• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.142-144
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• 2019

Nowadays, multi-MHz wireless power transfer (WPT) system has received a great concern of study due to its desirable characteristics such as user convenience, system compact and better safety as compared to the conventional DC-DC with cord. This paper presents a solution for WPT Lithium Batteries charger with Constant Current (CC) and Constant Voltage (CV) charging process. The proposed system consists of a high frequency class D power amplifier, a pair of PCB coil, transformable high-order resonant network and a full-bridge rectifier. The charger can be implemented CC /CV charging profile thanks to automatic reconfigurable resonant compensator. Therefore, the battery can be fully charged without the help of an additional DC/DC converter. The simulation and 50W-6.78-MHz hardware experimental results are presented to verify the feasibility of the proposed method and to evaluate the performance of the proposed wireless battery charger.

• Proceedings of the Korea Water Resources Association Conference
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• 2001.05b
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• pp.1133-1138
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wane interactions with a system composed of full submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing. The fully submerged systems allow surface and bottom clearances to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of fille second kind) tat satisfy the Helmholz governing equation. Using this computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, clearances. spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters call, if it is properly tuned to the coming waves, have good performances ill reflecting the obliquely incident waves over a tilde range of wave frequency and headings.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.4 s.119
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• pp.358-363
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• 2007

The multi-band and wide-band antenna for a portable broadcasting terminal is proposed. The proposed antenna consists of two radiators with a parallel structure. The antenna has an enough wide impedance bandwidth for the DVB-H(Digital Video Broadcasting-Handheld) service band since two radiators have adjacent resonance frequencies and operates in the DAB(Digital Audio Broadcasting) service band using the third harmonic of the radiator 1. The fabricated antenna has VSWR characteristics of less than 2:1 in the frequency band $470{\sim}740\;MHz$ for DVB-H and $1,450{\sim}1,480\;MHz$ for DAB. The measured peak gain of the antenna is $1.97{\sim}4.10\;dBi$ in the DVB-H band and $1.98{\sim}2.04\;dBi$ in the DAB band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.985-995
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• 2003

In this paper, a study on optimization of three dimensional multi-layered metallic disk array structure(MDAS) excited by circular waveguides was performed to shape efficient flat-topped element patterns(FTEP) of ${\pm}$20$^{\circ}$ beam width. Each radiating element of the MDAS is composed of input, transition and radiation circular waveguides and finite metal disks stacked on radiation circular waveguide. It has an array structure of a hexagonal lattice appropriate for the conical beam scanning. The analytic algorithm for the MDAS was proposed and the code was also programmed using it. Optimal design parameters of the MDAS were determined through the optimal simulation process to obtain ${\pm}$20$^{\circ}$ FTEP. Also, bandwidth characteristics for FTEP and reflection coefficients of the MDAS were investigated and, as the results, it was shown that the MDAS could shape good FTEPs of ${\pm}$20$^{\circ}$ beam width in main planes at least within a 5.6 % frequency band.

• Journal of Sensor Science and Technology
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• v.31 no.1
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• pp.45-50
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• 2022

Multi-rod type Ag-AgCl electrodes have been developed for use in underwater electric field sensors. The developed cylindrical electrode had a diameter of 50 mm and a height of 130 mm. The electrode had five Ag-AgCl rods with a diameter of 2 mm and a height of 80 mm to enlarge the reaction surface area. Each Ag-AgCl rod was fabricated under the same conditions as the usual anodizing method in an electrolyte. The two developed electrodes were placed in the center of a 500-mm long, 400-mm wide, and 300-mm high acrylic tank filled with artificial seawater, at an interval of 100 mm, to evaluate their characteristics as uniaxial underwater electric field sensors. The underwater external electric field was generated using titanium plate electrodes installed at both ends of the tank. The noise level at 1 Hz of the developed electrode was approximately 3.7 nV/√Hz. The reception of the underwater electric field signal using the developed electrode was linear, within an error of approximately 0.6 %, in the range of 1-10000 ㎶/m at 1 Hz. In addition, its frequency response was flat within an error of 1.1 % in the range of 1-1000 Hz at 10000 ㎶/m.

