Liquid Interface Detection Using Dual Polarized Microwave Sensor

Detecting the interface between liquid components is crucial for flow and level measurements. This paper presents a simple, safe, and non-invasive technique for liquid interface detection using a dual-polarized microwave sensor (DPS). The sensor is a circular slot fed by two orthogonal microstrip lines to generate two orthogonal field polarizations. The sensor is used to irradiate the material and intercept the scattered waves from it at the two polarizations. Operating at two polarizations allows detecting the interface and determining its orientation. A prototype sensor was designed to operate in the frequency range of 20 to 22 GHz. The proposed sensing technique was validated using both simulations and measurement. The prototype sensor was used to detect the interface between three materials (water, crude oil, and air). A change of about 9 dB in the magnitude of the reflection coefficient is observed when the probe is scanned from the full water region to the air region in measurement.