• Journal of Advanced Navigation Technology
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• v.20 no.1
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• pp.45-52
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• 2016

In this paper, the method of interference analysis and its simulation have been suggested for the frequency sharing between aeronautical radio navigation systems and Link-16 platforms. In order to get the criteria for interoperability, the algorithm of interference analysis and protection ratio are derived to assure frequency sharing. Also the receiving power of wireless system has been illustrated with the help of radio propagation model of ITU-R Rec. P.1546 in VHF-UHF band. Finally the required receiving power or separation distance between DME/TACAN beacons and Link-16 ground station terminals has been considered based on system link budget in terms of evaluating interoperability as well as actual applications. As a result, if the suggested interference analysis and test set-up are applied to the field trial, it will lead to easy means to make a decision on interoperability over the existing incumbent systems.

• The Transactions of the Korea Information Processing Society
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• v.6 no.4
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• pp.1112-1119
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• 1999

Digital watermarking is to embed imperceptible mark into image, video, audio and text data to prevent the illegal copy of multimedia data, arbitrary modification, and also illegal sales of the copes without agreement of copyright ownership. The DCT(discrete Cosine Transforms) transforms of original image is conducted in this research and these DCT coefficients are expanded by Fourier series expansion algorithm. In order to embed the imperceptible and robust watermark, the Fourier coefficients(lower frequency coefficients) can be calculated using sine and cosine function which have a complete orthogonal basis function, and the watermark is embedded into these coefficients, In the experiment, we can show robustness with respect to image distortion such as JPEG compression, bluring and adding uniform noise. The correlation coefficient are in the range from 0.5467 to 0.9507.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.65.2-66
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• 2016

국제전기통신연합(ITU)는 지구상의 인류가 사용하는 전파의 공정한 사용과 국가별 분쟁조정을 위한 각종 회의를 주재하는 UN산하의 국제기관으로 현재 200 여 회원국이 참여하고 있다. 그리고 이를 위한 국제법 제정과 각종 연구결과와 기술문서 작성, 사전의견조율 등은 세계전파통신회의(WRC) 및 ITU산하의 관련 연구그룹(SG7)과 작업반(WP7D)에서 이루어진다. 따라서 기존에 제정된 ITU의 각종 기술문서(권고서, 보고서 등) 또는 의제 관련 연구결과를 WRC 의제 특성에 맞도록 결과를 도출하는 작업은 향후의 국제법 제정에 있어서 매우 중요한 변수로 작용한다. 이에 우리나라의 관련 주관청(미래부 전파정책국)에서는 매년 2회 개최되는 ITU-R 연구그룹회의에 정부 대표단을 파견하여, 과학업무(전파천문, 기상, 과학위성 등)와 관련된 기술문서 개정과 WRC의제 연구동향을 주시하면서 우리나라 이익과 관련된 사항에 대한 의견개진을 추진하고 있다. 특히 2019년 및 2023년에 개최되는 WRC-19, 23회의 의제를 위해, 태양활동의 감시, 원활한 기상위성운영, 80-1,000GHz 대역의 전파천문 보호 등에 대한 연구가 관련 연구그룹(SG7)에서 본격화되고 있으며, 이에 대한 지속적인 동향분석과 국내의 입장정리 또는 관련 ITU 기술문서에 대한 정부차원의 적절한 대응정책이 필요하다. 따라서 본 발표에서는 WRC-19 및 WRC-23의제와 관련하여 2016년 4월 5-8일에 스위스 제네바에서 진행되었던 ITU-R 제7연구반 산하작업반별 회의의 공유연구와 주요 결과를 소개하고, 향후 우리나라의 입장, 대응방안 등에 대해 알아보고자 한다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.6
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• pp.51-60
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• 2003

The watermarking is the technique that embeds or extracts the certain data without the change of the original data for the copyright protection of the multimedia contents. Watermark-embedded contents must not be distinguished by human's eye and must be robust to the various image processing and the intentional distortions. In this paper, we propose a new watermarking technique applied in the wavelet domain which has both the spatial and frequency information of a image. For both the robustness and the invisibility, the positions for embedding the watermark is selected with the multi-threshold. We search the similarity between highly correlated coefficients in the each subband and decide the mark space after verifying the significance in the specified subband. The similarity is represented by the coefficient difference between the subbands and its distribution is used in the watermark embedding and extracting. The embedded watermark can be extracted without the original image using the relationship of the subbands. By these properties the proposed watermarking algorithm has the invisibility and the robustness to the attacks such as JPEG compression and the general image processing.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.5
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• pp.22-28
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• 2003

This paper describes the frequency dependence of the grounding impedance. In order to propose the evaluation method of the transient response of powered grounding systems, the grounding impedances were measured with varying the frequency of incoming currents by way of the variable frequency inverter and band pass filter. The magnitude and phase of the grounding impedance were analyzed in the frequency range of 20 [Hz]∼2.1[kHz]. The grounding impedance were increased with increasing the frequency of the test current. The grounding impedance at the frequency of 2[kHz] in the actual 22.9[kV] substation grounding system was approximately 3 times as large as the 60[Hz] grounding impedance. It was found that the frequency dependence of the grounding impedance is mainly subject to the inductive reactance of the grounding conductors. As a result, it is critical to determine the shape and size of grounding grid reducing the resultant inductance in grounding systems for lightning surge protection.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.929-934
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• 2015

Because of the recent rapid advances in the development of ships with a larger proportion of electrical and electronic equipment, The usable frequency spread spectrum on ships is global trend. Therefore, concerns have been raised regarding the possible hazardous health effects of electromagnetic fields radiating from electronic devices. Although studies and investments on electro-magnetic fields in terrestrial areas are being conducted, they are not applied to a ship. In this paper, we measured electromagnetic fields in ship propulsion systems, and we analyzed the measured values against Korean and international standards. While the measured results satisfied the Korean standard, the Italian standard was not met in the switchboard area. However, the measured values were close to meeting the Italian standard. Therefore, further studies should be conducted for performing a comparative analysis of data in order to specify a standard of electromagnetic fields in propulsion systems that can be applied in the construction of government infrastructures.

