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.
Highlights
The interaction of electromagnetic waves with matter is sensitive to various physical and chemical parameters ([1,2])
The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interfacial processes
The measured broadband electromagnetic material properties of COx were used as input data in
Summary
The interaction of electromagnetic waves with matter is sensitive to various physical and chemical parameters ([1,2]). Time or frequency domain reflectometry (TDR [4] or FDR [5]) methods fulfill this requirement for quantitative estimation of spatial and temporal evolution of the water content in porous media. In this context, the HF-EM method represents a powerful tool for the safety solutions of management for nuclear structure or nuclear waste repository. The broadband dielectric characterization of non-disturbed clay rock as a function of water content in laboratory scale is necessary These aspects were addressed in the first part of this study, based on the previous experimental investigations according to [14].
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