A Noncontact Microwave Sensor Based on Cylindrical Resonator for Detecting Concentration of Liquid Solutions

This article presents a microwave sensor composed of a cylindrical cavity resonator and thin plastic liquid container for noncontactual detection of the liquid solution concentration. The resonant frequency is tuned to around 11 GHz, resulting in miniaturized dimensions and easy integration with a wireless sensor system. The sensor is with a small volume of 21 cm3 and sensitivity of 0.4 kHz/(mg/L). Simulated results show a good linear relationship between the concentration of the sample solution and resonant frequency shift with the high sensitivity, which is consistent with the experimental result. Compared with other designs, the sensor also has a simple structure, low cost and easy implementation to in-situ and in-vitro detection scenarios.