A Non-Contact Method for Detecting and Distinguishing Chloride and Carbonate Salts Based on Dielectric Properties Using a Microstrip Patch Sensor

Abstract

A non-contact method for detecting salt concentration in water using a microstrip patch sensor is presented in this work. The microstrip patch sensor, which has a low cost and simple build process, consists of a circular split ring resonator (SRR) with a hole drilled through the substrate in the middle area, and a microstrip patch antenna. The sensor was designed and fabricated using a printed circuit board (PCB) technique based on a negative dry film photoresist and photolithography method. It was built on an Arlon DiClad 880 substrate with a thickness of 1.6 mm and a relative permittivity of 2.2. The resonant frequencies (Fr) and reflection coefficients (S11) in the frequency range from 0.5 GHz to 0.8 GHz were recorded for analysis, both through simulation and experiment. The concentration of chloride and carbonate salts was varied from 0 mg/mL to 20 mg/mL in the tests using the sensor. The statistical analyses of S11 and Fr data obtained from measurements of five different salts at seven different concentrations (using the Shapiro–Wilk test, Bartlett test, and Kruskal–Wallis H test) were conducted using R version 4.2.0 to determine the relationship between the individual salts. The experimental results showed that the frequency response and resonance amplitude are functions of the concentration of each salt. The proposed method has the potential to be used for the non-contact measurement of industrial products, food quality, and health in the future.