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F. Patocka, C. Schneidhofer, N. Dörr, M. Schneider, U. Schmid:
"Novel MEMS Sensor for the Detection of Particles with Dielectric Properties in Aged Lubricating Oils";
Sensors and Actuators A: Physical, 315 (2020), 1 - 13.

We present a novel resonant MEMS sensor for the detection of particles with dielectric properties in liquid
environments. The sensor consists of a piezoelectrically excited silicon microcantilever with integrated
tailored electrodes on the surface that accumulate particles due to dielectrophoresis. By monitoring the
mass-induced shift of the cantilever-related resonance frequency, the accumulated particle mass during
the measurement cycle is deduced. We evaluated the mass-sensing performance by exposing the sen-
sor to four artificially aged lubricating oils, thus containing different particle concentrations due to the
oxidative degradation of the oil constituents. The measured resonance frequency shift showed a clear
correlation to the degree of oil oxidation and is used to determine the accumulated mass by applying
an automated particle detection scheme. The measured mass responsivity and limit of detection are
in the range of 13 Hz/ng and 3.5 ng, respectively. Compared to standard laboratory methods, such as
infrared spectroscopy, the analysis of the sensor response with respect to the oil quality shows that even
subtle changes of the oil condition can be detected. These results pave the way for on-line monitor-
ing of oil degradation in industrial applications, such as needed for the condition-based and predictive
maintenance of lubricated machinery.

http://dx.doi.org/10.1016/j.sna.2020.112290