Roman Cimbala

Electrode polarization and unusual magnetodielectric effect in a transformer oil-based magnetic nanofluid thin layer

In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid based on transformer oil and iron oxide nanoparticles stabilized by oleic acid. The complex dielectric permittivity measured in the frequency range from 1 mHz to 200 kHz shows an obvious electrode polarization effect and a Debye-like dielectric relaxation process. Both effects stem from the presence of space charge in the oil due to impurity ions, and in the nanofluid represented predominantly by a residual surfactant and uncompensated particle surface charge. It is shown that the spectra, which were measured in the temperature range from 298 K to 358 K, can be well represented by a fitting function consisted of one Havriliak-Negami term and the Jonschers power law. In the investigated magnetic nanofluid layer, we found that the onset of the electrode polarization is suppressed to lower frequencies by the application of an external magnetic field (300 mT). This phenomenon is explained by a slowed-down migration of the space charge due to the Lorentz force and by a hindering effect of the formed magnetic nanoparticle aggregates. Surprisingly, a moderate decrease in the whole permittivity spectrum was observed for both parallel and perpendicular orientations of the electric and magnetic fields. This is in contradiction with the usual magnetodielectric anisotropy effect. Based on our qualitative analysis, we discuss potential reasons accountable for the observed effect.

Ticks and radio-frequency signals: behavioural response of ticks ( Dermacentor reticulatus ) in a 900 MHz electromagnetic field

Abstract The electromagnetic field (EMF) is present in the environment throughout the world and encompasses both natural and human-made sources of electromagnetic fields. It has been shown that EMF influences a variety of biological systems, including the behavioural responses of both vertebrates and invertebrates. As such, determining the effects of the EMF on the ecosystem in detail may be important for understanding the ecology and biology of organisms, particularly those, such as ticks, that are important in disease transmission. Our main goal was to determine if the tick, Dermacentor reticulatus, interacts with the EMF. An experimental behavioural test of tick sensitivity to radio frequency power radiation was performed under laboratory conditions. Tests were performed in an electromagnetic compatibility laboratory in a radio frequency electromagnetic field (RF-EMF) anechoic chamber. Ticks were irradiated using a Double-Ridged Waveguide Horn Antenna with 900 MHz RF-EMF. The applied radio-frequency power was tuned below the proposed limit for public exposure to mobile phone base stations. We found that exposure induces an immediate tick locomotor response manifested either in a previously unreported jerking movement of the whole body or in jerking of the first pair of legs. Overall, ticks exhibited significantly greater movement in the presence of the RF-EMF. Significant sex differences relative to RF-EMF exposure were observed in both response variables. In the presence of RF-EMF, body jerking by females was greater than in males and vice versa for leg jerks. This study represents the first experimental evidence of a behavioural response of D. reticulatus ticks to exposure to RF-EMF.

The impact of electromagnetic radiation on the dielectric properties of magnetic nanofluids

Presented article discusses the impact of electromagnetic radiation on dielectric properties of magnetic fluids based on transformer oil ITO 100. For measurements and evaluation of the samples we used the PDC analysis. The measurements were performed in two variants, specifically when individual samples were irradiated and were not irradiated with the external magnetic field. To minimize undesired electromagnetic fields, the measurements were realized in the anechoic EMC chamber. The main objective of this experiment was to determine if the electromagnetic radiation can change properties of magnetic liquid. Used samples of magnetic fluids were with different concentrations of magnetic nanoparticles. In the experiment was generated electromagnetic field, used to charge and discharge streams, of which are indicative of the state of the insulation system. For comparison of the results the samples were analyzed before irradiation with EM field and after irradiation with EM field.

Thermal degradation of transformer pressboard impregnated with magnetic nanofluid based on transformer oil

In this paper, the thermal ageing of pressboard impregnated with two kinds of insulation liquids is studied by means of frequency domain spectroscopy which involves the measurement of real and imaginary part of complex permittivity as function of frequency. The magnetic nanofluid was composed by mineral transformer oil as carrier liquid, nanoparticles of magnetite and surfactant. The thermal aging test was performed at the temperature 90°C for 1000 hours. Each sample had two variations, with and without copper, which has function catalyst. Then frequency domain spectroscopy was investigated at 40°C for restriction of moisture influence from surrounding. From the data and curves, it can be shown that the undried samples are dried with the aging time and cooper considerably getting worse the imaginary part of complex permittivity. In case of magnetic nanofluid, the colloidal suspension was unstable after 800 hours of the thermal ageing. There was found much more resistance of moisture at the nanofluids than in case of mineral oil impregnated pressboard.

Experimental observation of interaction between radiofrequency electromagnetic field and blood tissue

The exposition of biological and technical systems to electromagnetic radiation has increased with the rapid development of wireless data transfer. Recent studies are incrementally aiming at electromagnetic compatibility between electromagnetic radiation sources and biological and technical systems. No source of electromagnetic radiation should affect operation of other technical systems and endanger biological systems. Studies show that biological organism reacts to electromagnetic fields. This paper is focused on experimental observation of interaction between electromagnetic radiation and biological samples in the form of blood preparations. Results of interaction of radiofrequency electromagnetic radiation produced by mobile phone and biological tissue are presented. Samples of animal blood were used. The first part is focused at actual research in the world. In the second part there is presented workplace setup for exposing biological tissues to non-ionizing electromagnetic field. Results of this exposure are presented in the end.

Influence of electromagnetic interference on time-domain spectroscopy of magnetic nanofluids

The article deals about magnetic fluids based on a transformer ITO100 oil and about behaviour of these fluids under influence of permanent magnetic field represented by time-current characteristics. The measurements were performed in an anechoic EMC chamber and outside the chamber for comparing the results on the same samples. The main objective was to determine how much is the measurement influenced by external electromagnetic fields that generate around electrical equipment and the impact of higher harmonics in the power supply voltage. The measurement is dependent from orientation of actuating magnetic field, this behaviour mainly shows the effect of nanoparticles structuring during exposition of specimen by magnetic field. These particles also changes polarization processes in fluid influence of nanoparticles concentration contained in the fluid.

Dielectric spectroscopy of transformer oil based ferrofluid from view of i(t) characteristics at initial stage of ageing

The article deals with thermal ageing of transformer oil based ferrofluid at initial stage of ageing. Influence of ageing in this article observes changes caused by polarization current, which triggers structural changes in liquid insulation. Except the influence of ageing of polarization current on these samples it has to be noted, that concentration of magnetic nanoparticles in these fluids can also affects capacitance of samples. This assumption is confirmed in article.