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밀리미터파 대역용 유전체 소재와 자유공간법에 의한 특성평가기술 연구개발 동향
전병혁,한진우,김동영,이상석,Jun, B.H.,Hahn, J.W.,Kim, D.Y,Lee, S.S. 한국전자통신연구원 1999 전자통신동향분석 Vol.14 No.5
최근 정보사회에 따른 전파수요가 높아지고 있으며 이에 따른 주파수의 요구가 점차 고주파화되고 있고 미개척분야인 밀리미터파의 개발이 중요한 과제로 대두되고 있다. 본 고에서는 밀리미터파 대역 수동부품용 세라믹 유전체 소재에 관한 동향을 서술하였으며, 이 대역에서 세라믹 소재의 유전특성을 측정, 평가하는 여러 방법 중에서 자유공간법을 이용한 기술에 관하여 소개하고자 한다.
NRD(Nonradiative Dielectric) 도파로의 기술 개발 동향
김동영,한진우,전병혁,이상석,Kim, D.Y.,Hahn, J.W.,Jun, B.H.,Lee, S.S. 한국전자통신연구원 1999 전자통신동향분석 Vol.14 No.5
NRD(Nonradiative Dielectric) 도파로는 평행한 평판 전도체 사이에 유전체가 삽입된 간단한 구조를 가지는 도파로로 유전체 도파로의 불연속부나 벤딩(bending)에서 발생되는 복사신호를 평행평판 도파로의 차단 주파수 특성으로 인해 효과적으로 억압할 수 있으며, 유전체 도파로가 갖는 저 손실 특성을 이용하여 신호를 손실 없이 전송할 수 있기 때문에 밀리미터파 응용시스템에 적용 가능한 신기술로 널리 연구되어 지고 있다. 본 고에서는 이러한 NRD 도파로의 기본적인 동작원리에 대해서 알아보고 또한 NRD 도파로의 기술개발 동향에 대해서 정리하였다.
시간 경과에 따른 YBCO 초전도 복합체의 포획 자기장 감쇄
이만수,장건익,전병혁,하동우,손명환,한영희,박병준,Lee, M.S.,Jang, G.E.,Jun, B.H.,Ha, D.W.,Son, M.H.,Han, Y.H.,Park, B.J. 한국초전도학회 2011 Progress in superconductivity Vol.12 No.2
We studied the trapped field properties of bulk Y-Ba-Cu-O superconductors by applying 3 T of the permanent or $Nb_3Ti$ superconducting magnet. The 28 mm circular type of YBCO bulk superconductor was prepared and then hole at the center of bulk, parallel to the c-axis, was mechanically drilled. Typical size of hole in YBCO bulk was 10 mm in diameter. In order to examine the trapped field variation in terms of different impregnated materials, a hole in YBCO bulk was filled with resin and indium respectively. The trapped field decay due to flux flow was determined in terms of time. Our preliminary result indicates the trapped field value measured on the YBCO without hole after 30 minute by applying 3 T, was 6,500 G, which is much higher than that, 4,500 G, measured on YBCO with hole. Also, we confirmed that the tendency of a trapped field decrement with time was almost the same regardless of the impregnated materials in YBCO.
어트리션 볼 밀링에 의한 보론 분말의 미세화 및 $MgB_2$의 초전도특성
이지현,신승용,전병혁,김찬중,박해웅,Lee, J.H.,Shin, S.Y.,Jun, B.H.,Kim, C.J.,Park, H.W. 한국초전도학회 2008 Progress in superconductivity Vol.10 No.1
We report refinement of crystalline boron by an attrition ball milling system and the superconducting properties of the $MgB_2$ pellets prepared from the refined boron. In this work, we have conducted the ball milling with only crystalline boron powder, in order to improve homogeneity and control the grain size of the $MgB_2$ that is formed from it. We observed that the crystalline responses in the ball-milled boron became broader and weaker when the ball-milling time was further increased. On the other hand, the $B_{2}O_{3}$ peak became stronger in the powders, resulting in an increase in the amount of MgO within the $MgB_2$ volume. The main reason for this is a greater oxygen uptake. From the perspective of the superconducting properties, however, the sample prepared from boron that was ball milled for 5 hours showed an improvement of critical current density ($J_c$), even with increased MgO phase, under an external magnetic field at 5 and 20 K.
