This article shows the design of dielectric resonator antenna with nickel ferrite as dielectric material. Its main characteristics and measurements are described. Nickel ferrite was synthetized by sol–gel modified by ionic coordination reaction technique. Calcination was performed at 1100°C (10 h, 10°C/min step), followed by compression procedure at 227 MPa, to manufacture the bulk. Sintering process was applied at calcination temperature, for 4 h, to ensure bulk's physical resistance, and its electrical characterization was performed for antenna design and simulations. Simulated radiation patterns are presented, as reflection coefficient, which is compared with measurements. Measured reflection coefficient presented good agreement with performed simulations, with a difference of 0.74% in resonance frequency. Simulated radiation patterns also presented good results, with relatively high gain in co‐polarization planes, 2.11 dB for E plane, and low cross‐polarization E plane value, −47 dB.
This work deals with the synthesis of superparamagnetic cobalt ferrite (CoFe 2 O 4 ) nanoparticles, via a sol-gel method that uses gelatin as an organic precursor and a rapid thermal processing furnace with halogen lamps as a heat source. TEM, HRTEM, XRD, VSM and Mössbauer spectroscopy measurements were performed, at room temperature, to characterize the samples. Nanoparticles with an average size of 5-10 nm and microstrain of the order of 10 −4 -10 −3 were obtained. Magnetic hardening was also observed with increased nanoparticle size, in addition to an increase in the anisotropy constant, which ranged from 1.7 to 4.7•10 6 erg/cm 3 . The saturation magnetization decreased with decreasing size due to the formation of a magnetically dead layer on the surface (thickness = 0.6-0.7 nm). The Mössbauer spectra showed an increase in the superparamagnetic phase for samples with smaller nanoparticles and less dispersion.
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