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ITO박막/세라믹유전체 구조의 이동통신 주파수대역용 박형 전파흡수체의 설계 및 제조
윤여춘,김성수,Yoon, Yeo-Choon,Kim, Sung-Soo 한국재료학회 2003 한국재료학회지 Vol.13 No.4
For the aim of thin microwave absorbers used in mobile telecommunication frequency band, this study proposed a high permittivity dielectrics(λ/4 spacer) coated with ITO thin films of 377 $\Omega$/sq(impedance transformer). High frequency dielectric properties of ferroelectric ceramics, electrical properties of ITO thin films and microwave absorbing properties of ITO/dielectrics were investigated. Ferroelectric materials including $BaTiO_3$(BT), 0.9Pb($Mg_{1}$3/Nb$_{2}$3/)$O_3$-0.1 $PbTiO_3$(PMN-PT), 0.8 Pb (Mg$_{1}$3/$Nb_{2}$3/)$O_3$-0.2 Pb($Zn_{1}$3$_Nb{2}$3/)$O_3$(PMN-PZN) were prepared by ceramic processing for high permittivity dielectrics,. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave frequency range. The microwave absorbance (at 2 ㎓) of BT, 0.9PMN-0.1PT, and 0.8PMN-0.2PZN were found to be 60%(at a thickness of 3.5 mm), 20% (2.5 mm), and 30% (2.5 mm), respectively. By coating the ITO thin films on the ferroelectric substrates with λ/4 thickness, the microwave absorbance is greatly improved. Particularly, when the surface resistance of ITO films is closed of 377 $\Omega$/sq, the reflection loss is reduced to -20 ㏈(99% absorbance). This is attributed to the wave impedance matching controlled by ITO thin films at a given thickness of high permittivity dielectrics of λ/4 (3.5 mm for BT, 2.5 mm for PMN-PT and PMN-PZN at 2 ㎓). It is, therefore, successfully proposed that the ITO/ferroelectric materials with controlled surface resistance and high dielectric constant can be useful as a thin microwave absorbers in mobile telecommunication frequency band.
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Fe-Si-Al 합금 분말 · 고무 복합 자성체의 전파 흡수 특성
이경섭,윤여춘,최광보,김성수,이준영,Lee Kyung-Sub,Yoon Yeo-Choon,Choi Gwang-Bo,Kim Sung-Soo,Lee Jun-Young 한국전자파학회 2005 한국전자파학회논문지 Vol.16 No.2
준 마이크로파 대역용 전자파 노이즈의 흡수체로서 자성 복합 시트를 개발하였다. Fe-Si-Al 자성 분말을 attrition mill을 이용해 편상화한 후 이것을 polymer와 혼합 분산시켜 전자파의 입사 방향에 수직한 방향으로 배향된 자성 복합 시트를 제조하였다. Attrition milling 시간이 긴 편상 분말일수록 제조된 자성 복합체의 유전율은 증가하나 투자율은 다소 감소하는 경향을 보인다. 또한 오랜 시간 milling한 편상 분말일수록 임피던스 정합 주파수는 저주파 쪽으로 이동하나 정합 주파수에서의 전자파 흡수율은 감소한다. 이러한 결과들로부터 복합 자성체의 유전율과 투자율의 주파수 특성을 제어하여 1.4 GHz에서 -8.2 dB의 반사 손실 특성을 갖는 두께 1.0 mm의 노이즈 흡수 시트를 개발하였다. A magnetic composite as noise absorber of quasi-microwave band was developed. The Fe-Si-Al alloy powder were forged by attrition mill to get flaky shape. The magnetic composite sheet was fabricated in which powders are dispersed in polymer and aligned in the direction perpendicular to electromagnetic wave propagation. The permittivity of magnetic composite is increased as forging time increasing, while the permeability is decreased slightly. The maximum attenuation peak of reflection loss is shifted to lower fiequency range as milling time increasing, and the value of maximum attenuation peak is to get smaller gradually. From these result, we could designed a noise absorber sheet (t=1.0 mm) for quasi-microwave band, which is impedance matched at 1.4 GHz with respect to -8.2 dB reflection 1055.
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이동통신주파수 대역에서 순철 분말 - 고무 복합체 Sheet의 전파흡수특성
김선태(Sun-Tae Kim),김상근(Sang-Keun Kim),김성수(Sung-Soo Kim),윤여춘(Yeo-Choon Yoon),이경섭(Kyung-Sub Lee),최광보(Kwang-Bo Choi) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.4
For the aim of thin electromagnetic wave absorbers used in mobile telecommunication frequency band (0.8~2.0 ㎓), we investigate high-frequency magnetic, dielectric and microwave absorbing properties of iron particles dispersed in rubber matrix in this study. The major experimental variables are particle shape (sphere and flake) and initial particle size (in the range 5~70 ㎛) of iron powders. High value of magnetic permeability and dielectric permittivity can be obtained in the composites containing thin plate-shape (flake) iron particles (of which thickness is less than skin depth in ㎓ frequency), which can be produced by mechanical forging of spherical iron powders using an attrition mill. This result is attributed to the reduction of eddy current loss (increase of permeability) and the increase of space charge polarization (increase of permittivity). The optimum initial particle size is found to be about 10 ㎛ for the attainment of the material parameters (particularly, real part of complex permeability) satisfying the wave impedance matching. With the iron powders controlled in size and shape as absorbent fillers in rubber matrix, the thickness can be reduced to about 0.7 ㎜ with respect to -5 ㏈ reflection loss (70% power absorption) in mobile telecommunication frequency band.
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실업계 고교와 전문대학간 컴퓨터 교과 관련 연계교육의 운영실태 및 개선방안에 관한 교원들의 인식 연구
윤여춘,김창석 한국컴퓨터교육학회 2002 컴퓨터교육학회 논문지 Vol.5 No.4
컴퓨터 산업과 IT산업의 눈부신 발전으로 컴퓨터 관련 교육은 숙련된 인력을 양성하기 위하여 교육의 체제와 방법의 변화가 절실히 필요하게 되었다. 직업교육 훈련 촉진법 및 고등교육법 시행령의 법적 지원과 '신교육 체제의 수립을 위한 교육 개혁 방안(Ⅱ)' 발표로 실업계 고등학교와 전문대학간 교과 과정을 상호 연계하여 운영되고 있다. 그러나 실업계 고등학교와 전문대학간 컴퓨터 교과 관련 연계교육을 성공적으로 운영되기 위한 연구는 미흡한 실정이다. 이에 본 연구는 실업계 고교와 전문대학간 컴퓨터 교과와 관련하여 조사 연구결과 연계교육의 개선방안을 제안한다. With the rapid development of computer and IT industry, the education related to computer come to need computer need sincerely the system of an education and transform of a method in order to rear experienced people. With the publication of legal support of professional educational training promotional rule and high educational enforcement's rule and 'Educational reformation plan for establishing a new educational enforcement's rule and 'Educational reformation plan for establishing a new educational system (Ⅱ)', associated actions between a vocational high schools and technical colleges are being conducted together. But there have rarely been researches which operates successfully the computer curriculum between vocational high school and technical colleges. Accordingly the purpose of this research is proposed to improve the associated actions of the two schools.
ScienceON
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