000001479 001__ 1479
000001479 035__ $$a34694 
000001479 037__ $$aROMDOC-THESIS-2017-962
000001479 041__ $$arum
000001479 100__ $$aPopescu, Simona-Alexandra
000001479 245__ $$aSinteza şi caracterizarea nanostructurilor feritice cu absorbţie pronunţată în microunde 
000001479 260__ $$c2012-09-29
000001479 520__ $$aThe 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. 
000001479 6531_ $$aEcranare electromagnetică -- Teză de doctorat
000001479 6531_ $$aNanostructură -- Materiale ferimagnetice
000001479 8560_ $$ff_costache@library.pub.ro
000001479 8564_ $$uhttp://romdoc.upb.ro/record/1479/files/$$zAccess to Fulltext
000001479 980__ $$aTHESIS