• 한국인터넷방송통신학회논문지
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• 제16권6호
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• pp.239-242
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• 2016

본 논문에서는 이중 곡률을 갖는 오목 렌즈를 제안하였다. 이중 곡률 렌즈는 HDPE (High Density Polyethylene)를 이용하여 제작하였다. 이중 곡률 렌즈는 두 개의 오목 구조로 구성되었다. 두 개의 오목 구조의 역할은 빔을 균일하게 넓게 보내기 위함이다. 작은 오목 구조는 큰 오목 구조 보다 더 큰 곡률 반경을 갖는다. 이러한 이중 곡률 렌즈는 밀리미터파 이미징 시스템에 적용 가능하다. 제작된 이중 곡률 렌즈를 250 GHz VDI 소스를 이용하여 검증하였다. 광학 시뮬레이션 툴인 ZEMAX를 이용하여 설계하고 제작된 렌즈는 균일한 빔과 확장 성능을 충분히 수행함을 확인하였다.

• Journal of the Optical Society of Korea
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• 제16권3호
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• pp.270-276
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• 2012

An off-axis integral floating system using a concave mirror is analyzed to resolve the image distortion incurred by the off-axis optical arrangement. The concave mirror can be adopted as the floating device to improve the optical efficiency. The image distortion due to the tilting axis of the concave mirror needs to be analyzed precisely to generate the pre-distortion image. In this paper, we calculate the image deformation in the off-axis structure of the concave mirror using the geometrical optics. Using the calculation results, the compensated elemental image can be generated for the pre-distortion integrated image, which can be projected to the floating 3D image without image distortion. The basic experiments of the off-axis integral floating are presented to prove and verify the proposal.

• Corrosion Science and Technology
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• 제2권5호
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• pp.243-246
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• 2003

We have used a plasma etching method in order to develop a concave-type Pt electrode capacitor to overcome the limitation of conventional stack-type capacitor in a small critical-dimension (CD) pattern. We have deposited Pt layer on the concave-type structure made by patterning of $SiO_2$ and subsequently we separated the adjacent nodes by etch-back process with photoresist (PR) as a protecting layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.138-143
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• 2008

Recently, a new periodic cellular metal(PCM) named as Wire wove Bulk Kagome(WBK) was introduced. Based on the shape of tetrahedra composing a WBK, WBKs are classified into two types, namely, concave and convex type. They are easily differentiated by changing the assembling sequence. The effect of geometrical parameters such as the wire diameter, strut length and number of layers on the compressive behavior of concave type WBK has already been investigated. In this work, the similar works were performed with the convex type WBKs. It was shown that the compressive strength of the convex type WBK was quite similar to that of the concave type. The compressive strengths of convex type specimens also depend on the slenderness ratio, but a little different from those of concave type specimens in the detailed behavior. And densification occurs earlier than the concave type WBK.

• 대한기계학회논문집
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• 제16권2호
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• pp.302-312
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• 1992

Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices

• Earthquakes and Structures
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• 제11권1호
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• pp.25-43
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• 2016

The uneven distribution of rolling friction coefficient may lead to great uncertainty in the structural seismic isolation performance. This paper attempts to improve the isolation performance of a spring-damper-rolling isolation system by artificially making the uneven friction distribution to be concave. The rolling friction coefficient gradually increases when the isolator rolls away from the original position during an earthquake. After the spring-damper-rolling isolation system under different ground motions was calculated by a numerical analysis method, the system obtained more regular results than that of random uneven friction distributions. Results shows that the concave friction distribution can not only dissipate the earthquake energy, but also change the structural natural period. These functions improve the seismic isolation efficiency of the spring-damper-rolling isolation system in comparison with the random uneven distribution of rolling friction coefficient, and always lead to a relatively acceptable isolation state even if the actual earthquake significantly differs from the design earthquake.

• 한국산학기술학회논문지
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• 제14권6호
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• pp.3074-3080
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• 2013

평면 수리실험을 통해 경사식구조물의 오목부 구간에 대한 파고 증폭을 검토하였다. 실험에 적용된 경사식 구조물 단면은 1:1.5의 경사면에 테트라포드가 2층 피복되어 있는 형상이다. 실험파는 Bretschneider-Mitsuyasu 스펙트럼을 적용한 불규칙파를 적용하였으며, 오목부의 중심각도는 $120^{\circ}$, $140^{\circ}$와$160^{\circ}$를 적용하였다. 실험결과에 따르면 오목부 구간에서의 입사파고에 대한 파고증폭비는 본 실험에서 적용한 실험조건 내에서 최대 1.5배로 계측되었으며, 상대파고비의 분포형태는 오목부의 중심에서 최대가 되고, 오목부를 중심으로 거리가 멀어질수록 감소했다 다시 증가하는 형태인 W자 형태를 나타내었다.

• 한국경영과학회지
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• 제10권2호
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• pp.15-23
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• 1985

A multi-product multi=facility production planning model is in which known demands must be satisfied. The model considers concave production costs and piecewise concave inventory costs in the introduction of production capacity constraints. Backlogging of unsatisfied demand is permitted. The structure of optimal production schedules is characterized and then used to solve an illustrative numerical problem.

• Journal of electromagnetic engineering and science
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• 제6권2호
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• pp.135-145
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• 2006

This paper presents the theory, design, fabrication and characterization of the novel low actuation voltage capacitive shunt RF-MEMS switch using a corrugated membrane with HRS MEMS packaging. Analytical analyses and experimental results have been carried out to derive algebraic expressions for the mechanical actuation mechanics of corrugated membrane for a low residual stress. It is shown that the residual stress of both types of corrugated and flat membranes can be modeled with the help of a mechanics theory. The residual stress in corrugated membranes is calculated using a geometrical model and is confirmed by finite element method(FEM) analysis and experimental results. The corrugated electrostatic actuated bridge is suspended over a concave structure of CPW, with sputtered nickel(Ni) as the structural material for the bridge and gold for CPW line, fabricated on high-resistivity silicon(HRS) substrate. The corrugated switch on concave structure requires lower actuation voltage than the flat switch on planar structure in various thickness bridges. The residual stress is very low by corrugating both ends of the bridge on concave structure. The residual stress of the bridge material and structure is critical to lower the actuation voltage. The Self-alignment HRS MEMS package of the RF-MEMS switch with a $15{\Omega}{\cdot}cm$ lightly-doped Si chip carrier also shows no parasitic leakage resonances and is verified as an effective packaging solution for the low cost and high performance coplanar MMICs.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.170-175
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• 2009

Shock focusing is related with explosive release of shock wave energy on a narrow spot in a short duration of time triggering a spontaneous high pressure near the focal point. It is well known that reflection of planar incident shock wave from the metallic concave mirror such as ellipsoidal, paraboloidal or hemispherical cavities will focus on a focal point. We intend to improve the computational results using a wave propagation algorithm and to resolve the mushroom-like structure. For computation of the concave cavity flow, it is not easy to use a single-block mesh because of the many singular points in geometry and coordinates. We have employed a uniform Cartesian-grid method for the wave propagation algorithm.