• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.1022-1027
• /
• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered metal bearing and flexible structures by using the finite element method and the mode superposition method considering the asymmetry of the gyroscopic effect and sintered metal bearing. The eigenvalues and eigenvectors are calculated by solving the eigenvalue problem and the adjoint eigenvalue problem by using the restarted Arnoldi iteration method. The decoupled equations of motion can be obtained from global finite element motion equations by using the orthogonal relation between the right eigenvectors and left eigenvectors. The decoupled equations of motion are used to analyze the unbalance response of a high speed polygon mirror scanner motor. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.5A
• /
• pp.674-681
• /
• 2000

We proposed polymer based vertical asymmetric optical coupler. And we optimized the proposed device by coupling characteristic analysis In 1.33um wavelength, TE mode, we obtained very short coupling length(L=277.6um), high coupling efficiency(94%). The merits of proposed device are low propagation loss due to very short full device, low production cost and time, and high integrated fabrication. We will use this to fabricate optical switch, modulator and tunable WDM devices, etc.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.41 no.10
• /
• pp.51-56
• /
• 2004

We propose and fabricate an 1${\times}$2 asymmetric optical switch by TOE using SOI wafer based on silicon which has very large TOE figure and it is a good material for optical devices. SOI wafer consists of 3 layers; upper Si layer for device(waveguide;core, n=3.5), buried oxide layer for insulator(clad, n=1.5) and Si substrate layer. We designed 1${\times}$2 asymmetric y-branched single mode optical waveguide switch by BPM simulation and metal heater by heat transfer simulation. Fabricated switch shows about 3.5 watts of power consumption and over 20dB of crosstalk between output channels.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.170-170
• /
• 2010

a-plane 혹은 m-plane면을 사용하는 무분극 GaN LED는 c축 방향으로 발생하는 분극의 영향을 받지 않기 때문에 분극 GaN LED에 비해 높은 내부 양자효율을 가진다. 또한 무분극 GaN는 상대적으로 고농도의 p-type 도핑이 가능하기 때문에 광효율을 높일 수 있다. 하지만 이와 같은 장점에도 불구하고 무분극 GaN는 성장모드의 비대칭으로 인해 높은 결정성과 mirror-like한 표면을 얻기가 힘들다. 본 논문에서는 Metalorganic chemical-vapor deposition (MOCVD) 장비를 사용하여 r-plane 사파이어 기판위에 a-plane GaN을 성장시켰다. 일반적으로 사용하는 저온에서의 nucleation layer 성장 대신 $1050^{\circ}$의 고온에서 성장 시킨후 일반적으로 사용하는 two-step 성장방법으로 그위에 5.5um정도의 GaN을 성장시켰다. 성장시 Trimethylgallium(TMGa)와 암모니아를 각각 Ga과 N 소스로 이용하였고 캐리어 가스는 수소를 사용하였다. 비대칭 결정성을 줄이기 위해 3D island growth mode에서의 성장조건을 바꾸어 c축과 m축 방향으로의 X-ray 결정성(FWHM) 차이가 564 arcsec에서 206 arcsec로 변화 시켰다. Normarski 현미경으로 표면을 관찰한 결과 v-defect이 없고 a-plane GaN에서 볼 수 있는 전형적인 줄무늬 패턴을 가지는 표면을 얻었으며 광학적 특성을 보기 위해 Photoluminescence (PL)을 측정하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.24 no.4
• /
• pp.81-94
• /
• 2010

This paper presents a high efficiency resonant asymmetrical half-bridge flyback converter. The primary half-bridge circuit of the converter operates by a soft-switching type using the asymmetrical pulse-width modulation (PWM) method with the resonant capacitance and transformer leakage inductance. The secondary flyback circuit of the proposed converter utilizes a synchronous rectifier, which operates by a new voltage-driven method with a simple drive circuit. Thus the proposed converter improves the total efficiency. This paper explains the operational principle of the proposed converter by each mode and shows the converter design consideration and a design example for the prototype converter, respectively. After that, the proposed simple driving technique of the synchronous rectifier by a voltage-driven method is explained, briefly. The designed prototype converter has wide input voltage (AC $V_{in,rms}$=75~265[V]), 5[V] DC output voltage, and 100[W] output power. To verify the excellent performance of the proposed converter, the designed prototype is implemented and experimented. The good performance of the proposed converter is shown through the experimental results.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.3 no.1
• /
• pp.41-54
• /
• 1999

