• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.118-126
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• 2002

The Altitude Engine Test Facility(AETF) was built at the Korea Aerospace Research Institute and has been being operated for the gas turbine engines in the class of 3,000 lbf thrust. To enhance the confidence level of AETF to the international level, a series of studies and facility modification have been conducted to improve the measurement uncertainty and reliability. In this paper, some part of the facility evaluation tests performed with a single spool turbojet engine are introduced. Tests were performed simulating the flight conditions as steady state, sea level for various flight speeds (i.e., Mn=0.3, 0.5, 0.7, 0.9). The obtained test results are compared with the predicted values of the engine DECK. The measurement uncertainties of airflow, net thrust, fuel flow and SFC showed 0.791~0.914%, 0.851~1.706%, 1.372~7.348% and 1.642~5.205%, respectively. Thus, from this research, the improvement methods of uncertainties on AETF has been confirmed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.11
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• pp.2081-2093
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• 1994

In this study, we design and implement 64 QAM demodulator which has 155 Mbps, first level of CCITT G707 SDH(Synchronous Digital Hierachy) for STM 1 signal transmission. Carrier recovery which effects the demodulator performance uses decision feedback carrier using 8 bits A/D converter. Also, PSF(Pulse Shaping Filter) is 7 order elliptic filter. Carrier recovery circuit is designed and implemented digital type which use high 3 bits of 8 bits conversion data as data and the order low bits as error data and hybrid type which use VCO and analog integrator. Therefore we obtain stable performance recovery.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.5
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• pp.193-197
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• 2017

In this paper, we present a low-power delta-sigma based digital frequency synthesizer with high frequency resolution for bio sensor networks. Biomedical radio-frequency (RF) transceivers require miniaturized forms with a long battery life and low power consumption. For the technology scaling, digital circuits have become preferable compared to analog circuits because of the aggressive cost, size, flexibility, and repeatability. Therefore, the digital circuits based on standard-cell library are used to reduce a power consumption. Additionally, a delta-sigma is used for making fractional frequency tuning range. From the simulation, we confirmed that proposed scheme has good performance in accordance with power and frequency resolution.

• Journal of Broadcast Engineering
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• v.15 no.2
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• pp.217-223
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• 2010

In this paper, an interchannel interference (ICI) cancellation method is proposed for multiple frequency offsets in orthogonal frequency division multiplexing (OFDM) systems. When several same signals are received from different transmitters simultaneously, multiple frequency offsets may occur at the receiver because of the frequency difference of the oscillators of the two transmitters and the receiver. This causes degradation of system performance because OFDM systems are very sensitive to the frequency offsets. In this paper, we propose a method to eliminate the effect of the multiple frequency offsets for OFDM systems. The method is accomplished in two steps: compensation of the frequency offset in the time domain and subsequent cancellation of the ICI in the frequency domain. Through computer simulations, we verify the effectiveness of the proposed ICI cancellation method.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.49-57
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• 2002

The accurate wind speed information at the hub height of a wind turbine is very essential to the exact estimation of the wind turbine power performance testing. Several methods on the site calibration, which is a technique to estimate the wind speed at the wind turbine's hub height based on the measured wind data using a reference meteorological mast, are introduced. A site calibration result and the wind resource assessment for the Taekwanryung test site are presented using a one-month wind data from a reference meteorological mast and a temporal mast installed at the site of wind turbine. From this analysis, it turns out that the current location of the reference meteorological mast is wrongly determined, and the self-developed codes for the site calibration are working properly. Besides, an analysis on the uncertainty allocation for the wind speed correction using site calibration is performed.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.2
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• pp.44-52
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• 2002

본 논문에서는 RF와 마이크로파 응용을 위한 MEMS 수동 소자에 대한 내용이다. 이 수동 소자들을 만들기 위해서 개발된 3타원 MEMS공정은 기존의 실리콘 공정과 완전한 호환성을 가지고 한 칩으로 집적화 시킬 수 있는 공정이다. 이 3차원 MEMS 공정은 기존 실리콘 긍정이 가지고 있는 한계를 극복하기 위한 방법으로써 개발되었다. 개발된 공정을 이용하여 실리콘 공정에서 구현할 수 없었던 좋은 성능의 인덕터, 트랜스포머 및 전송선을 RF와 마이크로파 응용을 위해서 구현하였다. 저 전압, 높은 차단율을 위한 push-pull 개념을 도입한 MEMS 스위치를 구현하였다. 또한 높은 Q를 갖는 MEMS 인덕터를 최초로 CMOS 칩과 집적화에 성공하여 600kHz 옵셋 주파수에서 -122 dBc/Hz의 특성을 갖는 2.6 GHz 전압 제어 발진기를 제작하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.183-191
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• 2003

In this paper, the interference cancellation system, which is used to cancel the feedback signal In the wireless communication system with the same frequency, is studied. The time-varying feedback signal generated from transmitter antenna to receiver antenna reduces the performance of the receiver system. The interference cancellation system using adaptive feedback method(AF-ICS) is suggested to prevent the oscillation of the receiver system and maintain the maximum output power of the power amplifier by the reduction of time-varying feedback signal.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.994-1000
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• 2011

In this study, the piezoelectric fan cooling system is investigated. In order to find the proper geometry and configuration, the numerical model for the flow field and heat transfer investigation is used. A simplified nonlinear deformation model is employed for transient solutions of a piezoelectric fan with the dynamic mesh and user defined function capability. The results show that the cooling is most effective when the length of a piezoelectric fan is 5 cm and the cooling plate is 3 cm. The results can be used to develop a new design method of heat sink for piezoelectric fans.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.1-8
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• 1994

This study carried out to investigate the spray characteristics of diesel oil through out ultrasonic fuel supply system in comparison with conventional. Size of the droplets comprising diesel spray was measured by immersed liquid method at different positions along the spray axis. Droplets distribution diagram was ploted and Sauter Mean Diameter(SMD) was also calculated. The effects of the ultrasonic vibration and injection pressure on the droplet size distribution and SMD were investigated. As the ultrasonic vibration supply SMD decreases on the same injection pressure conditions with conventional injector's. But the effect of ultrasonic vibration decreases with injection pressure increasing.

• Journal of Advanced Navigation Technology
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• v.3 no.1
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• pp.1-12
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• 1999

For the phase measurement of radar signal in the coherent-on-receiver system, the COHO(Coherent Oscillator) generates the signal which locks to the phase of the transmit pulse. In this paper, COHO unit is developed to generate 60 MHz phase-locked signal. ILO(Injection Locking Oscilator) locks to the sample of the transmit pulse. Gate circuit, ILO, buffer amplifier, and pulse generator are designed and implemented.