• Investigative Magnetic Resonance Imaging
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• v.9 no.1
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• pp.36-42
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• 2005

Purpose : To develop a novel approach to calculate the sensitivity profiles of the phased array coil for use in non-uniform intensity correction. Materials and Methods : The proposed intensity correction method estimates the sensitivity profile of the coil to extract intensity variations that represent the scanned image. The sensitivity profile is estimated by fitting a non-linear curve to various angles of projections through the imaged object in order to eliminate the high-frequency image content. Filtered back projection is then used to compute the estimates of the sensitivity profile of each coil. The method was applied both to phantom and brain images from 8-channel phased-array coil and 4-channel phased-array coil, respectively. Results : Intensity-corrected images from the proposed method have more uniform intensity than those from the commonly used 'sum-of-squares' approach. By using the proposed correction method, the intensity variation was reduced to $6.1\%$ from $13.1\%$, acquired from the 'sum-of-squares'. Conclusion : The proposed method is more effective at correcting the intensity non-uniformity of the phased-array surface-coil images than the conventional 'sum-of-squares' method.

• Wind and Structures
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• v.39 no.1
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• pp.31-45
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• 2024

This paper examines the flow characteristics around an inclined prism with a U-shaped cross-section ("U-profile") and investigates the connection between the flow and flow-induced vibrations. The study employs a combined approach that involves wind tunnel experiments and computational fluid dynamics (CFD) using an unsteady Reynolds-averaged Navier-Stokes (RANS) turbulence model. Distinct vortex formation patterns are observed in the flow field surrounding the stationary inclined profile. When the cavity of the profile faces away from the incoming flow, large vortices develop behind the profile. Conversely, when the cavity is oriented towards the oncoming flow, these vortices form within the cavity. Notably, due to the slow movement of these large vortices through the cavity, the frequency at which vortices are shed in the negative inclination case is lower compared to the positive inclination, where they form in the wake. Wind tunnel experiments reveal an intermittent transition between the two vortex formation patterns at zero inclination. Large vortices sporadically emerge both in the cavity and behind the profile. The simulation results demonstrate that when these large vortices occur at a frequency close to the structure's natural frequency, they induce prominent pitch vibrations. This phenomenon is also sought after and presented in coupled vibration experiments. Additionally, the simulations indicate that when the natural frequency of the structure is considerably lower than the vortex shedding frequency, this type of vibration can be observed.

• Korean Journal of Remote Sensing
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• v.26 no.5
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• pp.527-536
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• 2010

This paper reports a reliable GRD (Ground Resolved Distance) measurement method of using natural targets instead of the method using artificial targets. For this, we developed an edge profile extraction technique suitable for natural targets. We demonstrated the accuracy and stability of this technique firstly by comparing GRD values generated by this technique visually inspected GRD values for artificial targets taken in laboratory environments. We then demonstrated the feasibility of GRD estimation from natural targets by comparing GRD values from natural targets to those from artificial targets using satellite images containing both artificial and natural targets. The GRDs measured from the proposed method were similar to the values from visual inspection and the GRDs measured from the natural targets were similar to the values from artificial targets. These results support our proposed method is able to measure reliable GRD from natural targets.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.569-577
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• 2010

Nonplanar surface geometries of components are frequently encountered in real ultrasonic inspection situations. Use of rigid array transducers can lead to beam defocusing and reduction of defect image quality due to the mismatch between the planar array and the changing surface. When a flexible array is used to fit the complex surface profile, the locations of array elements should be known to compute the delay time necessary for adaptive heam focusing. An alternative method is to employ the time reversal focusing technique that does not require a prior knowledge about the properties and structures of the specimen and the transducer. In this paper, a time reversal method is applied to simulate beam focusing of flexible arrays and imaging of point-like defects contained in specimens with nonplanar surface geometry. Quantitative comparisons are made for the performance of a number of array techniques in terms of the ability to focus and image three point-like reflectors positioned at regular intervals. The sinusoidal profile array studied here exhibits almost the same image quality as the flat, reference case.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.48 no.4
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• pp.38-48
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• 2011

