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Sensors 2019, 19(8), 1765; https://doi.org/10.3390/s19081765

Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes

1
NORCE Norwegian Research Centre AS, Fantoftvegen 38, NO-5892 Bergen, Norway
2
Department of Physics and Technology, University of Bergen, Allégaten 55, NO-5007 Bergen, Norway
*
Author to whom correspondence should be addressed.
This manuscript is extension version of the conference paper: Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes. In Proceedings of the 12th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances (ISEMA), Lublin, Poland, 4–7 June 2018.
Received: 25 February 2019 / Revised: 9 April 2019 / Accepted: 11 April 2019 / Published: 12 April 2019
(This article belongs to the Special Issue Selected Papers from ISEMA 2018)
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PDF [2588 KB, uploaded 12 April 2019]
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Abstract

This paper presents a method to simultaneously determine the thickness and permittivity of thin layers from multi-frequency reflection coefficient measurements using an open-ended coaxial probe. This is achieved by exploiting that the probe becomes radiating at frequencies higher than the probe’s typical operating range. Permittivity information is extracted from measurements in the typical frequency range, whereas thickness information is obtained from high frequency measurements by exploiting resonances that occur when the radiated waves are reflected at the layer boundary. A finite element model of the measurement set-up is made in COMSOL MultiphysicsTM, and a matrix of simulations spanning the relevant layer thicknesses and permittivity range is generated. The measured permittivity spectra of unknown samples are compared to the simulation matrix to estimate layer thickness and permittivity. The method is verified by measurements of water–ethanol mixtures. An application example where the water fraction and layer thickness of a gas hydrate deposition layer is estimated from permittivity measurements in a multiphase flow loop is also presented. View Full-Text
Keywords: open-ended coaxial probe; permittivity; thickness measurement; finite element method open-ended coaxial probe; permittivity; thickness measurement; finite element method
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Folgerø, K.; Haukalid, K.; Kocbach, J.; Peterson, A.S. Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes. Sensors 2019, 19, 1765.

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