• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.3
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• pp.59-68
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• 2023

Currently, yellow phosphor of Y3Al5O12:Ce3+ (YAG:Ce) fluorescent material is applied to a 450~480nm blue LED light source to implement a white LED device and it has a simple structure, can obtain sufficient luminance, and is economical. However, in this method, in terms of spectrum analysis, it is difficult to mass-produce white LEDs having the same color coordinates due to color separation cause by the wide wavelength gap between blue and yellow band. There is a disadvantage that it is difficult to control optical properties such as color stability and color rendering. In addition, this method does not emit purple light in the range of 380 to 420nm, so it is white without purple color that can not implement the spectrum of the entire visible light spectrum as like sunlight. Because of this, it is difficult to implement a color rendering index(CRI) of 90 or higher, and natural light characteristics such as sunlight can not be expected. For this, need for a method of implementing sunlight with one LED by using a method of combining phosphors with one light source, rather than a method of combining red, blue, and yellow LEDs. Using this method, the characteristics of an artificial sunlight LED device with a spectrum similar to that of sunlight were demonstrated by implementing LED devices of various color temperatures with high color rendering by injecting phosphors into a 405nm deep blue LED light source. In order to find the spectrum closest to sunlight, different combinations of phosphors were repeatedly fabricated and tested. In addition, reliability and mass productivity were verified through temperature and humidity tests and ink penetration tests.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.491-496
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• 2023

As the demand for p-type semiconductors increases, much effort is being put into developing new p-type materials. This demand has led to the development of novel new p-type semiconductors that go beyond existing p-type semiconductors. Copper iodide (CuI) has recently received much attention due to its wide band gap, excellent optical and electrical properties, and low temperature synthesis. However, there are limits to its use as a semiconductor material for thin film transistor devices due to the uncontrolled generation of copper vacancies and excessive hole doping. In this work, p-type CuI semiconductors were fabricated using the chemical vapor deposition (CVD) process for thin-film transistor (TFT) applications. The vacuum process has advantages over conventional solution processes, including conformal coating, large area uniformity, easy thickness control and so on. CuI thin films were fabricated at various deposition temperatures from 150 to 250 ℃ The surface roughness root mean square (RMS) value, which is related to carrier transport, decreases with increasing deposition temperature. Hall effect measurements showed that all fabricated CuI films had p-type behavior and that the Hall mobility decreased with increasing deposition temperature. The CuI TFTs showed no clear on/off because of the high concentration of carriers. By adopting a Zn capping layer, carrier concentrations decreased, leading to clear on and off behavior. Finally, stability tests of the PBS and NBS showed a threshold voltage shift within ±1 V.

• Advances in nano research
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• v.15 no.5
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• pp.385-399
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• 2023

Hexagonal boron nitride (h-BN), commonly referred to as Boron Nitride Nanoribbons (BNNRs), is an electrical insulator characterized by high thermal stability and a wide bandgap semiconductor property. This study delves into the electronic properties of two BNNR configurations: Armchair BNNRs (ABNNRs) and Zigzag BNNRs (ZBNNRs). Utilizing the nearest-neighbour tight-binding approach and numerical methods, the electronic properties of BNNRs were simulated. A simplifying assumption, the Hamiltonian matrix is used to compute the electronic properties by considering the self-interaction energy of a unit cell and the interaction energy between the unit cells. The edge perturbation is applied to the selected atoms of ABNNRs and ZBNNRs to simulate the electronic properties changes. This simulation work is done by generating a custom script using numerical computational methods in MATLAB software. When benchmarked against a reference study, our results aligned closely in terms of band structure and bandgap energy for ABNNRs. However, variations were observed in the peak values of the continuous curves for the local density of states. This discrepancy can be attributed to the use of numerical methods in our study, in contrast to the semi-analytical approach adopted in the reference work.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.4
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• pp.1042-1058
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• 2024

