Direct Current Resistivity Research Articles

Roof and floor anomalous response of mine resistivity method

As the exploitation level of coal seams increases in China, mine water inrush is becoming increasingly serious. Effectively detecting the roof and floor anomalous bodies of mines in whole space has always been the focus and challenge of research with the direct current (DC) resistivity method. Based on the finite element theory and the ANSYS finite element software, the ANSYS parametric design language (APDL) of 600 m pole–dipole array A-MN or MN-B of the mine DC resistivity method is given, and the floor model with a distance of 40 m from the abnormal body to the roadway and the roof and floor model with a distance of 40 m, 30 m, 20 m, and 10 m from the abnormal body to the roadway are established, respectively. According to the analysis of calculation error, the maximum relative average error is 2.18%, which shows the correctness of the calculation of model. The calculation results of the above model are plotted, and then the anomalous response characteristics of the roof and floor of the pole–dipole array in the whole-space are obtained by comparing the figures. According to the anomalous response characteristics of roof and floor, it is conducive to accurately interpret the measured data.

3-D dc resistivity modelling based on spectral element method with unstructured tetrahedral grids

SUMMARY In this paper, we propose a spectral element method (SEM) based on unstructured tetrahedral grids for direct current (dc) resistivity modelling. Unlike the tensor-product of 1-D Gauss–Lobatto–Legendre (GLL) quadrature in conventional SEM, we use Proriol–Koornwinder–Dubiner (PKD) polynomials to form the high-order basis polynomials on tetrahedral grids. The final basis functions are established by using Vandermonde matrix. Compared to traditional SEM, our method truly takes into account the high precision of spectral method and the flexibility of finite element method with unstructured grids for modelling the complex underground structures. After addressing the theory on the construction of basis functions and interpolation and integration nodes, we validate our algorithm using the analytical solutions for a layered earth model and the results from other methods for multiple geoelectrical models. We further investigate a dual-track scheme for improving the accuracy of our SEM by increasing the order of interpolation polynomials or by refining the grids.

Multidisciplinary Characterization of Chlorinated Solvents Contamination and In-Situ Remediation with the Use of the Direct Current Resistivity and Time-Domain Induced Polarization Tomography

Soil contamination is a widespread problem and action needs to be taken in order to prevent damage to the groundwater and the life around the contaminated sites. In Sweden, it is estimated that more than 80,000 sites are potentially contaminated, and therefore, there is a demand for investigations and further treatment of the soil. In this paper, we present the results from a methodology applied in a site contaminated with chlorinated solvents, for characterization of the contamination in order to plan the remediation and to follow-up the initial step of in-situ remediation in an efficient way. We utilized the results from three different methods; membrane interface probe for direct measurement of the contaminant concentrations; seismic refraction tomography for investigating the depth to the bedrock interface; and direct current resistivity and time-domain induced polarization tomography to acquire a high-resolution imaging of the electrical properties of the subsurface. The results indicate that our methodology is very promising in terms of site characterization, and furthermore, has great potential for real-time geophysical monitoring of contaminated sites in the future.

3-D DC Resistivity Forward Modeling Using the Multi-resolution Grid

We implemented a novel multi-resolution grid approach to direct current resistivity (DCR) modeling in 3-D. The multi-resolution grid was initially developed to solve the electromagnetic forward problem and helped to improve the modeling efficiency. In the DCR forward problem, the distribution of the electric potentials in the subsurface is estimated. We consider finite-difference staggered grid discretization, which requires fine grid resolution to accurately model electric potentials around the current electrodes and complex model geometries near the surface. Since the potential variations attenuate with depth, the grid resolution can be decreased correspondingly. The conventional staggered grid fixes the horizontal grid resolution that extends to all layers. This leads to over-discretization and therefore unnecessary high computational costs (time and memory). The non-conformal multi-resolution grid allows the refinement or roughening for the grid’s horizontal resolution with depth, resulting in a substantial reduction of the degrees of freedom, and subsequently, computational requirements. In our implementation, the coefficient matrix maintains its symmetry, which is beneficial for using the iterative solvers and solving the adjoint problem in inversion. Through comparison with the staggered grid, we have found that the multi-resolution grid can significantly improve the modeling efficiency without compromising the accuracy. Therefore, the multi-resolution grid allows modeling with finer horizontal resolutions at lower computational costs, which is essential for accurate representation of the complex structures. Consequently, the inversion based on our modeling approach will be more efficient and accurate.

