Accuracy and precision of resonant piezoelectric MEMS viscosity sensors in highly viscous bituminous materials

This paper reports on the dynamic viscosity analysis of bituminous materials with piezoelectric MEMS plate-type resonators. To enable measurements even under such strong damping conditions in this high viscous environment, the 10th order roof-tile shaped vibrational mode is exploited. For actuation and sensing, a piezoelectric aluminium nitride (AlN) thin film is used in combination with a tailored electrode design. The resonator is calibrated by measuring its conductance frequency spectrum when immersed in six high viscosity (range: 150-45.000 mPa s) test liquids at temperatures from 30 degrees C to 100 degrees C. The determination of dynamic viscosity values of bituminous materials is done using the calibration function from the linear relationship between the quality factor Q and the inverse square root of the density-viscosity product (p mu)-1/2 of the test liquids. Next, Q is mapped to (p mu)-1/2 for bituminous materials measured at operating temperatures from 70 degrees C to 150 degrees C. Within the measurement accuracy a very good agreement of dynamic viscosity values determined by both the MEMS resonator and a rotational viscometer is demonstrated up to a maximum dynamic viscosity of about 60.000 mPa.s. Despite this limitation these results show the outstanding potential of piezoelectric MEMS sensors for the monitoring of even super high-viscous liquid properties.