• Journal of the Optical Society of Korea
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• v.11 no.2
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• pp.67-70
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• 2007

A Wide Color Gamut Backlight system was studied using a three-band white Light-Emitting Diode. A three-band white light-emitting diode (LED) was fabricated using an InGaN-based blue LED chip that emits 445-nm blue peak, and a green phosphor and red phosphor that emit 535-nm green and 621-nm red peak emissions, respectively, when excited by 450-nm blue light. Using for this three-band white LED, wide color gamut backlight unit (BLU) was attained. The luminance of BLU and CIE 1931 chromaticity coordinates was $1,700Cd/m^2$ and (0.337, 0.346). Color filter matching simulations for this configuration show that the three-band white LED backlight can be enhanced by up to 16% over conventional white LED backlight color gamut.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.145-150
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• 2006

Various colors of light emitting diodes(LED) and four-band white light sources are obtained using a violet LED and various phosphor films. $BaMg_2Al_{16}O_{27}:Eu\;(blue),\;SrGa_2S_4:Eu\;(green),\;and\;Eu(TTA)_3(PTA)$ (red) phosphors are dispersed in poly-vinyl-alcohol aqueous solutions, and phosphor films are prepared by coating the suspensions to PET film. The narrow band emission of $Eu(TTA)_3(PTA)$ phosphor has excellent red luminescent property for four-band white light excited by the violet LED.

• Journal of Information Display
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• v.9 no.2
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• pp.18-21
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• 2008

We report on white organic light-emitting diodes (WOLEDs) based on single white dopants, $Ir(pq)_2$($F_2$-ppy) and $Ir(F_2-ppy)_2$(pq), where $F_2$-ppy and pq are 2-(2,4-difluorophenyl) pyridine and 2-phenylquinoline, respectively. The similar phosphorescent lifetime of two ligands lead to luminescence emission in two ligands simultaneously. However, the emission color of the devices was reddish, because the energy was not transferred efficiently from the 4,4,N,N'-dicarbazolebiphenyl (CBP) to the $F_2$-ppy ligand, due to the small band gap of the CBP. Accordingly, we used 1,4-phenylenesis(triphenylsilane) (UGH2) with a large band gap, instead of CBP as the host material. As a result, it was possible to adjust the emission color by the host material. The luminous efficiency of the device with $Ir(F_2-ppy)_2$(pq) doped in UGH2 was about 11 cd/A at 0.06 cd/$m^2$.

• Journal of electromagnetic engineering and science
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• v.16 no.1
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• pp.19-23
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• 2016

This paper presents a novel design for dual-band bandpass filters. The proposed filters are applicable to the carrier aggregation of the TV white space (TVWS) band and long-term evolution (LTE) band for cognitive radio applications. The lower passband is the TVWS band (470-698 MHz) whose fractional bandwidth is 40 %, while the higher passband is the LTE band (824-894 MHz) with 8 % fractional bandwidth. Since the two passbands are located very close to each other, a transmission zero is inserted to enhance the rejection level between the two passbands. The TVWS band filter is designed using magnetic coupling to obtain a wide bandwidth, and the LTE band filter is designed using dielectric resonators to achieve good insertion loss characteristics. In addition, in the proposed design, a transmission zero is placed with cross-coupling. The proposed dual-band bandpass filter is designed as a two-port filter (one input/one output) as well as a three-port filter (one common input/two outputs). The measured performances show good agreement with the simulated performances.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.8
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• pp.890-894
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• 2014

In this paper, we derive the CRLB (Cramer-Rao Lower Bound) of effective carrier-to-noise power ratio ($C/N_0$) estimation for a GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal under band-limited white noise jamming environments. The quality of a received GPS signal is commonly described in terms of its $C/N_0$, implying that the noise is white and thus can be described by scalar noise density. However, if some intentional interference is received to a victim GPS receiver, then the $C/N_0$ is no longer the efficacious performance indicator. The correct and straightforward measurement to analyze the receiving situation is the effective $C/N_0$. In this paper, we consider a band-limited white noise jamming whose bandwidth is 2MHz and is the same as one of the first null-to-null bandwidth of the GPS L1 C/A signal.

