Yeats와 Maud Gonne : Maud Gonne의 이미지를 중심으로

경지수 한국 예이츠 학회 1994 한국예이츠 저널 Vol.3·4 No.-

Lightweight Design Method for Three-Wheeled Mobility Frame Using Discrete Material and Thickness Optimization Technique

경지수,신동석,전의식 사단법인 한국융합기술연구학회 2023 아시아태평양융합연구교류논문지 Vol.9 No.1

Personal mobility (PM) is a means of transporting cargo and people. The use of PM, which can be used personally, has increased since the COVID-19 pandemic. According to the report by the Gyeonggi Research Institute in August 2020[1], the occurrences of safety accidents have also increased in proportion to the amount of the PM used. Although the causes of accidents vary, high-intensity design measures for mobility frames are required to reduce the injuries caused by accidents. However, high-strength design models reduce the energy efficiency due to excessive weight. Generally, the transportation sector is challenged by high-intensity-lightening problem. Moreover, PM is a subject of research based on high-intensity-lightening. In order to solve these problems, research was conducted on the high-strength and lightweight design of PM. finite element analysis modeling was performed, and a high-strength lightweight design of the PM frame was performed and compared using DMTO (Discrete Material and Thickness Optimization) and DTO (Discrete Thickness Optimization) techniques. Various experimental points for changes in material and thickness were based on the theory of experimental design, and finite element analysis was performed for each experimental point. The reaction of each experimental point was set with displacement and weight, and global optimization was used to derive a value that satisfies the weight minimization condition and the strength criterion on the reaction surface. Furthermore, validated the optimization results through finite element analysis on the meta-model optimization points. According to the study, the optimal model and the existing model derived from this study had a weight reduction effect of 53% compared to the weight and satisfied the maximum displacement for the limiting condition. Since DMTO utilizes a discretization factor, the results that can be actually produced were derived. The optimization results did not require separate post-processing. Prototype manufacturing and evaluation were not required in this process. Therefore, it is believed that this research process can reduce the resources required for detailed design.

A Theoretical Study on the Low Transition Temperature of VO 2 Metamaterials in the THz Regime

경지수 한국광학회 2022 Current Optics and Photonics Vol.6 No.6

Vanadium dioxide (VO 2 ) is a well-known material that undergoes insulator-to-metal phase transition near room temperature. Since the conductivity of VO 2 changes several orders of magnitude in the terahertz (THz) spectral range during the phase transition, VO 2 -based active metamaterials have been extensively studied. Experimentally, it is reported that the metal nanostructures on the VO 2 thin film lowers the critical temperature significantly compared to the bare film. Here, we theoretically studied such early transition phenomena by developing an analytical model. Unlike experimental work that only measures transmission, we calculate the reflection and absorption and demonstrate that the role of absorption is quite different for bare and patterned samples; the absorption gradually increases for bare film during the phase transition, while an absorption peak is observed at the critical temperature for the metamaterials. In addition, we also discuss the gap width and VO 2 thickness effects on the transition temperatures.

