• Journal of the Optical Society of Korea
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• v.19 no.2
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• pp.165-168
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• 2015

A simple method to determine the focal length of a lens using the Talbot image is presented. This method uses only one grating, requiring neither Moir$\acute{e}$ fringe analysis nor the angle between the gratings. The original Fourier transform was used to access the spectrum beyond the limitation set of the usual fast Fourier transform to determine the (de)magnification accurately enough to be used for the focal length. A set of Talbot images simulated numerically with the Fresnel diffraction integral was used to demonstrate the method. For focal lengths between 5550 mm and 5650 mm, the mean difference between the focal lengths determined from the Talbot images and the true values was 3.3 mm with the standard deviation of the difference being 3.8 mm. The true focal lengths can be recovered with an accuracy of 0.06%.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.6
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• pp.601-608
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• 2011

This paper presents the damage assessment of a building structure by using a novel optical fiber accelerometer system. Especially, a sub-scaled building model is designed and manufactured to check up the feasibility of the optical fiber accelerometer for structural health monitoring. The novel accelerometer exploits the moir$\acute{e}$ fringe optical phenomenon and two pairs of optical fibers to measure the displacement with a high accuracy, and furthermore a pendulum to convert the displacement into acceleration. A prototype of optical fiber accelerometer system has been successfully developed that consists of a sensor head, a control unit and a signal processing unit. The building model is also designed as a 4-story building with a rectangular shape of $200{\times}300$ mm of edges. Each floor is connected to the next ones by 6 steel columns which are threaded rods. Basically, a random vibration test of the building model is done with a shaker and all of acceleration data is successfully measured at the assigned points by the optical fiber accelerometer. The experiments are repeated in the undamaged state and the damaged state. The comparison of dynamic parameters including the natural frequencies and the eigenvectors is successfully carried out. Finally, the optical fiber accelerometer is proven to be prospective to evaluate dynamic characteristics of a building structure for the damage assessment.

• Journal of the Optical Society of Korea
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• v.19 no.3
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• pp.265-271
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• 2015

We propose a reactive mesogen (RM) lens array to obtain good focusing behavior along with a short focal plane, where the focusing behavior is switchable according to the polarization state of incident light. Polarization-dependent focusing behavior is obtained using a planoconvex RM microlens array on a planoconcave isotropic lens template. Even though the sagitta of our RM lens is high, to obtain the short focal length, the RM layer can be aligned well by introducing a top-down alignment effect, using a nanogrooved template. The optical noise due to the $moir{\acute{e}}$ effect generated by the nanogrooves on the surface of the planoconvex RM layer can be removed simply by overcoating a thin RM layer, which is self-aligned by the geometric surface effect, without an additional alignment process. We demonstrate a hexagonal-packed RM lens array that has a very high fill factor and symmetric phase profile, for an ideal lens.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1377-1384
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• 2010

The objective of this study is to determine the best material model that represents the deformation behavior of the Sn37Pb solder alloy accurately. First, a specimen is fabricated and subjected to a thermal cycle with temperatures ranging from the room temperature to $125^{\circ}C$. An experiment is conducted to examine deformation by Moire interferometry. Three different constitutive equation models are used in the finite element analysis (FEA) of the thermal cycle. In order to minimize the difference between the FEA results and the experimental results, the material parameters of the solder alloy are considered to be unknown and are determined by conducting optimization. As a result of the study, the Anand model is found to represent the deformation behavior of the solder most accurately.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.86-94
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• 2009

This paper deals with the creation of a new, low-cost point/position tracking system that can measure deformations in engineering structures with simple commercially widespread cameras. Though point tracking systems do exist today, such as Stereo Pattern Recognition (SPR) and Projection Moir$\acute{e}$ Interferometry (PMI) systems, they are far too costly to use to analyze small, simple structures because complex optical components such as large flashes, high-resolution cameras and data acquisition systems with several computers are required. We developed a point tracking system using commercial cameras. This system used IR LEDs and commercial IR CCD cameras to minimize the interference posed by other extraneous light sources. The main algorithm used for this system is an optical point tracking algorithm, which is composed of the point extraction algorithm and the point matching algorithm for 3-D motion estimation. a series of verification tests were performed. Then, the developed point tracking system was applied to measure deformations of an acrylic plate under a mechanical load. The measured deformations of the acrylic plate matched well with the numerical analysis results. The results indicate that the developed point tracking system is reliable enough to measure continuous deformed shapes of various engineering structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.157-163
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• 2008

