• 조명전기설비학회논문지
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• 제26권7호
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• pp.1-8
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• 2012

In this paper, we improved the light extraction efficiency by structural change of LEDs on conventional LEDs. We simulated the LEDs light emission as functions of LED side wall angle, various refractive indices the geometrical structures and analyzed the condition improved the light efficiency. We present the results of experimerns and simulations for light output power from LEDs for various refractive indices and the geometrical structures of the LED encapsulants. When the side wall angle range was from 40[$^{\circ}$] to 30[$^{\circ}$], the LED emission increased. LED side wall angle onto LED using the simulation system with a fine tuning of the structure of the LEDs side wall angle is fabricated. Additionally, we changed the side wall angle of LED package with spherical structure and flat structure. The result of spherical structure ray tracting is higher compared with flat structure about 14[%].

• 한국세라믹학회지
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• 제46권3호
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• pp.249-252
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• 2009

Nanocrystalline ceria particles were prepared by using the ultrasonic spray pyrolysis method. The prepared ceria particles were found to be spherical and non-agglomerated by the SEM and TEM analyses. It was found that carrier gas influences the size and morphology. It was found that the air stream of carrier gas results in porous agglomerated structure of ceria abrasives, whereas solid nano-sphere can be obtained in a more oxidizing atmosphere.

• 한국재료학회지
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• 제23권1호
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• pp.24-30
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• 2013

Today, the modification of carbon foam for high performance remains a major issue in the environment and energy industries. One promising way to solve this problem is the optimization of the pore structure for desired properties as well as for efficient performance. In this study, using a sol-gel process followed by carbonization in an inert atmosphere, hollow spherical carbon foam was prepared using resorcinol and formaldehyde precursors catalyzed by 4-aminobenzoic acid; the effect of carbonization temperature and re-immersion treatment on the pore structure and characteristics of the hollow spherical carbon foam was investigated. As the carbonization temperature increased, the porosity and average pore diameter were found to decrease but the compression strength and electrical conductivity dramatically increased in the temperature range of this study ($700^{\circ}C$ to $850^{\circ}C$). The significant differences of X-ray diffraction patterns obtained from the carbon foams carbonized under different temperatures implied that the degree of crystallinity greatly affects the characteristics of the carbon form. Also, the number of re-impregnations of carbon form in the resorcinol-formaldehyde resin was varied from 1 to 10 times, followed by re-carbonization at $800^{\circ}C$ for 2 hours under argon gas flow. As the number of re-immersion treatments increased, the porosity decreased while the compression strength improved by about four times when re-impregnation was repeated 10 times. These results imply the possibility of customizing the characteristics of carbon foam by controlling the carbonization and re-immersion conditions.

• 대한기계학회논문집
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• 제18권11호
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• pp.2846-2859
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• 1994

This work deals with kinematic analysis of fault-tolerant 3 degree-of-freedom spherical modules which have force redundancies in its parallel structure. The performance of a redundantly actuated four-legged module with no actuator failure, a single actuator failure, partial and half failure of dual actuator are compared to that of a three-legged module, in terms of maximum force transmission ratio, isotropic characteristics, and fault-tolerant capability. Additionally, a system with an excess number of small floating actuators is considered, and the contribution of these small actuators to the force transmission and fault-tolerant capability is evaluated. This study illustrates that the redundant actuation mode allows significant saving of input actuation effort, and also delivers a fault tolerance.

• 센서학회지
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• 제7권6호
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• pp.377-385
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• 1998

This paper describes the application of a coupled finite element-boundary element method to obtain the steady-state response of a hydrophone. The particular structure considered is a flooded piezoelectric spherical shell. The hydrophone is three-dimensionally simulated to transduce an incident plane acoustic pressure onto the outer surface of the sonar spherical shell to electrical potentials on inner and outer surfaces of the shell. The acoustic field formed from the scattered sound pressure is also simulated. And the displacement of the shell caused by the externally incident acoustic pressure is shown in temporal motion. The coupled FE-BE method is described in detail.

• 항공우주기술
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• 제11권2호
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• pp.158-163
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• 2012

구형비행체는 기존의 항공기와 달리 비행체가 원형 프레임으로 보호되는 구조로 되어있다. 항우연에서 개발중인 본 비행체(Flying Ball)는 수직이착륙 및 정지비행이 가능한 배터리로 구동되는 프로펠러를 장착하고 있으며 실내외에서 운용이 가능하도록 개발이 진행중이다. 최종적으로는 자율비행이 가능토록 하여 정찰용이나 감시용으로 활용할 수 있도록 할 예정이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.6-8
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• 2008

Electrical machineries have been developed as following with various and high technical application in these days. Especially the robot is integrated system including mechanical structure, electronic control, and electrical technology. The robot system is not compact and has not natural motion like human, although the technology of robot has been developing continuously. The spherical wheel motor is useful electric machine for using robot joint as operation of 3-degrees of freedom. In this paper, a permanent magnet spherical wheel motor is introduced and performance characteristics are analyzed for improving of operation stability.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1998년도 춘계종합학술대회
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• pp.394-399
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• 1998

This paper describes the application of a coupled finite element-boundary element method to obtain the steady-state response of a hydrophone. The particular structure considered is a flooded piezoelectric spherical shell. The hydrophone is three-dimensionally simulated to transduce an incident plane acoustic pressure onto the outer surface of the sonar spherical shell to electrical potentials on inner and outer surfaces of the shell. The acoustic field formed from the scattered sound pressure is also simulated. And the displacement of the shell caused by the externally incident acosutic pressure is shown in temporal motion. The coupled FE-BE method is described in detail.

• 한국태양에너지학회 논문집
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• 제31권2호
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• pp.53-62
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• 2011

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a proper design of structure of the heliostat reflective surface could be the most important step in the construction of such power plant. The work presented here is a design of structure of optical surface of heliostat, which will be used in 200kW solar thermal power plant. The receiver located at 43(m) high from ground in tower has $2{\times}2$(m) rectangular shape. We first developed the software tool to simulate the energy concentration characteristics of heliostat using the ray tracing technique. Then, the shape of heliostat reflective surface is designed with the consideration of heliostat's energy concentration characteristics, production cost and productivity. The designed heliostat's reflective surface has a structure formed by canting four of $1{\times}1$(m) rectangular flat plate mirror facet and the center of each mirror facet is located on the spherical surface, where the spherical surface is formulated by the mirror facet mounting frame.

• 전기학회논문지
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• 제56권9호
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• pp.1614-1618
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• 2007

We have demonstrated the experimental results to obtain the immunity of FN (Fowler Nordheim) stress for S-RCAT (Spherical-Recess Cell Array Transistor) which has been employed to meet the requirements of data retention time and propagation delay time for sub-100-nm mobile DRAM (Dynamic Random Access Memory). Despite of the same S-RCAT structure, the immunity of FN stress of S-RCAT depends on the process condition of gate oxidation. The S-RCAT using DPN (decoupled plasma nitridation) process showed the different degradation of device properties after FN stress. This paper gives the mechanism of FN-stress degradation of S-RCAT and introduces the improved process to suppress the FN-stress degradation of mobile DRAM.