• The Journal of Society for e-Business Studies
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• v.12 no.3
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• pp.75-93
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• 2007

This paper presents real-time online early fire warning systems developed for preserving cultural properties of Bulguksa which is a world heritage designated by UNESCO. The system is based on the ubiquitous sensor network employing 900MHz and 2.4GHz bands. In this paper, we analyze requirements that should be considered in building effective management systems of cultural heritages by using wireless sensor network. Finally, we introduce the architecture, sensor and network design, and software design of the fire warning systems which is an initial version of U-Bulguksa. The current version of systems has been operating in Bukguksa for a few months. U-Bukguksa project sponsored by National Information Society Agency is ultimately aimed at developing an integrated system of U-cultural heritage management and U-tourism. The former aims to conserve and manage intangible cultural properties by providing a variety of environmental information such as erosion, crack, and gradient as well as fire which are important causes of loss and damage in real-time and online. The latter refers to the intelligent tourism information and guidance systems allowing tourists to get the personalized content on cultural heritages and help guidance with mobile devices in Bulguksa.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.6
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• pp.1253-1259
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• 2005

This paper dealt with the development of surge protection devices (SPDs) that can protect high speed computer network devices from overvoltages caused by switching operations or lightning surges. The designed SPD is a form of hybrid circuit which is composed of a gas tube having large current diverting capability, high response bi-directional avalanche diodes, and fast recovery diodes to reduce insertion loss on high frequency domain. Surge protection and signal transmission characteristics of the fabricated SPD was tested according to the international standards, IEC 61000-4-5 and IEC 61643-21. From the test results, the SPD is satisfied with the international standards and the high cut-off frequency was 204 MHz. Also, the SPD showed a good performance without an insertion loss on a field test of 100 Mbps class Local Area Network.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.397.1-397.1
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• 2014

최근 방사선 진단 영역에 이용되고 있는 증감지는 입사된 방사선의 감도를 증가시키기 위해 형광체를 사용하고 있으며, 외부의 에너지를 흡수하여 빛으로 방출하는 역할을 한다. 이는 방사선 검출기, 디스플레이, 의료기기 등 다양한 분야에 활용되고 있다. 필름에 X선을 노출 할 경우 형광체의 사용 유무에 따라 방사선 흡수 효율에 영향을 미치며, 이는 발광 효율 및 감도에 주요한 인자로 작용한다. 현재 상용화되어 있는 형광체는 낮은 발광 효율로 인한 한계를 가지므로, 발광 효율 향상을 위하여 제작 구조에 대한 연구가 진행되고 있다. 이 중 반사막을 활용하는 연구가 활발히 진행되고 있다. 일반적으로 형광체의 제조를 위하여 보편적으로 이용하고 있는 스크린프린팅 방법에서 건조 공정을 수행 시 균일도가 감소하는 현상이 발생한다. 이러한 현상은 반사막의 증착을 불균일하게 만드는 원인으로 작용하고 빛의 산란을 초래하는 현상을 초래한다. 이에 본 연구에서는 증착 시 투명도 저하에 따라 반사율이 증가되는 반사막 성질을 가지며, 방수성 및 절연성과 같은 보호층 특성을 지닌 유기성 투명 박막 페를린에 대하여 연구하고자 한다. 본 연구에서는 화학적 증기 증착법(Chemical Vapor Deposition, CVD)을 이용하여 투명 필름의 상단에 페를린을 코팅한 시편과 코팅하지 않은 시편으로 구분하여 제작하였고, 상단에 스크핀프린팅 방법을 활용하여 형광체를 도포 하였다. 시편 제작 후 실험은 시편을 필름 상단에 위치시키고, 일반진단에너지 대역(Model-SF 80)의 X선을 조사하였다. 이 후 현상기(model-pro14)를 통해 현상된 필름에 나타난 광학적 농도(Optical Density, O.D)를 농도계(Fluke Biomedical Nuclear Associates Densitometer)로 측정하였는데, 불확실성을 줄이기 위하여 총 5회를 측정하여 그 중 2번째로 높은 값을 도출하였다. 측정 결과, 페를린을 코팅한 형광체에서는 1.71의 O.D 값이 측정되었고, 페를린을 코팅하지 않은 형광체에서는 1.43의 O.D 값이 측정되었다. 이를 이용하여 투명도를 산출한 결과 상대적으로 약 1.76% 차이가 나타났다. 이러한 결과는 페를린 활용 시 환자의 피폭 선량 저감화 및 해상력 개선을 도모할 수 있을 것으로 사료된다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.390-394
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• 2013

Observation satellites carrying high precision optical payload require extremely stringent pointing stability that may be violated in the presence of the disturbances corning from reaction wheels, cryocoolers or other actuating components onboard the satellite. The most common method to protect the sensitive payloads from external disturbances is implementation of vibration isolator. In this paper development of a single axis active vibration isolator using electromagnet and its performance in isolating micro-vibration is presented. The main components of the developed isolator are membrane structure providing the isolator with the required stiffness and an electromagnet for active control. The performance test results show that additional damping can be achieved by active control without degrading isolation performance in high frequency region and that the developed isolator can effectively isolate micro-vibration.