• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.5
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• pp.373-380
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• 1998

The prediction of bone strength by ultrasound velocity and broadband ultrasound attenuation was examined. Ultrasound velocity and broadband attenuation were measured for sixty specimens of human trabecular bone. Samples were divided into two equal groups and loaded in compression at the strain rates of $0.0004\;s^{-1}$ and of $0.08\;s^{-1}$. The ultimate strength was determined for each specimen. Specimens tested at $0.08\;s^{-1}$ had a mean value of strength 63% higher than the specimens tested at $0.0004\;s^{-1}$. Ultrasound velocity and broadband attenuation were significantly associated with compressive strength at both strain rates. Mechanical strength was also correlated strongly with a linear combination of ultrasound velocity and broadband attenuation for both the low and high loading rates. The use of ultrasound parameters may provide good clinical means for assessing the resistance of trabecular bone to both low and high energy trauma.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.2116-2124
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• 2001

It's required mechanical properties of in-service facilities to maintain safety operation in power plants as well as chemical plants. In this studdy the four classes of the thermally aged 1Cr-lMo-0.25V specimens were prepared using an artificially accelerated aging method at 630$\^{C}$. Ultrasonic tests, tensile tests, K$\_$IC/ tests and hardness tests were performed in order to evaluate the degree of degradation of the material. The mechanical properties were decreased as degraded, but the attenuation coefficient and the harmonic generation level of a ultrasonic signal were increased. Expecially the nonlinear parameter derived from the harmonic generation level is sensitive and will be a good parameter to evaluate the material degradation.

• The Journal of the Acoustical Society of Korea
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• v.26 no.8
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• pp.426-431
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• 2007

In this paper we have studied the underwater vector channel modeling for MIMO(Multiple Input Multiple Output) to increase the performance and efficiency for ultrasound communication in underwater channel environments. Also we have analyzed the MIMO techniques using the proposed channel modeling. For underwater MIMO channel modeling. experiments were done in real channel environments and the data were analyzed to estimate parameters such as fading, Doppler, time delay, angle of arrival, and receiving power. These were used for modeling of underwater vector channel modeling for MIMO. Additionally, we have analyzed the performance of MIMO systems using our proposed channel models. As a result we could see that the BER has decreased severely with the same SNR when using the MIMO system.

• Journal of the Korean Society of Radiology
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• v.6 no.5
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• pp.351-356
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• 2012

Ultrasonic cavitation is a physical phenomenon that generates and collapses microbubbles in media (mainly fluids) under conditions of strong ultrasonic irradiation. In this study, changes in the ultrasonic acoustic characteristics of bubble clouds in relation to ultrasonic irradiation were observed by the quantitative evaluation of cavitation yields. Concave-type single ultrasonic transducers with center frequencies of 500 kHz and 1.1 MHz were used to produce cavitation, and 2.25 MHz interference ultrasonic waves that would traverse any bubble clouds generated were used to analyze the cavitation. The parameters used for the evaluation of cavitation yields (changes in the center frequency, attenuation characteristics, and the propagation time of penetrating waves) were analyzed in relation to the cavitation-generating conditions (irradiation intensity, excitation signal, and center frequency). On the basis of these results, correlations between the changes in the center frequency and irradiation intensity were identified. Although the correlation coefficient was low, notable changes were observed in the center frequency under certain irradiation conditions. Attenuation trends in the interference ultrasonic waves showed high correlations with all the irradiation conditions, and it was noted that these trends were not affected by the forms of cavitation generated. No differences in the propagation time were observed among different irradiation conditions. These findings suggest that bubble yields can be quantitatively evaluated effectively by evaluating the diverse irradiation conditions and that such a quantitative evaluation could be used to study the basic cavitation phenomenon occurring in high-intensity ultrasonic wave treatment.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.190-197
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• 2014

In this paper, we present a method for optical parameter-based material rendering with measuring the thickness of a material using ultrasonic waves. Thickness is an important element in determining the reflectance and transmittance of a material along with its optical characteristics and plays a crucial role in more realistic object rendering. In studies conducted thus far, thickness has been measured and used for rendering. The proposed method is a novel method attempted for the first time ever to render a material considering the thickness of a material whose thickness cannot be measured by visual assessment, using ultrasonic waves. It was implemented by measuring the sound velocity of the reference sample and applying the results to the thickness measurement of other objects that have the same characteristics. The characteristics of the objects measured are reflected in the quality of the final rendering, thus verifying the importance of thickness in rendering.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.149-154
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• 2002

