• Macromolecular Research
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• 제10권5호
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• pp.253-258
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• 2002

The multi-wall carbon nanotubes (MWNTs) with graphite crystal structure were synthesized by the catalytic decomposition of a ferrocene-xylene mixture in a quartz tube reactor to use as the conductive filler in the binary polymer matrix composed of poly(vinylidene fluoride) (PVdF) and poly(vinyl pyrrolidone) (PVP) for the EMI (electromagnetic interference) shielding applications. The yield of MWNTS was significantly dependent on the reaction temperature and the mole ratio of ferrocene to xylene, approaching to the maximum at 800 $^{\circ}C$ and 0.065 mole ratio. The electrical conductivity of the MWNTs-filled PVdF/PVP composite proportionally depended on the mass ratio of MWNTs to the binary polymer matrix, enhancing significantly from 0.56 to 26.7 S/cm with the raise of the mass ratio of MWNTs from 0.1 to 0.4. Based on the higher electrical conductivity and better EMI shielding effectiveness than the carbon nanofibers (CNFs)-filled coating materials, the MWNTs-filled binary polymer matrix showed a prospective possibility to apply to the EMI shielding materials. Moreover, the good adhesive strength confirmed that the binary polymer matrix could be used for improving the plastic properties of the EMI shielding materials.

• 한국분말재료학회지
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• 제21권2호
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• pp.124-130
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• 2014

The automotive industry is moving from the internal combustion engine to electric drive motors. Electric motors uses a high voltage system requiring the development of resources and components to shield the system. Therefore, in this study, we analyze electromagnetic interference (EMI) shielding effectiveness (SE) characteristics of an auto crash pad according to the ratio of electrically conductive materials and propylene. In order to combine good mechanical characteristics and electromagnetic shielding of the automotive crash pad, metal-coated glass fiber (MGF) manufacturing methods are introduced and compared with powder-type methods. Through this study, among MGF methods, we suggest that the chopping method is the most effective shielding method.

• 한국산학기술학회논문지
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• 제22권1호
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• pp.801-807
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• 2021

전기 전자 부품을 기반으로 하는 통신장비, 컴퓨터, 이동 수단, 전산망, 군사용 장비 등 여러 산업 분야 및 사회기반시설에 있어 전자파 차폐의 필요성이 커지고 있다. 구조물의 전자파 차폐 방법은 차폐 콘크리트, 차폐 문, 차폐 창문과 같이 차폐성능을 가지고 있는 자재를 사용하여 시공하는 방법, 그리고 차폐성능이 없는 재료에 차폐 도료를 코팅하는 방법이 있다. 전자파 차폐 도료는 탄소나노튜브, 흑연, 카본 블랙, 탄소 섬유와 같은 전도성 물질을 사용하여 만들어지며, 일반적으로 사용되고 있는 수성도료에서 전자파 차폐 성능이 추가된 도료이다. 이 연구에서는 전자파 차폐 무기계 도료를 개발하기 위한 목적으로 전도성 흑연, 카본 블랙을 차폐원료로 사용한 도료의 차폐성능 및 부착성능을 평가하였다. 차폐 재료의 종류 및 사용량을 달리한 6개 배합에 대해 차폐성능과 부착강도를 평가하였다. 실험 결과, 전도성 흑연과 카본 블랙을 무게비 1:0.2로 혼합한 배합이 33.6 dB로 차폐성능이 가장 좋은 것으로 확인되었고, 부착성능은 전도성 흑연만 사용한 배합이 1.06 MPa로 가장 높은 것으로 확인되었다.

• 전자공학회논문지SC
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• 제40권3호
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• pp.181-188
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• 2003

본 논문에서는 영구자석 자기공명영상시스템에 나쁜 영향을 기치는 외부 자기 잡음을 효율적으로 차폐하는 기술을 서술하였다. 유한요소법 전자계 해석을 통하여 영구자석의 주자계 방향과 일치하는 자기 잡음 성분이 자기공명영상에 주로 영향을 미치는 것을 밝혔고, 이의 해석 결과를 기반으로 자기잡음센서, 보상코일, 그리고 코일구동기로 구성되는 능동형 자기 잡음 차폐시스템을 개발하였다. 개발된 자기 잡음 차폐시스템은 수 Hz 미만의 저주파 대역의 자기 잡음에 대하여 30dB 이상의 차폐율을 보였으며, 0.3Tesla 전신형 자기 공명영상시스템에 자기 잡음 차폐시스템을 적용하여 자기 잡음에 의한 영상 잡음이 크게 개선됨을 실험적으로 밝혔다.

• E2M - 전기 전자와 첨단 소재
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• 제10권1호
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• pp.54-60
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• 1997

The electrical and electromagnetic shielding properties have been investigated in polyaniline free standing films with different degrees of elongation cast from N-methyl 2-pyrrolidone(NMP) solution and camphorsulfonic acid(HCSA) doped polyaniline film. The degree of crystallinity of the crosslinked films increased with increasing the draw ratio. For the case of the oriented films doped with hydrochloric acid, we have the values of conductivities up to 173 S/cm. It is considered that the physical micro-crystalline crosslinking domains act as nucleation sites for the increase of relative crystallinity during stretching. We have obtained the value of conductivity 210 S/cm in the HCSA doped polyaniline film cast from the solvent of m-cresol, which is higher than that of the crosslinking oriented films. The electromagnetic shielding efficiency of HCSA doped polyaniline film obtained 37-41 dB in the frequency range of 10MHz-1GHlz, which is higher than that of the crosslinking oriented films. The higher value of electromagnetic shielding efficiency of HCSA doped polyaniline film suggests strong possibility of electromagnetic shielding material.

