• Journal of the Korean Society for Precision Engineering
• /
• 제18권3호
• /
• pp.169-174
• /
• 2001

We proposed a new fabrication method using electrochemical process for microshafts. This method is a kind of atomic removal process by chemical reaction. Therefore, it is possible to make thin and long shafts regardless of the stiffness of materials. Because shaping process is simply switched to polishing process by varying process conditions, we can precisely fabricate microshafts with very smooth surface. We also fabricated a very thin shaft with the diameter as small as 10$\mu$m and a microshaft with high aspect ratio.

• Tribology and Lubricants
• /
• 제26권2호
• /
• pp.129-135
• /
• 2010

Geckos have a unique ability to cling to ceilings and walls utilizing dry adhesion. Their foot pads are covered by a large number of small hairs (setae) that contain many branches per seta with a lower level of spatulae. Their fibrillar structure is the primary source of high adhesion. In this study, we construct the adhesion design database for biomimetic adhesive system. A simple idealized fibrillar structure consisting of single array of beams is modeled. The fibers are assumed as oriented cylindrical cantilever beams with spherical tip. We consider three necessary conditions; buckling, fracture and sticking of fiber structure, which constrain the allowed geometry. The adhesion analysis is performed for the attachment system in contact with rough surfaces with different s values for different main design variables-fiber radius, aspect ratio and material elastic modulus and so on. The developed adhesion design databases are useful for understanding biological systems and for guiding of fabrication of the biomimetic attachment system.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• 제22권5호
• /
• pp.218-222
• /
• 2012

FeNi alloy nanofibers have been prepared by an electrospinning process followed by air-calcination and H2 reduction to develop electromagnetic (EM) wave absorbers in the giga-hertz (GHz) frequency range. The thermal behavior and phase and morphology evolution in the synthetic processes were systematically investigated. Through the heat treatments of calcination and H2 reduction, as-spun PVP/FeNi precursor nanofiber has been stepwise transformed into nickel iron oxide and FeNi phases but the fibrous shape was maintained perfectly. The FeNi alloy nanofiber had the high aspect ratio and the average diameter of approximately 190 nm and primarily composed of FeNi nanocrystals with an average diameter of ~60 nm. The FeNi alloy nanofibers could be used for excellent EM wave absorbing materials in the GHz frequency range because the power loss of the FeNi nanofibers increased up to 20 GHz without a degradation and exhibited the superior EM wave absorption properties compared to commercial FeNi nanoparticles.

• Carbon letters
• /
• 제14권3호
• /
• pp.131-144
• /
• 2013

The carbon nanotube (CNT) represents one of the most unique inventions in the field of nanotechnology. CNTs have been studied closely over the last two decades by many researchers around the world due to their great potential in different fields. CNTs are rolled graphene with $SP^2$ hybridization. The important aspects of CNTs are their light weight, small size with a high aspect ratio, good tensile strength, and good conducting characteristics, which make them useful as fillers in different materials such as polymers, metallic surfaces and ceramics. CNTs also have potential applications in the field of nanotechnology, nanomedicine, transistors, actuators, sensors, membranes, and capacitors. There are various techniques which can be used for the synthesis of CNTs. These include the arc-discharge method, chemical vaporize deposition (CVD), the laser ablation method, and the sol gel method. CNTs can be single-walled, double-walled and multi-walled. CNTs have unique mechanical, electrical and optical properties, all of which have been extensively studied. The present review is focused on the synthesis, functionalization, properties and applications of CNTs. The toxic effect of CNTs is also presented in a summarized form.

• Progress in Superconductivity and Cryogenics
• /
• 제15권2호
• /
• pp.44-47
• /
• 2013

Large AC loss from the second generation (2G) high temperature superconducting (HTS) wires has been one of the major bottlenecks in power applications with HTS materials. Moreover, the large power applications also require the large current capacity from the HTS wires, which makes them produce larger AC losses. In order to reduce the AC loss from the HTS conductors with large current capacity, an HTS compact cable with some striations on the superconducting layers has been proposed. In this paper, we prepared some sample HTS compact conductors with striations, and measured their magnetization loss from the external magnetic field. We also made some slits on the superconducting layer of the HTS wire by laser cutting to reduce the aspect ratio of the superconducting layers. It would make the low eddy current loss and magnetic decoupling. Finally, the magnetization losses of the sample HTS compact conductors were measured and analyzed.

