Piezoelectrically Excited MEMS Resonators with Integrated Planar Coil for the Detection of Ferrous Particles in Liquids

Abstract

We present a novel MEMS sensor which allows the detection of ferrous particles in liquid environments. The device is based on a resonantly excited silicon microcantilever with an integrated planar coil on its surface, which attracts and accumulates ferrous particles on the sensor viamagnetophoresis. The additional mass leads to a shift in resonance frequency of the microcantilever, which in turn can be used to deduce the accumulated particle mass. A reference microcantilever of the same design, which does not actively accumulate particles, is operated in close vicinity to cancel out any parasitic environmental influences, such as fluid temperature fluctuations on the viscosity. The sensor performance is determined by measuring the sensor response to 250 nm iron oxide (Fe3O4) particles, dispersed in deionized water. After a measurement duration of 100 min., a differential resonance frequency shift of 5916 Hz is found, which corresponds to a total accumulated mass of approximately 0.49 μg and a mass responsivity of 82.85 pg/Hz. Based on this result, the detection limit for the sensor in the current design is derived to about 4 ng. Besides its compact and robust architecture, these results promise the successful operation in a broad range of industrial applications, such as predictive maintenance in lubricated machinery.