Reflective-Mode Phase-Variation Permittivity Sensors Based on Coupled Resonators
Pau Casacuberta, Paris Vélez, Jonathan Muñoz-Enano, Lijuan Su, Marta Gil, Ferran Martı́n
Abstract
This paper presents a novel strategy for the implementation of highly sensitive reflective-mode (one-port) phase-variation permittivity sensors based on coupled resonators (the sensing elements). It is demonstrated that by tuning the frequency of the feeding harmonic signal in the vicinity of the resonance frequency of the isolated resonators, and by weakly coupling the resonant elements, the phase of the reflection coefficient (the output variable) experiences a significant variation with the dielectric constant of the material under test (MUT), resulting in a high sensitivity. Two prototype examples, based on a pair of step-impedance resonators (SIRs), are presented as proof-of-concept demonstrators for validation purposes. The achieved sensitivity in one of the sensors is 468°, providing an unprecedented figure of merit (or ratio between the maximum sensitivity and the area of the sensing region expressed in terms of the squared guided wavelength) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{FoM}=27419^{\circ}/\lambda^{2}$</tex> .