• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1999.06a
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• pp.25-30
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• 1999

자동차의 정면 충돌시 발생하는 충돌에너지를 흡수하여 인명을 보호하기 위한 장비중 구조 역학적 관점에서 고려될 수 있는 것으로 범퍼와 사이드멤버(Side Member)가 있다. 이들중 범퍼는 시속 8km/hr 이하의 저속 충돌시에 탄성 변형에너지로서 충돌에너지를 흡수하는 역할을 하나, 그 이상의 고속 정면 충돌시에는 일반적으로 사이드멤버가 충돌에너지의 60∼70%를 부재의 연속적인 대변형에 의한 소성에너지에 의해 흡수하고 있다. (중략)

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.385-386
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• 2014

본 논문에서는 자심 테슬라 변압기를 이용한 400kV급 소형 고전압 펄스 발생기를 개발하였다. 테슬라 변압기의 효율 및 출력전압 향상을 위해 4분할 적층 원통형 자심 구조를 새롭게 제안 하였다. 제안 된 자심 구조를 적용하여 테슬라 변압기를 제작 한 결과, 최대 출력전압 425kV, 에너지 변환 효율 50%를 확인하였다.

• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.300-305
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• 1998

Crystallinity and structual properties of the epitaxially grown Pt films on $Al_2O_3$(0001) substrate by rf magnetron sputtering at a substrate temperature of $600^{\circ}C$ were studied by using backscattering spectrometry (BS)/channeling and transmission electron microscopy (TEM) measurements. $MeV^4$He ion BS/channeling results showed that the channeling minimum yield of Pt film with a thickness of 3500$\AA$ was 4%. This indicates an excellent crystallinity of Pt film. When the thickness of Pt film was less than 200 $\AA$, the channeling minimum yield of Pt film increased sharply with the decrease in film thickness. The Pt layer on $Al_2O_3$(0001) substrate grew epitaxially to the direction of (111) with six-fold symmetry. Cross-sectional TEM images also showed that Pt film on $Al_2O_3$(0001) substrate consist of twinned domains to release the strain induced by the lattice mismatch and the surface roughness of the film increased at the twin boundaries where the strain was contcentrated.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.159-160
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• 2012

지난 30년 동안 플래시 메모리의 주류 역할을 하였던 부유 게이트 플래시 메모리는 40 nm 기술 노드 이하에서 셀간 간섭, 터널 산화막의 누설전류 등에 의한 오동작으로 기술적 한계를 맞게 되었다. 또한 기존의 비휘발성 메모리는 동작 시 높은 전압을 요구하므로 전력소비 측면에서도 취약한 단점이 있다. 그러나 이러한 문제점들을 기존의 Si기반의 소자기술이 아닌 새로운 재료나 공정을 통해서 해결하려는 연구가 최근 활발하게 진행되고 있다. 특히, 플래시 메모리의 중요한 구성요소의 하나인 터널 산화막은 메모리 소자의 크기가 줄어듦에 따라서 SiO2단층 구조로서는 7 nm 이하에서 stress induced leakage current (SILC), 직접 터널링 전류의 증가와 같은 많은 문제점들이 발생한다. 한편, 기존의 부유 게이트 타입의 메모리를 대신할 것으로 기대되는 전하 포획형 메모리는 쓰기/지우기 속도를 향상시킬 수 있으며 소자의 축소화에도 셀간 간섭이 일어나지 않으므로 부유 게이트 플래시 메모리를 대체할 수 있는 기술로 주목받고 있다. 특히, TBM (tunnel barrier engineered memory) 소자는 유전율이 큰 절연막을 적층하여 전계에 대한 터널 산화막의 민감도를 증가시키고, 적층된 물리적 두께의 증가에 의해 메모리의 데이터 유지 특성을 크게 개선시킬 수 있는 기술로 관심이 증가하고 있다. 본 연구에서는 Si3N4/Ta2O5를 적층시킨 staggered구조의 tunnel barrier를 제안하였고, Si기판 위에 tunnel layer로 Si3N4를 Low Pressure Chemical Vapor Deposition (LPCVD) 방법과 Ta2O5를 RF Sputtering 방법으로 각각 3/3 nm 증착한 후 e-beam evaporation을 이용하여 게이트 전극으로 Al을 150 nm 증착하여 MIS- capacitor구조의 메모리 소자를 제작하여 동작 특성을 평가하였다. 또한, Si3N4/Ta2O5 staggered tunnel barrier 형성 후의 후속 열처리에 따른 전기적 특성의 개선효과를 확인하였다.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.489-497
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• 2002

