UHF 대역 동작을 위한 철계 연자성 Nano-복합체 분말의 제조 및 투자율 거동에 관한 연구

Abstract

Fe-based soft magnetic nano-composites were synthesized using simple procedures of solution combustion, ultrasonic spray pyrolysis and hydrogen reduction in order to accomplish a high permeability and a low magnetic loss in UHF band. Four material systems were prepared to make the nano-composites: Fe-Al2O3, Fe@SiO2, Fe@MgO, Fe@FeSiAl oxide. The fabricated nano-composite powders were characterized using TG-DTA, XRD, SEM, and TEM, with their dispersive permeability behaviors in relation to fabrication process parameters for the high-frequency applications. To accomplish the weakly dispersive permeability characteristics with high real values and low magnetic loss in UHF band, the most critical process parameters were identified to be the composition of mixed fuel, the composition of metallic precursors, and reduction temperature. The phases and particle size of oxides from combustion reactions were important to high-frequency permeability behaviors and determined by both combustion reaction mode dependent on a pre-heating environment and the heat released from the redox reaction among the functional groups of the fuels and the nitrate ion of metal precursors. The composition of metallic precursors and H2 reduction temperature were also critical for the goal of high permeability with low magnetic loss in UHF band, because they control the amount, the size, and the distributed morphology of Fe phase to carry out high Ms with suppressed eddy current loss. Finally, using the magneto-dielectric (MD) properties of its composite sheet composed of the fabricated Fe-based soft magnetic nano-composite powder and a polymer binder, the MD loaded PIFA antenna was designed and evaluated with 3D electromagnetic solver, where the measured MD values were a permittivity of 2.5 with a dielectric loss of 1% and a permeability of 2.0 with a magnetic loss of 15% at 1GHz. The impedance bandwidth at 6 dB return loss and the radiation efficiency were calculated to be 7.1% and 42%, respectively, with the resonance frequency decreased from 0.99GHz to 0.86GHz. Based on the calculation results it was proved that the MD composite using the ferromagnetic filler fabricated in this work successfully achieves antenna miniaturization without deteriorating impedance bandwidth. However, the magnetic loss should be much more suppressed to a few percents for more enhanced radiation efficiency by electrically insulating each Fe particle.