• 한국안전학회지
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• 제18권4호
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• pp.98-104
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• 2003

Various nondestructive evaluation (NDE) techniques have been studied to locate steel rebars of dowel, and to detect invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes. In this study, the aurhors developed 3-dimensional (3D) electromagnetic (EM) imaging technology to detect such damage and to identify exact location of steel rebars of dowel. The authors have developed sub-surface two-dimensional (2D) imaging technique using tomographic antenna array in previous works. In this study, extending the earlier analytical and experimental works on 2D image reconstruction, a 3D microwave imaging system using tomographic antenna array was developed, and multi-frequency technique was applied to improve quality of the reconstructed image and to reduce background noises. This paper presents the analytical expressions of numerical focusing procedures for 3D image reconstruction and numerical simulation to study the resolution of the system and the effectiveness of multi-frequency technique. Also, the design of 4?4 antenna array with switching devices is introduced as a preliminary study for the final design of whole array.

• 한국전기전자재료학회논문지
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• 제21권5호
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• pp.481-485
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• 2008

In stator windings of 6.6 kV rotating machine, corona discharge, surface discharge and internal discharge are caused mainly by internal voids and insulation degradation. Also, if partial discharge occurs in inner-part of stator windings, it will be happened electromagnetic pulses at wide frequency range. In case of discharge spark, electromagnetic pulse generated from discharge source, and we can detect it by using various RF resonators as an EM sensor. In order to detect these kind of electromagnetic sources, we have designed and fabricated planar patch sensor using CST MWS simulation, and also PD signals from artificial defected cable were measured by our proposed sensor. Furthermore, HFCT was used as a reference sensor and compared with our proposed new planar patch sensor.

• 한국군사과학기술학회지
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• 제17권1호
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• pp.57-63
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• 2014

In this paper, we have proposed a wide band antenna for manpack SDR(Software Defined Radio). The proposed antenna consists of feeding post, flexible gooseneck and two radiating elements composed of a upper and lower radiators. The upper radiator has a longer electrical length than the lower radiator in order to operate in the lower frequency. Also, the resonant frequency and impedance characteristics of the antenna can be adjusted independently for two radiators. Therefore, the proposed antenna can be achieved wide impedance bandwidth by the combination of two independent resonance modes. To analyze the characteristics of the antenna in the design process is employed the equivalent circuit theory and EM(Electro-Magnetic) simulation. The measurement results show that the proposed antenna have the sufficient wide bandwidth, above -3.4dBi of the gain and fairly good radiation pattern over the wide bandwidth.

• 전기학회논문지
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• 제60권4호
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• pp.811-816
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• 2011

In this paper, we propose a optimal design using the Evolution Strategy of a high gain $4\times4$ array antenna that have the resonant frequency of a 19.05GHz with 18.86GHz~19.26GHz bandwidth. The proposed array antenna structure is designed to be allocated equally electric power by microstrip patch power splitter. Thus the optimal array antenna with power splitter are determined by using an optimal design program based on the evolution strategy. To achieve this, an interface program between a commercial EM analysis tool and the optimal design program is constructed for implementing the evolution strategy technique that seeks a global optimum of the objective function through the iterative design process consisting of variation and reproduction. The simulation result of $4\times4$ array antenna is confirmed that the Gain is 19.36 dBi at resonance frequency 19.05GHz.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2299-2318
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• 2019

Location-aware networks are of great importance for both civil lives and military applications. Methods based on line-of-sight (LOS) measurements suffer sever performance loss in harsh environments such as indoor scenarios, where sensors can receive both LOS and non-line-of-sight (NLOS) measurements. In this paper, we propose a data association (DA) process based on the expectation maximization (EM) algorithm, which enables us to exploit multipath components (MPCs). By setting the mapping relationship between the measurements and scatters as a latent variable, coefficients of the Gaussian mixture model are estimated. Moreover, considering the misalignment of sensor position, we propose a space-alternating generalized expectation maximization (SAGE)-based algorithms to jointly update the target localization and sensor position information. A two dimensional (2-D) circularly symmetric Gaussian distribution is employed to approximate the probability density function of the sensor's position uncertainty via the minimization of the Kullback-Leibler divergence (KLD), which enables us to calculate the expectation step with low computational complexity. Moreover, a distributed implementation is derived based on the average consensus method to improve the scalability of the proposed algorithm. Simulation results demonstrate that the proposed centralized and distributed algorithms can perform close to the Monte Carlo-based method with much lower communication overhead and computational complexity.

• 한국물환경학회지
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• 제36권6호
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• pp.592-610
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• 2020

In South Korea, the concept of water environment was expanded to include aquatic ecosystems with the Integrated Water Management implementation. Watershed-scale modeling is typically performed for hydrologic component analysis, however, there is a need to expand to include ecosystem variability such that the modeling corresponds to the social and political issues around the water environment. For this to be viable, the modeling must account for several distinct features in South Korean watersheds. The modeling must provide reasonable estimations for peak flow rate and apply to paddy areas as they represent 11% of land use area and greatly influence groundwater levels during irrigation. These facts indicate that the modeling time intervals should be sub-daily and the hydrologic model must have sufficient power to process surface flow, subsurface flow, and baseflow. Thus, the features required for watershed-scale modeling are suggested in this study by way of review of frequently used hydrologic models including: Agricultural Policy/Environmental eXtender(APEX), Catchment hydrologic cycle analysis tool(CAT), Hydrological Simulation Program-FORTRAN(HSPF), Spatio-Temporal River-basin Ecohydrology Analysis Model(STREAM), and Soil and Water Assessment Tool(SWAT).

