Measurement of liquid complex dielectric constants using non-contact sensors

Our primary objective in this work is the accurate measurement of complex dielectric constant and conductivity of unknown liquids. In this paper we present design, fabrication, and testing results for an IDC (interdigitated capacitor) electrode sensor for use as a fluid monitoring component that can be integrated into a microfluidic system. Unlike prior work we show how to accurately extract both the conductivity and permittivity of liquids, for loss tangents ranging from much less than one to greater than one (i.e., from lossy dielectrics to conductors); this has not been shown in previous work. In addition, we also demonstrate a method of remotely accessing the IDC sensor by wireless inductive coupling similar to EAS (electronic article surveillance) tags.