• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.208-208
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• 2009

최근 광섬유 센서기술의 수요는 전 산업분야에 걸쳐 높아지고 있으며, 이에 비례하여 기업 간, 국가 간 경쟁이 첨예화되고 있다. 또한 소형화, 경량화, 고성능화 센서에 대한 요구도 높아지고 있어 종래의 각종 센서들의 형태와 개선을 위한 연구개발이 매우 활발하게 전개되고 있으므로 이를 대체할 수 있는 광섬유 센서의 수요가 급격히 늘어날 전망이다. 기존 침입자 감지 시스템은 태풍, 낙뢰, 폭설, 폭우 등의 기상변화나 지반 흔들림, 통행차량 진동 및 전자기 간섭 등에 영향을 받아 오작동, 오경보가 빈번히 발생된다. 이러한 문제의 해결책으로 광섬유 센서 케이블을 이용한 시스템이 대안으로 부각되고 있다. 현재 국내에서 군부대, 공항을 중심으로 펜스와 휴전선 철책에 힘입자 감지를 위하여 도입되고 있다. 광섬유 센서 케이블을 사용하는 광망경비시스템은 광섬유 센서 케이블을 그물망 형태(광망)로 만들어 경계 지역에 설치된다. 광망경비시스템의 원리는 광섬유에 광펄스를 입사시켜 순환시키는데 침입자가 광망을 절단하거나 외력을 가할 경우 발생되는 레일리 산란에 기인하는 후방산란과 접속점과 파단점에서 생기는 반사광을 OTDR(Optical Time Domain Reflectometer)로 검출하여 침입상황 및 침입위치를 탐지한다. 그러나 이러한 침입자 감지를 위한 광망경비시스템의 핵심부품인 광섬유 센서 케이블은 기존에 전량 해외수입에 의존하고 있는 실정이며, 지금까지 국내에서 생산하기 위한 제작 기술과 노하우가 초보단계에 머물러 있다. 이러한 광섬유 센서 케이블 제작에 있어서 중요한 부분이 패키징 기술이라 할 수 있다. 이는 광섬유 센서를 일반적인 피복 구조로 패키징하게 되면, 센서 고유의 특성이 패키징 과정과 운반과정, 포설과정에서 변하게 되고 센서로써의 신뢰성이 크게 저하된다. 본 연구에서는 힘입자 감지용 광섬유 센서 케이블의 설계와 제작을 위한 제조공법을 확립하고, 이를 이용해 제작된 광섬유 센서 케이블의 신뢰성 특성을 평가하였다. 설계 제작된 광섬유 센서 케이블의 구조는 멀티모드광섬유(MMF) 에 0.9 mm Tight buffer를 코팅하고, 광심선 주위에 아라미드 얀을 삽입시킨 후 고문자 수지를 적용하여 외부 피복 (jacket)을 하였다. 제작된 광섬유 센서 케이블의 외경 측정결과 기준치 ($2.95\;{\pm}\;0.03$ mm)를 모두 만족하였고, 850 nm 파장에서의 광 손실 측정 결과 4.0 dB/km 이하였다. 또한 주요 항목의 신뢰성 특성 시험결과, 인장강도는 8~10 kg의 인장력을 갖으며 온도순환시험 ($-30^{\circ}C\;{\sim}\;+75^{\circ}C$)에서의 광 손실은 0.6 dB 이하로 나타나 침입자 감지용 광섬유 센서 케이블로 적합함을 확인할 수 있었다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.1
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• pp.47-58
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• 2018