• Nuclear Engineering and Technology
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• 제50권3호
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• pp.462-469
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• 2018

The background spectrum of a $3^{{\prime}{\prime}}{\times}3^{{\prime}{\prime}}$ NaI(Tl) well-type scintillation SILENA detector was measured without shielding, in 6 cm thick lead shielding, and with 2 mm thick electrolytic copper covering the detector inside the lead shielding. The relative remaining background of the lead shield lined with copper was found to be ideal for low-level environmental radioactive spectroscopy. The background total count rate in the (20-2160 KeV) was reduced 28.7 times by the lead and 29 times by the Cu + Pb shielding. The effective reduction of background (1.04) by the copper mainly appeared in the energy range from X-ray up to 500 KeV, while for the total energy range the ratio is 1.01 relative to the lead only. In addition, a strong relation between the full-energy peak absolute efficiency and the detector well height was found using gamma-ray isotropic radiation point sources placed inside the detector well. The full-energy peak efficiency at a midpoint of the well (at 2.5 cm) is three times greater than that on the detector surface. The energy calibrations and the resolution of any single energy line are independent of the locations of the gamma source inside or outside of the well.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.4142-4149
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• 2021

In the radiation protection application, the metal-polymer composites have been developed for their radiation shielding properties. In this research, the elastomer composites doped by 10 ㎛ and 100nm size of lead, bismuth and tungsten particles as filler with 30 and 60 wt percentages were prepared. To survey the shielding properties of the polymer composites using gamma-ray emitted from 152Eu and 137Cs sources, the gamma flux was measured by using NaI(Tl) detector, then the linear attenuation coefficient was calculated. Also, the Monte Carlo simulation (MCs) method was used. The results showed a direct relationship between the linear attenuation coefficients of the absorbent and filler ratio. Also, the decrease in the particle size of the shielding material in each weight percentage improved the radiation shielding features. When the dimension of the particles was in the order of nano-size, more attenuation was achieved. At low energies used for medical diagnostic X-ray applications due to the predominance of the photoelectric effect, bismuth and lead were suitable selection as filler.

• 한국건축시공학회지
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• 제20권2호
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• pp.129-135
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• 2020

핵 및 방사능전 상황에서 방사선에 의한 인명피해를 줄이기 위한 방안으로서 유개호에 자철석이 포함된 중량 콘크리트의 적용 가능성을 확인해보았다. 이에 본 연구에서는 자철광 콘크리트의 방사선 차폐효과를 분석하기 위하여 감마선원을 사용하여 차폐실험을 진행하였고 실험조건과 동일한 몬테칼로 모델링도 하였다. 그 결과 자철광의 함량이 증가할수록 감마선에 대한 차폐효과가 향상됨을 확인할 수 있었다. 향후 자철광 콘크리트가 군사적 목적의 시설물에 적용될 경우 방사선 차폐 측면에서 효과를 얻을 수 있을 것이라 기대한다.

• Journal of Welding and Joining
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• 제22권1호
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• pp.58-64
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• 2004

The control of the weld bead shape is important in laser welding of the small parts. The effects of laser welding parameters on the weld bead shape in the pulsed Nd:YAG laser welding of STS 304L material were investigated. Shielding gas type, flow rate, pumping voltage, pulse frequency, pulse width, focal position and overlap distance were selected as laser welding parameters. Experiments were designed and conducted using the Taguchi method which was a statistical experimental method. The weld bead width, penetration, area and aspect ratio were measured and analysed as the weld bead shape properties and the welding parameters were optimized to maximize the weld aspect ratio. Weld aspect ratio were greatly affected by the pulse width, pumping voltage and pulse frequency, and somewhat by the overlap distance, and little by the shielding gas type, flow rate and focal position. A confirmation experiment were conducted using the optimized welding parameters.

• 한국추진공학회지
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• 제25권3호
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• pp.42-55
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• 2021

본 연구에서는 중심선 방정식 선정에 따른 노즐 성능 영향성을 확인하고자 하였다. 곡선 방정식과 설계 형상 파라미터를 활용하여 S-형 노즐 3조와 Double S-형 노즐 3조를 설계하였고 노즐 차폐 성능은 차폐율 정의를 이용하여 평가하였다. 그리고 내부 유동을 분석하기 위해 속도 분포도와 압력분포도로 특성을 연구하였고, 노즐 성능 계수로는 총 추력 비(f)와 노즐 단열 효율계수(η)를 통해 노즐의 성능을 평가하였다. 중심선에 따른 S-형 노즐의 성능 영향성을 분석한 결과 출구에서 급격한 곡률 변화가 있는 중심선은 노즐 성능이 우수한 반면 차폐율이 낮은 특징이 있다. 반면에 입구에서 급격한 곡률 변화가 있는 중심선은 노즐 성능이 낮아지고 차폐율이 높은 특징이 있다. Double S-형 노즐은 첫 번째 곡률에서 완만한 특징을 보이는 중심선을 사용하는 것이 노즐 성능과 차폐율이 우수하였다.