• Composites Research
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• v.23 no.2
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• pp.17-23
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• 2010

The stealth technology can increase the survivability of aircrafts or warships and enhance the capability of mission completion in hostile territory. The purpose of this paper is to present the low observable structure with curved surfaces made by fiber-reinforced composites and to show the possibility of developing omnidirectional stealth platforms for military applications. In this study, we developed a radar absorbing structures(RAS) based on a circuit analog absorber to reduce the radar cross section(RCS) of an object with curved surfaces. Firstly, the RAS with a periodic square patterned conducting polymer layer was designed and simulated using a commercial 3-D electromagnetic field analysis program. Secondly, the designed semi-cylindrical structure with low RCS was fabricated using fiber-reinforced composites and conducting polymer. To make the periodic pattern layer, acts as resistive sheet, the intrinsic conducting polymer paste containing PEDOT with a polyurethane binder was used. Finally, the radar cross section was measured to evaluate the radar absorbing performances of the fabricated RAS by the compact range facility in POSTECH.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.71-75
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• 2005

For the damage tolerance improvement of conventional laminated composites, stitching process have been utilized for providing through-thickness reinforcements. 2D preforms were stacked with S-2 glass plain weave and S-2 glass MWK (Multi-axial Warp Knit) L type. 3D preforms were fabricated using the stitching process. All composite samples were fabricated by RTM (Resin Transfer Molding) process. To examine the damage resistance performance the low speed drop weight impact test has been carried out. For the assessment of damage after the impact loading, specimens were examined by scanning image. CAI (Compressive After Impact) tests were also conducted to evaluate residual compressive strength. Compared with 2D composites, the damage area of 3D composites was reduced by 20-30% and the CAI strength showed 5-10% improvement.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.129-134
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• 2001

Novel supervisory system for WDM transmission link using conventional optical time domain reflectometry was presented. By modifying the structure of erbuim doped fiber amplifier to support bi-directional transmission at arDR pulse wavelength and launching the optical pulse into transmission link in the opposite direction of data signal propagation to avoid the distortion by cross-gain modulation, it is possible to monitor the WDM link in service. To prove the validity of proposed scheme, the supervision result of 2.5 Gbps $\times$ 8 channel WDM 320 km transmission system in service by arDR was presented. And power penalty due to monitoring was measured as smaller than 0.3 dB. .3 dB.

• Textile Coloration and Finishing
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• v.10 no.2
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• pp.8-17
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• 1998

In this study we have examined electroless chemical plating on the plasma grafted poly [ethylene terephathalate］(PET) fabric in order to improve the interfacial adhesion between metal and fiber. The vapour phase of acrylic acid introduced on the PET surface and the graft polymerization was carried out by using cold plasma, resulting in the grafting yield of 0.8-1.3 wt％. The carboxyl group of the plasma grafted was identified by FT-IR-ATR spectra. The Interfacial adhesion was related to the carboxyl group. After electroless chemical plating of nickel, it showed that the more the carboxyl, the better the interfacial adhesion. Comparing to the untreated, the plasma grafted fabric showed fairly good interfacial adhesion(5B grade, ASTM D3359) . The shielding effect of electromagnetic wave showed 95dB. The shielding effect depends on the fabric structure, the surface structure, and the cross sectional shape of fibers. The dense fabric structure, the etched surface like a microcrater, and the trigonal cross sectional shape were prefered.

• Journal of Advanced Information Technology and Convergence
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• v.9 no.1
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• pp.89-102
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• 2019

Collagen can be used in building artificial skin replacements for treatment of burns and towards the reconstruction of bone as well as researching cell behavior and cellular interaction. The strength of collagen in connective tissue rests on the characteristics of collagen fibers. 3D confocal imaging of collagen fibers enables the characterization of their spatial distribution as related to their function. However, the image stacks acquired with confocal laser-scanning microscope does not clearly show the collagen architecture in 3D. Therefore, we developed a new method to reconstruct, visualize and characterize collagen fibers from fluorescence confocal images. First, we exploit the tensor voting framework to extract sparse reliable information about collagen structure in a 3D image and therefore denoise and filter the acquired image stack. We then propose to segment the collagen fibers by defining an energy term based on the Hessian matrix. This energy term is minimized by a min cut-max flow algorithm that allows adaptive regularization. We demonstrate the efficacy of our methods by visualizing reconstructed collagen from specific 3D image stack.