The heterogeneous cellular network (HCN) is most significant as a key technology for future fifth generation (5G) wireless networks. The heterogeneous network considered consists of randomly macrocell base stations (MBSs) overlaid with femtocell base stations (BSs). The stochastic geometry has been shown to be a very powerful tool to model, analyze, and design networks with random topologies such as wireless ad hoc, sensor networks, and multi- tier cellular networks. The HCNs can be energy-efficiently designed by deploying various BSs belonging to different networks, which has drawn significant attention to one of the technologies for future 5G wireless networks. In this paper, we propose switching off/on systems enabling the BSs in the cellular networks to efficiently consume the power by introducing active/sleep modes, which is able to reduce the interference and power consumption in the MBSs and FBSs on an individual basis as well as improve the energy efficiency of the cellular networks. We formulate the minimization of the power onsumption for the MBSs and FBSs as well as an optimization problem to maximize the energy efficiency subject to throughput outage constraints, which can be solved the Karush Kuhn Tucker (KKT) conditions according to the femto tier BS density. We also formulate and compare the coverage probability and the energy efficiency in HCNs scenarios with and without coordinated multi-point (CoMP) to avoid coverage holes.

• Analytical Science and Technology
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• v.16 no.5
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• pp.391-398
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• 2003

Basic research for the determination of boron content in biological sample has been carried out using the PGAA facility of the 24MW research reactor(HANARO). For investigation of characteristics for the measurement condition, neutron flux and its homogeneity were measured at irradiating geometry. The size of thermal neutron beam collimated from beam guide is $2{\times}2cm^2$ at the sample position. The neutron flux measured was the range of $1.0{\sim}6.5{\times}10^7n{\cdot}cm^{-2}{\cdot}s^{-1}$, and flux distribution from center within the radius of 4.5 mm and 9.0 mm was $5.77{\pm}0.71{\times}10^7n{\cdot}cm^{-2}{\cdot}s^{-1}$ and $4.68{\pm}1.64{\times}10^7n{\cdot}cm^{-2}{\cdot}s^{-1}$, respectively. Accordingly, sample size is adjusted within 10 mm for a homogeneous irradiation of high quality. Measurement system is designed to reduce the background source by Compton scattering and to improve the analytical sensitivity. To investigate the energy calibration and Compton suppression effect of gamma-ray counting system, the background conditions on both of Compton and single-mode were measured using NaCl standard. On the other hand, degree of spectral interference for sodium 472 keV peak as a matrix effect in the sample is established for an accurate boron analysis, and then boron content in three certified reference materials (NIST SRM 1570a, 1547, 1573a) was measured by using two modes and the results were compared with each other.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1085-1097
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• 2009

We present a structure and design method of the D8PSK modem compatible with the VDL mode-2 standard and performance test results of the developed modem. In VDL mode-2, the raised cosine filter is used only in the transmitter and a general low pass filter is used in the receiver. Consequently, we can not achieve ISI reduction but can have better spectrum characteristics. Although there is 1~2 dB performance degradation with an un-matched filter compared to that with a matched filter, it is more important to minimize adjacent channel interference in narrow band communications. The transmit signal is generated digitally to avoid the problems(I/Q imbalance and DC offset etc.) of analog modulators. In addition the digital down converter using digital IF sampling technique is adopted for the receiver. This paper contains the overall configuration, design method and simulation results based in part on the previously proposed structures and algorithms. It is confirmed that the modem transmits and receives messages successfully at a speed of max. 870 km/h over ranges of up to 310 km through the ground and in-flight communication tests.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.669-672
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• 2015

Recent Internet of Things (IoT, Internet of Things) that can be applied to various fields as the development of technology has been developed a lot of service and has been developed with the service also for crop management. To manage the essential elements of soil moisture in the crop growth but existing a direct person measuring the fluid point to carry the measuring instrument, if you take advantage of the WPAN (Wireless Personal Area Network) in this paper to manage sensor data, a fixed 3 points (30, 60, 90 cm) and can be managed can be scientifically analyzed the state of growth of the crop. Open field environment is utilized as it is less disturbance of the interference and the frequency of the radio frequency signal of the structure provides a relatively comfortable environment. Therefore, WPAN building and data transmission scheme of the minimum cost is to be developed. In addition, the operation to enter low power mode, the algorithm is necessary because a lot of restrictions on the power supply applied to the sensor nodes and the gateway is constructed in the open field. In the experiment, verifying the effectiveness by using a network configuration of each of the sensor nodes and the gateway, and provides a method for time synchronization of the operation and a low power mode. The study protocol for the RF communication with the LoRa and to enhance communication efficiency is needed in the future.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.1
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• pp.129-135
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• 2003

