Electric fields in fluidic channels and sensor applications with capacitance

Abstract

The application of common printed circuit board (PCB) technology to fluidic microsystems allows the generation of an electric field around two opposite copper walls of a fluidic channel. The shape of the electric field depends on the geometry of the channel construction and the fluid inside the channel. When passing a fluid between the tracks, the electrical capacitance changes as well as other properties between these copper tracks. Simulations of the distributed electric field around and inside of the channel are described and compared with practical measurements. Two application examples are given: the first is a compact bubble detector applied to find gas bubbles in a fluid, operating on the principle of capacitance measurement between channel walls. The second is a flow sensor using the Faraday principle of magnetic induction that measures the electric potential across capacitors. It works without direct contact with the electrodes and the fluid.