고전 역학에서 라그랑지안 운동 방정식을 계산하는 효율적인 방법

경지수 한국물리학회 2020 새물리 Vol.70 No.11

The equation of motion is essential for understanding and predicting the behavior of a dynamics system. In classical mechanics, the equations of motion are obtained using the Newtonian method and the Lagrange method. Because the Newton method treats the force as a vector quantity, obtaining the equation of motion is difficult when the constraint force is complex. On the other hand, the Lagrange method uses the scalar quantities of kinetic energy and potential energy, making the obtaining the equation of motion relatively easy. In this paper, we examined the physical meaning of the Lagrange equation through a coordinate transformation. As a result, Lagrange’ s motion equation in the generalized coordinate can be seen to be a linear transformation of the constraint force in Cartesian coordinate into the transpose of the Jacobian matrix. Furthermore, when the x, y, and z coordinates are explicit functions of the time t, the method proposed in this paper is more efficient than the conventional Lagrange method for obtaining the equation of motion. 운동 방정식은 역학 시스템을 이해하고 예측하는데 필수이다. 고전 역학에서는 뉴턴 방식과 라그랑주방식을 이용하여 운동 방정식을 구한다. 뉴턴 방식은 힘을 벡터량으로 다루기 때문에 속박 힘 (constraint force) 이 복잡한 경우 운동 방정식을 구하기가 까다로운 반면 라그랑주 방식은 스칼라량인 운동에너지와위치에너지를 사용하기 때문에 상대적으로 운동 방정식을 구하는 것이 용이하다. 본 논문에서는 좌표변환을 통해 라그랑주 방정식이 가진 물리적인 의미를 살펴보았다. 그 결과 일반 좌표계 (generalized coordinate) 에서의 라그랑지안 운동 방정식은 직교좌표계 (Cartesian coordinate) 에서의 속박힘을야코비안 전치 행렬로 일차 변환 (linear transformation) 한 것임을 알 수 있었다. 나아가 x, y, z 좌표가시간 t에 대한 명시적 (explicit) 함수일 경우 본 논문에서 제안한 방식이 운동 방정식을 얻는데 기존라그랑지안 방식보다 더 효율적임을 보였다.

DMTO 기법을 이용한 모빌리티 프레임의 경량 최적화

경지수(J. S. Kyoung),신동석(D. S. Shin),전의식(E. S. Jeon) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월

개인 및 화물의 이동수단으로서 친환경 퍼스널 모빌리티(Personal Mobility)의 활용이 증가하고 있다. 퍼스널 모빌리티는 안전성과 편의성을 만족시키기 위하여, 박판 부품의 활용과 다양한 편의장치가 부가되어 있다. 그러나 박판 프레임은 가변이 불가하여 다목적 활용이 어렵고, 다양한 편의장치들은 중량을 증가시킴으로써 구동저항의 원인이 되고 있다. 그러므로 다목적성을 만족시키기 위해서 프레임을 골격형으로 선정해야 하고, 구동저항을 감소시키기 위해서 공학적인 최적화 방법으로 프레임 및 결합 부품들에 대한 소재 및 두께 최적화를 수행해야 한다. 본 논문에서는 골격형 퍼스널 모빌리티 모델에 대하여, 메타모델 기반 최적설계 이론을 이용하여 경량최적화 하는 과정을 제시했다. 먼저 퍼스널 모빌리티 모델에 대한 유한요소모델링을 수행했다. 그리고 프레임 부품들을 소재의 변화, 두께의 변화가 가능한 변수로 설정했다. 소재는 미리 입력되어 있는 경우의 수로 이산화 하였으며, 두께도 미리 입력된 경우의 수로 이산화 하였다. 각 부품의 소재와 두께의 조합은 실험계획법에 의거하여 배치하였고 각 실험점에 해당하는 유한요소해석을 수행하였다. 각 실험점의 반응은 강도와 중량을 취했으며, 실험계획표에 의거하여 반응표면생성을 수행하였다. 반응표면생성 모델은 2 차 다항식으로 선정했다. 반응표면에서 중량 최소화 조건과 강도기준을 만족하는 도출하기 위하여 유전알고리즘을 활용했다. 그리고 메타모델기반 최적점에 대한 유한요소해석을 통해 최적화 결과에 대한 검증을 수행했다. 이러한 연구 과정은 다양한 퍼스널 모빌리티 프레임의 개념설계 단계에서 활용할 수 있을 것으로 사료된다.

복합 소재를 고려한 3륜 모빌리티 프레임의 소재-두께 최적화

경지수(J. S. Kyoung),박대호(D. H. Park),신동석(D. S. Shin),전의식(E. S. Jeon) Korean Society for Precision Engineering 2022 한국정밀공학회 학술발표대회 논문집 Vol.2022 No.5

