A2.4 - A Suspended Plate In-Plane Resonator for Rheological Measurements at Tunable Frequencisies

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A2 - Surface Acoustic Wave Sensors
M. Heinisch, E. Reichel, B. Jakoby - Johannes-Kepler-University Linz (Austria)
61 - 66


In this contribution a rheometric sensor based on a suspended in-plane vibrating plate with tunable resonance frequencies is presented. A sample liquid is subjected to time harmonic shear stress induced by a vibrating plate. By measuring the resonant behavior of this fluid-structure interaction, the liquid’s rheological properties such as viscosity and mass density can be deduced. The sensor consists of a non-conductive platelet and two conductive tungsten wires placed in a constant magnetic field. The platelet (for first prototypes transparent polymers or thin glass slides have been used) is affixed to the wires using fusing technology, thus yielding a mechanical coupling of the two wires. One of these wires is used to deflect the plate in lateral direction by means of Lorentz forces on ACcurrents flowing through the wire. The other wire, following the movement of the first, is used as pick-up representing the in-plane movement of the plate by an induced voltage. By varying the normal stresses within both wires by an appropriate tensioning mechanism the desired resonance frequency can be adjusted.

To determine the physical properties of a liquid such as viscosity or mass density using a resonator based principle, the change of the resonator’s quality factor and the shift of its resonant frequency (which are both known in vacuum or air) are evaluated from the recorded frequency response in a test liquid. For the investigation of some complex (viscoelastic) liquids, it can be important to analyze the liquid’s physical behavior at tunable frequencies in a certain bandwidth.

Resonating sensors can be used to characterize the physical properties of both, simple Newtonian and very complex non-Newtonian liquids showing viscoelastic behavior. Vibrating viscometers are mechanically simpler than other types and the volume of fluid required for their use is much smaller making operation at high pressures and temperatures easier. The advantage of mechanically vibrating resonators compared to piezoelectric or quartz crystal oscillators is their applicability in the low kilohertz range.