• 비파괴검사학회지
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• 제34권1호
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• pp.1-9
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• 2014

A two-dimensional numerical model based on the finite element method was built to simulate the wave propagation phenomena that occur during the ultrasonic time of flight diffraction (TOFD) process. First, longitudinal-wave TOFD was simulated, and the numerical results agreed well with the theoretical results. Shear-wave TOFD was also investigated because shear waves have higher intensity and resolution. The shear wave propagation was studied using three models with different boundary conditions, and the tip-diffracted shear-to-longitudinal wave was extracted from the A-scan signal difference between the cracked and non-cracked specimens. This signal showed very good agreement between the geometrical and numerical arrival times. The results of this study not only provide better understanding of the diffraction phenomena in TOFD, but also prove the potential of shear-wave TOFD for practical application.

• 전기의세계
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• 제24권5호
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• pp.82-90
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• 1975

This study investigated the deterioration phenomena of the Polyethylene surface contaminated with organic(Saccharose) or inorganic(NaCl) matters through electrical and optical experiments. And also these experimental results relatively well coincided with which was treated by theoretical process. On the electrical experiment, relation between electric field intensity in corona discharge and time reached to the breakdown, and relation between total amount of charges discharged and increment of applied voltage were investigated. On the optical experiment, discharge time dependence of surface deterioration rate and process of surface deterioration in the X-ray diffraction pattern were investigated. It was concluded that chemical effects by the corona discharge deteriorated insulation characteristics of Polyethylene surface.

• 대한전자공학회논문지
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• 제26권11호
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• pp.1752-1758
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• 1989

For many different types of apertures the diffraction phenomenon on the electromagnetic wave is analyzed by unsing Kirchhoff and Fresnel's diffraction theory. The signal intensity in variation of aperture's parameters is numerically calculated by a computer. To obtain the experimental data many types of apertures were made on an acryl board on which a special materical Elecoat was painted for preventing some reflections on the board surface and transmissions through it. Two Yagi antennas were used for a transmitting and receiving antenna and the frequency was 820MHz. The theoretichal values agreed reasonably with experimental data and these results will be used for a system design in the mobile communication between many buildings in the middle of a city.

• 한국진공학회지
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• 제8권3A호
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• pp.187-193
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• 1999

In this study, PVDF thin films which show the excellent piezoelectricity and pyroelectricity, are prepared by PVD (physical vapor deposition) method, and thir electrical conduction phenomena for analyses of the electrical conduction mechanism and TSC (Thermally Stimulated Current) for identification of the behavior of conductive carriers are investigated. As a result of FT-IR(Fourier Transform Infrared Spectroscopy) spectra, the crystalline phase transforms $\alpha$ type into $\beta$ type with increasing electric field. From XRD (X-Ray diffraction) analyses patterns, the degree of crystallinity increases from 49.8% to 67%, as the substrate temperature increases from $30^{\circ}C$ to $80^{\circ}C$. As a result of electrical conduction phenomena, the electrical conduction mechanism of PVDF thin films is identified as ionic conduction mechanism. From TSC analyses, there are three peaks as P1, P2, P3 with increasing temperature, and with increasing substrate temperature, the peak temperature of TSC increases and the peak intensity of TSC decreases.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.78-78
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• 2015

Metamaterials, artificially structured nanomaterials, have enabled unprecedented phenomena such as invisibility cloaking and negative refraction. Especially, hyperbolic metamaterials also known as indefinite metamaterials have unique dispersion relation where the principal components of its permittivity tensors are not all with the same signs and magnitudes. Such extraordinary dispersion relation results in hyperbolic dispersion relations which lead to a number of interesting phenomena, such as super-resolution effect which transfers evanescent waves to propagating waves at its interface with normal materials and, the propagation of electromagnetic waves with very large wavevectors comparing they are evanescent waves and thus decay quickly in natural materials. In this abstract, I will focus discussing our efforts in achieving the unique optical property overcoming diffraction limit to achieve several extraordinary metamaterials and metadevices demonstration. First, I will present super-resolution imaging device called "hyperlens", which is the first experimental demonstration of near- to far-field imaging at visible light with resolution beyond the diffraction limit in two lateral dimensions. Second, I will show another unique application of metamaterials for miniaturizing optical cavity, a key component to make lasers, into the nanoscale for the first time. It shows the cavity array which successfully captured light in 20nm dimension and show very high figure of merit experimentally. Last, I will discuss the future direction of the hyperbolic metamaterial and outlook for the practical applications. I believe our efforts in sub-wavelength metamaterials having such extraordinary optical properties will lead to further advanced nanophotonics and nanooptics research.

