• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.18-24
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• 2010

A Ka-band microstrip array antenna for wide-range detection of moving targets is analyzed through a photonicassisted reactive-near-field characterization technique. The antenna array employs a 3-dB-tapered feed network to suppress the sidelobe level while retaining a wide azimuth beamwidth for a wide detection range. The relative nearelectric field patterns of the array and its 3-dB-tapered feed lines have been measured using an electro-optic fieldmapping technique for minimally invasive millimeter-wave sensing. A number of typical limitations on the technique, involving bandwidth, low signal-modulation depth, and high laser-induced noise in high-frequency applications, have been overcome by suppressing the carrier portion of the optical interrogation beam.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.385-385
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• 2012

Understanding the thermodynamics and structural transformation during the Metal-Insulator Transition (MIT) is critical to better understand the underlying physical origin of phase transition in the vanadiumdioxide ($VO_2$). Here, through the temperature-dependent in-situ high resolutiontransmission electron microscopy (HR-TEM), and systematic electrical transport study, we have shown that the tunable MIT transition of $VO_2$ nanowires is strongly affected by interplay between strain and domain nucleation by ion beam irradiation. Surprsingly, we have also observed that the $VO_2$ rutile (R) metallic phase could form directly in a strain-induced metastable monoclinic (M2) phase. These insights open the door toward more systematic approaches to synthesis for $VO_2$ nanostructures in desired phase and to use for applications including ultrafast optical switching, smart window, metamaterial, resistance RAM and synapse devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.389.2-389.2
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• 2016

The flexible solid state device has been widely studied as portable and wearable device applications such as display, sensor and curved circuits. A zero-bias operation without any external power consumption is a highly-demanding feature of semiconductor devices, including optical communication, environment monitoring and digital imaging applications. Moreover, the flexibility of device would give the degree of freedom of transparent electronics. Functional and transparent abrupt p/n junction device has been realized by combining of p-type NiO and n-type ZnO metal oxide semiconductors. The use of a plastic polyethylene terephthalate (PET) film substrate spontaneously allows the flexible feature of the devices. The functional design of p-NiO/n-ZnO metal oxide device provides a high rectifying ratio of 189 to ensure the quality junction quality. This all transparent metal oxide device can be operated without external power supply. The flexible p-NiO/n-ZnO device exhibit substantial photodetection performances of quick response time of $68{\mu}s$. We may suggest an efficient design scheme of flexible and functional metal oxide-based transparent electronics.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.266-272
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• 2016

This paper presents the investigation of the propagation behavior of bulk longitudinal waves generated by an ultrafast laser system in thin films. A train of femtosecond laser pulses was focused onto the surface of a 150-nm thick metallic (chromium or aluminum) film on a silicon substrate to excite elastic waves, and the change in thermoreflectance at the spot was monitored to detect the arrival of echoes from the film/substrate interface. The experimental results show that the film material characteristics such as the wave velocity and Young's modulus can be evaluated through curve-fitting in numerical solutions. The material properties of nanoscale thin films are difficult to measure using conventional techniques. Therefore, this research provides an effective method for the nondestructive characterization of nanomaterials.

• Journal of the Korean Society of Clothing and Textiles
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• v.42 no.4
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• pp.708-725
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• 2018

The advancement of digital technology has made changes in the fashion system and trend development process inevitable. This article clarifies changes in the modern fashion industry system and the causes of comprehensive changes that result from the development of digital technology. The methodology of this study is based on literature and case studies based on the information magazine most used by fashion industry workers. This study classifies fashion systems into 5 types and 14 types in detail. The study results indicate the way to change the fashion style trend schedule per year, fast/ultrafast fashion system, fashion rental system, DTC system and change of fashion system by consumer participation. The causes of the changes in fashion system are indicated that an increase of trend sensitivity due to an increase in the diffusion rate of information, expansion of expression of personality through digital network, increase of possibility of grouping of small number of tastes and change of prosumer possible changes in the environment. This study provides basic data on fashion system research and the construction of an appropriate response strategy for a changing environment.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.6
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• pp.620-624
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• 2010

