A Dielectric Cavity Antenna Based Microwave Sensor for Analysis of Engine Oils and Liquid Chemicals

Abstract A dielectric cavity antenna–based resonant microwave sensor with enhanced sensitivity has been proposed for detecting the quality and volume of engine oils. Unlike conventional microwave sensors, the proposed design uses a single‐port configuration, and the cavity is entirely fabricated using FR‐4 dielectric material. The resonant frequency of the cavity antenna operating in the TM 10​ mode is shown to be highly responsive to variations in both oil quality and volume. For an air‐filled cavity, the sensor resonates at 3.23 GHz. When fully loaded (10 mL) with fresh and used engine oil samples (the latter collected after 5,000 km of engine operation), the resonant frequencies shift to 2.642 and 2.540 GHz, respectively. The dielectric sensitivity of the sensor, measured between the air‐filled and fresh‐oil‐loaded conditions, is 443 MHz/ε. Additionally, the sensor exhibits a volume sensitivity of 85 MHz/mL for fresh oil and 92 MHz/mL for used oil, demonstrating its capability to distinguish both oil condition and volume with high resolution. Beyond engine oil characterization, the sensor effectively differentiates between chemical liquids such as xylene, acetic acid, and benzene, based on their distinct resonant frequencies. These results confirm the potential of the proposed cavity‐based microwave sensor as a reliable, low‐cost, and high‐sensitivity solution for liquid quality monitoring and volume measurement in industrial applications.