김남규,김이정,전병혁,김찬중,Tan, Tan Kai,Kim, N.K.,Kim, Y.I.,Jun, B.H.,Kim, C.J. 한국초전도학회 2007 Progress in superconductivity Vol.9 No.1
The most common technique to fabricate $MgB_2$ superconducting wire is by powder-in-tube (PIT) technique. Therefore, the starting powder for the processing of $MgB_2$ superconductors is an important factor influencing the superconducting properties and performance of the conductors. In this study, the influence of magnesium precursor powders and annealing temperatures on the transition temperatures ($T_c$) and critical current densities ($J_c$) of $MgB_2/Fe$ wires was investigated. All the $MgB_2/Fe$ wires were fabricated by in situ PIT process. It was found that higher $J_c$ was obtained for $MgB_2$ wires with smaller particle size of magnesium precursor powders. The $J_c$ also increases with decreasing annealing temperatures.
종자 결정 성장법으로 제조된 $GdBa_2Cu_3O_{7-y}$ 벌크 초전도체의 자기적 특성
김광모,박순동,전병혁,고태국,김찬중,Kim, K.M.,Park, S.D.,Jun, B.H.,Ko, T.K.,Kim, C.J. 한국초전도학회 2012 Progress in superconductivity Vol.14 No.1
The fabrications condition and superconducting properties of top-seeded melt growth (TSMG) processed $GdBa_2Cu_3O_{7-y}$ (Gd123) bulk superconductors were studied. Processing parameters (a maximum temperature ($T_{max}$), a temperature for crystal growth ($T_G$) and a cooling rate ($R_G$) through a peritectic temperature ($T_P$) for the fabrication of single grain Gd123 superconductors were optimized. The magnetic levitation forces, trapped magnetic fields, superconducting transition temperature ($T_c$) and critical current density ($J_c$) of the Gd123 bulks superconductors were estimated. Single grain Gd123 bulk superconductors were successfully fabricated at the optimized processing condition. The $T_c$ of a TSMG processed Gd123 sample was 92.5 K and the $J_c$ at 77 K and 0 T was approximately $50kA/cm^2$. The trapped magnetic field contour and magnetic levitation forces were dependent on the top surface morphology of TSMG processed Gd123 samples. The single grain Gd123 samples, field-cooled at 77 K using a Nd-B-Fe permanent magnet with 5.27 kG and 30 mm dia., showed the trapped magnetic field contour of a single grain with a maximum of 4 kG at the sample center. The maximum magnetic levitation forces of the single grain Gd123 sample, field-cooled or zero field-cooled, were 40 N and 107 N, respectively.
인가 자기장에 의한 YBCO 초전도체 복합체의 포획 자기장 특성
이만수,장건익,최연석,전병혁,한영희,박병준,Lee, M.S.,Jang, G.E.,Choi, Y.S.,Jun, B.H.,Han, Y.H.,Park, B.J. 한국초전도학회 2010 Progress in superconductivity Vol.12 No.1
We have measured the trapped field of YBCO bulk with different configuration by applying the magnetic field of $Nb_3Sn$ superconducting magnet. Initially the circular type of YBCO bulk superconductor was prepared and then hole, parallel to the c-axis and located at the center of bulk was mechanically drilled. The YBCO bulk with hole was filled with resin. Typical size of hole in YBCO bulk was 10 mm in diameter. Trapped field characteristics were compared with different specimen conditions. Our preliminary result indicates the increment rate of trapped field, 0.232 kG, measured on the YBCO without hole was much higher than that, 0.011 kG, measured on YBCO with hole.
YBCO 초전도체의 효과적인 플럭스 피닝 센터로서의 나노 크기 $BaCeO_3$ 합성
윤재성,노광수,김영하,전병혁,이정필,정세용,김찬중,Youn, J.S.,No, K.S.,Kim, Y.H.,Jun, B.H.,Lee, J.P.,Jung, S.Y.,Kim, C.J. 한국초전도학회 2008 Progress in superconductivity Vol.10 No.1
In this work, nano size $BaCeO_3$, which is a possible flux pinning medium of melt processed $YBa_{2}Cu_{3}O_x$ superconductor, was synthesized by the conventional solid state reaction method using powders. $BaCeO_3$ and $CeO_2$ were mixed thoroughly using a ball milling for 24 hours and calcined at $1200^{\circ}C$ for 5 hours for the formation $BaCeO_3$ powder. The obtained $BaCeO_3$ powder was attrition milled at various milling times of 60 min, 120 min and 240 min. The $BaCeO_3$ powders of various milling times were mixed with $YBa_{2}Cu_{3}O_x$ powder. Seed melt processed $YBa_{2}Cu_{3}O_x$-$BaCeO_3$ (15wt.%) superconductors were prepared and the superconducting properties were investigated. It was found that $T_c$ of $Y_{1.5}Ba_{2}Cu_{3}O_x$ samples was not significantly affected by $BaCeO_3$ addition, but $J_c$ of samples was increased by $BaCeO_3$ addition. The $J_c$ improvement by fine $BaCeO_3$ powder (120 min attrition-milled) was effective at low magnetic fields less than 2 T.