A flexible metamaterial with negative refractive index at visible wavelength

최무한,Jong-Ho Choe,Byungsoo Kang,Choon-Gi Choi 한국물리학회 2013 Current Applied Physics Vol.13 No.8

In this paper, we demonstrated a realization of a flexible metamaterial with negative refractive index operating at visible wavelength. With the help of Finite-Difference Time-Domain (FDTD) method, we could establish design rules for the metamaterial and analyze the characteristics of it. To this end, the fishnet structure with the unit cell size 185 nm by 240 nm was fabricated. Due to the polymer dielectric spacer between the metal-layers, the metamaterial is freestanding without base substrate and additional backside etching process.

테라헤르츠 이미징을 위한 능동형 메타디바이스

최무한(Muhan Choi),김인보(Inbo Kim),유정완(Jung-Wan Ryu),한재형(Jae-Hyung Han) 대한전자공학회 2015 대한전자공학회 학술대회 Vol.2015 No.6

地域經濟發展의 地域産業關聯分析에 의한 方案 : 束草地域經濟圈을 중심으로

崔茂一,權春植 관동대학교 1996 關大論文集 Vol.24 No.2

The purpose of this study is to examine the relationships and roles between local industries and local government under the conditions of regional economic potentialities. The local industry in our county, we know, has played a major role in National economic growth and made a great contribution to employment and income increase since 1989, the beginning year of the sixth economic development plan. But we can regard the rapid urbanization and the severe local capital shortage phenomena as a characteristic of modern local society. thus, the purpose of this study is searching for the appropriate local policies to solve the problem of local capital accumulation shortage, by analyzing the demand and supply situation to solve the problem of local capital accumulation shortage, by analyzing the demand and supply situation or condition in local Industrial organization. The nature of local problem must be explained by the widening gap between demand and supply for local industries. In our case study, we also know that regional economy is affected greatly according to the local industry structure. So, we must cultivate many local firms and our local government must help the effort local firm. Them we can describe the following problems for the present regional industries. 1) Shortage of local capital accumulation. 2) Low rate of local government investment for local industry program. 3) Shortage of regional characteristic in national industry polices. And so, we can suggest the several policies for to break through the local industry shortage. 1) Strengthen the control system of the factors related to regional capital demand. 2) Cultivate lots of local firms and their local funds. 3) Increase the public industry supply of local government. 4) Develope the high tech-tour town in the main city district.

제품 정보의 검색에 온톨로지 활용 방법

최무라(Choi, M. R.),유상봉(Yoo, S. B.) (사)한국CDE학회 2001 한국CDE학회 논문집 Vol.6 No.4

디지털 혼돈시스템을 이용한 수동형 RFID 인증 프로토콜 설계

최무한(Muhan Choi),임거수(Geo-Su Yim) 한국정보기술학회 2014 한국정보기술학회논문지 Vol.12 No.10

Passive RFID systems which are being used often in logistics and distribution have limited program development space unlike the active system and difficulty in the application of a robust security algorithm. In order to certify this RFID system, we designed a protocol using the chaos signals which are similar to random numbers, and digitalized the chaos system of a difference equation in order to efficiently apply it to the limited development space of a passive system. Among the signals that have been generated from the difference equation X<SUB>n+1</SUB>=F(X<SUB>n</SUB>), X<SUB>n</SUB> was used as the certification code, and X<SUB>n+1</SUB>?Key was designed for data transmission. The X<SUB>n+1</SUB> signal was calculated by X<SUB>n</SUB> and these two signals can certify each other. Furthermore, the output value is similar to a random number and it can efficiently cope with the illegal attacks that occur during communication. The proposed RFID certification protocol using digital chaos signals is a new method that presents a new direction to RFID which is vulnerable to tapping attack, spoofing attack, denial of service attack, and location tracking.

