• Journal of Powder Materials
• /
• v.25 no.5
• /
• pp.375-378
• /
• 2018

Conductive and dielectric SiC are fabricated using electroless plating of Ni-Fe films on SiC chopped fibers to obtain lightweight and high-strength microwave absorbers. The electroless plating of Ni-Fe films is achieved using a two-step process of surface sensitizing and metal plating. The complex permeability and permittivity are measured for the composite specimens with the metalized SiC chopped fibers dispersed in a silicone rubber matrix. The original non-coated SiC fibers exhibit considerable dielectric losses. The complex permeability spectrum does not change significantly with the Ni-Fe coating. Moreover, dielectric constant is sensitively increased with Ni-Fe coating, owing to the increase of the space charge polarization. The improvements in absorption capability (lower reflection loss and small matching thickness) are evident with Ni-Fe coating on SiC fibers. For the composite SiC fibers coated with Ni-Fe thin films, a -35 dB reflection loss is predicted at 7.6 GHz with a matching thickness of 4 mm.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.63 no.4
• /
• pp.283-289
• /
• 2014

A Fresnel lens is an optical component which can be used as a cost-effective, lightweight alternative to conventional continuous surface optics. Fresnel lens solar concentrators continue to fulfill a market requirement as a system component in high volume cost effective Concentrating Photovoltaic (CPV) electricity generation. The basic principles of the fresnel lens are reviewed and some practical examples are described. To investigate the performance space of the Fresnel lens, a fast simulation method which is a hybrid between raytracing and analytical computation is employed to generate a cache of simulation data. Injection molders are warming up to the idea of cycling their tool surface temperature during the molding cycle rather than keeping it constant. Heat and cool process are now also finding that raising the mold wall temperature above the resin's glass-transition or crystalline melting temperature during the filling stage and product performance in applications from automotive to packaging to optics. This paper deals with the suitability of Fresnel lenses of imaging and non-imaging designs for solar energy concentration. The concentration fresnel lens confirmed machinability and optical transmittance and roughness measure through manufactured the prototype.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.8 no.7
• /
• pp.979-986
• /
• 2013

Recently, in the electric, electronic, robotic, and medical industries, a great attention has been paid to the development of MEMS-based smart devices with a compact size and highly intelligency. The MEMS technology is very effective in designing into a compact size and lightweight by combining into one the complex electrical, mechanical, chemical, and biological features which are required by smart devices, and at the same time, in bulk batch manufacturing. Therefore, this study, to prepare for upcoming new MEMS-based technological paradigm, analyzes MEMS processes and then considers its Applications.

• Ceramist
• /
• v.22 no.2
• /
• pp.122-132
• /
• 2019

Wearable electronic devices with batteries must be lightweight, flexible and highly durable. Most importantly, the battery should be able to self-generate to operate the devices without having to be too frequently charged externally. An eco-friendly energy harvesting technology from various sources, such as solar energy, electromagnetic energy and wind energy, has been developed for a self-charging flexible battery. Although the energy harvesting from such sources are often unstable according to the surrounding environment, the energy harvesting from body movements and vibrations has been less affected by the surrounding environment. In this regard, flexible piezoelectric modules are the most attractive solution for this issue, because they convert mechanical energy to electrical energy and harvest energy from the human body motions. Among the various flexible piezoelectric modules, piezoelectric nanofibers have advantages when used as an energy harvester in wearable devices, due to their simple manufacturing process with good applicability to polymers and ceramics. This review focused on diverse flexible piezoelectric nanofibers and discusses their applications as various energy harvesting systems.

• Design & Manufacturing
• /
• v.11 no.2
• /
• pp.42-45
• /
• 2017

Currently, the mobile device is required to be miniaturized and lightweight according to the needs of the consumer. For this purpose, each part is produced and assembled in units of modules. Accordingly, the display part is also composed of a cover glass, a touch screen, And it costs a large amount to replace the whole when it is damaged. Therefore, we propose a method to improve the durability of display part using ANOVA (Analysis of Variance) and MR fluid polishing. Before MR fluid polishing process, surface treatment was performed to obtain a polishable surface. A series of experiments were carried out to very fine surface roughness and to secure durability of cover glass. Polishing depth, feed rate, and abrasive size were selected to examine the MR fluid polishing results.

