A low-cost viscosity sensor based on electrowetting on dielectrics (EWOD) forces

Abstract

We study the fluid dynamics of polar high-k fluids immersed in non-polar insulating fluids, which are excited by Electrowetting-On-Dielectric (EWOD) forces inside a tube with pressure compensation channels (PCCs). The fluids are set in motion using the electrowetting effect resulting in a pressure difference inside the tube. A model of the pressure field for various viscosities of the surrounding fluid is obtained by finite element analysis of the Navier-Stokes equation. From the time-dependent pressure response and the associated viscous damping, a correlation with the fluid’s dynamic viscosity is obtained. In the next step, we study the pressure evolution after driving the polar fluid in one direction and stopping it rapidly at the edge of the driving electrode. The decay time of the pressure induced height difference inside the PCCs can also be related to the surrounding non-polar fluid’s viscosity. Subsequently, an alternative low-cost fabrication process of an EWOD stack is used to build the device simulated. The built device is tested by measuring silicon oils and a comparison between already established methods for viscosity sensing and our “tube” method is made.