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Reliability Assessment on Different Designs of a SMES System Based on the Reliability Index Approach
Dong-Wook Kim,Young Hwa Sung,Giwoo Jeung,Sang Sik Jung,Hongjoon Kim,Dong-Hun Kim 대한전기학회 2012 Journal of Electrical Engineering & Technology Vol.7 No.1
The current paper presents an effective methodology for assessing the reliability of electromagnetic designs when considering uncertainties of design variables. To achieve this goal, the reliability index approach based on the first-order reliability method is adopted to deal with probabilistic constraint functions, which are expressed in terms of random design variables. The proposed method is applied to three different designs of a superconducting magnetic energy storage system that corresponds to initial, deterministic, and roust designs. The validity and efficiency of the method is investigated with reference values obtained from Monte Carlo simulation.(bloodkdw@nate.com, jeunggw@ee.knu.ac.kr, hongjoon@knu.ac.kr)
A Suspended Stripline Frequency Tripler Using a Left-Handed Nonlinear Transmission Line
Kim, In Bok,Kim, Hongjoon,Choi, Hyun Chul,Kim, Kang Wook Hindawi Limited 2015 International journal of antennas and propagation Vol.2015 No.-
<P>A suspended stripline frequency tripler using a left-handed nonlinear transmission line (LH NLTL) is presented. The proposed tripler using the LH NLTL is composed of a series of varactor diodes, shunt inductances, and a high-pass filter implemented with suspended stripline (SSL). An ultrawideband microstrip-to-suspended stripline transition is also utilized. The fabricated LH NLTL provides the minimum insertion loss of 1.7 dB and the maximum insertion loss of 4.7 dB for a wide frequency band from 2.6 to 18 GHz. As a tripler, the measured minimum third harmonic conversion loss is 15.3 dB at an input frequency of 2.4 GHz and typically 17 dB from 2 to 3.1 GHz.</P>
Appropriate model selection methods for nonstationary generalized extreme value models
Kim, Hanbeen,Kim, Sooyoung,Shin, Hongjoon,Heo, Jun-Haeng Elsevier 2017 Journal of hydrology Vol.547 No.-
<P><B>Abstract</B></P> <P>Several evidences of hydrologic data series being nonstationary in nature have been found to date. This has resulted in the conduct of many studies in the area of nonstationary frequency analysis. Nonstationary probability distribution models involve parameters that vary over time. Therefore, it is not a straightforward process to apply conventional goodness-of-fit tests to the selection of an appropriate nonstationary probability distribution model. Tests that are generally recommended for such a selection include the Akaike’s information criterion (AIC), corrected Akaike’s information criterion (AICc), Bayesian information criterion (BIC), and likelihood ratio test (LRT). In this study, the Monte Carlo simulation was performed to compare the performances of these four tests, with regard to nonstationary as well as stationary generalized extreme value (GEV) distributions. Proper model selection ratios and sample sizes were taken into account to evaluate the performances of all the four tests. The BIC demonstrated the best performance with regard to stationary GEV models. In case of nonstationary GEV models, the AIC proved to be better than the other three methods, when relatively small sample sizes were considered. With larger sample sizes, the AIC, BIC, and LRT presented the best performances for GEV models which have nonstationary location and/or scale parameters, respectively. Simulation results were then evaluated by applying all four tests to annual maximum rainfall data of selected sites, as observed by the Korea Meteorological Administration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We compared the AIC, AICc, BIC, and LRT for nonstationary GEV models. </LI> <LI> Monte Carlo simulation was conducted for evaluating the performances of all tests. </LI> <LI> Under stationary conditions, the BIC shows the best performance (N>40). </LI> <LI> Under nonstationary conditions, regression lines for model selection were proposed. </LI> <LI> The results of simulations were verified through the application of observed data. </LI> </UL> </P>
김홍준(Hongjoon Kim),유형석(Hyoungsuk Yoo) 대한전기학회 2015 전기학회논문지 Vol.64 No.3
Radio Frequency (RF) coils in Magnetic Resonance Imaging (MRI) systems interact with a patient’s tissues, resulting in the absorption of RF energy by the tissues. The presence of an electrically conducting medical implant may concentrate the RF energy and causes tissue heating near the implant devices. Here we present a novel design for a medical lead to reduce this undesired heating. Specific Absorption Rate (SAR), an indicator of heating, was calculated. Remcom XFdtd software was used to calculate the peak SAR distribution (1g and 10 g) in a realistic model of the human body. The model contained a medical lead that was exposed to RF magnetic fields at 64 MHz (1.5 T MRI), 128 MHz (3 T MRI) and 300 MHz (7 T MRI) using a model of an MR birdcage body coil. Our results demonstrate that, our proposed design of adding nails to the medical lead can significantly reduce the SAR for different MRI systems.