• Journal of Electrical Engineering and information Science
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• v.3 no.3
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• pp.336-341
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• 1998

We describe the architecture of an optical cross-connect (OXC) which is modular in structure and is able to be upgraded to a virtual wavelength path by adding wavelength converters. The additional feature of the OXC is the all-optical nature. It can be implemented with commercial components including mechanical optical switches. As a result of the test on the experimental OXC, it has been shown that 2.5 Gb/s signal can be transmitted via the OXC through 100 km length o an ordinary single mode fiber with 3 dB penalty.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1002-1008
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• 2001

The absorbing structure composed of multi-layered fiber reinforced composite materials was designed and microwave absorbing properties are investigated. On the basis of transmission line theory, the theoretical equations to predict the reflection loss and the appropriate composite material for each functional layer are suggested. The most significant result of this study is the successful design and fabrication of triple-layered composite laminates which has the superior microwave absorbing porperties (more than 10 dB in 4∼12 GHz range), without using the ferrite filler in the impedance transforming layer. In the two-layered composite laminate (absorber/substrate), however, the use of ferrite filler (about 40 wt %) in the absorbing layer is necessary to obtain the certain level of microwave absorbance. By combining the glass-fiber composite with ferrite filler and carbon-fiber composite substrate, the microwave absorbing properties more than 10 dB in 4∼12 GHz frequencies than be obtained.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.248-253
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• 1999

In this paper, we have investigated a fiber type active coupler which utilizes the mode coupling between the side polished single mode optical fiber and the active multimode planar waveguide. The proposed device can be used for not only tunable wavelength filter or optical intensity modulator but also a tool for measuring optical properties of guiding material such as refractive index, birefringence, electro-optic coefficient, and thermo-optic coefficient. We gave designed and optimized a coupler structure using the BPM and fabricated the device using thermo-optic polymer as active planar waveguide overlay. The device showed that insertion loss was less then 0.5 dB, extinction ratio was -13 dB at the resonance wavelength, and the wavelength tunablity due to thermo-optic effect was -1.5 nm/$^{\circ}C$. The active coupler using thermo-optic effect can be used as a wavelength tunable filer, an optical intensity modulator and an optical sensor. pulses that are subsequently compressed by a dispersive optical fiber. Experimental results show that $sech^2$ shape pulses with a pulse width of ~14 ps and a time bandwidth product of ~0.34 are successfully generated at 10 GHz repetition rate. In contrast to other methods, such as higher order soliton compression, this approach does not depend on the optical power and thus shows promise for application to low-power lasers.

• Carbon letters
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• v.14 no.2
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• pp.94-98
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• 2013

Isotropic pitch fibers were stabilized and carbonized for preparing carbon fibers. To optimize the duration and temperature during the stabilization process, a thermogravimetric analysis was conducted. Stabilized fibers were carbonized at 1000, 1500, and $2000^{\circ}C$ in a furnace under a nitrogen atmosphere. An elemental analysis confirmed that the carbon content increased with an increase in the carbonization temperature. Although short graphitic-like layers were observed with carbon fibers heat-treated at 1500 and $2000^{\circ}C$, Raman spectroscopy and X-ray diffraction revealed no significant effect of the carbonization temperature on the crystalline structure of the carbon fibers, indicating the limit of developing an ordered structure of isotropic pitch-based carbon fibers. The electrical conductivity of the carbonized fiber reached $3.9{\times}10^4$ S/m with the carbonization temperature increasing to $2000^{\circ}C$ using a four-point method.

• Composites Research
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• v.37 no.4
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• pp.291-295
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• 2024

Vibration occurs not only in daily life but also in various fields such as semiconductors, aerospace, vehicles, and ships. Unexpected vibrations can cause fatigue damage to structures and degrade the performance of the entire system, having very detrimental effects. Particularly, low-frequency vibrations can be very harmful to precision equipment, human bodies, and buildings. Therefore, mitigating low-frequency vibrations is essential for effective vibration reduction. In this study, a kirigami-inspired composite meta-structure is proposed for low-frequency vibration reduction. Inspired by kirigami, the meta-structure is designed to transform from a three-dimensional to a two-dimensional form upon compression, leveraging structural advantages. Additionally, it is designed to have quasizero stiffness characteristics, providing excellent vibration reduction performance even at low frequencies. The kirigami composite meta-structure was fabricated using carbon fiber reinforced TPU through 3D printing. Its structural and vibrational characteristics were evaluated and analyzed through compression and vibration tests.