Terahertz (THz) communication is becoming a key technology for future 6G wireless networks because of its ultra-wide band. However, the implementation of THz communication systems confronts formidable challenges, notably beam splitting effects and high computational complexity associated with them. Our primary objective is to design a hybrid precoder that minimizes the Euclidean distance from the fully digital precoder. The analog precoding part adopts the delay-phase alternating minimization (DP-AltMin) algorithm, which divides the analog precoder into phase shifters and time delayers. This effectively addresses the beam splitting effects within THz communication by incorporating time delays. The traditional digital precoding solution, however, needs matrix inversion in THz massive multiple-input multiple-output (MIMO) communication systems, resulting in significant computational complexity and complicating the design of the analog precoder. To address this issue, we exploit the characteristics of THz massive MIMO communication systems and construct the digital precoder as a product of scale factors and semi-unitary matrices. We utilize Schatten norm and Hölder's inequality to create semi-unitary matrices after initializing the scale factors depending on the power allocation. Finally, the analog precoder and digital precoder are alternately optimized to obtain the ultimate hybrid precoding scheme. Extensive numerical simulations have demonstrated that our proposed algorithm outperforms existing methods in mitigating the beam splitting issue, improving system performance, and exhibiting lower complexity. Furthermore, our approach exhibits a more favorable alignment with practical application requirements, underlying its practicality and efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.5
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• pp.1317-1340
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• 2024

With the rapid development of information technology, people's demands on precise indoor positioning are increasing. Wireless sensor network, as the most commonly used indoor positioning sensor, performs a vital part for precise indoor positioning. However, in indoor positioning, obstacles and other uncontrollable factors make the localization precision not very accurate. Ultra-wide band (UWB) can achieve high precision centimeter-level positioning capability. Inertial navigation system (INS), which is a totally independent system of guidance, has high positioning accuracy. The combination of UWB and INS can not only decrease the impact of non-line-of-sight (NLOS) on localization, but also solve the accumulated error problem of inertial navigation system. In the paper, a fused UWB and INS positioning method is presented. The UWB data is firstly clustered using the Fuzzy C-means (FCM). And the Z hypothesis testing is proposed to determine whether there is a NLOS distance on a link where a beacon node is located. If there is, then the beacon node is removed, and conversely used to localize the mobile node using Least Squares localization. When the number of remaining beacon nodes is less than three, a robust extended Kalman filter with M-estimation would be utilized for localizing mobile nodes. The UWB is merged with the INS data by using the extended Kalman filter to acquire the final location estimate. Simulation and experimental results indicate that the proposed method has superior localization precision in comparison with the current algorithms.

• Broadcasting and Media Magazine
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• v.11 no.4
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• pp.104-117
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• 2006

In this Paper, we analyze the application of Interactive Data Broadcasting in DMB(Digital Multimedia Broadcasting) in the accordance with convergence of service and technology. With the acceleration of digital convergence in the Ubiquitous period substantial development of digital media technology and convergence of broadcasting and telecommunication industry are being witnessed. Consequently these results gave rise to newly combined-products such as DMB(Digital Multimedia Broadcasting), WCDMA(Wide-band code division multiple access), Wibro(Wireless Broadband Internet), IP-TV (Internet protocol TV) and HSDPA(High speed downlink packet access). The preparatory stage for the implementation of Interactive Data Broadcasting Service will be reached by the end of December, 2006. DMB is the first result of a successful convergence service between Broadcasting and Telecommunication in new media era. Multimedia technology and services are the core elements of DMB. The Data Broadcasting will not only offer various services of interactive information such News, Weather, Broadcasting Program etc, but also be linked with characteristic function of mobile phone such as calling and SMS(Short Message Service) via Return Channel.

• Korean Journal of Remote Sensing
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• v.18 no.4
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• pp.187-199
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• 2002

Correlation between chlorophyll a in the East China Sea and spectral bands (412, 443, 490, (510), 555, (676, 765)nm) of Ocean Scanning Multi-Spectral Imager (OSMI) including the profile multi-spectral radiometer (PRR-800) was studied. The values of remote sensing reflectance (Rrs) at the bands corresponding to the field chlorophyll $\alpha$ in the East China Sea were much higher than those in clear waters off California, USA. In case of the particle absorptions related to the chlorophyll a concentration at the spectral bands (440, 670nm) were much higher in the East China Sea than the ones in the clean waters off California. The normalized water leaving radiances (nLw) at 412, 443, 490, 555 nm of OSMI and the field chlorophyll a in the East China Sea were correlated each other. According to the results, the relationship between field chlorophyll $\alpha$ and nLw 410 nm in OSMI bands was the lowest, whereas that between field chlorophyll a and nLw 555 nm in the bands was the highest. Reciprocal action between the field chlorophyll a and the band ratio of the OSMI bands (nLw410/nLw555, nLw443/nLw555, nLw490/nLw555) was also studied. Relationship between the chlorophyll $\alpha$ and the band ratio (nLw490/nLw555) was highest in the OSMI bands. Relationship between the chlorophyll $\alpha$ and the ratio (nLw490/nLw555) was higher than one in the nLw410/nLw555. The difference in the estimated chlorophyll $\alpha$ (mg/m$^3$) between OSMI and SeaWiFS (Sea Viewing Wide Field-of-View Sensor) at the special observing stations in the northern eastern sea of Jeju Island in February 25, 2002 was about less than 0.3 mg/m$^3$ within 3 hours. It is suggested that OC2 (ocean color chlorophyll 2 algorithm) be used to get much better estimation of chlorophyll $\alpha$ from OSMI than the ones from the updated algorithms as OC4.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.4
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• pp.109-116
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• 2024

