• 한국항행학회논문지
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• 제21권4호
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• pp.371-376
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• 2017

본 논문에서는 6.78 MHz 에서 공진하는 대형 코일을 이용한 자기공진방식 무선전력전송 시나리오를 제시하고 3차원 전자계 시뮬레이션, 자기공진방식 무선전력전송 등가회로를 통한 특성을 비교하였다. 본 논문에서 제시한 자기공진방식의 무선전력전송 등가회로는 기존 등가회로에 추가적으로 코일 간에 발생하는 기생 커패시턴스를 고려하였다. 이를 바탕으로 제작한 자기공진방식 무선전력전송 코일을 측정하고 시뮬레이션 예측과 비교하였다. 비교 결과 전송 특성 및 공진 주파수 천이 정도를 예측할 수 있었다. 제시한 자기공진방식 무선전력전송 등가회로 특성과 측정치의 오차는 ${\Delta}{\mid}S11{\mid}$이 최대 1.31 dB, ${\Delta}{\mid}S21{\mid}$이 최대 1.36 dB로 유사하게 예측하였다.

• Journal of electromagnetic engineering and science
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• 제17권3호
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• pp.126-132
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• 2017

In this study, we designed, measured, and analyzed a rearranged L-shape magnetic resonance coupling wireless power transfer (MR-WPT) system for practical applications with laptops. The typical four resonator MR-WPT (Tx part: source loop and Tx coil; Rx part: Rx coil and load loop) is difficult to apply to small-sized stationary and mobile applications, such as laptop computers, tablet-PCs, and smartphones, owing to the large volume of the Rx part and the spatial restrictions of the Tx and Rx coils. Therefore, an L-shape structure, which is the orthogonal arrangement of the Tx and Rx parts, is proposed for indoor environment applications, such as at an L-shaped wall or desk. The relatively large Tx part and Rx coil can be installed in the wall and the desk, respectively, while the load loop is embedded in the small stationary or mobile devices. The transfer efficiency (TE) of the proposed system was measured according to the transfer distance (TD) and the misaligned locations of the load loop. In addition, we measured the TE in the active/non-active state and monitor-open/closed state of the laptop computer. The overall highest TE of the L-shape MR-WPT was 61.43% at 45 cm TD, and the TE decreased to 27.9% in the active and monitor-open state of the laptop computer. The conductive ground plane has a much higher impact on the performance when compared to the impact of the active/non-active states. We verified the characteristics and practical benefits of the proposed L-shape MR-WPT compared to the typical MR-WPT for applications to L-shaped corners.

• Investigative Magnetic Resonance Imaging
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• 제22권1호
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• pp.65-70
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• 2018

The objective of this study was to describe a radiofrequency (RF) coil design for in vivo sodium magnetic resonance imaging (MRI) for use in small animals. Accumulating evidence has indicated the importance and potential of sodium imaging with improved magnet strength (> 7T), faster gradient, better hardware, multi-nucleus imaging methods, and optimal coil design for patient and animal studies. Thus, we developed a saddle-shaped sodium volume coil with a diameter/length of 30/30 mm. To evaluate the efficiency of this coil, bench-level measurement was performed. Unloaded Q value, loaded Q value, and ratio of these two values were estimated to be 352.8, 211.18, and 1.67, respectively. Thereafter, in vivo acquisition of sodium images was performed using normal mice (12 weeks old; n = 5) with a two-dimensional gradient echo sequence and minimized echo time to increase spatial resolution of images. Sodium signal-to-noise ratio in mouse kidneys (renal cortex, medulla, and pelvis) was measured. We successfully acquired sodium MR images of the mouse kidney with high spatial resolution (approximately 0.625 mm) through a combination of sodium-proton coils.

