Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect

Bore, Thierry, Wagner, Norman, Lesoille, Sylvie Delepine, Taillade, Frederic, Six, Gonzague, Daout, Franck and Placko, Dominique (2016) Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect. Sensors, 16 4: 1-14. doi:10.3390/s16040554


Author Bore, Thierry
Wagner, Norman
Lesoille, Sylvie Delepine
Taillade, Frederic
Six, Gonzague
Daout, Franck
Placko, Dominique
Title Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect
Journal name Sensors   Check publisher's open access policy
ISSN 1424-8220
1424-8239
Publication date 2016-04-18
Sub-type Article (original research)
DOI 10.3390/s16040554
Open Access Status DOI
Volume 16
Issue 4
Start page 1
End page 14
Total pages 14
Place of publication Basel, Switzerland
Publisher MDPI AG
Collection year 2017
Language eng
Abstract Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling.
Keyword Water content measurement
TDR probe
Clay-rock
Dielectric spectroscopy
Frequency domain finite element modeling
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Civil Engineering Publications
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