Nowadays, various surveillance and security systems are used to detect undesirable violation of the monitored area. The physical principles of information’s gathering, methodology of their processing and subsequent evaluation are the main differences in the operational methods of surveillance and security systems, which allow a wide range of their use in applications with a large variability of potential intruders. Assuming that the surveillance and security systems are used in specific applications where the position and the total number of used individual sensing elements within the monitoring area can change over time, it is necessary, mainly due to the practical and economic reasons, to reduce their dependence on the external galvanic power connections to increase the mobility of system. The technical implementation of a power supply that is independent on the external galvanic connection can be generally in the case of complex surveillance and safety systems considered as an issue with a specific approach of solution, because their individual functional modules may require mutually different power requirements to achieve the proper system operation. In consequence, this article is devoted to the conceptual design of a power supply for a mobile monitoring system, intended to prevent human entry into a defined area to restrain the spread of viral diseases in the groups of the population. In this case, the energy independence of the system is ensured by a suitable configuration of accumulator cells designed to meet the power requirements of the monitoring unit. An additional source of energy is a photovoltaic panel, which, depending on a solar activity, recharges the accumulator cells, and therefore prolong the energy autonomy of the monitoring system. The power supply is also supplemented by a protection circuit extending the accumulators lifetime and power-tracking circuit that increases the efficiency of the photovoltaic panel. The relevant parameters of all considered components of the proposed power supply are summarized in this article, including the analysis of solar irradiance captured by the intended photovoltaic panel during the specific month of the year in a given geographic location.

The aim of this study was to test the suitability of poly-L-lysine coated magnetic nanoparticles for combined magnetic hyperthermia and magnetic resonance imaging (MRI) to unify the therapeutic and diagnostic approach. For this purpose, we have synthetized magnetic iron oxide (Fe3O4) nanoparticles of core diameter similar to 10 nm and modified with Poly-L-lysine (PLL) to stabilize the particles and improve their biocompatibility. These modified nanoparticles (MFPLL) were tested for magnetic hyperthermia suitability by calorimetric measurements. Based on the estimated heating rates the specific absorption rates (SAR) for MFPLL particles were calculated. The SAR values of MFPLL particles were about 14-15 Wg(-1) at frequency 190 kHz and applied field similar to 8 kAm(-1). In the MRI parametric mapping measurements we demonstrated the significant effect of MFPLL on transversal relaxation time T-2 with the relaxivity r(2) equal to 487.94 mM(-1) s(-1). The combination of the heating properties with the cytotoxic activities of MFPLL and MRI parameters holds great promise for the future development of targeted synergistic cancer treatment. Furthermore, as our previous results confirmed the cytotoxic activities of MFPLL in a cell type-dependent manner and the binding to cells expressing carbonic anhydrase (CA IX) when conjugated with the CA IX-specific antibody we have studied the antibody conjugated MFPLL nanoparticles in 3D spheroidal culture.

It is known that the permittivity of a magnetic nanofluid is controllable by external magnetic fields. The resulting effect of magneto-dielectric anisotropy originates in the magnetic nanoparticle assembly formation induced by the applied magnetic field. The particle assembly in magnetic nanofluids can be induced even by a dc electric field. Then, analogous to the magneto-dielectric effect, a question arises concerning the effect of the dc bias electric field on the nanofluid permittivity in a wide frequency range. We present dielectric spectra (1 mHz-1 MHz) measured on a transformer oil-based magnetic nanofluid at various temperatures. Electrode polarization and an interfacial relaxation process are analyzed. We show that the applied dc bias voltage results in permittivity sign switching at low frequencies. The critical frequency at which the sign is reversed depends on the nanofluid temperature and the dc bias voltage level. The nanoparticle assembly and conductive percolative paths are considered as key mechanisms leading to the transition from capacitive to inductive reactance. The measurement of apparent negative permittivity in a dc electric field can be used as a simple method for the detection of electric field-induced particle assembly and percolation. The permittivity sign control by means of a dc bias voltage may open an alternative avenue for research and applications of magnetic nanofluids.

