• Journal of Sensor Science and Technology
• /
• v.9 no.1
• /
• pp.76-82
• /
• 2000

PTC thermistors with multilayer structure were fabricated by internal electrode bonding technique in order to realize low resistance. MLPTC (Multilayer Positive Temperature Coefficient) possess various features, such as small size, low resistivity and large current. We describe the effect of additives on the PTC characteristics, voltage - current characteristics, temperature dependence of resistance and complex impedance spectra as a function of frequency range 100 Hz to 13MHz to determine grain boundary resistance. It was found that MLPTC thermistor has both highly nonlinear effects of temperature dependent resistance and voltage dependent current behaviors, which act as passive element with self-repair mechanisms. Decrease of room temperature resistance with increasing the number of layers was demonstrated to be a grain boundary effect. Switching characteristics of current were caused by heat capacity of PTC thermistor with multilayer structure. Switching times are lengthened by increasing the number of layers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.1
• /
• pp.108-113
• /
• 2014

This paper presents the influence on the transmission characteristics of swelling in rectangular waveguides for Q-band. We derived the Green's functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a swelling is calculated by using internal impedance in order to investigate the influence of swelling in the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.2
• /
• pp.800-811
• /
• 2018

This paper presents a regenerative braking control scheme for Switched Reluctance Machine (SRM) drive in Electric Vehicles (EVs). The main purpose is to maximize the recovered energy during battery charging by taking into account the nonlinear physical characteristics of the Switched Reluctance Machine. The proposed regenerative braking method employs the back-EMF in the generation process as a complicated position-dependent voltage source. The proposed maximum power recovery (MPR) operation of the regenerative braking is first based on the maximization of the extracted power from the machine and then the maximization of the power transferred to the battery. The maximum power extraction (MPE) from SRM is based on maximizing the energy conversion ratio by the calculation of the optimum PWM switching duty cycle, turn-on, and turn-off angles. By using the impedance matching theorem that allows the maximum power transfer (MPT) of the MPE, the proposed MPR is achieved. The parametric averaged value modeling of the machine phase currents in the chopping control mode is used for MPR realization. By following this model, a nonlinear equivalent input resistance is derived for the battery internal resistance matching. The effectiveness of the proposed regenerative braking method is demonstrated through simulation results and experimental implementation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2017.05a
• /
• pp.61-62
• /
• 2017

In this study, a circular polarization patch antenna operates at the wide bandwidth of 1.5GHz~1.7GHz was designed. To obtain the wide bandwidth and high gain, the high air substrate was applied. The impedance bandwidth is improved by adjusting the sizes of patch, the distance between main patch and ground plate, the length of internal slots, the position of feeding point, the length of external stub, etc. The antenna is designed by simulation for an operation in the frequency range of 1.5GHz~1.7GHz band, and the antenna characteristics such as return loss, gain, radiation patterns are examined.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.188.1-188.1
• /
• 2012

인공위성에 사용되는 배터리 기술은 1960년대 최초로 사용된 니켈 카드뮴(NiCd)을 시작으로 발전하기 시작해서 현재는 리튬-이온(Li-Ion)에 이르렀다. 리튬-이온 배터리는 높은 Energy Density(작은 크기와 무게), 낮은 자가 방전율을 가짐과 동시에 메모리 효과가 거의 없다는 장점이 있다. 하지만 리튬-이온 배터리 팩의 성능(Voltage, Capacity, Lifetime)은 사용된 Cell간 특성차이(State of Charge, Total Capacity Difference, Internal Impedance)에 의해 제한된다. 일반적으로 배터리는 원하는 전압과 용량을 확보하기 위해 직렬-병렬 혹은 병렬-직렬 구조를 가지는 팩 형태로 제작 된다. Cell간 특성차이가 존재하는 상태에서 배터리 팩을 사용할 경우 특정 Cell의 과충전 및 과방전이 발생하며 이로 인해 수명이 단축될 수 있고 심한 경우 폭발이 발생할 수 도 있다. 또한 Cell간 특성차이는 배터리팩의 사용가능 용량을 제한하는 효과를 가져 온다. 본 논문에서는 Battery 팩을 구성하는 Cell들에 특성 차이가 존재할 경우 발생할 수 있는 Battery 팩의 수명 단축 및 용량 감소 Mechanism에 대해서 고찰한다. 또한 Cell간 특성차이를 극복하기 위해 실제 위성 운용에 적용될 수 있는 배터리팩의 Balancing 방안과 함께 위성에 장착을 위해 보관중인 4p12s Battery의 Balancing 방안에 대해 고찰하고 Balancing 전후의 Cell간 특성(Voltage Dispersion) 차이 측정결과를 보인다. 이렇게 본 논문에서 소개한 리튬-이온 배터리의 전반적인 Balancing 방안은 추후 인공위성에 적용되는 리튬-이온 배터리의 운용 및 보관에 Guide Line을 제시할 것이라고 판단한다.

