A Novel Sensor System for Liquid Properties Based on a Micromachined Beam and a Low-Cost Optical Readout

For the measurement of liquid parameters like viscosity and density vibrating micromachined structures offer useful alternatives to bulky conventional measurement equipment. Evaluating the shift of the resonance frequency and the change of the damping factor of such devices allows the simultaneous determination of viscosity and density. Furthermore, these sensors can even be used for complex liquids like emulsions where other microacoustic sensors like TSM quartz resonators, in comparison to conventional laboratory viscometers, measure in a different rheological domain. In our contribution we present a novel implementation of a viscosity and density sensor system utilizing a doubly-clamped vibrating micromachined beam. The beam deflection is determined by means of a laser pickup head as it is used, e.g., in DVD drives, yielding high sensitivity and a low-cost setup at the same time. The measured damping factor correlates well with the viscosity of the respective liquid, whereas the resonance frequency is also influenced by the liquid's density.