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International Society for Industrial Process Tomography

6th World Congress on Industrial Process Tomography

Advanced electrical impedance tomography system with high phase accuracy


E. Zimmermann1, J. A. Huisman2, A. Kemna3, J. Berwix1, W. Glaas1,

H. Meier1, B. Wolters1, O. Esser2


1 Central Institute for Electronics (ZEL), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

2 Agrosphere (ICG­4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

3 Department of Geodynamics and Geophysics, University of Bonn, Nussallee 8, 53115 Bonn, Germany


ABSTRACT


Spectral electrical impedance tomography (EIT) is a powerful method for non­invasive characterization of materials. Especially for geophysical applications, where the method is used to measure the spectral induced polarization properties of soils and rocks, it represents an advanced approach for structural characterization. Except for rocks with electronically conductive minerals, the polarizability of these media is relatively low. Typical complex resistivity phase values lie in the range of 0.1 – 20 mrad, and typically a frequency range of 1 mHz to some kHz is used for spectral characterization. Given the increasing interest in the application of spectral EIT on soil and rock materials, there is a high demand for tomographic data acquisition systems capable of operating in the relevant frequency range with the required phase accuracy.


To meet these requirements, we have developed a new, advanced spectral EIT data acquisition system for laboratory and near­surface borehole applications. The new system operates in the frequency range from 1 mHz to 45 kHz. It is equipped with 40 dual­functionality electrode modules with integrated amplifiers for electric potential measurements and with integrated switches for current injection that allow reciprocal measurements. In addition, electrode chains for near­surface borehole measurements have been developed. In this contribution, we will 1) present the design of the system, including a method to estimate the true excitation currents, 2) analyze reciprocal measurements, and 3) evaluate the spectra of the measured transfer impedances and reconstructed (3D) complex resistivity of a well defined target inside a water­filled tank and of field data. The electrical properties of the targets are known from independent measurements with an established impedance spectrometer.


Keywords EIT, imaging, impedance spectroscopy, spectral induced polarization, electrical soil and rock properties, plant roots.


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