• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.786-795
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• 2010

In this paper, we propose a new EBG structure that the two unit cells are connected by the bridge line in signal transmission plane. The SSN of the power plane is reduced effectively by via holes and bridge lines connecting the unit cells. The superior signal transfer characteristic is shown between the signal lines in the signal transmission plane. The proposed EBG structure contains 1.2 GHz cut-off frequency and less than －30 dB suppression in the 8.3 GHz broad bandwidth. In addition, To improve the SI(Signal Integrity) in signal transmission plane keeping the same bandstop frequency range, the optimized location of the reference plane is proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1542-1548
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• 2009

This paper describes a size-reduced Wilkinson power divider using substrate integrated artificial dielectric(SIAD). SIAD transmission lines have increased effective refractive index, so the line width and length are reduced from those of standard transmission lines. Therefore the "size-reduction effect" is achieved if SIAD lines are applied to high frequency circuits. An efficient simulation method is proposed for SIAD lines which have an enormous number of via-holes. A 2GHz Wilkinson power divider is designed and measured using SIAD transmission line as an example of application. The size of the fabricated divider is reduced by 32% due to the increased effective refractive index of SIAD, while the performances are maintained similarly.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.325-330
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• 2017

Photoelectron-hole separation efficiency plays an important role in the enhancement of the photocatalytic activity of photocatalysts towards the degradation of organic molecules. In this study, $TiO_2/TiOF_2$ heterostructured composite powders with suitable band structures, which structures are able to separate photoelectron-hole pairs, have been synthesized using a simple and versatile ultrasonic spray pyrolysis process. In addition, their phase volume fractions have been controlled by varying the pyrolysis temperature from $400^{\circ}C$ to $800^{\circ}C$. The structural and optical properties of the synthesized powders have been characterized by X-ray diffraction, scanning electronic microscopy and UV-vis spectroscopy. The powder with a phase volume ratio close to 1, compared with single $TiOF_2$ and other composite powders with different phase volume fractions, was found to have superior photocatalytic activity for the degradation of rhodamine B. This result shows that the $TiO_2/TiOF_2$ heterostructure promotes the separation of the photoinduced electrons and holes and that this powder can be applicable to environmental cleaning applications.

• Nano
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• v.13 no.10
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• pp.1850118.1-1850118.17
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• 2018

Nanoparticles of the semiconductor catalyst $Cd_xZn_{1-x}S$ were embedded into the metal organic framework MIL-101(Cr) to obtain $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites. These materials not only possess high surface areas and mesopores but also show good utilization of light energy. The ultraviolet-visible diffuse reflectance patterns of $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites showed that $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) possessed good visible light response ability among the synthesized nanocomposites. The photocatalytic performance of the $Cd_xZn_{1-x}S@MIL-101$(Cr) nanocomposites were tested via degradation and mineralization of methylene blue in neutral water solution under light irradiation using a 300W xenon lamp. As a result, using $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) as a catalyst, 99.2% of methylene blue was mineralized within 30 min. Due to the synergistic effect of adsorption by the MIL-101(Cr) component and photocatalytic degradation provided by the $Cd_{0.8}Zn_{0.2}S$ component, the $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) catalyst displayed superior photocatalytic performance relative to $Cd_{0.8}Zn_{0.2}S$ and MIL-101(Cr). Furthermore, $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) possessed excellent stability during photodegradation and exhibited good reusability. The remarkable photocatalytic performance of $Cd_{0.8}Zn_{0.2}S@MIL-101$(Cr) is likely due to the effective transfer of electrons and holes at the heterojunction interfaces.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.9 s.112
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• pp.811-820
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• 2006

Ultra wideband CPW batons are proposed in this paper. The proposed talons are consisted of ultra wideband multi-stage Wilkinson dividers and 'X'-shaped $180^{\circ}$ out-of-phase generator. Bottom-bridges and via-holes are used to connect CPW ground lines instead of the conventional air-bridges which require troublesome manual working in fabrication with HMIC(Hybrid Microwave Integrated Circuits) substrates. The proposed CPW batons have ultra wideband of 3 or $10(=F_{figh}/F_{low})$ theoretically, the wideband characteristics and S-parameters of the basis Wilkinson divider are directly converted to those of the proposed batons. The proposed batons are so compact and small compared to the conventional Wilkinson batons because no additional area for out-of-phase section is required. So the size of the proposed batons is exactly the same as that of the basis Wilkinson dividers. As examples, 3-stage and 7-stage wideband Wilkinson dividers are converted to the proposed batons. Their measured operating bandwidth are $1\sim3GHz$ and $0.8\sim5GHz$, respectively, with excellent matching, isolation and power division performances. The measured magnitude and phase balance errors are ${\pm}0.5dB\;and\;0.45\;dB,\;and\;{\pm}5^{\circ}\;and\;{\pm}10^{\circ}C$ over $1\sim3GHz\;and\;0.8\sim5GHz$, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.585-593
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• 2010

Geographic routing has been considered as an efficient, simple, and scalable routing protocol for wireless sensor networks since it exploits pure local location information instead of global topology information to route data packets. Geographic routing requires the sources nodes to be aware of the location of sinks. Most existing geographic routing protocols merely assume that source nodes are aware of the locations of sinks. How can source nodes get the locations of sinks was not addressed in detail. In this paper, we propose a sink location service via circle path for geographic routing in wireless sensor networks. In this scheme, a sink sends a Sink Location Announcement (SLA) message along a circle path, and a source node sends a Sink Location Query (SLQ) message along a straight path that certainly passes through the circle path. By this way we can guarantee the SLQ path and SLA path have at least one crossing point. The node located on the crossing point of the two paths informs the source node the sink location. This procedure can correctly work in any irregular profile sensor networks such as network that has holes or irregular shape by some rules. Simulation results show that our protocol is superior to other protocols in terms of energy consumption and control overhead.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2674-2685
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• 1997