The Utility of a Fully-distributed Direct Current Resistivity and Induced Polarisation System with Common Voltage Referencing

SummaryThe direct current electrical resistivity and induced polarization (DCIP) method has received another significant upgrade through the introduction of common voltage referencing (CVR) in a fully-distributed array system. An array of single-channel receivers with a CVR wire allows for the extraction of an unprecedented volume of dipole data for the number of receivers deployed. In 3D implementation, this new method reduces noise levels and allows for the derivation of multi-scale and multi-azimuth receiver dipoles.Operational efficiencies in the CVR method include lower overall wire lengths, less equipment weight and less crew fatigue when compared with conventional and other distributed array methods. Cable-free mesh network capability in each receiver allows for real-time assessment of data quality metrics, safety information, location data, and system health data. These operational efficiencies translate directly to improvements in safety.With several hundred active receivers, data volume can reach 10s of millions of data records. Careful processing and selection of an optimised data subset with multi-scale and multi-azimuth information will inform highly accurate inversion imaging.

Co-operative inversion of geoelectrical data sets acquired from different electrode arrays

Direct current resistivity (DCR) method is one of the most commonly applied geophysical exploration methods. The development of data acquisition techniques enables the acquisition of multiple data ...

3-D DC resistivity modeling and inversion using multi-resolution framework

We discuss the implementation of multi-resolution framework to 3-D Direct Current (DC) problem. Commonly used staggered (SG) grid fixes the horizontal grid resolution for all depths. Thus, employin ...

Two dimensional joint inversion of direct current resistivity and radiomagnetotelluric data based on unstructured mesh

Using the unstructured mesh, a new two-dimensional joint inversion algorithm has been developed for Radiomagnetotelluric and Direct current resistivity data. The unstructured mesh is generated with triangular cells, whose vertical and lateral lengths increase towards the depths. The Finite Element Method (FEM) has been used in the forward modelling part of the developed joint inversion algorithm. In the previous studies, structured grid-based joint inversion algorithms have been developed using the Finite Difference Method (FDM). In the structured grid-based algorithms, when the mesh is being generated with rectangular cells, the vertical lengths of the cells get bigger towards the depths while the lateral lengths remain constant. With the structured mesh, the undulated surface topography cannot be represented well enough. Also, because of the incompatible aspect ratio of model cell sizes in deeper model sections, the resolution of the model parameters will get smaller and cannot be resolved well with the structured grids. Imaging of surface topography and underground resistivity structures by the new algorithm requires fewer elements than those using structured grids. Therefore, the developed algorithm is faster than traditional 2D inversion algorithms. Furthermore, the resolution of the deeper model parameters has been increased by using the definition of the unstructured grid. A regularized inversion scheme with a smoothness-constrained stabilizer has been employed to invert the data. First, we have tested the developed joint inversion algorithm using synthetic data simplified from archaeological and mine site scenario and the results have been compared with the conventional algorithms using structured grids. We have also tested our algorithm with the real data which were collected from mineral investigation site at approximately 10 km east of the Elbistan district of Kahramanmaraş province, in the west of the Taurus Mountains, Turkey. The results show that the developed joint inversion algorithm is a powerful tool to detect both resistive and conductive targets.

