• Resources Recycling
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• v.11 no.5
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• pp.30-33
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• 2002

Recently in the progress of electronic equipment, power transformer was considered an important part. To make power transformer with miniaturization, lightening, low Power, we need a high efficiency core material. In this paper, we added $V_2$$O_{5}$ and $CaCo_3$ to Mn-Zn Ferrite to make a high efficiency, low loss core material. The compositions are MnO : ZnO : $Fe_2$$O_3$=37 : 11 : 52 mol%. They were sintered at 1250 for Three hours. Initial permeability was measured at 0.1 MHz. At 200 mT, Power loss was measured by temperature changing at 25 KHz, 50 KHz, 100 KHz. When we added $V_2$$O_{5}$ and $CaCo_3$, 0.08 wt%, 0.05 wt% respectively, we get 415 ㎾/㎥ at 200 mT, 100 KHz, $60^{\circ}C$. We can reduce eddy current loss as a main loss of high frequency by addition of a little mount of $V_2$$O_{5}$ $CaCo_3$. So we can decrease the power transformer's power loss.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.37-43
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• 2017

This review investigates the basic principle of physical interactions and failure mechanisms introduced in the materials and inner parts of semiconducting components under electromagnetic pulses (EMPs). The transfer process of EMPs at the semiconducting component level can be explained based on three layer structures (air, dielectric, and conductor layers). The theoretically absorbed energy can be predicted by the complex reflection coefficient. The main failure mechanisms of semiconductor components are also described based on the Joule heating energy generated by the coupling between materials and the applied EMPs. Breakdown of the P-N junction, burnout of the circuit pattern in the semiconductor chip, and damage to connecting wires between the lead frame and semiconducting chips can result from dielectric heating and eddy current loss due to electric and magnetic fields. To summarize, the EMPs transferred to the semiconductor components interact with the chip material in a semiconductor, and dipolar polarization and ionic conduction happen at the same time. Destruction of the P-N junction can result from excessive reverse voltage. Further EMP research at the semiconducting component level is needed to improve the reliability and susceptibility of electric and electronic systems.

• Resources Recycling
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• v.27 no.1
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• pp.45-54
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• 2018

This study aimed to investigate the effects of mechanical factors such as agitation speed and air rate in fly ash flotation. Specifically, we used thermal power plant fly ash with unburned carbon content of 3.4 to 3.7%. The effect of pH, agitation speed, collector dosage, and frother dosage - the key factors of froth flotation - showed unburned carbon recovery and unburned carbon content of 63% and 34%, respectively, when the dosage of safflower oil used as collector was 800 g/ton, pH was 7, agitation speed was 1,200 rpm, and frother dosage was 400 g/ton. The SEM/EDS analysis of fly ash in that case indicated that the spherical fly ash particles lowered the unburned carbon content as they floated with the air bubbles without being dissolved in the unburned carbon or settled in the ore solution. The other experiment of changing the mechanical factors such as agitation speed and air rate resulted in unburned carbon recovery and unburned carbon content of 74% and 67%, respectively, at air rate of 8 L/min and agitation speed of 900 rpm. The recovery and unburned carbon content increased as the low agitation speed and additional air injection decreased the strength of the eddy current in the ore solution and consequently prevented the floating of fine fly ash particles with unburned carbon. In addition, the recovery rate and unburned carbon increased further to 80% and 70%, respectively, showing the best performance when the agitation speed and air rate were lowered to 800 rpm and 6 L/min, respectively.

• Composites Research
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• v.30 no.3
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• pp.181-187
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• 2017

The effect of nanoscopic and microscopic Fe, $Fe_3O_4$, and Ni particles and their shapes and substrate materials on the heating behavior of thermoplastic polyurethane (TPU) adhesive films was investigated via induction heating. The heat generation tendency of $Fe_3O_4$ particles was higher than that shown by Fe and Ni particles in the TPU adhesive films. When the Fe and Ni particle size was larger than the penetration skin depth, the initial heating rate and maximum temperature increased with an increase in the particle size. This is attributed to the eddy current heat loss. The heating behavior of the TPU films with Ni particles of different shapes was examined, and different hysteresis heat losses were observed depending on the particle shape. Consequently, the flake-shaped Ni particles showed the most favorable heat generation because of the largest hysteresis loss. The substrate materials also affected the heating behavior of the TPU adhesive films in an induction heating system, and the thermal conductivity of the substrate materials was determined to be the main factor affecting the heating behavior.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.145-150
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• 2020

Water wall tube is one of the major factors consisting of a fluidized bed boiler and it plays very important role for the generation of electricity within the boiler. But these water wall tubes within the fluidized bed boiler are subject to the ware and corrosion caused by the high temperature gas and the flowing medium. If water leak is occurred, the secondary damage by the water leak will occur. As a result of that, the power generation efficiency decreases noticeably. Therefore, the maintenance of the water wall tube is very important. In this study, we designed a exciter sensor based on simulation and composed a remote field eddy current system for the defect evaluation of the outer water wall tube. Starting from the shape design of exciter, we conducted simulations for various design factors such as the water wall tube size, material, frequency, lift-off and so on. Based on the results, we designed the optimum exciter sensor for the water wall tube test within the fluidized bed boiler.

