Reflective-Mode Submersible Microwave Sensor

This paper presents a submersible sensor devoted to the dielectric characterization of liquids and/or to the determination of liquid composition. The device is a one-port microwave permittivity sensor operating in reflective mode and implemented in microstrip technology. Particularly, the sensor consists of a step-impedance open-ended transmission line, and the sensing region, the one that should be in contact with the liquid under test (LUT), is the open-ended section. Such section is designed to exhibit an electrical length of roughly 90° at the operating frequency and a high characteristic impedance, since this enhances the sensitivity. In order to avoid substrate absorption, a PET film covers the sensing region, whereas the non-sensitive region of the device is coated with rubber and PLA in a mechanical arrangement (case) that prevents from liquid leakage to that region. The device exhibits good sensitivity, and it is validated by submersing it in various mixtures of DI water and ethanol.