A double membrane sensor for liquid viscosity facilitating measurements in a large frequency range

Abstract

In this contribution a resonating sensor for viscosity and mass density facilitating measurements at different frequencies is presented. A sample liquid is subjected to time harmonic shear stress induced by two opposed vibrating polymer membranes. These membranes, placed in an external static magnetic field, carry two conductive paths each. The first path is used to actuate the membranes by means of Lorentz forces while the second acts as a pick-up coil providing an induced voltage representing the movement of the membrane. From the resulting frequency response the liquid’s viscosity and mass density can be obtained. This double membrane based setup allows to examine the test liquid at adjustable frequencies in the low kilohertz range from 500 Hz to 20 kHz. This novel sensor design is suitable, e.g., for low cost handheld devices with inline capabilities and disposable sensor elements.