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Generation of Fe₃O₄ Nanoparticle Aggregates in a Ferrofluid Driven by External Electric Field

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Kurimský J., Rajňák M., Cimbala R., Paulovičová K., Timko M., Kopčanský P., Kolcun M., Kosterec M., Kruželák L.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
907-909
EN
In the paper the experimental study of magnetic nanoparticle aggregation in a transformer oil based ferrofluid driven by an external electric field is reported. The studied ferrofluid was composed of the magnetite nanoparticles, oleic acid surfactant, and transformer oil. Generally, it is considered that superparamagnetic nanoparticles do not interact in the absence of external magnetic field. In the paper we present an experimental observation of the particle assembly formation in a direct current external electric field by optical microscopy. During the observation no external magnetic field was applied. A diluted low-polarity ferrofluid drop on a glass surface was exposed to the external static inhomogeneous electric field. It is assumed that induced dipole-dipole interaction and subsequent dielectrophoretic motion give rise to the electrohydrodynamic flow in the fluid after a certain time period. As a result, a visible particle chain was formed at the drop electrical equator. This demonstration is expected to contribute to the understanding of the streamer formation and electrical breakdown in transformer oil based ferrofluids.
2
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Additional Modification of Thermomagnetic Properties of Objects of Low Relative Permeability in Electromagnetic Field

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Medveď D., Zbojovský J., Pavlík M., Ilenin S., Čonka Z., Kanálik M., Kolcunová I., Mészáros A., Beňa L., Kolcun M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1138-1140
EN
This paper presents the characteristics of the foodstuff heating phenomenon using induction heating process by an induction cooker. The simulation setup was prepared according to the proposed magnetic material and configuration of the pot and induction cooker. The material properties of pot were varied among the several alternatives. The helical coil was designed on the base of the limitation of the induction cooker size and given number of coil turns and coil tube diameter with specific supplied electric current density. The data from the simulation analysis have to determine the enhancing of the highest heat transfer from induction cooker into pot. These data led to the modification of the material and geometrical properties of the pot in accordance to a minimum heating time and enhanced safety operation, especially close to unshielded magnetic objects.
3
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Influence of Electromagnetic Shield on the High Frequency Electromagnetic Field Penetration through the Building Material

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Kolcunová I., Pavlík M., Beňa L., Čonka Z., Ilenin S., Kanálik M., Kolcun M., Mészáros A., Medveď D., Zbojovský J.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1135-1137
EN
This paper studies how to protect people against electromagnetic radiation inside a building. Widespread usage of the mobile communication led to building of more and more new GSM base-station antennas. These antennas are often placed in the areas with high population density. These antennas emit electromagnetic radiation in standard mobile operator frequencies, i.e. 0.9, 1.8 and 2.1 GHz. Many studies have shown potential biological and thermal effects of GSM electromagnetic fields, therefore people are concerned about their health. Electromagnetic wave does not penetrate the wall of the building as a whole. A small part of the wave is reflected and a small part is absorbed by the building material. In this paper the penetration of electromagnetic waves through the commercially available building materials is measured with specific focus on frequencies of 0.9, 1.8, and 2.1 GHz. Next, the surface of the chosen building material was coated with a magnetic conductive paint in order to improve the shielding effect of the building material. The results of experiment show how the electromagnetic shield reduces the penetration of electromagnetic waves through the building wall.
4
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The Investigation on the E-J Characteristics and the Role of Nanoparticle Concentration in Weakly Polar Magnetic Fluids

100%
Kurimský J., Dolník B., Marton K., Kolcun M., Tomčo L., Rajňák M., Timko M., Kopčanský P.
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vol. 126
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issue 1
246-247
EN
The paper presents investigation on the magnetic fluids that are stable colloidal suspensions of single-domain magnetic particles in a liquid carrier of dielectrics nature. Studies were made on the electric field vs. current density, e.i. E-J characterization commonly observed in insulating liquids under uniform low electric or magnetic fields. High performance oil was used as the dielectric carrier. The experiments were carried out at different volume concentrations of magnetite nanoparticles up to 4%.
5
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Hall Effect in ZnO Extrinsic Structure

100%
Dolník B., Kurimský J., Marton K., Kolcun M., Tomčo L., Briančin J., Fabián M., Halama M., Vojtko M., Rajňák M.
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vol. 126
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issue 1
76-77
EN
Zinc oxide-based extrinsic composite was investigated. The sample was selected from a series of components of one production batch, prepared by standard sintering technology. The content of extrinsic elements in ZnO base was determined by SEM. Van der Pauw method with four-point electrode fixture was used for study of conducting phenomena in square-shaped sample. It is normaly preferred to assume the symmetric uniformity of the electrical properties of sample, for which sheet resistance, bulk resistivity and Hall mobility, sheet carrier density and carrier concentration can be calculated. When the uniformity of measured parameters is breached, the anisotropy in the arrangement of the internal structure may be the cause. There remains the question of whether the extrinsic ZnO material can be isotropic, regarding the electrical conductivity. Although the Hall effect has been measured, preliminary measurements indicate the presence of anisotropy in the measured samples. Before measurement the following phenomena should be taken into account: magneto-electric effect, photo-electric effect and the isothermal condition should be preserved. Paper discusses the uniformity deviations for the defined setup configurations for positive and negative magnetic field directions. Bulk resistivity has been calculated by numerical solution of van der Pauw equation. Large offset voltage during the measurement is discussed.
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