Block based LCD backlight nonideality and crosstalk compensation methodologies are proposed based on the analysis of backlight profiles and image pixel homogeneity. Large computation complexity required in the conventional compensations is minimized without the degradation of image qualities by optimizing image block size, image area inside the block to be excluded from the compensation computation and the required backlight range to be computed. The optimization results of computation complexity as well as image qualities are verified for the proposed compensation by real image data simulations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.263-266
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• 2002

An optical method for surface roughness estimation based on statistical analysis of the light intensity of a scattered laser beam pattern. The method is very simple but has a disadvantage that no more information than the averaged roughness is estimated. In this study a new try was conducted to derive more advanced surface information from the details of the light intensity distribution. Some periodic ripples among the light intensity distribution being assumed to relate with scratch left on the machined surface, a corresponding surface profile is estimated from the ripples using FFT and IFFT algorithm. IFFT technique is used to extract some dominant signal components among the intensity distribution. Compared to the measured profiles by a stylus type surf-tester, the profiles obtained through the proposed method are probably acceptable in a sense of the profile shape. Calibration of the amplitude needs more works in the future.

• ETRI Journal
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• v.36 no.4
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• pp.617-624
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• 2014

Through-silicon via (TSV) technology provides much of the benefits seen in advanced packaging, such as three-dimensional integrated circuits and 3D packaging, with shorter interconnection paths for homo- and heterogeneous device integration. In TSV, a destructive cross-sectional analysis of an image from a scanning electron microscope is the most frequently used method for quality control purposes. We propose a quantitative evaluation method for TSV etch profiles whereby we consider sidewall angle, curvature profile, undercut, and scallop. A weighted sum of the four evaluated parameters, nominally total score (TS), is suggested for the numerical evaluation of an individual TSV profile. Uniformity, defined by the ratio of the standard deviation and average of the parameters that comprise TS, is suggested for the evaluation of wafer-to-wafer variation in volume manufacturing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1530-1535
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• 1992

An optical method of phase shifting interferometry is presented for the 3-dimensional profile measurement of mirror surfaces with nanometer resolution. A series of optical interferometric fringes are generated by comparing the surface to be measured with a reference flat. The fringes are captured by a CCD camera and then analyzed to obtain actual surface profile. Detailed principles are described along with necessary image processing algorithms. finally, several measurement examples are discussed which were performed on lapped surfaces, hard discs, and semiconductor wafers.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.12
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• pp.1079-1085
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• 2012

For precise motion control, S-curve velocity profile is generally used but it has disadvantage of relatively long calculation time for floating-point arithmetics. In this paper, we present a new generating method for velocity profile to reduce delay time of profile generation so that it overcomes such disadvantage and enhances the efficiency of precise motion control. In this approach, the velocity profile is designed based on the gamma correction expression that is generally used in image processing to obtain a smoother movement without any critical jerk. The proposed velocity profile is designed to support both T-curve and S-curve velocity profile. It can generate precise profile by adding an offset to the velocity profile with decimals under floating point that are not counted during gamma correction arithmetic operation. As a result, the operation time is saved and the efficiency is improved. The proposed method is compared with the existing method that generates velocity profile using ring buffer on a 8-bit low-cost MCU. The result shows that the proposed method has no delay in generating driving profile with good accuracy of each cycle velocity. The significance of the proposed method lies in reduction of the operation time without degrading the motion accuracy. Generated driving signal also shows to verify effectiveness of the proposed method.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.138-141
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• 1995

This paper describes a 3-dimensional measuring method for cylindrical huge ingot pressed with forging machine. Target ingot we consider here is rotated around a fixed axis during measurement. Using an image processing technique every profile of cross-section is obtained, and 3D image is reconstructed. One method to calibrate the system setting is also presented. Experimental results reveal that the method are applicable and the algorithm is feasible.