One of the perspective methods for the magnetic field measurement is the methodology based on the GMI effect measurement. The improvement of the sensor is in term of the sensor sensitivity and the wide-band measurement range in comparison to the commercially available magnetometers. For the evaluation of the impedance of the sample the lock-in amplifier capable to make a decomposition of the impedance to the real and imaginary part was used. The designed and constructed measurement workstation can be used for the precise impedance measurement. Specification of the related metrological properties of the samples improve the precision of the magnetic field measurement that is important for vehicles navigation or for precise mapping of the magnetic fields if unmanned aerial vehicles are used in non-destructive archaeology.

An important feature of lyotropic liquid crystals is the self-assembly of the amphiphilic molecules as supermolecular structures. We have studied the formation of nematic liquid crystal phase in solutions containing lysozyme amyloid fibrils and magnetic nanoparticles using oscilloscopic method. Interaction of fibrils with magnetic nanoparticles under the external magnetic field resulted in fibril re-arrangement. The analysis of the obtained results suggests that the decrease in conductivity of solutions in presence of magnetic field is due to decrease of the ion mobility caused by re-arrangement of structures in the solution. The obtained results allow determination of the optimum ratio of the components which can lead to preparation of solutions with a more ordered structure in presence of magnetic field.

Studied in this work has been the effect of nanoparticles - magnetite and single-wall carbon nanotubes - separately and together on the conductivity of nematic liquid crystal 6CHBT dispersed in polyvinyl alcohol. Morphology of these films was analyzed using an electron microscope. When using selected technology of homogenizing the mixture components, there takes place formation of liquid crystals dispersed in the polymer matrix with the average sizes of liquid-crystal droplets close to 500 nm (nanoPDLC). It has been found that simultaneous introduction of magnetite and nanotubes results in lowering the conductivity of nano-PDLC as compared to the total conductivity of nano-PDLC with each kind of nanoparticles separately. It has been suggested that the main mechanism of this effect lies in formation of deep centers for electron capture by complexes with different types of nanoparticles, which leads to a decrease in electronic conductivity through the polymer matrix.

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 nanopaxticles up to 4%.

In this paper the experimental study of the breakdown eld strength in a transformer oil based ferro uid is reported. The experiments are conducted on ve ferro uid samples with di erent magnetic volume fraction. The in uence of external magnetic eld on the breakdown eld strength is investigated, when a quasi-homogenous magnetic eld was applied in parallel and perpendicular con guration in regard to the electric eld. The obtained results are analysed in accordance to the electron charging of ferro uid nanoparticles theory.

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 normal), 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.

Prepared in this work are dispersions of nematic liquid crystal in polyvinyl alcohol with sizes of liquid phase inclusions less than one micrometer (nano-polymer dispersed liquid crystal (PDLC)) by changing technology of mixing the components. It was shown that, like to the case of earlier examined dispersions with the droplet sizes 6 to 10 mu m (micro-PDLC), the conductivity of nano-PDLC has two components: the ion one, which value does not depend on frequency, and the electron one, the value of which depends on frequency according to a power law. It was found that the ion conductivity of nano-PDLC is three orders of magnitude higher than that for micro-PDLC, and the exponent for the electron components of nano-PDLC conductivity is less than that for micro-PDLC. It was shown that the spherical and rod-like magnetic nanoparticles (MNs) influence in a different manner on the conductivity components of nano-PDLC. If for the maximum concentration of spherical MNs 2.10(-3) wt.% the ion conductivity is 2-fold increased, then at the same concentration of rod-like MNs the ion conductivity value increases by more than one order of magnitude.

