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Timeline of Norman Wagenr

2018
Aug
30
Published new article




Article

An iono-elastomer based wearable strain sensor with real-time thermo-mechano dual response

Published: 30 August 2018 by American Chemical Society (ACS) in ACS Applied Materials & Interfaces

doi: 10.1021/acsami.8b10672

An ultrastretchable iono-elastomer with resistance sensitive to both elongation strain and temperature has been developed by hierarchical self-assembly of an end functionalized triblock copolymer in a protic ionic liquid (ethylammonium nitrate) followed by cross-linking. Small-angle X-ray scattering experiments in situ with uniaxial elongation reveal a nanoscale microstructural transition of the hierarchically self-assembled cross-linked micelles that is responsible for the material’s remarkable mechanical and ionic conductivity responses. The results show that the intermicelle distance extends along the deformation direction while the micelles organize into a long-range ordered face-centered-cubic structure during the uniaxial elongation. Besides good cyclability and resistance to selected physical damage, the iono-elastomer simultaneously achieves an unprecedented combination of high stretchability (340%), highly linear resistance vs elongation strain (R2 = 0.998), and large temperature gauge factor (ΔR/R = 3.24%/°[email protected] °C). Human subject testing demonstrates that the iono-elastomer-based wearable thermomechanical sensor is able to effectively and accurately register both body motion and skin temperature simultaneously.

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2018
Aug
23
Published new article




Article

Spatial Retrieval of Broadband Dielectric Spectra

Published: 23 August 2018 by MDPI in Sensors

doi: 10.3390/s18092780

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.

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2018
Aug
01
Published new article




Article

A New Broadband Dielectric Model for Simultaneous Determination of Water Saturation and Porosity

Published: 01 August 2018 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Geoscience and Remote Sensing

doi: 10.1109/tgrs.2018.2835447

In this paper, we propose a novel approach to broadband model relative effective complex permittivity of soils (augmented broadband complex dielectric mixture model). The approach involves a combination of mixture equation and relaxation model. The mixture equation is an extension in frequency domain developed from a volume average approach. The relaxation model aims at integrating polarization effects that would occur over the frequency range under interest. In this framework, the relative effective complex permittivity is computed from a set of parameters including water saturation, porosity, cementation exponent, and relaxation parameters. The proposed model was tested and validated on a new set of data measured over the 1-MHz-3-GHz frequency range on compacted kaolin. The model was fit to the measured spectra with satisfactory agreement in terms of root-square-mean error. Furthermore, the comparison between estimated and experimentally measured water saturation and porosity has shown a good correlation. This indicates the great potential of this new model for monitoring state parameters for applications in geophysics and geotechnics.

0 Reads | 1 Citations
2018
Jun
01
Published new article






Electromagnetic Characterization of Coarse-Grained Soils with a One Port Large Coaxial Cell

Published: 01 June 2018 by Institute of Electrical and Electronics Engineers (IEEE) in 2018 12th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances (ISEMA)

doi: 10.1109/isema.2018.8442281

This paper reports the design, the calibration and the application of a one port large coaxial cell. The objective of the device is to characterize the electromagnetic properties of compacted and partly saturated coarse grained soil under controlled boundary conditions. The dielectric spectra were obtained by means of fitting the measured scattering function using a Transvers electromagnetic mode (TEM) propagation model considering the frequency dependent complex permittivity. The method was applied on a construction site material with aggregate up to 15 mm. 6 samples were characterized, the results showing a good agreement in terms of Root Mean square error.

0 Reads | 0 Citations
2018
Jun
01
Published new article






Dielectric Spectra Reconstruction of Layered Multi-Phase Soil

Published: 01 June 2018 by Institute of Electrical and Electronics Engineers (IEEE) in 2018 12th International Conference on Electromagnetic Wave Interaction with Water and Moist Substances (ISEMA)

doi: 10.1109/isema.2018.8442324

A broadband soil dielectric spectra retrieval approach (1 MHz to 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 of a power law soil mixture rule (Complex Refractive Index Model - CRIM) considering (i) the volume fractions of the soil phases, (ii) dielectric relaxation of the aqueous pore solution, (iii) electrical losses and (iv) low frequency dispersion due to the interactions between the pore solution and solid particles. The spatially distributed reconstruction of broadband dielectric spectra is achieved with a global optimization approach based on a Shuffled Complex Evolution (SCE) algorithm using the full set of the scattering parameter. The possibilities and limitations of the inverse parameter estimation were numerically analyzed.

