• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.124-135
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• 2000

In this study, a numerically efficient method for the analysis of microstrip structures is considered in conjunction with the use of closed-form spatial Green's functions. As is well-known, the use of the closed-form Green's functions can reduce the evaluation time of impedance matrix elements. However the problematic aspect that in general the evaluation results of diagonal elements of the matrix converge slowly, has been observed. The main cause of the slow convergence has been due to the terms of closed-form Green's functions with small exponent. In other to resolve the problematic aspect, a method of numerical integration based on the change of variable is considered in evaluating matrix elements. The present method is applied for the analysis of a coaxial-fed microstrip antenna. When the present results are compared with the previous results in order to check the validity of the present method, fairly good agreements between them are observed.

• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.1
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• pp.50-69
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• 2001

Three kinds of high-speed signaling methods for synchronous DRAM (SDRAM) bus interface channels (PC-133, Direct-Rambus, and SSTL-2) were analyzed in terms of the timing budget and the physical transmission characteristics. To analyze the SDRAM bus interface channels, loss mechanisms and the effective characteristic impedance method were reviewed and the ABCD matrix method was proposed as an analytic and yet accurate method. SPICE simulations were done to get the AC responses and the eye patterns of the three SDRAM bus interface channels for performance comparisons. Recent progress and future trend for SDRAM bus interface standards were reviewed.

• ETRI Journal
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• v.40 no.3
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• pp.303-308
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• 2018

This paper proposes a simple yet accurate method for estimating the antenna correlation coefficient (ACC) of a high-order multiple-input multiple-output (MIMO) antenna. The conventional method employed to obtain the ACC from three-dimensional radiation patterns is costly and difficult to measure. An alternate method is to use the S-parameters, which can be easily measured using a network analyzer. However, this method assumes that the antennas are highly efficient, and it is therefore not suitable for lossy MIMO antenna arrays. To overcome this limitation, we define and utilize the non-coupled radiation efficiency in the S-parameter-based ACC formula. The accuracy of the proposed method is verified by the simulation results of a 4-port highly coupled lossy MIMO array. Further, the proposed method can be applied to N-port arrays by expanding the calculation matrix.

• JSTS:Journal of Semiconductor Technology and Science
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• v.12 no.3
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• pp.270-277
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• 2012

This paper presents a new DAC design strategy to achieve a wideband dynamic linearity by increasing the bandwidth of the output impedance. In order to reduce the dominant parasitic capacitance of the conventional matrix structure, all the cells associated with a unit current source and its control are stacked in a single column very closely (stacked unit cell structure). To further reduce the parasitic capacitance, the size of the unit current source is considerably reduced at the sacrifice of matching yield. The degraded matching of the current sources is compensated for by a self-calibration. A prototype 6-bit 3.3-GS/s current-steering full binary DAC was fabricated in a 1P9M 90 nm CMOS process. The DAC shows an SFDR of 36.4 dB at 3.3 GS/s Nyquist input signal. The active area of the DAC occupies only $0.0546mm^2$ (0.21 mm ${\times}$ 0.26 mm).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.5
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• pp.1342-1348
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• 1998

The major limitation of MOM solution has alaways been the computer CPU time and storage size, needed to carry out the impedance matrix computation. A new formulation technique using Sorce Superimposion method is presented in order to cut down computerstorage requirements and CPU time based on the equivalence principle and induction theorem. The numerical results are shown to give good agreement to those calculated by the conventional method and also application example is presented.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.141-145
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• 1998

The electrical properties of the mixed conducting yttria(8 mol%) stabilized zirconia(YSZ)-nickel oxide(NiO) composites were examined by a.c. impedance, 4-probe d.c. conductivity between 400 and $1000^{\circ}C$. The oxygen partial pressure dependence of conductivity, and electromotive force measurement of galvanic cell enabled to determine the electronic contribution to the conduction. Up to 6 vol% NiO addition, the conductivity decreased since the electronic NiO acted as an insulator in ionic matrix. However the ionic transport was dominant until NiO content reaches 26 vol%. Mixed conduction was observed between 26 and 68 vol% of NiO. The effect of composition on the electrical property was explained by the microstructure and thus by the distribution of two phases.

• Proceedings of the KIEE Conference
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• 2007.11b
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• pp.148-150
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• 2007

This paper presents a calculation method of an induced voltage on telecommunication lines using primitive impedance matrix. The advantages of the method are using actual neutral current value and not using screening factor for considering the overhead ground wire and neutral wire. To verify the effectiveness and accuracy of the method, case studies are performed with EMTP (Electro-Magnatic Transient Program).

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.395-397
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• 2009

현재의 전력 사용량 증가로 인해 보호설비의 보수 및 증설이 불가피하게 되었다. 계통상의 사고 전류를 제한하기 위한 방안으로 초전도 한류기의 연구 개발 중이다. 본 논문에서는 사고시 사고전류를 제한하기 위한 매트릭스형 초전도 한류기의 사고전류가 제거 된 이후 회복특성을 조사하였다. 초전도 소자의 ��치로 인해 사고전류를 제한하는 것도 중요하지만 사고 후 회복 특성 또한 계통적용에 있어 큰 영향을 미친다. 초전도 소자와 병렬 연결된 자장인가 코일의 임피던스 차이에 따른 특성을 비교하여 좀 더 나은 설계 파라미터 값을 도출하였다. 자장인가 코일의 임피던스가 커짐에 따라 초전도 소자의 전력부담을 감소시켜 회복 시간을 줄일 수 있었고, 초전도 소자의 수명에도 큰 영향을 미치는 것을 확인할 수 있었다.

• Composites Research
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• v.14 no.6
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• pp.38-46
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• 2001

In this study, An optimization code that can design microwave absorbing composite laminates is developed, and 3-layered microwave absorbing composite laminates are developed by optimizing the thickness of each layer. The layers are 3 different composite laminates. Many variables including lay-up angles of electromagnetically orthotropic composite layer can be considered in this code. The developed laminate is composed of an impedance matching layer of glass/epoxy fabric laminate, a glass/epoxy fabric laminate layer containing aluminum filler and carbon/epoxy fabric laminate layer. Permittivities of the materials are obtained using a network analyzer and a coaxial air line.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1650-1658
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• 2003

This paper deals with a novel shunt circuit, which is capable of suppressing multimode vibration amplitudes by using a pair of piezoceramic patches. In order to describe the characteristic behaviors of a piezoelectric damper connected with a series and a parallel resistor-negative capacitor branch circuit, the stiffness ratio and loss factor with respect to the non-dimensional frequency are considered. The mechanism of the shunt damper is also described by considering a shunt voltage constrained by shunt impedance. To obtain a guideline model of the piezo/beam system with a negative capacitive shunting, the governing equations of motion are derived through the Hamilton's principle and a piezo sensor equation as well as a shunt-damping matrix is developed. The theoretical analysis shows that the piezo/beam system combined with a series and a parallel resistor-negative capacitor branch circuit developed in this study can significantly reduce the multiple-mode vibration amplitudes over the whole structural frequency range.