Optical fiber has many advantages, such as high reliability, long lifetime, immunity to the electromagnetic interference, high speed response and low cost. In this study, we proposed and developed an optical fiber impact and pressure sensor for prevention of accident which occurs in the automatic system or auto door. The principle of the sensor is to detect different optical intensity caused by variation of a speckle pattern due to the external perturbation. Speckle pattern appears at the end of a multimode fiber in which coherent beam propagates. The fabricated sensor in this study was tested. As a result of experiments, amplitude of the output signal isn't linear, but it has sufficient sensitivity for a sensor. Moreover, we can control sensitivity of the sensor by an amplifier at receiver. It has several advantages which are ability of detection at all point on the multimode fiber, large sensitive area, and many application areas for a sensing impact and pressure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.29-35
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• 2010

This paper studies causes of the L-1 blade damage of a low pressure turbine, which was found during the scheduled maintenance, in 500 MW fossil power plants. Many failures of turbine blades are caused by the coupling of aerodynamic forcing with bladed-disk vibration characteristics. In this study the coupled vibration characteristics of the L-1 turbine bladed-disk in a fossil power plant is shown for the purpose of identifying the root cause of the damage and confirming equipment integrity. First, analytic and experimental modal analysis for the bladed-disk at zero rpm as well as a single blade were performed and analyzed in order to verify the finite element model, and then steady stresses, natural frequencies and corresponding mode shapes, dynamic stresses were calculated for the bladed-disk under operation. Centrifugal force and steady steam force were considered in calculation of steady and dynamic stress. The proximity of modes to sources of excitation was assessed by means of an interference diagram to examine resonances. In addition, fatigue analysis was done for the dangerous modes of operation by a local strain approach. It is expected that these dynamic characteristics will be used effectively to identify the root causes of blade failures and to perform prompt maintenance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.291-298
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• 2013

In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.1
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• pp.39-45
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• 2015

Applications of smart sensors have been extended to safety systems in the aerospace, transportation and civil engineering fields. In particular, structural health monitoring techniques using smart sensors have gradually become necessary and have been developed to prevent dangers to human life and damage to assets. Generally, smart sensors are based on electro-magnets and have several weaknesses, including electro-magnetic interference and distortion. Therefore, fiber optic sensors are an outstanding alternative to overcome the weaknesses of electro-magnetic sensors. However, they require expensive devices and complex systems. This paper proposes a new, affordable and simple sensor system that uses a single fiber to monitor pressures at multiple-points. Moreover, a prototype of the sensor system was manufactured and tested for a feasibility study. Based on the results of this experimental test, a relationship was carefully observed between the bend loss conditions and light-intensity. As a result, it was shown that impacts at multiple-points could be monitored.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.5
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• pp.66-74
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• 2002

OFDM(Orthogonal Frequency Division Multiplexing)is a one of the nst promising digital modulation techniques adapted for Digital audio broadcasting or Digital TV since it is very robust against multipath fading channels. From 1997, since the OFDM technique was considered as the physical layer standard for the high data rate wireless LAN systems in the 5㎓ band, related studies have been studied actively. The key element to implement high data rate wireless LAN system using OFDM technique are IFFT and FFT modules. In this paper, new IFFT and FFT module are designed and implemented using current cut circuit based on the matrix-rounding process for the low-power consumptive operation and high-speed data processing. In addition to, we certify the available operation of the rounded IFFT/FFT module in the AWGN channel by using the BER performance simulation of IEEE 802.11TGa based OFDM modem with rounded IFFT/FFT module.