• Investigative Magnetic Resonance Imaging
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• v.13 no.1
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• pp.15-21
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• 2009

Purpose : A method to estimate a real k-space trajectory based on a circuit model of the gradient system is proposed for spiral imaging. The estimated k-space trajectory instead of the ideal trajectory is used in the reconstruction to improve the image quality in the spiral imaging. Materials and Methods : Since the gradient system has self resistance, capacitance, and inductance, as well as the mutual inductance between the magnet and the gradient coils, the generated gradient fields have delays and transient responses compared to the input waveform to the gradient system. The real gradient fields and their trajectory in k-space play an important role in the reconstruction. In this paper, the gradient system is modeled with R-L-C circuits, and real gradient fields are estimated from the input to the model. An experimental method to determine the model parameters (R, L, C values) is also suggested from the quality of the reconstructed image. Results : The gradient fields are estimated from the circuit model of the gradient system at 1.5 Tesla MRI system. The spiral trajectory obtained by the integration of the estimated gradient fields is used for the reconstruction. From experiments, the reconstructed images using the estimated trajectory show improved uniformity, reduced overshoots near the edges, and enhanced resolutions compared to those using the ideal trajectory without model. Conclusion : The gradient system was successfully modeled by the R-L-C circuits. Much improved reconstruction was achieved in the spiral imaging using the trajectory estimated by the proposed model.

• Journal of the Korea Society of Computer and Information
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• v.16 no.5
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• pp.61-71
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• 2011

To measure the fatigue of metallic objects at high speed vibration while non-contact precision displacement measurement on how to have a lot of research conducted. Noncontact high-speed vibration detection sensor of the eddy current sensors and laser sensors are used, but it is very expensive. Recently, High-speed vibrations detection using an inexpensive inductive sensor to have been studied, but is still a beginner. In this paper, a new design of an inexpensive inductive proximity sensor has been suggested in order to measure high frequency dynamic displacements of metallic specimens in a noncontact manner. Detection of the existing inductive sensors, detection, integral, and amplified through a process to detect the displacement noise due to weak nature of analog circuits and integral factor in the process of displacement detection is slow. The proposed method could be less affected by noise, the analog receive and high-speed signal processing is a new way, because AD converter (Analog to Digital converter) without using the vibration frequency signals directly into digital signals are converted. In order to evaluate the sensing performance, The proposed sensor module using non-contact vibration signals were detected while shaker vibration frequencies from 30Hz to 1,100 Hz at intervals of vibrating metallic specimens. Experimental results, Vibration frequency detection range of the metallic specimins within close proximity to contactless 5mm could be measured from DC to 1,100Hz and vibration amplitude of the resolution was $20{\mu}m$. Therefore, the proposed non-contact inductive sensor module for precision vibration detection sensor is estimated to have sufficient performance.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.208-218
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• 1992

Analytic solutions for the gradient of surface elevation and vertical profiles of velocity driven by the wind stress in the one-dimensional rectangular basin were obtained under the assumption of steady-state. The approach treats the bottom frictional stress $\tau$$_{b}$ as known and includes vertically varying eddy viscosity $textsc{k}$$_{M}$, which is constant, linear and quadratic of water depth. When the $\tau$$_{b}$ is param-terized with surface stress, depth averaged velocity and bottom velocity, the result shows the relation of the no-slip bottom velocity condition and the bottom frictional stress $\tau$$_{b}$. The results of a mode splitted, (x-$\sigma$) coordinate, numerical model were compared with the derived analytic solutions. The comparison was made for the case such that $textsc{k}$$_{M}$ is the constant, linear and quadratic function of water depth. In the case of constant $textsc{k}$$_{M}$, the gradient of surface elevation and vertical profiles of velocity are discussed for a uniform depth, a mild slope and a relatively steep slope. When $textsc{k}$$_{M}$ is a linear and quadratic function of water depth, the vertical structures of velocities are discussed for various $\tau$$_{b}$. The result of the comparison shows that the vertical structure of velocities depends not only on the value of $textsc{k}$$_{M}$ but also on the profile of $textsc{k}$$_{M}$ and bottom stress $\tau$$_{b}$. Model results were in a good agreement with the analytic solutions considered in this study.his study.y.his study.

