• Smart Structures and Systems
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• v.22 no.4
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• pp.369-382
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• 2018

Novel design of interdigitated electrodes capable of increasing the performance of piezoelectric transducers are proposed. The new electrodes' geometry improve the electromechanical coupling by offering an enhanced adaptation of the electric field to the interdigitated electrode configuration. The proposed analysis is based on finite element modeling and takes into account local polarization effect. It is shown that the proposed electrodes considerably increase the strain generation compared to flat electrode arrangement used for Macro Fiber Composite (MFC) and Active Fiber Composite (AFC) actuators. Also, electric field singularities are reduced allowing better reliability of the transducer against electric failure.

• Journal of the Optical Society of Korea
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• v.8 no.1
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• pp.17-20
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• 2004

An in-line variable attenuator has been proposed and demonstrated exploiting a side-polished single-mode (SM) fiber evanescently coupled with an index matched dielectric plate. The attenuation can be controlled by fine mechanical sliding of the index matched dielectric plate. We have achieved 49 ㏈ dynamic range and very low excess loss of 0.2 ㏈ at 1550 nm wavelength. The measured polarization dependent losses (PDL) were 0.1, 0.2, and 0.4 ㏈ at 10, 20, and 30 ㏈ attenuation, respectively. Wavelength sensitivity was measured to be -0.017/nm ㏈ at 20 ㏈ attenuation.

• Korean Journal of Optics and Photonics
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• v.4 no.1
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• pp.66-72
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• 1993

Additive-pulse mode-locking (APM) was performed in a $1.053{\mu}m$ cw Nd:YLF laser by coupling a nonlinear external external cavity to the main cavity. The APM pulsewidth was 4.5 ps and the average output power was 1.5 W. This APM pulse was compressed by an optical fiber and a grating pair to be as short as 210 fs with a peak power of 17 kW.

• Journal of Korean Association for Spatial Structures
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• v.21 no.2
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• pp.67-79
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• 2021

This paper aims to develop numerical models for seismically-deficient reinforced concrete columns retrofitted using a fiber-reinforced polymer jacketing system under blast loading scenarios. To accomplish the research goal, a coupling model reproducing blast loads was developed and implemented to the column model. The column model was validated with a past experimental study, and the blast responses were compared to the numerical responses produced by past researchers. The validated modeling method was implemented to the non-retrofitted and retrofitted column models to estimate the effectiveness of the retrofit system. Based on the numerical responses, the retrofit system can significantly reduce the peak dynamic responses under a given blast loading scenario.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.1
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• pp.35-41
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• 2017

The use of engineering plastics in automotive components is increasing with the trend towards improving the car strength and reducing weight. Among the different choices of materials, engineering plastic emerged as the necessary material for achieving lower costs, reduced weight and improved production efficiency. To produce the automotive parts, it is important to predict defect and validation of injection molding prior to design. Injection molding analysis and structural analysis are widely applied as a part of the design process when developing automotive parts. Injection molding analysis, in particular, involves a highly complicated mechanism that requires deep knowledge of polymer properties as well as an analytic approach different from that used for a general isotropic material when the molded material is used as a structural material. This is because the parts made of polymer have pre-stress factors such as intrinsic deformation and residual stress. The most important factors for injection molded plastic products are injection molding condition and cavity design, taking into account ease of molding, mass production and application. Despite optimal injection molding conditions and cavity design, however, glass fiber orientation is critically linked to strength reduction. The application of injection molding and structural coupled analysis provides a low-cost solution for product molding and structural validation, all prior to the actual molding. The purpose of this study involves the validation, pre-study, and solution of defect in injection-molded polymer automotive parts using the simulation software for injection molding and structural coupled analysis. Finally, this thesis provides validation of an injection molding and structural coupled analytic mechanism that can demonstrate the effect of glass fiber orientation on mechanical strength. Design improvement ideas for the injection molded product of PPS (Poly Phenylene Sulfide)+40% glass fiber are also suggested.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.6
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• pp.589-598
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• 2001