0 Reads | 0 Citations
2017
Dec
14
Published new article




Article

A large coaxial reflection cell for broadband dielectric characterization of coarse-grained materials

Published: 14 December 2017 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/1361-6501/aa9407

Knowledge of the frequency-dependent electromagnetic properties of coarse-grained materials is imperative for the successful application of high frequency electromagnetic measurement techniques for near and subsurface monitoring. This paper reports the design, calibration and application of a novel one-port large coaxial cell for broadband complex permittivity measurements of civil engineering materials. It was designed to allow the characterization of heterogeneous material with large aggregate dimensions (up to 28 mm) over a frequency range from 1 MHz–860 MHz. In the first step, the system parameters were calibrated using the measured scattering function in a perfectly known dielectric material in an optimization scheme. In the second step, the method was validated with measurements made on standard liquids. Then the performance of the cell was evaluated on a compacted coarse-grained soil. The dielectric spectra were obtained by means of fitting the measured scattering function using a transverse electromagnetic mode propagation model considering the frequency-dependent complex permittivity. Two scenarios were systematically analyzed and compared. The first scenario consisted of a broadband generalized dielectric relaxation model with two Cole–Cole type relaxation processes related to the interaction of the aqueous phase and the solid phase, a constant high frequency contribution as well as an apparent direct current conductivity term. The second scenario relied on a three-phase theoretical mixture equation which was used in a forward approach in order to calibrate the model. Both scenarios provide almost identical results for the broadband effective complex relative permittivity. The combination of both scenarios suggests the simultaneous estimation of water content, density, bulk and pore water conductivity for road base materials for in situ applications.

0 Reads | 1 Citations
2017
Apr
01
Published new article




Article

Thermal and dielectric behaviour of fine-grained soils

Published: 01 April 2017 by Thomas Telford Ltd. in Environmental Geotechnics

doi: 10.1680/jenge.15.00042

0 Reads | 3 Citations
2017
Apr
01
Published new article






Soil Collapse Monitoring with EM Measurements

Published: 01 April 2017 by Avestia Publishing in The 2nd World Congress on Civil, Structural, and Environmental Engineering

doi: 10.11159/icgre17.158

0 Reads | 0 Citations
2017
Feb
06
Published new article




Article

Experimental investigation of the dielectric properties of soil under hydraulic loading

Published: 06 February 2017 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/1361-6501/aa5442

0 Reads | 1 Citations
2017
Feb
01
Published new article




Article

Electromagnetic techniques in geoenvironmental engineering

Published: 01 February 2017 by Thomas Telford Ltd. in Environmental Geotechnics

doi: 10.1680/envgeo.13.00104

0 Reads | 1 Citations
2016
Dec
08
Published new article




Article

Broadband electromagnetic analysis of compacted kaolin

Published: 08 December 2016 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/1361-6501/28/1/014016

The mechanical compaction of soil influences not only the mechanical strength and compressibility but also the hydraulic behavior in terms of hydraulic conductivity and soil suction. At the same time, electric and dielectric parameters are increasingly used to characterize soil and to relate them with mechanic and hydraulic parameters. In the presented study electromagnetic soil properties and suction were measured under defined conditions of standardized compaction tests. The impact of external mechanical stress conditions of nearly pure kaolinite was analyzed on soil suction and broadband electromagnetic soil properties. An experimental procedure was developed and validated to simultaneously determine mechanical, hydraulic and broadband (1 MHz–3 GHz) electromagnetic properties of the porous material. The frequency dependent electromagnetic properties were modeled with a classical mixture equation (advanced Lichtenecker and Rother model, ALRM) and a hydraulic-mechanical-electromagnetic coupling approach was introduced considering water saturation, soil structure (bulk density, porosity), soil suction (pore size distribution, water sorption) as well as electrical conductivity of the aqueous pore solution. Moreover, the relaxation behavior was analyzed with a generalized fractional relaxation model concerning a high-frequency water process and two interface processes extended with an apparent direct current conductivity contribution. The different modeling approaches provide a satisfactory agreement with experimental data for the real part. These results show the potential of broadband electromagnetic approaches for quantitative estimation of the hydraulic state of the soil during densification.

0 Reads | 1 Citations
2016
Apr
18
Published new article




Article

Error Analysis of Clay-Rock Water Content Estimation with Broadband High-Frequency Electromagnetic Sensors—Air Gap Effec...

Published: 18 April 2016 by MDPI in Sensors

doi: 10.3390/s16040554

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.

1 Reads | 1 Citations
2016
Mar
31
Published new article




Article

Dielectric measurement method for real-time monitoring of initial hardening of backfill materials used for underground c...

