• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.144-149
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• 2011

The lock-in thermography was employed to evaluate the integrity of railway bogies. Prior to the actual application on railway bogies, in order to assess the detectability of known flaws, the calibration reference panel was prepared with various dimensions of artificial flaws. The panel was composed of structural steel, which was the same material with actual bogies. Through lock-in thermography evaluation, the optimal frequency of heat source was determined for the best flaw detection. Based on the defects information, the actual defect assessments on railway bogie were conducted with different types of railway bogies, which were used for the current operation. In summary, the defect assessment results with thermography method showed a good agreement as compared with the conventional inspection techniques. Moreover, it was found that the novel infrared thermography technique could be an effective way for the inspection and the detection of surface defects on bogies since the infrared thermography method provided rapid and non-contact mode for the investigation of railway bogies.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.153-169
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• 2018

A submarine has a pressure hull that can withstand high hydraulic pressure and therefore, requires the use of highly advanced shipbuilding technology. When producing a pressure hull, periodic inspection, repair, and maintenance are conducted to maintain its soundness. Of the maintenance methods, Non-Destructive Testing (NDT) is the most effective, because it does not damage the target but sustains its original form and function while inspecting internal and external defects. The NDT process to detect defects in the welded parts of the submarine is applied through Magnetic particle Testing (MT) to detect surface defects and Ultrasonic Testing (UT) and Radiography Testing (RT) to detect internal defects. In comparison with RT, UT encounters difficulties in distinguishing the types of defects, can yield different results depending on the skills of the inspector, and stores no inspection record. At the same time, the use of RT gives rise to issues related to worker safety due to radiation exposure. RT is also difficult to apply from the perspectives of the manufacturing of the submarine and economic feasibility. Therefore, in this study, the Phased Array Ultrasonic Testing (PAUT) method was applied to propose an inspection method that can address the above disadvantages by designing a probe to enhance the precision of detection of hull defects and the reliability of calculations of defect size.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6432-6439
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• 2014

The NAUT (Non-contact Air coupled Ultrasonic Testing) technique is one of the ultrasonic testing methods that enables non-contact ultrasonic testing by compensating for the energy loss caused by the difference in acoustic impedance of air with an ultrasonic pulser receiver, PRE-AMP and high-sensitivity transducer. As the NAUT is performed in a state of steady ultrasonic transmission and reception, testing can be performed on materials of high or low temperatures or specimens with a rough surface or narrow part, which could not have been tested using the conventional contact-type testing technique. For this study, the internal defects of spot weld, which are often applied to auto parts, and CFRP parts, were tested to determine if it is practical to make the NAUT technique commercial. As the spot welded part had a high ultrasonic transmissivity, the result was shown as red. On the other hand, the part with an internal defect had a layer of air and low transmissivity, which was shown as blue. In addition, depending on the PRF (Pulse Repetition Frequency), an important factor that determines the measurement speed, the color sharpness showed differences. With the images obtained from CFRP specimens or an imaging device, it was possible to identify the shape, size and position of the internal defect within a short period of time. In this paper, it was confirmed in the above-described experiment that both internal defect detection and image processing of the defect could be possible using the NAUT technique. Moreover, it was possible to apply NAUT to the detection of internal defects in the spot welded parts or in CFRP parts, and commercialize its practical application to various fields.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.288-294
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• 2016

This paper aims to compare the ability to detect notch defects existing in the plate and welded area using a flexible ECA (eddy current array) probe with OmniScan MX and MS-5800E. The characteristics of signals with various frequencies and lift-offs were also compared. As a result, when signals of frequencies 500, 1000, and 1500 kHz were used, the amplitude of the signal increased, as the depth of the notch increased, but reduced linearly in accordance with the lift-off variation. In addition, the detection sensitivity of the weld defect was found to be closely related to the contact surface of the probe and specimen. In this paper, it was demonstrated that the detection sensitivity was excellent when the contact surface of the probe and the specimen was sufficient, but it was poor when the contact surface was insufficient.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.434.2-434.2
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• 2014

We observe enhanced pH response of solution-gated field-effect transistors (SG-FET) having 1D-2D hybrid channel of vertical grown ZnO nanorods grown on CVD graphene (Gr). In recent years, SG-FET based on Gr has received a lot of attention for biochemical sensing applications, because Gr has outstanding properties such as high sensitivity, low detection limit, label-free electrical detection, and so on. However, low-defect CVD Gr has hardly pH responsive due to lack of hydroxyl group on Gr surface. On the other hand, ZnO, consists of stable wurtzite structure, has attracted much interest due to its unique properties and wide range of applications in optoelectronics, biosensors, medical sciences, etc. Especially, ZnO were easily grown as vertical nanorods by hydrothermal method and ZnO nanostructures have higher sensitivity to environments than planar structures due to plentiful hydroxyl group on their surface. We prepared for ZnO nanorods vertically grown on CVD Gr (ZnO nanorods/Gr hybrid channel) and to fabricate SG-FET subsequently. We have analyzed hybrid channel FETs showing transfer characteristics similar to that of pristine Gr FETs and charge neutrality point (CNP) shifts along proton concentration in solution, which can determine pH level of solution. Hybrid channel SG-FET sensors led to increase in pH sensitivity up to 500%, compared to pristine Gr SG-FET sensors. We confirmed plentiful hydroxyl groups on ZnO nanorod surface interact with protons in solution, which causes shifts of CNP. The morphology and electrical characteristics of hybrid channel SG-FET were characterized by FE-SEM and semiconductor parameter analyzer, respectively. Sensitivity and sensing mechanism of ZnO nanorods/Gr hybrid channel FET will be discussed in detail.

• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.16-23
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• 2007

This study was performed as part of a research project aimed at developing an ultrasonic computed tomography (CT) system of wood for field application. In this reports, we investigate the variation of wave velocities on the cross section of real size wooden structural member to confirm the reason of image distortion on CT image of wood, and then proposed a new image reconstruction method by considering the velocity variation on wood cross section. First of all, the effect of wood anisotropy on ultrasonic velocities of wooden members was investigated. Based on the relationship between ultrasonic velocity and annual ring angle, which was obtained from test results of small clear specimens, ultrasonic velocities of each measuring angle were predicted. Next, they were compared with the ultrasonic velocities measured on five wood disks. There were very large differences between predicted and measured results, thought to be caused by the skewing effect of ultrasound and the presence of juvenile-wood. Based on these findings, a new method was proposed to reconstruct cross-sectional image of wood. By using this method, some distortions on reconstructed images could be removed, and defects were more easily and clearly detected. The minimum size of detectable defect was decreased remarkably, from 33 mm to 13 mm. However, the size of the detected defect was enlarged and the position somewhat shifted to the specimen surface on the CT images, which was also thought to be caused by the skewing effect of ultrasound. Additional research has been planned to solve these problems.

• Journal of Korea Multimedia Society
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• v.7 no.4
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• pp.451-458
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• 2004

A leather quality inspection by naked eyes has known as unreliable because of its biological characteristics like accumulated fatigue caused from an optical illusion and biological phenomenon. Therefore it is necessary to automate the leather quality inspection by computer vision technique. In this paper, we present automatic leather qua1ity classification system get information from leather surface. Leather is usually graded by its information such as texture density, types and distribution of defects. The presented algorithm explain how we analyze leather information like texture density and defects from the gray-level images obtained by digital camera. The density data is computed by its ratio of distribution area, width, and height of Fourier spectrum magnitude. And the defect information of leather surface can be obtained by histogram distribution of pixels which is Windowed from preprocessed images. The information for entire leather could be a standard for grading leather quality. The proposed leather inspection system using machine vision can also be applied to another field to substitute human eye inspection.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.7
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• pp.1737-1742
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• 2015

In the industrial field for product inspection needs not only on the surface of the product but also the internal components defect inspection. Generally, optical inspection is mainly used for item inspection from production process. However, this is only to check defect of surface it is difficult to perform inspection of goods internal. To overcome these limitations, Instead of optical device by using the portable X- ray DR image acquisition device system developed to obtain an image in real time at the same time and determine product defects. After obtaining the X- ray image, the inspection product within error range is passed after machine image processing. Also, the results and numbers are stored by users.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.53-58
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• 2002

New nondestructive inspection (NDI) technique to detect the defect in metal was developed in which an electromagnetic field is induced in a metal by AC current flowing in the magnetic coil and the leak magnetic-flux disturbed by defects is measured using a tape-recorder head with air gap. This technique can be applied in evaluating the location and sizing of surface defects in components of the ferromagnetic body by means of the non-contacting measurement. In this paper, we have applied this technique to the evaluation of two-dimensional surface cracks in ferromagnetic metal, and also investigated the influence of the various frequencies and lift-off. Defects were detected with maximum values in the distribution of voltage and it was found that the maximum values tend to increase with the defect depth. Although the maximum values for defects are affected by the frequency and lift-off, the depth of small defects can be estimated from the linear relationship between the depth and voltage rate$(V_0/V_{ave})$.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.29-33
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• 2010

Among several critical topics in semiconductor fabrication technology, particles in addition to bonded surface contaminations are issues of great concerns. This study reports the development of a system which inspects wafer bond integrity by analyzing laser beam transmittance deviations and the variations of the intensity caused by the defect thickness. Since the speckling phenomenon exists inherently as long as the laser is used as an optical source and it degrades the inspection accuracy, speckle contrast is another obstacle to be conquered in this system. Consequently speckle contrast reduction methods were reviewed and among the all remedies have been established in the past 30 years the most adaptable solution for inline inspection system is applied. Simulation and subsequently design of experiments has been utilized to discover the best solution to improve irradiance distribution and detection accuracy. Comparison between simulation and experimental results has been done and it confirms an outstanding detection accuracy achievement. Bonded wafer inspection system has been developed and it is ready to be implemented in FAB in the near future.