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.131-137
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• 2004

For the aim of thin electromagnetic wave absorbers used in mobile telecommunication frequency band (0.8-2.0㎓), we investigate high-frequency magnetic, dielectric and microwave absorbing properties of iron particles dispersed in rubber matrix in this study. The major experimental variables are particle shape (sphere and flake) and initial particle size (in the range 5-70 $\mu\textrm{m}$) of iron powders. High value of magnetic permeability and dielectric permittivity can be obtained in the composites containing thin plate-shape (flake) iron particles (of which thickness is less than skin depth in ㎓frequency), which can be produced by mechanical forging of spherical iron powders using an attrition mill. This result is attributed to the reduction of eddy current loss (increase of permeability) and the increase of space charge polarization (increase of permeability). The optimum initial particle size is found to be about 10 $\mu\textrm{m}$ for the attainment of the material parameters (particularly, real part of complex permeability) satisfying the wave impedance matching. With the iron powders controlled in size and shape as absorbent fillers in rubber matrix, the thickness can be reduced to about 0.7mm with respect to -5㏈ reflection loss (70% power absorption) in mobile telecommunication frequency band.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.129-134
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• 1996

1차 년도 G-7 개발 과제로 수행된 자기 공명 진단 장치 (Magnetic Resonance Imaging System)의 개발 내용을 간략히 소개하였다. 성공적인 IT Compact 자기 공명 진단 장치의 완성을 위해 일차적으로 (1)RF (고주파), Gradient(경사 자계), Spectrometer 등의 Hard-ware 관련 MRI 핵심부분, (2) RF, Gradient, Spectrometer, Magnet 등의 각 Sub-system을 연결, 조합, 조정하여 하나의 체계적인 시스템으로 통합하고 운영하는 과정(System Integration), (3)사용자와 시스템을 연결하는 User Interface, Data Base Management, Real time 운영 SW 등과 (4)임상에 적용하여 구체적인 성능과 효용성을 확인하는 기술 등에 대하여 집중 연구하였다. 개발 방법은 (1)지난 16년간 국내에 축적 된 연구 개발 인력들을 최대한 활용하고 (2)연구 개발을 국제화 시켜 필요한 경우 부분별로 개발 인력을 해외에서 보완하고 (3)소수 정예 전문 인력 주의와 요소 기술 또는 중요 부품을 경쟁성 검토 후 필요 시 Out-sourcing 활용으로 최저의 비용으로 개발 기간을 최소화 하는 데 두었다. 개발된 1.0Tesla자기 공명 영상 장치는 미국 물리 학회에서 규격화한 Phantom및 임상 적용을 통하여 서울대 의대 연구 팀과 지속적으로 성능을 평가해 왔다. 개발된 시스템의 해상도는 $256{\times}256$ head 영상에서 1mm 이 하의 해상도를 가짐을 resolution phantom 을 통하여 확인할 수 있었고, $512{\times}512$ 영상에서 는 약 0.5 mm 의 물체를 분리 해냄으로써 외제 시스템들 보다 우수하게 평가 되었다. 차폐 경사코일의 Eddy current영향은2%이내로 촬영 시 영향은 거의 무시할 수 있었다. 또한, 개발된 영상 기법들, 즉 Multislice/Multi Echo, Oblique angle imaging, 64 Echo train을 갖는 고속 촬영 기술들이 자기 공명 장치에 장착되어 임상 적용에 문제가 없도록 하였다. 또한 20mT/m/Amp의 강력한 능동 차폐 경사 자계 코일(Active Shield Gradient Coil)을 기본 사양으로 하고, 수신단을 최대 6개로 확장토록 하여 2차년도의 초고속 촬영 기법(EPI) 및 Phased Array 코일 촬영이 가능토록 하였다. 1차 년도 개발 과제 수행 결과와 향후 개발 과제를 바탕으로 최종 목표인 국제 경쟁력이 있는 자기 공명 진단 장치 즉 기능과 영상의 질은 선진국 제품과 동일하거나 우수하되, 저가격을 구현한 상용화 제품이 완성되어, 첨단 의료기기로서 산업 구조 고도화에 기여하고 수입대체 뿐만 아니 라 수출을 통한 국익 창출과 국가의 기술을 통한 위상 제고에 기여되길 기대한다.