators for Shear-Wave Rheometry of Viscoelastic Fluids

Description

Mechanical resonators are devices highly sensitive to loading with mass or liquid. The linear viscoelastic parameters of a fluid in contact can in principle be derived from the shift in resonance frequency and change in bandwidth. Using micromachined cantilevers or suspended plates viscosity sensors with high sensitivity at low viscosities can be designed [1]. With increasing viscosity high damping limits the applicable range to about 0.5 Pa*s. We present a system of two electrodynamic plate resonators aligned parallel to each other - the sample in between - where one is used for excitation and readout, and the second for measuring only. This way the high sensitivity at low viscosities is preserved when observing the resonance of the exciting transducer. The shear-wave coupling between the two resonators increases with viscosity and elasticity of the fluid, enabling measurements at viscosities of tens of Pa*s. The complex coupling coefficient is determined by the gap height and the product of density and viscoelastic modulus [2]. We fabricated resonators with circular plates with diameters between 6 and 10 millimeters, and spacers between 200 micrometers and 2 millimeters. The resonators are mounted in a temperature controlled block of dimensions 50x90x18 millimeters. We present measurements of liquids between 1 mPa*s. and 10 Pa*s and the mathematical modeling of the resonators coupled by the shear-wave in viscoelastic media. [1] E.K. Reichel, C. Riesch, F. Keplinger, C.E.A. Kirschhock, B. Jakoby, Analysis and experimental verification of a metallic suspended plate resonator for viscosity sensing, Sens. Act. A: Phys.,162/2 (2010); [2] John L. Schrag, Deviation of Velocity Gradient Profiles from the ”Gap Loading” and ”Surface Loading” Limits in Dynamic Simple Shear Experiments, Trans. Soc. Rheol. 21, 399 (1977)

Period	11 Apr 2014
Event title	Annual European Rheology Conference 2014
Event type	Conference
Location	GermanyShow on map