Low-loss magnetodielectric spinel-ferrite based ceramic with constant permeability and permittivity in the UHF range

Abstract : Present antennas are too large to allow satisfactory integration into such devices, and the present techniques used to reduce their size degrade the performances of the antennas [1]. The present study aims to investigate materials for electromagnetic applications in the UHF range. Actually, materials that show low electromagnetic signature, that is reduced impedance-matched to free space ( =1, with µ'=ε', and where µ' and ε' are real parts of relative permeability and permittivity), and a refractive index (n= ) large enough, could be useful to the design of antennas with reduced physical dimensions. Our laboratory synthesized spinel ferrite powders with the composition Ni0.5ZnxCo0.5-xFe2O4, using co-precipitation technique. From SEM, mean grain size is found to be ~50nm. Focusing on the composition with x=0.3, no relaxation phenomenon is found below 0.5GHz. Complex permeability and permittivity are almost constant in the range from 100MHz to 0.5GHz and equal to ~4.9+j0.15 (loss tangent~0.03) and ~4.8+j0.075 (loss tangent~0.015) respectively. The refractive index n is 4.8, and Z/Z0 is 1. Hysteresis loop (DC) shows initial permeability value that we ascribe to spin rotation phenomenon only. These EM performances can be advantageously compared with data from literature [3-5]: to date, to our best of knowledge, no such performances were reported in this frequency range and that by using spinel ferrites.