• 한국군사과학기술학회지
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• 제24권2호
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• pp.165-174
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• 2021

This study describes a method of measurement and verification of array manifold of uniform circular array antenna applicable to multistatic Passive Coherent Location(PCL) system using FM broadcasting. In an environment of outdoor test where FM broadcast signals are scattered, array manifold measurement methods using network analyzer and multi-channel digital receiver are introduced. Also, the descriptions and solutions for the test limits of each measurement method and the considerations affecting the measurement accuracy are presented. In addition, to verify the validity of the measured array manifold, the gain and phase difference were compared with the array manifold data obtained by EM simulation, and the effectiveness and accuracy of the measured array manifolds were compared and analyzed by estimating the direction of arrival of the FM broadcast signal received from the multistatic PCL system.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1429-1435
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• 2021

The temperature distribution of an electromagnetic pump was analyzed with a flow rate of 1380 L/min and a pressure of 4 bar designed for the sodium thermo-hydraulic test in the Sodium Test Loop for Safety Simulation and Assessment-Phase 1 (STELLA-1). The electromagnetic pump was used for the circulation of the liquid sodium coolant in the Intermediate Heat Transport System (IHTS) of the Prototype Gen-IV Sodium-cooled Fast Reactor (PGSFR) with an electric power of 150 MWe. The temperature distribution of the components of the electromagnetic pump was numerically analyzed to prevent functional degradation in the high temperature environment during pump operation. The heat transfer was numerically calculated using ANSYS Fluent for prediction of the temperature distribution in the excited coils, the electromagnet core, and the liquid sodium flow channel of the electromagnetic pump. The temperature distribution of operating electromagnetic pump was compared with cooling of natural and forced air circulation. The temperature in the coil, the core and the flow gap in the two conditions, natural circulation and forced circulation, were compared. The electromagnetic pump with cooling of forced circulation had better efficiency than natural circulation even considering consumption of the input power for the air blower. Accordingly, this study judged that forced cooling is good for both maintenance and efficiency of the electromagnetic pump.

• 마이크로전자및패키징학회지
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• 제28권4호
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• pp.97-101
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• 2021

본 연구에서는 실험 설계법을 통해 인터포저에서 Through Silicon Via (TSV) 및 Redistributed Layer (RDL)의 구조적 변형에 따른 삽입 손실 특성 변화를 확인하였다. 이때 3-요인으로 TSV depth, TSV diameter, RDL width를 선정하여, 구조적 변형을 일으켰을 때 400 MHz~20 GHz에서의 삽입 손실을 EM (Electromagnetic) tool Ansys HFSS(High Frequency Simulation Software)를 통해 확인하였다. 반응 표면법을 고려하였다. 그 결과 주파수가 높아질수록 RDL width의 영향이 감소하고 TSV depth와 TSV diameter의 영향이 증가하는 것을 확인했다. 또한 분석 범위 내에서 RDL width를 증가시키면서 TSV depth를 감소시키고 TSV diameter를 약 10.7 ㎛ 고정하는 것이 삽입 손실을 가장 최적화 시키는 결과가 관찰되었다.

• 항공우주산업기술동향
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• 제6권2호
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• pp.40-50
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• 2008

대부분의 위성 프로그램 개발공정은 임무해석, 열, 구조, 전장박스 설계, 조립, 검증, 운용 등으로 나누어지며, 이는 각 서브시스템에 대한설계, 개발, 검증 등의 공정을 거쳐 이루어진다. 이 같은 공정을 수행하기 위하여 위성 개발자들은 막대한 비용, 개발기간을 소요하며 그리고 각 개발공정마다 위험을 수반하여 수행하고 있다. 이에 소요비용의 감소와 개발기간의 단축, 저 위험도의 위성 프로그램을 위하여, 위성 모사 환경시스템이 개발되어 사용되어 왔다. 초기의 위성 모사 환경시스템들은 각 서브시스템의 단편적인 검증만을 위하여 개발되어 그 유용성이 한정되어 사용되어 왔다. 하지만 현재의 위성수요자 들은 획기적인 저 비용, 개발기간단축, 저 위험도의 위성 프로그램을 점점 더 강하게 요구하고 있으며, 이에 발맞추어 위성 개발자들은 위성 전체 개발공정 개선 등의 각고의 노력을 통하여 일정부분 성과를 이룩하였다. 하지만 이는 수요자가 요구하는 만큼의 성과는 충족하지 못하였고, 이에 위성 개발자들은 위성 전체 개발 공정에 대한 근본적인 재고를 통하여 획기적으로 비용을 절감하고, 위험도를 낮추며, 개발기간을 단축할 수 있는 방법을 제시하였다. 이는 기존의 사용되어 온 단편적인 위성모사 환경시스템을 설계단계에서부터 개발, 검증 기간에 공통적으로 적용할 수 있는 모사 환경시스템을 개발하여 위성 프로그램에 적용하는 것으로, 본 논문에서는 근래에 각 위성제작사에서 개발하여 사용하고 있는 모사 환경시스템의 종류와 현재까지의 개발 상황을 알아보고 현재 우리가 나아갈 바를 제시하였다.