• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.7
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• pp.1224-1233
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• 1994

The error performance of BPSK and QPSK signals in mobile satellite channel is investigated considering nonlinearity of TWTA (Traveling Wave Tube Amplifier) in the presence of AWGN(Additive White Gaussian Noise) on the uplink and downlink paths. It is assumed that the fading on the downlink path forms a Rician distribution. The Rician distribution is approximated by discrete probability values. The values are firstly found by Classical Moment Technique. Finally, the error probability is evaluated using approximate discrete values of Rician distribution and the Gaussian Quadrature Formula.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.256-258
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• 2010

MPM(Microwave Power Module)은 진공 전력증폭기인 진행파관(TWT,Traveling Wave Tube)과 반도체 전력증폭기(SSA, Solid State Amplifier)를 결합한 구조로서, 미세한 RF신호를 입력 받아 고출력의 RF 신호로 증폭하는 장치이다. 본 논문은 MPM을 구동하기 위해, 필요한 수 kV이상의 높은 전압을 TWT에 공급해주는 고전압 전원공급기(HVPS, High Voltage Power Supply)에 관한 것이다. Main Topology는 Resonant Phase Shift Full Bridge Converter이며, 승압의 효과를 높이기 위해 2차 측에는 Voltage Multiplier를 사용하였다. MPM을 구동하는데 필요한 전압인Cathode(-4kV), FE_Bias(-5.25kV), Collector(-2kV)를 생성하며, FE_ON, OFF신호에 따라 고전압 스위칭 동작을 하여, RF 증폭을 제어 할 수 있다. 최종적으로 Prototype을 제작하고, 고찰된 실험결과를 제시하여 개발된 HVPS의 우수성을 검증한다.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1827-1829
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• 2002

This paper describes AC test for long delivered drum length of cable using pre-breakdown partial discharge detection(PPD) method, which can be applied to observe the causes of electrical breakdown of EHV XLPE insulation. This method is to de-energize applied voltage to cable rapidly using pre-breakdown partial discharge, and is able to prevent complete breakdown. By this effect, defects such as voids, metal particles and protrusion in cable can be observed clearly. AC resonant test set was used for PPD method. Localization of partial discharge was performed by time difference detection of the traveling wave. Accuracy of localization was 1% to the length of test cable. Through several experiments with XLPE cable, successful results of PPD method were obtained.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.285-285
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• 2000

A continuous and reliable electrical energy supply is the objective of any power system operation. A transmission line is the part of the power system where faults are most likely to happen. This paper describes the use of wavelet transform for analyzing power system fault transients in order to determine the fault location. Synchronized sampling was made possible by precise time receivers based on GPS time reference, and the sampled data were analyzed using wavelet transform. This paper describes a fault location monitoring system and fault locating algorithm with GPS, DSP processor, and data acquisition board, and presents some experimental results and error analysis.

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.145-146
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• 1998

A planar-type silicon microelectrode array has been fabricated and used successfully in obtaining simultaneous multichannel recordings from peripheral nerve of invertebrates. This paper demonstrates that planar-type semiconductor electrode arrays are useful for studying traveling wave properties of action potential.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.554-558
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• 2002

A magnetostrictive sensor is used to measure stress waves propagating in a ferromagnetic cylinder without physical contact. The performance of a magnetostrictive sensor is affected most significantly by the bias magnetic field applied around the measurement location. The goal of this paper is to carry out the topology optimization of the bias magnet and yoke assembly to maximize the sensor output for traveling bending waves. We will use the multi-resolution topology optimization strategy to find the assembly of the bias magnet and the yoke that is easy to realize. The effectiveness of the present design is confirmed by an actual measurement of the sensor signal with the proposed bias magnet and yoke configuration.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2186-2188
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• 1999

A high frequency and energy density pulse transformer is a critical component of a high voltage power supply in a traveling wave tube (TWT) amplifier system. In this paper, processes of design, manufacturing, and test of the transformer are discussed. Primary voltage of the transformer is 240 V. The transformer secondary have two outputs which are 4100 V (Helix) and 2050 V (Collector). Total output power is 860 W. Normal operating frequency of the transformer is 10 kHz. In high energy density pulse transformers, temperature rise is a main problem during its operation. From our study, it was found that resonant current due to leakage inductance and stray capacitance was the main cause of temperature rise. This happens because of the inherently high turn-ratio in high voltage transformers. Solutions to reduce stray components are presented.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2151-2155
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• 1998

The traveling wave type ultrasonic motor(USM) has no electro-magnetic circuits( coil or core). The driving principle of the USM is based on high-frequency mechanical vibrations and frictional force. The USM, thus, is fed by two-phase high - frequency sinusoidal inverter using its series resonant parasitic components. For the using of series resonant type inverter, it should be needed to a USM parasitic capacitance and a proper inductor chosen. In this paper, the values of optimal inductance are designed and the efficiency of USM drives is achieved. The effectiveness of the proposed design is demonstrated by experiments.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.473-478
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• 2002

Circular slab waveguides are conformally mapped into straight waveguides. In the outer cladding region with monotonically increasing index profile, modified Airy functions (MAF) of traveling-wave form are introduced to express the leaky mode. Field distributions and losses calculated by the proposed method are compared with those obtained by the WKB (Wentzel-Kramers-Brillouin) method. Detailed numerical examples are presented and compared with the conventional WKB methods, demonstrating our method not only allows a converging field at turning points but also guarantees fine accuracy.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.87-90
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• 1995

A new solution to the two-dimensional scalar wave equation is presented, which descries a diffraction-limited beam maintaining the lateral field response expressed by the sinc function. Physically, it is a superposition of plane waves having different wavelengths traveling in different directions. The beam can attain a line focus with one-dimensional array transducer in ultrasonic medial imaging.