Slow Microwave Sensor Based on Engineered −1/x-Like Function Transmission for Improved Sensitivity

Abstract

A novel sensing method that uses the separate design of a sensitivity enhancer and sensing zone is reported. Unlike most resonance-based sensors, the flexible design of a sensing zone is beneficial to the increment of effective material-under-test volume. A novel technique to enhance sensitivity is proposed by engineering the −1/<inline-formula> <tex-math notation= LaTeX >$x$ </tex-math></inline-formula>-like function microwave transmission to slow the energy-flow velocity. The measured large group delay is up to <inline-formula> <tex-math notation= LaTeX >$\\sim 16~\\mu \\text{s}$ </tex-math></inline-formula> at 2.967 GHz. A lumped model is built to study the condition of the engineered transmission. Compared with a regular coplanar waveguide sensor, the sensitivity is improved up to ~227 times when it is connected to the slow microwave circuit.