This paper presents a novel fiber optic tiltmeter system for the health monitoring of large-size structures. The system is composed of a sensor head, a light control unit and a signal processing unit. The sensing mechanism of the sensor head is based on a novel integration of the moire fringe phenomenon with fiber optics to achieve a robust performance in addition to its immunity to EM interference, easy ratting, and low cost. In this paper, a prototype of the fiber optic tiltmeter system has been developed successfully. A low-cost light control unit has been developed to drive the system's optic and electronic components. From an experimental test, the fiber optic tiltmeter is proven to be a prospective sensor for the monitoring of the tilting angle of civil structure with a good linearity. Finally, the test also successfully demonstrates the performance and the potential of the novel fiber optic tiltmeter system to monitor the health of civil infrastructures.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.175-182
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• 2012

The scattered radiation always occurs when X-ray strikes the object. To absorb the scattered X-rays, the antiscatter grids are used, however these grids images are superimposed in the projection radiography images. When those images are displayed on the monitor, moir$\acute{e}$ patterns are overlapped over the images and disturb the anatomical informations. Most of the researches performed to date removed the grid noises by calculating or observing those frequencies in one dimensional frequency domain, two dimensional wavelet transform or Fourier transform. Those methods filtered not only the grid noises but also diagnostic informations. In this paper, we proposed the combined wavelet packet-Fourier method to remove the grid artifact in CR images. For the phantom image, the proposed method achieved from 5.2 to 7.4 dB better than others in SNR and for CR images by rejecting the grid noise bands effectively while leaving the remaining bands unchanged, the loss of images could get minimal results.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.349-356
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• 2017

The purpose of this study is to provide guidelines for effective osteoarthritis passive aquatic rehabilitation program and form of exercise prescription through passive aquatic rehabilitation exercise for 24 weeks for women with osteoarthritis. The subjects of this study were the passive aquatic rehabilitation group (CG, n = 10) and the control group (AREG, n = 10) among the subjects who had been diagnosed with osteoarthritis by the K orthopedic surgeon and visited the hospital more than 3 times were selected. The results of this study showed that the change of shoulder height in the group was significantly different in passive aquatic rehabilitation exercise group (p <.001). There were significant differences in passive aquatic rehabilitation exercise group (p <.001) between the groups with inhaled sacpula patterns. Changes in the pelvis patterns inferior pattern of the left and right pelvis patterns in the group were significantly different in passive aquatic rehabilitation exercise group (p <.001).

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.141-148
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• 2019

Electronic substrates used in a mobile device is composed of various materials, and when the temperature is changed during manufacturing or operating, thermal deformation and stress concentration occur due to the difference in thermal expansion coefficient of each material. The shadow moiré technique is a non-contact optical method that measures shape or out-of-plane displacement over the entire area, but it is necessary to overcome the Talbot effect for high sensitivity applications. In this paper, LED light sources of various wavelengths was used to overcome the Talbot effect caused in the shadow moiré technique. By using the phase shift method, an experimental method to retain the measurement sensitivity within 10 ㎛/fringe was proposed and evaluated, and this method is applied to the thermal deformation measurement of the mobile electronic substrate. In the case of using white light, there were several areas that could not be measured due to the Talbot effect, but in the case of using blue LED light, it was shown that a precise moiré pattern with a sensitivity of 6.25 ㎛/fringe could be obtained in most areas.

• Journal of the Semiconductor & Display Technology
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• v.20 no.1
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• pp.77-82
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• 2021

Using a multi-array needle module developed for coating of high-density cylindrical microlens array (C-MLA), we have fabricated an anti-Moiré filter for LED screens. The Moiré phenomenon appears due to the interference between the array pattern of image sensors in a camera and the non-emission area (grid pattern) of a LED screen. To suppress it, we have employed poly(methyl methacrylate) (PMMA) and coated it on a glass substrate in the form of a grid and non-grid (parallel lines). We have rotated the needle module in order to increase the number of C-MLAs. With this scheme, we have fabricated the 150 mm × 150 mm anti-Moiré filters where 836 microlens lines are formed. They show the average width of 255.4 ㎛, the average distance between CMLs of 94.6 ㎛, and C-MLA width non-uniformity of 4.7%. We have shown that the Moiré patterns still appear in the presence of the parallel (non-grid)-type filter, whereas they disappeared completely by the grid-type filter. It is due to the fact that the Moiré patterns are diffused more effectively by the grid-type C-MLA.