Published: 31 March 2016 by IOP Publishing in Journal of Geophysics and Engineering

doi: 10.1088/1742-2132/13/2/s19

The broadband dielectric measurement method based on the vector network analysis technique, in combination with an open-ended coaxial probe, was applied to the determination of the dielectric relaxation behaviour of one- and two-component backfilling grout materials in the frequency range from 40 MHz to 2 GHz. The cement hydration process and the gelling of commercial grouts was monitored in real-time to investigate the application of non-destructive testing methods in the tunnelling industry. It was found that the time-dependent dielectric relaxation behaviour can accurately reveal the different stages of the hydration process and delineate the start of gel hardening. These measurement results demonstrate the practicability of the real-time dielectric measurement method to determine the broadband dielectric parameters of conventional backfill materials used in underground construction to determine construction integrity using non-destructive testing methods.

0 Reads | 1 Citations
2016
Jan
01
Published new article




Article

Spectral Decomposition of Soil Electrical and Dielectric Losses and Prediction of \textit{In Situ} GPR Performance

Published: 01 January 2016 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing

doi: 10.1109/jstars.2015.2424152

The performance of high-frequency ground-penetrating radar (GPR) for high-resolution imaging of the near surface can essentially be controlled by the soil electromagnetic (EM) properties. One of these properties influencing sensing depth and image resolution of GPR is the intrinsic attenuation. We investigated the frequency-dependent electrical and dielectric properties of a broad range of soil samples. In order to derive the effective complex dielectric permittivity between 1 MHz and 10 GHz, we applied the coaxial transmission line (CTL) technique. A generalized dielectric response model, consisting of one Debye and one Cole-Cole type relaxation and a constant low-frequency conductivity term was used to analyze the dielectric relaxation behavior. Splitting the spectra into individual loss processes shows that dielectric relaxation mechanisms play a crucial role in most natural soils. Especially for high-frequency applications, attenuation cannot be described by a dielectric constant and dc-conductivity alone. Therefore, a simple conductivity-attenuation relation without dielectric losses can highly overestimate the GPR performance. As an alternative to the CTL technique in the lab, we suggest to use time-domain reflectometry (TDR) for the in Situ assessment of high-frequency electrical properties and deduced prediction of GPR performance.

0 Reads | 3 Citations
2015
Aug
26
Published new article




Article

A cylindrical guarded capacitor for spectral permittivity measurements of hard rock samples in the MHz-range

Published: 26 August 2015 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/0957-0233/26/10/105902

0 Reads | 0 Citations
2015
Apr
17
Published new article






Gekoppelte strukturelle Veränderungen in schrumpfenden, verdichteten Tonen und deren dielektrische Eigenschaften

Published: 17 April 2015 by Springer Nature in Aktuelle Forschung in der Bodenmechanik 2015

doi: 10.1007/978-3-662-45991-1_9

In diesem Beitrag wurden systematische Untersuchungen variierender Anfangsparameter an einem Ton vorgenommen, um den Einfluss der Änderungen der hydraulisch-mechanisch gekoppelten Eigenschaften im Schrumpfungsprozess sowie deren dielektrische Charakteristik zu analysieren. Es wurden Saugspannungs- und freie Schrumpfversuche durchgeführt. An den Schrumpfproben wurden die dielektrischen Eigenschaften mittels einer minimalinvasiven hochfrequenten elekromagnetischen Messtechnik (HF-EM), basierend auf einer offenen koaxialen Nadelsonde, im breitbandigen Frequenzbereich (100 MHz bis 10 GHz) bestimmt. Die Abhängigkeit zu den initialen Randbedingungen konnte sowohl durch die strukturellen Anpassungen im Schrumpfungprozess, als auch auf die komplexe effektive relative Permittivität bewiesen werden. Die Änderungen in der Bodenstruktur stehen dabei in direkter Beziehung zu den elektromagnetischen Eigenschaften des Bodens. Die breitbandige dielektrische Spektroskopie stellt eine vielversprechende Anwendung dar, die komplexen Zusammenhänge gekoppelt hydraulisch-mechanischer Prozesse zu ergründen.

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2015
Apr
01
Published new article






3D-FEM modeling of F/TDR sensors for clay-rock water content measurement in combination with broadband dielectric spectr...

