• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1162-1166
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• 2001

NiZn-ferrite was synthesized from waste catalysts, which were produced from styrene monomer process and buried underground as an industrial wastes, and its magnetic properties were investigated. Nickel oxide and zinc oxide powders were mixed with finely ground waste catalysts, and spinel type ferrite was obtained by calcination at 900$\^{C}$ and sintering at 1230$\^{C}$ for 5 hours. The intial permeability was measured and reflection loss was calculated from S-parameters for the composition of Ni$\_$x/Zn$\_$1-x/Fe$_2$O$_4$(x=0.36, 0.50, 0.66). NiZn-ferrite synthesized from waste iron oxide catalyst showed a feasibility for the use as electromagnetic wave absorber in X-band.

• Journal of IKEEE
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• v.24 no.1
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• pp.260-268
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• 2020

This paper presents the high frequency resonant inverter of class D SEPP(Single-Ended Push Pull) type using LS-ZVS-LSTC, which can reduce the switching losses during the turn-on and turn-off switching time. The analysis of high frequency resonant inverter using LS-ZVS-LSTC(Low-loss Turn-off Snubber Capacitor) proposed in this paper is described in general by adopting the normalized parameters. The operating characteristics of the proposed high frequency resonant inverter were also evaluated by using the control parameters such as the normalized control frequency(μ), the normalized load time constant(τ), the coupling factor(κ) and so on. Based on the characteristic values through the characteristics of evaluation, an example of the design method of the 1.8[kW] class D SEPP type high frequency inverter is suggested, and the validity of the theoretical analysis is verified using the experimental data.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.1
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• pp.92-98
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• 1997

In this paper, the results of the measurement and analysis of extremely low freqency(ELF) eletric field in the vicinity of 154[kV] overhad transmission lines have been described. The planar-type electric field sensor has been fabricated by three dimensional structure with special consideration of taking the power frequency and lower components. The calibration experiments have been carried out according to the procedures of IEEE recommendation. The electric field measuring system has the frequency bandwidth of 7[Hz] to 2.7[MHz] and the response sensitivity of 0.094[mV/V/m]. Also the practical measurements of electric field under an 154[kV] double corcuit overhead transmission lines have been made abd abalyzed. It was known that the lateral electric field profiles under an 154[kV] double circuit overhead transmission lines show the asymmetrical distributions owing to the environmental metal frame structures and their maximum electric field magnitude is less than 3[kV/m]. It can be concluded that the measured results of the electric fields satisfy with all limits or guide -lines of the various authorized international institutes' recommendations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.163-166
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• 2002

The underwater acoustic communication has been widely applied to various objects such as ocean exploration-development and military affairs. And recently for embodiment of the communication system that is installed in a submarine and underwater work system, many studies have been progressing. This scope of the main studies in the meantime. It made it possible for a diver and a scuba diver who arc difficult to notice the situation of the outside because of staying in the water to hear a sound through a small speaker by using a ultra sound transducer that a central frequency is 32KHz after modulation of a voice to give the information of the outside. Also in case of happening an emergency to a diver in the water, it made him/her ask for help to a person in the outside by pressing a key and send a letter data to a person in the outside by using a keyboard. Through this system, it is possible to send a voice or data between the underwater and the outside and it is available to a diver or skin scuba diver.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.132-135
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• 2002

In radio communication technology, SDR(Software Defined Radio) technology is emerging as a trendy technology for future. SDR is expected to change existing radio systems including central hardware. SDR is equipment that wireless parameters (frequency, modulation, additional service, power level, receive sensitivity, etc.) are controlled by software. In the world, equipments using the new technology are spreading. Not only equipments being imported but also local manufacturers are making this equipment, developing software and offering upgraded service. In the future, as SDR spreads and users choose the service, diverse equipments will be developed through competition and individual development. This diversity of equipment and services will introduce problems in compatibility and interoperation issues. So the government will have to make technical standard for SDR service and will have to make theses standards available to users and manufacturers alike. Therefore I am investigating the elements that can be used to establish these standards.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.9
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• pp.1818-1825
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• 2017

An Acoustic Doppler Current Profiler(ADCP) measures the current velocity and analyzes the degree of turbulence using Doppler effects of ultrasonic waves. Therefore, the autocorrelation or FFT spectrum estimates are obtained for extraction of current velocity in each spatial region. However, if the correlation method does not satisfy the assumption that the return signal spectra are symmetric Gaussian, the large bias errors can occur. Also, the accurate estimation of autocorrelation or FFT spectrum is difficult due to the short acquisition interval when the rapid changes of current velocity occur. Thus, in this paper, the estimation method of the autoregressive spectrum peak is suggested for the accurate current velocity measurement of both symmetric and asymmetric spectra. It is shown that estimation quality can be improved using the suggested method comparing with the conventional methods. Many return signals under the various environment are simulated and the results are compared and analyzed for evaluation of the suggested method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.405-408
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• 2013

