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J. Toledo, T. Manzaneque, V Ruiz-Díez, M. Kucera, G. Pfusterschmied, E Wistrela, U. Schmid, J.L. Sànchez-Rojas:
"Out-of-plane Piezoelectric Microresonator and Oscillator Circuit for Monitoring Engine Oil Contamination with Diesel";
Talk: Smart Sensors, Actuators and MEMS VII - 2015, Barcelona, Spain; 05-04-2015 - 05-06-2015; in: "Proc. of SPIE Vol. 9517-9520", SPIE, 9517 (2015), ISSN: 0277-786x; Paper ID 95170C, 9 pages.

Real-time monitoring of the physical properties of liquids is an important subject in the automotive industry.
Contamination of lubricating oil by diesel soot has a significant impact on engine wear. Resonant microstructures are
regarded to be a precise and compact solution for tracking the viscosity and density of lubricant oils. Since the
measurement of pure shear forces do not allow an independent determination of the density and viscosity, two out-ofplane
modes for the monitoring of oil dilution with diesel have been selected. The first one (12-mode) is working at 51
kHz and the second mode (14-mode) at 340 kHz. Two parameters were measured: the quality factor and the resonance
frequency from which the viscosity and density of the fluids under test can be determined, requiring only a small amount
of test liquid.
A PLL-based oscillator circuit was implemented based on each resonator. Our results demonstrate the performance of
the resonator in oils with viscosity up to 90 mPa·s. The quality factor measured at 25ºC was 7 for the 12-mode and 19 for
the 14-mode. A better resolution in density and viscosity was obtained for the 14-mode, showing a resolution of
3.92·10-5 g/ml for the density and 1.27·10-1 mPa·s for the viscosity, in pure lubricant oil SAE 0W30. An alternative
tracking system, based on a discrete oscillator circuit, was tested with the same resonator, showing a comparable stability
and supporting our approach.

Real-time monitoring of the physical properties of liquids is an important subject in the automotive industry.
Contamination of lubricating oil by diesel soot has a significant impact on engine wear. Resonant microstructures are
regarded to be a precise and compact solution for tracking the viscosity and density of lubricant oils. Since the
measurement of pure shear forces do not allow an independent determination of the density and viscosity, two out-ofplane
modes for the monitoring of oil dilution with diesel have been selected. The first one (12-mode) is working at 51
kHz and the second mode (14-mode) at 340 kHz. Two parameters were measured: the quality factor and the resonance
frequency from which the viscosity and density of the fluids under test can be determined, requiring only a small amount
of test liquid.
A PLL-based oscillator circuit was implemented based on each resonator. Our results demonstrate the performance of
the resonator in oils with viscosity up to 90 mPa·s. The quality factor measured at 25ºC was 7 for the 12-mode and 19 for
the 14-mode. A better resolution in density and viscosity was obtained for the 14-mode, showing a resolution of
3.92·10-5 g/ml for the density and 1.27·10-1 mPa·s for the viscosity, in pure lubricant oil SAE 0W30. An alternative
tracking system, based on a discrete oscillator circuit, was tested with the same resonator, showing a comparable stability
and supporting our approach.

Microresonators, piezoelectric, density, viscosity, rheology, AlN, lubricant oil, oscillator circuits

http://dx.doi.org/10.1117/12.2179251