• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.11
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• pp.28-33
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• 2002

In this paper, the impedance-tuned monopole microstrip antenna designed for PCS is analyzed using finite difference time domain(FDTD) method. The perfectly matched layer(PML) absorbing material condition proposed by Berenger is used for the truncation of finite difference time domain lattice. A Gaussian pulse is selected as an excitation signal and a resistive voltage source model is used to reduce the error caused by the reflection waves. The FDTD method is inherently a near field technique. Therefore, the near field to far field transformation is need to compute far field antenna parameters such as radiation patterns and gain. The near field to far field transformation can be done both in the time domain and the frequency domain. We use the frequency domain transformation to compute the far field radiation patterns at single frequency. All the numerical results obtained by the FDTD method are compared with simulation results using the HFSS software. Good agreements are obtained in all cases.

• Journal of Wind Energy
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• v.14 no.1
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• pp.29-36
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• 2023

The analysis of the floating offshore wind turbine platform is based on the procedures provided by the IEC including the International Classification Society, which recommends the analysis in the time domain. But time-domain simulation requires a lot of time and resources to solve tens of thousands of DLCs. This acts as a barrier in terms of floating structure development. For final verification, it requires very precise analysis in the time domain, but from an initial design point of view, a simplified verification procedure to predict the quantity of materials quickly and achieve relatively accurate results is crucial. In this study, a structural design procedure using a design wave applied in the oil and gas industries is presented combined with a conservative turbine load. With this method, a quick design spiral can be rotated, and it is possible to review FOWTs of various shapes and sizes. Consequently, a KRISO Semi-Submersible FOWT platform was developed using a simplified design procedure in frequency-domain analysis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.10
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• pp.2299-2304
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• 2010

A sensorless vector control of an induction motor provides a good performance in the middle and high speed region. However, in the low speed region, it is very difficult to implement the sensorless vector controller because the feeding voltage measured by the motor is very low. In this paper, we designed the sensorless vector controller of an induction motor using the estimate of the slip frequency. To verify the performance of the proposed controller, an experiment has been performed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.673-677
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• 2003

In this study, we propose the new filter bank that is adaptive filter bank using neural networks in time domain. Also, we proposed a new filter neuron as neuron with filter window, the structure and algorithm for filter banks. The performance of neural filter banks is shown from two examples. It show characteristics the simple structure and higher speed processing than traditional methods (filter banks in frequency domain, etc.). In many applications, the proposed method will provide the high performance to features detection of signals in time domain.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2255-2256
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• 2008

음성인식 시스템을 설계함에 있어서는 대표적으로 사람의 성도 특성을 모방한 LPC(Linear Predict Cording)방식과 청각 특성을 고려한 MFCC(Mel-Frequency Cepstral Coefficients)방식이 있다. 본 논문에서는 MFCC를 통해 특징파라미터를 추출하고 해당 영역에서의 수행된 작업을 매틀랩 알고리즘을 이용하여 그래프로 시현하였다. MFCC 방식의 추출과정은 최초의 음성신호로부터 전처리과정을 통해 아날로그 신호를 디지털 신호로 변환하고, 잡음부분을 최소화하며, 음성 부분을 강조한다. 이 신호는 다시 Windowing을 통해 음성의 불연속을 제거해 주고, FFT를 통해 시간의 영역을 주파수의 영역으로 변환한다. 이 변환된 신호는 Filter Bank를 거쳐 다수의 복잡한 신호를 몇 개의 간단한 신호로 간소화 할 수 있으며, 마지막으로 Mel-cepstrum을 통해 최종적으로 특징 파라미터를 얻고자 하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.227-230
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• 1999

