Simultaneous measurement of fluids viscosity and density using a microbeam

In this paper a piezoelectrically actuated microsensor for simultaneous measurement of fluids viscosity and density is presented. The sensor consist of a beam with two piezoelectric layers, which are located on the upper and lower surfaces of it and a sensing plate at the end of it which is immersed in a fluid. In the developed model, the governing coupled partial differential equations of longitudinal vibration of the beam and the fluid field have been derived. A novel model for reconstruction of the governing differential equations has been proposed and the equations have been discretized over the beam and the fluid domain, using Galerkin based reduced order model. The dynamic response of the sensing plate for different piezoelectric actuation voltages and different exciting frequencies has been investigated. The effect of the viscosity and density of a fluid on the sensing plate´s response has been studied and has been shown that a fluid has dissipative and inertial effects on the sensor´s response. The effect of geometrical parameters of the sensor also on its response has been examined. The results indicate that with this sensor design, it is possible to measure kinematic viscosity values of 2times10^-6 m².s^-1 and lower with maximum uncertainty of 10%. Apparently, uncertainty depends on magnitude of kinematic viscosity and voltage applied to piezoelectric layers. The lower the value of kinematic viscosity and higher the value of applied voltage are, the smaller uncertainty becomes. If we need the sensor to detect kinematic viscosity values higher than 2times10^-6 m².s^-1 with the same accuracy cited, it is essential to replace the sensing microplate of device with a thinner one having high surface area and also it is essential to apply higher voltages to piezoelectric layers.