• Information Display
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• v.10 no.1
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• pp.15-21
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• 2009

다중 도메인 수직배향 LCD는 러빙 공정을 필요치 않는 다는 장점에서 출발해 현재 액정 TV 시장에서 주를 이루고 있다. 하지만 현재 사용화 되고 있는 제품들이 투과율, 응답속도, 명암대비율 등 성능부분의 개선이 필요하고 공정 측면에서 돌기를 사용하거나 상판 패턴을 필요로 하는데 이러한 공정을 제거하면서도 성능이 우수한 새로운 형태의 수직배향 LCD가 최근 대두되고 있다. 기 발표된 기술들을 정리해 보면 신기술에서는 액정에 UV curing이 가능한 모노머를 소량 도핑 한 후 적절한 셀 구조를 형성해 전압 인가시 중간에 액정 배열에 충돌이 있더라도 최종적으로 안정한 배열을 갖게 만든 다음 UV조사를 통해 양 기판 표면에 모노머가 고분자화되면서 액정 배향 방향과 프리틸트각을 갖게 하도록 만든다. 이러한 신개념의 수직배향 LCD는 종래 LCD에 비해 전기광학 특성이 우수해지고 제조공정도 단순해져 향후 수직배향 LCD의 주를 이룰 것으로 예상된다. 더불어 수직배향 기술은 해마다 새로운 진화를 하고 있으며 앞으로 더 진화를 할 것으로 예상되어 이 부분에 대한 적극적인 연구 지원이 필요하다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.1
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• pp.77-83
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• 2010

Radiation characteristics of $5{\times}4$ pin array patch antennas are compared to those of $5{\times}2$ pin array patch antennas for several substrate thicknesses using the computer simulation. Since the number of unit cells of a $5{\times}2$ pin array patch antenna is half of that of a $5{\times}4$ pin array patch antenna, the number of pins used in a $5{\times}2$ pin array patch antenna is half of that in a $5{\times}4$ pin array patch antenna and the patch width of a $5{\times}2$ pin array patch antenna is very small compared to that of a $5{\times}4$ pin array patch antenna. However, the radiation characteristics of a $5{\times}2$ pin array patch antenna are almost similar to those of a $5{\times}4$ pin array patch antenna.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.6
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• pp.1514-1525
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• 1998

Two main characteristics of VBR MPEG video traffic are different statistics according to different picture types and the periodic traffic pattern due to GOP structure. Especially, the I-pictures at the beginning of each GOP generate $$\mu$h more traffic than other pictures. When several VBR Mpeg video sources are superposed, the I-picture starting times of these sources may significantly affect the cell loss characteristics of ATM $$\mu$tiplexers. In this paper, we propse a performance model for ATM $$\mu$tiplexers with VBR MPEG video sources whose starting times are arbitrary given. For analysis, both single and superposed source traffic are modeled as NDPPs (non-deterministic periodic processes), and the ATM $$\mu$tiplexer is modeled as a U-state NDPPD/D/1/B queueing system. It is hown that the numerical results are very close to the si$$\mu$ation results. From the relationships between the starting tiem distributions and the corresponding $$\mu$tiplexer performances, some considerations for designing a scheduling policy in order to obtain the maxi$$\mu$ $$\mu$tiplexing gain are presented.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.16-17
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• 2001

광결정(photonic crystal)은 서로 다른 유전체가 규칙적으로 배열되어 있는 구조로서, 빛이 진행할 수 없는 진동수 영역인 광밴드갭(photonic bandgap)이 존재한다. 광밴드갭 특성으로 빛의 자발 방출과 진행 방향이 조절될 수 있기 때문에, 광결정은 나노 레이저, 광도파관, LED(Light Emitting Diode) 등의 광소자 개발에 응용되고 있다. 지금까지 2차원, 3차원의 광결정에 대한 많은 연구가 수행되어 왔으며, 현재에는 2차원의 슬랩(slab) 구조에 대해 활발하게 연구되고 있다. (중략)

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.6
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• pp.664-670
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• 2014

Generally, the properties of metamaterials are analyzed based on the infinite array of the unit cells. In real application of the metamaterial, however, the array has to be finite. Hence, it is important that a method can analyze the effect of the finite array of the metamaterial. In this paper, a model is proposed which can calculate the scattering by a large-size finite array of an I-shaped metamaterial without a full-wave simulation. The proposed model is based on the surface current estimation of each unit cells. The ratio of the current distribution on a finite array of the metamaterial to that of the infinite array of the same metamaterial for a TM polarized incident wave is approximated as a quartic polynomial. The coefficients of the polynomial are a function of the physical dimension of the metallic patch. Hence, the current distribution of the finite metamaterial can be estimated based on the proposed polynomial and the current of the infinite array. The scattered field is calculated by using the surface current model. The proposed model is numerically and experimentally verified by comparing calculated and measured RCS(Radar Cross Section) data.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.1
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• pp.47-51
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• 2014

