Density Sensitive Driving Mode of a Double Membrane Viscometer

This contribution shows the applicability of the double membrane sensor presented earlier for high sensitivity mass density sensing. The sensor is based on two opposed membranes vibrating in parallel in a sample liquid. Excitation and read-out of the membrane vibration are based on Lorentz forces induced in a static magnetic field. Each membrane carries three conductive paths for excitation which can be separately connected to the excitation currents. This possibility allows for switching between viscosity or mass density sensitive driving mode, which is analyzed in this contribution. Measurements with various test liquids show, that the frequency of the fundamental mode strongly decreases with increasing mass density. Comparing the results with measurements achieved with earlier designs indicates an increased sensitivity on density featuring a reasonably sustained quality factor for increasing viscosities.