• Proceedings of the KSME Conference
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.529-533
• /
• 2008

Thick pipes have been used in fields of ocean and industrial plants, and pipe arrangement of oil and water pipelines. Mostly, roll bending process has been used in manufacture of the pipes. Recently, however, studies on the pipe forming processes using brake press have been performed. Normally, the brake press has high aspect ratio, so structural integrity evaluation should be conducted. In this study, finite element analysis of structural integrity for the brake bending press was carried out for thick pipe forming process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
• /
• pp.233-236
• /
• 2003

수소 가스발생을 위한 마이크로 수소 발생기 개발에서 MEMS 공정을 이용하여 기판에 반응 유로를 위해 HAR(High Aspect Ratio) 구조물을 형성하고 Ru(ruthenium) 박막을 증착하여 수소 발생량을 측정하였다. Pyrex glass 기판상에 sand blast 방법으로 반응 구조물을 만들었으며, 그 위에 sputter system을 이용하여 Ru 박막을 $5500{\AA}$었다. 수소 발생량은 촉매 박막이 증착된 기판 재질과 기판의 표면 상태 그리고 마이크로 수소 발생기에 두께로 증착하였다. 반응 구조물의 전체 크기가 가로 2.0 cm, 세로 2.0cm의 면적에서 약 12.3 ml/min의 수소가 측정되 형성한 구조물의 형상에 의존하였다. Pyrex glass 기판을 사용하여 HAR로 반응 구조물을 형성한 경우에 단위 면적당 Ru 박반응 막의 반응 표면적이 증가되어 기존에 구조물을 형성하지 않은 평면 기판에 비교하여 약 5.5배 이상의 수소 발생이 증가하였다.

• International Journal of Quality Innovation
• /
• 제2권2호
• /
• pp.69-92
• /
• 2001

The laser-assisted seeding (LAS) process has potential to replace conventional electroless copper plating in Printed Circuit Board (PCB) manufacturing since it combines the steps of laser drilling and plating into one single process. In the LAS process, the single extra LAS step can metallize a microvia. Thus, the process steps can be greatly reduced and the productivity enhanced, but also the high aspect ratio microvias can be metallized. The objectives of this paper are to study the LAS copper thickness within PCB microvias and the thermal reliability of the microvias produced by this process. It was found that results were satisfactory in both the reliability test and also the LAS copper thickness which both comply with IPC standard, the copper thickness produced by the LAS process is sufficient for subsequent electro-plating process. The reliability of the microvias produced by LAS process is acceptable which are free from any voids, corner cracks, and distortion in the plated copper.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 한국정밀공학회 2004년도 춘계학술대회 논문요약집
• /
• pp.132-132
• /
• 2004

카본나노튜브는 나노튜브의 종류에 따라 1~10nm의 직경과 수 $\mu\textrm{m}$정도의 길이를 가지는 고종횡비(high aspect ratio)가 가능하며, 고강성, 전기화학적 내성, 마모에 대한 강인성 때문에 원자력간 현미경(AEM)의 프로브로서 이상적인 재료로 인식되어 왔다. 따라서 단백질이나 DNA를 측정하는 바이오 분야, 나노 일렉트로닉스 분야, 나노 구조 측정분야 등 나노 관련 측정분야에서 점차 그 활용도가 높아 져가고 있다. 특히 100nm이하의 반도체의 CD(critical Dimension)을 측정하는데 있어서 나노튜브는 가장 이상적인 후보라고 할 수 있겠다.(중략)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.813-816
• /
• 2006

Complex pressure pulsation phenomenon in fuel rails is generated by rapid opening and closing of injectors and it commonly causes undesirable noise. In this study, fluid-structure interaction analyses based on CFD and FEM have been conducted to examine the pulsation damping characteristics for different shapes of fuel rails. It is shown from the present results that the fuel rail with a high aspect ratio rectangular cross section seems to be best in order to reduce the pressure pulsations. It also agrees well with the previous experimental test by Mizuno, K. et al.