Electrical Tomography Technique Research Articles

An assessment of miniaturised electrical imaging equipment to monitor pollution plume evolution in scaled centrifuge modelling

This paper demonstrates the capabilities and limitations of a miniaturised electrical imaging technique (resistivity tomography) developed at Cardiff University to image contaminant plumes in scaled centrifuge models of the vadose zone. For this purpose a generic model of contaminant infiltration into unsaturated sand was designed. The imaging technique produces two-dimensional contoured plots of the resistivity distribution before and during contaminant infiltration experiments. During the experiments, dyed NaCl solution was released into the model and the change in resistivity associated with the contaminant plume evolution was imaged as a function of time and g-level. Capillary pressure was monitored constantly by matrix potential probes (tensiometers) in order to investigate the effect of capillary forces on plume evolution. Tests at 1 g (static conditions) and 10 g are described in this paper. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the 1 g test showed this imaging technique to be highly effective. Contaminant plume evolution in the unsaturated sand model was observed to be mainly gravity-driven, with plume migration and geometry being strongly affected by a tenfold increase in gravity in the centrifuge experiment. It is concluded that miniaturised electrical imaging can be a useful tool for monitoring pollution plume evolution during centrifuge tests, but when plume evolution is rapid, the time taken to interrogate each array restricts the effectiveness of the technique in monitoring changes in plume geometry. However, in such cases, resistivity tomography does provide valuable information on residual levels of contaminant fluid retained within the soil after passage of the plume.

Application of electrical imaging techniques for the investigation of natural dams: an example from the Thulagi Glacier Lake, Nepal

The Thulagi Glacier Lake in the Gorkha District of western Nepal was investigated by electrical resistivity tomography (ERT) to delineate buried glacier ice and permafrost zones within the dam. Data were processed using a 2-D inversion program and by finite-difference forward modelling. Interpretation of the processed electrical images indicates that the method can be used for detecting the buried ice and permafrost by virtue of their very high electrical resistivity values (>20,000 Ohm.m and >5.000 Ohm.m, respectively). The resistivity of permafrost seems to be strongly dependent on the material particle size: the finer the particle size the lower is the value of electrical resistivity. Water-saturated glacier sediments have values of electrical resistivity less than 3,000 Ohm.m. The ERT method was useful in mapping of buried glacier ice and permafrost as well as in differentiating other geological materials constituting the dam.

Electric Current Density Imaging of Pedunculate Oak(Quercus RoburL.) Twigs by Magnetic Resonance Imaging

The use of Electric Current Density Imaging (CDI) technique to map spatial distribution of induced electric currents through two years old twigs of pedunculate oak (Quercus robur L.) is presented. Specifically, this magnetic resonance technique was implemented to image conductivity contrast in different tree tissues. Imaged electric conductivity distributions of pith, wood, and phloem together with cambial zone and undifferentiated xylem were compared with flame atomic absorption spectrometry measurements of potassium. Good correlation was observed. The undifferentiated xylem + cambial zone + complete phloem showed higher electrical conductivity and normalized potassium values than both differentiated xylem and pith. By a novel magnetic resonance imaging technique it is demonstrated that the path of least resistance to an electric current was along tissues of maximum free potassium concentration.

Combustion imaging from electrical impedance measurements

The development of stray-immune circuits to measure very small floating capacitances has enabled the technique of electrical capacitance tomography (ECT) to be developed. Burning fuel, for example in an internal combustion engine, produces a high concentration of ions, thus modifying the dielectric constant of the combustion volume. Thus ECT can be applied to produce tomographic images inside a combustion chamber, independent of flame luminosity. However, the major effect of the increase in ion concentration is to increase the conductivity of the volume. The ECT technique has been extended to measure both the change in permittivity and change in conductivity, yielding additional information on the flame composition. Current spatial and temporal resolution is poor but developments are in hand to overcome these limitations. Alternatively, the way forward may well be to abandon images and instead use extremely simple and cheap sensors to monitor knock on a cycle-by-cycle basis. An alternative use of such a simple sensor would be to monitor cycle dispersion in a lean burn engine. Both these techniques could help minimize fuel consumption, whilst maximizing power output and keeping emissions low.