In this paper, unit cell and arrayed cover for improving the transfer efficiency of resonant wireless power transfer system is proposed. We used the characteristic of zero refractive index for focusing a magnetic field between the transmitting resonator and receiving resonator. For zero refractive index, we designed the unit cell structure that have a negative value of effective permeability. The size of proposed unit cell based on metamaterial structure is $70mm{\times}70mm{\times}3.2mm$, operating frequency is 13.56 MHz. And, the size of arrayed cover is $400mm{\times}400mm{\times}3.2mm$, is consists of 2-layers. The transfer efficiency of the proposed wireless power transfer system are 94.8 %, 93.2 %, 91.4 %, 90.8 % at 100 mm, 200 mm, 300 mm and 400 mm (distance between transmitting and receiving resonator), respectively. And proposed WPT system has a transfer efficiency high than 90 % over the overall distances.

• Progress in Medical Physics
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• v.19 no.4
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• pp.219-226
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• 2008

In this study, we have conducted characterization of imaging performance for a flat panel digital X-ray detector using amorphous Selenium and a-Si TFT which was developed by the authors. The procedures for characterization were in concordance with internationally recommended standards such as IEC (international electrotechnical commission). The measures used for imaging performance characterization include response characteristic, modulation transfer function (MTF), detective quantum efficiency (DQE), noise power spectrum (NPS), and quantum limited performance. The measured DQEs at lowest and highest spatial frequencies were 40% and 25% respectively, which was superior to that of commercial products by overseas vendor. The MTF values were significantly superior to that of CR and indirect type DRs. The quantum limited performance showed the detector was limited by quantum noise at the entrance exposure level below 0.023 mR, which is sufficiently low for general X-ray examination.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.214-222
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• 2008

The equivalent circuit for the RLH-TL is proposed considering radiation effects due to the inclusion of a series capacitor and shunt inductor in a unit cell for the right/left-handed transmission line(RLH-TL). The design equations to realize a specific phase shift at a given frequency is also provided. The S-parameters for unit cells with N=1, 3, 5, and 10 are analyzed in various aspects based on the EM and circuit simulations especially for the purpose of controlling radiation along RLH-TL's. A modification formula for the radiation rate per unit cell is also proposed for good agreement between the EM and circuit simulation results.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.32-39
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• 2011

The object of this study is to evaluate and discriminate nondestructively the dislocation substructures of Cu and Cu-Zn alloy subjected to the low-cycle-fatigue. The ultrasonic wave velocity, electrical resistivity and positron annhilation lifetime(PAL) were measured to the nondestructive testing. Cyclic fatigue test of Cu and Cu-Zn alloy with much different stacking fault energies was conducted and the correlations between dislocation behavior and nondestructive parameters were studied. Dislocation cell substructure was developed in Cu, while planar array of dislocation structure was developed in Cu-35Zn alloy only increasing dislocation density with fatigue cycles. Decrease in ultrasonic wave velocity, increase in electrical resistivity and PAL were shown because of the development of lattice defects, dislocations and vacancies, by cyclic fatigue at room temperature. In contrast to Cu-Zn alloy of the planar-array dislocation substructure showing continuous changes in the nondestructive parameters, it does not make any noticeable changes in the nondestructive parameters after the evolution of dislocation cell substructure in Cu.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.444-450
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• 2010

In the present study, the microscopic degradation of copper and copper alloy subjected to cyclic deformation has been evaluated by the electrical resistivity measurement using the DC four terminal potential method. The copper (Cu) and copper alloy (Cu-35Zn), whose stacking fault energy is much different each other, were cyclically deformed to investigate the response of the electrical resistivity to different dislocation substructures. Dislocation cell substructure was developed in the Cu, while the planar array of dislocation structure was developed in the Cu-35Zn alloy increasing dislocation density with fatigue cycles. The electrical resistivity increased rapidly in the initial stage of fatigue deformation in both materials. Moreover, after the fatigue test it increased by about 7 % for the Cu and 6.5 % for the Cu-35Zn alloy, respectively. From these consistent results, it may be concluded that the dislocation cell structure responds to the electrical resistivity more sensitively than the planar array dislocation structure evolved during cyclic fatigue.