Published: 01 April 2015 by Institute of Electrical and Electronics Engineers (IEEE) in 2015 IEEE Sensors Applications Symposium (SAS)

doi: 10.1109/sas.2015.7133601

The use of electromagnetic sensors such as Time Domain Reflectometry (TDR) probes has gained increasing importance for long term monitoring of the water content in radioactive waste repositories. TDR probes are sensitive to changes in electromagnetic properties of the surrounding material, a clay rock in our case. Prior to the in situ application, it is mandatory to have an accurate relationship between the electromagnetic properties of the intact host clay rock and the water content. For this purpose, the dielectric properties of intact clay rock samples were systematically studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. Samples were conditioned to achieve a water saturation range from 16 % to nearly saturation. 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 which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). In a second step, these data are introduced 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 rode based TDR-probe embedded in the clay rock. The results are analyzed with classical travel time analysis (onset/inflection) which under/overestimates the value of the permittivity compared to effective permittivity at 1 GHz. Indeed, apparent permittivity contains not only the water-content contribution but also effects due to water-mineral interaction processes. The results demonstrate the capabilities of a combined TD/FD analysis procedure for the monitoring of physical and chemical properties of materials with high frequency electromagnetic sensor techniques.

0 Reads | 0 Citations
2014
Jun
01
Published new article






Frequency-dependent attenuation analysis in soils using broadband dielectric spectroscopy and TDR

Published: 01 June 2014 by Institute of Electrical and Electronics Engineers (IEEE) in 15th International Conference on Ground-Penetrating Radar (GPR) 2014

doi: 10.1109/icgpr.2014.6970415

Our objective is the development of a prognosis system that predicts the soil-dependent GPR performance in landmine and improvised explosive device (IED) contaminated areas. One of the soil properties influencing sensing depth and image resolution of GPR is intrinsic attenuation. We investigated the frequency-dependent electromagnetic properties of a broad range of soil samples. In order to derive the complex dielectric permittivity between 1 MHz and 10 GHz, we applied the coaxial transmission line (CTL) method using two coaxial cells. A model was fitted to the data consisting of a combination of one Debye and one Cole-Cole type relaxation and a constant low-frequency conductivity term. We show that relaxation mechanisms play a crucial role in most natural soils. Attenuation cannot be described by dc-conductivity alone, especially for high-frequency applications. Therefore, a simple conductivity-attenuation relation without relaxations can highly underestimate GPR performance. As an alternative to the CTL technique, we propose to use time-domain reflectometry (TDR) for a quick prediction of high-frequency effective conductivity and GPR performance in the field. Author(s) Loewer, M. Leibniz Inst. for Appl. Geophys., Hannover, Germany Igel, J. ; Wagner, N.

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2014
Apr
29
Published new article




Article

Thermohaline energy geo-storage: evaluation of fluid–fluid layers and fluid–rock salt interaction

Published: 29 April 2014 by Thomas Telford Ltd. in Géotechnique Letters

doi: 10.1680/geolett.13.00058

The storage of power to cover the partial seasonal requirements of larger urban or industrial regions requires storage capacities in the GWh range. Current technologies are site-dependent and area-wide designable, as well as being cost-inefficient. An innovative concept for large-scale energy storage based on a thermohaline base is presented in this article. In particular, the fluid and solid interfaces are a focus of the geomechanical investigations. Besides the principal thermal application study and rock salt removal gradient, a high-frequency electromagnetic open-ended coaxial measurement was carried out to analyse temperature and concentration distribution and dependencies.

0 Reads | 0 Citations
2014
Feb
01
Published new article






Non-destructive coaxial transmission line measurements for dielectric soil characterization

Published: 01 February 2014 by Institute of Electrical and Electronics Engineers (IEEE) in 2014 IEEE Sensors Applications Symposium (SAS)

doi: 10.1109/sas.2014.6798955

A high-frequency electromagnetic measurement technique is employed to investigate dielectric properties of a fine-grained soil. As a case study, a standardized compacted fine-grained soil was investigated using a coaxial transmission line cell in combination with vector network analyzer technique in a frequency range from 1 MHz to 3 GHz. The measurement results indicate that this type of sensor enables the broadband determination of soil dielectric spectra, i.e. the frequency dependent relative effective complex permittivity. Hence, with the introduced coaxial transmission line setup the dielectric relaxation behavior of the investigated soil can reliably characterize defined structural states. Moreover, it was found that dielectric material parameters at high frequencies are mainly related to the volume fractions of the soil phases, i.e. water content whereas at low frequencies to soil structure and density due to interface processes.

