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E. Benes, R. Thalhammer, M. Gröschl, H. Nowotny, S. Jary:
"Viscosity sensor based on a symmetric dual quartz thickness shear resonator";
in: "Proc. 2003 IEEE Int. Frequency Control Symp. / 17th Europ. Frequency and Time Forum", herausgegeben von: J.R. Vig; IEEE, Tampa, Florida/USA, 2003, ISBN: 0-7803-7689-7, S. 1048 - 1054.

Abstract - The paper describes a novel quartz crystal sensor for
the measurement of the density-viscosity product of Newtonian
liquids. The sensor element consists of two circular quartz
crystal plates with an air-gap in between and the liquid sample
in contact with the outer plate surfaces. Plane-convex AT-cut
quartz crystals arranged in mirror symmetric crystallographic
orientation and vibrating in an even-symmetric thickness-shear
fundamental mode at 2.77 MHz are utilized. The two outer
plane sides of the crystals are fully covered by gold electrodes,
which are both connected to ground potential. This special mirror
symmetric set-up allows the compensation of spurious displacements
in the circular clamping zones of the two crystals.
The measurement values of the sensor are the fundamental
resonance frequency f and the associated resonance Q-value,
which are analytically dependent on the density-viscosity product
of the liquid in contact with the sensing surfaces. In contrast
to an earlier report [1] about a sandwich resonator sensor,
which entrapped the liquid sample between two quartz plates,
the immersible sensor presented here is not restricted to low
viscosity samples. The sensor covers a viscosity range from almost
zero (air!) up to 2000 Pa.s, and is not restricted to electrically
insulating liquids.
Keywords - Resonant sensors, BAW sensors, viscosity, dough

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC04405875