• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.4
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• pp.377-387
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• 2016

Design of X-band frequency FMCW based imaging radar with multi-resolutions and performances of the self-manufactured radar system are presented in this study. In order to implement the multi-bandwidths, a ramp sequence of the FMCW signal is consisting of two kinds of 'saw-tooth' waveform with different bandwidth, and a receiver circuit consisting of L-band source and frequency converter circuit is used to effectively extract spectra of beat-frequency from the received signal of X-band frequency. The system setups for performance measurement of self-manufactured radar system are maximum output power of 35 dBm, sampling frequency of 1.2 MHz and sweep time of 1 ms. Then, the measured resolutions of the modulated signal having bandwidth of 500 MHz and 300 MHz in range & azimuth-direction are (0.28 m, 0.26 m) and (0.44 m, 0.27 m), respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2618-2624
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• 2009

Harmonics (or distortion in wave form) has always existed in electrical power systems. It is harmless as long as its level is not substantial. However, with the recent rapid advancement of power electronics technology, so-called nonlinear loads, such as variable frequency drives for motor power/speed control, are increasingly finding their way to shipboard or offshore applications. In this paper a new approach to direct torque control (DTC) of induction motor drive is presented. In comparison with the conventional DTC methods the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the current harmonics. As compared to the existing DTC approach with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.1
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• pp.70-75
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• 2022

Accurately measuring location is necessary to provide a variety of services. The data for indoor positioning measures the RSSI values from the WiFi device through an application of a smartphone. The measured data becomes the raw data of machine learning. The feature data is the measured RSSI value, and the label is the name of the space for the measured position. For this purpose, the machine learning technique is to study a technique that predicts the exact location only with the WiFi signal by applying an efficient technique to classification. Ensemble is a technique for obtaining more accurate predictions through various models than one model, including backing and boosting. Among them, Boosting is a technique for adjusting the weight of a model through a modeling result based on sampled data, and there are various algorithms. This study uses Xgboost among the above techniques and evaluates performance with other ensemble techniques.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.286-286
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• 2020

인공함양은 대수층함양관리 중 하나의 기법이며 하수처리장 방류수의 영향을 직·간접적으로 받은 물을 지하대수층에 함양하여 수질의 향상을 기대할 수 있다. 그러나 방류수의 영향으로 인해 다수의 미량유해물질들이 대수층으로 유입됨에 따라 함양 후 회수할 때 이들의 검출이 빈번해졌다. 이에 따라 이 미량유해물질의 제거를 위해 인공함양의 후속 공정으로 나노막 여과를 고려하여 인공함양과 나노막 공정을 통하여 미량유해물질의 거동을 파악하고자 하였다. 본 연구에서는 인공함양 지하저수지 모사 컬럼을 설계하여 실험하였다. 서울특별시 탄천 하류에서 샘플링한 물을 원수로 사용하였으며 인공함양에 앞서 염소, 과망간산염, 오존의 3종류 산화 전처리를 통하여 그 영향을 확인하고자 하였다. 함양기간은 2.5일이었으며 함양 후 나노막 장치를 통하여 최종 유출수를 획득하였다. 인공함양 결과 용존유기물은 45%~63% 수준에서 제거가 되어 인공함양시 용존유기물의 제거가 가능함을 확인하였다. 산화 전처리에 따른 동화가능유기탄소의 증가로 인하여 생분해가 주요 기작인 인공함양 처리를 통하여 동화가능유기탄소의 제거율이 유기용존탄소의 제거율에 직접적으로 영향을 주었음을 알 수 있었다. 미량유해물질로 알려진 과불화화합물의 경우 산화 전처리에 따른 제거는 관찰되지 않았으며 잔류의약물질의 경우 대상 물질의 물리·화학적 특성에 따라 산화시 제거가 가능함을 확인하였다. Iopromide와 같은 조영제의 경우 오존 산화를 통하여 98% 이상 제거되어 산화를 통한 제거가 가능함을 확인하였다. 인공함양시 과불화화합물은 분자량이 큰 PFNA, PFDA, PFOS 등이 제거되었으며 그 제거율은 각각 최대 >99%까지 도달하였다. 분자량이 작은 과불화화합물의 경우 인공함양을 통과하는 경향을 보였다. 잔류의약물질의 경우 생분해가 용이한 물질은 제거가 됨을 확인하였으며 carbamazepine 등 제거가 안 되는 물질은 제거율이 18% 미만으로 확인하였다. 나노막 여과 결과 과불화화합물이 최대 >99%까지 제거됨을 확인하였으며 미량유해물질의 경우에도 대부분의 물질이 제거됨을 확인하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.1
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• pp.61-69
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• 1998

