• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.42-50
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• 2007

This paper presents design methods for dual-frequency(2.4/5.8GHz) active receiving antennas. The proposed active receiving antennas are designed to interconnect the output port of a wideband antenna to the input port of an active device of High Electron Mobility Transistor directly and to receive RF signals of 2.4GHz and 5.2GHz simultaneously where the impedance matching conditions are optimized by adjusting the length of $1/20{\lambda}_0$(@5.8GHz) CPW transmission line in the planar antenna The bandwidth of implemented dual-frequency active receiving antennas is measured in the range of 2.0GHz to 3.1GHz and 5.25GHz to 5.9GHz. Gains are measured of 17.0dB at 2.4GHz and 15.0dB at 5.2GHz. The measured noise figure is 1.5dB at operating frequencies.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.5-12
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• 2009

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.306-311
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• 2000

This paper deals with the development of Laser Doppler Vibrometer (LDV) that can mea~ure the tlequency and amphlude of the ultrasonic vibralion. Hc-Ne laser (632.8 om) is used as a light source, and Michelson interferometer in winch frequency of the objective beam is shIfted by Bragg cell IS adopted The frequency modulated signal centered at 40 MHz flom the PIN diode IS amplified. down-col1vel1ed to 2.5 MHz, filtered and digiLized. The voltage output that is proportional to the velocity of the vibratwg surface is obtawed using digItal PLL. A microprocessor is used to extract the frequcncy aud amplitude of the vibratIOn from the voltage output. It is found that the developed LDV can measure up to 300 kHz vibratIOn and the mlillmUITI measurable amplitude is I nm at 300 kHz. We believe thatlhis LDV can be used to measure the vibratIOn of the heavy electric maclllnery and micro-size structures. tures.

• The Journal of the Acoustical Society of Korea
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• v.21 no.6
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• pp.510-521
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• 2002

MBE (multi-band excitation) coder can achieve high qualify synthetic speech below 4.0 kbps. There are, however, significant differences of the fine structure between the original spectrum and the synthetic spectrum. They are mainly due to the exclusive partition of voiced and unvoiced regions in frequency domain and the decision procedure based on the experimental threshold. This paper proposes MMBE (mixed multi-band excitation) speech model to overcome drawbacks of a MBE coder. In addition, two analysis methods, which do not need my decision procedure based on a threshold, are presented. Both voiced and unvoiced components can be mixed over all the frequency axis in the MMBE speech model. To illustrate the potential of the proposed speech model, we develop a 2.6 kbps MMBE coder and compare it with a 2.9 kbps MBE coder by both objective and subjective methods. The results have shown that the proposed coder has a better performance even at a lower bit-rate compared with the MBE coder.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.256-268
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• 2008

This paper proposes an efficient scheme to track the time variant channel induced by multi-path Rayleigh fading in mobile wireless Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems with null sub-carriers. In the proposed method, a blind channel response predictor is designed to cope with the time variant channel. The proposed channel tracking scheme consists of a frequency domain estimation approach that is coupled with a Minimum Mean Square Error (MMSE) time domain estimation method, and does not require any matrix inverse calculation during each OFDM symbol. The main attributes of the proposed scheme are its reduced computational complexity and good tracking performance of channel variations. The simulation results show that the proposed method exhibits superior performance than the conventional channel tracking method [4] in time varying channel environments. At a Doppler frequency of 100Hz and bit error rates (BER) of 10-4, signal-to-noise power ratio (Eb/N0) gains of about 2.5dB are achieved relative to the conventional channel tracking method [4]. At a Doppler frequency of 200Hz, the performance difference between the proposed method and conventional one becomes much larger.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.345-356
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• 2021

In order to increase the structural stability of existing caisson breakwater, the design and the construction is carried out by installation of new caissons on the back or the front of old caissons. In this study, we use the ANSYS AQWA program to analyze the wave forces acting on individual caisson according to effects of wave structure interaction when new caissons are additionally installed on existing caisson breakwater. Firstly, the wave force characteristics acting on the individual caisson were analyzed for each period (frequency) in the frequency domain. In time domain analysis, the dynamic wave force characteristics were strongly influenced by the distance between caissons on the frequency at which the unusual distribution of wave forces occurs.

