scholarly journals Spatial Retrieval of Broadband Dielectric Spectra

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 2780 ◽  
Author(s):  
Jan Bumberger ◽  
Juliane Mai ◽  
Felix Schmidt ◽  
Peter Lünenschloß ◽  
Norman Wagner ◽  
...  
Keyword(s):  
Transmission Line ◽  
Frequency Domain ◽  
Water Saturation ◽  
Complex Refractive Index ◽  
Homogeneous Material ◽  
Optimization Approach ◽  
Dielectric Spectra ◽  
Index Model ◽  
Shuffled Complex Evolution ◽  
Automatic Adaptation

A broadband soil dielectric spectra retrieval approach ( 1 MHz– 2 GHz) has been implemented for a layered half space. The inversion kernel consists of a two-port transmission line forward model in the frequency domain and a constitutive material equation based on a power law soil mixture rule (Complex Refractive Index Model - CRIM). The spatially-distributed retrieval of broadband dielectric spectra was achieved with a global optimization approach based on a Shuffled Complex Evolution (SCE) algorithm using the full set of the scattering parameters. For each layer, the broadband dielectric spectra were retrieved with the corresponding parameters thickness, porosity, water saturation and electrical conductivity of the aqueous pore solution. For the validation of the approach, a coaxial transmission line cell measured with a network analyzer was used. The possibilities and limitations of the inverse parameter estimation were numerically analyzed in four scenarios. Expected and retrieved layer thicknesses, soil properties and broadband dielectric spectra in each scenario were in reasonable agreement. Hence, the model is suitable for an estimation of in-homogeneous material parameter distributions. Moreover, the proposed frequency domain approach allows an automatic adaptation of layer number and thickness or regular grids in time and/or space.

Comparison of different dielectric models to calculate water saturation and estimate textural parameters in partially saturated cores

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. E303-E318
Author(s):  
Vasileios-Marios Gkortsas ◽  
Lalitha Venkataramanan ◽  
Kamilla Fellah ◽  
David Ramsdell ◽  
Chang-Yu Hou ◽  
...  
Keyword(s):  
Water Saturation ◽  
Complex Refractive Index ◽  
Proton Nuclear Magnetic Resonance ◽  
Accurate Estimation ◽  
Porous System ◽  
Dielectric Measurements ◽  
Index Model ◽  
Carbonate Cores ◽  
Textural Parameters ◽  
Good Agreement

Accurate estimation of water saturation is central in predicting capillary pressure and relative permeability, under special core analysis in the laboratory. We have explored the use of dielectric measurements at different frequencies to estimate water saturation. In addition to water saturation, dielectric measurements are sensitive to the distribution of water and oil in a porous system, reflected by the apparent cementation factor [Formula: see text], which describes the water phase tortuosity. We have performed an experimental study to benchmark water saturation from dielectric measurements on eight carbonate cores and estimated their cementation exponent [Formula: see text] and saturation exponent [Formula: see text] in Archie’s equation from dielectric data. All cores went through a series of drainage/imbibition steps, creating varying saturations of brine/fluorocarbon. Fluorocarbon was chosen because it is invisible to proton nuclear magnetic resonance (NMR). Therefore,NMR porosity represents only the water-filled porosity and can be used to benchmark dielectric water-filled porosity. Three dielectric models were used for the comparison of the dielectric water-filled porosity with the one from NMR, i.e., the complex refractive index model (CRIM), bimodal model, and Stroud-Milton-De (SMD) model, and very good agreement of 1.5 porosity units on average is found. Despite its simplicity, CRIM predicted well the water-filled porosity in this experiment. However, it cannot provide information about the texture, which is captured by bimodal and SMD models. We also estimated [Formula: see text] and [Formula: see text] based on [Formula: see text] found from bimodal and SMD models, and good agreement with [Formula: see text] from resistivity data was shown. This is the first time to our knowledge that such a rich set of dielectric and NMR measurements was acquired at different saturation stages in a surface laboratory. This study is useful in benchmarking the water saturation from dielectrics, comparing different dielectric models, and demonstrating feasibility of estimating textural parameters.

scholarly journals Simultaneous measurement of hysteresis in capillary pressure and electric permittivity for multiphase flow through porous media

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. A41-A45 ◽  
Author(s):  
Willem-Jan Plug ◽  
Evert Slob ◽  
Johannes Bruining ◽  
Leticia M. Moreno Tirado
Keyword(s):  
Multiphase Flow ◽  
Capillary Pressure ◽  
Complex Permittivity ◽  
Phase Distribution ◽  
Water Saturation ◽  
Complex Refractive Index ◽  
Complex Impedance ◽  
Electric Permittivity ◽  
Index Model ◽  
Unconsolidated Sand

