• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(5)
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• pp.199-202
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• 2000

RFID (Radio Frequency Identification) is a technique which is used for identifying different types of objects and tracking people and animals. Passive RFID consists of reader, a passive tag. The reader transmit energy to a tag and read information back from tag. The tag is energized by a carrier frequency which is transmitted by the reader and transmit information back to the reader. In this paper, the circuit for read and write RFID system is presented. The presented RFID system adopts 125kHz carrier frequency, backscattering and PSK for communication method.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제4권2호
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• pp.143-152
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• 2000

As muscular contraction is sustained, the Fourier spectrum of the myoelectric signal is shifted toward the lower frequency. This spectral density is associated with muscle fatigue. This paper describes a quantitative measurement method that performs the measurement of localized muscle fatigue by tracking changes of median frequency based on stationary wavelet transform. Applying to the human masseter muscle, the proposed method offers the much information for muscle fatigue, comparing with the conventional FFT-based method for muscle fatigue measurement.

• 대한의용생체공학회:의공학회지
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• 제31권5호
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• pp.401-406
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• 2010

Recently, many implantable medical devices have been developed and manufactured in many countries. In these devices, generally, energy is supplied by a transcutaneous method to avoid the skin penetration due to the power wires. As the most transcutaneous power transmission methods, the electromagnetic coupling between two coils and resonance at a specific frequency has been used widely. However, in case of a transcutaneous power transmitter with a fixed switching frequency to drive an electromagnetic coil, inefficient power transmission and thermal damage by the undesirable current variation may occur, because the electromagnetic coupling state between a primary coil and a secondary coil is very sensitive to skin thickness of each applied position and by person. In order to overcome these defects, a transcutaneous power transmitter of which operating frequency can be automatically tracked into the resonance frequency at each environment has been designed and implemented. Through the results of experiments for different coil surroundings, we have been demonstrated that the implemented transcutaneous power transmitter can track automatically into a varied resonance frequency according to arbitrary skin thickness change.

• 한국전자파학회논문지
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• 제25권2호
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• pp.245-250
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• 2014

본 논문은 선형 주파수 변조-주파수 편이(Linear Frequency Modulation-Frequency Shift Keying: LFM-FSK) 신호와 위상비교 모노펄스 방식을 사용하는 후방 감시 차량용 레이다의 ISAR(Inverse Synthetic Aperture Radar) 영상 형성 기법에 관하여 제시한다. 두 개의 계단 주파수(stepped frequency) 신호를 순차적으로 연결한 LFM-FSK 신호를 이용하여 후방 관측을 통해 차량에 대한 ISAR 영상을 형성할 수 있다. 그러나 운전자 후방에 위치한 차량을 관측하여 ISAR 영상을 형성할 경우, 레이다 관측 각도(radar's aspect angle)의 변화율이 일정하지 않기 때문에 ISAR 영상이 흐려진다. 이를 해결하기 위해 위상비교 모노펄스 방식으로 추정한 각도 정보와 각도-주파수 영역(domain)에서의 레이다 수신데이터를 사용하여 각 주파수에서 각도별로 1차원 라그랑주 보간법(Lagrange interpolation)을 수행한다. 이를 통해 관측 각도 변화율이 일정한 각도-주파수 데이터를 획득할 수 있다. 시뮬레이션 결과는 제시된 기법을 적용하여 초점이 맞는 ISAR 영상이 형성됨을 보여준다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.3100-3102
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• 2000

In this paper, we propose to a robust frequency offset estimation method of OFDM signals. A carrier frequency offset may be decomposed into an integer multiple of the subcarrier spacing and a residual frequency offset. Fractional part of frequency offset is obtained by using the maximum likelihood estimation(MLE) method. And we use the correlation of the samples at the output of the discrete Fourier transform(DFT) to estimate integer part of frequency offset. The result shows that the estimation frequency offset is almost linear to frequency offset. We propose to an improved estimation error variance of the carrier frequency offset estimation. The proposed estimator has better performance than the conventional ones in terms of error variance and tracking range.

• Journal of Power Electronics
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• 제14권1호
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• pp.175-182
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• 2014

Tracking harmonic current quickly and precisely is one of the keys to designing active power filters (APF). In the past, the current state feedback decoupling PI control was an effective means for three-phase systems in the current control of constant voltage constant frequency inverters and high frequency PWM reversible rectifiers. This paper analyzes in detail the limitation of the conventional PI conditioner in the APF application field and presents a novel PI control method. Canceling the delay of one sampling period and the misadjustment for tracking the harmonic current is the key problem of this PI control. In this PI control, the predictive output current value is obtained by a state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by a repetitive predictor synchronously. The repetitive predictor can achieve better predictions of the harmonic current. By this means, the misadjustment of the conventional PI control for tracking the harmonic current is cancelled. The experiment results with a three-level NPC APF indicate that the steady-state accuracy and dynamic response of this method are satisfying when the proposed control scheme is implemented.