Characterization of the bridge pillar foundations using 3d focusing inversion of DC resistivity data

We investigated the effectiveness of a focusing regularization technique for the inversion of direct current (DC) resistivity data for a typical engineering problem. A smoothing stabilizer (Laplacian of model parameters) is generally preferred in the inversion (OCCAM's inversion) of DC resistivity data. Smooth reconstructions may be produced with this stabilizer, but some specific problems might require more focused images for adequate interpretations. For this reason, we investigated the capabilities of the minimum gradient support (MGS) stabilizer for providing shaper results. This stabilizer allows the a sharper reconstruction because its main effect is to minimize the area where strong differences occur between adjacent model parameters. We also analyze the effects of the focusing parameter, which is the parameter in the MGS expression controlling the level of sharpness of the final result. Our strategy for the selection of the optimal focusing parameter allows the resolution of distinct resistivity contrasts. Moreover, some artifacts that may arise in the use of the a very small focusing parameter disappear while using the normalized focusing parameter. We demonstrate these results by using both synthetic and field data examples. In the field data test, the subsurface image reconstructed using the proposed MGS approach matches well with the lithology inferred from borehole drillings.

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

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.

Synthesis and Characterization of Structural, and Electrical Properties of Mg(0.25x)Cu(0.25x)Zn(1 – 5x)Fe2O4 Ferrites by Sol-Gel Method

The effects of magnesium, copper, and zinc substitutions on spinel ferrites have been investigated by the sol-gel technique. Ferrite compositions of Mg0,25xCu0,25xZn(1−0,5x)Fe2O4 (where x = 0.6, 0.7, 0.8 & 0.9) were prepared at a sintering temperature of 1100 ∘C with a presintering at 500 ∘C. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-precision impedance analysis are used to characterize structural and dielectric properties, as well as the surface topography and morphology of the samples. A single phase, cubic spinel structure, with decreased lattice constant was observed. SEM micrographs revealed a homogeneous microstructure with uniform size distributions. Both the dielectric constant and dielectric loss tangent decrease, as the incident frequency increases up to a certain saturation point. The direct current (dc) resistivity profile shows that the resistivity increases with the temperature up to the Curie point, then it goes to a constant value. The quality factor (Q-factor) increases with the incident frequency. Hence, the high Q-factor will make ferrites highly useful in applications, especially in multilayer chip inductors.

Geostatistical and multi-fractal modeling of geological and geophysical characteristics in Ghalandar Skarn-Porphyry Cu Deposit, Iran

This work aims at figuring out the spatial relationships between the geophysical and geological models in a case study pertaining to copper-sulfide mineralization through an integrated 3D analysis of favorable target. The Ghalandar Skarn-Porphyry Cu Deposit, which is located in NW Iran, is selected for this research work. Three geophysical surveys of direct current electrical resistivity and induced polarization tomography along with magnetometry are performed to construct the physical properties of electrical resistivity, chargeability, and magnetic susceptibility, respectively. Inverse modeling and geostatistical interpolation are utilized to generate the physical 3D models. A 3D model of Cu grade is generated using ordinary kriging; however, the indicator kriging method is run to design a 3D model of rock types through incorporating the drilling results. Block models of geophysical and geological characteristics are cast in a similar 3D mesh to investigate their relationships in copper mineralization. A concentration-volume multi-fractal method is utilized to divide each model into its sub-sets, where the most productive portions in association with Cu-bearing mineralization are distinguished. Note that sub-sets of geophysical models are spatially matched with geological models of Cu grade and rock types. The zones with low electrical resistivity, high chargeability, and low magnetic susceptibility correspond to the main source of Cu mineralization in a dominated skarn rock type setting.

Investigation of Structural, Dielectric and Electrical Properties of Barium Titanate Ceramics Co-Doped with Bismuth and Yttrium

