Planar microwave sensor for detection and discrimination of aqueous organic and inorganic solutions

A planar microwave sensor based on a coplanar waveguide (CPW) loaded with a circular split ring resonator (SRR) was developed for the detection and estimation of salts, sugars and organic acids in aqueous solution. The magnitudes of the spectra at resonance frequencies of 2.3-2.6 GHz were shown to provide a rapid and reliable way to measure concentrations of materials such as sucrose, sorbitol, glucose, fructose, CaCl2, NaCl, KCl, MgCl2, Na2CO3 and citric acid. We generated linear and nonlinear regression prediction models built from correlations between the magnitudes of the transmission coefficient (S21) and concentration of materials using coefficient of determination (R2). Principle component analysis (PCA) method was used for discrimination of liquid solution samples. The studies clearly showed sample concentrations in the range from 4 to 20% (w/V) were correlated with the magnitude of S21 and could be detected by using the proposed sensor. Aqueous solution samples could be discriminated into two groups based on magnitude of the spectra of S21 of different solutions at various concentrations. The proposed device can be used to distinguish between organic and inorganic materials in aqueous solution.