• 재활복지공학회논문지
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• 제11권1호
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• pp.63-71
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• 2017

본 논문에서는 달팽이관의 정원창 이식용으로 최근 새롭게 제안된 3코일 벨로우즈형 진동체(tri-coil bellows transducer, TCBT)를 이용하는 반이식형 인공중이(semi-implantable middle ear hearing device)를 위한 신호처리회로를 설계하였다. 설계된 반이식형 인공중이는 높은 효율을 가지는 유도결합 방법을 이용하여 귀 뒤편에 착용되는 체외기와 대응되는 피부 내측에 위치하는 체내기 간에 데이터를 전송한다. 귀 뒤 부위의 피부두께를 포함하는 반이식형 인공중이의 송수신 거리를 고려하여 송수신 코일과 신호처리 회로를 설계 및 구현하였다. 또한 데이터 전송 효율을 높이기 위하여, 전력을 충분히 증폭하기 위한 체외기의 출력부도 설계 하였다. 유도결합 방식을 이용한 반이식형 인공중이의 동작을 확인하기 위하여, PSpice를 이용하여 회로해석을 수행하였으며, 활용 가능한 크기의 신호처리 보드를 제작하여 그 성능을 검증하였다.

• 대한화학회지
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• 제42권5호
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• pp.512-518
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• 1998

정적 광산란, 동적 광산란, 점성도 실험을 통해 수용액에서 안정한 콜로이드를 형성하는 폴리에틸렌계 아이오노머 입자의 질량평균분자량$(M_w)$, 관성회전반경$(R-g)$, 2차 비리얼계수$(A_2)$, 유체역학적 반경$(R-H)$, 크기 분포, 고유 점성도 등이 측정되었다. 측정값을 토대로 아이오노머 측기 조성에 따른 입자의 특성과 용액 거동을 조사하였다. 카르복시산염의 함량이 높은 아이오노머는 chain stiffness, $R-H$, $R-g$가 크고, 아마이드기 함량이 높은 아이오노머는 크기가 작고, 고분자 사슬이 조밀한 구조의 입자를 형성하였다. 또한 CMC 부근의 매우 묽은 농도 영역에서 확산계수와 점성도의 농도 의존성은 아마이드기가 도입된 아이오노머와 그렇지 않은 아이오노머에서 서로 상반되는 경향성을 보여, 수용액에서 형성된 아이오노머 입자간의 상호 작용이 아이오노머에 도입된 측기 조성에 따라 크게 달라짐을 알 수 있었다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권8호
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• pp.404-410
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• 2006

Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 40[K] should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. In order to take advantage of a greater critical current density of high temperature superconducting (HTS) and considerably reduce the size and weight of the system, conduction-cooled HTS superconducting magnetic energy storage (SMES) at temperatures well below 40[K] should be investigated. This work focuses on the breakdown and flashover phenomenology of dielectrics exposed in air and/or vacuum for temperatures ranging from room temperature to cryogenic temperature. Firstly, we summarize the insulation factors of the magnet for the conduction cooled HTS SMES. And Secondly a surface flashover as well as volume breakdown in air and/or vacuum with two kind insulators has been investigated. Finally, we will discuss applications for the HTS SMES including aging studies on model coils exposed in vacuum at cryogenic temperature. The commercial application of many conduction-cooled HTS magnets, however, requires refrigeration at temperatures below 40[K], in order to take advantage of a greater critical current density of HTS and reduce considerably the size and weight of the system. The magnet is driven in vacuum condition. The need to reduce the size and weight of the system has led to the consideration of the vacuum as insulating media. We are studying on the insulation factors of the magnet for HTS SMES. And we experiment the spacer configure effect in the dielectric flashover characteristics. From the results, we confirm that our research established basic information in the insulation design of the magnet.

• 전기학회논문지
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• 제57권3호
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• pp.398-402
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• 2008