The performance of underwater acoustic(UWA) communication system is sensitive to the Inter-Symbol Interference(ISI) due to delay spread develop of multipath signal propagation. And due to limited frequency using acoustic wave, UWA is a low transmission rate. Thus, it is necessary technique of Space-time code, equalizer and channel code to improve transmission speed and eliminate ISI. In this paper, UWA communication system were analyzed by simulation using these techniques. In the result of simulation, the proposed Space-time code, Turbo code, and Zero forcing techniques is shown that improved performance than conventional UWA communication.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.347-348
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• 2007

전력산업에 당초 도입 예정되었던 도매경쟁시장을 운영지원하기 위하여 전력거래소는 지난 2002년 도매경쟁 전력시장 운영시스템(Two Way Bidding Pool Market Operation System; TWBP MOS, 이하 전력시장운영시스템)을 구축하였다. 그러나 이후 배전분할 잠정 중단정책에 따라 구축 완료된 시스템은 실 업무에 적용해보지도 못한 채 폐기될 수도 있는 상황이 발생하였다. 하지만 전력거래소는 배전분할 잠정 중단에 따른 발전 경쟁시장(CBP; Cost-Based Pool) 장기화에 대비, 운영상의 효율성을 개선하고 기 개발된 전력시장운영시스템을 활용하여 급전체계를 개선하는데 성공하였다. 실시간 급전 운영을 위해 기존 EMS에 전력시장운영시스템을 연계하여 전력시장운영시스템의 5분 단위 수요 예측량을 기반으로 송전망 제약과 예비력 요구량 등을 고려한 발전기별 경제부하 배분량 및 예비력 배분량을 결정하고, 추가적으로 EMS에서 수요예측 오차 및 주파수 보정량을 실시간으로 계산하여 발전기별로 배분하도록 함으로써, 1일 전 시행하던 급전계획을 취득 자료를 기반으로 5분 단위로 실시간 계산할 수 있도록 급전 개선하였다. 이를 통해 실시간으로 에너지와 예비력을 동시에 최적화함으로써 전력시장 및 전력계통 운영을 한층 선진화 할 수 있는 계기를 마련하였으며 또한 저비용 발전기 사용을 극대화함으로 발전비용의 절감에도 기여하는 효과를 가져왔다. 이러한 긍정적인 효과에도 불구하고, 전력시장윤영 시스템은 구축된 모든 설비 및 프로그램을 당초 목적에 맞게 활용하지 못한다는 이유 등으로 시스템의 최적화 및 성능 개선에 대한 투자가 망설여지는 현실이다. 특히 온라인 실시간 시스템과 별도로 전력시장운영을 모의 할 수 있는 시뮬레이터가 구축되지 않아 시장의 흐름을 사전 예측하거나 시스템 오류 등을 재현하여 재발 대책 등을 마련하기가 매우 어려운 실정이다. 이에 본 논문에서는 그동안 쌓아온 전력거래소의 전력시장운영시스템 운영관리에 대한 다양한 경험을 바탕으로 구축비용을 획기적으로 절감할 수 있는 전력시장운영시스템 시뮬레이터의 구축방안을 제시하고자 한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.470-473
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• 2018

Using High-order Modulation in wideband system is sensitive to change of wireless channel environment as well as changes in ripple characteristics that can occur when baseband signals pass through RF equipment. Therefore, it is necessary to design and RF tuning that minimizes ripple characteristics change, which is difficult to implement systematically and takes a long time. In this paper, we analyze the fixed ripple characteristics of the baseband signal distored through the RF transmitting and receiving equipment. And the function of compensating the compensation filter by the modem receiver is implemented in 256 TCM. Also, it is confirmed that SNR and received sensitivity are improved by applying a digital compensation filter in a channel with poor RF equipment ripple characteristics.

• Korean Chemical Engineering Research
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• v.45 no.4
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• pp.356-363
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• 2007

The stability of paste solutions for electroluminescence display(ELD) device was found to be greatly affected by kind and dosage of a stabilizer used. The stabilizer Disperbyk-180 showed the best stability performance against phosphor paste solutions among the stabilizers used during this study. The phosphor paste solutions remained stable over 90 days with a wide range of added amounts of Disperbyk-180. Based on the above results, screen printing test was performed. The addition of Disperbyk-180 into phosphor and dielectric paste solutions produced improved qualities such as no phase separation, no bubble generation and no significant viscosity change during printing process. Especially for the phosphor paste solution, both uniformity and brightness were significantly improved and the excellent adhesion onto the ITO film was found. The ELD device fabricated using the above same paste solutions showed brightness of $57.6cd/m^2$ at 100V and 400 Hz. The half lifetime of ELD device was measured as 1,250 hours and almost the same value observed with imported commercial paste solutions.