• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.3
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• pp.151-156
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• 1994

Exertion has been made to develop high-temperature (about $250{\sim}650^{\circ}C$) immersion ultrasonic sensor for the visualization of objects, temperature measurement, dimensional check, or nondestructive testing of welds under liquid sodium. In this study, the feasibility of the ultrasonic sensor taking advantage of a strip waveguide was confirmed by water-experiment. The lowest order of antisymmetric Lamb wave was used in the frequency range with negligible dispersion. This plate wave was excited in the stainless steel strip waveguide of 1.0mm thickness and 13mm width by the comb-structure transducer of 2.3MHz frequency. Its attenuation coefficient was 1.2dB/m in air and 380dB/m in water. The signal to noise ratio of 25dB was obtained from a planar reflector 270mm away from the beam aperture of $13mm{\times}39mm$ size.

• The Journal of the Acoustical Society of Korea
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• v.13 no.6
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• pp.50-59
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• 1994

Spectral analysis of transient elastic waves were carried out in order to identify the propagation modes in glass and unidirectional carbon fibre reinforced plastic (CFRP) plates. Pencil leads were broken on the surface of plates to generate elastic waves, and two broad band transducers of 6.35 mm in diameter and 10 MHz center frequency were placed at the linear location from the source. The frequency spectra of detected signals showed that the wave propagation in the plates obeyed the Lamb wave dispersion relation. The transient signals were the fast propagating modes around maximum group velocity of the lowest and first order symmetric $modes(S_{0} and S_{1}),$ and first order antisymmetric $mode(A_{1})$. The transient signals were not severely distorted due to relatively small dispersion of those modes around the maximum group velocity. The fastest propagating mode in the plates was shown to be $S_{0}$ mode less the than cut-off frequency of $A_{1}$ mode.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.4
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• pp.307-314
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• 2004

A circumferential guided wave method was developed to detect the axial crack on the bent feeder pipe. Dispersion curves of circumferential guided waves were calculated as a function of curvature of the pipe. In the case of thin plate, i.e. infinite curvature, as the frequency increases, the $S_0$ and $A_0$ mode coincide and eventually become Rayleigh wave mode. In the case of pipe, however, as the curvature increases, the lowest modes do not coincide even in the high frequencies. Based on the analysis, a rocking technique using angle beam transducer was applied to detect an axial defect in the bent region of PHWR feeder pipe. Based on the analysis of experimenal data for artificial notches, the vibration modes of each signal were identified. It was found that the notches with the depth of )0% of wall thickness can be detected with the method.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.56-62
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• 2011

In the present study, the phase velocities of guided ultrasonic waves such as the first arriving signal (FAS) and the slow guided wave (SGW) propagating along the long axis on the 12 tubular cortical bone samples in vitro were measured and their correlations with the cortical thickness were investigated. The phase velocities of the FAS and the SGW were measured by using the axial transmission method in air with a pair of unfocused ultrasonic transducers with a diameter of 12.7 mm and a center frequency of 200 kHz. The phase velocity of the FAS measured at 200 kHz exhibited a very high negative correlation with the cortical thickness and that of the SGW arriving after the FAS showed a high positive correlation with the cortical thickness. The simple and multiple linear regression models with the phase velocities of the FAS and the SGW as independent variables and the cortical thickness as a dependent variable revealed that the coefficient of determination of the multiple linear regression model was higher than those of the simple linear regression models. The phase velocities of the FAS and the SGW measured at 200 kHz on the 12 tubular cortical bone samples were, respectively, consistent with those of the S0 and the A0 Lamb modes calculated at 200 kHz on the cortical bone plate.

• Smart Structures and Systems
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• v.8 no.3
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• pp.303-320
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• 2011

Comparing to active damage monitoring, impact localization on composite by using time reversal focusing method has several difficulties. First, the transfer function of the actuator-sensor path is difficult to be obtained because of the limitation that no impact experiment is permitted to perform on the real structure and the difficulty to model it because the performance of real aircraft composite is much more complicated comparing to metal structure. Second, the position of impact is unknown and can not be controlled as the excitation signal used in the active monitoring. This makes it not applicable to compare the difference between the excitation and the focused signal. Another difficulty is that impact signal is frequency broadband, giving rise to the difficulty to process virtual synthesis because of the highly dispersion nature of frequency broadband Lamb wave in plate-like structure. Aiming at developing a practical method for on-line localization of impact on aircraft composite structure which can take advantage of time reversal focusing and does not rely on the transfer function, a PZT sensor array based phase synthesis time reversal impact imaging method is proposed. The complex Shannon wavelet transform is presented to extract the frequency narrow-band signals from the impact responded signals of PZT sensors. A phase synthesis process of the frequency narrow-band signals is implemented to search the time reversal focusing position on the structure which represents the impact position. Evaluation experiments on a carbon fiber composite structure show that the proposed method realizes the impact imaging and localization with an error less than 1.5 cm. Discussion of the influence of velocity errors and measurement noise is also given in detail.