0 Reads | 0 Citations
2014
Feb
01
Published new article






Estimation of the Soil Water Characteristics from dielectric relaxation spectra

Published: 01 February 2014 by Institute of Electrical and Electronics Engineers (IEEE) in 2014 IEEE Sensors Applications Symposium (SAS)

doi: 10.1109/sas.2014.6798954

The frequency dependence of dielectric material properties of water saturated and unsaturated porous materials such as soil is not only disturbing in applications with high frequency electromagnetic (HF-EM) techniques but also contains valuable information of the material due to strong contributions by interactions between the aqueous pore solution and mineral phases. Hence, broadband HF-EM sensor techniques enable the estimation of soil physico-chemical parameters such as water content, texture, mineralogy, cation exchange capacity and matric potential. In this context, a multivariate (MV) approach was applied to estimate the Soil Water Characteristic Curve (SWCC) from experimentally determined dielectric relaxation spectra of a silty clay soil. The results of the MV-approach were compared with results obtained from empirical equations and theoretical models as well as a novel hydraulic/electromagnetic coupling approach. The applied MV-approach gives evidence, (i) of a physical relationship between soil dielectric relaxation behavior and soil water characteristics as an important hydraulic material property and (ii) the applicability of appropriate sensor techniques for the estimation of physico-chemical parameters of porous media from broadband measured dielectric spectra.

0 Reads | 2 Citations
2014
Feb
01
Published new article




Article

Numerical 3-D FEM and Experimental Analysis of the Open-Ended Coaxial Line Technique for Microwave Dielectric Spectrosco...

Published: 01 February 2014 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Geoscience and Remote Sensing

doi: 10.1109/TGRS.2013.2245138

Open-ended coaxial line probes (OCs) are systematically analyzed by means of numerical 3-D finite element calculations in combination with experimental investigations for microwave dielectric spectroscopy on fine grained soils. The probes, based on conventional coaxial lines and connectors (N, SMA), are broadband characterized in the frequency range from 1 MHz to 10 GHz. The sensitive region for dielectric measurements is ±7-mm lateral and 7-mm perpendicular to the midpoint of the sensor aperture. The spatial spreading of the sensitive zone is stable for the investigated low-loss and high-loss strongly dispersive standard liquids, as well as the saturated and unsaturated soils. Dielectric spectra are determined based on a bilinear relationship between effective permittivity and complex reflection coefficient of the probe after probe-calibration with known standards. The mean relative error of the real part of the complex permittivity from 100 MHz to 10 GHz is smaller than 3.5% and is less than 10% for the imaginary part. A lower limit of the measurement range of 50 MHz with the used procedure and materials is suggested. Complex effective permittivity of saturated fine-grained soils is determined with the developed probes and procedure. The soil dielectric spectra were analyzed with a broadband relaxation model, as well as a novel, coupled hydraulic-dielectric mixture approach. The results demonstrate the suitability of the investigated OCs for the determination of high resolution soil dielectric spectra.

0 Reads | 11 Citations
2014
Feb
01
Published new article






Spatial Time Domain Reflectometry (spatial TDR) in geo-environmental engineering

Published: 01 February 2014 by Institute of Electrical and Electronics Engineers (IEEE) in 2014 IEEE Sensors Applications Symposium (SAS)

doi: 10.1109/sas.2014.6798953

Spatial Time Domain Reflectometry (spatial TDR) is a measurement method for determining water content profiles along electrically insulated probes (transmission lines). The method is based on the inverse modeling of TDR reflectograms using an optimisation algorithm. By means of using flat ribbon cables as sensors it is possible to take two independent TDR reflectograms from both ends of the probe, which are used to improve the spatial information content of the optimisation results and to consider effects caused by electrical conductivity. The method has been used for different geo-environmental purposes, such as the monitoring of water content distributions on a sand island for investigating groundwater recharge processes and the monitoring of a mine waste cover.

0 Reads | 0 Citations
2013
Dec
06
Published new article




Article

Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Published: 06 December 2013 by Copernicus GmbH in The Cryosphere

doi: 10.5194/tc-7-1839-2013

Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 °C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to −70 °C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m2 g−1, up to 9.4% w / w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m2 g−1, up to 7.4% w / w). Three soil-specific relaxation processes are observed in the investigated frequency–temperature range: two weak high-frequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell–Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to −70 °C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.

0 Reads | 3 Citations
2013
Sep
16
Published new article




Article

Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach

Published: 16 September 2013 by Wiley in Journal of Geophysical Research: Solid Earth

doi: 10.1002/jgrb.50343

[1] Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo‐Oxfordian (COx) clay formation. High‐frequency electromagnetic (HF‐EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF‐EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. 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 interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell‐Wagner effects). The frequency‐dependent HF‐EM properties were further modeled based on a novel hydraulic‐mechanical‐electromagnetic coupling approach developed for soils. The results show the potential of HF‐EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations.