• Journal of Sensor Science and Technology
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• v.6 no.3
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• pp.194-199
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• 1997

When voltage or current gets out of the magnetic sensor as it is, we have often faced the problems such as introduction of noise and loss of voltage. In order to reduce these problems, a 2 drain MAGFET operating in the saturation region and fabricated by CMOS process, the system of I/V converter, VCO with operational amplifier, and V/F conversion circuits with Schmitt Trigger are designed and fabricated in one package. The absolute sensitivity of magnetic sensor shows 1.9 V/T and the product sensitivity is $3.2{\times}10^{4}\;V/A{\cdot}T$. The characteristic of V/F conversion is very stabilized and has the value of 190 kHz/T.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.56-56
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• 2003

최근 정보통신 분야의 급격한 발달로 인하여 무선통신에 사용되는 주파수 영역 또한 계속 높아짐에 따라 대역통과 필터 소자의 삽입 손실, 소비 전력, 크기, MMIC화에 대한 많은 연구가 진행되고 있다 압전 현상을 이용한 박막형 공진기가 이러한 요구를 충족시키고, 현재의 SAW filter를 대체할 소자로 떠오르고 있다. 본 실험에서는 단결정 미세 구조를 만들 수 있고, 압전 효과 또한 우수하며, Surface Micromachining보다 비교적 제조 공정이 간단하고 선택적 에칭이 가능한 Bulk Micromachining을 이용하여 Si$_3$N$_4$ Membrane을 이용한 중심주파수 5.2GHz인 두께 진동모드 Film Bulk Acoustic Wave Resonator(FBAR)를 제작하고 공진기의 고주파 특성을 평가하였다. Membrane구조 형성을 위해 Backside면인 Si$_3$N$_4$, Si은 RIE(Reactive Ion Etching)와 선택적 에칭용액인 KOH로 각각 에칭하여 Membrane을 갖는 구조로 중심주파수 5.2GHz인 두께 진동모드 FBAR를 설계 및 제조하였다. 체적 탄성파 공진 현상은 r.f Magnetron Sputtering법으로 증착한 AIN 압전박막과 Mo전극으로부터 발생 가능하였다. 본 연구에서는 0.9$\mu\textrm{m}$-Si$_3$N$_4$ Membrane을 이용해 FBAR를 제작/평가하고, RIE을 통해 Membrane을 제거해 가면서 공진기의 특성 즉, Quality factor와 유효전기기계결합계수(K$_{eff}$) 및 S parameter특성을 비교 측정해 보았다. 측정해본 결과 Membrane Free일때가 훨씬더 공진 특성이 우수함을 볼 수 있다

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.155-158
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• 2009

원활한 방송 서비스를 제공하고 손쉬운 방송망 구축을 위해서 가장 중요한 것은 서비스 하 고자 하는 주파수 대역과 환경에 맞는 전파 모델을 선택하는 것이다. 적절한 전파 모델을 선택하여 수신 전계 강도를 정확하게 예상함으로써 효율적인 방송망을 설계할 수 있는 것이다. 방송망 주파수 대역에서 전파 분석 시 널리 이용되고 있는 모델은 ITU-R 권고안 P.1546 모델이다. 이 모델은 기존의 Okumura 나 Hata 모델처럼 측정을 기반으로 하여, 송신단 높이, 수신단 높이, 주파수, 거리, 시간율, 공간율 들을 고려하여 완성한 점대 영역 경로 손실 예측 모델이다. 측정을 기반으로 완성된 경로 손실 모델이기 때문에 실제 환경에 적용하기 위해서는 전계강도 예측 지역의 수신 환경 특성을 반영한 보정값을 더해줘야 한다. 이러한 문제를 해결하기 위해서 ITU-R 연구 3그룹은 지형 프로파일에 기반한 새로운 모델들을 개발하였다. 송, 수신단 사이의 지형 데이터가 고도화되면서 좀 더 정밀한 송, 수신단 사이의 지형 프로파일을 추출해 낼 수 있으며 이는 정확한 전계강도 예측을 가능하게 하였다. 이에 연구 3그룹은 고도화된 디지털 지형 데이터를 이용하여 자유 공간에서 경로 손실, 지형에 의한 회절 손실, 대류권 산란 손실 그리고 ducting 현상을 반영하여 전계강도를 산출해 내는 ITU-R P.1812 모델을 제안하였다. 본 논문에서 우리는 ITU-R 권고안 P.1812를 분석 구현하고 기존의 대표 모델인 P.1546 모델과의 비교 분석을 시도하였다.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.125-131
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• 2017

In this paper, an efficient structure of device-to-device (D2D) synchronization preamble is proposed to meet the enhanced time and frequency synchronization requirements for D2D communication. D2D communication can be applied not only for the cellular communications, but also unmaned aerial vehicle communications and vehicle-to vehicle communication. The proposed preamble structure is transmitting signals at every odd subcarriers, and empty the other subcarriers to minimize the effect of inter-carrier interference. According to the simulation results, the proposed preamble structure provides improved time offset estimation performance, without degrading frequency offset estimation performance compared to the current LTE D2D preamble.