The fracture of acrylic resin dentures remains an unsolved problem. Therefore, many investigations have been performed and various approaches to strengthening acrylic resin, for example, the reinforcement of heat-cured PMMA resin using glass fibers, have been suggested over the years. The aim of the present study was to investigate the effect of short glass fibers treated with silane coupling agent on the transverse strength of heat-polymerized PMMA denture base resin. To avoid fiber bunching and achieve even fiber distribution, glass fiber bundles were mixed with PMMA powder in conventional mixer whose blade was modified to be blunt. Composite of glass fiber($11{\mu}m$ diameter, 3mm & 6mm length, silane treated) and PMMA resin was made. Transverse strength and Young's modulus were estimated. Glass fibers were incorporated with 1%, 3%, 6% and 9% by weight. Plasticity and workability of dough was evaluated. Fracture surface of specimens was investigated by SEM. The results of this study were as follows 1. 6% and 9% incorporation of 3mm glass fibers in the PMMA resin enhanced the transverse strength of the test specimens(p<0.05). 2. 6% incorporation of 6mm glass fibers in the PMMA resin increased transverse strength, but 9% incorporation of it decreased transverse strength(p<0.05). 3. When more than 3% of 3mm glass fibers and more than 6% of 6mm glass fibers were incorporated, Young's modulus increased significantly(p<0.05). 4. Workability decreased gradually as the percentage of the fibers increased. 5. Workability decreased gradually as the length of the fibers increased. 6. In SEM and LM, there was no bunching of fibers and no shortening of fibers.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.494-499
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• 2005

We have demonstrated a fiber short-wavelength filter with a good cut-off property using dissimilar dispersive properties between? a thermally expanded cored fiber and an external medium. Side-polishing is applied to coupling between the fiber and the external medium. The experimental results revealed that the bend edge wavelength can be adjusted by controlling the degree of core expansion. Futhermore, the sharpness of wavelength response? was significantly? improved by employing expanded core fiber instead of a conventional single mode fiber. Tuning range of the band edge wavelength exceeded 400 m based on thermo-optic effect of the external medium.

• Composites Research
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• v.22 no.4
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• pp.41-49
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• 2009

Natural fiber reinforced composites are emerging as low-cost, lightweight, recyclable, and eco-friendly materials. These are biodegradable and non-abrasive. Due to eco-friendly and biodegradable characteristics of natural fibers, they are being considered as potential candidates to replace the conventional fibers. The chemical, mechanical, and physical properties of natural fibers have distinct features depending upon the cellulose content of the fibers which varies from fiber to fiber. The mechanical properties of composites are influenced mainly by the adhesion between matrix and fibers. Several chemical and physical modification methods of fiber surface were incorporated to improve the tiber-matrix adhesion resulting in the enhancement of mechanical properties of the composites. This paper outlines the works reported on natural tiber reinforced composites with special reference to the type of fibers, polymer matrix, processing techniques, treatment of fibers, and fiber-matrix interface.

• Korean Journal of Optics and Photonics
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• v.20 no.1
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• pp.1-5
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• 2009

Recently, much research has been done for to realizeing nano-scale photonic circuits based on photonic crystal, plasmonics and silicon photonics in order to overcome fundamental limits of electronic circuits. These limits include such as bottleneck of speed, and size that cannot be reduced. Even though several kinds of coupling schemes have been reported, coupling structures are still large when it is compared with the nano-scale optical circuit. In this paper, we proposed using a very thin Fresnel lens while shortening the focal length of the Fresnel lens as much as possible. We proposed, for the first time, to utilize metal slits that are able to use the optical coupling system between a nano-scale optical circuit and the standard single mode optical fiber for overcoming the limitation of focal length shortening of the Fresnel lens. Comparative study has been carried out with a FDTD simulation between normal and metal slit assisted Fresnel lens. From the result of simulation, we can achieve 65% coupling efficiency for the metal-slit Fresnel lens when the focal length of metal-slit Fresnel lens is just $4{\mu}m$. On the other hand, the coupling efficiency of the normal Fresnel lens is about 43%.

• Carbon letters
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• v.24
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• pp.18-27
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• 2017

Multiwall carbon nanotubes (MWCNT) with two different (L/D) aspect ratios ($7{\pm}2{\mu}m/140{\pm}30nm$ and $0.5-2{\mu}m/8-15nm$) were surface treated using nitric acid ($HNO_3$) and polyethyleneimine (PEI) prior to their deposition on carbon fibers (CF). Before the hierarchical reinforcement with CF-MWCNT, the CFs were treated with 3-glycidoxypropyltrime-thoxysilane, a coupling agent (Z6040) and with poly(amidoamine) (PAMAM) a dendrimer containing an ethylenediamine core and amine surface groups. The MWCNT were deposited on the CF using two methods, by electrostatic attraction and by chemical reactions. The changes in the CF surface morphology after the MWCNT deposition were analyzed using SEM, which revealed a higher density and uniform coverage for the PAMAM-treated CF and the short MWCNTs. The interfacial adhesion of the composite materials was evaluated using the single fiber fragmentation technique. The results indicated an improvement in the interfacial shear strength with the addition of the short-MWCNTs treated with acid solutions and grafted onto the surface of the CF fiber using electrostatic attraction.