Bismuth and Yttrium co-doped Barium Titanate (BaTiO3) ceramics with the general formula (Ba[Formula: see text]BiX) (YxTi[Formula: see text]) O3(where [Formula: see text], 0.01, 0.03, 0.05) have been synthesized at 1300∘C for 3[Formula: see text]h by the standard solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Impedance Analyzer. Temperature-dependent dielectric properties of the samples were also measured. The XRD result revealed perovskite structure for un-doped and co-doped BaTiO3with tetragonal phase. However, with increasing doping concentration, a Pseudo cubic phase occurs also confirmed by the twin peaks (002) and (200) of XRD pattern. From SEM micrograph, submicron size particles were observed for all synthesized BaTiO3samples and exhibit a narrow size distribution with quiet uniform morphology. The crystalline size for un-doped BaTiO3found was 24.26[Formula: see text]nm, the size decreases (minimum 19.59[Formula: see text]nm for [Formula: see text]) for all compositions of co-doped BaTiO3. Dielectric constant values were apparently high and direct current (DC) resistivity follows a decreasing trend at higher doping concentration. The sample doped with [Formula: see text] shows minimum DC resistivity and maximum dielectric constant among the samples investigated.

Effect of Fe and Bi doping on LaCoO3 structural, magnetic, electric and catalytic properties

La1-xBixCo1-yFeyO3 perovskite was prepared by micro-emulsion method and effect of the Fe and Bi doping on the properties of perovskite was investigated. As-prepared perovskite was characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Energy-dispersive X-ray (EDX) and atomic force microscopy (AFM) techniques. La1-xBixCo1-yFeyO3 perovskite showed distorted rhombohedral structure and particle size was in the range of 33.05–57.41nm. Doping of perovskite with Bi and Fe enhanced the direct current (DC) resistivity. Dielectric parameters were studied in the range of 20 to 20MHz and vibrating magnetometery revealed that the Mr and Ms values were higher for La0.75Bi0.25Co0.75Fe0.25O3, whereas LaCoO3 showed higher value of Hc. Photocatalytic activity (PCA) was evaluated by degrading congo red dye and Bi and Fe doped perovskite showed significantly higher activity versus LaCoO3. Results revealed that the doping of LaCoO3 with Bi and Fe enhanced the magnetic, dielectric and catalytic properties of LaCoO3.

A framework for petrophysically and geologically guided geophysical inversion using a dynamic Gaussian mixture model prior

SUMMARYWe propose a new framework for incorporating petrophysical and geological information into voxel-based geophysical inversion. By developing the geophysical inverse problem from a probabilistic perspective, we redesign the objective function and the iteration steps as a suite of cyclic optimization problems in which three separate MAP optimization problems are solved using geophysical, petrophysical and geological data, respectively. By quantitatively linking these data into a single framework, we recover a final inverted model that reproduces the observed, or desired, petrophysical and geological features while fitting the geophysical data. To achieve our goal we replace the Gaussian prior, used in the Tikhonov inversion approach, by a Gaussian mixture model. After each geophysical model update, the mixture parameters (means, variances and proportions) are determined by the geophysical model and the expected characteristics of the lithologies through another optimization process using the expectation–maximization algorithm. We then classify the model cells into rock units according to the petrophysical and geological information. These two additional steps over the petrophysical and geological data result in a dynamic update of the reference model and associated weights and guide the inversion towards reproducing the expected petrophysical and geological characteristics. The resulting geophysical objective function does not require extra terms to include the additional petrophysical and geological information; this is an important distinction between our work and previous frameworks that carry out joint geophysical and petrophysical data inversion. We highlight different capabilities of our methodology by inverting magnetotelluric and direct-current resistivity data in 1-D and 2-D, respectively. Finally, we apply our framework to inverting airborne frequency domain data, acquired in Australia, for the detection and characterization of saline contamination of freshwater.

Dielectric and electrical study of zinc copper ferrite nanoparticles prepared by exploding wire technique

