Detection of methanol contamination in ethyl alcohol employing a purpose-designed high-sensitivity microwave sensor

Abstract A novel method for detection of low methanol contamination in ethyl alcohol is introduced. The approach is centered around sensing the electrical permittivity of the solution at low microwave frequency range where the difference in permittivity between two liquids is very high. A high-sensitivity substrate-less coplanar strip sensor is employed featuring an application-specific design maximizing sensitivity. The open-ended one-port-differential sensor is immersed in a methanol-ethanol solution and its differential reflection coefficient is measured, out of which the concentration of methanol can be determined in real time. The sensor‘s design procedure is provided that relies on analysis of the predicted solution‘s permittivity. The theoretical study was validated by measurements of a solutions with gradually increasing methanol concentration. The obtained results show the possibility to detect methanol content in ethyl alcohol being as low as 0.02% and prove the usefulness of the presented approach for, among others, neutral spirit quality control.