Highly Sensitive Reflective-Mode Phase-Variation Permittivity Sensor Based on a Coplanar Waveguide Terminated With an Open Complementary Split Ring Resonator (OCSRR)

• Published in: IEEE access Vol. 9; pp. 27928 - 27944
• Main Authors: Su, Lijuan, Munoz-Enano, Jonathan, Velez, Paris, Gil-Barba, Marta, Casacuberta, Pau, Martin, Ferran
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Coplanar waveguide (CPW); Coplanar waveguides; dielectric characterization; Electric contacts; Figure of merit; Impedance; Integrated circuit modeling; microwave sensor; Microwave sensors; open complementary split ring resonator (OCSRR); Permittivity; phase-variation sensor; Reflectance; reflective-mode sensor; Resonators; Sensitivity; Sensors; Topology; Transmission line measurements; Transmission lines
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2021.3058575

This paper presents a one-port reflective-mode phase-variation microwave sensor consisting of a coplanar waveguide (CPW) transmission line terminated with a grounded open complementary split ring resonator (OCSRR). The sensor is useful for measuring the dielectric constant of the so-called material under test (MUT), which should be placed in contact with the OCSRR, the sensitive element. The output variable is the phase of the reflection coefficient. Design guidelines for the implementation of highly sensitive sensors are derived in the paper, and validated through simulation and experiment. As compared to other reflective-mode phase-variation sensors based on open-ended sensing lines, the designed and fabricated devices exhibit a very small sensitive region by virtue of the use of an electrically small resonant element, the OCSRR. The relevant figure of merit, defined as the ratio between the maximum sensitivity and the size of the sensing area (expressed in terms of the squared wavelength), is as high as FoM <inline-formula> <tex-math notation="LaTeX">= 5643^{\circ }/\lambda ^{2} </tex-math></inline-formula> in one of the reported prototypes. Moreover, the paper analyzes the effects of losses. From this study, it is concluded that MUT losses do not significantly affect the output variable, provided losses are small. It is also demonstrated that the sensor is useful to estimate the loss tangent of the considered MUT samples.