Investigated in this work has been the effect of impurities - magnetic nanoparticles (MN) and multiwall carbon nanotubes (MWNT) - separately and together on morphology and dielectric properties of nematic liquid crystal 6CHBT dispersed in polyvinyl alcohol (PDLC). It has been shown that the nanoparticles and nanotubes together change the morphology of PDLC practically in the same manner as every type of impurity singly. The impurities influence also additively on the permittivity at low frequencies and electron component of the conductivity in the polymer matrix. We have found that when MN and MWNT act jointly their ion component of the conductivity exceeds the total changes in conductivity by six times greater than when each type of impurity acts singly. The most probable reason for this nonadditive change in conductivity can be aggregation of these nanoparticles.

We have studied dielectric properties (complex permittivity and dielectric loss factor) of a transformer oil ITO 100 based magnetic fluid with various concentrations of magnetic Fe3O4 nanoparticles covered with oleic acid as a surfactant. The experiments were carried out at different volume concentrations of magnetite nanoparticles up to 4% at room temperature and in a frequency range from 100 Hz up to 2MHz, with and without external magnetic field up to 30 mT. The linear increase of the dielectric constant with volume concentration has been confirmed. The presence of magnetic field causes the increase of the real part of complex permittivity and the decrease of both the imaginary part of complex permittivity and the dielectric loss factor.

This article describes influence of strong (ionizing) electric field on sprayability of magnetic fluid containing colloid particles with size in the range from 10 to 20 nm of magnetite Fe3O4. Magnetic fluids can be based for example on both transformer oil and physiological solution for application in medical using (in human medical science research), that supports a fluid colloidal system. Further component of magnetic fluid is surfactant. It is acting as surface-active substance that prevents from nanometric dimension particle settlement. Magnetic fluid gets off nozzle with diameter in range 0.3-1.0 mm from container in surroundings of ionizing (i.e. strong) electric field (E > 10(7) V m(-1)). As a consequence of action of electric field it gives out suppression surface tension in fluid what leads onwards to decomposition of magnetic fluid ligament at the end of nozzle. The diameter of nozzle oneself respects basic theoretical calculations in regards of fluid concentration and thereinbefore its selected size. Magnetic fluid in dependency on its used liquid base has weak-polar till polar orientation polarization character. It gives out sprayability in non-homogeneous electric field E in combination with magnetic field of intensity H. Orientation of vectors (E) over cap and (H) over cap, resp. induction of magnetic field B is defined by parallel or vertical direction. Results are confronted with measurements realized explicitly only at action of electric field (variable B = 0). In the case of magnetic field applications with permanent magnet together with electric non-homogeneous field it gives out unconventional dynamics of electrical charging particles of macroscopic dimension. Orientation particle track is influenced by orientation of field vector combinations. This phenomenon develops magneto-dielectric anisotropy, which oneself manifests behaviour of electrophysical quantities characterizing examination system. In consideration of technology utilization of this method it is very important to respect applied magnetic fluid concentration. Electrical characteristics were examined for volume concentration of magnetite particles in the range from 0.125% to 18%. Nevertheless efficiency optimization of given media suggests to boundary concentration of magnetic fluid of 4.0%, when it is in the regions of weak polar till polar material. Electrophysical research refers to exploitation of applied magnetic layer technology on dielectric insulating substances with inorganic origin as well as thin layer technology coating plastic foils created from macromolecular organic substance. (C) 2013 Elsevier B.V. All rights reserved.

In this article, our experimental study of the dynamic dielectric behaviour of transformer oil-based ferrofluid with magnetite nanoparticles is presented. Frequency-dependent dielectric permittivity and dissipation factor were measured within the frequency range from 20 Hz to 2 MHz by a capacitance method. The ferrofluid samples were placed in a liquid crystal cell, and experiments were carried out in an electromagnetically anechoic chamber. Two polarization processes and corresponding relaxations were revealed within the applied frequency range. Schwarz theory of electric double layer polarization is used to explain the low frequency relaxation maximum. Moreover, the shift of the maximum position towards higher frequencies is observed as the magnetic volume fraction in the ferrofluid increases. The related decrease in relaxation time due to higher counterion mobility is analysed. Reduced electric field intensity due to depolarization field, which is dependent on the particle concentration, is proposed as the reason for the maxima shift. This assumption is wholly supported by a complementary experiment.