Recently, the development of superconducting fault current limiters (SFCLs) has been required as power demands increase in the power system. A distribution-level prototype resistive SFCL using coated conductor (CC) has been developed by Hyundai Heavy Industries Co., Ltd. and Yonsei University for the first time in the world. The ratings of the SFCL are 13.2kV/630A at normal operating condition. A novel non-inductive winding method is used in fabricating coils so there is almost zero impedance during normal operation. The distribution SFCL is cooled by sub-cooled liquid nitrogen $(LN_2)$ of 65K and 3 bar to enhance cryo-dielectric performance, critical current density, and thermal conductivity. In order to make reliable operation of an SFCL in real power systems, we monitored and controled its operation conditions by using supervisory control and data acquisition (SCADA) method. Thus, a monitoring system for the SFCL employing information technology (IT) is proposed and developed to be on the lookout for the operation conditions such as inside temperature, inside pressure, $LN_2$ level, voltage and current. Since operation temperature should be kept constant, bang-bang control for temperature feedback with a heater attached to the cold head of cryo-cooler is applied to the system. Short-circuit tests with prospective fault current of 10kA and AC dielectric withstand voltage tests up to 143kV for 1 minute were successfully performed at Korea Electrotechnology Research Institute. This paper deals with the development of a distribution level SFCL and its monitoring system for reliable operation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.199-201
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• 1996

The design and manufacturing results of a 16 tesla/45mm bore superconducting magnet is presented. The system consists of an 8.2 tesla(at 4.2K) outer NbTi coil with a bore I.D. of 261mm, a winding O.D. of 453mm and the length of 430mm which is connected in series with a 5.6 tesla(at 4.2K) middle and a 4.7 tesla(at 4.2K) inner insert coil constructed of multifilamentary $Nb_3Sn$. The middle and inner insert coil are reacted after winding. Also, epoxy impregnation is accomplished at $Nb_3Sn$ coils using a low viscosity crack resistant epoxy which is forced into the coil with a series of vacuum and over atmosphere pressure cycle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.92-94
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• 2003

The autotransformer currently used on the electric railway system is made of class A insulation material and uses the paper insulation method. As a power converter supplying power to the trolley wire, the autotransformer is one of critical equipment in the railway system. In the autotransformer, load irregularly changes and overload often occurs. These cause overheating of the autotransformer and facilitate deterioration of the autotransformer resulting in burnout accidents due to insulation breakdown. Also, the current autotransformer has poor insolation and short-circuit strength which often badly affect the service life of the transformer, and needs to improve its quality urgently. To overcome one of existing shortcomings of the mold transformer, manufacturers use epoxy resins that have superior flame retardancy to get rid of fro and explosion possibilities during accidents. Currently, new mold transformers are used in indoor distribution facilities with fire-fighting equipments. Coils molded in epoxy resins do not have their insulation performance compromised by humidity, dust, etc enabling easy inspection and maintenance. Comparing to the oil immersed transformer, the mold transformer does not have any concern about environmental pollutions by oil leak or replacement Therefore, to reduce breakdowns and improve reliability of the autotransformer, it is necessary to develop a new mold autotransformer with low loss suitable for our environment to suppress breakdowns of the autotransformer and improve the reliability. This study is about development of a low-loss mold autotransformer necessitated by reasons mentioned earlier.

• 한국환경과학회지
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• 제27권1호
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• pp.27-38
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• 2018

This study was carried out in the Bukhan River in the summer of 2014 and 2015, to identify the relationship between geosmin and the morphological changes in Anabaena. Identification of Anabaena was conducted using morphological and molecular analyses. Anabaena in this study was similar to Anabaena circinalis, A. crass, and A. spiroides with regard to regular coils, vegetative cell, akinete shape, and size, hoever, it was distinguishabl from A. crass and A. spiroides because of its larger trichome coil size. Additionally, the sequences of phycocyanin (PC) gene from Anabaena showed a 99% genetic similarity with A. circinalis NIES-1647 strain. The coil diameter of trichome ranged from 106 to $899{\mu}m$, and the diameter and abundance showed an insignificant positive correlation (r=0.544, p<0.05). The result of relationship between the coil diameter and the cell number per 360-degree rotation was kept at $33.8{\pm}5.2$ cells per $100{\mu}m$ diameter despite variable diameter. The average geosmin concentrations in 2014 and 2015 were investigated to be 99 ng/L and 35 ng/L, respectively. A. circinalis cell density contributed considerably to the change in geosmin and was positively correlated with geosmin concentration (2014; r=0.599, p<0.01, 2015; r=0.559, p<0.01). Our results suggest that geosmin and coil diameter could be estimated with the help of cell density.