β-Ga₂O₃ is a representative ultra-wide bandgap (UWBG) semiconductor that has attracted much attention for power device applications due to its wide-bandgap of 4.9 eV and high-breakdown voltage of 8 MV/cm. In addition, because solution growth is possible, it has advantages such as fast growth rate and lower production cost compared to SiC and GaN [1-2]. In this study, we have successfully grown Si-doped 10 mm thick Si-doped β-Ga₂O₃ single crystals by the EFG (Edge-defined Film-fed Growth) method. The growth direction and growth principal plane were set to [010] / (010), respectively, and the growth speed was 7~20 mm/h. The as-grown β-Ga₂O₃ single crystal was cut into various crystal planes (001, 100, ${\bar{2}}01$) and off-angles (1^o, 3^o, 4^o), and then surface processed. After processed, the homoepitaxial layer was grown on the epi-ready substrate using the HVPE (Halide vapor phase epitaxy) method. The processed samples and the epi-layer grown samples were analyzed by XRD, AFM, OM, and Etching to compare the surface properties according to the crystal plane and off-angle.

• Journal of Korean Society of Forest Science
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• v.78 no.3
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• pp.287-301
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• 1989

A tree of Ailanthus altissima Swingle was fastened with a plastic band, 19mm wide, around the stem 180cm above ground level and was left to grow under this condition for one year, By removal of this band the tumorous tissue gradually developed and the tree bearing distinct tumorous tissue, an overgrowth surrounding the stem, was harvested two years after the band removal. For the investigation of this tumorous part and its comparison with adjacent normal parts in the anatomical features of individual elements, the tumorous part and parts directly and 40cm above and below the tumorous part were obtained from the tree. The tumor wood having remarkably wider growth increment occurred in the 3rd growth ring the first year after removal of the fastened band, and the barrier zone which delimited the discolored wood from the normal-colored wood inwards appeared u1 the intra-2nd growth ring produced during the fastened period in the tumorous part and the false ring-like zones equivalent to barrier Zone were shown in the normal-colored 2nd growth rings of the parts directly and 40cm above and below the tumorous part, as well. The tumor wood, the 3rd growth ring, and proportion of the 2nd growth ring formed after barrier zone in the tumorous part shared common characteristics in the irregular growth ring boundary, misshapen and shorter individual fibers and vessel elements, and large ray widths and heights. The springwood pores were smaller in diameter in the tumor wood, and the larger radial and smaller tangential diameters of summerwood solitary pores and individual pores consisting of pore multiples in proportion of the 2nd growth ring formed after the barrier zone were transformed into near-isodiametric in the tumor wood, the 3rd growth ring, in the tumorous part. Only in proportion of the 2nd growth ring formed after the barrier zone were transformed into near-isodiametric in the tumor wood, the 3rd growth ring, in the tumorous part, ray densities greatly increased. And the massive tumor wood was caused not by cell size but by cell number because the radial and tangential diameters of fibers in the tumor wood, the 3rd growth ring, in the tumorous part were not sufficiently different from those in the same aged growth rings of the directly and 40cm above and below the tumorous part.

• Korean Journal of Optics and Photonics
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• v.24 no.1
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• pp.1-8
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• 2013

In this paper, we report design, fabrication and characterization of the WBRM (Wide Band Receiver Module) for LADAR (LAser Detection And Ranging) application. The WBRM has been designed and fabricated using self-made APD (Avalanche Photodiode) and TIA (Trans-impedance Amplifier). The APD and TIA chips have been integrated on 12-pin TO8 header using self-made ceramic submount and circuit. The WBRM module showed 450 ps of rise time, and corresponding 780 MHz bandwidth. Furthermore, it showed very low output noise less than 0.8 mV, and higher SNR than 15 for 150 nW of MDS(Minimum Detectable Signal). To the author's knowledge, this is the best performance of an optical receiver module for LIDAR fabricated by 200 um InGaAs APD.