• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.510-510
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• 2012

반도체, 디스플레이, 태양광 등의 공정에서 사용되는 웨이퍼의 크기가 증가하고, 생산률이 플라즈마의 밀도에 비례한다는 연구 결과가 발표되면서 대면적 고밀도 플라즈마 소스 개발에 대한 연구가 활발히 진행되고 있다. 특히, ECR, ICP, Helicon plasma 등 고밀도 플라즈마 소스에 대한 관심이 높아지고 있다. 이에 따라, 여러 개의 ICP를 결합한 multiple ICP를 이용해 대면적 고밀도 플라즈마 소스 개발을 진행했다. Multiple ICP의 경우 각 ICP 소스에 같은 power (current)를 공급해야만 균일한 플라즈마 방전이 발생되어 균일도를 확보 할 수 있다. Current controller 같은 추가적인 장비를 설치하지 않고, power를 분배하는 transmission line을 coaxial 형태로 설계하고 같은 길이로 병렬 연결함으로써 각각의 ICP소스에서 균일한 플라즈마를 방전시킬 수 있었다. Power generator에서 보는 각 ICP의 total impedance는 각 ICP 소스의 impedance와 coaxial 형태의 transmission line의 characteristic impedance, frequency, 길이의 함수로 구할 수 있고, 이 total impedance가 일정하기 때문에 current가 균등하게 분배되어 각 ICP소스에 균등한 power 분배가 가능한 것이다. 실질적으로 ICP 소스의 impedance는 플라즈마 방전 유무에 따라 변화하기 때문에 일정하게 유지하는 것은 어렵다. Transmission line의 characteristic을 사용함으로써 ICP의 impedance의 변화에 상관없이 Total impedance를 일정하게 유지시킴으로써 균등한 power 분배가 가능하다는 것을 연구했다. Frequency는 13,56MHz, characteristic impedance를 $50{\Omega}$ (coaxial cable)으로 고정하고, ICP 소스의 플라즈마 방전 유무/antenna turn/소스 위치에 따른 total impedance를 transmission line의 길이에 따라 측정하고, 이를 이론값, 그래프와 비교하였다. 특정 length에서 플라즈마 방전 유무(ICP의 impedance 변화)와 상관없이 비교적 일정한 total impedance를 유지하는 것을 확인 했다. 이것은 특정 길이를 갖는 coaxial형태의 transmission line를 연결하면, total impedance는 플라즈마 방전 유무로 발생하는 ICP의 impedance 변화와 상관없이 일정하게 유지되어 각 ICP소스에 균등한 파워 분배가 가능하다는 것을 보여준 결과이다. 이것을 토대로 frequency에 따라(또는 characteristic impedance에 따라) 균등한 파워 분배가 가능한 coaxial 형태 transmission line의 특정 길이를 구할 수 있고, 대면적 소스에서 균등한 파워 분배를 위한 병렬연결에 적용할 수 있을 것이다.

• Earthquakes and Structures
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• v.13 no.2
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• pp.211-220
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• 2017

Observations from past strong earthquakes revealed that near-fault ground motions could lead to the failure, or even collapse of electricity transmission towers which are vital components of an overhead electric power delivery system. For assessing the performance and robustness, a high-fidelity three-dimension finite element model of a long span transmission tower-line system is established with the consideration of geometric nonlinearity and material nonlinearity. In the numerical model, the Tian-Ma-Qu material model is utilized to capture the nonlinear behaviours of structural members, and the cumulative damage D is defined as an index to identify the failure of members. Consequently, incremental dynamic analyses (IDAs) are conducted to study the collapse fragility, damage positions, collapse margin ratio (CMR) and dynamic robustness of the transmission towers by using twenty near-fault ground motions selected from PEER. Based on the bending and shear deformation of structures, the collapse mechanism of electricity transmission towers subjected to Chi-Chi earthquake is investigated. This research can serve as a reference for the performance of large span transmission tower line system subjected to near-fault ground motions.

• Carbon letters
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• v.25
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• pp.55-59
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• 2018

Carbon chain inserted carbon nanotubes (CNTs) have been experimentally proven having undergone pronounced property change in terms of electrical conductivity compared with pure CNTs. This paper simulates the geometry of carbon chain inserted CNTs and analyzes the mechanism for conductivity change after insertion of carbon chain. The geometric simulation of Pt doped CNT was also implemented for comparison with the inserted one. The results indicate that both modification by Pt atom on the surface of CNT and addition of carbon chain in the channel of the tube are effective methods for transforming the electrical properties of the CNT, leading to the redistribution of electron and thereby causing the conductivity change in obtained configurations. All the calculations were obtained based on density functional theory method.

• Journal of electromagnetic engineering and science
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• v.11 no.3
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• pp.156-160
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• 2011

We have proposed and analyzed an equivalent circuit for a magnetically coupled wireless power transmission (WPT) system between two loop resonators by considering its coupling coefficient and radiation-related parameters. A complete formulation is provided for all the necessary circuit parameters. The mechanism of radiation loss is sufficiently explained. The circuit and electromagnetic (EM) simulation results have been shown to be in good agreement. Based on the proposed circuit formulation, a specific load impedance for maximum WPT efficiency was found to exist. The proposed modeling of the WPT in terms of circuit characterizations provides sufficient insight into the problems associated with WPT.

