scholarly journals Calibration, Conversion, and Quantitative Multi-Layer Inversion of Multi-Coil Rigid-Boom Electromagnetic Induction Data

Sensors ◽  
2019 ◽  
Vol 19 (21) ◽  
pp. 4753 ◽  
Author(s):  
von Hebel ◽  
van der Kruk ◽  
Huisman ◽  
Mester ◽  
Altdorff ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Electromagnetic Induction ◽  
Depth Range ◽  
Electrode Arrays ◽  
Average Value ◽  
Bulk Electrical Conductivity ◽  
Electrical Conductivities ◽  
Electrical Soundings ◽  
And Inversion

Multi-coil electromagnetic induction (EMI) systems induce magnetic fields below and above the subsurface. The resulting magnetic field is measured at multiple coils increasingly separated from the transmitter in a rigid boom. This field relates to the subsurface apparent electrical conductivity (σa), and σa represents an average value for the depth range investigated with a specific coil separation and orientation. Multi-coil EMI data can be inverted to obtain layered bulk electrical conductivity models. However, above-ground stationary influences alter the signal and the inversion results can be unreliable. This study proposes an improved data processing chain, including EMI data calibration, conversion, and inversion. For the calibration of σa, three direct current resistivity techniques are compared: Electrical resistivity tomography with Dipole-Dipole and Schlumberger electrode arrays and vertical electrical soundings. All three methods obtained robust calibration results. The Dipole-Dipole-based calibration proved stable upon testing on different soil types. To further improve accuracy, we propose a non-linear exact EMI conversion to convert the magnetic field to σa. The complete processing workflow provides accurate and quantitative EMI data and the inversions reliable estimates of the intrinsic electrical conductivities. This improves the ability to combine EMI with, e.g., remote sensing, and the use of EMI for monitoring purposes.

scholarly journals Field Comparison of Electrical Resistance, Electromagnetic Induction, and Frequency Domain Reflectometry for Soil Salinity Appraisal

Soil Systems ◽  
2020 ◽  
Vol 4 (4) ◽  
pp. 61
Author(s):  
Fernando Visconti ◽  
José Miguel de Paz
Keyword(s):  
Electrical Conductivity ◽  
Frequency Domain ◽  
Soil Salinity ◽  
Electrical Resistance ◽  
Electromagnetic Induction ◽  
Linear Regression Models ◽  
Bulk Electrical Conductivity ◽  
Mass Fractions ◽  
Frequency Domain Reflectometry ◽  
Different Depths

By using different physical foundations and technologies, many probes have been developed for on-site soil salinity appraisal in the last forty years. In order to better understand their respective technical and practical advantages and constraints, comparisons among probes are needed. In this study, three different probes, based on electrical resistance (ER), electromagnetic induction (EMI), and frequency domain reflectometry (FDR), were compared during a field survey carried out in a large salt-threatened agricultural area. Information about the soil bulk electrical conductivity (σb) at different depths was obtained with each of the probes and, additionally, other soil properties were also measured depending on the specifications of each instrument and, moreover, determined in samples. On average, the EMI and FDR techniques could be regarded as equivalent for σb measurement, whereas ER gave higher σb values. Whatever the case, EMI, and also ER, had to be supplemented with information about soil clay, organic matter, and water mass fractions to attain, despite this effort, poor soil salinity estimations by means of multiple linear regression models (R2 < 0.5). On the contrary, FDR needed only probe data to achieve R2 of 0.7, though root mean standard error (RMSE) was still 1.5 dS m−1. The extra measurements and calculations that modern electrical conductivity contact probes integrate, specifically, those based on FDR, remarkably increase their ability for soil salinity appraisal, although there is still room for improvement.

scholarly journals GEOELECTRICAL INVESTIGATION OF GROUNDWATER QUALITY THROUGH ESTIMATES OF TOTAL DISSOLVED SOLIDS AND ELECTRICAL CONDUCTIVITY IN PARTS OF AKWA IBOM STATE, SOUTHERN NIGERIA

2020 ◽  
Vol 4 (1) ◽  
pp. 32-37
Author(s):  
Akpan Emmanuel F. ◽  
Akpan Veronica M. ◽  
Inyang Udeme U.
Keyword(s):  
Electrical Conductivity ◽  
Groundwater Quality ◽  
Total Dissolved Solids ◽  
Geophysical Investigation ◽  
Dissolved Solids ◽  
Average Value ◽  
Transverse Resistance ◽  
Southern Nigeria ◽  
Electrical Soundings ◽  
Dar Zarrouk Parameters

