This article presents a novel microstrip patch sensor featuring four rectangular rings represented by single complementary split-ring resonance (SC-SRR) to calculate the complex permittivity of saline solutions within the range of 0 ppt to 100 ppt. This sensor operates via the turbulence technique, utilizing its resonant properties as indicators to find the parameters of the liquid under test (LUT), which arise due to the variations in the salt concentration altering the complex permittivity. This alteration influences the resonant frequency (f_r), reflection coefficient (S₁₁), and quality factor (Q). The sensor was designed by using a high-frequency structure simulator (HFSS) and by using an FR-4 substrate and a Teflon box with a height of 1.4 mm and 13.7 mm, respectively. The values of S₁₁ at resonance frequency were −34.48 dB, and 2.1328 GHz, respectively. A computer numerical control (CNC) machine was used to fabricate the sensor and Teflon box, and the Teflon box was situated above the four rings to create a strong interaction between the induced electric field and the LUT, thereby achieving high sensitivity in a non-contacting and non-destructive manner. The measurement and simulation results were consistent and aligned with those of Klien and Meissner (in comparison to the theoretical values derived from the single and double Debye models). We derived numerical equations for the conductivity (S/m), dielectric constant permittivity, and concentrations (ppt) using curve fitting origin software, and the results are in good agreement. Due to its performance, we expect that the proposed sensor could be used in agricultural applications to identify freshwater and in medical applications to detect the concentration of salt in saliva or blood and to identify diseases, in addition to many other applications involving mixed liquids.

This paper presents design of a microwave sensor based on circular split ring resonator (SRR) and coplanar waveguide (CPW) transmission line with two ports. The proposed sensor is used to measurement dielectric constant characteristics for different dielectric materials. The overall dimensions of the proposed sensor configuration are of 30x 30 mm2. The measurement parameter is the transmission coefficient (S21). When the material under tested (MUT) is placed over the split ring resonator, the transmission coefficient resonance shifts. Rogers (RO3210) substrate material with dielectric constant of 10.2 and height of 1.27 mm is utilized as substrate for the proposed sensor. The resonance frequency of the proposed circular SRR sensor is 5.33 GHz. For suggested sensor, there is a non-linear relationship between the dielectric constant and resonance shift. The dielectric constant is predicted using the non-linear equation, and a good coefficient of determination is achieved.