The experimental investigation of electrical and dielectric characteristics of spinel Zn–Cu ferrite (ZCFO) nanoparticles, synthesized adopting an exploding wire technique (EWT)-based approach, is reported in this paper. The direct current (DC) electrical parameters of prepared nanoparticles were studied by two-probe method in the range of 300 K (RT) to 423 K. The activation energy for hopping of charge carriers, drift mobility and charge concentration was determined through DC analysis. The attributes of dielectric behavior like dielectric constant (e′), loss tangent (tan δ), dielectric loss (e″) and alternating current (AC) conductivity (σAC) were measured at various temperatures in the frequency range of 10 Hz–10 MHz. The increase in AC conductivity with frequency, observed in our study, represented the normal behavior of spinel ferrite. The two-layer model based on space charge polarization could satisfactorily elucidate variation in dielectric constant with frequency. The dielectric parameters at different frequencies were also determined in temperature range of 300–673 K. The decrease in DC resistivity as well as the increase in AC conductivity, with rise in temperature, affirms the semiconducting nature of prepared nanoferrite with the band gap energy of 3.16 eV, as calculated through UV–visible analysis. The capacitance of thin grain boundary region (Cgb), grain boundary resistance (Rgb) and relaxation time (τg) of zinc–copper nanoferrite were estimated through Cole–Cole plot analysis.

Groundwater resources survey of tongchuan city using the audio magnetotelluric method

The development of the Tongchuan city, Shaanxi, located in northwestern region of China is restricted by water resources. The application of direct current resistivity method and induced polarization (IP) sounding method are usually used to find urban groundwater. These methods, however, are not effective due to its complicated topography and geological conditions. The application practice shows that the audio magnetotelluric method (AMT) is of large depth of exploration, high work efficiency and high lateral resolution. To investigate the distribution of groundwater resources, we deployed three audio-frequency magnetotelluric profiles in the city area. The impedance tensor information of AMT data is obtained using SSMT2000. AMT data dimension analysis reveals that the two-dimensional structure features of the observation area are obvious. The main structure of the observation area is about 45° northeast by structural trend analysis. A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by a two-dimensional nonlinear conjugate gradient inversion.. Finally, combined with regional geological information, the geological structure characteristics reflected by the electrical profile were obtained with detailed the characteristics of water-rich structures in the area. The influence of the structure on the distribution of groundwater was analyzed and the water-rich areas were trapped. That contributes prospective development of Tongchuan city.

Boron 10B—11B Isotope Substitution as a Probe of the Mechanism Responsible for the Record Thermionic Emission in LaB6 with the Jahn—Teller Instability1

We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC (direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope contents. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70% of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6.

Dynamic monitoring of the mining-induced fractured zone in overburden strata, based on geo-electrical characteristics

Studies of the development height of mining-induced fractured zone in overburden strata are of great significance for safety and green mining of coal resources. Using geo-electrical response, a dynamic monitoring method for the fractured zone is investigated using the direct current resistivity method. Firstly, a numerical model of the mining-induced overburden is established and forward modeling is achieved from which the development of the caved zone and fractured zone is interpreted by inversion. The physical model then is designed, based on similarity theory and physical experiments, that displays visually dynamic deformation of the mining-induced overburden. After acquiring electrical data for the model, the inversion is done, based on which the development height of the fractured zone could be dynamically predicted. Finally, in order to prevent water inrush disasters, in situ investigations are carried out in one mine and height of the water-conducting fractured zone is determined. The researches show that the apparent resistivity inversion results, as the interpretation of caved zone and fractured zone, are approximately identical and the direct current resistivity method is proved to be an effective tool for dynamic monitoring of the mining-induced fractured zone.

Short-Lived Electron Excitations in FeTe1 –xSex as Revealed by Microwave Absorption

The $\rm Fe_{1+y}Te_{1-x}Se_x$\ single crystals with the various Se/Te ratios were studied by the microwave absorption and direct current resistivity measurements. The comparison of the microwave absorption data and the resistivity versus temperature made it possible to separate the contributions of two types of spin fluctuations. One of them is due to the anisotropic magnetic (nematic) fluctuations. It is observed over the wide temperature range from 30K to 150 or 200K. In FeSe it has the maximum close to the structural transition temperature. Another MWA anomaly is located in the narrow temperature range above the superconducting transition. It is likely due to the antiferromagnetic fluctuations. Annealing of a sample at the temperature around 300 C in the oxygen atmosphere made it possible to exclude the effect of excess iron on the observed anomalies.