B2.4 - Spring-Plate Resonator Sensor for Measuring Viscosity of Small Amounts of Complex Fluids

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B2 - Sensor Design and Modeling
E. Reichel, C. Kirschhock, J. Vermant - Katholieke Universiteit Leuven, Heverlee (Belgium), B. Jakoby - Johannes Kepler University Linz (Austria)
246 - 251


Viscosity and density are physical properties of fluids that are critical for manifold processes in industry. Beside their direct importance of determining the flow characteristics, they can also be used to quantify the chemical condition, e.g., of lubricants, fuels, electrolytes, or the progress of crystallization or polymerization. Rheometers are commonly used for measuring the material properties to a high accuracy.
In complex fluids the reaction force depends on the rate, amount, frequency, or duration of the deformation. Often these effects are accompanied by an elastic behavior, so the respective dynamic property is known as viscoelasticity.
Electromechanical resonators are sensitive to the parameters of the surrounding medium and therefore can be used as sensors for viscoelastic properties and density. The deformation is usually small (displacements in the range of micrometers) so that the response is linear. With appropriate sensor design and modeling methods, it is in the best case possible to measure the dynamic storage and loss moduli as well as the density of fluids exhibiting complex rheological behavior.
In our recent work, we presented a metallic plate resonator excited by Lorentz forces in a permanent magnetic field. The resonance frequency and bandwidth is measured via the motion-induced voltage. In highly viscous media, the low Q-factor limits the sensor operation. To overcome this limitation, the shear wave is reflected by a wall parallel to the resonator plane, so that standingwave resonances are observed. Alternatively, the placement of droplets stabilized by the surface tension on the round resonator leads to novel ways of measuring the viscoelastic properties. Sample liquids of interest include colloidal suspensions, aqueous polymeric solutions, microemulsions, and polymerized siloxanes.
The aim of the ongoing research is to achieve better theoretical understanding, establish novel sensor principles, and use state-of-the-art fabrication teqchniques to increase the range of applications for online measurement of rheological properties.