For free vibration of non-symmetric thin-walled circular arches including restrained warping effect, the elastic strain and kinetic energy is derived by introducing displacement fields of circular arches in which all displacement parameters are defined at the centroid axis. The cubic Hermitian polynomials are utilized as shape functions for development of the curved thin-walled beam element having eight degrees of freedom. Analytical solution for in-plane free vibration behaviors of simply supported thin-walled curved beams with monosymmetric cross-sections is newly derived. Also, a finite element formulation using two noded curved beams element is presented by evaluating elastic stiffness and mass matrices. In order to illustrate the accuracy and practical usefulness of this study, analytical and numerical solutions for free vibration of circular arches are presented and compared with solutions analyzed by the straight beam element and the ABAQUS's shell element.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.5
• /
• pp.39-48
• /
• 2000

We newly proposed a polymer based vertical asymmetric optical coupler, which was characterized by simple fabricating procedure and short coupling length. And we fabricated a thermo-optic modulator using the polymeric optical coupler. We optimized the proposed device by coupling characteristic analysis. In a TE polarized 1.33${\mu}{\textrm}{m}$ wavelength, we obtained very short coupling length(L=277.6${\mu}{\textrm}{m}$) with 0.4${\mu}{\textrm}{m}$ thickness of middle layer, high coupling efficiency(94%), and asymmetric vertical waveguides with n$_{u}$ = 1.522, n$_{l}$ = 1.51. We implemented vortical asymmetric thermo-optic modulator with lower inverted rib waveguide and upper slab waveguide. In the 600Hz bandwidth and 4.5㎽ input power, the extinction ratio of the mode was 17㏈ with an insertion loss of 4.5㏈.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.7 no.4
• /
• pp.1-13
• /
• 2003

For spatial free vibration of non-symmetric thin-walled curved beams with shear deformation, an improved formulation is proposed in the present study. The elastic strain and the kinetic energies are first derived by considering constant curvature and shear deformation effects due to shear forces and restrained warping torsion. Next equilibrium equations and force-deformation relations are obtained using a stationary condition of total potential energy. And the finite element procedures are developed by using isoparametric curved beam element with arbitray thin-walled sections. Particularly not only shear deformation and thickness-curvature effects on vibration behaviors of curved beams but also mode transition and crossover phenomena with change in curvatures of beams are parametrically investigated. In order to illustrate the accuracy and the reliability of this study, various numerical solutions for spatial free vibration are compared with results by available references and ABAQUS's shell element.

• The Journal of the Acoustical Society of Korea
• /
• v.13 no.6
• /
• pp.50-59
• /
• 1994

Spectral analysis of transient elastic waves were carried out in order to identify the propagation modes in glass and unidirectional carbon fibre reinforced plastic (CFRP) plates. Pencil leads were broken on the surface of plates to generate elastic waves, and two broad band transducers of 6.35 mm in diameter and 10 MHz center frequency were placed at the linear location from the source. The frequency spectra of detected signals showed that the wave propagation in the plates obeyed the Lamb wave dispersion relation. The transient signals were the fast propagating modes around maximum group velocity of the lowest and first order symmetric $modes(S_{0} and S_{1}),$ and first order antisymmetric $mode(A_{1})$. The transient signals were not severely distorted due to relatively small dispersion of those modes around the maximum group velocity. The fastest propagating mode in the plates was shown to be $S_{0}$ mode less the than cut-off frequency of $A_{1}$ mode.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.11
• /
• pp.1829-1834
• /
• 2001

The aim of this study is to investigate the ductile fracture behavior under mixed mode (I/II) loading using SA533B pressure vessel steel. Anti-symmetric 4-point (AS4P) bonding tests were performed to obtain the J-R curves under two different mixed mode (I/II) loadings. In addition, the fractographic examination of fracture surfaces was carried out to compare with those of pure Mode I and Mode II. In conclusions, the J-R curves under Mixed Mode (I/II) loading were located between those of Mode I and Mode II loadings. When the mixture ratio of mixed mode (I/II) loading was high, the J-R currie of mixed mode (I/II) loading approached that of pure mode I loading after some amount of crack propagation. In contrast with the above fact, if the mixture ratio was low, the J-R curve looked after that of pure mode II loading. The fractographic evidences such as the shape of dimples under different loading conditions supported these conclusions.