• 한국실내디자인학회논문집
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• 제25권1호
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• pp.73-80
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• 2016

Street is the most fundamental component of city and place to promote diverse actions of people. Pedestrians gaze at various street environments. A visual gaze means that there are interesting elements and these elements need to be preferentially improved in the street environment improvement project. Therefore, this study aims to set up the priorities of street environment components by analyzing eye movements from a pedestrian perspective. In this study, street environment components were classified into road, street facility, building(facade) and sky and as street environment images, three "Streets of Youth" situated in Gwangbok-ro, Seomyeon and Busan University of Busan were selected. The experiment targeted 30 males and females in their twenties to forties. After setting the angle of sight through a calibration test, an eye-tracking experiment regarding the three images was conducted. Lastly, the subjects were asked to fill in questionnaires. The following three conclusions were obtained from the results of the eye-tracking experiment and the survey. First, building was the top priority of street environment components and it was followed by street facility, road and sky. Second, as components to be regarded as important, fast 'Sequence', many 'Fixation Counts' and 'Visit Counts', short 'Time to First Fixation' and long 'Fixation Duration' and 'Visit Duration' were preferred. Third, after voluntary eye movements, the subjects recognized the objects with the highest gaze frequency and the lowest gaze frequency.

• 천문학논총
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• 제30권3호
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• pp.811-819
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• 2015

The e-CALLISTO is a network of CALLISTO (Compact Astronomical Low-frequency, Low-cost Instrument for Spectroscopy in Transportable Observatories) spectrometers which detect solar radio bursts 24 hours a day in frequency range 45-870 MHz. The number of channels per spectrum is 200 and the time resolution of whole spectrum is 0.25 second. The Korean e-CALLISTO station was developed by Korea Astronomy and Space Science Institute (KASI) collaborating with Swiss Federal Institute of Technology Zurich (ETH Zurich) since 2007. In this paper, we report replacement of the tracking mount and development of the control program using Visual C++/MFC. The program can make the tracking mount track the Sun and schedule CALLISTO to start and to finish its observation automatically using the Solar Position Algorithm (SPA). Daily tracking errors (RMSE) are 0.0028 degree in azimuthal axis and 0.0019 degree in elevational axis between 2014 January and 2015 July. We expect that the program can save time and labor to make the observations of solar activity for space weather monitoring, and improve CALLISTO data quality due to the stable and precise tracking methods.

• Geomechanics and Engineering
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• 제12권5호
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• pp.849-862
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• 2017

With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than $20{\mu}m$, showing large pores > $2{\mu}m$ and small pores within the solid matrix whose sizes are less than $1{\mu}m$. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (${\omega}>0.2Hz$), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of ${\sim}0.1-10^{-3}Pa$ and the increasing loss modulus in the range of ${\sim}10^{-4}-1\;Pa$. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.

• 한국전자파학회논문지
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• 제20권12호
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• pp.1297-1307
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• 2009

본 논문의 목적은 3.1~4.8 GHz 대역에서 UWB를 허용하기 위해 MB-OFDM UWB 통신을 수행하지 않는 silent time 동안 MB-OFDM UWB 시스템 수신 구조를 이용하여 국내 DAA 기술 기준에서 정한 －80 dBm/MHz 이상의 피 간섭 신호를 검출하고 피 간섭 신호의 주파수 대역을 추정하는 알고리즘을 제안하는 것이다. 국내 DAA 기술 기준에서는 UWB 기기에서 -80 dBm/MHz 이상의 피 간섭 신호를 검출할 경우, 2초 이내에 회피 동작을 수행하도록 정의하고 있다. 본 논문에서는 UWB 통신 채널 변경을 통한 간섭 회피 동작을 수행하기 위해 -80 dBm/MHz 이상의 피 간섭 신호를 시간 영역 수신 신호 정보를 이용하여 검출하는 피 간섭 신호 검출 알고리즘과 UWB 통신 대역을 유지하면서 피 간섭 신호가 존재하는 대역에서만 송신 출력을 -70 dBm/MHz 이하로 낮추는 tone-nulling 회피 동작을 수행하기 위해 주파수 영역 정보를 이용하여 피 간섭 신호의 subcarrier 위치를 추적하는 알고리즘을 제시하고, 시뮬레이션을 통해 성능을 검증하였다.