P8.6 - A Sensor for Mechanical Liquid Properties Utilizing Pressure Waves

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P8 - Mechanical
H. Antlinger, B. Jakoby - Johannes Kepler University, Linz (Austria), R. Beigelbeck - Austrian Academy of Sciences, Wiener Neustadt (Austria), S. Cerimovic, F. Keplinger - Vienna University of Technology (Austria)
865 - 870


Sensors for online monitoring of fluid properties facilitate characterization, controlling, and optimization of many processes. Particularly, for industrial applications small, reasonably priced, and robust sensors are required. A lot of recent work has been focused on sensing viscosities of liquids (often in combination with their density), which can be used as characteristic parameter representing the state of the liquid to be monitored. Typically used laboratory equipment for viscosity measurements involve motor-driven rotating objects resulting in bulky and highmaintenance devices. Vibrating small structures (preferably microstructures) can be seen as interesting alternative to such apparatus. Their working principle is based on the viscosityinduced change of the resonance characteristics caused by the liquid loading of the structure. Examples for the successful application of this concept include shear wave resonators, which are often fabricated in quartz technology. However, owing to the strong attenuation of the excited shear wave, only a small layer (often in the order of microns or below) of the liquid is being sensed. Consequently, such devices are prone to surface contamination and they do not sense the bulk properties of the liquid. The presented approach relies on the implementation of a simple alternative concept, where the viscous attenuation of pressure waves in the sample liquid is utilized so that the bulk of the liquid is characterized rather than a surface layer. In order to increase the sensitivity, a resonant setup is chosen, where the pressure wave is resonating between two rigid boundaries. By means of an extensive analytical model, the influence of the first (shear) and the second (dilatational) coefficient of viscosity on the resonance characteristics are studied in detail. In our contribution, we will outline the proposed system including a detailed analysis of the sensor effect and the achievable sensitivities, a mathematical model describing the functional chain of transducer-liquid-sensor, and experimental results obtained from a fabricated device prototype.