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Choa, Yong Ho,Nakayama, Tatachika,Sekino, Tohru,Niihara, Koichi 대한금속재료학회(대한금속학회) 1999 METALS AND MATERIALS International Vol.5 No.2
Nanocrystalline iron-oxide powder was fabricated with an inert gas condensation (IGC) method combined with evaporation, and in-situ oxidation techniques. The particle size of iron-oxide powder was controlled by varying the helium gas pressure between 0.1 and 10 Torr, with the smallest one =10 nm at 0.1 Torr. The nanostructure was characterized by TEM. Nanocrystalline iron-oxide powder was sintered with the pulse electric current sintering (PECS) method to obtain densified γ-Fe₂O₃ materials, and suitably densified nano-grained γ-Fe₂O₃ materials (◎ 40 nm) of great hardness were obtained. The correlation between the nanostructure and magnetic properties of nanocrystalline powder and densified γ-Fe₂O₃ materials was also investigated.
Processing and Mechanical/Electronical Properties of Oxide Based Nanocomposites
Choa,Yong-Ho,Niihara,Koichi 국립경상대학교 공과대학 부설 첨단소재연구소 1997 尖端素材 Vol.7 No.-
Application of Nanocomposites .Micro / Nano-type: Inter type, Intra type Structural Ceramic Materials; Alumina/SiC, MgO/SiC, Silicon Nitride/SiC etc. Electronic Ceramic Materials; Zirconia/SiC, ZnO/NiO, BaTiO₃/NiO or SiC Magnetic Materials; Alumina/Ni, Alumina/Co,Alumina/SmCo? MgO/PbTiO₃etc. .Nano / Nano-Type: Superplastic Materials; Silicon Nitride/SiC, Zirconia/Alumina etc. Electronic Ceramic Materials; Ag/ZnO?? Magnetic Materials; Ag /Fe₂O₃ as a Functional Materials
Choa Yong-Ho,Yoo Seung-Hwa,Yang Jae-Kyo,Park Jin-Woo,Oh Sung-Tag,Kang Kae-Myung,Kang Sung-Goon 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The microstructure and electrical conductivity of CNTs dispersed nanocomposites depending on the powder processing and CNTs content were demonstrated. The composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for direct formation of CNTs on nano-sized Fe dispersed powders. The sintered nanocomposite using the composite powder with directly synthesized CNTs showed homogeneous microstructure and enhanced elelctrical conductivity. The influence of powder processing on the properties of sintered nanocomposites was discussed by the observed microstructural features.
Kim, Yong-Dae,Sunwoo, Kuk-Hyun,Sul, Sang-Chul,Lee, Ju-Ho,Kim, Duck-Hwan,Song, In-Sang,Choa, Sung-Hoon,Yook, Jong-Gwan Professional Technical Group on Microwace Theory a 2006 IEEE transactions on microwave theory and techniqu Vol.54 No.3
Highly miniaturized RF bandpass filter using a thin-film bulk acoustic wave resonator (TFBAR) is designed and fabricated for 5-GHz-band application. The topology of the fabricated filter is based on a ladder-type configuration that has a common trimming inductor connected concurrently with two shunt TFBARs and the trimming inductor is directly connected to the ground. The role of unit the TFBAR's physical characteristics such as the size and thickness of the TFBAR determine the performance of the TFBAR filter, including the effect of the electrical impedance-matching characteristics of the TFBAR filter. The shape of the fabricated TFBARs are tetragons with unparallel sides and the sizes of resonator are smaller than 70×70 μm<SUP>2</SUP> to ensure the ranges of impedance-matched filter performance. The insertion loss and bandwidth of fabricated TFBAR filters are less than 2.8 dB and 160 MHz at 3 dB. The out-of-band rejection is over 30 dB. The actual size of filter is smaller than 700×600 μm<SUP>2</SUP>, including signal and ground pad sizes.
Broadband RF Noise Suppression by Magnetic Nanowire-Filled Composite Films
Baekil Nam,Yong-Ho Choa,Sung-Tag Oh,Sang Kwan Lee,Ki Hyeon Kim IEEE 2009 IEEE transactions on magnetics Vol.45 No.6
<P>The characteristics of the electromagnetic noise suppression have evaluated using magnetic nanowire-filled composite film on a microstrip line in the broadband radio-frequency range from 0.5 to 20 GHz. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by Kittel's and Landau-Lifshitz-Gilbert equations. The FMR frequency is gradually increased with the increment of aspect ratio (up to 50) of magnetic nanowire. When the magnetic nanowires were mixed with various aspect ratio in composite, the FMR frequency exhibited the broadband frequency regions with 10-28 GHz, 5-14 GHz, 2.5-7 GHz, and 1-2.7 GHz for the change of magnetizations (4piM<SUB>s</SUB>: 20, 10, 5, and 2 kG), respectively. Using the calculated FMR frequency profile, the power losses were obtained in broadband frequency region. The transmission power absorption of the composite film on microstrip line was simulated using a 3-D FEM HFSS simulation program. The microstrip line model was composed of Cu conductor line and grounded dielectric substrates, which was designed by IEC standard (IEC 62333-2). The conduction electromagnetic noise was suppressed by the various aspect ratios of the magnetic nanowire-filled composite films in broadband frequency region.</P>
Comparison of the Magnetic Properties for the Surface-Modified Magnetite Nanoparticles
Joonsik Lee,Yong-Ho Choa,Jongryoul Kim,Ki Hyeon Kim IEEE 2011 IEEE transactions on magnetics Vol.47 No.10
<P>The Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles were synthesized by a coprecipitation method, and their particles were capsulated by 3-thiopheneacetic acid (3TA), 2, 3-meso-dimercaptosuccinic acid (DMSA) and Polyethylene glycol (PEG), respectively. The 3TA-, PEG-, and DMSA-coated Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles are well dispersed in aqueous solution. The average particle sizes of the Fe<SUB>3</SUB>O<SUB>4</SUB> and the 3TA-, PEG-, and DMSA-coated magnetite nanoparticles were exhibited approximately 10.4, 12, 11, and 12 nm by TEM results. The mean blocking temperatures of the uncoated Fe<SUB>3</SUB>O<SUB>4</SUB> and the 3TA, PEG, DMSA surface-coated Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles exhibited about 245±10 K, 220±10 K, 142±12 K, and 200±10 K, respectively. The values of g factor of the uncoated Fe<SUB>3</SUB>O<SUB>4</SUB> and the 3TA-, PEG-, and DMSA-coated Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles were obtained 2.22, 2.21, 2.22, and 2.19, respectively.</P>