• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1749-1754
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• 2007

In this paper, we propose a new Intra-body communication system for bio-sensor which is one of applications in PAN(Personal Area Network) using body channel. The communication systems for bio-sensor network usually transmits a lot of data acquired in sensor to the receiver in wrist or waist. So we deign the intra-body modem with high data rate, low power, and small size which are achieved by baseband communication techniques. It is noted that the baseband transmission does not requires any analog IF and RF frontends, and can be operated in lower frequency than bandpass transmission. The proposed modem operates at 10MHz band according to the characteristics of intra-body channel, and shows the capability of 5Mbps data rate at distance of 20cm, with $BER=10^{-5}$. In addition, we implement the modem within $2{\times}2cm$ area.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.250-250
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• 2019

현재 우리나라에서 이용하고 있는 소류사량 직접계측방법에는 Arnhem 소류사 채취기와 Helley-Smith 소류사 채취기 등이 있다. 하지만 이러한 방법은 현장에서 계측하기가 매우 어렵고 많은 비용과 인력, 시간이 소모되며 특히 연속적인 계측이 어려워 소류사량의 직접계측자료를 기초로 하는 연구는 거의 전무한 상태이다. 이에 대한 대안으로 최근 국내외에서는 마이크로폰을 내장한 금속관에 토사가 충돌 시 발생하는 음향데이터를 수집 및 분석하여 소류사량을 계측하는 간접계측방법 하이드로폰을 사용하고 있다. 하이드로폰 시스템의 대부분이 증폭채널방법을 사용하고 있는데 이러한 방법은 개별입자에 대한 음향특성을 반영하기에는 다양한 크기를 가지는 소류사 입자에 대한 음향신호를 하나의 임계치 기준으로 필터링 하기 때문에 한계가 있다. 즉 기존의 방법은 소류사량의 상대적인 크기만 추정할 수 있을 뿐 소류사량을 정량화할 수 없다. 따라서 본 연구는 소류사가 이동할 때 발생하는 충돌음향을 신호 처리하여 소류사량을 추정하는 계측기기인 하이드로폰을 이용하여 기존 소류사량의 계측 방법을 개선하기 위한 실험적 연구를 수행하였다. 실험은 하이드로폰을 적용한 수리모형 실험 장치를 구축하고 현장에서 취득한 시료 중 대표시료로 분류된 두 가지 입자에 대해서 수리 조건 변화에 따른 충돌음향을 계측 및 분석하였다. 연구결과 입자크기 및 수리조건 변화에 따른 하이드로폰의 인지특성을 파악할 수 있었고 소류사 충돌음과 연관성 높은 주파수 대역을 분리하여 소류사 충돌음을 판독할 수 있는 계측알고리즘을 제시하였다. 특히 본 연구에서 제안하는 하이드로폰 충돌음향 분석법 B-P Method는 낮은 유속과 작은 입경의 소류사의 조건일 때 타 방법에 비해 제안된 B-P Method가 높은 판독률을 보여주었다.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.84-93
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• 1994

The purpose of present study is to investigate the surface roughness on tip-vortex cavitation and its induced noise, emanating from an elliptic wing of NACA 0012 section. Roughness elements of $200{\mu}m$ are applied to the 10% portion of wing tip, and then, the wing tip as well as the leading edge. It is shown from cavitation observation that the cavitation inception is first visible at about half chord downstream of wing tip for most experimental conditions, and developed into the tip-vortex cavitation and finally the fully developed cavitation as cavitation number is decreased. Acoustic noise generated by a tip-vortex cavitation has its frequency range of 3 kHz to 50 kHz, while the fully-developed cavitation at lower cavitation number induces a broad band spectrum. It is also shown that, when the roughness elements are applied to the wing tip and the leading edge, the cavitation characteristics and its induced noise are improved. Moreover, it is appeared that the condition at which the rough surface is at pressure side gives a better result. although its lift-drag ratio is reduced.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.667-674
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• 2009

The researches on the development of composite material underwater vehicle propeller have been actively attempted for the reduction of radiation noise with outstanding damping effects. Composite material propellers have almost been designed and produced by the foreign experts, and it is difficult to obtain the related informations about their flow, vibration, material characteristics because they are treated as the secrets with close relationship to the military technology, especially in the case of underwater vehicles. For the security of domestic manufacture of composite material propeller and the comparison and examination of its performance and radiation noise characteristics with those of German CONTUR composite material propeller, two propellers were self-produced according to the fiber weaving and array using compressible molding process and their self performances and radiation noise characteristics were measured. The mean fluctuations of blade tip of self-produced composite material propeller were increased and the radiation noises in the low frequency band were reduced compared to those of CONTUR, which could be estimated as the change of material characteristics and also be thought to be used for the future research informations.

• Journal of the Korean Magnetics Society
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• v.21 no.6
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• pp.208-213
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• 2011

We calculated the EPR (electron paramagnetic resonance) line-shape function. The line-widths of a -doped single crystal was studied as a function of the temperature with 0.5 and 2 at. at a frequency of (X-band). The line-width decreases with increasing temperature, such temperature behavior of the line-width can indicate a motional narrowing of the spectrum, when impurity ions substitute for host ions in an off-center position, and thus there can be fast jumping of dipoles between several symmetrically equivalent configurations. Therefore, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition problems.

