• Journal of the Korean Society of Propulsion Engineers
• /
• v.23 no.6
• /
• pp.11-20
• /
• 2019

A Radome protects the radar from the external environment, and as a part of the stealth technology, a frequency-selective surface (FSS) was applied to the radome. Our study investigates the changes in the electrical transmission characteristics of the missile's FSS radome due to aerodynamic heating in various flight scenarios. Accordingly, we designed a FSS radome with a Jerusalem-cross(JSC) geometry and referred the missile flight scenario in the precedent research. Subsequently, electrical transmission characteristics affected by aerodynamic heating were numerically analyzed over time according to the position of radome. As a result, we found that the average transmission value maximally varies -14.3 dB compared to the initial bandwidth owing to changes in electrical transmission characteristics in flight scenarios.

• 전자공학회논문지 IE
• /
• v.44 no.2
• /
• pp.21-25
• /
• 2007

Multilayer transparent electromagnetic wave shielding film with 1 m wide, was fabricated by using roll to roll DC plasma coating with ITO and Ag layer on PET substrate. By optimizing properly the design parameters, such as a processing condition, the surface resistance and the thickness of each layers, the homogeneous film could be obtained. Electromagnetic wave shielding film showed the high shielding effectiveness of 23dB(99.5%) in 2-18 GHz range and the transmittance of 83.1% in 400-700nm.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.2
• /
• pp.123-130
• /
• 2013

In this paper, the delamination and failures in frequency selected surface(FSS) caused by residual stresses in the FSS embedded hybrid composites due to the difference between the coefficients of thermal expansion of components and the transmission characteristic changes due to deformation of FSS patterns by residual stresses were studied. FSS may have different electromagnetic characteristics depending on the type of element, design variables, and arrangement. Design variables of dipole FSS were determined using PSO(Particle Swarm Optimization) to obtain the transmission characteristic for the target resonant frequency. Subsequently, the design variables of other types of N-pole(tripole, cross dipole, and Jerusalem cross) were determined based on the dimensions of the dipole for the comparisons of residual stresses of FSS embedded composite structures and transmission characteristics. In addition, effects of FSS pattern, and stacking sequence of composite laminates were considered.

• Composites Research
• /
• v.26 no.5
• /
• pp.279-288
• /
• 2013

In this paper, the delamination and deformed FSS caused by residual stresses in the Loop type FSS embedded composites and the transmission characteristic changes due to deformation of FSS by residual stresses were studied. FSS may have different electromagnetic characteristics depending on the type of element, design variables, and array. Therefore, design variables of square loop FSS embedded composites structures were determined to obtain the transmission characteristic for X-band (8~12 GHz). Then the design variables of other types of loops (triangular loop and circular loop) were determined based on the dimensions of square loop. Thereafter, the residual stresses and transmission characteristics of FSS embedded composite structures with various single and double loop FSS's, and stacking sequence of composite laminates were compared.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.10B
• /
• pp.1876-1884
• /
• 1999

The next generation of wireless LAN AND PBX systems will make use of the unlicensecd band at 2.5 GHz. Deployment of these systems inside buildings requires and understanding of propagation characteristics within buildings. Because the wavelength is small compared to building dimensions, ray methods can be used to predict propagation, but they require knowledge of the transmission and reflection properties of walls. This paper reports on transmission measurements made at walls made of gypsum board on metal studs, and at concrete block walls using directive antennas. The measurements are found to give good agreement with theoretical results that account for the periodic nature of the wall structure.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1998.06c
• /
• pp.445-448
• /
• 1998

고유음향 임피던스가 다른 물질이 층상구조를 이루고 있는 매질내에서 임의의 한 층에 형성된 이차원 초음파 음장이 다른 매질로 전파될 때에의 특성을 각스펙트럼법에 의해 해석하였다. 음원으로서는 baffle된 원형 트랜스듀서를, 층상구조를 매질로서는 물과 생체조직(지방)의 경계를 각각 고려하였다. 해석에 있어서는 먼저 각스펙트럼 분해요소, 즉, 음원의 크기 및 거리에 의존하는 기준음장의 최적 크기와 샘플링 간격을 균질매질을 이용하여 결정한 다음, 그 요소를 층상매질에 적용하였다. 그 결과, 경계면에서의 입사각(공간주파수)의 의존하는 투과계수에 입사음장의 곱으로 나타내어지는 투과음장은 각스펙트럼법에 의해 짧은 시간내에 정도 높게 산출될 수 있음을 보인다.

• Korean Journal of Materials Research
• /
• v.8 no.2
• /
• pp.161-164
• /
• 1998

탄소섬유-에폭시 복합재료의 전파 반사특성을 전파전송 이론에 근거하여 해석하였다. 탄소섬유 복합재료의유전상수를 투과/반사법에 의해 4-12GAz 주파수 범위에서 측정하였다. 측정된 재료정수로부터 반사손실을 시편의두께와 주파수의 함수로 계산하였다. 탄소섬유 복합재료는 높은 유전상수와 도전손실 특성에 의해 전파의 반사율이 매우 높았다. 그러나 파장에 비해 시편의 두께가 작은 경우 반사손실은 두께에 매우 민감하였으며, 이는 입력 임피던스의 변화에 기인하는 것으로 해석되었다. 이러한 결과로부터 전자파 차폐를 극대화시키기 위해서는 특히 저주파 대역에서 시편의두께 조절이 매우 중요함을 제시할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.985-996
• /
• 2012

An unsteadily propagating permeable crack in piezoelectric materials (PMs) under anti-plane shear mechanical loading and in-plane electric loading is studied. The equilibrium equations for a transiently propagating crack in a PM are developed, and the solutions on the stress and displacement fields for a permeable crack though an asymptotic analysis are obtained. The influences of piezoelectric constant, dielectric permittivity, time rate of change of the crack tip speed and time rate of change of stress intensity factor on the stress and displacement fields at the transiently propagating crack tip are explicitly clarified. By using the stress and displacements, the characteristics of the stress and displacement at a transiently propagating crack tip in a PM are discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.19 no.7
• /
• pp.733-740
• /
• 2008

In this paper, an indoor propagation model based on 3d ray tracing is presented for wireless communications. In case of indoor propagation models, various radio propagation paths such as wall-transmitted wave and scattered wave from ceilings, pillars, and furnitures arises and 3-D formulation is needed. To accommodate such scatterers, objects are modeled by triangulated surfaces and ray tubes using those surfaces are introduced and efficient calculation methods using the tubes are presented.

• The Magazine of the IEIE
• /
• v.36 no.6
• /
• pp.52-63
• /
• 2009

2004년 이후 미국 IEEE802 표준화 기구에서는 지역별로 사용되지 않는 유휴 TV 방송채널을 비면허 방식 무선접속 서비스용도로 사용하기 위한 기술표준 및 서비스모델 제정 작업이 진행되고 있다. 작은 전파감쇄 특성과 높은 전파투과 특성을 지니는 방송대역 주파수를 활용한 서비스로는 일반적인 이동통신망의 기지국 커버리지 보다 넓은 지역을 커버하는 무선 지역접속망(WRAN)부터 확장된 형태의 무선랜에 이르기까지 다양한 모델이 논의되고 있다. 본 고에서는 미국을 중심으로 논의되고 있는 서비스모델을 중심으로 기술적, 사업적 관점에서 고려될 수 있는 다양한 서비스모델에 대하여 논하고자 한다.