김홍준(Hongjoon Kim) 대한전기학회 2020 전기의 세계 Vol.69 No.3
전자기파를 이용한 비접촉식 생체신호의 인식 방법은 다른 소스 (빛, 열, (초)음파)를 이용한 방식 보다 환경의 변화에 영향을 적게 받으며, 제조 단가가 저렴한 장점이 있다. 하지만 인체의 유해성과 간섭등의 영향으로 전력의 크기가 제한되고, 잡음의 영향에 민감한 특성을 보이므로 신호대 잡음비 (SNR) 개선을 위한 많은 하드웨어적, 소프트웨어적 방법이 보고 되고있다. 본고에서는 저자의 최근연구 결과 중심으로 SNR향상을 위한 알고리듬과 위상배열 안테나를 이용한 위치추적 시스템에 대해 소개한다. Non-contacting human vital signal recognition using microwaves has many advantages compared to other methods (light, heat, sonic waves, etc) in terms of environmental variation and price. However, because it can be harmful to the human body and may interfere with other electronic devices, the power output is limited and the device can be sensitive to the noise. Therefore, many hardware and software methods are reported to minimize those effect and maximize the Signal-to-Noise Ratio (SNR). This paper demonstrates the author’s recent research results to increase SNR to acquire human vital signal and to localize such a signal using a phased antenna array.
김홍준(Hongjoon Kim),아르빈드 싱(R. Arvind Singh),윤의성(Eui-Sung Yoon),공호성(Hosung Kong) 한국트라이볼로지학회 2005 한국트라이볼로지학회 학술대회 Vol.2005 No.11
Surfaces found in nature, including biological surfaces have been providing inspiration to modify/fabricate artificial surfaces as solutions for tribological applications. As an example, the concept of 'lotus-effect' has motivated tribologists world wide to modify/fabricate surfaces for enhanced tribological performance. These was done by creating nano/micro-scaIe asperities on various surfaces using ion beam milling and ion-beam assisted roughening. In order to understand the attributes of natural surfaces, which are inspirational to tribologists, we characterized the surface of two natural surfaces - Nelumbo nucifera (lotus) and Colocasia esculenta leaves. Further, we evaluated their micro-scale friction property, both in their fresh and dried conditions. The characterization of surfaces was conducted using a confocal microscope and SEM, which involved the evaluation of size and distribution of protuberances. The micro-scale friction property was evaluated using a ball-on-flat type micro-tribo tester, under reciprocating motion. A soda lime glass ball (2 ㎜ diameter) was used in these tests. Tests were conducted at the applied normal load of 3000μN, at a sliding speed of \ mm/sec for a scan length of 3 ㎜. All experiments were conducted at ambient temperature (24±1℃) and relative humidity (45±5%). It was observed that the friction behaviour of the natural surfaces was influenced by their surface characteristics (morphology and distribution of protuberances) and also by the condition (fresh or dried) in which they were tested.
레이더 센싱을 위한 빔 조정 기술과 센싱을 막기 위한 메타 반사판 기술
김홍준(Hongjoon Kim) 대한전기학회 2021 전기의 세계 Vol.70 No.12
레이더를 이용한 사물의 탐지 및 위치추적 기술은 현대 사회에서 군용뿐 아니라 민간용 등 많은 분야에서 활용 가능하다. 본 고에서는 전자기 센싱을 통한 위치추적 방법의 핵심이 되는 빔 조정(steering) 기술과 최근 대두되고있는 메타물질을 이용한 탐지 회피 기술에 대해 설명하고자 한다. Detection and ranging of an object using a RADAR is widely used for both military and civilian purpose. Here, the author explains the antenna beam steering technology which is a core in RADAR. In addition, a recent RADAR jamming technology using a Meta-surface is explained.