• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.3
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• pp.311-317
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• 2019

We first numerically analyzed the characteristics of a silicon-based grating structure for beam steering. The analysis includes the basic principle of the grating structure according to the wavelength, peak radiation angle, radiation efficiency, and full-width at the half maximum(FWHM) of the radiation angle. Based on the analysis, we propose a silicon-based grating structure integrated with distributed Bragg reflector(DBR) to obtain a high radiation efficiency and narrow beam width simultaneously. We performed the numerical optimization of the radiation efficiency and FWHM of the radiation angle according to the DBR position. By the design optimization using the proposed grating structure compatible with the complementary metal-oxide semiconductor(CMOS) process, we achieved a maximum radiation efficiency of 87.1% and minimum FWHM of radiation angle of $4.68^{\circ}$.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.68-72
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• 2008

Fiber-optic strain sensors based on Bragg reflection gratings produce the change of reflection spectrum when an external stress is applied on the sensor. To measure the Bragg reflection wavelength in high speed, an arrayed waveguide grating device is incorporated in this work. By monitoring the output power from each channel of the AWG, the peak wavelength corresponding to the applied strain could be obtained. To enhance the accuracy of the AWG wavelength interrogation system, a chirped fiber Bragg grating with a 3-dB bandwith of 5.4 nm is utilized. The high-speed response of the proposed system is demonstrated by measuring a fast varying strain produced by the damped oscillation of a cantilever. An oscillation frequency of 17.8 Hz and a damping time constant of 0.96 second are obtained in this measurement.

• Journal of the Korean Society of Radiology
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• v.15 no.6
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• pp.771-779
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• 2021

It is necessary to overlap several peaks to form spread out Bragg peak (SOBP) in order to cover the tumor volume because a mono-energetic proton beam forms a narrow Bragg peak. The tumor density has been considered as a brain tissue and then the absorbed dose of the tumor is calculated using Monte Carlo simulations. However, densities of tumors were not a constant. In this study, the SOBP of proton beams was calculated according to changing density of tumors by using Geant4. Tumors were selected as 10 mm and 20 mm width which were the treatment range in the brain phantom. The energies and relative weights of the proton beams were calculated using mathematical formula to form the SOBP suitable for the location and size of the tumor. As the density of the tumor was increased, the 95% modulation range and the practical range were decreased, and average absorbed dose in the 95% modulation range was increased. The change of the tumor density affects the dose distribution of the proton beams, which results in short SOBP within the tumor volume. The consideration of the tumor density affects the determination of the range, so that the margin of the treatment volume can be minimized, and the advantages of proton therapy can be maximized.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.27-30
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• 2002

PMFBG sensor was fabricated using phase mask and Excimer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To discover the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurements. Experiments showed that the PMFBG sensor could successfully measure the transverse strain. This PMFBG sensor is useful for the structures that require measuring transverse stram.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.354-357
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• 1995

Measurements of X-ray diffuse scatterings were made in disordered single crystal of Fe-28.3 at%Pt Invar alloy around a 200-Bragg peak in a wide temperature range between 15 K and 300 K. Observed diffuse scatterings were almost spherical, suggesting a homogeneous disordered alloy. However, the qdependence of the observed thermal diffuse scattering was different from the usual type, indicating a possibility of existence of local distortion of lattice accompanied by a large gradient of stress.

• Composites Research
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• v.15 no.4
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• pp.32-36
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• 2002

Recently, the applications of composite materials become broader to civil engineering as well as mechanics and aerospace engineering. Cracks on the civil structures like bridges can cause stress concentration, which induces Peak splitting of fiber Bragg grating sensor and it makes strain measurements difficult. In this study, 4-point bending test of concrete beam with initial crack reinforced by composite patch was conducted in order to verify the effects of the stress concentration on the peak signal of FBG sensor and a novel method for signal maintenance.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.383-386
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• 2008

