An electric field solver based on a finite volume method using refined structural mesh is proposed to implement a quadtree structure and estimate the electric flux in the mesh cell. Numerical experiments were carried out using uniform and non-uniform meshes to assess quality of numerical modeling. The proposed method of verification of the quality of numerical calculations based on circular symmetry of the electrical capacitance tomography (ECT) probe allows to assess the effectiveness of mesh refinement and to reduce the number of mesh elements. Experiments showed that even a moderate level of mesh refinement is sufficient to significantly reduce the simulation error that occurs in modeling of cylindrical probes. The reduced number of mesh elements and applied implementation of the quadtree ensures high speed of forward problem calculations.

Electrical capacitance tomography (ECT) is a technique of imaging the distribution of permittivity inside an object under test. Capacitance is measured between the electrodes surrounding the object, and the image is reconstructed from these data by solving the inverse problem. Although both sinusoidal excitation and pulse excitation are used in the sensing circuit, only the AC method is used to measure both components of complex capacitance. In this article, a novel method of complex capacitance measurement using pulse excitation is proposed for ECT. The real and imaginary components are calculated from digital samples of the integrator response. A pulse shape in the front-end circuit was analyzed using the Laplace transform. The numerical simulations of the electric field inside the imaging volume as well as simulations of a pulse excitation in the front-end circuit were performed. The calculation of real and imaginary components using digital samples of the output signal was verified. The permittivity and conductivity images reconstructed for the test object were presented. The method enables imaging of permittivity and conductivity spatial distributions using capacitively coupled electrodes and may be an alternative measurement method for ECT as well as for electrical impedance tomography.

Selenium is the first member of the group 16 elements O, S, Se, Te, and Po that shows some metallic character. The increasing metallic character in the series O, S, Se, Te, Po is reflected also in the lower electronegativity, in the less acid character of the oxides, and in the lower stability of the oxidation number +VI for selenium compared to sulfur. There is a large variety of compounds of SeII, SeIV, and SeVI with the electronegative elements N, O, F, Cl, and Br. Thus, there are several types of compounds containing those elements in one molecule. The review will describe the diverse range of cations, oxo‐ and halo‐compounds that selenium forms and their relative structures as haloselenates, selenates, and oxohaloselenates as well as their analogous compounds containing nitrogen and selenium bonded together. Selenides, where selenium as an anion with −2 oxidation number, are presented very briefly, just to underline their properties and wide applications as photoconductors.

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