Enhanced Displacement Sensing via Selective Excitation of Higher-Order Modes in a Cylindrical Dielectric Resonator

This paper presents the systematic design and characterization of a cylindrical dielectric resonator (CDR)-based displacement sensor operating under dual excitation modes. To begin with, the CDR is investigated through radar cross-section analysis to identify the natural resonant modes. Each mode is subsequently excited by using a simple microstrip feed line to evaluate its suitability for displacement sensing in terms of resonant frequency, sensitivity, and dynamic range. Numerical simulations identify the TE011+δand HEM12δmodes are found to exhibit superior sensing capabilities compared to all other supported modes. Further, a transmission-mode sensor configuration is then proposed, wherein both modes are simultaneously excited using a pair of 180° aligned offset microstrip lines integrated within the same CDR structure, allowing to compare the sensitivity performance of the higher-order mode with respect to the fundamental mode. This dual-mode excitation enables the sensor to harness the complementary features of both modes simultaneously. Comprehensive full-wave simulations are carried out in HFSS to validate the concept, and a prototype is fabricated and experimentally characterized. The measured results show good agreement with simulations, confirming that the proposed sensor achieves a nearly threefold improvement in sensitivity with the higher-order mode, though at the expense of reduced dynamic range.