A technique for non-contact identification of liquids in closed containers using microwave planar metamaterial

At present, the fast non-contact identification of liquids is a real-life task for security systems and quality testing of various drinks. The possibility of identifying liquids in containers using a technique based on two oppositely connected planar photonic crystals (PPCs) with microwaves was experimentally demonstrated. The influence of the thickness of the container's walls, the container's diameter, and the inclination angle of the container axis relative to the plane of the planar photonic crystal on the reliability of the non-contact identification of liquids was experimentally investigated. The minimum change in the concentration of aqueous solutions of ethyl alcohol, sugar, and food salt that could be reliably distinguished in solutions was defined. For liquids containing water in thin plastic containers, the optimum operating frequency band (about 2 GH to 4 GHz) of the experimental setup for their identification was found. The maximum thickness of the container wall at which the required reliability of the identification of liquids was achieved was evaluated for several selected operating frequencies. The possibility of non-contact analysis of not only aqueous solutions of ethyl and methyl alcohol, but also of their mixes, was experimentally shown. The developed technique for fast non-contact identification of liquids can be applied for food quality control, security systems, and chemical technologies.