0 Reads | 5 Citations
2013
Apr
09
Published new article




Article

Supercooled interfacial water in fine grained soils probed by dielectric spectroscopy

Published: 09 April 2013 by Copernicus GmbH in The Cryosphere Discussions

doi: 10.5194/tcd-7-1441-2013

0 Reads | 0 Citations
2012
Dec
01
Published new article




Article

Permittivity of ice at radio frequencies: Part II. Artificial and natural polycrystalline ice

Published: 01 December 2012 by Elsevier BV in Cold Regions Science and Technology

doi: 10.1016/j.coldregions.2012.05.010

0 Reads | 3 Citations
2012
Oct
01
Published new article




Article

Permittivity of ice at radio frequencies: Part I. Coaxial transmission line cell

Published: 01 October 2012 by Elsevier BV in Cold Regions Science and Technology

doi: 10.1016/j.coldregions.2012.05.011

0 Reads | 6 Citations
2012
Jul
01
Published new article






Spatial time domain reflectometry for monitoring of the hydrological water balance at a lysimeter test site in Thuringia...

Published: 01 July 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 IEEE International Geoscience and Remote Sensing Symposium

doi: 10.1109/igarss.2012.6351466

For monitoring of the hydrological water balance in top and subsoil during plant growth accurate knowledge of the spatial and temporal variation of soil water content is essential. In this context, a new full two port spatial time domain reflectometry (Spatial TDR) technique in combination with elongated microwave transmission line sensors were developed for advanced data acquisition and analysis. The technique is tested at a lysimeter station in Thuringia/Germany and compared with neutron moisture meter probes.

0 Reads | 0 Citations
2012
Jul
01
Published new article






Simultaneous determination of the dielectric relaxation behavior and soilwater characteristic curve of undisturbed soil ...

Published: 01 July 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 IEEE International Geoscience and Remote Sensing Symposium

doi: 10.1109/igarss.2012.6350743

The frequency dependence of soil electromagnetic properties contain valuable information of the porous material due to strong contributions to the dielectric relaxation behavior by interactions between aqueous pore solution and mineral phases due to interface effects. Soil hydraulic properties such as matric potential are also influenced by different surface bonding forces due to interface processes. For this reason, a new analysis methodology was developed, which allows a simultaneous determination of the soil water characteristic curve and the dielectric relaxation behavior of undisturbed soil samples. This opens the possibility to systematically analyze coupled hydraulic/dielectric soil properties for the development of pedotransfer functions to estimate physico-chemical parameters with broadband HF-EM measurement techniques.

0 Reads | 0 Citations
2012
Jun
01
Published new article






Frequency-dependant dielectric parameters of steel fiber reinforced concrete

Published: 01 June 2012 by Institute of Electrical and Electronics Engineers (IEEE) in 2012 14th International Conference on Ground Penetrating Radar (GPR)

doi: 10.1109/icgpr.2012.6254918

Steel Fiber Reinforced Concrete (SFRC) is increasingly being used in civil constructions, especially precast tunnel segment linings. Fibers are mixed with fresh concrete, which results in a more or less random distribution of fibers within the concrete matrix. Because of this, SFRC demonstrates a great challenge when it is being investigated using GPR. In order to investigate the frequency-dependent dielectric parameters of SFRC; (I) PET/CT scans of concrete were conducted to understand the nature of orientation and density of fibers being distributed within the concrete sample and (Π) a two-port coaxial transmission line technique developed for the determination of dielectric spectra of undisturbed soil samples was used to investigate the concrete's complex permittivity with and without steel fibers in the frequency range from 1 MHz to 5 GHz.

0 Reads | 1 Citations
2012
Apr
25
Published new article






Mechanical Spectroscopy of Natural and Synthetic Silicate Glasses and Melts

Published: 25 April 2012 by Wiley in Biomaterials Science: Processing, Properties, and Applications V

doi: 10.1002/9781118408063.ch10

This chapter contains sections titled: IntroductionNatural Volcanic Glass SamplesMethodicBasic RelationsDiscussion and Conclusion

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2012
Mar
12
Published new article




Article

A new technique for measuring broadband dielectric spectra of undisturbed soil samples

