• International Journal of Precision Engineering and Manufacturing
• /
• 제4권5호
• /
• pp.41-46
• /
• 2003

Electronic Speckle Pattern Interferometry (ESPI) has been recently developed and widely used because it has the advantage of being able to measure surface deformations of engineering components and materials in industrial areas without contact. The speckle patterns formed with interference and scattering phenomena can measure not only the out-of-plane but also the in-plane deformations. Digital image equipment processes the information included in the speckle patterns and displays the consequent interferogram on a computer monitor. In this study, the experimental results of a canti-levered plate using ESPI were compared with those obtained from the simple beam theory. The ESPI results of the canti-levered plate, analyzed by 4-step phase shifting method, are close to the theoretical expectation. Similarly, out-of-plane displacements of a spot welded canti-levered plate were also measured by ESPI with 4-step phase shifting technique. The phase map of the spot welded canti-levered plate is quite different from that of the canti-levered plate without spot welding.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2005년도 춘계학술대회논문집
• /
• pp.69-73
• /
• 2005

The arc dispersion and contacts characteristics were analyzed according to switching off Residual Current Protective Device(RCD) switch. Arc dispersion process was taken by high speed imaging system at a rate of 10,000 frames per second. When RCD was switched from on to off, art was observed and it took about 2.3[ms] from the generation of arc to the extinction of arc. When RCD was switched from off to on, arc was not observed. We repeated switching on and off 1000, 3000 and 6000 times. After repetition, the surface characteristics of contacts were taken by stereo microscope and Scanning Electron Microscope(SEM). From the scattering patterns analysis of arc and the analysis of deteriorated contacts, it could be applicable to the research of electric fire and arc suppression.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.629-629
• /
• 2013

Graphene is a carbon based material and it has intriguing features, such as phenomenally strong, thin, flexible, transparent and conductive, those make it attractive for a broad range of applications.Unfortunately, graphene is extremely sensitive to contamination. When we fabricate graphene devices, electrical properties of graphene are altered [1], and the charge carrier mobility drops accordingly by orders of magnitude. This significant impact on electron mobility occurs because any surrounding medium could act as a dominant source of extrinsic scattering, which effectively reduces the mean free path of carriers [2,3]. The dominant contaminant is generated through fabrication stage by polymethyl methacrylate (PMMA) [4], or photo resist (PR). Surface contamination by these residues has long been a critical problem in probing graphene's intrinsic properties. If we clearly solve this problem, we can get highly performed graphene devices. Here, we will report on graphene cleaning process by Induced Coupled Plasma (ICP). We demonstrated how much decomposition of residue impact on improving electrical properties of graphene.

• 한국분말재료학회지
• /
• 제24권3호
• /
• pp.216-222
• /
• 2017

Synthesized monocrystalline nanodiamond (nD) particles are heat-treated at various temperatures to produce highly structured diamond crystals. The heat-treated nDs show different weight loss ratios during thermogravimetric analysis. The crystallinities of the heat-treated nDs are analyzed using Raman spectroscopy. The average particle sizes of the heat-treated nDs are measured by a dynamic light scattering (DLS) system and direct imaging observation methods. Moreover, individual dispersion behaviors of the heat-treated nD particles are investigated based on ultrasonic dispersion methods. The average particle sizes of the dispersed nDs according to the two different measurement methods show very similar size distributions. Thus, it is possible to produce highly crystallized nD powder particles by a heat-treatment process, and the nD particles are relatively easy to disperse individually without any dispersant. The heat-treated nDs can lead to potential applications such as in nanocomposites, quantum dots, and biomedical materials.

