• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.208-212
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• 2003

Silicon transient voltage suppressors (TVSs) are clamping devices that limit voltage spikes by low impedance avalanche breakdown of a rugged silicon PN junction. They are used to protect sensitive components from electrical overstress such as that caused by induces lightning, inductive load switching and electrostatic discharge. In this paper, we present static and dynamic characteristics of TVS diode using thermal analysis simulation software. And also, it is presented that the thermal dissipation characteristics of TVS diode in the transient state.

• Journal of Power Electronics
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• v.3 no.4
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• pp.259-264
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• 2003

Photovoltaic (PV) array, which is generally installed outside, has the possibility of being damaged by high voltage due to lightning. primarily because the electrical characteristics of PV array have not been fully identified by lightning yet, there is a very important issue whether PV array should be connected with a ground or not. In this paper, a basic model of PV array is provided considering the PV cell's barrier capacitance and ground capacitance for analysis of electrical characteristics by lightning.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.170-171
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• 2005

Generally when Power MOSFET is operated, a heat sink is attached to it to emit heat caused by the operation. As the surface area of a heat sink is smaller, the thermal impedance is larger, which causes a negative influence on the characteristics of the chips and the devices and shortens the lifespan of them. In this experiment, we've compared and analysed different effects of heat sinks with 5 different surface areas on the characteristics of Thermal Transient when they are applied respectively.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.957-959
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• 2005

A noise reduction equipment in power systems was device combined in a passive element such as the form of L, R and C. A analysis of frequency characteristics for the transformer models shall be considered the additional capacitance between the windings($C_{ps}$), terminals($C_s$), and winding-ground($C_g$). A noise in transformer is modeled by take account into the different frequency. In case of the high frequency, transformer windings with stray capacitance have lower impedance. Therefore a noise is transferred from primary winding to secondary winding. Noise Cut Transformer(NCT) was the noise reduction device and was normally single phase two-winding type transformer. We analyzed frequency characteristics using the nodal network analysis with the equivalent circuit and the simulation of the MATLAB.

• Journal of the Korean Society for Nondestructive Testing
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• v.12 no.2
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• pp.7-13
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• 1992

In this study, we examine the characteristics of beam and the effect of these characteristics on the flaw detection by using different type of two transducers, which are PZT and PVDF film transducer. Consequently, the detection of infinitesimal flaw is more possible than PZT, since it has beam width at focus of $60%{\sim}65%$ in contrast with PZT's. Moreover we can know PVDF transducer has superiority in detecting ability for sub-surface flaw detection in view of its acoustic impedance is near to water's and its focusing range is narrower than PZT's as $65{\sim}85%$ because it has spherical surface.

• Journal of the Korean Society for Railway
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• v.7 no.1
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• pp.60-64
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• 2004

Harmonic current originating from electric locomotives can be magnified due to the impedance characteristics of power supply circuit and bring about various problems. That is, electromagnetic interference with communication lines, operational trouble in signaling, overheat and/or vibration in power capacitor, mis-operation in protection relay and so on. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. for these reasons, this study propose a new approach to model and to analyse traction power feeding system focused on system response to current and voltage harmonic(PART I). Measurements of harmonics are also performed for railway power supply systems under normal operation. Spectrum and distortion analyses in measurement data are variously described in PART II.

• Journal of Korean Port Research
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• v.12 no.1
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• pp.145-154
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• 1998

Protection characteristics of the corroded steel pile which was served as a pier structure over 8 years in seawater have been examined in terms of corrosion potential, electrochemical impedance spectroscopy(EIS) and anodic/cathodic polarization curves. The steel structure was sectioned into two parts, waterline(splash zone, just above the seawater surface) and in-water(underwater), and protection characteristics for the two parts were investigated with the application of cathodic protection(CP) by sacrificial anodes using Zn and Al alloys. The main results obtained were as follows; (1) The corrosion potential of waterline zone was higher than that of in-water, which implied that the corrosion of waterline was more severe than that of in-water, (2) As a result of EIS examination, the transition period from the apparent CP to the substantial CP took about twenty to thirty days according to the corrosion condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.29-36
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• 2012

3-D linear acoustic analysis has been performed to elucidate damping characteristics of large Helmholtz acoustic cavities in FASTRAC thrust chamber. Acoustic impedance concept has been introduced to quantify combustion stabilization capacity. For a given acoustic cavity, sonic velocity in the cavity to achieve an optimal tuning has been determined and satisfactory agreement with the previous results has been obtained. Feasible estimation of sonic velocity in the acoustic cavity has been devised. Results show similar trends without significant deviations, which can be used in the procedure of design and verification of acoustic cavity. From the satisfactory results, investigation of other thrust chambers with acoustic cavities which have shown combustion instabilities will be done as future works.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.119-123
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• 2017

This paper presents a unique and miniaturized dual-band coplanar waveguide (CPW-fed) antenna for modern wireless communication. A new technique of using a modified ground structure (MGS) and frequency shifting strips (FSS) has been employed in the design to achieve dual-frequency operation. The proposed antenna generates two separate impedance bandwidths and covers the minimum required frequency bands of GSM 1800, GSM 1900, and Wi-Fi/WLAN 5 GHz. The proposed antenna is relatively small ($17{\times}20mm^2$) and operates over frequency ranges 1.51~2.06 and 4.43~6.70 GHz. The designed antenna was simulated using Ansoft HFSS, a FEM based simulator, and antenna characteristics, such as reflection coefficient, gain, radiation efficiency, radiation pattern, impedance bandwidth, VSWR, surface current, and electric field distributions, are reported in this paper. The effect of the antenna's key structural parameters on its performance is also analyzed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.221-228
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• 1997

A strong combustion-driven sound from a surface burner made of a perforated metal fiber plate for premixed gas was investigated to clarify the physical mechanism of its generation. A simple model was developed for the acoustic power generation in terms of the heat transfer response function and the acoustic impedance of the burner. The acoustic impedance of the perforated metal fiber placed on the open exit was measured and the heat release response of the burner to the oscillating flow associated with the acoustic disturbance was expressed in terms of a response function. It was found that the power is generated by the heat release in response to the downstream particle velocity, in contrast to the upstream velocity in the case of the Rijke oscillation driven by a heater placed in the lower half of a columm with upstream flow. The measured frequencies of the oscillation were in agreement with the estimated resonance frequencies and their excitation was varied with the combustion conditions. For the same fuel rate, the excited frequency increases with the air ratio if it is low but decreases with the ratio if not so low. Such frequency characteristics were explained by assuming a heat release response function with a time constant and it was shown that the excited frequency decreases as the time constant increases.