Analysis of chaos in fluidization using electrical capacitance tomography

Fluidized beds display a degree of structure which it is vital to understand in any design and scale-up of equipment. This paper is on the employment of chaos theory to describe this structure. The measuring technique of electrical capacitance tomography is used to determine the local porosity of a gas - solids fluidized bed and to monitor its fluctuation with time. These raw data are translated into invariants characteristic of the structure mentioned, such as the Kolmogorov entropy. Initial measurements have shown a strong variation in these chaotic invariants with bed position and operational parameters. First results are compared with earlier data from pressure measurements.

Electrical tomography techniques for process engineering applications

This paper summarizes the characteristics of electrical tomography techniques, highlights their current applications and gives an indication of their future applications in the chemical process engineering environment.

感度合成解析による電位法電極配置探査特性の評価

For the geoelectrical measurements and their inversion analysis, a more accurate and reliable resistivity data aquisition system is needed more than ever. As the direct current resistivity method most commonly used for the exploration and evaluation of the target inhomogeneity is a very useful and practical tool for the electrical imaging technique so-called resistivity tomography, it may be exceedingly important to incorporate a new sensitivity method developed by the author for determining more exactly the earth resistivity target inhomogeneity, for examples, faults, fractures, layers, water bearing zones, and geological structures under various conditions and environments. Especially, no technique has been investigated to interprete the local and lateral resistivity changes of the near surface inhomogeneities and detailed deep massive resistivity structures.In this paper, by composite analysis of sensitivity distributions, the author has clarified the relation among various surface electrode arrays. The two-electrode system, the four-elctrode systems such as the Wenner, the Eltran and the Staggered electrode configuration (so-called the tripotential system) and the six-electrode system have been discussed. Also an example of the sensitivity composite analysis for the solid electrode array system has been investigated as an aid to analyze the response caused by target inhomogeneity more practically.

Borehole electrical imaging and structural analysis in a granitic environment

SUMMARY The crucial problem of fracture detection and analysis has long challenged the capability of conventional logging. The electrical imaging technique is able to elegantly solve this problem. Electrical imaging of the borehole wall will take a growing part, with acoustical imaging, in exploration programmes. It can be expected that its applications will expand in the future with the constant improvement of the measurement devices. The present paper describes experience acquired with the Elias probe developed by BRGM Instruments. This probe is characterized by full coverage of the borehole wall, slim diameter of the probe and non-ambiguous depth matching between pads. After instrument design, data processing and enhancement is an important step before interpretation. Finally the visualization of fracture distribution and its statistical description provides a comprehensive tool for the analysis of borehole images and of structural data. The Elias probe, together with the processing and interpretation software, provides an integrated package for exploiting the full potential of high-resolution borehole investigations and the petrophysical sensitivity of formation resistivity. This paper describes the functioning of the tool, the processing of image data and the interactive curve matching used for the visual recognition of fracture surfaces. A field example from the Auriat well, located in the French Massif Central and drilled in a granitic intrusion, is used to validate the accuracy of the method and to define the spatial properties of a fracture network, by comparison with the complete sets of fracture observed along a full oriented coring of this borehole.

Impedance tomography and its application in deep venous thrombosis detection

The authors have developed an impedance imaging prototype system and tested its functionality. They describe some enhancements made to their previous system and three algorithms for reconstructing impedance images. The system is capable of reconstructing cross-sectional impedance distributions from surface measured data. They discuss some experimental results with the saline tank and a preclinical study of applying the electrical imaging technique to detect deep venous thrombosis (DVT). Other potential applications include monitoring pulmonary edema, imaging the lungs, and noninvasive temperature monitoring during hyperthermia treatment.