This paper presents the results of a geophysical investigation of groundwater quality in parts of Akwa Ibom State, Southern Nigeria. A total of 11 vertical electrical soundings (VES) was carried out in the study area using the Schlumberger electrode configuration. The results of the interpretation show that the area comprises 4 geoelectric layers. The third layer constitutes the major economic hydrogeological unit in the area and has resistivity of between 50.3 Ωm and 2088.9 Ωm and thickness of between 36.8 m and 149.0m respectively. The groundwater quality was assessed through estimates of the electrical conductivity and total dissolved solids in water. The conductivity ranges from 74.5 to 604.4µS/cm with an average value of 244.0µS/cm while the TDS values range from 47.7 to 386.8 ppm with an average value of 156.1 ppm. Based on these values, which are within the permissible limits, the water is considered to be fresh and suitable for drinking and other domestic/agricultural usages. The results show excellent correlation between the estimated TDS and the Dar-zarrouk parameters (longitudinal conductance and transverse resistance) on one hand and the aquifer bulk resistivity on the hand which demonstrate the ease of deriving TDS from surface resistivity data.

FIELD SCALE PATTERNS OF SOIL WATER STORAGE FROM NON-CONTACTING MEASUREMENTS OF BULK ELECTRICAL CONDUCTIVITY

1990 ◽  
Vol 70 (3) ◽  
pp. 537-542 ◽  
Author(s):  
R. G. KACHANOSKI ◽  
I. J. VAN WESENBEECK ◽  
E. De JONG
Keyword(s):  
Electrical Conductivity ◽  
Soil Water ◽  
Electromagnetic Induction ◽  
Water Storage ◽  
Soil Water Storage ◽  
Fast Method ◽  
Field Patterns ◽  
Neutron Probe ◽  
Bulk Electrical Conductivity ◽  
General Field

Soil water storage (0–1.7 m) was measured every 10 m in a 660-m-long transect using a neutron probe and compared to bulk electrical conductivity, ECA, measurements obtained using noncontacting electomagnetic induction meters. Coherency analysis indicated a lack of correlation at scales less than 40 m. At scales greater than 40 m, ECA explained more than 80% of the variation of soil water storage. Measurement of ECA should be a simple and fast method of determining general field patterns of soil water storage. Key words: Spatial variability, soil water, coherency, electromagnetic induction

Some novel electromagnetic effects in the conductivity of molten organic salts

1976 ◽  
Vol 347 (1650) ◽  
pp. 301-310 ◽  
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Liquid Crystal ◽  
Frequency Dispersion ◽  
Domain Size ◽  
Organic Salts ◽  
Middle Range ◽  
Electrical Conductivities ◽  
Size Dispersion ◽  
Applied Fields

Considerable frequency dispersion of electrical conductivity has been ob­served in the liquid crystal phases of organic ionic melts, depending on their molecular structure and domain size. Dispersion began to be detectable above about 10000 Hz for sodium isovalerate (in which there are large domains), and above about 2000 Hz for sodium n -butyrate (domains about 0.1 mm across). Neither molten salt showed dispersion in a middle range of frequencies (between 1000 Hz and 100Hz). Previous researches had shown a marked diamagnetic anomaly of molten organic salts when these are cooled through their mesophases, while applying static magnetic fields. The kind of response observed can be attributed to interaction between ‘liquid crystal’ domains and the applied fields. A related effect has now been observed when a static magnetic field (approx. 10kG) was applied in the course of the above measurements of electrical conductivities. With sodium isovalerate melts, a magnetic field applied perpendicular to the electric field reduced by a factor of two the drop in electrical conductivity when the isotropic melt passed into its mesophase. No effect (≯ 2%) was detected with sodium n -butyrate under the same conditions.

Simultaneous calibration and inversion algorithm for multiconfiguration electromagnetic induction data acquired at multiple elevations

Geophysics ◽  
2019 ◽  
Vol 84 (1) ◽  
pp. EN1-EN14 ◽  
Author(s):  
Xihe Tan ◽  
Achim Mester ◽  
Christian von Hebel ◽  
Egon Zimmermann ◽  
Harry Vereecken ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Electromagnetic Induction ◽  
Synthetic Data ◽  
Ground Surface ◽  
Acquisition Time ◽  
Inversion Algorithm ◽  
Transect Line ◽  
Promising Tool ◽  
Reference Measurements ◽  
And Inversion

