• Journal of Power Electronics
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• v.16 no.1
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• pp.84-92
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• 2016

Compared with Si MOSFETs, the GaN FET has many advantages in a wide band gap, high saturation drift velocity, high critical breakdown field, etc. This paper compares the electrical properties of GaN FETs and Si MOSFETs. The soft-switching condition and power loss analysis in a flyback-forward high gain DC/DC converter with a GaN FET is presented in detail. In addition, a comparison between GaN diodes and Si diodes is made. Finally, a 200W GaN FET based flyback-forward high gain DC/DC converter is established, and experimental results verify that the GaN FET is superior to the Si MOSFET in terms of switching characteristics and efficiency. They also show that the GaN diode is better than the Si diode when it comes to reverse recovery characteristics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.5
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• pp.486-491
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• 2008

The plasma processing is applied to many industrial fields as thin film deposition or surface treatment technique. In this study, we investigated large-area uniformed surface treatment of PET film at low temperature by using Scanning Plasma Method(SPM). Then, we measured difference and distribution of temperature on film's surface by setting up a thermometer. We studied the condition of plasma for surface treatment by examining intensity of irradiation of uniformed plasma. And we compared contact angles of treated PET film by using Ar and $O_2$ plasma based low temperature. In our result, surface temperature of 3-point of treating is low temperature about $22^{\circ}C$, in other hands, there is scarcely any variation of temperature on film's surface. And by using Ar plasma treatment, contact angle is lower than untreatment or $O_2$ plasma treatment. In case of PET film having thermal weak point, low temperature processing using SPM is undamaged method in film's surface and uniformly treated film's surface. As a result, Ar plasma surface treatment using SPM is suitable surface treatment method of PET film.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.267-273
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• 1998

The band structures of $Si_{1-x}Ge_x$ layers grown on $Si_{1-y}Ge_y$ substrate are calculated using k$\cdot$p and strain Hamiltonians. The hole drift mobilities in the plane direction are then calculated by taking into account the screening effect and the density-of-states of the impurity band. When $Si_{1-x}Ge_x$ is grown on Si substrate, the mobilities of (110) and (111) $Si_{1-x}Ge_x$ layers are larger than that of (001) $Si_{1-x}Ge_x$. However, due to the large defect and surface scattering, (110) and (111) $Si_{1-x}Ge_x$ layers may not be useful for the development of the fast device. Meanwhile, when Si is grown on $Si_{1-y}Ge_y$ substrate, the mobilities of (001) and (110) Si layers are greatly enhanced. Based on the amount of defect and the surface scattering, it is expected that Si grown on (001) $Si_{1-y}Ge_y$ substrate, where the Ge contents is larger than 10%(y>0.1), has the highest mobility.

• Journal of Electrical Engineering and Technology
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• v.9 no.3
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• pp.843-847
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• 2014

In Super Junction (SJ) MOSFETs, charge balance is the most important issue of the SJ fabrication process. In order to achieve the best electrical characteristics, such as breakdown voltage and on-resistance, the N-type and P-type drift regions must be fully depleted when the drain bias approaches the breakdown voltage, which is known as the charge balance condition. In conventional charge balance analysis, based on multi-epi process SJ MOSFETs, analytical model has only N, P pillar width and doping concentration parameter. But applying a conventional charge balance principle to trench filling process, easier than Multi-epi process, is impossible due to the missing of the trench angle parameter. To achieve much more superior characteristics of on-resistance in trench filling SJ MOFET, the appropriate trench angle is necessary. So in this paper, modulated charge balance analysis is proposed, in which a trench angle parameter is added. The proposed method is validated using the TCAD simulation tool.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2011.11a
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• pp.20-27
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• 2011

A system for fine-resolution long-range weather forecast is introduced in this study. The system is basically consisted of a global-scale coupled general circulation model (CGCM) and Weather Research and Forecast (WRF) regional model. The system makes use of a data assimilation method in order to reduce the initial shock or drift that occurs at the beginning of coupling due to imbalance between model dynamics and observed initial condition. The long-range predictions are produced in the system based on a non-linear ensemble method. At the same time, the model bias are eliminated by estimating the difference between hindcast model climate and observation. In this research, the predictability of the forecast system is studied, and it is illustrated that the system can be effectively used for the high resolution long-term weather prediction. Also, using the system, fine-resolution climatological data has been produced with high degree of accuracy. It is proved that the production of agrometeorological variables that are not intensively observed are also possible.