In this paper, discrete current control of voltage source inverters is proposed. As a current control scheme, the constant switching frequency predictive current control is adopted and implemented with DSP microprocessor system. In particular, the proposed method is for the compensation of the control lagging due to calculation delays in the microprocessor controller. In controlling the current, the inverter output voltage saturation problem is inevitable and usually affects the current control performance. So, the saturation boundary condition of the inverter output voltage and its effects on the current controal performance of the proposed current control scheme are investigated with experiment. Finally, the proposed scheme is applied to the active power filter system and some results are described for validation.

• Journal of Broadcast Engineering
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• v.18 no.1
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• pp.10-20
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• 2013

Nowadays, video technology has been successfully improved creating tremendous results. As video technology improve, multimedia devices and demands from users are diversified. Therefore, a video codec used in these devices should support various displays with different resolutions. The technology to generate a higher resolution image from the associated low-resolution image is called interpolation. Interpolation is generally performed in either the spatial domain or the DCT domain. To use the advantages of both domains, we have proposed the new adaptive interpolation algorithm based on edge direction, which adaptively exploits the advantages of both domains. The experimental results demonstrate that our algorithm performs well in terms of PSNR and reduces the blocking artifacts.

• Journal of IKEEE
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• v.14 no.2
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• pp.16-23
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• 2010

Since the interest of a brain science research is increased recently, various devices using brain waves have been developed in the field of brain training game, education application and brain computer interface. In this paper, we have developed a portable EEG measurement and a bluetooth based wireless transmission device measuring brain waves from the frontal lob simply and conveniently. The low brain signals about 10~100${\mu}V$ was amplified into several volts and low pass, high pass and notch filter were designed for eliminating unwanted noise and 60Hz power noise. Also, PIC24F192 microcontroller has been used to convert analog brain signal into digital signal and transmit the signal into personal computer wirelessly. The sampling rate of 1KHz and bluetooth based wireless transmission with 38,400bps were used. The LabVIEW programing was used to receive and monitor the brain signals. The power spectrum of commercial biopac MP100 and that of a developed EEG system was compared for performance verification after the simulation signals of sine waves of $1{\mu}V$, 0~200Hz was inputed and processed by FFT transformation. As a result of comparison, the developed system showed good performance because frequency response of a developed system was similar to that of a commercial biopac MP100 inside the range of 30Hz specially.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.391-399
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• 2005

Laser-generated ultrasonic inspection system is a non-contact scanning inspection device with high spatial resolution and wide bandwidth. The amplitude of laser-generated ultrasound is varied according to the energy of pulse laser and the surface conditions of an object where the CW measuring laser beam is pointing. In this paper, we correct the generating errors by measuring the energy of pulse laser beam and correct the measuring errors by extracting the gain information of laser interferometer at each time. h dynamic stabilizer is developed to stably scan on the surface of an object for an laser-generated ultrasonic inspection system. The developed system generates ultrasound after adaptively finding the maximum gain time of an laser interferometer and processes the signal in real time after digitization with high speed. In this paper, we describe hardware configuration and control algorithm to build a stable laser-generated ultrasonic inspection system. Also, we confirmed through experiments that the proposed correction method for the generating errors and measuring errors is effective to improve the performance of a system.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.74-82
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• 2007

