Jo Dec 29, 2025
IGBT is a high-voltage high-power integrated circuit device and has a wide range of high-power switching applications such as mobile driving, power supply, railway transportation, industry control, etc.
The NPT-IGBT is a composite device of MOSFET and BJT. Since NPT-IGBT usually operates at high voltage and strong current, hot-carrier-induced degradation will be generated inside the device. Hot carriers with high energy will damage the oxide region of the device and the interface between silicon and silicon-dioxide, and will increase the trap charge of the interface and the oxide region.
Many researchers have described the issues on hot carriers of IGBT device, However, there have been reported a little literature that dealt with the reliability of hot carriers of NPT-IGBT.
Kim Hak Bong, a section head at the Institute of Semiconductor, analyzed the degradation mechanisms due to the hot carrier effect in NPT-IGBT through the voltage stress measurement, TCAD simulation and charge pumping measurement.
The results of the voltage stress measurement, TCAD simulation and the charge pumping measurement were consistent with the theoretical analysis.
For more information, you can refer to his paper “Analysis on Effect of Hot-Carrier-Induced Degradation of NPT-IGBT” in “Solid-State Electronics” (SCI).
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Jo Dec 28, 2025
The Trucklift slope hoisting system is an innovative transport technology for open-pit mines, and it considerably accelerates and cheapens transport from mines.
When a truck drives onto or off the platform at the lower loading station in the Trucklift slope hoisting system with varying profile of track, the platform motion influences the operation of the Trucklift slope hoisting system, and the configuration of inclined ropes hitched to the platform is varied.
In order to estimate the movement of platform at the lower loading station when a truck drives off or onto the platform, the movement of the truck on the platform and the lower loading station and the effect of sagged inclined ropes hitched to the platform should be considered simultaneously. The platform motion is related to not only the profile of track and parameters of truck and platform, but also the parameters of sagged inclined ropes hitched to the platform.
Kim Kwang Hyok, a researcher at the Faculty of Mining Engineering, has investigated the platform motion with consideration of sagged inclined ropes when a truck drives off or onto a platform at the lower loading station in the Trucklift slope hoisting system with varying profile of track. He proposed a system of non-linear equations to furnish an explicit solution for extensible sagged inclined ropes with edges on the inclined track, simulated platform motion by using the ADAMS software, and modeled the sagged inclined ropes hitched to the platform as a flexible body with consideration of elasticity and bend.
The simulation result shows that the displacement of platform is not considerable in comparison with the diameter of a tire, and proper design of a lower loading station enables safe movement of trucks on the platform without arresters.
You can find the details in his paper “Platform Motion at Lower Loading Station in Trucklift Slope Hoisting System with Varying Profile of Track” in “Journal of Mining and Environment” (SCI).
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Jo Dec 26, 2025
In recent years, more and more industrial robots have been applied to modern manufacturing systems. They need to be fast, smooth and precise to ensure high productivity and quality in many fields. Therefore, they should be designed to move smoothly with high speed and precision under kinematical and geometrical constraints. In particular, smoothness in motion is essentially required in the delicate industrial setting such as spot-welding or precise assembly, and what is important is that the planned trajectories should be continuous within the capability of actuators.
Han Chol Jun, a researcher at the Institute of Robotics, has proposed a method of planning the expanded S-curve trajectory of robotic manipulators to minimize execution time as well as to achieve smoother trajectory generation in the deceleration stage for point-to-point motions.
The simulation results of 3 DOF and 6 DOF robotic manipulators show that the proposed approach effectively reduces the jerk and snap (the derivative of jerk) in the deceleration stage while decreasing the total execution time. Also, the analysis of a single DOF mass-spring-damper system indicates that the residual vibration could be reduced to 10% more than the benchmark techniques.
For more information, please refer to his paper “An asymmetric S-curve trajectory planning based on an improved jerk profile” in “Robotica” (SCI).
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Jo Dec 25, 2025
An electrostatic precipitator is essential for thermal power plants, cement plants, chemical plants and mines. Its function is to clean the particulate dust contained in the smoke and gas that are discharged from the processes, thus improving the environmental pollution caused by them and improving the quality of air.
A high-voltage rectifier transformer, one of the most important parts of electrostatic precipitation equipment, is a kind of special transformer. The high-voltage rectifier transformer for electrostatic precipitation is a transformer operated under constantly varying load conditions, i.e., no-load, rated, and short-circuit conditions, and properly setting and accurately calculating the short-circuit voltage in its design is important to ensure efficient manufacturing cost and safe operation.
Yu Kwang Chol, a section head at the Faculty of Electrical Engineering, analyzed and compared the calculation methods of leakage reactance traditionally used in transformer design, and proposed an approach to calculate the leakage reactance more accurately using ANSYS Maxwell for two-winding transformers with different winding heights and a large number of windings.