Electromagnetic induction (EMI) is a contactless and fast geophysical measurement technique. Frequency-domain EMI systems are available as portable rigid booms with fixed separations up to approximately 4 m between the transmitter and the receivers. These EMI systems are often used for high-resolution characterization of the upper subsurface meters (up to depths of approximately 1.5 times the maximum coil separation). The availability of multiconfiguration EMI systems, which measure multiple apparent electrical conductivity ([Formula: see text]) values of different but overlapping soil volumes, enables EMI data inversions to estimate electrical conductivity ([Formula: see text]) changes with depth. However, most EMI systems currently do not provide absolute [Formula: see text] values, but erroneous shifts occur due to calibration problems, which hinder a reliable inversion of the data. Instead of using physical soil data or additional methods to calibrate the EMI data, we have used an efficient and accurate simultaneous calibration and inversion approach to avoid a possible bias of other methods while reducing the acquisition time for the calibration. By measuring at multiple elevations above the ground surface using a multiconfiguration EMI system, we simultaneously obtain multiplicative and additive calibration factors for each coil configuration plus an inverted layered subsurface electrical conductivity model at the measuring location. Using synthetic data, we verify our approach. Experimental data from five different calibration positions along a transect line showed similar calibration results as the data obtained by more elaborate vertical electrical sounding reference measurements. The synthetic and experimental results demonstrate that the multielevation calibration and inversion approach is a promising tool for quantitative electrical conductivity analyses.

Electrical conductivity studies on silica phases and the effects of phase transformation

2019 ◽  
Vol 104 (12) ◽  
pp. 1800-1805
Author(s):  
George M. Amulele ◽  
Anthony W. Lanati ◽  
Simon M. Clark
Keyword(s):  
Electrical Conductivity ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Hydrogen Charge ◽  
Charge Compensation ◽  
Composition Analysis ◽  
Conductivity Measurements ◽  
Pressure System ◽  
Electrical Conductivities ◽  
Silica Phases

Abstract Starting with the same sample, the electrical conductivities of quartz and coesite have been measured at pressures of 1, 6, and 8.7 GPa, respectively, over a temperature range of 373–1273 K in a multi-anvil high-pressure system. Results indicate that the electrical conductivity in quartz increases with pressure as well as when the phase change from quartz to coesite occurs, while the activation enthalpy decreases with increasing pressure. Activation enthalpies of 0.89, 0.56, and 0.46 eV, were determined at 1, 6, and 8.7 GPa, respectively, giving an activation volume of –0.052 ± 0.006 cm3/mol. FTIR and composition analysis indicate that the electrical conductivities in silica polymorphs is controlled by substitution of silicon by aluminum with hydrogen charge compensation. Comparing with electrical conductivity measurements in stishovite, reported by Yoshino et al. (2014), our results fall within the aluminum and water content extremes measured in stishovite at 12 GPa. The resulting electrical conductivity model is mapped over the magnetotelluric profile obtained through the tectonically stable Northern Australian Craton. Given their relative abundances, these results imply potentially high electrical conductivities in the crust and mantle from contributions of silica polymorphs. The main results of this paper are as follows:The electrical conductivity of silica polymorphs is determined by impedance spectroscopy up to 8.7 GPa.The activation enthalpy decreases with increasing pressure indicating a negative activation volume across the silica polymorphs.The electrical conductivity results are consistent with measurements observed in stishovite at 12 GPa.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

Investigating flexible textile-based coils for wireless charging wearable electronics

2019 ◽  
Vol 50 (3) ◽  
pp. 333-345 ◽  
Author(s):  
Danmei Sun ◽  
Meixuan Chen ◽  
Symon Podilchak ◽  
Apostolos Georgiadis ◽  
Qassim S Abdullahi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Electromagnetic Field ◽  
Electric Field ◽  
Dimensional Stability ◽  
Screen Printing ◽  
Wearable Electronics ◽  
Wireless Charging ◽  
The Magnetic Field ◽  
Screen Printed

Smart and interactive textiles have been attracted great attention in recent years. This research explored three different techniques and processes in developing textile-based conductive coils that are able to embed in a garment layer. Coils made through embroidery and screen printing have good dimensional stability, although the resistance of screen printed coil is too high due to the low conductivity of the print ink. Laser cut coil provided the best electrical conductivity; however, the disadvantage of this method is that it is very difficult to keep the completed coil to the predetermined shape and dimension. The tested results show that an electromagnetic field has been generated between the textile-based conductive coil and an external coil that is directly powered by electricity. The magnetic field and electric field worked simultaneously to complete the wireless charging process.

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