Sintered microstructure effect on RF-wave shielding properties of a Cu-doped Ni–Zn-polycrystalline ferrite

Abstract

The shielding properties of a Cu-doped Ni–Zn polycrystalline ferrite in the frequency range 1 MHz to 1 GHz were explored. Samples of composition (Cu_0.12Ni_0.23Zn_0.65)Fe₂O₄ were prepared by the traditional ceramic route. The complex relative permittivity (${\epsilon }_r={\epsilon }^{\prime }-j{\epsilon }^{″}$) and permeability (${\mu }_r={\mu }^{\prime }-j{\mu }^{″}$) of the absorber ceramics were measured, and the minimum reflection-loss $RL$, matching frequency $f_m$, matching thickness $d_m$ and bandwidth for $\text{RL}\le -20\text{dB}$ were calculated using the theory of the absorbing wall. Effect of the main process parameters (pressing pressure P, sintering temperature T, and sintering time t) on the electromagnetic properties and microwave-absorbing characteristics was deeply investigated. The rise of the three selected process parameters was observed to improve the sintered microstructure of the final specimens (monitored by the relative density $\varphi$ and the average grain size G), provided that abnormal grain growth does not occurred. The increase in sintered relative density and average grain growth modifies complex permeability and permittivity in the explored frequency range, enhancing the shielding properties of the material.