Microwave Cylindrical Cavity Resonator Sensor for Detection and Characterization of Contaminants in Lubricating Oil

Accurate monitoring of contaminants, such as wear particles in lubricating oil, is critical for the efficient maintenance of engines. Here, a TE011-mode cylindrical cavity resonator-based sensor system is presented. In the measurement, a glass test tube was used to contain the oil sample under test and placed in the center of the cavity. Particles in oil change the dielectric properties and perturb the resonance parameters, thereby achieving sensing. Sensitivity to both the presence of conductive and nonconductive powders is demonstrated. Linear relationships between the powder weight and the quality factor are established. Hence, the degree of contamination can be better evaluated compared with existing microwave sensors. Powder differentiation can be achieved using the resonance frequency and quality factor. In addition, analytical modeling of the sensing system incorporating field analysis is proposed, and the effective permittivity of the mixture can be determined. The sensor developed is compact, portable, easy to implement, complementary to other approaches for liquid evaluation, and has the potential for high-throughput online measurement.