• Journal of Korea Society of Digital Industry and Information Management
• /
• v.17 no.4
• /
• pp.53-62
• /
• 2021

Deep learning models such as convolutional neural networks and recurrent neual networks process a huge amounts of data, so they require a lot of storage and consume a lot of time and power due to memory access. Recently, research is being conducted to reduce memory usage and access by compressing data using the feature that many of deep learning data are highly sparse and localized. In this paper, we propose a compression-decompression method of storing only the non-zero data and the location information of the non-zero data excluding zero data. In order to make the location information of non-zero data, the matrix data is divided into sections uniformly. And whether there is non-zero data in the corresponding section is indicated. In this case, section division is not executed only once, but repeatedly executed, and location information is stored in each step. Therefore, it can be properly compressed according to the ratio and distribution of zero data. In addition, we propose a hardware structure that enables compression and decompression without complex operations. It was designed and verified with Verilog, and it was confirmed that it can be used in hardware deep learning accelerators.

• Progress in Superconductivity and Cryogenics
• /
• v.21 no.1
• /
• pp.25-30
• /
• 2019

This paper presents a conceptual design approach of air-cored synchronous machine with high temperature superconductor (HTS) field winding. With a given configuration of a target machine, boundary conditions are set in the cylindrical coordinate system and analytic field calculation is performed by solving a governing equation. To set proper boundary conditions, current distributions of the field winding and the armature winding are expressed by the Fourier expansion. Based on analytic magnetic field calculation results, key machine parameters are calculated: 1) inductance, 2) critical current of field winding, 3) weight, 4) HTS conductor consumption, and 5) efficiency. To investigate all potential design options, 6 sweeping parameters are determined to characterize the geometry of the machine and the parameter calculation process is performed for each design options. Among design options satisfying constraints including >80 % critical current margin and >95 % efficiency, in this paper, a first-cut design was selected in terms of overall machine weight and HTS conductor consumption to obtain a lightweight and economical design. The goal is to design a 5-MW machine by referring to the same capacity machine that was previously constructed by another group. Our design output is compared with finite element method (FEM) simulation to validate our design approach.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.35 no.8
• /
• pp.139-148
• /
• 2019

The lightweight structures such as domes are particularly vulnerable when it has been subjected to high temperature induced by the fire. It is therefore crucial to predict the possible instability path of structures exposed to the fire in structural design process. In this study, the instabilities of single-layer domes is investigated by using finite element technologies with the consideration of high temperature. The material properties of members under high temperature are considered by using the reduction factors which is provided in Eurocodes 3. Some damage patterns are assumed with use of a structural unit which is symmetric in radial direction. For numerical evaluations, the geometrically nonlinear truss element is implemented and the arch-length control method is employed to trace the post-buckling behaviour of domes. From numerical results, it is found to be that a significant change of post-buckling behaviour is detected in dome structures when structural members are exposed to the fire.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.21 no.5
• /
• pp.161-168
• /
• 2011

In 2009, Jeon et al proposed the lightweight strong authentication and strong privacy protocol, where the tag requrires only simple bitwise operations and random number generator. JK-RFID authentication protocol provides strong security: eavesdropping, replay, spoofing, Location tracking, DoS attack and forward security. Nevertheless, this paper points out the vulnerability of the forward security and improve the process of key updating. As a result, proposes an enhanced JK-RFID authentication protocol providing forward security and verify its satisfaction. In addition, a security and an efficiency of the proposed scheme analyze. Since partial adjustments of the key updating operation in JK-RFID authentication protocol, our protocol improve the forward security.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.34 no.1
• /
• pp.68-72
• /
• 2021

Aluminum is a lightweight metal and has excellent properties with regard to conductivity, workability, and strength. It has been used in various industries owing to its economic benefits. To improve upon the mechanical properties and processability by adding various alloying elements to aluminum, improving the corrosion resistance and heat resistance by electrochemically forming a porous anodic film having a thickness and hardness on the surface of the aluminum alloy is crucial. In this study, the aluminum 6061 alloy was controlled by an anodization process in a 0.3M oxalic acid electrolyte at room temperature to investigate the oxide film parameters such as porosity and thickness depending on the modulating applied voltage and time. The anodizing experiment was performed by increasing the time from 1 h to 9 h at 2-h intervals at applied voltages of 50 V and 60 V.