Metamaterials can cover whole range of refractive indices

Muhan Choi(최무한) 한국가시화정보학회 2011 한국가시화정보학회 학술발표대회 논문집 Vol.2011 No.5

거대 스케일 광학 센서 설계를 위한 파동 시뮬레이션(Wave Simulation) 기법 연구

이용훈,최무한,권태윤 한국센서학회 2023 센서학회지 Vol.32 No.1

The wave mode calculation of a large-scale optical system in comparison to the working wavelength is practically impossible because the computational cost increases exponentially. In this paper, we propose a method that can obtain the optical mode in a large-scale optical system. The method carries out simulations by dividing the calculation area into blocks and moving along the light axis along which the light propagates. By applying this method to the calculation of resonant modes in a ring-type optical resonator, which is mainly used for ring laser optical gyro sensors, the efficiency of the proposed method was verified.

다양한 변환 공진기에 형성되는 비등방성 속삭임의 회랑 모드

김인보,최무한,Kim, Inbo,Choi, Muhan 한국광학회 2018 한국광학회지 Vol.29 No.3

이 논문에서는 변환 광학의 기본 원리를 설명하고 이를 적용하여 공진기 모양이 원형으로부터 크게 변형되어도 속삭임의 회랑 모드(WGM)의 특성을 유지할 수 있는 다양한 변환 공진기 설계 기법을 소개한다. 특정 등각 변환 하에서 다양한 변환 공진기를 얻는 방법으로서 초기 정의역을 평행 이동시키는 방법과, 타원을 정의역으로 잡고 회전시키는 방법을 제시하였고, 이를 통해 설계된 몇 가지의 공진기 모드에 대한 내부 파형 및 원거리장 출력 특성을 수치해석적으로 계산하였다. 이러한 결과로부터, 하나의 주어진 등각 좌표변환과 관련된 다양한 GRIN 공진기가 가능하다는 것을 확인하였다. We explain the basic principle of transformation optics, and introduce several design techniques for transformation cavities that can maintain the characteristics of whispering gallery modes (WGMs) even if the cavity is strongly deformed from a circular shape. As a method of obtaining various transformation cavities under a specific conformal mapping, we suggest a method of parallel movement of the initial cavity domain, and a method of rotating the ellipse as a cavity domain. The internal wave pattern and the far-field output characteristics of several designed resonant modes are numerically calculated. From these results, it is confirmed that a variety of GRIN resonators are possible for a given conformal coordinate transformation.

폴리디메틸실록산(PDMS)을 이용한 그래핀 전사법 개선을 위한 계면처리 연구

한재형,최무한,Han, Jae-Hyung,Choi, Mu-Han 한국응용과학기술학회 2015 한국응용과학기술학회지 Vol.32 No.2

In this paper, we study the dry transfer technology utilizing PDMS (Polydimethylsiloxane) stamp of a large single-layer graphene grown on Cu-foil as catalytic metal by using Chemical Vapor Deposition (CVD). By changing the surface property of the target substrate through $UV/O_3$ treatment, we can transfer the graphene on the target substrate while minimizing mechanical damages of graphene layer. Multi-layer (1~4 layers) graphene was stacked on $SiO_2/Si$ wafer successfully by repeating thetransfer method/process and then optical transmittance and sheet resistance of graphene layers have been measured as a quality assessment. 화학기상증착법(CVD)을 이용하여 Cu-foil 위에 합성된 대면적의 단층 그래핀(Graphene)을 폴리머 탄성융합체 PDMS(Polydimethylsiloxane)를 이용하여 건식으로 전사하는 기술을 연구하였다. 이때, $UV/O_3$처리를 통해 목표 기판(target substrate)의 표면 개질을 변화시켜 그래핀의 손상이 최소화되로록 그래핀을 전사하였다. 이 과정을 반복 실행하여 그래핀을 다층(1~4 layers)으로 $SiO_2/Si$기판 위에 적층하였으며, 전사된 다층 그래핀의 품질평가를 위하여 광투과율과 면저항의 변화를 측정하였다.

Phase Synchronization Between Geographically Remote Stock Markets

임승환,김칠민,최무한,Won-Ho Kye 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.3

We have investigated the synchronous movement of stock market indices between geographically remote markets, i.e., between the United States and the countries in Europe. Our results show that the price dynamics between remote countries, indeed, move synchronously. Alos, the effect can be seen more pronouncely for a frequency band corresponding to a major period of eight trading days. This indicates that the dynamics of geographically remote markets can be qualitatively interpreted as two coupled chaotic oscillators. We also quantify the dependencies between two geographically remote financial markets by calculating the measures of the coupling strength and the directionality.