• Smart Structures and Systems
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• v.5 no.1
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• pp.69-79
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• 2009

A non-clipped semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers is developed based on the stochastic averaging method and stochastic dynamical programming principle. A nonlinear stochastic control structure is first modeled as a semi-actively controlled, stochastically excited and dissipated Hamiltonian system. The control force of an MR damper is separated into passive and semi-active parts. The passive control force components, coupled in structural mode space, are incorporated in the drift coefficients by directly using the stochastic averaging method. Then the stochastic dynamical programming principle is applied to establish a dynamical programming equation, from which the semi-active optimal control law is determined and implementable by MR dampers without clipping in terms of the Bingham model. Under the condition on the control performance function given in section 3, the expressions of nonlinear and linear non-clipped semi-active optimal control force components are obtained as well as the non-clipped semi-active LQG control force, and thus the value function and semi-active nonlinear optimal control force are actually existent according to the developed strategy. An example of the controlled stochastic hysteretic column is given to illustrate the application and effectiveness of the developed semi-active optimal control strategy.

• Journal of Korean Association for Spatial Structures
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• v.18 no.4
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• pp.105-111
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• 2018

In this study, the seismic performance and behavior characteristics of the upper truss structure of the large stadium are analyzed by nonlinear dynamic analysis. In the nonlinear dynamic analysis, the earthquake records were generated by site response analysis to simulate the nonlinear behavior of the relevant soil condition where the structure is located. Nonlinear dynamic analysis was performed using Perform-3D and the nonlinear properties of the substructure and the superstructure were determined in accordance with KISTEC guideline. According to the analysis results, excessive deformation occurred in the upper truss element, and plastic hinges exceeded the target performance in some members. Buckling-restrained brace is used for seismic retrofit of stadium structures and the analysis results shows the interstory drift satisfies the target performance level with dissipating the seismic energy efficiently.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.55.2-55.2
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• 2019

The firehose instability is driven by a pressure anisotropy in a magnetized plasma when the temperature along the magnetic field is higher than the perpendicular temperature. Such condition occurs commonly in astrophysical and space environments, for instance, when there are beams aligned with the background magnetic field. Recently, it was argued that, in weak quasi-perpendicular shocks in the high-β intracluster medium (ICM), shock-reflected electrons propagating upstream cause the temperature anisotropy. This electron temperature anisotropy can trigger the electron firehose instability (EFI), which excites oblique waves in the shock foot. Scattering of electrons by these waves enables multiple cycles of shock drift acceleration (SDA) in the preshock region, leading to the electron injection to diffusive shock acceleration (DSA). In the study, the kinetic properties of the EFI are examined by the linear stability analysis based on the kinetic Vlasov-Maxwell theory and then further investigated by 2D Particle-in-Cell (PIC) simulations, especially focusing on those in high-β (β~100) plasmas. We then discuss the basic properties of the firehose instability, and the implication of our work on electron acceleration in ICM shock.

• Smart Structures and Systems
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• v.31 no.3
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• pp.301-309
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• 2023

Tilt is a key indicator of structural safety. Real-time monitoring of tilt responses helps to evaluate structural condition, enable cost-effective maintenance, and enhance lifetime resilience. This paper presents a prototype wireless sensing system for structural tilt measurement. Long range (LoRa) technology is adopted by the sensing system to offer long-range wireless communication with low power consumption. The sensor integrates a gyroscope and an accelerometer as the sensing module. Although tilt can be estimated from the gyroscope or the accelerometer measurements, these estimates suffer from either drift issue or high noise. To address this challenging issue and obtain more reliable tilt results, two sensor fusion algorithms, the complementary filter and the Kalman filter, are investigated to fully exploit the advantages of both gyroscope and accelerometer measurements. Numerical simulation is carried out to validate and compare the sensor fusion algorithms. Laboratory experiment is conducted on a simply supported beam under moving vehicle load to further investigate the performance of the proposed wireless tilt sensing system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.211-218
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• 2006

From the development of residential flat plate system, continuously bended shear reinforcement is developed for the prevention of punching shear. To know the punching shear capacity of developed shear reinforcement in slab-column joint, structural test is performed. The testing parameters are shear reinforcement types, such as no reinforcement, bended shear reinforcement, and head stud reinforcement. To verify the lateral capacity, cyclic load is applied under the constant vertical load condition. The results of tests are compared to as global displacement, slab-column joint strength. From the test results, the resisting capacity of developed shear reinforcement system has a good performance in the story drift ratio.