This article deals with magnetic nano-fluids, which are the part of transformer oil ITO 100 and their behavior is influenced by a permanent magnetic field. We performed an IRC analysis in the time domain on the three different samples. Measurements were made before and after radiation of an electromagnetic field. The main objective was to examine changes in the properties of the samples due to the influence of the electromagnetic field. The measurements depend on the orientation of the external magnetic field. This behavior occurs especially during the structuring of the nanoparticles in the sample exposed to the magnetic field. These processes change the polarization of the liquid because the nanoparticles concentration is contained in the fluid.

Improving the dielectric properties of liquid-insulating materials is a current problem in research into the insulation system of a power transformer. Modern optimization of insulating liquids involves the potential use of unique synthetic esters enriched with nanoparticles. This study presents the results of the dielectric response of liquefied gas-based (GTL) insulating liquids during accelerated thermal aging. The dielectric relaxation spectroscopy method was used in the frequency domain to point out power losses as an imaginary part of a complex electric modulus. The relaxation spectra express the validity of applying this complex dielectric parameter. The polarization processes of the base oil alternately change position in the low-frequency band during thermal aging. Fullerene nanofluid undergoes three phases of dielectric loss changes during thermal aging. In the case of magnetic nanofluid, the effect of electric double-layer polarization disappeared after 500 h of thermal aging. It was found that with the gradual increase in the thermal aging time, there is no gradual increase in the dielectric losses investigated in the measured frequency spectrum. This study shows that the concentration of the two types of nanoparticles independently causes a different dielectric response to an applied AC electric field in the GTL base fluid.

An environment with a higher accumulation of electromagnetic non-ionising radiofrequency (RF) emissions generated by various telecommunication, data transport and navigation devices (mobile phones, Wi-Fi, radar, etc.) may have a major impact on biological systems. This study aimed to evaluate the incidence of an electromagnetic field (EMF) on the development of bacterial biofilm. Quantification of biofilm production was done by using microtiter plate assay. Bacterial isolates of Escherichia coli, Klebsiella oxytoca and Pseudomonas aeruginosa were exposed with EMF of frequencies 1–5 and 2.4 GHz with an exposure time 3 or 24 h, respectively. Exposure of bacteria to EMF produced a statistically significant increase in biofilm production mainly at 1, 2 and 4 GHz, and in contrast, a significant inhibition of biofilm development occurred at frequencies 3 and 5 GHz, both with exception of K. oxytoca and P. aeruginosa. Wi-Fi operating at 2.4 GHz caused biofilm reduction. The results indicate that EMF exposure act on bacteria in both ways, depending on the frequency: as stressful by enhancing bacterial biofilm formation (under environmental stress, bacteria produce a polysaccharide matrix and aggregate to form biofilms to increase virulence and resistance), although some frequencies leading to biofilm damage could be caused by changes to the physicochemical properties of bacteria. GRAPHICAL ABSTRACT

This paper deals with the negative abrasive effect of magnetic nanofluids on paper insulation. Nanofluid with magnetite Fe ₃ O ₄ nanoparticles and conventional transformer paper was used in the experimental part. The simple degradation device based on magnetic properties of nanofluid for the simulation of fluid flow was constructed. Frequency dependent spectroscopy in 20 Hz - 2 MHz domain for analysis of results was used. Moreover, the analysis of samples under the microscope was additionally carried for detection of paper insulation disruption. The microscopic images were processed in 8-bits scale of grey and analysed by a software tool. The results of the experiment indicate the possible negative effect of nanoparticles on cellulose fibres.