• 한국전기전자재료학회논문지
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• 제18권5호
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• pp.445-449
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• 2005

Aging phenomena of 0.2PMN-0.8PZT multilayered ceramic actuators(MCA) have been investigated at the room temperature. The piezoelectric materials were synthesized as conventional ceramic process, and MCA were fabricatedby tape casting methods. The crystalline structures and lattice parameters were investigated by X-ray diffraction analysis, showing the structure was tetragonal and c/a was about 1.01. And, the effective electromechanical coupling coefficient keff and pseudo-piezoelectric constant $d_{33}$were measured. Variable unipolar electric fields, $2{\sim}4kV/mm$, were applied to MCh to investigate the aging characteristics. After 2 kV/mm unipolar electric field, keff and $d_{33}$ were 0.454 and 4.44 respectively. The measured and simulated values using for aging phenomena analysis, had a good fit to the linear logarithmic stretched exponential law.

• 한국해양공학회지
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• 제8권1호
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• pp.84-95
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• 1994

In recent years Jin-Beach and Hyeya River mouth have experienced severe erosion phenomena. The cause of erosion is examined using a 3-dimensional nunumerical sediment transport model. The model is composed of three components : wave model, wave-induced current model and 3-dimensional sediment transport model. In the wave analysis component we consider refraction, diffraction and reflection based on Maruyama and Kajima method. For the wave-induced current model we use depth-integrated continuty equation and momentum equations. For the 3-dimensional sediment transport model we consider bed load and suspended load simutaneously. Model results obtained for Jin-ha Beach and Hyeya River mouth agreed well with experimental results.

• 분석과학
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• 제5권1호
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• pp.111-114
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• 1992

$Ba(Zn_{1/3}Ta_{2/3})O_3$는 고온에서 열처리시 Zn과 Ta 이온이 ordering을 일으키며 이때 격자 비틀림이 일어난다. 본 실험에서는 이러한 격자비틀림을 X-선 분말회절법을 사용하여 1/10,000 이상의 정밀도로 측정하였으며, 그 결과 $Ba(Zn_{1/3}Ta_{2/3})O_3$는 $1350^{\circ}C$ 30분 소결시에도 상당한 정도의 격자 비틀림이 발생하며 이러한 격자비틀림은 소결시간이 길어질수록 증가함을 관찰하였다.

• Applied Microscopy
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• 제43권2호
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• pp.88-97
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• 2013

Technical investigation to figure out the problems arising during in-situ heating electron backscatter diffraction (EBSD) analysis inside scanning electron microscopy (SEM) was carried out. EBSD patterns were successfully acquired up to $830^{\circ}C$ without degradation of EBSD pattern quality in steels. Several technical problems such as image drift and surface microstructure pinning were taking place during in-situ experiments. Image drift problem was successfully prevented in constant current supplying mode. It was revealed that the surface pinning problem was resulted from the $TiO_2$ oxide particle formation during heating inside SEM chamber. Surface pinning phenomenon was fairly reduced by additional platinum and carbon multi-layer coating before in-situ heating experiment, furthermore was perfectly prevented by improvement of vacuum level of SEM chamber via leakage control. Plane view in-situ observation provides better understanding on the overall feature of recrystallization phenomena and cross sectional in-situ observation provides clearer understanding on the recrystallization mechanism.

• Applied Microscopy
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• 제37권3호
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• pp.199-208
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• 2007

본 장치는 실험자가 레이저 빔과 광학 렌즈를 조정하여 이미지 및 회절도형의 형성, 보강 및 소멸간섭과 같은 파동광학 현상을 이해하도록 제작된 실험 장치이다. 실험장치는 광원으로 쓰이는 레이저빔과 빔의 광축을 정렬하는 광원 부분과 시료대, 대물렌즈, 중간렌즈, 확대렌즈, CCD system, 컴퓨터, 그리고 렌즈를 상하 조절하는 경통부분으로 구성된다. 본 장치를 통해서 다양한 회절격자의 이미지 및 회절도형을 최대 약 44배 확대할 수 있고, 최대 약 5um의 분해능을 가지고 분석할 수 있다. 이 장치는 전자현미경 이용자들이 TEM의 원리를 보다 쉽게 이해하는데 도움을 주리라 기대한다.