• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.207-210
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• 2001

Recently, the study on the vibration analysis of machinery is greatly important and ESPI is widely used because of its many attractive features. Firstly, ESPI can be used to measure the vibration mode shape and the phase in real-time. Secondly, the conventional measuring methode, such as accelerometers, take much time to measure the whole field of object, but ESPI needs shorter time than other methods. Because ESPI is a field-inspection method. Thirdly, ESPI is a non-contact measuring system. ESPI does not have influence on the specimen. Beyond these features, there are several advantages in ESPI system. In this paper, the Stroboscopic ESPI system is described for measurement of a vibration mode shape. The Stroboscopic ESPI system had been used to visualize the vibration mode shape, in which EO(Electro-Optic)modulator was used to chop CW(Continuous Wavefront)laser. But it was not easy to control EO modulator and quantified the vibration amplitude and the phase of circular metal plate. At first, we found resonant frequency of the specimen by using time-averaged ESPI method. Nextly, the amplitudes of specimen were quantified by using Stroboscopic ESPI and we compare the results which were obtained in several chopping ratio.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1394-1397
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• 2006

Polymer Dispersed Liquid Crystal (PDLC) films, of which the liquid crystal has negative dielectric anisotropy, were prepared from the phase separation between MJ001317 and a variety of compositions of resins by common polymerization induced phase separation method. In this work, the effects of resin compositions have been systematically investigated and it was found that the morphology and size of droplet, which is closely related to electro-optic properties, mainly depend on the rate of polymerization and cross-linking density for each resin composition. The reverse mode PDLC films from this newly developed formulation containing TPGDA/EHA/HMPPO showed the good off-state transmittance, contrast ratio (19/1), and relatively low driving voltage(10V).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.1054-1057
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• 2003

We have studied $90^{\circ}$ twisted nematic (TN) mode driven by fringe electric field, where two polarizers are parallel each other such that the cell shows a black state before a voltage is applied. According to the studies by computer simulation for a LC with negative dielectric anisotropy, the LC twists perpendicular to the horizontal field direction of fringe electric field and the degree of tilt angle is very low, when a voltage is applied. Therefore, the new device exhibits wide viewing angle characteristic due to in-plane switching and high transmittance since the LC director aligns parallel to the polarizer axis.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.739-743
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• 2003

[ $Ba_2NaNb_5O_{15}$ ], hereafter BNN, thin films are attractive candidates for nonvolatile memory and electro-optic devices. In the present work, thin films that have different contents of Ba, Nb and Na have been prepared by H-MOD technique on silicon and Pt substrates. XRD and SEM were used to investigate the phase evolution behavior and the microstructure of the films. It was found that the films of about 500nm thick were crack-free and uniform in microstructure. Nb content strongly influenced the phase formation of the films, where unwanted phases were always formed at the stoichiometric BNN composition. However, the unwanted phases decreased with the increase of excess Nb content, and the single phase (tetragonal tungsten bronze structure) BNN thin film was obtained when the niobium content reached some point. From this study, the sub-solidus phase diagram below $850^{\circ}C$ for $BaO-Na_2O-Nb_2O_5$ ternary system is proposed.

• 한국광학회지
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• 제6권1호
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• pp.26-32
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• 1995

Kerr cell 광스위치를 옥소 레이저 증폭단에서 짧은 펄스를 발생시키는 광절단기로서 그리고 이후의 증폭기들을 광학적으로 분리하는 격리기로 사용하였다. Kerr cell 양단에 인가된 전위차에 따른 편광의 회전에 의해 입사된 펄스를 자를 수 있음을 보였으며 회로의 전기적 특성을 이용하여 케이블의 길이차에 의해 5ns와 1ns 펄스를 발생시켰다. 공진기에서 펄스폭이 긴 펄스가 발생한 경우 한개 이상의 단축된 출력 펄스가 발생함을 확인하였다. 또한 Kerr cell의 동작전압을 변화시켜 얻은 투과도를 Kerr 이론과 비교하였다. 단축된 펄스를 옥소레이저 전 증폭기를 통해 증폭하여 4ns 펄스에서 2J의 출력을 얻어 0.5GW의 최종출력을 얻었다.

