Test tube dedicated microwave liquid dielectric sensor for non-contact properties change monitoring and material characterization with tube exchange capability

The paper presents a novel measurement technique for non-contact properties change monitoring and material characterization which is suitable for in-progress monitoring of processes, especially ones using corrosive reagents or reactive materials. The method relies on sensing of dielectric properties of liquids contained inside a test tube at microwave frequencies by a quasi-parallel-plate transmission line type sensor. The theoretical study is validated with experimental data in terms of extracting complex effective permittivity and response reproducibility on an example of various alcohols. This is followed by measurements of ethanol-water and water sodium persulfate solutions. The determined concentration-normalized differential reflection coefficient transfer curves for a discrete set of frequencies up to 2 GHz indicated sensitivity up to 14 dB/ml and -172 degrees/ml with a resolution in the range of 6-7 mu l for the former solution and up to -17 dB/g and -31 degrees/g. The obtained results prove the usability of the developed method.