Prispevok je venovaný javu magneto - dielektrickej anizotropie vyskytujucej sa v magnetických kvapalinach o roznej koncentracii pri posobeni striedaveho elektrickeho poľa o intenzite E sinusoveho priebehu v sirokom pasme frekvencii. Na kvapalne medium, ktoreho zaklad tvori transformatorový olej, povrchovo aktivna latka a nanocastice magnetitu posobi sucasne elektricke pole E a magneticke pole H. Výskum je realizovaný v oblasti priemyselnej frekvencie cez oblasť ultrazvukovu po radiofrekvencnu a poukazuje na priebeh relativnej permitivity a ciniteľa dielektrických strat v magnetických kvapalinach. Clanok je doplnený teoretickou analýzou a experimentom, ktorý vyusťuje do aplikacie skumaných kvapalin vo forme nahrady transformatoroveho oleja magnetickou kvapalinou.

The paper presents a study of the polymer dispersed liquid crystals that consist of liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT) microdroplets dispersed in polyvinyl alcohol and doped with various kinds of magnetic particles. As magnetic nanoparticles there were used single walled carbon nanotubes and magnetite labeled single walled carbon nanotubes. The volume concentration of the particles was 2 x 10(-3). Magnetic properties were investigated by a SQUID magnetometer. The higher saturation magnetization has been achieved in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes. The phase transition temperature from isotropic to nematic phase at the external magnetic field 0 T and 12 T was monitored by precise capacitance measurements in the capacitance cell filled with prepared sample. The significant shift of the phase transition temperature (0.2 degrees C) at the external magnetic field 12 T has been observed in sample polymer dispersed liquid crystal doped with magnetite labeled single walled carbon nanotubes.

M. Timkoa,∗, P. Kopcansky, M. Molcan, L. Tomco, K. Marton, S. Molokac, P. Rybar, F. Stoian, S. Holotescu and A. Taculescu Institute of Experimental Physics, Slovak Academy of Sciences, 040 01 Kosice, Slovakia Faculty of Aeronautic, Technical University in Kosice, 041 21 Kosice, Slovakia Faculty of Electrical Engineering and Informatics, Technical University in Kosice, 042 00 Kosice, Slovakia Faculty of Mining, Ecology, Process Control and Geotechnology, TU Kosice, Letna 9, 042 00 Kosice, Slovakia Politehnica University of Timisoara, Timisoara 300222, Romania Laboratory of Magnetic Fluids, Romanian Academy Timisoara Division, Timisoara, Romania

We have studied dielectric and magnetodielectric properties of transformer oil UTR 40 based magnetic fluid with various concentrations of magnetic nanoparticles of Fe3O4 covered with oleic acid as a surfactant. The experiments were conducted at different volume concentrations of magnetite nanoparticles at room temperature and in a frequency range from 100 Hz up to 2 MHz with and without external magnetic field up to 30 mT. The quasilinear increase of the dielectric constant with volume concentration has been confirmed. The variation in dielectric permittivity with frequency reveals that the dispersion exhibited by the samples is due to a Maxwell-Wagner type interfacial polarization. The dielectric anisotropy factor g (B, omega) is very close to g = 1.

Polymer dispersed liquid crystals (PDLCs) are currently considered as promising materials for specific applications such as creation of window blinds controlled by electric field, fog simulators, UV protective glasses, etc. The samples consisted of liquid crystal 6CHBT dispersed in polyvinyl alcohol and doped with spherical or rod-like magnetic particles showed significant changes in the effective value of the permittivity in the frequency range 0.1 Hz - 10(6) Hz. In this frequency range the conductivity of PDLC has two components: the ions in LC and the electrons in polymer. The presence magnetic particles in PDLC increases the ion component of the conductivity as well as the electron component of the conductivity.