Thesis /

ROMDOC-THESIS-2017-962

Sinteza şi caracterizarea nanostructurilor feritice cu absorbţie pronunţată în microunde

Popescu, Simona-Alexandra
2012-09-29

Abstract: The main objective of the Ph.D thesis has been the synthesis of nanoferites doped with zinc and nickel for shielding electromagnetic radiation from cellular antennas. Thus, nanoferites with the stoichiometries ZnxFe3-xO4 and NixFe3-xO4 with x = 0.2, 0.5, 0.8, 1, 1.2, 1.5 have been prepared by chemical coprecipitation and hydrothermal techniques and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and measurements of some electrical and magnetic properties. Electronic microscopy (SEM) investigation has shown that the ferrites obtained by coprecipitation has agglomerated nanoparticles of 40 nm size, while those obtained by the hydrothermal technique had spherical and polyhedral nanoparticles of about 30-40 nm in diameter. Using the tehnique of X ray diffraction the measured dimensions of ferrites nanoparticles had a mean diameter of 2.5 - 6 nm. From the experimental results, the magnetic permeability obtained for zinc and nickel nanoferrites with x = 0.8 - 1.2 show important variations in several bands in the domain of 0.1 - 6 GHz. Thus, the attenuation constant of zinc nanoferrites, has important values in the domain 1 - 4 GHz, and for nickel nanoferrites in the range 1.4 – 4.5 GHz (allowing for efficient shielding of the electromagnetic radiation). In this work, correlations have been made between the magnetic properties of the nanoferrites and their morphology and the optimal synthesis conditions established for temperature, pH, pressure and reaction time to improve the ferrites electrical and magnetical properties for selective absorbtion of electromagnetic waves of wireless cellulars antennas. Also, an experimental study was made to find the stoichiometric coefficient (x) influence on the electrical permittivity, magnetical susceptibility and attenuation constant, establishing the optimal values of x for which the attenuation constant has maximum values. Finally, in this work the posibility of realizing some applications for these new ferrites (for selective shielding in different microwave zones) has been analyzed, with the intent of improving their characteristics in the future.

Keyword(s): Ecranare electromagnetică -- Teză de doctorat ; Nanostructură -- Materiale ferimagnetice
OPAC: See record in BC-UPB Web OPAC
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