Novel resonant MEMS sensor for the detection of particles with dielectric properties in aged lubricating oils

Abstract

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 sensor 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 monitoring of oil degradation in industrial applications, such as needed for the condition-based and predictive maintenance of lubricated machinery.