• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.118-124
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• 2016

In this paper, contribution analysis method using a partial coherence function is dealt with in the case of underwater radiation noise. When performing the contribution analysis using a partial coherence function, it is important to select the order of system input. But in the case of frequency correlated systems, it is very difficult to properly select the order of system input. In order to solve this problem, the contribution analysis is performed by subdividing the area of contribution using multiple coherence function. And the new contribution analysis method is presented by using the relationship between the contribution characteristic matrix and multiple coherence function. In order to validate the new method, calculation is performed about multi-input / single-output model which is composed of sine waves. The result of calculation shows that it is possible to derive the exact contribution values.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.1
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• pp.74-79
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• 2010

Many control techniques have been purposed in order to improve the control performances of the control system. The freedom on control in the control system is decided by the number of the closed-loop transfer function which can adjust independently. The design method of the controller with two degrees of freedom(TDOF) is used extensively for following the desired value and rejecting the disturbance. In this paper, the control system with the disturbance observer(DOB) for rejecting the disturbance is transformed by the control system with TDOF and the rejection of a transient response is easy at the starting time and load variation. The design method of the DOB is proposed in the frequency-domain and the control system with TDOF is constructed by using the DOB which is designed with this method. Through the simulation results, the usefulness of the proposed algorithm is proved.

• Journal of the Korean Institute of Telematics and Electronics
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• v.9 no.1
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• pp.17-24
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• 1972

A method utilizing vector representation is investigated for determining a faulty elenlent in passive and active networks by simple external measurements. A large system may be considered as an interconnection of a number of subnetlvorks. By utilizing the relationships between the magintudes of a transfer function at various frequencies and the deviations of a circuit element, the fault simulation curves can be drawn. The fault identification regions are defined from the fault simulation curves. A fault identlfication matrix is constructed corresponding the defined fault identification regions. The fault identification matrix, when premultiplied by a vector whose components are measured from a network, yieldg another vector whose components identify a network element which is faulty. A test procedure for the fault identification method is presented and verified by experiments.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.14 no.5
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• pp.30-37
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• 2015

The study for enhancing the data transmission rate of the next generation wireless communication system using MIMO system operating in the frequency selective fading environment is currently actively conducted. Mixed signal from each transmitted antennas are received at antennas. The training signal with orthogonal property is needed to separate the mixed signal and enable to estimate channel and time synchronization. In this paper we introduce several training sequences used in MIMO communication system and proposed the modified WeCAN sequence with good auto-correlation property in interested area. We compared auto-correlation property of each sequence via simulation and compared the performance of sequences in doppler shift and multipath fading channel.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.297-297
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• 2010

KSTAR 토카막의 두번째 실험 캠페인 동안 고속파 전자가열 (FWEH)을 위한 ICRF 고주파입사 실험을 실시하였다. 토로이달 자기장은 2 T, 플라즈마 전류는 200-300 kA, 주반경은 1.8 m, 부반경은 0.5 m의 원형 플라즈마가 가열 대상이 되었으며, 네개의 ICRF 안테나 전류띠 가운데 중심부의 두개의 전류띠를 최대 300 kW로 구동하기 위한 운전 주파수는 44.2 MHz가 선택 되었다. 이 주파수는 플라즈마의 모든 영역에서 이온 사이클로트론 공명을 일으키지 않으므로 플라즈마에 흡수되는 대부분의 출력은 전자에게 전달될 것으로 기대되었다. 낮은 고주파-플라즈마 결합으로 인하여 전송선의 최대 고주파 전압이 허용치를 초과하기 때문에 비교적 낮은 최대 출력만이 허용 되었으나, ECE에 의해 관측된 전자의 온도는 국지적으로 최대 150 % 까지 증가하는 것을 확인 할 수 있었다. 낮은 고주파-플라즈마 결합의 첫번째 원인은 FWEH의 효율이 이온을 가열할 때 보다 상대적으로 낮기 때문이다. 플라즈마 내에 이온 사이클로트론 공명층이 형성되면 높은 효율로 고주파를 입사 할 수 있다는 것은 잘 알려진 사실이다. 또다른 원인은 D 형상의 플라즈마에 맞도록 만들어진 안테나와, 원형 플라즈마간의 부조화로 인하여 고속파 차단층이 (Fast Wave Cutt-off Layer) 평균적으로 넓게 형성되기 때문이다. 플라즈마 외곽에 반드시 존재하는 낮은 플라즈마 밀도의 고속파 차단층 내부에서, 중심부로 향하는 고주파의 진폭은 지수함수로 감쇠하므로 가능하면 플라즈마 밀도를 높여 차단층 자체의 폭을 줄이거나, 안테나 전류띠를 플라즈마에 바짝 접근시켜야만 한다. 고주파 진단 장치로는 송출기의 출력과 반사파 측정 장치, 공명루프의 전압 측정 장치가 있는데, 이것들을 이용하여 안테나에 전달되는 출력 및 고주파-플라즈마 결합 효율을 나타내는 플라즈마에 대한 고주파 부하 저항을 구할 수 있다. 측정 결과, 부하 저항의 최소값은 진공시 또는 ICRF만의 방전시의 값 0.25 Ohm 보다 큰 0.5 Ohm을 나타냈으며, 최대값은 플라즈마의 상태에 따라 1 Ohm에서 2 Ohm 사이에서 매우 빠르게 요동하는 것을 확인했다. Mm 파 반사계의 측정에 의하면 플라즈마 언저리의 위치가 약 3 cm 정도의 크기로 요동하는 것으로 나타났는데, 부하 저항과 언저리 위치의 파형이 정확하게 일치하지 않지만 유사한 경향성을 가진 것으로 보인다. 따라서 플라즈마 언저리 위치의 제어를 통하여 가열 효율을 높게 유지할 수 있음을 알 수 있다. 본 발표에서는 실험의 소개와 함께 부하 저항의 관점에서 가열 효율을 높일 방안을 토론하도록 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.2
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• pp.293-305
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• 1994