Nonlinear behavior and large deformation cannot be analyzed using techniques based on linear theory. Nonetheless, they are emerging as gradually huge and complex structures. In addition, the optimum design of structure is necessary in the development of high-performance computation and numerical methods. as well as stricter design-criterion. Therefore, the structural problems in engineering that are limited to the linear region must be extended to the nonlinear region. Likewise, structural behavior must be accurately analyzed. In turn, this requires considering the expected problems beforehand. Only then can an efficient, economical, and optimized structure be designed. This paper presents the solution of the geometrical nonlinear problem of anisotropic cylindrical shell. The characteristics of the geometrical nonlinear behavior of anisotropic circular cylindrical shells may vary according to several causes. e.g., change of fibers, curvature in the circumferential direction, subtended angle, aspect, etc. Parametric studies were conducted to determine the effect of factors on the large deflection behavior of laminated shells, with interesting observations.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.6
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• pp.1315-1320
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• 2012

In this study, piezoelectric AC-DC converter using ring-dot type multilayer piezoelectric transformer with no anisotropic of polarization was developed. Considering the characteristics of piezoelectric transformer which is very narrow operating frequency range, piezoelectric converter was designed with mixed structure of PFM driving method for feedback control of oscillation frequency and PWM driving method for output control. Maximum power and allowed current of the developed piezoelectric converter showing stable driving with minimum heat was 25W and 900mA, respectively. The output voltage of the piezoelectric converter was controlled by the driving oscillation frequency and showed stable and efficient operating characteristics at the maximum power.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1395-1396
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• 2008

본 논문에서는 초소형 DC-DC 컨버터에 쓰이는 파워인덕터를 설계하였다. 제안된 인덕터는 Ni-Zn 페라이트와 Polyimide 혼합물질을 이용하여, 경화온도를 낮추어 유기기판(FR-4)에서도 적용될 수 있는 인덕터를 설계했다. 인덕터의 크기는 $5mm{\times}4.5mm{\times}0.5mm$ 이고, 도선의 물질은 구리(Cu)를 사용하였으며, 18${\mu}m$의 두께, 85${\mu}m$의 선폭, 85${\mu}m$의 선 간격으로 디자인 하였다. 그리고 구조는 2층 적층의 스파이럴 구조를 제안하여 소형화에 보다 유리하도록 설계를 하였다. 페라이트 혼합물질을 샌드위치 타입으로 EMI shielding한 인덕터의 경우 동작 주파수 5MHz에서 912nH의 인덕턴스, 29의 품질계수 특성을 나타냈으며, 그 결과 초소형 DC-DC 컨버터용 인덕터로서 소형화와 높은 효율을 만족하였다.

• Composites Research
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• v.14 no.6
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• pp.9-15
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• 2001

In the present work, a linear static analysis is presented for thin-walled prismatic box-beams made of generally anisotropic materials. A mixed beam theory has been used to model and carry out the analysis. Several different constitutive assumptions for the shell-wall of the beam section are assessed into the beam formulation. Simple layup cases of box-beams representing bending-torsion or extension-torsion coupled configuration have been considered and tested to clearly show the effects of elastic couplings of the beam. A detailed finite element structural analysis using the MSC/NASTRAN has been carried out to validate the current analytical results. Numerical results show that appropriate assumptions for the constitutive relations are important and crucial for the accurate prediction of beam stiffness constants and also thor the beam behavior.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.3
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• pp.467-474
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• 2019

In this paper, we studied a method for a broadband stacked patch antenna structure which is widely used for bandwidth improvement. The characteristics according to the distance between the two patches were analyzed and the impedance matching was optimized by connecting parallel open stubs to the main patch feed line. The shunt matching stub is inserted underneath the parasitic patch and so it does not require additional space, which enables the proposed antenna structure to be advantageous in miniaturizing antenna. The effects of the various parameters on the antenna performance are examined, and we introduced the design procedure for the proposed antenna to operate in the frequency range of 2.3~2.7GHz. Experimental results show that the bandwidth of the proposed antenna is about 480MHz with 2.27~2.75GHz bandwidth. And the antenna gain was 5.8dBi at 2.3GHz and 7.8dBi at 2.6GHz within the bandwidth.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.491-499
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• 2002

A p-version finite element model based on degenerate shell element is proposed tot the analysis of orthotropic laminated plates. In the nonlinear formulation of the model, the total Lagrangian formulation is adopted with large deflection and moderate rotation being accounted tot in the sense of yon Karman hypothesis. The material model is based on the Huber-Mises yield criterion and Prandtl-Reuss flow rule in accordance with the theory of strain hardening yield function, which is generalized lot anisotropic materials by introducing the parameters of anisotropy. The model is also based on extension of equivalent-single layer laminate theory(ESL theory) with shear deformation, leading to continuous shear strain at the interface of two layers. The integrals of Legendre polynomials are used for shape functions with p-level varying from 1 to 10. Gauss-Lobatto numerical quadrature is used to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed P-version finite element model is demonstrated through several comparative points of iew in terms of ultimate load, convergence characteristics, nonlinear effect, and shape of plastic tone.