Detection of liquid mixtures by using a novel microwave sensor based on a multi-band one-port interdigitated split ring resonator structure

The design, fabrication and measurement of a novel multi-band microwave sensor based on a one-port interdigitated split ring resonator able to detect liquids mixtures is presented in this work. The sensitive region of the proposal is 13.5mm×21.55mm allowing for measuring samples with a maximum volume of 1 ml. In addition, a sample holder is proposed to avoid the possible oxidation of the electrodes due to the direct contact with the liquid under test. Empty sensor was designed to present four resonances between 0.5 GHz and 3.2 GHz in order to operate the sensor at different bands. Experimental validation was performed using 11 mixtures of water with alcohols (isopropyl and methanol) and glyphosate-based herbicide mixtures with different concentrations between 0% and 100%. From measurements, it was found that for the herbicide case, the Band-2 (1.3 GHz – 1.6 GHz) exhibits the best response and for the alcohol-based mixtures two bands are useful for sensing applications (Band-3 between 2.1 GHz – 2.7 GHz, and Band-4 between 2.9 GHz and 3.1 GHz) with a maximum sensitivity of 1.12%. Finally, results demonstrated that the proposed sensor could have potential for environmental applications.