A novel microwave dielectric resonator-based differential frequency sensor for angular displacement detection

Abstract

A differential frequency microwave sensor for angular displacement detection is reported. A metal strip-loaded cylindrical dielectric resonator (SL-CDR) is excited with a 50 Ω-microstrip transmission line through a rectangular slot made on the transmission line’s ground plane. Analysis of the transmission coefficient spectrum (|S21| vs frequency) of the resulting circuit shows that for the parallel alignment of SL-CDR relative to the slot (θ = 00), dual-transmission zeros are excited at frequencies fL and fH. In contrast, for the perpendicular alignment (θ = 900), a single transmission zero is excited at f0 where fL < f0 < fH. When θ increases from 00 to 900, fL increases towards f0 while fH decreases towards f0. This opposing trend observed at fL and fH is attributed to the difference in the perturbation experienced by the respective electromagnetic modes of the SL-CDR after loading the metal strip. The resulting differential frequency parameter Δf = fH−fL is adopted to indicate θ, the angular displacement, following a simulation study with ANSYS HFSS. Subsequent prototype fabrication and Vector Network Analyzer (VNA) measurement confirm the simulations with 15.5 MHz/0 sensitivity and excellent linearity over the dynamic range of 900. As the final step, the measured differential frequencies are mapped to the angular displacement (θ←Δf) using linear inverse regression, and the extracted regression parameters confirm accurate mapping.