He verified the accuracy of the proposed method by comparing it with conventional leakage reactance calculation methods and analyzing the error of the experimental results.
The result of the analysis shows that the ANSYS Maxwell program is a more precise and easy tool for calculating the leakage inductance and short-circuit voltage of transformers.
You can find the details in his paper “Research on the Method of Calculating Short-circuit Voltage for High-voltage Rectifier Transformer for Electrostatic Precipitation by Using the ANSYS Maxwell” in “Journal of Electrical Power & Energy Systems” (EI).
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Jo Dec 24, 2025
Industrially, direct reduction of iron oxides is a strong endothermic reaction, so only the temperatures above 1 000 to 1 100℃ enable reduction reactions to proceed at a rapid rate.
However, it is thermodynamically impossible to industrially enforce the reduction process by solid carbon since the temperature does not rise to 1 100℃ in the sponge iron manufacturing process and to more than 1 350℃ in the case of granulated iron. In other words, if the feed is not mixed evenly, CO gas will not participate in the reduction reaction but will be gone. In addition, the CO2 produced by indirect reduction is not modified to CO, so the carbon required by the sponge iron manufacturing process is two to three times more than the theoretical amount.
Therefore, making coal composite iron ore with fine iron concentrate and coal powder to produce reduced iron can further improve the reduction reaction characteristics of iron oxide and reduce coal consumption.
Ro Myong Su, a researcher at the Faculty of Metallic Engineering, has investigated the characteristics of direct reduction reactions by solid carbon and decided the optimum reduction conditions of the coal composite iron ore—the main materials in a new smelting reduction iron-making furnace.
Firstly, he conducted a softening test to choose the optimum agglomerant. Secondly, he investigated the effect of factors on the reduction characteristics of coal composite iron ore by the mass flop-out method, and decided the optimum reduction conditions.
The results show that the optimum reduction conditions for more than 80% of the reduction ratio in the case of direct reduction of coal composite iron ore by solid carbon are as follows: temperature 1 250℃, carbon-containing ratio 1 and its size 30mm.
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Jo Dec 23, 2025
Copper (Cu) is widely used as electrical contact materials because of its relatively low electrical wear and low cost compared to metallic materials such as silver (Ag), platinum (Pt), palladium (Pd) and cadmium (Cd). However, the electrical and mechanical properties of copper are not good compared to other metal contacts.
The working conditions of contact materials require thermal, electrical, mechanical and chemical properties to be excellent. It is because when capacitive and inductive loads are switched on and off, the temperature of contact generated at the contact surface is high, with a large number of switches and high contact pressure, and they work under the conditions of electrical wear and mechanical wear caused by arc discharges. The electrical and mechanical properties are not negligible in contact materials.
Several methods have been applied to improve the properties of contact materials. Recently, worldwide research on carbon nanotubes (CNT) has been active and the range of their application has been extended. CNTs have been widely used as reinforcement materials for metal matrix composites because of their good mechanical, physicochemical and electrical properties.
The tensile strength of CNT is 50-200GPa and its modulus of elasticity is about 1TPa. When carbon nanotubes are added to copper matrix, the tensile and flexural strength of carbon nanotube reinforced copper matrix composites increases by over 20% compared to pure copper. In addition, carbon nanotubes can be either conductors or semiconductors depending on what angle the hexagonal ring takes on the tube wall. In the case of conductors, the electrical transport capacity of carbon nanotubes is 1×109A/cm2, which is 1 000 times higher than that of copper wires.
This indicates that carbon nanotubes can be incorporated into metal matrix to enhance the mechanical and electrical properties of metal matrix composites. The addition of carbon nanotubes, excellent carbon nanomaterial, is the best way to realize the refinement of the matrix microstructure. Carbon nanotubes are placed at the boundary of the matrix microstructure and hinder grain growth, and thus grain refinement has a positive effect on both strength and toughness.
Nevertheless, the content of carbon nanotubes should not be too high. Because of the large surface area of carbon nanotubes, carbon nanotubes with relatively large surface activation energy are easily aggregated and negatively affect the microstructure and properties of metal matrix.
Jon Song Won, a researcher at the Faculty of Material Science and Technology, investigated the effect of carbon nanotubes on the properties and texture of contact carbon nanotube reinforced copper matrix composites prepared by direct addition of carbon nanotubes by blocking them in molten state.
When the CNT content was 2.0vol.%, the grain size of the CNT-reinforced Cu matrix composites was 21-23μm, and grain refinement was observed in their microstructure. However, no change in size, distribution and shape of inclusions was observed. The electrical and mechanical properties of carbon nanotube reinforced copper matrix composites are as follows: Tensile strength is 315MPa, elongation is 12%, hardness is HB 80 and electrical resistivity is 0.017 3μΩ·m.
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