Loaded Re-Entrant Cavity Microwave Sensor for Dielectric Constant Measurement

This paper presents a novel microwave sensor combining a planar sensor with a 3D re-entrant cavity structure for measuring the permittivity of materials. The sensor is based on a re-entrant cavity loaded with a complementary split-ring resonator (CSRR). The proposed structure enhances electric field concentration at the top of cavity and excites the CSRR on the top layer. This configuration effectively couples the internal electric field of the re-entrant cavity through the CSRR and facilitates high-intensity electric fields outside the cavity for sensing material properties. The design leverages the low-loss characteristics of the cavity and provides the non-intrusive measurement advantages of the CSRR. Moreover, sensitivity for relative dielectric constants in the range of 2-10 is improved by 77.6% compared to the structure with top-open design.