Microwave Characterization of Liquid Mixtures with a Miniaturized Interdigital Sensor

A miniaturized microstrip interdigital capacitor based sensor is proposed herein to characterize liquid mixtures. For low RF/microwave measurements, the sensing area is modeled as a capacitance in parallel with a conductance. According to the conformal mapping technique, a linear relationship between the capacitance and the permittivity of the liquid under test is obtained, which is further validated through a three-dimensional finite element simulation method. The sensor is then successfully used to characterize deionized water, pure isopropanol, and water-isopropanol mixtures.