• Journal of the Korean Geotechnical Society
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• v.37 no.10
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• pp.65-76
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• 2021

There is a possibility of cavities occurring inside and behind the lining of an aged tunnel structure. In most cases, it is not easy to check the cavity because it exists in a place where visual inspection is impossible. Recently, attempts have been made to evaluate the condition of the tunnel lining and the backfill materials using non-destructive tests such as Ground Penetrating Radar, and various related model tests and numerical analysis studies have been conducted. In this study, the GPR signal characteristics for tunnel lining model testing were analyzed using gprMax software, which was compared with model test results. The numerical model applied to the model test reasonably simulated the electromagnetic wave signal according to the change of the material such as tunnel lining and internal cavity. Using the verified GPR model, B-scan data for the development of the GPR signal analysis technique were obtained, which can evaluate the thickness of the tunnel lining, the presence of the cavity, the effect of the waterproof membrane, and the frequency band.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.325-333
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• 2021

A 3 kW grid-tied PV inverter with Gallium nitride high-electron mobility transistor (GaN HEMT) for domestic commercialization was developed using boost converter and full-bridge inverter with LCL filter topology. Recently, many GaN HEMTs are manufactured as surface mount packages because of their lower parasitic inductance characteristic than standard TO (transistor outline) packages. A surface mount packaged GaN HEMT releases heat through either top or bottom cooling method. IGOT60R070D1 is selected as a key power semiconductor because it has a top cooling method and fairly low thermal resistances from junction to ambient. Its characteristics allow the design of a 3 kW inverter without forced convection, thereby providing great advantages in terms of easy maintenance and high reliability. 1EDF5673K is selected as a gate driver because its driving current and negative voltage output characteristics are highly optimized for IGOT60R070D1. An LCL filter with passive damping resistor is applied to attenuate the switching frequency harmonics to the grid-tied operation. The designed LCL filter parameters are validated with PSIM simulation. A prototype of 3 kW PV inverter with GaN HEMT is constructed to verify the performance of the power conversion system. It achieved high power density of 614 W/L and peak power efficiency of 99% for the boost converter and inverter.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.6
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• pp.651-657
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• 2018

A novel PLL with a delta-sigma modulator and a spur reduction circuit is proposed. delta-sigma modulator makes the LF remove noise easily by moving the spur noise to a higher frequency band. Therefore, the magnitude of spur can be reduced the reasonable bandwidth. The spur reduction circuit reduces the spur size by reducing the LF voltage change generated during the period of reference signal. The spur reduction circuit is designed as simple as possible not to increase the size of PLL. The proposed PLL with the previous two techniques is designed with a supply voltage of 1.8V in a 0.18um CMOS process. Simulation results show an almost 20dB reduction in the magnitude of spur. The spur reduced PLL can be used in narrow bandwidth communication system.

• Journal of Ocean Engineering and Technology
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• v.33 no.1
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• pp.33-41
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• 2019

Estimating fatigue damage is a very important issue in the design of ships. The springing and whipping response, which is the hydro-elastic response of the ship, can increase the fatigue damage of the ship. So, these phenomena should be considered in the design stage. However, the current studies on the the application of springing and whipping responses at the design stage are not sufficient. So, in this study, a prediction method was developed using fluid-structural interaction analysis to assess of the fatigue damage induced by springing and whipping. The stress transfer function (Stress RAO) was obtained by using the 3D FE model in the frequency domain, and the fatigue damage, including linear springing, was estimated by using the wide band damage model. We also used the 1D beam model to develop a method to estimate the fatigue damage, including nonlinear springing and whipping by the vertical bending moment in the short-term sea state. This method can be applied to structural members where fatigue strength is weak to vertical bending moments, such as longitudinal stiffeners. The methodology we developed was applied to 325K VLOC, and we analyzed the effect of the springing and whipping phenomena on the existing design.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.387-392
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• 2019

$Dy^{3+}$ and $Eu^{3+}$-co-doped $La_2MoO_6$ phosphor thin films were deposited on sapphire substrates by radio-frequency magnetron sputtering at various growth temperatures. The phosphor thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy, ultraviolet-visible spectroscopy, and fluorescence spectrometry. The optical transmittance, absorbance, bandgap, and photoluminescence intensity of the $La_2MoO_6$ phosphor thin films were found to depend on the growth temperature. The XRD patterns demonstrated that all the phosphor thin films, irrespective of growth temperatures, had a tetragonal structure. The phosphor thin film deposited at a growth temperature of $100^{\circ}C$ indicated an average transmittance of 85.3% in the 400~1,100 nm wavelength range and a bandgap energy of 4.31 eV. As the growth temperature increased, the bandgap energy gradually decreased. The emission spectra under ultraviolet excitation at 268 nm exhibited an intense red emission line at 616 nm and a weak emission line at 699 nm due to the $^5D_0{\rightarrow}^7F_2$ and $^5D_0{\rightarrow}^7F_4$ transitions of the $Eu^{3+}$ ions, respectively, and also featured a yellow emission band at 573 nm, resulting from the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of the $Dy^{3+}$ ions. The results suggest that $La_2MoO_6$ phosphor thin films can be used as light-emitting layers for inorganic thin film electroluminescent devices.