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R. Schnitzer, S. Radel, C. Hauser, E. Benes, R. Möslinger, M. Gröschl:
"Influence of the liquid's permittivity on measurements with resonant ultrasonic viscosity sensors";
Vortrag: 3rd Congress of the Alps Adria Acoustics Association, Hotel Weitzer, Graz; 27.09.2007; in: "3rd Congress of the Alps Adria Acoustics Association, Hrsg: Joanneum Research", (2007), 7 S.

The novel general-purpose on-line measurement system ("QxSens") for resonant piezoelectric bulk-acoustic-
wave (BAW) sensors has been reported elsewhere (R. Schnitzer et al., IEEE Sensors Journal 6 (2006) 1314-1322). This
system supports various sensor types for different physical measurands, such as temperature, humidity, viscosity,
density and speed of sound of liquids, and film thickness. In the work presented here, the QxSens system was evaluated
by using different types of BAW sensors for the measurement of the viscosity of various liquids, such as water, rayon
fibers solutions, and lubricating oils. Thereby, cross sensitivities of the sensors to the sample liquid´s permittivity as
well as the temperature have been observed. By calculating the viscosity values out of the sensors' admittance spectra
recorded by the QxSens system, it became evident that the piezoelectric quartz sensors are affected by the dielectric
properties of the sample liquid, even if no electrically conducting part of the sensor is in direct contact to the liquid. The
paper gives an explanation of this effect and discusses design rules and a special calibration routine to eliminate the
observed cross sensitivities.

Viscosity sensor, quartz crystal sensor, BAW sensor, high shear rate, cross sensitivity, permittivity