• Nuclear Engineering and Technology
• /
• v.36 no.6
• /
• pp.559-570
• /
• 2004

A computational fluid dynamics model for predicting moderator circulation inside the Canada deuterium uranium (CANDU) reactor vessel has been developed to estimate the local subcooling of the moderator in the vicinity of the calandria tubes. The buoyancy effect induced by the internal heating is accounted for by the Boussinesq approximation. The standard $k-{\varepsilon}$ turbulence model with logarithmic wall treatment is applied to predict the turbulent jet flows from the inlet nozzles. The matrix of the calandria tubes in the core region is simplified to a porous media in which the anisotropic hydraulic impedance is modeled using an empirical correlation of pressure loss. The governing equations are solved by DFX-4.4, a commercial CFD code developed by AEA technology. The resultant flow patterns of the constant-z slices containing the inlet nozzles and the outlet port are "mined-type", as observed in the former 2-dimensional experimental investigations. With 103% full power for conservatism, the maximum temperature of the moderator is $82.9^{\circ}C$ at the top of the core region. Considering the hydrostatic pressure change, the minimum subcooling is $24.8^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.7
• /
• pp.722-729
• /
• 2013

This paper presents the influence on the transmission characteristics of dimensional tolerances of rectangular waveguides usually used as a low-loss transmission line in the millimeter-wave band. We derived the Green's functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a post is calculated by using internal impedance in order to investigate the influence of dimensional tolerances of the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.05b
• /
• pp.69-72
• /
• 2004

In recent, there have been several developments in lamp technology that promise savings in electrical power consumption and improved quality of the lighting space. Above all, the advantage of ring-shaped electrodeless fluorescent lamp is the removal of internal electrodes and heating filaments that are a light-limiting factor of conventional fluorescent lamps. The ring-shaped electrodeless lamp is intended as a high efficacy replacement for the incandescent reflector lamp in many applications. Therefore, the life time of ring-shaped electrodeless fluorescent lamps is substantially higher than that of conventional fluorescent lamps and last up to 60,000 hours. In this paper, we present measurement results of electrical characteristics of a ring-shaped electrodeless fluorescent lamp as a function of frequency and number of coil turns using a highly permeable Mn-Zn ferrite. It is found that the impedance are increased while the quality factor decreases as frequency increases.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.1
• /
• pp.85-88
• /
• 2012

DSCs are based on a dye-adsorbed porous $TiO_2$ layer as a photo electrode [1]. Under the illumination, dye molecules are excited and electrons are produced. The injected electrons in the conduction band of $TiO_2$ may recombine with the electrolyte. To obtain high performance DSCs, it is essential to retard the recombination. The charge recombination can be reduced by forming core-shell structure. In this work, we investigated the core-shell structure with $Al_2O_3$ and MgO coating layer on the porous $TiO_2$ layer. We confirmed the photovoltaic properties by I-V characteristics. The current and the efficiency was improved. In addition to, Through decrease in the width of EIS arc, which is the sum of the interfacial charge transfer resistances of both electrodes, we can be indicated that the block effect.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.11a
• /
• pp.384-388
• /
• 2000

One-port acoustic characteristics of an in-duct source can be measured by the multi-load method using an overdetermined set of open pipes with different lengths as applied loads. The input data. viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. An error analysis is applied to each case of possible loads, which consist of open pipes. It is noted that, frequently, only a set of open pipes is used when applying the multi-load method to the intake or exhaust sides of internal combustion engines. A set of pipe lengths which cause the calculated results to be least sensitive to the input data error can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.