Liquid sensing in aquatic environment using high quality planar microwave resonator

This paper describes a non-contact liquid sensor operating in an aquatic environment using an active, feedback loop assisted, planar, micro strip microwave resonator. The proposed sensor has the ability to operate in noncontact fashion within a distance of 0 to 8 cm. The active loop technique is shown to increase the primary quality factor from 210 to 500,000 in air when measured at a resonant frequency of 1.52 GHz. The quality factor of the proposed resonator is adjustable with the direct current (DC) bias voltage and is set to 450,000 in the presence of an aquatic medium. The ability to adjust the quality factor of the reported microwave sensor allows for larger dynamic range and permittivity variation monitoring. Different shifts in resonant frequency are reported in the presence of various liquid samples in tubes which are submerged in deionized (DI) water. The proposed device is used to distinguish between Water, Ethanol, Methanol, Isopropanol, and Acetone in a submerged tube inside a water filled container.