• Journal of the Korean Chemical Society
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• v.47 no.4
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• pp.370-375
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• 2003

$BaMg_2Al_16O_27:Eu,\SrGa_2S_4:Eu$, and ZnCdS:Ag,Cl phosphors were chosen to produce blue, green, and red emissions, respectively, under excitation from a violet light emitting diode (LED). A four-band white LED was obtained by a combination of nonabsorbed violet emission from a violet LED and blue, green, and red emissions from $BaMg_2Al_16O_27:Eu,\SrGa_2S_4:Eu$, and ZnCdS:Ag,Cl phosphors. The luminescent properties of the four-band white LED were also discussed.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1280-1284
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• 2007

A series of Ca1-xSrxS:Eu (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) phosphors were synthesized by solid-state reactions. The Ca1-xSrxS:Eu phosphors have a strong absorption at 455 nm, which corresponds to the emission wavelength of a blue LED. The emission peak of Ca1-xSrxS:Eu is blue shifted from 655 to 618 nm with increasing Sr content. The characteristics of Ca1-xSrxS:Eu phosphors make them suitable for use as wavelengthtunable red-emitting phosphors for three-band white LEDs pumped by a blue LED. In support of this, we fabricated a three-band white LED by coating SrGa2S4:Eu and Ca0.6Sr0.4S:Eu phosphors onto a blue LED chip, and characterized its optical properties.

• Journal of Welding and Joining
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• v.27 no.3
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• pp.52-59
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• 2009

Flash butt welding is applied in many industries. New technology was developed recently for joining billets which called "EBROS (Endless Bar Rolling System)". After reheating billets in furnace, two billets were joined using flash butt welding. The objective of this study was to investigate the effect of alloying elements on mechanical properties of flash butt welded zone of hot rolled steel bar. The tensile properties on welded zone of Fe-Mn steel and Fe-Mn-V steel were dropped as compared with non-welded zone. Fe-Mn-Nb steel was opposed to the former. It was found that the white band at the welded zone had high ferrite volume fraction and large ferrite grain size. The vertical white band between flash butt welded billets was transformed into an arrowhead it of steel bar. According to this band, softening has been appeared. There was a interesting phenomenon with HAZ of Fe-Mn-Nb Steel, 40nm scale of particles were observed and hardness of HAZ was higher than non-welded zone.

• Journal of Welding and Joining
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• v.12 no.2
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• pp.87-96
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• 1994

Correlation between microstructural features and segregation of elements (Si, Mn, P and S) near the mid of thickness in the base metal and the synthetic HAZ was investigated. Furthermore, the relationship between the degree of center segregation and weld cold cracking susceptibility in the thickness direction was also conducted by evaluating the effect of P concentration on the critical applied stress. The results obtained are as follows: 1) Pearlite band, containing the MnS type inclusion and a locally transformed structure with a higher hardness, was observed in the center segregation region. 2) By the weld thermal cycle, center segregation region was transformed to the white band which had a higher hardness than that of base metal due to a greater hardenability of concentrated Mn, P etc.. 3) Weld cold cracking susceptibility in the thickness direction was mainly dependent on the concentration of impurity elements rather than on the number of the segregated particles near the mid of thickness. 4) During welding, the higher concentrated region was easily changed into white band. Therefore, it could be predicted that the initiation and propagation of a cold crack would be promoted by increasing the restraint stress and hydrogen content.

• Journal of electromagnetic engineering and science
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• v.17 no.1
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• pp.34-38
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• 2017

In this paper, we propose an active tunable bandpass filter (BPF) for efficient spectrum sensing in the TV White Space (TVWS) band. By designing a narrow bandwidth, it is possible to improve the sensing probability. The basic circuit configuration involves switching the PIN diode compromising capacitor bank to change the capacitance of the LC resonant circuit. To cover the whole TVWS band effectively, we add a varactor diode, and the bandwidth is set to 25-MHz. We improve the insertion loss by using the active capacitance circuit. The tunable BPF in the TVWS band with a 20-MHz interval is designed to have 11 channels with a bandwidth of 25 MHz and a low insertion loss of 1.7-2.0 dB.