• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.443-449
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• 2015

In this paper, we proposed Channel allocation scheme according to the user's location with IR. In VLC System, LED can generate various colors of light by controlling the mixing ratio of each individual RGB color element. Thus, each RGB channel will have a different signal power, and each channel will have different performance. This proposed system using Visible light(RGB) as way to transmit signals, it depends on the mixture RGB, which decided the color of light, moreover, each things determined their performance. However, if the signal were fixed allocated RGB to transmit such as the original system, the importance of the each signals a different occur the limit on the quality of signals. To solve this problem in this paper, according to the RGB mixture ratios analyze the performance for the LED, which analyzed based on allocating the signal by transmitting to improve the quality was about how researched. In addition, our proposed system is able to improve the performance of BER and satisfied the Qos to desire users.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.125-125
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• 2010

극성 [0001] 방향으로 성장된 질화물 기반의 LED (light emitting diode) 는 분극현상에 의해 발생하는 강한 내부 전기장의 영향을 받게 된다. 이러한 내부 전기장은 양자우물 내의 전자와 정공의 공간적 분리를 야기하고 quantum confined Stark effect (QCSE)에 의한 발광 파장의 적색 편이가 발생하며 양자효율의 저하를 가져오게 된다. 이러한 문제를 해결하기 위해 InGaN/GaN이나 AlGaN/GaN 양자 우물구조를 GaN의 m-plane (1$\bar{1}$00) 이나 a-plane (11$\bar{2}$0) 등 비극성면 위에 성장하려는 시도를 하고 있다. 그러나 비극성 면의 비등방성 (anisotropy) 으로 인하여 결정성이 높은 비극성 GaN을 성장하는 데에는 많은 어려움이 있다. GaN 층의 표면을 평탄화하고 결정성을 향상시키기 위해서 저온 GaN 또는 AlN 버퍼층을 성장하는 2단계 방법이나 고온 버퍼층을 이용하여 성장하는 연구들이 많이 진행되고 있다. 본 연구에서는 고온 GaN 버퍼층을 이용하여 기존의 2단계 성장과정을 단순화한 비극성 a-plane GaN을 r-plane 사파이어 기판위에 유기금속 화학증착법 (MOCVD)으로 성장하였다. 사파이어 기판위에 AlN 층을 형성하기 위한 nitridation 과정 후 1030 도에서 두께 45 ~ 800 nm의 고온 GaN 버퍼층을 성장하고 총 박막 두께가 2.7 ~ 3 um 가 되도록 a-plane GaN을 성장하여 표면 양상의 변화와 결정성을 확인하였다. 또한 a-plane GaN 박막 성장 시에 성장 압력을 100 ~ 300 torr 로 조절하며 박막 성장의 변화 양상을 관찰하였다. 고온 GaN 버퍼층 성장 두께가 감소함에 따라 결정성은 증가하였으나 표면의 삼각형 형태의 pit 밀도가 증가함을 확인하였다. 또한 성장 압력이 감소함에 따라 표면 pit은 감소하였으나 결정성도 감소하는 것을 확인하였다. 성장 압력과 버퍼층 성장 두께를 조절하여 표면에 삼각형 형태의 pit이 존재하지 않는 RMS roughness 0.99 nm, 관통전위밀도 $1.78\;{\times}\;10^{10}/cm^2$, XRD 반가폭이 [0001], [1$\bar{1}$00] 방향으로 각 798, 1909 arcsec 인 a-plane GaN을 성장하였다. 이 연구를 통해 고온 GaN 버퍼 성장방법을 이용하여 간소화된 공정으로 LED 소자 제작에 사용할 수 있는 결정성 높은 a-plane GaN을 성장할 수 있는 가능성을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.11
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• pp.801-807
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• 2022

In this paper, we propose an ultra compact S-Band PCM/FM telemetry transmitter. The equipment is compact, so it can be applied to a limited space and capable of stable data transmission was designed and manufactured even with specifications set differently for each operating environment and system. RF direct conversion structure is used for the miniaturization of equipment, an RF transmission board, Power distribution board, and a signal processing board were implemented on a single PCB, so that the function of the transmitter could be performed with a minimum device. According to the target specification, variable output of 1~10W and variable data rate of 390kbps~12.5Mbps is possible in S-Band(2,200~2,400MHz) without degradation of performance. To verify the performance of the equipment, the RF performance test and BER measurement test were performed after the equipment was manufactured. It was confirmed that the OBW, null-to-null bandwidth, 1st IMD, Spurious emission, Phase noise specification of the PCM/FM modulated signal which is presented by the IRIG standard were satisfied, and we can confirm the data received using the transmitter inspection equipment were transmitted normally without distortion.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.403-414
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• 2004

In the accompanying paper, we proposed a real. time volumetric imaging method using a cross array based on receive dynamic focusing and synthetic aperture focusing along lateral and elevational directions, respetively. But synthetic aperture methods using spherical waves are subject to beam spreading with increasing depth due to the wave diffraction phenomenon. Moreover, since the proposed method uses only one element for each transmission, it has a limited transmit power. To overcome these limitations, we propose a new real. time volumetric imaging method using cross arrays based on synthetic aperture technique with linear wave fronts. In the proposed method, linear wave fronts having different angles on the horizontal plane is transmitted successively from all transmit array elements. On receive, by employing the conventional dynamic focusing and synthetic aperture methods along lateral and elevational directions, respectively, ultrasound waves can be focused effectively at all imaging points. Mathematical analysis and computer simulation results show that the proposed method can provide uniform elevational resolution over a large depth of field. Especially, since the new method can construct a volume image with a limited number of transmit receive events using a full transmit aperture, it is suitable for real-time 3D imaging with high transmit power and volume rate.