Liquid Characterization of 2 GHz Complimentary Split Ring Resonator (CSRR) for Water Quality Applications

This study describes a complementary split-ring resonator (CSRR)-based planar microwave sensor. Its capability in detecting several samples which are based on the usual water contaminant in Malaysia was investigated. The CSRR sensor was designed with an unloaded resonant frequency of 2.0 GHz, and it was fabricated on an FR-4 substrate with a thickness of 1.6 mm and a dielectric constant of 4.3. The S-parameter responses of the sensor were measured under two conditions; i) unloaded and ii) loaded. For the latter, samples of tap water, salt water, isopropyl alcohol, filtered water and cooking oil were used to load the resonant element of the CSRR. The measurement result of unloaded CSRR shows that the designed sensor resonates at 1.99 GHz, which is in line with the simulation. The measurement results also showed that the presence of all samples caused the resonant frequency of the CSRR to shift, with filtered water and cooking oil showing the biggest frequency shifts (0.84 GHz and 0.96 GHz, respectively). A sensitivity analysis of the CSRR was carried out and it shows that it achieves 0.25% sensitivity. The proposed sensor may be a useful substitute for pricey commercial sensors for applications involving water quality because of the inexpensive materials and ease of fabrication.