Published: 12 March 2012 by Wiley in European Journal of Soil Science

doi: 10.1111/j.1365-2389.2012.01431.x

A new coaxial line cell for the determination of dielectric spectra of undisturbed soil samples was developed based on a 1.625‐inch ‐ 50 Ω coaxial system. Undisturbed soil samples were collected from a soil profile of the Taunus region (Germany) and capillary saturated followed by a step‐by‐step de‐watering in a pressure plate apparatus as well as oven‐drying at 40°C. The resultant water contents of the soil samples varied from saturation to air‐dry. Permittivity measurements were performed within a frequency range from 1 MHz to 10 GHz with a vector network analyser technique. Complex effective relative permittivity or electrical conductivity was obtained by combining quasi‐analytical and numerical inversion algorithms as well as the parameterizing of measured full set S‐parameters simultaneously under consideration of a generalized fractional dielectric relaxation model (GDR). The measurement of standard materials shows that the technique provides reliable dielectric spectra up to a restricted upper frequency of 5 GHz. For the soil samples investigated, the real part of complex effective relative permittivity ɛ′r,eff and the real part of complex effective electrical conductivity σ′eff decreased with increasing matric potential or decreasing water contents. Soil texture and porosity affect the dielectric behaviour at frequencies below 1 GHz. For frequencies above 1 GHz minor texture effects were found. The presence of organic matter decreases ɛ′r,eff and σ′eff. At 1 GHz, the empirical model of Topp et al. (1980) is in close agreement with the experimentally determined real part of the effective permittivity with RMSEs ranging from 1.21 for the basal periglacial slope deposit and 1.29 for bedrock to 3.93 for the upper periglacial slope deposit (Ah). The comparison of the experimental results with a semi‐empirical dielectric mixing model shows that data, especially for the organic‐free soils, tend to be under‐estimated below 1 GHz. The main advantage of the new method compared with conventional impedance and coaxial methods is the preservation of the natural in‐situ structure and properties such as bulk density of the investigated soil samples.

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2011
Jul
01
Published new article




Article

Experimental Investigations on the Frequency- and Temperature-Dependent Dielectric Material Properties of Soil

Published: 01 July 2011 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Geoscience and Remote Sensing

doi: 10.1109/TGRS.2011.2108303

Frequency- and temperature-dependent complex permittivity or conductivity of a silty clay loam were examined in a broad saturation and porosity range with network analyzer technique (1 MHz-10 GHz, 5 °C-40 °C, coaxial transmission line and open ended coaxial cells). An advanced mixture model based on the well-known Lichtenecker-Rother model (ALRM) was developed and used to parameterize complex permittivity or conductivity at a measurement frequency of 1 GHz under consideration of a dependence of the so-called structure parameter as well as the apparent pore water conductivity on saturation and porosity. The ALRM is compared with frequently applied mixture models: complex refractive index model, Looyenga-Landau-Lifschitz model, Bruggeman-Hanai-Sen model, and Maxwell-Garnet model as well as empirical calibration functions. Comparison of ALRM applied to the investigated frequency and temperature range with sophisticated broadband relaxation models indicates the potential and the limitation to predict the high-frequency electromagnetic material properties.

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2009
Oct
01
Published new article




Article

On the relationship between matric potential and dielectric properties of organic free soils: a sensitivity study

Published: 01 October 2009 by Canadian Science Publishing in Canadian Geotechnical Journal

doi: 10.1139/T09-055

High-frequency electromagnetic determination of moisture in porous media, (e.g., soil) is based on the strong relationship between volumetric water content and relative dielectric permittivity. In particular, in fine-grained soils the movement of water is influenced by different surface-bonding forces due to interface processes. The interface effects lead to a number of dielectric relaxation processes (free- and bound-water phase, Maxwell–Wagner effect, counterion relaxation effects). These relaxation processes are the reason for the strong frequency dependence of the electromagnetic material properties below 1 GHz. The matric potential is a measure of the bonding forces on water in the soil. Based on a thermodynamic relationship between soil matric potential and dielectric relaxation behaviour of water in different binding states, a broadband dielectric relaxation model was developed that considers low-frequency dispersion up to 1 MHz as well as losses due to direct-current conductivity. The sensitivity of the model on soil suction was systematically analyzed based on a pedotransfer function (PTF) for soil textures ranging from pure sand up to pure clay. The results are compared with known empirical and semiempirical calibration functions, as well as theoretical mixing models.

0 Reads | 6 Citations
2009
Feb
19
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Article

Spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribb...

Published: 19 February 2009 by American Geophysical Union (AGU) in Water Resources Research

doi: 10.1029/2008wr007073

[1] Spatial time domain reflectometry (spatial TDR) is a new measurement method for determining water content profiles along elongated probes (transmission lines). The method is based on the inverse modeling of TDR reflectograms using an optimization algorithm. By means of using flat ribbon cables it is possible to take two independent TDR measurements from both ends of the probe, which are used to improve the spatial information content of the optimization results and to consider effects caused by electrical conductivity. The method has been used for monitoring water content distributions on a full‐scale levee model made of well‐graded clean sand. Flood simulation tests, irrigation tests, and long‐term observations were carried out on the model. The results show that spatial TDR is able to determine water content distributions with an accuracy of the spatial resolution of about ±3 cm compared to pore pressure measurements and an average deviation of ±2 vol % compared to measurements made using another independent TDR measurement system.