• 한국결정성장학회지
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• 제1권2호
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• pp.1-14
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• 1991

비균질 용융을(incongruent melting behavior)보이는 단결정제조에 있어 화학성분을 일정성분비로 유지하는 것은 매우 어렵다. $LiNbO_3$는 이러한 성질을 보이는 대표적인 예인데 넓은 고용(固溶)영역에서 일정성분비를 유지하기 힘들다 . 정밀전기/ 광학장치에 있어 이런 변수는 치명적이라 할 수 있다. 결정의 조성과 질을 결정하는 방법으로 굴절율(n)을 측정하는 광학적 방법이 수행되어 왔다. 이 방법으로 성장결정의 광학적 균질성과 화학조성을 알아낼 수 있다. 여기서는 그런 특성분석에 사용 되는 기술을 설명하고 그 결과들을 제시해 보았다

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.297-298
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• 2005

We have fabricated twisted nematic (TN) liquid crystal cells doped by carbon nanotubes (CNTs) with different CNT wt. %. With a minute amount doping, multi-walled CNTs did not perturb the liquid crystal orientations at the off- and on-state. The hysteresis studies of voltage-dependent capacitance (V-C) under the influence of electric field generated by ac and dc voltage show that the residual do, which is tightly related to image sticking problem in liquid crystal displays, is greatly reduced due to ion trapping by CNTs. Also, the V-C hysteresis shows dependency of capacitance on concentration of multi-walled CNTs.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1961-1971
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• 2006

A soft recovery system (SRS) is a device that stops a high speed projectile without damaging the projectile. The SRS is necessary to verify the shock resistant requirements of microelectronics and electro-optic sensors in smart munitions, where the projectiles experience over 20,000 g acceleration inside the barrel. In this study, a computer code for the performance evaluation of a SRS based on ballistic compression decelerator concept has been developed. It consists of a time accurate compressible one-dimensional Euler code with use of deforming grid and a projectile motion analysis code. The Euler code employs Roe's approximate Riemann solver with a total variation diminishing (TVD) method. A fully implicit dual time stepping method is used to advance the solution in time. In addition, the geometric conservation law (GCL) is applied to predict the solutions accurately on the deforming mesh. The equation of motion for the projectile is solved with the four-stage Runge-Kutta time integration method. A small scale SRS to catch a 20 mm bullet fired at 500 m/s within 1,600 g-limit has been designed with the proposed method.

• 한국전기전자재료학회논문지
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• 제18권1호
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• pp.89-95
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• 2005

We derived a formula which can calculate the space distribution of refractive index variation by an applied electric field about Bi$_{12}$ GeO$_{20}$ single crystal. Stereographic projection maps of refractive index variation by an applied electric field were made out using numerical value to be calculated by this formula. By the calculated results, since an electric field had applied to [(equation omitted) 1 1] direction and [1 (equation omitted) 1] direction of Bi$_{12}$ GeO$_{20}$ crystal, positive variation of the refractive index of [(equation omitted) 1 1] direction and [1 (equation omitted) 1] direction was the largest. The incremented refractive index per unit electric field was +3.2410${\times}$10$^{-11}$ V$^{-1}$ for the wavelength of 6328 $\AA$. Since an electric field had applied to [1 1 1] direction and [(equation omitted) 1] direction, negative variation of the refractive index of [1 1 1] direction and [(equation omitted) 1] direction was the largest. The decremented refractive index per unit electric field was -3.2410${\times}$10$^{-11}$ V$^{-1}$ for the wavelength of 6328 $\AA$.

• 한국정밀공학회지
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• 제20권4호
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• pp.92-102
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• 2003

To detect electrical faults of a TFT (Thin Film Transistor) panel for the LCD (Liquid Crystal Display), techniques of converting electric field to an image are used One of them is the PDLC (polymer-dispersed liquid crystal) modulator which changes light transmittance under electric field. The advantage of PDLC modulator in the electric field detection is that it can be used without physically contacting the TFT panel surface. Specific pattern signals are applied to the data and gate electrodes of the panel to charge the pixel electrodes and the image sensor detects the change of transmittance of PDLC positioned in proximity distance above the pixel electrodes. The image represents the status of electric field reflected on the PDLC so that the characteristic of the PDLC itself plays an important role to accurately quantify the defects of TFT panel. In this paper, the image of the PDLC modulator caused by the change of electric field of the pixel electrodes on the TFT panel is acquired and how the characteristics of PDLC reflect the change of electric field to the image is analyzed. When the holding time of PDLC is short, better contrast of electric field image can be obtained by changing the instance of applying the driving voltage to the PDLC.