• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.345-352
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• 2016

As aircrafts are being operated at high altitude, wing structures experience various fatigue loadings under cryogenic environments. As a result, fatigue damage such as a crack could be develop that could eventually lead to a catastrophic failure. For this reason, fatigue damage monitoring is an important process to ensure efficient maintenance and safety of structures. To implement damage detection in real-world flight environments, a special cooling chamber was built. Inside the chamber, the temperature was maintained at the cryogenic temperature, and harmonic fatigue loading was given to a wing structure. In this study, piezoelectric active-sensing based guided waves were used to detect the fatigue damage. In particular, a beamforming technique was applied to efficiently measure the scattering wave caused by the fatigue damage. The system was used for detection, growth monitoring, and localization of a fatigue crack. In addition, a sensor diagnostic process was also applied to ensure the proper operation of piezoelectric sensors. Several experiments were implemented and the results of the experiments demonstrated that this process could efficiently detect damage in such an extreme environment.

• Journal of Conservation Science
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• v.32 no.2
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• pp.235-247
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• 2016

Conventional imaging techniques such as ultraviolet, infrared, and X-ray are used mainly to diagnose the damaged parts of the painted cultural assets in Korea. These techniques, however, have limits in diagnosing damages of interlayer parts. We have performed and extensive study on the applicability of Terahertz(THz) analysis technique, introduced recently to this field of study on cultural properties in Korea, to diagnose painted cultural assets. The specimens, produced to imitate the damage types of Korean painted properties, were analyzed over their painting, supporting, and backing layers by terahertz pulse imaging technique. The analyzed results provided information about the cracks, the separated areas, and the separated distances between layers on the specimens. Our research, then, was extended to real painted cultural remains, Birojana Sam-shin Gwebul-do at Bongseon Temple in Namyang-ju, Korea National Treasure Number 1792, through which we have obtained 3D information about the extent and pattern of damages to the asset. These results demonstrate that terahertz 3D imaging technique has the capability of noncontact 3D diagnosis on painted cultural properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.627-635
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• 2017

Modern warfare is gradually changing into a network war, and information electronic warfare is also progressing. In modern war, electronic warfare is all military activity concerned with electromagnetic field use, such as signal collecting, communication monitoring, information analysis, and electronic attack. The one key function of signal collecting for enemy signal analysis, direction finding, collects the signal radiated from enemy area and then calculates the enemy direction. This paper examined the Watson-Watt algorithm for an amplitude direction finding system and CVDF algorithm for phase direction finding system and analyzed the difference in the direction finding accuracy between in the clean electromagnetic field environment and in the real operating field environment of electronic warfare system. In the real field, the direction finding accuracy was affected by the reflected field from the surrounding obstacles. Therefore, this paper proposesan enhanced direction finding process for reducing the effect. The result of direction finding by applying the proposed process was enhanced above $1.24^{\circ}$ compared to the result for the existing process.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.219-226
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• 2020

Nondestructive testing is one of the most commonly used quality inspection methods for evaluating ship structures. However, accurate evaluation is dif icult because various composite materials, such as reinforcements, resin, and fiber-reinforced plastics (FRPs), are used in hulls, and manufacturing quality differences are likely to exist owing to the fabrication environment and the skill level of workers. This possibility is especially true for FRP ships because they are significantly thicker than other structures, such as automobiles and aircraft, and are mainly manufactured using the hand lay-up method. Because the density of a material is a critical condition for ultrasonic inspection, in this study, a hull plate was selected from a vessel manufactured using e-glass fiber, which is widely used in the manufacture of FRP vessels with the weight fraction of the glass content generally considered. The most suitable ultrasonic testing conditions for the glass FRP hull plate were investigated using a pulse-echo ultrasonic gauge. A-scans were performed with three probes (1.00, 2.25, and 5.00 MHz), and the results were compared with those of the hull plate thickness measured using a Vernier caliper. It was found that when the probe frequency was higher, the eco-pulse velocity of the receiver had to be lowered to obtain accurate measurement results, whereas fewer errors occurred at a relatively low probe frequency.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.12
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• pp.787-791
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• 2012

Characteristics of particle separation in water using labscale acoustic standing wave were studied. Acoustic standing wave is similar to either sound wave or ultrasonic, which makes a constant wave while returning to the origin by reflector. During that time, particulates dispersed in water are collected on the node of wave, where a sound pressure is zero. Acoustic standing wave transducer as of 28.0 kHz and 1.0 MHz were utilized and $6.8{\mu}m$ kaolin and $100.5{\mu}m$ redmud in average diameter were used as experimental materials in water. Once acoustic standing wave are generated in water, water temperature rises by $0.15{\sim}0.20^{\circ}C/min$ due to a sound pressure. Initial concentration of kaolin and redmud were controlled to have same as of 0.1, 0.2, 0.3, 0.4, 0.5 g/L, respectively. Removal efficiency of the turbidity in a reacting chamber after 5 minutes, when acoustic sound wave was formed in most distinct, was measured to have 18.2~56.2% for kaolin and 23.0~53.6% for redmud at 1.0 MHz. Particle separation was not observed at 28.0 kHz.

• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.421-426
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• 2006

In examining particulate deposits in the pipes of a chemical vapor deposition (CVD) system, vibration diagnostics is compared and studied against ultrasonic diagnostics, The latter method involves pulsing the outer wall of pipes with an ultrasonic sensor and analyzing the resulting echo to observe particulate deposits inside pipes. Vibration diagnostics examines the existence of particulate deposits by analyzing the difference in the frequencies generated when a vibrator is adhered to the outer wall of pipes. With ultrasonic diagnostics, good test results were obtained only when particulate deposits were attached to the inner wall of the pipes, After some time, however, particulate deposits were not detected properly, as the ultrasonic wave failed to cross the fine gaps created between the inner wall of the pipe and the deposits. The ultrasonic wave bounced back because of the dried particulate deposits on the wall. Thus, it has been proven that the ultrasonic diagnostics is not an appropriate means of examining the particulate deposits in a vacuum, On the other hand, vibration diagnostics succeeded in detecting the particulate deposits regardless of the lapsed time. In conclusion, the vibration diagnostics is being expected as the effective method in monitoring the particulate deposits inside pipes in the CVD system where the desired behavior is reduced frequency along with the particulate deposits in comparison to the case where the pipe is clean.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.400-409
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• 2017

We have studied a combiner that can withstand high power while minimizing insertion loss in high frequency band. In particularly, because the output power that can be output per unit elements is much lower in the Ku band and above than in the low frequency band, it is necessary to combine many semiconductor elements in order to make a high power SSPA. A planar combiner such as a microstrip, as the number of elements to be combined increases, the insertion loss increases proportionally, resulting in a reduction in the overall system efficiency and an increase heating value also. The planar combiner also have some problems due to the low power handling rate. To improve these problems, we proposed a Cavity Radial Combiner. A Ku band 16-way Cavity Radial Combiner was fabricated and measured. As a result, it was tested 14dB return loss and over 94.5 % output combining efficiency in design band.

• Journal of the Korean Geotechnical Society
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• v.32 no.8
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• pp.5-14
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• 2016

The leakage of water under sewer pipelines is one of main sources of sinkholes in urban areas. We performed laboratory model tests to investigate the presence of cavities using impact-echo method, which is a nondestructive test method. To simulate a concrete sewer pipe, a thin concrete plate was built and placed over container filled with sand. The cavity was modeled as an extruded polystyrene foam box. Two sets of tests were performed, one over sand and the other on cavity. A new impact device was developed to apply a consistent high frequency impact load on the concrete plate, thereby increasing the reliability of the test procedure. The frequency and transient characteristics of the measured reflected waveforms were analyzed via fast Fourier transform and short time Fourier spectrum. It was shown that the shapes of Fourier spectra are very similar to one another, and therefore cannot be used to predict the presence of cavity. A new index, termed resonance duration, is defined to record the time of vibration exceeding a prescribed intensity. The results showed that the resonance duration is a more effective parameter for predicting the presence of a cavity. A value of the resonance period was proposed to estimate the presence of cavity. Further studies using various soil types and field tests are warranted to validate the proposed approach.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.55-65
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• 2016

Detecting an object which is located at seabed is an important issue for various areas. This paper presents an approach to detection of an object that is placed at seabed in the shallow water. A conventional scheme is to employ a side-scan sonar to obtain images of a detection area and to use image processing schemes to recognize an object. Since this approach relies on high frequency signals to get clear images, its detection range becomes shorter and the processing time is getting longer. In this paper, we consider an active sonar system that is repeatedly sending a linear frequency modulated signal of 6~20 kHz in the shallow water of 100m depth. The proposed approach is to model consecutively received reflected signals and to measure their modeling error magnitudes which decide the existence of an object placed on seabed depending on relative magnitude with respect to threshold value. The feature of this approach is to only require an assumption that the seabed consists of an homogeneous sediment, and not to require a prior information on the specific properties of the sediment. We verify the proposed approach in terms of detection probability through computer simulation.

• Journal of Korea Multimedia Society
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• v.11 no.9
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• pp.1296-1301
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• 2008

Ultrasonography constructs pictures of areas inside the body needs in diagnosis by bouncing high-enorgy sound waves(ultrasound) off internal tissues or organs. In constructing an ultrasonographic image, the weakness of bounding signals induces noises and detailed differences of brightness, so that having a difficulty in detecting and diagnosing with the naked eyes in the analysis of ultrasonogram. Especially, the difficulty is extended when diagnosing muscle areas by using ultrasonographic images in the musculoskeletal test. In this paper, we propose a novel image processing method that computationally extracts a muscle area from an ultrasonographic image to assist in diagnosis. An ultrasonographic image consists of areas corresponding to various tissues and internal organs. The proposed method, based on features of intensity distribution, morphology and size of each area, extracts areas of the fascia, the subcutaneous fat and other internal organs, and then extracts a muscle area enclosed by areas of the fascia. In the extraction of areas of the fascia, a series of image processing methods such as histogram stretching, multiple operation, binarization and area connection by labeling is applied. A muscle area is extracted by using features on relative position and morphology of areas for the fascia and muscle areas. The performance evaluation using real ultrasonographic images and specialists' analysis show that the proposed method is able to extract target areas being approximate to real muscle areas.