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Study of an Electromagnetic Wave Absorber Prepared with Fe-Si-Cr for Mobile Phones
민의홍,김문석,고재귀 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4
We have investigated the microwave absorbing properties for Fe-Si-Cr electromagnetic (EM) wave absorber. Here, we discuss the requirements of a lower reflection coecient for the microwave permittivity and permeability. A Fe-Si-Cr composite microwave absorbers mixed with silicone rubber for mobile phones and the effects of the thickness of samples on the absorption. A Fe-Si-Cr electromagnetic wave absorber with a ratio of Fe-Si-Cr : silicone rubber = 60 : 40 wt% showed -2.99 dB, -4.77 dB, -8.12 dB and -8.53 dB at 1.8 GHz for thicknesses 0.7 mm, 1.0 mm, 1.3 mm and 1.6 mm, respectively. We suggest Fe-Si-Cr for use as a EM wave absorber in the L-band and the S-band and the fabricated EM wave absorber with a thickness of 1.6 mm has an absorption ability of -8.57 dB in the frequency range of 1.6 ∽ 2 GHz. This absorber should be very valuable for preventing unwanted microwave radiation from mobile phones.
민의홍,고재귀,Min Eui Hong,Koh Jae Gui 한국재료학회 2004 한국재료학회지 Vol.14 No.9
Magnetite was prepared by wet method and oil-based magnetic fluid also was prepared by its magnetite. Ahead of making magnetite, we investigated the variation of physical properties for changing $Fe^{3+}/Fe^{2+}$. Through the variation of the process mixing time, pH, magnetite content, we made magnetic fluid of magnetite. We examined the magnetic and frequency property by a toroidal mold. In result $Fe^{3+}/Fe^{2+}=1.2$, over the minute mixing time property of magnetite, Ms was 61.98 emu/g. Moreover, the B-H loop result indicated that the magnetic fluid followed paramagnetic behavior.
Ni-Cu-Zn Ferrite의 복합형 전파흡수체 특성 연구
민의홍(Eui Hong Min),김문석(Moon Suk Kim),고재귀(Jae Gui Koh) 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.6
Ni-Cu-Zn ferrites were prepared by the co-precipitation. Physical properties and Microwave absorbing properties were investigated in Ni-Cu-Zn ferrite for the aim of microwave absorbers. From the analysis of X-ray diffraction patterns, we can see that all the particles have only a single phase spinel structure. The loss factor was maximum at sintering temperature 1100 ℃. The initial permeability of sintered ferrite obtained was an average of 50. We found that the (Ni<SUB>0.7</SUB>Cu<SUB>0.2</SUB>Zn<SUB>0.1O</SUB>)<SUB>1.02</SUB>(Fe₂O₃)<SUB>0.98</SUB> can be used in ferrite rubber composite microwave absorber when sintering temperature at 1100 ℃.
송승원,민의홍,이동원,김정수,오원태,Song, Seung Won,Min, Eui Hong,Lee, Dong Won,Kim, Jungsoo,Oh, Weontae 한국재료학회 2017 한국재료학회지 Vol.27 No.2
Natural and expandable graphites were chemically treated in acidic aqueous solutions such as acetic acid or mixtures of acetic acid and nitric acid. Structures and thermal conductivities of the as-treated graphites were characterized in detail. Both graphites were significantly oxidized in the mixed acidic solution of $H_2SO_4$ and $HNO_3$, which condition was generally used for the oxidation of carbon nanotubes. This considerable oxidation of graphites caused a depression of their thermal conductivity. The structural characteristics, obtained by XRD and XPS, show that the graphites treated in the relatively weak acidic conditions (acetic acid or mixture of acetic acid and nitric acid) were quite similar to the untreated graphites. However, the thermal conductivities of both acidic-treated graphites were remarkably increased.
수산화나트륨 수용액으로 처리한 흑연의 열/전기전도 특성
송승원,민의홍,이동원,김정수,남대근,오원태,Song, Seung Won,Min, Eui Hong,Lee, Dong Won,Kim, Jungsoo,Nam, Dae-Geun,Oh, Weontae 한국전기전자재료학회 2016 전기전자재료학회논문지 Vol.29 No.10
Thermal and electrical conductivities of the natural, artificial, and expandable graphites were analyzed after treatment in NaOH aqueous solution. In order to investigate the elimination of the oxidized groups and impurities on the graphite surfaces after NaOH treatment, the graphite samples were structurally characterized by using XRD, XPS, Raman, FE-SEM. The thermal and electrical conductivities of the graphite samples were significantly improved after NaOH treatment. These results were caused by the structural rehabiliation.
Fe₉₄Si₅Cr₁을 이용한 Sheet 두께에 따른 전파흡수특성 연구
김문석(Moon Suk Kim),민의홍(Eui Hong Min),고재귀(Jae Gui Koh) 한국자기학회 2009 韓國磁氣學會誌 Vol.19 No.2
The soft magnetic FeSiCr were processed the ball-mill for 30 hours and the shape of FeSiCr particles was changed from sphere to flake type, which was observed using scanning electron microscope. The complex permittivity and permeability spectra and reflection loss of FeSiCr-rubber composite was measured using Network Analyzer in order to investigate the relationship between the microwave absorption and the material constants. The matching frequency shifted toward lower frequency range with microwave absorber thickness, and microwave absorber with FeSiCr-rubber composite showed a maxium reflection loss of ?8.3 ㏈ at 1.86 ㎓ for a 1.3 ㎜ thickness.