In this paper, design and manufactured UWB BPF. Manufactured UWB BPF can miniaturize the structure by controlling impedance and biographical one dimension that is allocated in transmission line each section. Proposed UWB BPF designed most suitable using Agilent company's ADS2008 Momentum and Ansoft company's HFSS 10. Manufactured UWB BPF has pass-band filter of 3.1 [GHz]~10.6 [GHz] and insertion loss is 0.39 [dB] in 8.3 [GHz], and reflection loss displayed special quality of 12.394 [dB] in 9.37 [GHz].

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.403-406
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• 2006

A new medical X-ray PIV technique was developed using a conventional medical X-ray tube. To acquire images of micro-scale particles, the X-ray PIV system consists of an x-ray CCD camera with high spatial resolution, and a X-ray tube with small a focal spot. A new X-ray exposure control device was developed using a rotating disc shutter to make double pulses which are essential for PIV application. Synchronization methodology was also developed to apply the PIV technique to a conventional medical X-ray tube. In order to check the performance and usefulness of the developed X-ray PIV technique, it was applied to a glycerin flow in an opaque silicon tube. Tungsten particles which have high X-ray absorption coefficient were used as tracer particles. Through this preliminary test, the spatial resolution was found to be higher than ultrafast MRI techniques, and the temporal resolution was higher than conventional X-ray PIV techniques. By improving its performance further and developing more suitable tracers, this medical X-ray PIV technique will have strong potential in the fields of medical imaging or nondestructive inspection as well as diagnosis of practical thermo-fluid flows.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.470-475
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• 2016

In this paper, the effects of filter parameters on a supercontinuum-based all-optical thresholder are experimentally investigated. By tuning the filter parameters, the power transfer function and power transmission function are tailored. The experimental results show that a thresholder with short center wavelength has a better power function, and the slope in the middle level of the thresholder increases with increasing bandwidth. Through tuning the filter parameters, the thresholder can achieve a steplike power transfer function for optical thresholding, and a steplike power transmission function for optical self-switching. This makes the supercontinuum-based thresholder more flexible, and allows customization of performance to meet different demands in various applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.424.1-424.1
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• 2014

Vanadium dioxide (VO2) is a strongly correlated oxide exhibiting a first-order metal-insulator transition (MIT) that is accompanied by a structural phase transition from a low temperature monoclinic phase to a high-temperature rutile phase. VO2 has attracted significant attention because of a variety of possible applications based on its ultrafast MIT. Interestingly, the transition nature of VO2 is significantly affected by stress due to doping and/or interaction with a substrate and/or surface tension as well as defects. Accordingly, there have been considerable efforts to understand the influences of such factors on the phase transition and the fundamental mechanisms behind the MIT behavior. Here, we present the influences of oxygen deficiency, hydrogen doping, and substrate-induced stress on MIT phenomena in single-crystalline VO2 nanobeams. Specifically, the work function and the electrical resistance of the VO2 nanobeams change with the compositional variation due to the oxygen-deficiency-related defects. In addition, the VO2 nanobeams during exposure to hydrogen gas exhibit the reduction of transition temperature and the complex phase inhomogenieties arising from both substrate-induced stress and the formation of the hydrogen doping-induced metallic rutile phase.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.490-493
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• 2005

We have experimentally studied supercontinuum generation in a photonic crystal fiber as a function of pump wavelength and intensity with 100 fs pulsewidth. A supercontinuum over 750 nm spectral width with amplitude variation less than 10 dB has been achieved. It was generated by coupling femtosecond pulses from a mode-locked Ti:Sapphire laser into a 2 m long photonic crystal fiber. Adjusting the parameters of the pump source, it was also possible to control different spectral features of the supercontinuum radiation.