잔향에 대한 인간의 주관적인 지각을 잔향기 설계에 객관적인 수치로써 반영하는 방법으로, 5 자유도 잔향 모델이 제안된 바 있다[1]. 5자유도 잔향 모델은 잔향에 대한 다섯 개의 객관적인 평가량들을 이용하여 시간에 따른 음 에너지 감쇠 곡선을 근사화한 것이다. 즉 5 자유도 잔향 모델을 이용하여 청취자가 원하는 특성을 갖는 잔향을 객관적으로 묘사할 수 있고, 이는 잔향을 합성할 때 잔향 필터의 설계 기준이 된다. 그러나 이 모델로부터 만들 수 있는 잔향 필터의 개수는 실로 무한하고, 그 중에는 인간이 듣기에 부자연스러운 합성음을 만들어 내는 경우도 있다. 즉 자연스러운 잔향을 만들기 위해서는 잔향 모델 외에도 부가적인 잔향 설계 기준이 필요하다. 시간, 주파수 영역에서 대표적인 특성을 갖는 몇 종류의 원음에 대한 청음실험을 통해, 필요한 잔향 설계 기준을 제시한다.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.10
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• pp.1086-1097
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• 1990

The design of multivariable control systems using the Inverse Nyquist Array method is described in this paper. The INA is a simple design technique, which permits a designer to achieve his objectives for a controller specification in a step-by-step fashion using Gershgorin band and Ostrowski circle. The application to a multivariable system of CANDU nuclear power plant with 5 inputs, 8 outputs, and 24 state variables is reviewed and the simulation shows satisfactory results.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.3
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• pp.66-74
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• 1999

InAlGaAs/InGaAs HBTs with the various emitter junction gradings(xf=0.0-1.0) and the modified collector structures (collector- I;n-p-n, collector-II;i-p-n) are simulated and analyzed by HMC (Hybrid Monte Carlo) method in order to find an optimum structure for the shortest transit time. A minimum base transit time($ au$b) of 0.21ps was obtainsed for HBT with the grading layer, which is parabolically graded from $x_f$=1.0 and xf=0.5 at the emitter-base interface. The minimum collector transit time($\tau$c) of 0.31ps was found when the collector was modified by inserting p-p-n layers, because p layer makes it possible to relax the electric field in the i-type collector layer, confining the electrons in the $\Gamma$-valley during transporting across the collector. Thus InAlGaAs/InGaAs HBT in combination with the emitter grading($x_f$=0.5) and the modified collector-III showed the transit times of 0.87 psec and the cut-off frequency (f$\tau$) of 183 GHz.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.599-606
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• 2010

In the present study, actuators with diaphragms of different thickness and chambers of different diameter are fabricated to examine experimentally how the behavior characteristics of the actuator diaphragm in a thermopneumatic micropump are affected by diaphragm thickness and chamber diameter under various operating conditions with different values of input voltage and frequency. The actuator comprises a microheater set on Pyrex glass, a chamber, and a diaphragm. For all values of the input energy, as the frequency decreases below 10 Hz, the maximum center deflection of the diaphragm greatly increases irrespective of diaphragm thickness and chamber diameter. At low frequencies, as the heat energy supplied to the chamber increases, the center of deflection of the diaphragm increases; the magnitude of deflection is high for thin diaphragms and for diaphragms whose chambers have small diameters. At frequencies higher than 10 Hz, all the design variables such as diaphragm thickness, chamber diameter, and the input energy have negligible effect on the center deflection of the diaphragm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1457-1467
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• 2015

Depending on the type of Tx-Rx pairs, VHF Data Exchange System (VDES) for maritime communication is expected to employ the different frequency channels. Load imbalance between the different channels turns out to be a critical problem for the multi-hop communication using Ad-hoc Self-Organizing TDMA (ASO-TDMA) MAC protocol, which has been proposed to provide the connectivity between land station and remote ship stations. In order to handle the inter-channel load imbalance problem, we consider a model of the stochastic geomety in this paper. After analyzing the spatial reuse efficiency in each hop region by the given model, we show that the resource utility can be maximized by balancing the inter-channel traffic load with optimal resource allocation in each hop region.