We developed a fiber-optic Bragg grating sensor system using a SOA fiber laser for over heat detection in power systems. To compensate the nonlinear wavelength tuning of the fiber laser, we used fixed passband wavelengths from Fabry-Perot ITU filter as reference wavelengths. Gaussian line-fitting algorithm was also used to reduce the FBG peak detection error. Compared with a highest-peak-detection and a polynomial-fitting method, the proposed Gaussian fitting algorithm could drastically reduce the measurement errors. Also the SOA fiber laser made it possible to enhance the signal-to-noise-ratio even with several kilometers of lead fiber.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.149-149
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• 2010

The origin of the inhomogeneous distribution of photoluminescence (PL) peak wavelength on a commercial 2" GaN wafer for green light emitting diode has been investigated by wide momentum transfer (Q) range x-ray diffraction (XRD) profile of InGaN/GaN multiple quantum wells. Near the GaN (0004) Bragg peak, wide-Q range XRD (${\Delta}Q$ > $1.4{\AA}-1$) was measured along the growth direction. Wide-Q XRD gives precise and direct information of ultra-thin InGaN quantum well structure. Based on the QW structural information, the variation of PL spectra can be explained by the combined effect of temperature gradient and slightly uneven flow of atomic sources during the QW growth. In narrow variations of indium composition and thickness of QW, an effective indium composition can be a good character to match structural data to PL spectra.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.7-13
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• 2010

We have investigated effects of the rapid thermal annealing of GaN epilayers by molecular beam epitaxy in nitrogen atmosphere. The improvement of structural properties of the samples was observed after rapid thermal annealing under optimum conditions. This improvement in crystal quality is due to a reduction of the spread in the lattice parameter in epilayers. The annealing has been performed in a rapid thermal annealing furnace at $950^{\circ}C$. The effect of rapid thermal annealing on the structural properties of GaN was studied by x-ray diffraction. The Bragg peak shifts toward larger angle as the annealing time increases. As the thermal treatment time increases, FWHM(full width at half maximum) of the peak slightly increase with its decreases followed and it increases again. Results demonstrate that rapid thermal annealing did not always promote qualities of GaN epilayers. However, rapid thermal annealing under optimum conditions improve structural properties of the samples, elevating their crystal quality with a reduction of inaccuracy in the lattice parameter of the epilayers.

• Journal of Radiation Protection and Research
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• v.41 no.3
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• pp.222-228
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• 2016

Background: We are developing a small size dosimeter for dose estimation in particle therapies. The developed dosimeter is an optical fiber based dosimeter mounting an radiation induced luminescence material, such as an OSL or a scintillator, at a tip. These materials generally suffer from the quenching effect under high LET particle irradiation. Materials and Methods: We fabricated two types of the small size dosimeters. They used an OSL material Eu:BaFBr and a BGO scintillator. Carbon ions were irradiated into the fabricated dosimeters at Heavy Ion Medical Accelerator in Chiba (HIMAC). The small size dosimeters were set behind the water equivalent acrylic phantom. Bragg peak was observed by changing the phantom thickness. An ion chamber was also placed near the small size dosimeters as a reference. Results and Discussion: Eu:BaFBr and BGO dosimeters showed a Bragg peak at the same thickness as the ion chamber. Under high LET particle irradiation, the response of the luminescence-based small size dosimeters deteriorated compared with that of the ion chamber due to the quenching effect. We confirmed the luminescence efficiency of Eu:BaFBr and BGO decrease with the LET. The reduction coefficient of luminescence efficiency was different between the BGO and the Eu:BaFBr. The LET can be determined from the luminescence ratio between Eu:BaFBr and BGO, and the dosimeter response can be corrected. Conclusion: We evaluated the LET dependence of the luminescence efficiency of the BGO and Eu:BaFBr as the quenching effect. We propose and discuss the correction of the quenching effect using the signal intensity ratio of the both materials. Although the correction precision is not sufficient, feasibility of the proposed correction method is proved through basic experiments.