[Zurück]

T. Manzaneque, V Ruiz-Díez, J. Hernando-Garcia, E Wistrela, M. Kucera, U. Schmid, J.L. Sànchez-Rojas:
"Piezoelectric MEMS resonator-based oscillator for density and viscosity sensing";
Sensors and Actuators A: Physical, 220 (2014), S. 305 - 315.

tThe resonant characteristics of a mechanical resonator immersed in liquid provide valuable parame-ters for density and viscosity sensing. In particular, the combination of microresonators with electroniccircuits, for tracking their natural frequency and quality factor, has great interest as low cost and sizesolution. In this work, we focus on an oscillator featuring an in-liquid piezoelectric microplate resonatoras the frequency-selective element. Specifically, by selecting the second-order bending mode in thelength-direction, a reliable oscillator operation, for a range of liquid properties, was achieved at moder-ate frequency. Besides, the out-of-plane vibration allowed for both density and viscosity to be deducedseparately. The influence of parasitic capacitances in the device response has been identified as the majordifficulty for the realization of the oscillator circuit. To minimize this effect, a compensation method basedon a non-released reference device and an instrumentation amplifier was implemented, which resultedin a clear resonance with low baseline and high phase step. In a first test with the resonator immersedin isopropanol, the circuit generated a stable wave with an Allan deviation of 2.32·10−7, improving byone order of magnitude the only published value, to the authors knowledge, for a comparable devicein liquid. An alternative tracking system, based on digital phase-locking benchtop instrumentation, wastested with the same resonator, showing a comparable stability (2.35·10−7) and supporting our approach.Finally, the operation of the system as a sensor was demonstrated. After a calibration process, the densityand viscosity of eight test liquids could be compared to measurements with a commercial instrument,showing differences lower than 0.4% in density and 8% in viscosity. The minimum detectable changeswere also evaluated, being 4.09·10−6g/ml for the density and 2.07·10−3mPa s for the viscosity, both fora viscosity of 7.36 mPa s at 10 samples per second.

tThe resonant characteristics of a mechanical resonator immersed in liquid provide valuable parame-ters for density and viscosity sensing. In particular, the combination of microresonators with electroniccircuits, for tracking their natural frequency and quality factor, has great interest as low cost and sizesolution. In this work, we focus on an oscillator featuring an in-liquid piezoelectric microplate resonatoras the frequency-selective element. Specifically, by selecting the second-order bending mode in thelength-direction, a reliable oscillator operation, for a range of liquid properties, was achieved at moder-ate frequency. Besides, the out-of-plane vibration allowed for both density and viscosity to be deducedseparately. The influence of parasitic capacitances in the device response has been identified as the majordifficulty for the realization of the oscillator circuit. To minimize this effect, a compensation method basedon a non-released reference device and an instrumentation amplifier was implemented, which resultedin a clear resonance with low baseline and high phase step. In a first test with the resonator immersedin isopropanol, the circuit generated a stable wave with an Allan deviation of 2.32·10−7, improving byone order of magnitude the only published value, to the authors knowledge, for a comparable devicein liquid. An alternative tracking system, based on digital phase-locking benchtop instrumentation, wastested with the same resonator, showing a comparable stability (2.35·10−7) and supporting our approach.Finally, the operation of the system as a sensor was demonstrated. After a calibration process, the densityand viscosity of eight test liquids could be compared to measurements with a commercial instrument,showing differences lower than 0.4% in density and 8% in viscosity. The minimum detectable changeswere also evaluated, being 4.09·10−6g/ml for the density and 2.07·10−3mPa s for the viscosity, both fora viscosity of 7.36 mPa s at 10 samples per second.

MEMS Oscillator Piezoelectric Liquid Density Viscosity

http://dx.doi.org/10.1016/j.sna.2014.10.002

Projektleitung Ulrich Schmid:
Mikrosystemtechnik Projektkonto Schmid