Journal
IEEE SENSORS JOURNAL
Volume 21, Issue 3, Pages 2864-2872Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JSEN.2020.3023848
Keywords
CPW technology; dielectric characterization; microwave sensors; phase-variation sensors; reflective-mode sensors
Funding
- MINECO-Spain [TEC2016-75650-R]
- Generalitat de Catalunya [2017SGR-1159]
- Institucio Catalana de Recerca i Estudis Avancats
- FEDER Funds
- Secreteraria d'Universitats i Recerca (Generator Cat.)
- European Social Fund
- Juan de la Cierva Program [IJCI-2017-31339]
- Universidad Politecnica de Madrid Young Researchers Support Program [VJIDOCUPM18MGB]
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The article introduces a sensor based on reflective-mode step-impedance transmission line, which is implemented in coplanar waveguide to increase sensitivity. The sensor is useful for dielectric characterization of solids and liquids, and measurement of variables related to changes in the dielectric constant of the material under test.
Reflective-mode step-impedance transmission line based sensors for dielectric characterization of solids or liquids have been recently proposed. In this article, in order to further increase the sensitivity, the sensor is implemented in coplanar waveguide (CPW technology), and this constitutes the main novelty of this work. The sensor thus consists of a high-impedance 90 degrees (or low-impedance 180 degrees) open-ended sensing line cascaded to a low-impedance 90 degrees (or high-impedance 90 degrees) line. The output variable is the phase of the reflection coefficient, which depends on the dielectric constant of the material under test (MUT), the input variable. Placing a MUT on top of the sensing line causes a variation in the effective dielectric constant of the line, thereby modifying the phase of such line. This in turn produces a multiplicative effect on the phase of the reflection coefficient, by virtue of the step-impedance discontinuity. The main advantage of the CPW-based sensor, over other similar sensors based on microstrip technology, is the stronger dependence of the phase velocity of the sensing line with the dielectric constant of the MUT, resulting in sensitivities as high as -45.48 degrees in one of the designed sensors. The sensor is useful for dielectric characterization of solids and liquids, and for the measurement of variables related to changes in the dielectric constant of the MUT (defect detection, material composition, etc.).
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