• Journal of Sensor Science and Technology
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• v.9 no.3
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• pp.203-207
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• 2000

The sensitivity of ISFET glucose sensor is improved by employing amperometric actuation method. However, this method takes long time to recover the primary output voltage after measurement because of slow migration of the hydrogen ion between internal and external sensing membranes. Consequently, such a recovery-time delaying problem is one of obstacles to a practical use. In this paper, a new method is proposed to control the concentration of hydrogen ion in internal membrane, which applies a reduction potential to the working electrode for supplying hydroxide ion. Experimental results show that the recovery-time was reduced within 2 minute against decades minute of conventional method.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.40-48
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• 2000

A fuel cell is an electrochemical device continuously converting the chemical energy in a fuel and an oxidant to electrical energy by going through an essentially invariant electrode-electrolyte system. Phosphoric acid fuel cell employs concentrated phosphoric acid as an electrolyte. The cell stack in the fuel cell, which is the most important part of the fuel cell system, is made up of anode where oxidation of the fuel occurs cathode where reduction of the oxidant occurs; and electrolyte, to separate the anode and cathode and to conduct the ions between them. Fuel cell performance is associated with many parameters such as operating and design parameters associated with the system configuration. In order to understand the design concepts of the phosphoric fuel cell and predict it's performance, we have here introduced the simulation of the fuel-cell stack which is core component and modeled in a 3-dimensional grid space. The concentration of reactants and products, and the temperature distributions according to the flow rates of an oxidant are computed by the help of a computational fluid dynamic code, i.e., FLUENT.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.194-195
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• 2013

초음속 공기 플라즈마 환경을 모사할 수 있는 0.4 MW급 Enhanced Huels형 초음속 공기 플라즈마 발생 장비가 2012년에 전북대학교에 설치 완료되었다. 초음속 공기 플라즈마 시험장비는 대기권으로 reentry 할 수 있는 비행체의 열차폐체 시험평가를 주목적으로 개발되었으며, 핵융합장치용 고온 내열체 소재개발에도 활용될 예정이다. 분절형 아크 플라즈마 토치는 전극부식에 의한 오염도를 적으면서 고출력의 안정적인 플라즈마를 발생시키며, 일반적인 직류 토치로는 얻을 수 없는 초고엔탈피 플라즈마 열유동을 얻을 수 있는 특징이 있다. 구축된 장비는 최대 직류 출력 1,200 kW의 DC 전원공급장치, 0.4 MW급의 분절형 아크 플라즈마 토치, ${\phi}1.5m{\times}2m$ 크기의 진공쳄버, 1 MW의 냉각 능력을 갖춘 디퓨저와 열교환기, 진공 용량 $100m^3$/min의 진공펌프 9대, 88 g/s의 공기유량에서 NOx를 50,000 ppm에서 100 ppm으로 저감할 수 있는 후처리 시스템, 4 bar 15 g/s의 공기를 공급할 수 있는 가스 공급장치, 30 bar 600 lpm의 저전도수와 4 bar 560 lpm의 일반수를 공급할 수 있는 냉각수 공급장치로 구성되어 있다. 초음속 공기 플라즈마의 발생 특성을 시험하기 위해 플라즈마 발생 조건으로 토치공급전력 350 kW와 410 kW, 토치 공기 공급 유량 16.3 g/s, 토치 내부압력 3.9~4.2 bar, 챔버압력 40 mbar으로 시험을 수행하였다. 발생된 플라즈마 상태를 진단하기 위해 속도는 쇄기 탐침기, 열유속은 Gardon 게이지, 엔탈피와 토치 효율은 토치의 공급전력과 냉각수에 의한 손실 전력으로 각각 측정하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.1010-1015
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• 2012

In this study, a thin-film thermo-electrochemical cell that directly converts waste thermal energy into electrical energy was fabricated. Electrical conductivity of conducting carbon fiber, which was used as flexible electrode, was increased through coating of carbon nanotube, and resistance of the CNT-coated fiber electrode was not changed even after bending test with various curvatures. Maximum output power of the thermocell was increased quadratically with the temperature difference, and showed a value of about 2.5 mW/kg at temperature difference of $3.4^{\circ}C$. As a result of discharge test for 12 hours, it is confirmed that the cell can operates continuously. And thin-film thermocell wrapped around a pipe with hot liquid flowing within was demonstrated. Internal resistance of the cell was decreased with various curvature of heat pipe, and maximum output power was increased by 30 %. Therefore, the cell can be applied to various heat source.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.5
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• pp.23-32
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• 2001

Electrical impedance tomography (EIT) is a relatively new imaging modality in which the resistivity (conductivity) distribution of the unknown object is estimated based on the known sets of injected currents and measured voltages on the surface of the object. In this paper, we propose a dynamical EIT reconstruction algorithm based on the regularized extended Kalman filter(EKF). The EIT inverse problem is formulated as dynamic equation which consists of the slate equation and the observation equation, and the unknown state(resistivity) is estimated recursively with the aid of the EKF. In doing so, the generalized Tikhonov regularization technique is employed in the cost functional to mitigate the ill-posedness characteristics of the inverse problem. Computer simulations for the 16-channel synthetic data are provided to illustrate the reconstruction performance of the proposed algorithm.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.847-853
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• 2016