• Korean small business review
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• v.43 no.1
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• pp.131-145
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• 2021

This study aims to diagnose research trends and to deduct implications from meta analysis of entrepreneurship studies in the Asia Pacific Journal of Small Business (APJSB), one of the most well-known academic journals in management and entrepreneurship field in Korea. Frequency and crossover analysis are executed in multi-dimensions by time period, topic, author, research level, data, and methodology by complete enumeration of every published paper for 40 years in APJSB which included core terms of entrepreneurship in its title, abstract, or keywords. From objective and quantitative schematization of research trends and characteristics of entrepreneurship studies, novel improvement plans which are highly applicable in research fields are suggested such as diversification of studies from ecosystem perspective, identification of authors, and standardized system of extended abstract of research papers. Implications and suggestions derived from the results propose future research directions and tasks when entrepreneurship studies have been rapidly increased. Furthermore, the innovation plans of management system of journals and papers are expected to contribute promotion of entire studies by significantly reducing trial and error, and inefficiency in research process.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.2
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• pp.135-147
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• 2015

With the miniaturization and digitalization of electronics industry, demand for Multi-Layer Ceramic Capacitor(MLCC) has increased steadily because of its various applications such as DC Blocking, Decoupling and Filtering etc. The modeling techniques of MLCC has been studied for a long time but most of these modeling method can only be applied after measurement and this has some losses of material, time in both production stage and measurement stage. This paper proposes the modeling method which can predict the frequency characteristics of MLCC from structure data and material data in design stage. The impedance of N-Layer Capacitor can be expressed in differential mathematical form based on coupled transmission line equations. By using this formula, we can predict the impedance of MLCC. As a result, proposed modeling is correspond with simulation, and it takes much less time to obtain the result than the simulation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.596-604
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• 2007

This article investigates the effects of geometric configuration on the vibro-acoustic characteristics of in-plane vibration of a thick annular disc. Disc thickness and outer radius for a given inner radius are selected as independent variables having reasonable ranges. Variations in structural eigensolutions for radial modes are investigated using pre-developed analytical method. Based on these data, far-field sound pressure distributions due to the modal vibrations for a given geometry are also calculated using an analytical solution. Modal sound powers and radiation efficiencies are calculated from the far-field sound pressure distributions and vibratory velocity distributions on the radial surfaces. Based on the results explained above, the geometric configuration that minimizes modal sound radiations in a given frequency range is determined. Finally sound power and radiation efficiency spectra for a unit harmonic force from the selected geometric configuration are obtained from structural and acoustic modal data using the modal expansion technique. Multi-modal sound radiations of the optimized disc that are obtained using proposed analytical methods are confirmed with numerical results. Using the procedure introduced in this article, sound radiation due to in-plane modes within a specific frequency range can be minimized by the disc geometry modifications in a comprehensive and convenient manner.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.6
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• pp.89-95
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• 2017

UFMC is known as a candidate for the 5G wireless communication system because it is robust against ICI and better performs in asynchronous situation than OFDM. In the UFMC system, the filtering is performed for each subband so the performance of the filter is very important. The Dolph-Chebyshev filter has been used in conventional UFMC system because of its small out-of-band radiation. However it has distortion in the sub-band and skirt characteristics is not good enough. Therefore, it is necessary to study a new type of UFMC filter which reduces the distortion in the subband and has sharp skirt characteristics. In this paper we analyze the effect of filter frequency response in UFMC system and suggest the wavelet based type of filter that substitutes the Dolph-ChebyShev filter used in the conventional UFMC system. The simulation results show that wavelet filter has better BER performance in multipath fading channels than conventional filters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.563-574
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• 2006

This paper implements SCM(Spatial Channel Model), a kind of ray-tracing method which has characteristics similar to realistic wave propagation environments, for link-level performance analysis of OFDM(Orthogonal Frequency Division Multiplexing) based multiple antenna systems. The SCM is proposed by 3GPP & 3GPP2 Spatial Channel AHG(Ad-hoc Group) for system-level performance validation. In this paper, we modify the system level parameters and channel coefficient of SCM to compare the link-level performances of OFDM based multiple antenna systems. Through computer simulations, we manifest the implemented SCM channel characteristics. We analyze a realistic link-level performance of OFDM based conventional MIMO(Multiple Input Multiple Output) system and smart antenna system in the implemented channel. We also include the link-level performance of OFDM based multiple antenna systems in I-METRA(Intelligent Multi Element Transmit and Receive Antenna) and independent channel environments with the same system parameters. We suggest appropriate multiple antenna system in the given environment by comparing the link-level performance in the spatial channels that have different channel correlation values.