The M-Method that measures the speed of actuator with counting the number of Reaction wheel Tacho Pulse has the many advantages such that a realization is simple and measuring time is uniform, but it also has the disadvantage that measuring speed becomes worse as the wheel speed goes lower. On the contrary, the T-Method that measures the time duration between the pulses is more accurate at lower-speed and its time delay is smaller than M-Method, but its realization is more difficult than M-Method because measuring time is varying with wheel speed variation. Thought M/T Method mixing M-Method with T-Method is widely used in order to measure the speed in the motor industrial area, one of two methods has been used in the spacecraft design area. Therefore, we try to apply both methods together to measuring the speed of Reaction Wheel, the core actuator for low earth orbit satellite. This paper provides the Reaction Wheel simulation board located in the Spacecraft Dynamic Simulator, ground support test set.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.448-448
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• 2013

최근 생물학적 분석 기구에서 시료를 처리, 분리, 검출, 샘플링 또는 분석하기 위해 사용되는 마이크로펌프(Micropump)에 대한 관심이 높아지고 있다. 또한 전자소자의 성능과 신뢰성의 증진을 위한 전자소자의 열 문제를 해결하기 위해 냉각장치로 마이크로 펌프가 적용되기도 한다. 그 외에도 마이크로펌프는 다양한 분야에 응용이 가능하다. 마이크로펌프는 작동 방식에 따라 압전형, 공압형, 열공압형, 연동형 등의 여러 종류로 분류되고 있다. 그중에서도 최근에는 연동형 마이크로 펌프의 개발이 각광받고 있다. 기존의 연동형 펌프들은 다중 챔버를 가지고 있으며, 각각의 챔버 내에서 Dead volume이 많이 발생할 뿐만 아니라 이상적인 연동운동과는 차이가 많이 나는 문제점을 가지고 있다. 또한 압전방식과 열공압방식은 느린 응답성으로 인해 효율적인 유체 이동이 어렵다. 본 논문에서는 이상적인 연동운동을 구현하기 위하여 기존의 연동형 펌프의 단점을 보완하고, 하나의 챔버에 다중전극 구조를 가지는 정전기력방식의 연동형 펌프를 개발하였다. 정전기력방식으로 펌프를 구동함으로써, 저전력으로 펌프구동이 가능하며, 하나의 챔버에 다중전극을 설치함으로써 이상적인 연동운동을 재현하였다. 그리고 Dead volume을 최소화 하였다. 또한, 빠른 반응속도로 인해 효율적인 유체 이동을 실현시킬 수 있었다. 본 연구에서 제안된 마이크로 펌프의 구성은 크게 챔버, 박막, Inlet/outlet hole으로 구성되었다. 챔버는 Si-wafer에 wet etching 공정으로 제작 하였고 그 위에 알루미늄 박막을 200 nm 증착시켰다. 챔버는 가로 32 mm, 세로 5 mm, 깊이는 $15{\mu}m$, 부피는 $200{\mu}l$으로 제작되었다. 박막은 폴리이미드(polyimide)를 사용하여 $3{\mu}m$의 두께로 제작 되었으며, 폴리이미드 박막 사이에는 200 nm 두께의 4개의 알루미늄 박막 전극을 삽입시켰다. 삽입된 4개의 전극에 개별적인 전기신호를 보냄으로써 연동운동이 가능하다. Inlet/outlet hole은 직경 2 mm의 크기로 제작되었으며, 튜브를 연결하여 유체가 흐를 수 있는 체널을 형성하였다. 제작된 마이크로 펌프의 구동전압은 115 V이며, 인가되는 주파수를 1 Hz~100 KHz까지 변화시켜 유량을 측정하였다. 작동 유체는 공기이며, 유량측정은 튜브 내에 물방울을 삽입하여 시간에 따른 이동거리를 관측하였다. 측정결과 2.2 KHz에서 2.4 mm/min의 가장 높은 유량을 확인할 수 있었다. 본 연구를 통해 제안된 연동형 마이크로펌프는 이상적인 연동운동이 가능함으로써 기존의 연동형 방식의 문제점을 보완하였으며, 생명과학, 의학, 화학 등의 분야에서 적용이 가능하리라 기대된다.