Liquids electrical characterization sensor using a hybrid SIW resonant cavity

Abstract

AbstractA new sensor based on substrate integrated waveguide (SIW) technology is proposed as an option for liquids electrical characterization. The sensor employs a rectangular waveguide resonant cavity filled with air, with two opposite side walls implemented by closely spaced metallic vias. The resulting structure is a hybrid SIW resonant cavity. The two noncontinuous walls of the hybrid SIW cavity allow the liquid insertion, filling its entire internal volume. The resonance frequency of the hybrid SIW cavity is used to determine the dielectric constant of the liquid to be characterized. A sensor using a hybrid SIW cavity operating in TE101 mode was designed to resonate at 5.9 GHz when filled with air. The sensor was employed to measure the dielectric constant of binary mixtures of distilled water and ethanol. Dielectric constants ranging from 21 to 79 were obtained, corresponding to measured resonance frequencies from 1,247 to 647 MHz, respectively. Good agreement was observed between computational electromagnetic simulation and experimental results. The dependence of the volumetric fraction of ethanol in the binary mixture on the sensor resonance frequency was expressed using a third‐order polynomial approximation.