• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.673-678
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• 2015

Terahertz dual-band frequency selective surface filters made by perforating two different rectangular holes in molybdenum have been designed, fabricated and measured. Physical mechanisms of the dual-band resonant responses are clarified by three differently configured filters and the electric field distribution diagrams. The design process is straightforward and simple according to the physical concept and some formulas. Due to the weak coupling between the two neighboring rectangle holes with different sizes in the unit cell, good dual-band frequency selectivity performance can be easily achieved both in the lower and higher bands by tuning dimensions of the two rectangular holes. Three samples are fabricated, and their dual-band characteristics have been demonstrated by a THz time-domain spectroscopy system. Different from most commonly used metal-dielectric structure or metal-dielectric-metal sandwiched filters, the designed dual-band filters have advantages of easy fabrication and low cost, the encouraging results afforded by these filters could find their applications in dual-band sensors, THz communication systems and other emerging THz technologies.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.162-163
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• 2002

1-D photonic band-gap structure is identified in a cholesteric liquid crystal system. The optical transmission spectrum is measured and compared with the theoretical analysis. Nonlinear transmission is measured near the band edge. Also 3-D photonic band-gap structures are fabricated from dielectric colloidal polystyrene beads through a centrifuge method. The fabricated photonic crystals exhibit opalescent colors under white light and show a clear diffraction peak dependent on the incident angle of the light beam. Also the scanning electron microscope image was taken to verify the face-centered cubic crystal structure. Bragg's law and Snell's law are employed to describe the position of angle resolved diffraction peaks. It was shown that the optically deduced effective refractive index and lattice constants were in good agreement with the crystal structure identified by scanning electron microscope.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.43-46
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• 2011

A novel circuit structure of dual-band bandstop filters is proposed in this paper. This structure comprises two shunt-connected tri-section stepped impedance resonators with a transmission line in between. Theoretical analysis from the equivalent circuit and design procedures are described. We represented graphs for filter design from the derived synthesis equations by resonance condition of circuits. Notably, advantages of the proposed filter structure are compact size in design, wide range of realizable resonance frequency ratio, and more realizable impedances.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.78-81
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• 2015

This paper investigates the performance of phone case with different permittivities like plastic, urethane and silicone. Then, we put an electromagnetic band gap (EBG) structure in phone case to reduce the specific absorption rate (SAR). In order to design the phone case, a loop antenna for PCS 1900 band was used. The phone case consists of a hairpin-like EBG structure that is more compact than other EBG structures. The SEMCAD X fdtd simulation results showed that, this proposed phone case can reduce SAR by 13 - 30% at similar power that is radiated by the antenna. This phone case can be used in future to reduce the SAR from mobile phones.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.1
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• pp.69-72
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• 2004

A bandpass filter has been designed by employing the PBG structure and the aperture on the ground together in this paper. The harmonics of band pass filter have been suppressed by employing the PBG structure and the bandwidth of it has been broadened by using the aperture on the ground. The three kinds of PBG structures has been combined to suppress the harmonics of the filter The center frequency of filter is 2.2 GHz and the bandwidth has been increased from $40\%$ by the aperture and all harmonics were suppressed about 35dBc by the PBG. The insertion loss has been reduced 3.0dB to 2.6dB.

• Vacuum Magazine
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• v.5 no.2
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• pp.4-9
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• 2018

The research field of graphene has been rapidly expanded ever since its first experimental realization of Dirac fermions in 2005, due to the fundamental importance in physics as a new paradigm for relativistic condensed matter physics as well as a potential building block for next generation device applications. Most of the intriguing physics observed so far in graphene can be traced to its peculiar electron band structure, which is in analogy with relativistic Dirac fermions. This article reviews recent progress in graphene research that has been done using angle-resolved photoemission technique, the most direct probing tool of the electron band structure. In particular, we discuss a few examples of novel properties so far explored ranging from the basic electron band structure to complicated many-body interactions.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.2
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• pp.53-58
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• 2004

In this paper, the low-phase dual-band VCO, by adding switching circuit with PIN diode at feedback loop of the oscillation part having negative-resistance, is realized. In order to reduce the phase noise of the VCO, PBG structure applied to the ground plane of the resonator. When applying for PBG structure, output power is -9.17㏈m and phase noise is -102㏈c/Hz at 5.25㎓, output power is -5.17㏈m and phase noise is -101㏈c/Hz at 1.8㎓, respectively.

• Nuclear Engineering and Technology
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• v.34 no.3
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• pp.202-210
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• 2002

The details of the electronic structure of the perfect crystal provides a critically important foundation for understanding the various defect states in uranium dioxide. In order to understand the local defect and impurity mechanism, the calculation of electronic structure of UO$_2$ in the one-electron approximation was carried out, using a semi-empirical tight-binding formalism(LCAO) with and without f-orbitals. The energy band, local and total density of states for both spin states are calculated from the spectral representation of Green’s function. The bonding mechanism in Perfect lattice of UO$_2$ is discussed based upon the calculations of band structure, local and total density of states.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.7 s.337
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• pp.41-48
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• 2005

We design and fabricate 3-dB tandem directional coupler using the coplanar waveguide structure which is applicable to balanced amplifiers and mixers for 60 GHz wireless local area network system. The coupler comprises the multiple-sectional parallel-coupled lines to facilitate the fabrication process, and enable smaller device size and higher directivity than those of the conventional 3-dB coupler employing the edge-coupled line. In this study, we adopt the structure of two-sectional parallel-coupled lines of which each single-coupled line has a coupling coefficient of -8.34 dB and airbridge structure to monolithically materialize the uniplanar coupler structure instead of using the conventional multilayer or bonded structure. The airbridge structure also supports to minimize the parasitic components and maintain desirable device performance in V-band (50$\~$75 GHz). The measured results from the fabricated couplers show couplings of 3.S$\~$4 dB and phase differences of 87.5$^{\circ}{\pm}1^{\circ}$ in V-band range and show directivities higher than 30 dB at a frequency of 60 GHz.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.504-510
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• 1994

In this work the crystal structure, optical absorption and photoluminescence of Cd$_{4}$GeSe$_{6}$ single srystals grown by the vertical bridgman method are investigated. From the observed results of the PICTS, we proposed on energy band model which contains deep levels between the conduction band and the valence band. The energy band model permit us to explain the mechanism of the radiative recombination for the Cd$_{4}$GeSe$_{6}$ single crystals.als.