A Novel Combined Rheometer and Density Meter Suitable for Integration in Microfluidic Systems

In this contribution we present a combined rheometer and density meter based on two vibrating membranes carrying electrically conductive paths for excitation and readout. The liquid is contained in a 100 mul volume between the rectangularly clamped membranes. The vibration is excited by Lorentz forces arising from a static magnetic field provided by a permanent magnet and the current through the excitation path going back and forth on the vibrating part of the membrane. The sensor element is designed in such a way that the viscous liquid is subjected to shear stress. Additional conductive loops on the membrane perform the sensor readout by means of the induced voltage due to motion in a static magnetic field. The measured frequency response in a range from 500 Hz to 15 kHz allows the determination of the fluid's mass density and viscosity. This novel sensor design is well suited for miniaturization and the integration in microfluidic platforms.