• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.56-62
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• 2004

We present a diffraction grating interferometer of large equivalent wavelength specially designed for flatness testing of rough surfaces. Two transmission diffraction gratings are illuminated on the object under test by use of two measurement beams with different angles of incidence, which yields a large equivalent wavelength. This interferometer design minimizes unnecessary diffraction rays and the systematic error caused by the diffraction gratings, and provides a large working distance and easy alignment. To improve the measurement accuracy, phase shifting technique is applied and the equivalent wavelength error caused by defocus is calibrated. Test results obtained from mirror surfaces and machined rough surfaces are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1129-1138
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• 1999

[$Moir\acute{e}$] technique is now being extensively investigated as a fast non-contact means of three-dimensional profile measurement especially for reverse engineering. One problem with $moir\acute{e}$ technique is so called $2\pi$-ambiguity problem that limits the maximum step height difference between two neighboring sampling points to be less than half the equivalent wavelength of $moir\acute{e}$ fringes. In this investigation, a new two-wavelength scheme of projection $moir\acute{e}$ topography is proposed and tested to cope with the $2\pi$-ambiguity problem. Experimental results are discussed to assess the new method in measuring large objects with high step discontinuities.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.68-75
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• 1996

More accurate inspection method for facilities of nuclear power plants is required to guarantee the continuous and stable energy supply. The portion of inspection for pipes and pressure vessels is relatively big in the power plants. Conventional inspection methods using ultrasonic wave, x-ray and eddy current for nondestructive testing in nuclear power plants have been performed as the method of contact with objects to be inspected. With this reason these methods have been taken relatively much time, money and manpower. And the area to be inspected is limited by the location of probe or film. These difficulties make the inspection into a time-consuming work. We propose an optical defect detection method using phase shifting realtime holographic interferometry. This method has an advantage that the inspection can be performed at a time for relatively wide area illuminated by the laser beam, a coherent light source and can help an inspector recognize not only defects but also the high stressed areas. In this paper we show that the quantitative measurement using holographic interferometry and image processing for defect in pressure vessels is possible.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.239-244
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• 1998

ESP(Electronic Speckle Pattern Interferometry) is an optical technique to measure deforamtion of engineering components and materials in industrial areas. ESPI, a non-contact and non-destructive measuring method, is capable of providing full-field results with high spatial resolution and high speed. One of important application aspects using electronic speckle pattern interferometry is to generate contours of a diffuse object in order to provide data for 3-D shape analysis and topography measurement. The electronic speckle contouring is suitable for providing measurement range from millimeters to several centimeters. In this study, we introduce the contouring method by modified dual-beam speckle pattern interferometer and a shift of the two illumination beams through optical fiber in order to obtain the contour fringe patterns. Before the experiments, we performed the geometric analysis for dual-beam-shifted ESPI contouring. And by this geometric analysis, we performed the electronic speckle contouring experiment. We used 4-frame phase shifting method with PZT for quantitative analysis of contour fringes. Finally, we showed good agreements between the geometric analysis and experimental results.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.313-320
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• 2004

We present a null testing method fer aspheric surfaces, utilizing a phase-shifting diffraction grating interferometer along with a binary amplitude computer generated hologram (CGH). The binary amplitude CGH is designed to compensate for the wavefront between a point source and the aspheric surface under test. The fringe visibility of the grating interferometer is controlled easily by selecting suitable grating diffraction orders for the measurement and reference wavefronts or by optimizing the groove shape of the grating used. The binary amplitude CGH is designed by numerical analysis of ray tracing and fabricated using e-beam lithography for autostigmatic testing. Experimental results of a large-scale aspheric mirror surface are discussed to verify the measurement performance of the proposed diffraction grating interferometer.

• Journal of the Optical Society of Korea
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• v.13 no.2
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• pp.251-255
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• 2009

In the non-contact 3-dimensional (3D) shape measurements, the fringe pattern projection method based on the phase-shifting technique has been considered very effective for its high speed and accuracy. The digital fringe projector in particular has great flexibility in generating fringe patterns since the patterns can be controlled easily by the computer program. In this work, we have developed a high-speed digital laser grating projection system using a laser diode and a polygon mirror, and evaluated its performance. It has been demonstrated that all the optical measurements required to find out the profile of a 3D object could be carried out within 31 ms, which confirmed the validity of our 3D measurement system. The result implies the more important fact that the speed in 3D measurement can be enhanced remarkably since, in our novel system, there is no device like a LCD or DMD whose response time limits the measurement speed.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.715-721
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• 2000

Residual stress is one of the causes which makes defects in engineering components and materials. These residual stresses can occur in many engineering structures and can sometimes lead to premature failures. There are commonly used methods by which residual stresses are currently measured. But these methods have a little damage and other problems; therefore, a new experimental technique has been devised to measure residual stress in materials with a combination of electronic laser interferometry, laser heating and finite element method. The electronic laser interferometer measures in-plane deformations while the laser heating and cooling provides for very localized stress relief. FEM is used for determining the heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heat-up and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.39 no.6
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• pp.24-35
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• 2002

The wavelet transform is combined with the boundary element method (BEM), to solve efficiently the Maxwell's equation and the proposed method is applied to the electromagnetic problem for the analysis of topological effects of phase-shifting masks. The accuracy of the module developed was verified by comparison with both analytic solutions and published results. In addition, it was found that the boundary element method in combination with the wavelet matrix transform would be more efficient than the conventional methods based on the BEM in views of the calculation speed and the usage of computer memory.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.43-48
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• 2000

In this paper, vortical integrated transformers using bondwires are proposed and characterized for MMIC's (Monolithic Microwave Integrated Circuits) In a wide range of frequencies (1∼20 GHz), where full-wave analysis by the FEM (Finite Element Method) was adopted. The electrical characteristics of the proposed transformers are compared with those of the spiral transformer. We extracted mutual inductances from S -parameters. The vertical transformers using bondwires have not only low insertion loss but also reduce parasitic capacitances and dielectric loss due to their separation from substrates. It can be fabricated easily by used of the modern automatic wirebonding technology. It is expected that the proposed transformers are to improve the performance of MMIC's applied to impedance matching, and phase shifting circuits.

• Journal of Photoscience
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• v.9 no.2
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• pp.243-245
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• 2002

Pigment-dispersing factor (PDF) is an octadecapeptide distributed in the optic lobe and the brain in a variety of insect species. There are lines of evidence suggesting possible involvement of PDF in the insect circadian system. However, its physiological roles in the circadian time keeping mechanism have not been clearly defined. In this study, we have examined the phase shifting effects of Gryllus-PDF on the circadian locomotor rhythm in the cricket Gryllus bimaculatus of which circadian clock is located in the optic lobe. Phase shifts in the circadian activity rhythm were measured following microinjection of 22nl of vehicle (Ringer's solution) or O.lmM PDF into the optic lobe through the compound eye at various circadian times. The results showed that PDF induced phase shifts of the circadian clock in a phase-dependent manner, suggesting that it may play a role as an input signal for the circadian clock.