• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.665-672
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• 2015

We demonstrate an ultrathin metamaterial for polarization independent perfect absorption as well as a band-pass filter (BPF) which works at a higher frequency band compared to the perfect absorption band. The planar metamaterial is comprised of three layers, symmetric split ring resonators (SSRRs) at the front and structured ground plane (SGP) at the back separated by a dielectric layer. The perfect metamaterial absorber (MA) can realize near 100% absorption due to high electromagnetic losses from the electric and/or magnetic resonances within a certain frequency band. The thickness of the structure is only 1/28 of the maximum absorption wavelength.

• Journal of the Korean Ceramic Society
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• v.31 no.1
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• pp.11-16
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• 1994

The impedance matching solution map is not a sufficient method for designing the broad-band absorber because of its difficulty to get numerical data about practical band-width. Therefore, we develope a new method to design the broad-band absorber. The complex permeability limits, which is necessary for designing the broad-band absorber in C-X band (4 GHz~12.4 GHz) were investigated and application was also examined. The complex permeability limits represent the frequency dependence of the complex permeability at a practical frequency band. These complex permeability limits can be used effectively to design broad-band single-layered absorber because they offer numerical data about the band-width in the case of various dielectric loss tangent, practical frequency bands and permitted reflection losses of an absorber.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2315-2317
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• 2005

In this paper, an iterative method to model the electromagnetic heating of electrically large lossy dielectrics is presented. Frequency domain finite element (FEM) solutions of the wave equation are determined for the lossy inhomogeneous dielectric as the material properties are change with temperature and time. The power absorbed from microwave losses is applied to a finite element time domain (FETD) calculation of the heat diffusion equation. Time steps appropriate for updating the piecewise material properties in the wave equation and the time stepping of the heat equation are presented. The effects of preheating and source frequency are investigated.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2166-2168
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• 2005

This paper presents the frequency - dependent characteristics of leakage currents flowing through ZnO varistor. The leakage current - voltage (V-I) characteristic curves of the commercial ZnO varistor were measured. The resistive leakage current was increased with increasing the magnitude and frequency of the applied voltage in the low conduction region. The power losses of ZnO varistor increase as the frequency of applied voltage increases, because of the dielectric loss related to the frequency of the test voltage.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.22-26
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• 2019

With an increasing potential to realize quantum computer, it has recently been an important issue to extend the capabilities of RF cavities to maintain longer coherent quantum system. Using superconductors instead of normal metals allows the quantum system to have a substantially enhanced quality factor. In this paper, surface impedances of superconducting cavities are calculated by the Mattis-Bardeen theory with Python & MATLAB programs. With a simulation of electromagnetic field distribution, the sensitivity to dielectric and surface losses of the superconducting cavities are determined. Then calculations of the resonance frequency and quality factor of three-dimensional superconducting resonators made of Al or Nb are discussed.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.2
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• pp.11-19
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• 1999

The design procedure as well as some test results of a low-cost commercial radome for mobile DBS(Direct Broadcasting Satellite) receiving antenna system are presented in this paper. At first the complex permittivity of dielectric material should be measured in order to select a material for radome design. The complex permittivities of low-cost plastics supplied by domestic vendors are measured and presented. And then the transmission losses of the sheets are calculated. The calculated results are verified by the measurements of wave transmission test of that sheets. Two kinds of radomes, ABS single-layer and A-Sandwich((PET-Foam-ABS), are fabricated and measured practically. The transmission losses of single-layer and A-sandwich radome are 1.5dB and 0.6dB respectively at the maximum wave incident angle of 57 degree. Also the calculated crosspolarization caused by A-sandwich radome is under 20dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.11
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• pp.1051-1061
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• 2004

In this Paper, a new antenna(VHMDA) characteristics of half-circular/elliptical disc-loaded planar antennas with horizontally top-loaded small disc is studied by simulation and measurements with additional resonant structure. The transfer function characteristics of Gaussian pulse from the designed UWB transmitter antenna has been investigated. The radiation pattern of the proposed antenna in azimuth is nearly omni-directional response, which is usulally required in conventional monopole antenna. In addition to that, the simulation and measured results show that the return loss characteristics of VHDMA covers considerably large bandwidth with small area. From the measured results of the circular and half-circular disc-loaded monopole antennas with small disc mounted on the top, it is found that the half disc-loaded monopole antenna with additional structure can be comparable to the circular disc-loaded monopole antenna in respect o( size and electrical performances. Surface wave and dielectric losses often caused by the printed antenna using high dielectric constant does not occur in metallic planar antenna with good impedance matching and without lossy matching unit. This structure implies that the performance of return loss is directly related with the radiation efficiency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.161-161
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• 2009

Ion bombarded inorganic materials for LC alignment has been researched as it provides controllability in a nonstop process for producing high-resolution displays. Many optically transparent insulators such as $SiOx$ and a-C:H have been investigated as potential candidates for inorganic alignment materials. Even so, LC orientation on a new material with superior capacity is required to produce high-performance displays. Many inorganic materials with high permittivities can reduce the voltage losses due to the LC alignment layer that are a trade-off for its capacitance. The minimum voltage for device operation can be applied to the LC under low external voltage using these materials. This means that low power consumption for LCD applications can be achieved using a high-k alignment structure in which the LC can be driven effectively with a low threshold voltage. Among the many other potential high-k oxides, HfO2 is considered to be one of the most promising due to its remarkable properties of high dielectric constant, relatively low leakage current, large band gap (5.68 eV), and high transparency. Due to these characteristics, HfO2 can be used in LC alignment to increase the capacitance of the inorganic alignment layer for low-voltage driving of LCs.

• Journal of electromagnetic engineering and science
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• v.4 no.3
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• pp.113-118
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• 2004

As an application of ring filters, a new and simple method to determine an inherent-ring-resonance frequency is introduced. The ring filter consists of a ring and two short stubs. They are connected at 90$^{\circ}$ and 270$^{\circ}$ points of the ring and the ring filter may be seen in such way that two filters are connected in parallel. Therefore, if the two powers of the two filters are out-of-phase at the output, the power excited at the input can not be delivered. That can be done by making difference in length of the two short stubs, and when a certain condition is satisfied, a frequency exists where all the excited power is reflected. That is the very inherent-ring-resonance frequency. In the lossless case, the return loss with the condition reaches 0 dB at the inherent-ring-resonance frequency but does not with conductor, dielectric losses and so on. Therefore, the effective loss tangent at a frequency of interest may be obtained correctly. To verify the method, two ring filters have been fabricated in microstrip lines and the measured results show good agreement with the predicted ones.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.107-110
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• 2003

High Temperature Superconductor (HTS) transmission cable can carry more than 2 to 5 times higher electricity and also obtain substantially lower transmission losses than conventional cables. Liquid nitrogen is to be used to cool the HTS power cable and its cost is much cheaper than the liquid helium used for the cooling of metal superconducting wire. In Korea the HTS power cable development project has been ongoing since July, 2001 with the basic specifications of 22.9kV, 50MVA and told dielectric type as the first 3-year stage. The cryogenic system of the HTS cable is composed of HTS cable cryostat termination and refrigeration system. Termination of HTS cable is a connecting part between copper electrical cable at room temperature and HTS cable at liquid nitrogen temperature. In order to design the termination cryostat, it is required that the conduction heat leak and Joule heating on the current lead be reduced, the cryostat be insulated electrically and good vacuum insulation be maintained during long time operation. Heat loads calculations on the copper current lead have been performed by analytical and numerical method and the feasibility study fer the other candidate materials has also been executed.