• Smart Structures and Systems
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• v.13 no.4
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• pp.587-614
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• 2014

In recent years the interest in online monitoring of lightweight structures with ultrasonic guided waves is steadily growing. Especially the aircraft industry is a driving force in the development of structural health monitoring (SHM) systems. In order to optimally design SHM systems powerful and efficient numerical simulation tools to predict the behaviour of ultrasonic elastic waves in thin-walled structures are required. It has been shown that in real industrial applications, such as airplane wings or fuselages, conventional linear and quadratic pure displacement finite elements commonly used to model ultrasonic elastic waves quickly reach their limits. The required mesh density, to obtain good quality solutions, results in enormous computational costs when solving the wave propagation problem in the time domain. To resolve this problem different possibilities are available. Analytical methods and higher order finite element method approaches (HO-FEM), like p-FEM, spectral elements, spectral analysis and isogeometric analysis, are among them. Although analytical approaches offer fast and accurate results, they are limited to rather simple geometries. On the other hand, the application of higher order finite element schemes is a computationally demanding task. The drawbacks of both methods can be circumvented if regions of complex geometry are modelled using a HO-FEM approach while the response of the remaining structure is computed utilizing an analytical approach. The objective of the paper is to present an efficient method to couple different HO-FEM schemes with an analytical description of an undisturbed region. Using this hybrid formulation the numerical effort can be drastically reduced. The functionality of the proposed scheme is demonstrated by studying the propagation of ultrasonic guided waves in plates, excited by a piezoelectric patch actuator. The actuator is modelled utilizing higher order coupled field finite elements, whereas the homogenous, isotropic plate is described analytically. The results of this "semi-analytical" approach highlight the opportunities to reduce the numerical effort if closed-form solutions are partially available.

• Journal of Convergence for Information Technology
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• v.8 no.2
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• pp.83-90
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• 2018

We have studied the optimal conditions for design and development on the communication device for a bilateral, and it's electrodes for transmitting electric signal are constructed on the $36^{\circ}$ rotated $LiTaO_3$ substrate by evaporating Al-Cu(W 30%) alloy. At first, we manufactured three kind of samples using this method, and selected two samples as similar with frequency, ripple and passband characteristics, and then we connect two samples by series in order to make bilateral devices. As results, we obtained that the electrode structure has better characteristics then the others, when it's width of reflector and electrode are $1{\lambda}/4$, $1{\lambda}/12$ respectively, and it's frequency is approximately 190.3MHz. Near future, I hope to help the manufacture for communication devices for the multi-channel and the duplex filter.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.587-592
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• 2021

Change in the cortical thickness of long bones occurring with aging and osteoporosis is known to be a risk factor for fracture. The present study aims to investigate the dependencies of phase velocities of ultrasonic guided waves on the cortical thickness in 7 soft tissue-bone mimicking phantoms consisting of acrylic plates covered by a 2 mm-thick silicone rubber layer by using the axial transmission technique with a pair of transducers with a center frequency of 200 kHz and a diameter of 12.7 mm. Two distinct propagating waves with different velocities, the First Arriving Signal (FAS) and the Slow Guided Waved (SGW), were consistently observed for all the soft tissue-bone mimicking phantoms. The FAS velocity decreased slightly with increasing thickness, whereas the SGW velocity increased strongly with increasing thickness. The FAS and the SGW velocities were found to be closely consistent with the S0 and the A0 Lamb mode velocities for a free acrylic plate, respectively, suggesting that the presence of the soft tissue mimicking material (2 mm-thick silicone rubber layer) covering the acrylic plates does not influence significantly the velocity measurements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.1
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• pp.48-57
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• 2015

In a sodium-cooled fast reactor, which is a Generation-IV reactor, refueling is conducted by rotating, but not opening, the reactor head to prevent a reaction between the sodium, water and air. Therefore, an inspection technique that checks for the presence of any obstacles between the reactor core and the upper internal structure, which could disturb the rotation of the reactor head, is essential prior to the refueling of a sodium-cooled fast reactor. To this end, an ultrasound-based inspection technique should be employed because the opacity of the sodium prevents conventional optical inspection techniques from being applied to the monitoring of obstacles. In this study, a ranging inspection technique using a plate-type ultrasonic waveguide sensor was developed to monitor the presence of any obstacles between the reactor core and the upper internal structure in the opaque sodium. Because the waveguide sensor installs an ultrasonic transducer in a relatively cold region and transmits the ultrasonic waves into the hot radioactive liquid sodium through a long waveguide, it offers better reliability and is less susceptible to thermal or radiation damage. A 10 m horizontal beam waveguide sensor capable of radiating an ultrasonic wave horizontally was developed, and beam profile measurements and basic experiments were carried out to investigate the characteristics of the developed sensor. The beam width and propagation distance of the ultrasonic wave radiated from the sensor were assessed based on the experimental results. Finally, a feasibility test using cylindrical targets (corresponding to the shape of possible obstacles) was also conducted to evaluate the applicability of the developed ranging inspection technique to actual applications.