• Journal of the Korea Society of Computer and Information
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• v.14 no.10
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• pp.101-110
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• 2009

The 6LoWPAN(IPv6 Low-power Wireless Personal Area Network) performs IPv6 header compression, TCP/UDP/IGMP header compression, packet fragmentation and re-assemble to transmit IPv6 packet over IEEE 802,15.4 MAC/PHY. However, from the point of view of security. It has the existing security threats issued by IP packet fragmenting and reassembling, and new security threats issued by 6LoWPAN packet fragmenting and reassembling would be introduced additionally. If fragmented packets are retransmitted by replay attacks frequently, sensor nodes will be confronted with the communication disruption. This paper analysis security threats introduced by 6LoWPAN fragmenting and reassembling, and proposes a re-transmission mechanism that could minimize re-transmission to be issued by replay attacks. Re-transmission procedure and fragmented packet structure based on the 6LoWPAN standard(RFC4944) are designed. We estimate also re-transmission delay of the proposed mechanism. The mechanism utilizes timestamp, nonce, and checksum to protect replay attacks. It could minimize reassemble buffer overflow, waste of computing resource, node rebooting etc., by removing packet fragmentation and reassemble unnecessary.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.176-187
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• 2015

DC bias will cause abnormal vibration of transformers. Aiming at such a problem, transformer vibration affected by DC bias has been studied combined with transformer core and winding vibration mechanism use multi-physical field simulation software COMSOL in this paper. Furthermore the coupling model of electromagnetic-structural force field has been established, and the variation pattern of inner flux density, distribution of mechanical stress, tension and displacement were analyzed based on the coupling model. Finally, an experiment platform has been built up which was employed to verify the correctness of model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1854-1868
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• 2018

A wireless body-sensor network (WBSN) refers to a network-configured environment in which sensors are placed on both the inside and outside of the human body. The sensors are much smaller and the energy is more constrained when compared to traditional wireless sensor network (WSN) environments. The critical nature of the energy-constraint issue in WBSN environments has led to numerous studies on the reduction of energy consumption of WBSN sensors. The transmission-power-control (TPC) technique adjusts the transmission-power level (TPL) of sensors in the WBSN and reduces the energy consumption that occurs during communications. To elaborate, when transmission sensors and reception sensors are placed in various parts of the human body, the transmission sensors regularly send sensor data to the reception sensors. As the reception sensors receive data from the transmission sensors, real-time measurements of the received signal-strength indication (RSSI), which is the value that indicates the channel status, are taken to determine the TPL that suits the current-channel status. This TPL information is then sent back to the transmission sensors. The transmission sensors adjust their current TPL based on the TPL that they receive from the reception sensors. The initial TPC algorithm made linear or binary adjustments using only the information of the current-channel status. However, because various data in the WBSN environment can be utilized to create a more efficient TPC algorithm, many different types of TPC algorithms that combine human movements or fuse TPC with other algorithms have emerged. This paper defines and discusses the design and development process of an efficient TPC algorithm for WBSNs. We will describe the WBSN characteristics, model, and closed-loop mechanism, followed by an examination of recent TPC studies.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.421-423
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• 2005

Power transmission lines have been playing a key role as the mainstay of national industry. When a power failure occurs, it can have severe effects on national security as well as national industry and economy. In this paper, we consider an insulator failure, which is one of the main causes of such a power failure. In spite of its importance, however, a shortage of manpower in the insulator maintenance field is getting more serious due to working environments with a high voltage and a high place. For this reason, a new active maintenance technique using a robot system is required to prevent such an insulator failure. In this paper, a new robot mechanism for insulator cleaning and inspection was developed. We confirmed its effectiveness through experiments.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.307-310
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• 2005

Most of the electric power in the power system of South Korea is flowing from the south area to the north area, Seoul, in the capital of South Korea. Almost of the needs of the electric power in the capital area are about 43% of the total loads and generation plants are mainly located in the south area of South Korea. As mentioned the earlier characteristic, transmission congestion is one of the important research issues. Because of the limits of the power flows from the south to the north which are anticipated to be increased more and more in the future, these congestion situations may cause a serious voltage stability problem in emergency of the power system. Accordingly, we are interested in an interruptible load control program so as to solve this problem in emergency. This problem can be solved by an interruptible load management in emergency, however, the systematic and effective mechanism has not been presented yet. In this paper, the algorithm of interruptible load management plan using the line sensitivity to the loads for the transmission congestion management in emergency is presented. The proposed method is applied to 6-Bus sample system and their results are presented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.8
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• pp.832-836
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• 2008

In this study, the electromagnetic coupling problem through narrow slit in an infinite conducting screen is considered for the case that the TM polarized plane wave is incident upon the slit. This study aims at explaining the mechanism of the maximum power transmission via the resonated slit using the equivalent circuit. It is shown that the transmitted power through the slit for the case of resonance corresponds to the power normally incident upon the conducting plane of the effective width 1/pi wavelengths, irrespective of the slit width. Some similarities between the maximum power transmissions observed in both the proposed structure and narrow slit in thick conducting screen are described from the viewpoint of equivalent circuit. In addition, it is found that, when the slit is resonated, the transmitted power equal to the scattered power.