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2007
Feb
27
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Article

TDR measurements and simulations in high lossy bentonite materials

Published: 27 February 2007 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/0957-0233/18/4/021

0 Reads | 2 Citations
2007
Feb
27
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Article

Determination of the spatial TDR-sensor characteristics in strong dispersive subsoil using 3D-FEM frequency domain simul...

Published: 27 February 2007 by IOP Publishing in Measurement Science and Technology

doi: 10.1088/0957-0233/18/4/022

0 Reads | 8 Citations
2007
Jan
01
Published new article




Article

Bestimmung von Feuchte- und Dichteverteilungen mit TDR-Sensoren (Determination of Moisture and Density Distributions usi...

Published: 01 January 2007 by Walter de Gruyter GmbH in tm - Technisches Messen

doi: 10.1524/teme.2007.74.5.298

Die Messung der Feuchteverteilung in Bentonit-Verschlussbauwerken ist für die Erkennung von Lösungszutritten und für Langzeitsicherheitsanalysen erforderlich. Dafür wurde ein TDR-Feuchtemesssystem mit flexiblen Kabelsensoren eingesetzt. Finite-Elemente-EM-Feldsimulationen vom Sensor und vom umgebenden Material dienten zur Vereinfachung von Kalibrierungen. Mit TDR-Messungen war es möglich, die Feuchte- und Dichteverteilung längs der Kabelsensoren zu detektieren. Im Druckversuchsstand konnte das Fortschreiten der Feuchtefront in Bentonit bei Druckerhöhung bestimmt werden. The measurement of moisture distribution in bentonite gate structures is stringently necessary for the indefinable trend of fluid access and for long-term security analyses. A TDR moisture measurement system using flexible cable sensors has been applied. Finite element electromagnetic field simulation of both the sensor and the surrounding material was used to simplify calibrations. Using TDR, it was possible to detect the moisture and density distribution along the cable sensors. In a pressure test stand it was possible to determine the moisture profile during a pressure increase.

0 Reads | 1 Citations
2006
Nov
16
Published new article






Determination of the spatial TDR-sensor characteristics in strong dispersive subsoil using 3D-FEM frequency domain simul...

Published: 16 November 2006 by ArXiv

doi:

The spatial sensor characteristics of a 6cm TDR flat band cable sensor section was simulated with finite element modelling (High Frequency Structure Simulator-HFSS) under certain conditions: (i) in direct contact to the surrounding material (air, water of different salinities, different synthetic and natural soils (sand-silt-clay mixtures)), (ii) with consideration of a defined gap of different size filled with air or water and (iii) the cable sensor pressed at a borehole-wall. The complex dielectric permittivity or complex electrical conductivity of the investigated saturated and unsaturated soils was examined in the frequency range 50MHz-20GHz at room temperature and atmospheric pressure with a HP8720D- network analyser. Three soil-specific relaxation processes are assumed to act in the investigated frequency-temperature-pressure range: one primary (main water relaxation) and two secondary processes due to clay-water-ion interactions (bound water relaxation and the Maxwell-Wagner effect). 3D finite element simulation is performed with a 1/3 wavelength based adaptive mesh refinement at a solution frequency of 1MHz, 10MHz, 0.1GHz, 1GHz and 12.5GHz. The electromagnetic field distribution, S-parameter and step responses were examined.

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2005
Jul
25
Published new article






Mechanical Spectroscopy on Volcanic Glasses

Published: 25 July 2005 by ArXiv

doi:

Mechanical relaxation behaviour of various natural volcanic glasses have been investigated in the temperature range RT-1200K using special low frequency flexure (f~0.63Hz) pendulum experiments. The rheological properties complex Young's modulus M* and internal friction 1/Q have been studied from a pure elastic solid at room temperature to pure viscous melt at log(eta[Pas])=8. Several relaxation processes are assumed to act: the primary alpha-relaxation (viscoelastic process, E_a=(344...554)kJ/mol) above the glass transition temperature T_g=(935...1105)K and secondary anelastic beta', beta and gamma-relaxation processes below T_g. With a simple fractional Maxwell model with asymmetrical relaxation time distribution, phenomenological the mechanical relaxation behaviour, is described. This establish a basis of realistic concepts for modelling of volcanic or magmatic processes.

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