In this paper the efficient channel models of the subscriber loops for the ISDN U-interface digital transmission are presented. Several configuration medels of the loop network are adopted from the CCITT recommendations, and various parameters specifying the physical dimensions are determined in accordance with the measurements of the loop characteristics of Korea. A typical loop interfacing circuit is applied at both ends of the loops and the overall transmissing circuit model is obtained. Based on this circuit model of transmission. 3 types of signal path models, related to transmission, echo, and near end crosstalk noise are defined and their transfer function are respectively derived as the channel models. As examples of the proposed channel models, numerical calculation has been performed for some loop configuration models and the channel responses are investigation in both domains of frequency and time. It is shown that various changes of the loop characteristics can well be explained in terms of the proposed models. And these models can efficiently be used for the simulation of the digital transmission over the subscriber loop.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.141-147
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• 2019

In this paper, a systematic beam splitter design for multi-beam forming is proposed. The objective of this research is to a design beam splitter that splits and focuses scattering microwaves into intense beams in multiple directions. It is difficult to split multi-beam to non-specific directions with theoretical approaches. Therefore, instead of using transformation optics(TO), which is a widely used process for controlling electromagnetic wave propagation, we used a systematic design process called the phase field design method to obtain an optimal topological structure of beam splitter. The objective function is to maximize the norm of electric field of the target areas of each direction. To avoid island structure and obtain the structure in one body, volume constraint is added to the optimization problem by using augmented Lagrangian. Target frequency is set to X-band 10GHz. The optimal beam splitter performed well in multi-beam forming and the transported electric energy of target areas improved. A frequency dependency test was conducted in the X-band to determine effective frequency range.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.55-62
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• 2009

In this paper, we propose a method on the training sequence based on channel estimation issues for relay networks that employ amplify-and-forward(AF) transmission scheme. In $^{[1]}$ and $^{[2]}$, we have to point out that jointly estimating the channel from source to relay and from relay to destination suffers from many drawbacks in fast fading case because the estimation of previous pilots is not suitable for current channel. In this paper, we consider a new joint estimation of overall channel impulse response(CIR) using one OFDM signal without pilots. Using the maximum likelihood(ML) function, we derive a channel estimator by taking the frequency domain of transmitted signal as Gaussian and averaging the ML function over the resulting Gaussian distribution. Simulation results show that our proposed channel estimator performs a fraction of 1dB compared with $^{[1]}$ in high SNR region.

• Journal of the Korean Wood Science and Technology
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• v.38 no.4
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• pp.292-297
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• 2010

Sound absorption capability and anatomical features of kagikazura (Uncaria rhynchophylla) and larch (lalix kaemferi) wood were estimated. Sound absorption coefficients had been measured by the two microphone transfer function method and anatomical features of kagikazura wood examined by SEM observation. The sound absorption coefficients of Uncaria rhynchophylla was higher than lalix kaemferi. Especially, in the frequency range of 1 to 4KHz, sound absorption coefficients of kagikazura was about 2~3 times higher than those of lalix kaemferi. Abundant and big vessel observed on the cross sectional surface of kagikazura wood and simple perforation plate observed on the longitudinal surface. It was surmised that the abundant big vessel element and simple perforation plate behaved as a sound absorbing pore.

• Journal of the Korean Wood Science and Technology
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• v.40 no.4
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• pp.237-243
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• 2012

Sound absorption capability and anatomical features of the organosolv pretreated Japanese larch and yellow poplar wood were estimated by stereoscopic observation and two microphone transfer function method. Sound absorption capabilities of organosolv treated wood, in the entire estimated frequency range (50~6,400 Hz), were higher than those of control specimen. Especially, the treated wood's absorption capabilities measured in the frequency range of 2~4 kHz were about two times higher than those of control specimen. By the organosolv pretreatment (at $70{\sim}120^{\circ}C$), the weight loss of wood occurred in less than 1% of total weight of wood and the porosity of wood increased slightly. In addition, it was presupposed that microstructural changes of wood occurred during organosolv pretreatment and this structural changes cause the increasing of the sound absorption capability of wood.