Feasibility study on real-time viscosity monitoring by miniaturized optical viscosity sensor

A new viscosity sensor enabling non-contact measurement at high speed, with less sample volume and high stability is required in a broad field. For example, in the industrial field, process control by in situ measurement of viscosity can enhance quality and process yield of ink, paint and coating films. Therefore, we have developed a new miniaturized optical viscosity sensor, namely MOVS (Miniaturized Optical Viscosity Sensor), based on a laser-induced capillary wave (LiCW) method which can meet the requirements above. MOVS measures viscosity by observing damping oscillation of laser-induced capillary wave (LiCW), which is generated by an interference of two excitation laser beams on a liquid surface. MOVS consists of five U-grooves fabricated by MEMS process and optical fibers. The newly integrated optical surface tracking system makes possible the stable viscosity measurement under external disturbances such as vibration and evaporation. In this study, by integrating the optical surface tracking system, nanosecond damping oscillation of LiCW is successfully observed in the presence of external forced vibration drying process of a liquid film (thickness of hundreds micrometer order).