In this paper, the design and imprlementation of dual-band power amplifier which is used as a critical part for mobile phone to be simultaneously working at a dual band, 800MHz CDAM and PCS frequency band is described. DC operating point of power FET is limited to Class-B to enable long talk time considering that the tyupical power range of CDMA phones in working is around 10 to Class-B to enable long talk time considering that the typical power range of CDMA phones in working is around 10 to 15dBm, i.e., liner range. The power amplifier which employs two GaAs FETs with good linerity at a low operating point has duplexer cuplexer circuit to separate two frequency bands at input and output stage. Electromagnetic analysis for via holes and coupling between narrow transmission lines is included to design a circuit. Moduld size of 0.96CC($22{\times}14.5{\times}3mm^3$) and maximum module current of 130mA at output power range, 10 to 15dBm are attained. The power amplifer module has achieved ACPR performance with 2 to 3dB marging from IS-95 requirement at output powers, 23.5dBm for PCS and 28dBm for 800MHz CDMA respectively.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.393-399
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• 2016

We have successfully fabricated 3D (3-dimensional) nanostructures of $TiO_2$ coated with a $g-C_3N_4$ layer via hydrothermal and sintering methods to enhance photoelectrochemical (PEC) performance. Due to the coupling of $TiO_2$ and $g-C_3N_4$, the nanostructures exhibited good performance as the higher conduction band of $g-C_3N_4$, which can be combined with $TiO_2$. To fabricate 3D nanostructures of $g-C_3N_4/TiO_2$, $TiO_2$ was first grown as a double layer structure on FTO (Fluorine-doped tin oxide) substrate at $150^{\circ}C$ for 3 h. After this, the $g-C_3N_4$ layer was coated on the $TiO_2$ film at $520^{\circ}C$ for 4 h. As-prepared samples were varied according to loading of melamine powder, with values of loading of 0.25 g, 0.5 g, 0.75 g, and 1 g. From SEM and TEM analysis, it was possible to clearly observe the 3D sample morphologies. From the PEC measurement, 0.5 g of $g-C_3N_4/TiO_2$ film was found to exhibit the highest current density of $0.12mA/cm^2$, along with a long-term stability of 5 h. Compared to the pristine $TiO_2$, and to the 0.25 g, 0.75 g, and 1 g $g-C_3N_4/TiO_2$ films, the 0.5 g of $g-C_3N_4/TiO_2$ sample was coated with a thin $g-C_3N_4$ layer that caused separation of the electrons and the holes; this led to a decreasing recombination. This unique structure can be used in photoelectrochemical applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.334-334
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• 2013

In the past decade, the infrared detectors based on intersubband transition in quantum dots (QDs) have attracted much attention due to lower dark currents and increased lifetimes, which are in turn due a three-dimensional confinement and a reduction of scattering, respectively. In parallel, focal plane array development for infrared imaging has proceeded from the first to third generations (linear arrays, 2D arrays for staring systems, and large format with enhanced capabilities, respectively). For a step further towards the next generation of FPAs, it is envisioned that a two-dimensional metal hole array (2D-MHA) structures will improve the FPA structure by enhancing the coupling to photodetectors via local field engineering, and will enable wavelength filtering. In regard to the improved performance at certain wavelengths, it is worth pointing out the structural difference between previous 2D-MHA integrated front-illuminated single pixel devices and back-illuminated devices. Apart from the pixel linear dimension, it is a distinct difference that there is a metal cladding (composed of a number of metals for ohmic contact and the read-out integrated circuit hybridization) in the FPA between the heavily doped gallium arsenide used as the contact layer and the ROIC; on the contrary, the front-illuminated single pixel device consists of two heavily doped contact layers separated by the QD-absorber on a semi-infinite GaAs substrate. This paper is focused on analyzing the impact of a two dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2DAu-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show the enhanced electric fields (thereby increasing the absorption in the active layer) resulting from a surface plasmon, a guided mode, and Fabry-Perot resonances. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors.

• Journal of the Korea Computer Graphics Society
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• v.13 no.4
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• pp.7-12
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• 2007

With the advent of digital cinema, more and more movies are digitally produced, distributed via digital medium such as hard drives and network, and finally projected using a digital projector. However, digital cameras capable of shotting at 2K or higher resolution for digital cinema are still very expensive and bulky, which impedes rapid transition to digital production. As a low-cost solution for acquiring high resolution digital videos, we propose a hybrid camera consisting of a low-resolution CCD for capturing videos and a high-resolution CCD for capturing still images at regular intervals. From the output of the hybrid camera, we can synthesize high-resolution videos by software as follows: for each frame, 1. find pixel correspondences from the current frame to the previous and subsequent keyframes associated with high resolution still images, 2. synthesize a high-resolution image for the current frame by copying the image blocks associated with the corresponding pixels from the high-resolution keyframe images, and 3. complete the synthesis by filling holes in the synthesized image. This framework can be extended to making NPR video effects and capturing HDR videos.