Highly sensitive reflective-mode phase-variation permittivity sensors using coupled line sections
Casacuberta Orta, Pau (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)
Vélez Rasero, Paris (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)
Muñoz Enano, Jonathan (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)
Su, Lijuan (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)
Martín, Ferran (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)

Date:	2023
Abstract:	Highly sensitive permittivity sensors operating in reflection and exploiting phase variation are presented in this article. The sensors are one-port structures implemented by means of a pair of coupled lines, the sensitive region, with an appropriate termination. In particular, it is demonstrated that by either short-circuiting the crossed port to the input port of the device (opening the remaining two ports), or opening the crossed port to the input port (terminating the other two ports with a short-circuit), the sensitivity can be driven to very high values, controlled by the coupling factor. For that purpose, the electrical length of the pair of coupled lines must be set to 90° when such lines are loaded with the reference (REF) material. Thus, the sensitivity is optimized for dielectric constants (the input variable) in the vicinity of the dielectric constant of the REF material, where the indicated phase condition is fulfilled. The output variable is the phase of the reflection coefficient, an easily measurable quantity. For validation purposes, three prototype sensors are designed and fabricated. The achieved sensitivities in two of the fabricated sensors are as high as 659. 6° and 736. 0°, with figures of merit (FoMs), or ratio between the maximum sensitivity and the area of the sensing region expressed in terms of the squared-wavelength, of FoM =9401∘/λ2 and 12690°/ λ , respectively, i. e. , very competitive values. Moreover, the indicated high sensitivities and FoMs have been achieved without the need to add further circuit stages to the sensing region, contrarily to other highly sensitive phase-variation sensors, where sensitivity optimization is achieved at the expense of an increase in the overall sensor size.
Grants:	Agencia Estatal de Investigación PDC2021-121085-I00 Agencia Estatal de Investigación FPU20/05700 Agencia Estatal de Investigación PID2019-103904RB-I00 Agencia Estatal de Investigación IJC2019-040786-I Agència de Gestió d'Ajuts Universitaris i de Recerca 2017/SGR-1159
Note:	Altres ajuts: the work of Ferran Martín was supported by the Institució Catalana de Recerca i Estudis Avançats
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Subject:	Coupled lines ; Dielectric characterization ; Microstrip ; Microwave sensor ; Phase-variation sensor ; Reflective-mode sensor
Published in:	IEEE transactions on microwave theory and techniques, Vol. 71, issue 7 (Jul. 2023) , p. 2970-2984, ISSN 0018-9480

DOI: 10.1109/TMTT.2023.3234272

Available from: 2025-07-30 Postprint

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Research literature > UAB research groups literature > Research Centres and Groups (research output) > Engineering > CIMITEC-UAB
Articles > Research articles
Articles > Published articles