열처리에 의한 Ti 기반 MXene 소재의 구조 변화와 전자파 간섭 차폐 특성에 관한 연구

슈에한,경지수,우윤성 한국마이크로전자및패키징학회 2023 마이크로전자 및 패키징학회지 Vol.30 No.3

높은 전기전도도와 우수한 기계적 강도, 열안정성을 가진 2차원 전이금속탄화물 또는 질화물인 MXene은 최근가볍고 유연한 전자파 차폐 소재로 많은 주목을 받고 있다. 특히, Ti 기반의 Ti3C2Tx와 Ti2CTx는 방대한 MXene 계열 시스템에서 전기 전도성과 전자파 차폐 특성이 가장 우수한 것으로 보고되고 있다. 따라서, 본 연구에서는 Ti3AlC2와 Ti2AlC의층간 금속 에칭과 원심 분리법을 통하여 합성된 Ti3C2Tx와 Ti2CTx 분산용액을 진공 여과법을 이용하여 수 마이크로 두께의 필름을 제작하였으며, 고온 열처리 후에 필름의 전기전도도 및 전자파 차폐 효율을 측정하였다. 그리고, X선 회절법과광전자 분광법을 이용하여 열처리 후의 Ti3C2Tx와 Ti2CTx 필름의 구조적 변화와 전자파 차폐에 미치는 영향을 분석하였다. 본 연구의 결과를 바탕으로 향후 소형 및 웨어러블 전자기기에 적용하기 위한 매우 얇고 가벼운 우수한 성능의 MXene 기반 전자파 차폐 필름을 위한 최적 구조를 제안하고자 한다. MXene, a two-dimensional transition metal carbide or nitride, has recently attracted much attention as a lightweight and flexible electromagnetic shielding material due to its high electrical conductivity, good mechanical strength and thermal stability. In particular, the Ti-based MXene, Ti3C2Tx and Ti2CTx are reported to have the best electrical conductivity and electromagnetic shielding properties in the vast MXene family. Therefore, in this study, Ti3C2Tx and Ti2CTx films were prepared by vacuum filtration using Ti3C2Tx and Ti2CTx dispersions synthesized by interlayer metal etching and centrifugation of Ti3AlC2 and Ti2AlC. The electrical conductivity and electromagnetic shielding efficiency of the films were measured after heat treatment at high temperature. Then, X-ray diffraction and photoelectron spectroscopy were performed to analyze the structural changes of Ti3C2Tx and Ti2CTx films after heat treatment and their effects on electromagnetic shielding. Based on the results of this study, we propose an optimal structure for an ultra-thin, lightweight, and high performance MXene-based electromagnetic shielding film for future applications in small and wearable electronics.

Software-based Simple Lock-in Amplifier and Built-in Sound Card for Compact and Cost-effective Terahertz Time-domain Spectroscopy System

남유진,경지수 한국광학회 2023 Current Optics and Photonics Vol.7 No.6

A typical terahertz time-domain spectroscopy system requires large, expensive, and heavy hardware such as a lock-in amplifier and a function generator. In this study, we replaced the lock-in amplifier and the function generator with a single sound card built into a typical desktop computer to significantly reduce the system size, weight, and cost. The sound card serves two purposes: 1 kHz chopping signal generation and raw data acquisition. A unique software lock-in (Python coding program to eliminate noise from raw data) method was developed and successfully extracted THz time-domain signals with a signal-to-noise ratio of ~40,000 (the intensity ratio between the peak and average noise levels). The built-in sound card with the software lock-in method exhibited sufficiently good performance compared with the hardware-based method.

A Breaching of Electromagnetic Shielding by Narrow Aperture in Metal Film

박두재,홍철,경지수,최수봉 한국광학회 2016 Current Optics and Photonics Vol.20 No.5

We report a theoretical research for the condition of electromagnetic shield breaching when a narrowaperture is punctured in thin metal film. To calculate electromagnetic field transmission through a narrowslit, a Rayleigh wave expansion has been applied for free standing, thin metal film. We found that theDC electric field allows perfect transmission when the length of the slit is infinite, regardless of the othergeometrical factors such as slitwidth and thickness. Slitwidth dependent transmission spectra as a functionof frequency shows a cutoff frequency that decreases almost linearly to the slitwidth, giving that almostsuccessful shielding is only possible when the slitwidth is smaller than 1 micron.