Here has been examined a 3-dimensional computational fluid dynamics (CFD) modeling in order to investigate the performance analysis of proton exchange membrane (PEM) fuel cells with serpentine flow fields. The present CFD model considers the isothermal transport phenomena in a fuel cell involving mass, momentum transport, electrode kinetics, and potential fields. Co-current flow patterns for a PEMFC are considered for various geometries in the single straight cell. Current density distribution from the calculated distribution of oxygen and hydrogen mass fractions has been determined, where the activation overpotential has been also calculated within anode and cathode. CFD results showed that profiles differ from those simulations subjected to each the calculated activation overpotential. It is interesting that the present serpentine flow field shows the specific distribution of current density with respect to the aspect ratio of depth to width and the ratio of reaction area for various serpentine geometries. Simulation results were considered reasonable with the other CFD results reported in literature and global comparisons of the PEMFC model.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.6
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• pp.72-78
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• 1998

An optical modulator Ti:LiNbO$_3$optical waveguide and CPW electrode structure were fabricated. The optical modulator was packaged using components such as ferrules, dirmy LN block and glass, vibration and shock absorbption pad, and alumina feeder through processings of pigtailing. Au wire bonding, epoxing, SMA connecting, sealing. The electrical and optical characteristics were measured after packaging. The electrical properties of S$_{21}$ and S$_{11}$ were obtained as 9.8 GHz at -3 dB and -8.9dB at 14.4GHz, respectively. Optical waveguide prepared met requirements for a single mode at a 1550nm wavelength range. Insertion loss was 4.3dB at room temperature after packaging, and was varied 4.3~6.4dB at various temperatures, 5~45$^{\circ}C$. E-O bandwidth measurement showed 3dB optical response at 7.8GHz, which means that it is applicable for 10Gbps optical communicationon

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.725-729
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• 2015

Organic light emitting diodes (OLEDs) are regarded as the next generation display and solid-state lighting due to their superb achievements from extensive research efforts on improving the efficiency and stability of OLEDs in addition to developing new materials. Herein, efficient green phosphorescent OLEDs were obtained by using hexaazatrinaphthylene (HAT) derivatives as a hole injection layer. External quantum and current efficiencies of OLEDs were enhanced from 8.8% and 30.8 cd/A to 13.6% and 47.7 cd/A, respectively by inserting a thin layer of HAT derivatives between the ITO and hole transporting layer. The enhancement of OLEDs was found to be originated from the inserted HAT derivatives, which resulted in the optimized hole-electron balance inside the emission layer.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.2 s.314
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• pp.18-23
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• 2007

Intra-body communication' is a wireless communication technology that uses a body as a transmission medium for electrical signals. Generally, an 'earth ground' is used to create an electric field for operating the system; however this operating method could not apply to telemetry for implanted neural prosthetic devices. So this paper suggests a newly designed intra-body communication for neural prosthetic devices. A floating system which has a couple of electrodes with body was studied to remove an influence of the 'earth ground'. We found that 10MHz is the most suitable carrier frequency in skin experiments and over 3MHz in subcutaneous experiments. The system has been applied to a current stimulator circuit for cochlear implant that uses pulse width modulation (PWM) method at 480kbps rate successfully.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2206-2207
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• 2008

본 논문에서는 분전반에서의 화재 위험 요소와 화재위험 요소에 대한 현장 실태조사 결과를 분석하였다. 분전반에서의 화재 위험 요소는 크게 전기적 요인, 환경적 요인, 물리적 요인으로 나눌 수 있으며 전기적 요인으로는 단락, 과부하(과전류), 접촉불량, 전류 불평형 등이 있으며 환경적 요인으로는 수분(염분 등), 먼지(분진, 목분, 철분 등), 온도(고온) 등에 의한 절연파괴, 기기 손상, 오동작 등이 있다. 물리적 요인으로는 기계적인 진동이나 충격 등에 의한 전기적 접속부의 이완에 의한 발열 등을 들 수 있다. 이러한 화재 위험 요인에 대하여 현장실태조사를 실시한 결과, 일부 분전반에서 내부에 먼지 등 이물질이 차단기, 전선, 단자대 등의 표면에 부착되어 있음을 확인할 수 있었으며 수분이나 염분 등의 영향으로 전극간 절연물 표면의 열화로 화재가 발생할 가능성이 있다. 또한, 적외선 열화상 분석결과, 일부 차단기 단자에서 국부 발열이 관측되었으며, 부하 분담의 불평형에 의한 발열도 확인되었다. 이러한 위험요인에 의한 화재 예방을 위하여 규정된 전선 굵기의 사용과 적정 체결압력의 확보, 상간 전류 불평형을 줄이기 위한 부하 분담의 조정이 필요하다. 향후, 분전반에서의 전기화재, 감전사고 등 전기재해의 예방을 위하여 지속적이고 체계적인 유지관리는 물론 사고 발생 전에 이상 징후를 사전에 감지하여 조치를 취할 수 있도록 하는 기술의 개발과 현장 적용이 요구된다.