An attempt was made to evaluate the changes of microstructures and mechanical properties with increasing aging time in 2.25Cr-1Mo steel. In this study, it was verified the feasibility of the evaluation for degraded 2.25Cr-1Mo steel by isothermal heat treatment at $630^{\circ}C$ up to 1,000 hours using surface SH wave and investigated the change of attenuation coefficient and propagation time. Attenuation coefficient had a tendency to increase according to degradation and propagation time drastically in the beginning of deterioration. A good correlation between ultrasonic attenuation coefficient and hardness was found, which made sure that attenuation coefficient is an potential parameter for evaluation of aging degradation. In addition, it has verified experimentally the frequency dependence of ultrasonic group velocity and attenuation coefficient using wavelet transform.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.484-493
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• 2012

Since the 1980s, there have been many research activities devoted to quantitatively characterizing and imaging human tissues based on sound speed, attenuation coefficient, density, nonlinear B/A parameter, etc., but those efforts have not yet reached the stage of commercialization. However, a new imaging technology termed elastography, which was proposed in the early 1980s, has recently been implemented in commercial clinical ultrasound scanners, and is now being used to diagnose prostates, breasts, thyroids, livers, blood vessels, etc., more quantitatively as a complementary adjunct modality to the conventional B-mode imaging. The purpose of this article is to introduce and review various elastographic algorithms for use in quasistatic or static compression type elasticity imaging modes. Most of the algorithms are based on the crosscorrelation or autocorrelation function methods, and the fundamental difference is that the time shift is estimated by changing the lag variable in the former, while it is directly obtained from the phase shift at a fixed lag in the latter.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.32 no.2 s.57
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• pp.123-127
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• 2006

In this study, we evaluated the crow's fret of 95 Korean female by using mechanical assessments; Skin-Visiometer SV 600 and Dermascan C. Transparency profilometry (Skin Visiometer) were using a very thin skin print which allowed parallel light to pass through and was analysed immediately after production. High-frequency (20 MHz) ultrasonography (Dermascan C) enabled non-invasive evaluation in skin thickness and echodensity. We found a correlation between skin roughness and dermal density. Particularly, we showed a significant correlation between skin roughness (R2) and dermal thickness. Also, we demostrated a significant negative correlation between dermal density and dermal thickness (p < 0.05). Therefore, the ultrasonography system might be considered a very useful method in wrinkle evaluation with the transparency profilometry. Further study will be required.

• Journal of the KSME
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• v.37 no.10
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• pp.41-46
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• 1997

철강구조물 부재 내에 노치나 균열이 존재할 수 있고, 외부의 피로하중에 의하여 취약부에서 발생한 균열이 진전하여 전구조물의 최종파손을 야기시킬 수 있다. 부재를 보다 안전하게 사용하고 또한 신뢰성을 확보하기 위해서는 이미 손상된 부재에서 균열의 진전상태를 계측할 수 있는 방법이 확립되어져야 하고, 파괴역학적 파라미터를 이용한 사용재의 균열진전거동특성이 평가되어야 한다. 균열길이의 측정방법은 지금까지 많은 연구자들에 의하여 개발되어져 왔는데 크게 광학현미경을 이용하여 육안으로 직접 균열길이를 측정하는 방법과 컴플라이언스, 초음파, AE 또는 전기적 신호를 통하여 얻어진 결괄부터 균열길이로 환산하는 간접적인 방법으로 대별된다. 대부분의 균열길이의 측정방법은 많은 수작업이 요구되고, 특히 하한계응력확대계수영역의 미세한 균열진전량을 측정하기에는 어려움이 따르고 있다. 이에 대하여 전도체 시험편에 일정전류를 흐르게 하고 균열길이의 증가에 따라 변화하는 전위차로 이를 균열길이로 평가하는 전기적인 측정방법이 있다. 이 방법은 실험장치가 비교적 간단하고 미세한 균열길이의 측정이 용이하여 균열길이의 직접적인 측정이 곤란한 고온역 그리고 충격하중하에서의 균열길이 측정에 이용이 확대되고 있다. 이 글에서는 여러 균열길이 측정방법의 장.단점에 대하여 고찰하고, 그 중 많은 장점을 갖고 있는 직류전위차법의 실험방법을 소개한다.