MAGNETOPOLYMERS FOR EMI SUPPRESSION IN PORTABLE AND WIRELESS ELECTRONICS

Rastislav Dosoudil – Marianna Ušáková – Jaroslav Franek – Vladimír Olah – Jozef Sláma – Elemír Ušák – Vladimír Jančárik

   The complex permeability spectra of ferrite-polymer composites have been measured in the frequency range 1 kHz - 1 GHz using short-circuit coaxial transmission line method and the effect of particle size and ferrite volume content was studied. The ferrite filler had the chemical composition Ni_0.276Zn_0.644Cu_0.08Fe₂O₄ and was synthesized by means of a ceramic method at 1200 °C/6 h in air. As the non-magnetic matrix, polyvinylchloride (PVC) polymer has been used. The frequency dispersion of permeability was due to a resonance of oscillating domain walls and a natural ferromagnetic resonance of precessing magnetic moments in domains. The permeability of composites seems to be strongly dependent on ferrite volume content and weakly on particle size. Based on the theoretical calculation of return loss (RL), the quasi-microwave absorption properties of the ferrite-polymer composites have been investigated in the frequency range concerned. In the developed single-layer EM-wave absorbers, the return loss as well as the matching thickness (d_m), matching frequency (f_m), and bandwidth for RL ≤ - 15 dB were affected by changes in ferrite particle size and volume content. The results indicate that the magnetopolymers have significant potential for quasi-microwave absorption applications in mobile electronic industry.

Keywords: complex permeability, domain wall, magnetopolymer, return loss, matching thickness, EM-wave absorber

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