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Khuyen Nguyen Quang,Kim ByungSun,Kim JinBong,Lee Soo 한국유화학회 2007 한국응용과학기술학회지 Vol.24 No.3
Effect of dispersion methods for Vapor Grown Carbon Fibers (VGCF) in epoxy caused the change in mechanical properties of VGCF/epoxy nanocomposites, such as tensile modulus and tensile strength. The influence of VGCF types - atmospheric plasma treated (APT) VGCF and raw VGCF - and their contents was discussed in detail. Treating VGCF with atmospheric plasma enhanced the surface energy, therefore improved the bonding strength with epoxy matrix. Two different methods used to disperse VGCF were ultrasonic and mechanical homogenizer methods. When using dispersion solutions, the VGCF demonstrated good dispersion in ethanol in both homogenizer and ultrasonic method. The uniform dispersion of VGCF was investigated by scanning electron microscopy (SEM) which showed well-dispersion of VGCF in epoxy matrix. The tensile modulus of raw VGCF/epoxy nanocomposites obtained by ultrasonic method was higher than that of one obtained by homogenizer method. APT VGCF/epoxy nanocomposites showed higher tensile strength than that of raw VGCF/epoxy nanocomposites.
Influence of Allylamine Plasma Treatment Time on the Mechanical Properties of VGCF/Epoxy
Khuyen, Nguyen Quang,Kim, Jin-Bong,Kim, Byung-Sun,Lee, Soo The Korean Society for Composite Materials 2009 Advanced composite materials Vol.18 No.3
The allylamine plasma treatment is used to modify the surface properties of vapor grown carbon fibers (VGCF). It is to improve the interfacial bonding between the VGCF and epoxy matrix. The allylamine plasma process was performed by batch process in a vacuum chamber, using gas injection followed by plasma discharge for the durations of 20, 40 and 60 min. The interdependence of mechanical properties on the VGCF contents, treatment time and interfacial bonding between VGCF/ep was investigated. The interfacial bonding between VGCF and epoxy matrix was observed by scanning electron microscopy (SEM) micrographs of nanocomposites fracture surfaces. The changes in the mechanical properties of VGCF/ep, such as the tensile modulus and strength were discussed. The mechanical properties of allylamine plasma treated (AAPT) VGCF/ep were compared with those of raw VGCF/ep. The tensile strength and modulus of allyamine plasma treated VGCF40 (40 min treatment)/ep demonstrated a higher value than those of other samples. The mechanical properties were increased with the allyamine plasma treatment due to the improved adhesion at VGCF/ep interface. The modification of the carbon nanofibers surface was observed by transmission electron microscopy (TEM). SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.
Ultrathin metamaterial-based perfect absorbers for VHF and THz bands
Khuyen, B.X.,Tung, B.S.,Yoo, Y.J.,Kim, Y.J.,Lam, V.D.,Yang, J.G.,Lee, Y.P. Elsevier 2016 CURRENT APPLIED PHYSICS Vol.16 No.9
<P>An ultrathin and angularly stable metamaterial perfect absorber (MPA) is demonstrated for VHF-band using four connected split-square resonators structure and low-cost fabrication process. The total incoming energy of electromagnetic wave (at 250 MHz) is consumed inside the efficient thickness, which is 240 times smaller than the absorption wavelength of MPA. Our MPA works well for a very wide range of incident angle up to 45 degrees of electromagnetic wave and exhibits the polarization-independent behavior. Furthermore, by scaling the initial design and integrating a ferroelectric material (strontium titanate), a thermo-tunable ultrathin MPA is realized in the THz region. At room temperature (300 K), the thickness of THz MPA reaches roundly 1/300 of the working wavelength. In addition, a fractional frequency shift of 49% at the absorption over 90% can be controlled in the varied temperature range from 150 to 400 K. Our results presents good candidates for potential devices operating from the radio to the THz range. (C) 2016 Elsevier B.V. All rights reserved.</P>
Effect of Atmospheric Plasma Treatments on Mechanical Properties of VGCF/Epoxy
Khuyen, Nguyen Quang,Kim, Jin-Bong,Kim, Byung-Sun,Lee, Soo The Korean Society for Composite Materials 2008 Advanced composite materials Vol.17 No.2
Vapor grown carbon fibers (VGCF) were treated with atmospheric plasma enhancing the surface area in order to improve the bonding to the matrix in epoxy composites. The changes in the mechanical properties of VGCF/epoxy nanocompostes, such as tensile modulus and tensile strength were investigated in this study. VGCF with and without atmospheric plasma treatment for surface modification were used in this investigation. The interdependence of these properties on the VGCF contents and interfacial bonding between VGCF/epoxy matrix were discussed. The mechanical properties of atmospheric plasma treated (APT) VGCF/epoxy were compared with raw VGCF/epoxy. The tensile strength of APT VGCF/epoxy nanocomposites showed higher value than that of raw VGCF. The tensile strength was increased with atmospheric plasma treatment, due to better adhesion at VGCF/epoxy interface. The tensile modulus of raw VGCF and APT VGCF/epoxy matrix were of the similar value. The dispersion of the VGCF was investigated by scanning electron microscopy (SEM), SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.
Design and Evaluation Setup of a Novel Steerable Flexible Needle for Percutaneous Therapy
Van Khuyen Bui,Sukho Park,Jong-Oh Park,Seong Young Ko 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
Recently, flexible needles with bevel tips for percutaneous intervention have attracted significant interest. However, there are remaining problems related to controlling by duty-cycle algorithm which prevents widespread adoption of this technology. This motivates development of a new steerable flexible needle model that can change its curvature without axial rotation. In this paper, we propose a new steerable flexible needle design including two parts: cannula and stylet. An inserting system was developed to control the needle. To measure the curvature, a calibrated camera was deployed, and then the obtained images and videos were analyzed using Matlab. Using this setup, we will perform a series of experiment to evaluate the performance of the proposed steerable flexible needle.