• Computational Structural Engineering
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• v.7 no.2
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• pp.101-109
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• 1994

A degenerated cylindrical shell element for modeling glass fiber reinforced plastic pipes is developed and its performance for static structural analysis under internal uniform pressure is evaluated. The element is a nine node degenerated solid shell element with reduced integration technique, addition of nonconforming displacement modes, and assumed strain method to improve convergence of analysis. Several numerical examples are solved and compared with analytical solutions and other F.E.M programs, The results show that the increment of fiber orientation in the GFRP pipes with reference to the longitudinal axis cause less radial displacements and much stiffness in the pipes. This is reasonable since the internal pressure will primarily cause hoop stresses in the ring and 90-angle ply GFRP ring carry these efficiently in pure tension.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.37-45
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• 2000

Though microstrip antenna has several advantages, it makes engineers struggle against the difficulties of narrow bandwidth and scan-blindness with probe-feeding and array configuration. To overcome these disadvantages, stacked patch and cavity-backed structure had been proposed. But this structure can not be analyzed easily because we have no concrete means to analyze it. So the algorithm to analyze the structure should be established to make it useful. This paper explained the algorithm of moment method to analyze the structure and verified it by comparing the calculated and measured results.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.219-224
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• 2017

This paper investigates equivalent stress and deformation happening at inner fiber structure when the tensile force acts on the specimen with arch type composed of carbon fiber. The countless many each fiber is applied on the unidirectional axis at CFRP and has the high specific strength and stiffness by comparing with iron. In this study, the distribution of stress due to radius is investigated at the structure of arch type composed with the optimum stacking angle of $60^{\circ}$. And the durability is seen to be lower as the radius increases at the same stacking angle. By applying the result of this study to the design of structure with arch type, it can be devoted to the safe design for the prevention of damage and the durabilty improvement. And it is possible to be grafted onto the convergence technique at the designed factor and show the esthetic sense.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.172-177
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• 2004

In this paper, DGS(Defected Ground Structure) is applied to multi-layer structure using LTCC(Low Temperature Co-fired Ceramics). Sprial DGS is adopted in order for size-reduction and higher quality factor, the multi-layer DGS has the same characteristics as the planar DGS. Multi-layer bandpass filter of new shape is confiured using two multi-layer spiral DGS and is designed with no via-hole for the simple process. 5.25 GHz Wireless LAN bandpass filter is designed and fabricated, the insertion loss of the filter is measured less than 1.5 dB, and the size is 2.0 mm${\times}$1.2 mm${\times}$1.1 mm(L${\times}$W${\times}$H).

• Electrical & Electronic Materials
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• v.10 no.8
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• pp.843-851
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• 1997

• Computational Structural Engineering
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• v.8 no.3
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• pp.135-141
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• 1995

Any arbitrarily shaped laminated composite shells of revolution can be sum of the conical shell elements. Therefore, finite element model of conical shell element will be developed in this study. To verify consistency and validity of this model, natural vibrations of this model is compared with the analytical solution of cylindrical shell. Herein, an extensive parametric study is presented to assess the modeling capability of this model in class of laminated composite cylinders. It is seen that the proposed model provides highly accurate results with analytical solution. Once development of this conical shell element is done, any arbitrarily shaped composite shells of revolution can be easily analyzed.

• Composites Research
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• v.13 no.2
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• pp.40-50
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• 2000

In an effort to construct a structure under the design principle of minimal use of materials for maximum performances, a discrete gradient structure has been introduced in laminate composite systems. Using a sequential linear programming method, the gradient structure of composites to maximize the buckling load was optimized in terms of fiber volume fraction and thickness of each layer. The buckling load showed maximum value with the outmost [$0^{\circ}$] layer concentrated by almost all the fibers when the ratio of length to width(aspect ratio) was less than 1.0. But when the aspect ratio was 2.0, the optimum was determined in a structure where the thickness and fiber volume fraction were well-balanced in each layer. From the optimization of gradient structure, the optimal fiber volume fraction and thickness of each layer were proposed. Gradient structures have also shown an advantage in the weight reduction of composites compared with the conventional homogeneous structures.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.2-2
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• 2010

텐덤형 태양전지는 다양한 에너지 대역을 동시에 흡수할 수 있도록 제작할 수 있어 단일접합 태양전지에 비해 높은 에너지변환효율을 기대할 수 있다. 본 연구에서는 GaAs를 기반으로 양자점 혹은 양자우물 구조를 이용한 고효율 텐덤형 태양전지를 설계하고, 완충층 및 활성층의 특성을 분석하였다. 분자선 단결정 성장 장비를 이용하여 GaAs 기판 위에 메타모픽 (metamorphic)성장법을 이용하여 convex, linear, concave 형태로 조성을 변화시켜 $In_xAl_1-_xAs$ 경사형 완충층을 성장한 후 그 특성을 비교하였다. 또한, 최적화된 경사형 완충층 위에 1.1 eV와 1.3 eV의 에너지 대역을 각각 흡수할 수 있는 적층 (5, 10, 15 층)된 InAs 양자점 구조 또는 InGaAs 양자우물구조를 삽입하여 p-n 접합을 성장하였다. 그리고 GaAs/AlGaAs층을 이용한 터널접합에서는 GaAs층의 두께 (20, 30, 50 nm)에 따른 터널링 효과를 평가하였다. 그 결과, 경사형 완충층을 통해 조성 변화로 인한 결함을 최소화하여 다양하게 조성 변화가 가능한 고품위의 구조를 선택적으로 성장할 수 있었으며, 적층의 양자점 구조 및 양자우물 구조를 이용해 고효율 텐덤형 태양전지의 구현 가능성을 확인하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.191-202
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• 2005

비정질 실리콘 태양전지 대신에 열화가 더 적은 프로터결정 실리콘(pc-Si:H)을 상층전지 흡수층으로 사용한 고효율 실리콘계 적층형(pc-Si:H/$\mu$c-Si:H) 박막 태양전지를 개발하였다. 우선, 높은 전도도와 넓은 에너지 밴드갭 특성을 갖는 p-a-SiC:H 박막을 개발하였고, p/i 계면의 특성 향상을 위해 p-nc-SiC:H 완충층을 개발하였다. 프로터결정 실리콘 다층막을 제작하고 FTIR, 평면 TEM, 단면 TEM 측정을 통해 프로터결정 실리콘 다층막의 우수한 열화 특성의 원인을 규명하였다. 적층형 태양전지의 성능향상을 위해 n-p-p 구조의 터널접합을 제안, 제작하고 특성을 분석하였으며, pc-Si:H/a-Si:H 적층형 태양전지에 적용하여 성능향상을 이루었다. 양질의 하층전지용 마이크로결정 실리콘 박막을 증착하기 위하여 광CVD법과 플라즈마CVD법을 결합한 2단계 마이크로결정 실리콘 증착법을 개발하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1542-1548
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• 2009

This paper describes a size-reduced Wilkinson power divider using substrate integrated artificial dielectric(SIAD). SIAD transmission lines have increased effective refractive index, so the line width and length are reduced from those of standard transmission lines. Therefore the "size-reduction effect" is achieved if SIAD lines are applied to high frequency circuits. An efficient simulation method is proposed for SIAD lines which have an enormous number of via-holes. A 2GHz Wilkinson power divider is designed and measured using SIAD transmission line as an example of application. The size of the fabricated divider is reduced by 32% due to the increased effective refractive index of SIAD, while the performances are maintained similarly.