We present a tool that simultaneously measures the complex permittivity and the capillary pressure characteristics for multiphase flow. The sample holder is a parallel plate capacitor. A precision component analyzer is used to measure the impedance amplitude and phase angle as a function of frequency ([Formula: see text] to [Formula: see text]). The complex impedance of the (partially) saturated sample is directly related to the effective complex permittivity. We have conducted main drainage and main imbibition cycles for unconsolidated sand-water-gas [Formula: see text] systems at 8-bar pressure and at temperatures between [Formula: see text] and [Formula: see text]. Hysteresis in capillary pressure and electric permittivity, as a result of phase distribution, is found between drainage and imbibition for [Formula: see text] and becomes more pronounced at higher water saturations. Good agreement of the measured electric permittivity with the complex refractive index model indicates that induced polarization is not observed for [Formula: see text] and the water saturation is reasonably predicted. The experiments have been performed to study the capillary pressure behavior during [Formula: see text] sequestration.

scholarly journals Optimising the Complex Refractive Index Model for Estimating the Permittivity of Heterogeneous Concrete Models

2021 ◽  
Vol 13 (4) ◽  
pp. 723
Author(s):  
Hossain Zadhoush ◽  
Antonios Giannopoulos ◽  
Iraklis Giannakis
Keyword(s):  
Refractive Index ◽  
Shape Factor ◽  
Complex Refractive Index ◽  
Fdtd Method ◽  
Air Voids ◽  
Water Fraction ◽  
Index Model ◽  
General Complex ◽  
Ground Penetrating ◽  
Fine Tune

Estimating the permittivity of heterogeneous mixtures based on the permittivity of their components is of high importance with many applications in ground penetrating radar (GPR) and in electrodynamics-based sensing in general. Complex Refractive Index Model (CRIM) is the most mainstream approach for estimating the bulk permittivity of heterogeneous materials and has been widely applied for GPR applications. The popularity of CRIM is primarily based on its simplicity while its accuracy has never been rigorously tested. In the current study, an optimised shape factor is derived that is fine-tuned for modelling the dielectric properties of concrete. The bulk permittivity of concrete is expressed with respect to its components i.e., aggregate particles, cement particles, air-voids and volumetric water fraction. Different combinations of the above materials are accurately modelled using the Finite-Difference Time-Domain (FDTD) method. The numerically estimated bulk permittivity is then used to fine-tune the shape factor of the CRIM model. Then, using laboratory measurements it is shown that the revised CRIM model over-performs the default shape factor and provides with more accurate estimations of the bulk permittivity of concrete.

Experimental determination of bulk dielectric properties and porosity of porous asphalt and soils using GPR and a cyclic moisture variation technique

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. K93-K102 ◽  
Author(s):  
W. L. Lai ◽  
W. F. Tsang ◽  
H. Fang ◽  
D. Xiao
Keyword(s):  
Water Saturation ◽  
Complex Refractive Index ◽  
Large Mass ◽  
Small Mass ◽  
Time Domain Reflectometry ◽  
Water Permeation ◽  
Moisture Variation ◽  
Wide Range ◽  
Test Materials ◽  
Variation Technique

This paper describes a new method for determining porosities in two porous construction and geologic materials (asphalt and soil) by using ground-penetrating radar (GPR) over a wide range of controlled degrees of water saturation [Formula: see text]. We call this method a cyclic moisture variation technique (CMVT). Freshwater is used as an enhancer or a tracer to allow GPR to easily detect and differentiate amounts of water or other moisture in these materials. The CMVT is based on measuring the changes of real permittivity [Formula: see text] and [Formula: see text] in the test materials as they transition from partially saturated states to a fully saturated state via cycles of water permeation and dewatering. This method does not disturb the test materials, as do the methods associated with traditional laboratory testing on cored samples. It also tests a large mass of in situ material, compared with the small mass tested by the conventional or electromagnetic coaxial transmission line (EMCTL) method (also known as a dielectric cell) and the time-domain reflectometry (TDR) method. Porosity values of asphalt [Formula: see text] and of soils [Formula: see text] were determined by fitting the data into the complex refractive index model (CRIM). Dielectric hysteresis of both soils and asphalt also is observable during the tests and shows that the pathways of water-ingress and water-egress processes are not identical in the plot of [Formula: see text] versus degrees of water saturation [Formula: see text].

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