• Journal of Astronomy and Space Sciences
• /
• 제15권1호
• /
• pp.175-182
• /
• 1998

SAR 영상은 speckle 잡음의 multiplicative 특성으로 인해 영상 해석에 많은 제약을 받고 있다. Speckle 잡음을 제거하기 위한 방법은 크게 여러 개의 독립 영상을 multi-looks 처리 방법과 디지털 영상 처리 기술을 이용하는 방법으로 speckle 잡음 특성에 따른 비선형필터의 적용이다. 본 연구에서는 국지적 통계 자료를 이용하는 LEE와 Refined LEE 필터 그리고 speckle 자체의 통계 특성을 이용하는 EPOS(Edge Preserving Optimal Speckle)필터를 이용하여 speckle 잡음을 제거하여 SAR 영상의 화질을 개선하고 그 결과를 기존의 mean과 median 필터와 비교하였다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
• /
• pp.397-400
• /
• 2004

Synthetic Aperture Radar(SAR) is an active micro­wave instrument that performs high-resolution observation under almost all weather conditions. Although there are many advantages of SAR instrument, many complicated steps are involved in order to generate SAR image products. Many research and algorithms have been proposed to process radar signal and to increase the quality of SAR products. However, it is hard to find research which compare the quality of SAR products generated with different algorithms and processing methods. In our previous research, a SAR processing s/w was developed for a ground station. In addition, quality assessment procedures and their test parameters inside a SAR processor was proposed. The purpose of this paper is to evaluate the quality of SAR images generated from the developed SAR processing s/w. However, If there are no direct measurements such as radar reflector or scattering field measurement values it is difficult to compare SAR images generated with different methods. An alternative procedures and parameters for SAR image quality evaluation are presented and the problems involved in the comparison methods are discussed. Experiments based on real data have been conducted to evaluate and analyze quality of SAR images.

• 한국재료학회지
• /
• 제16권9호
• /
• pp.529-532
• /
• 2006

Sn-filled $Co_8Sb_{24}$ skutterudites were synthesized by the encapsulated induction melting process. Single ${\delta}-phase$ was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conductivity of the Sn-filled $Co_8Sb_{24}$. Electrical resistivity increased with increasing temperature, which shows that the Sn-filled $Co_8Sb_{24}$ skutterudite is a highly degenerate semiconductor. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be $z{\leq}0.5$ in the $Sn_zCo_8Sb_{24}$ system.

• 한국자기학회지
• /
• 제17권5호
• /
• pp.210-214
• /
• 2007

저차원 구조체에서 스핀의존산란에 의한 거대자기저항의 주요 연구들을 정리하였다. 본 논문에서는 다층박막, 나노선, 그리고 나노필러 등의 저차원 구조체에서 효율적인 자기저항의 제어에 대한 연구결과들을 양자역학적 차원에서 되 집어 보고 앞으로 스핀트로닉스 분야의 연구가 나갈 방향에 대해 논의하고자 한다.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제15권4호
• /
• pp.454-461
• /
• 2015

Light enhancement of GaN based light emitting diodes (LEDs) have been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental results were further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), Surface nano-porous (porous LED) and Surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제6권3호
• /
• pp.199-205
• /
• 2006

Patterned sapphire substrates (PSS) were fabricated by a simple wet etching process with $SiO_2$ stripe masks and a mixed solution of $H_2SO_4$ and $H_3PO_4$. GaN layers were epitaxially grown on the PSS under the optimized 2-step growth condition of metalorganic vapor deposition. During the 1st growth step, GaN layers with triangular cross sections were grown on the selected area of the surface of the PSS, and in the 2nd growth step, the GaN layers were laterally grown and coalesced with neighboring GaN layers. The density of threading dislocations on the surface of the coalesced GaN layer was $2{\sim}4\;{\times}\;10^7\;cm^{-2}$ over the entire region. The epitaxial structure of near-UV light emitting diode (LED) was grown over the GaN layers on the PSS. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the PSS were remarkably increased when compared to the conventional LED structure grown on the flat sapphire substrate. The reduction in TD density and the decrease in the number of times of total internal reflections of the light flux are mainly attributed due to high level of scattering on the PSS.