• Journal of the Korean Society of Radiology
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• v.84 no.3
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• pp.666-675
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• 2023

Purpose This study aimed to determine whether the attenuation coefficient (AC) from attenuation imaging (ATI) was correlated with visual US assessment in patients with hepatic steatosis. Moreover, it aimed to assess whether the patient's blood chemistry results and CT attenuation were correlated with AC. Materials and Methods Patients who underwent abdominal US with ATI between April 2018 and December 2018 were included in this study. Patients with chronic liver disease or cirrhosis were excluded. The correlation between AC and other parameters, such as visual US assessment, blood chemistry results, liver attenuation, and liver-to-spleen (L/S) ratio, were analyzed. AC values according to visual US assessment grades were compared using analysis of variance. Results A total of 161 patients were included in this study. The correlation coefficient between US assessment and AC was 0.814 (p < 0.001). The mean AC values for the normal, mild, moderate, and severe grades were 0.56, 0.66, 0.74, and 0.85, respectively (p < 0.001). Alanine aminotransferase levels were significantly correlated with AC (r = 0.317, p < 0.001). The correlation coefficients between liver attenuation and AC and between L/S ratio and AC were -0.702 and -0.626, respectively (p < 0.001). Conclusion Visual US assessment and AC showed a strong positive correlation with the discriminative value between the groups. Computed tomography attenuation and AC showed a strong negative correlation.

• 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.15 no.2
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• pp.364-370
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• 1995

The purpose of this paper was to develop a nondestructive evaluation method of sintered material by ultrasonic method. The density distribution of sintered material becomes inhomogeneous partially because of the friction between the powder and the die during compaction. The inhomogeneity was investigated by measurement of the energy attenuation coefficient and the shift of the center frequency in the frequency spectrum of the ultrasonic reflection echo. The experimental results showed that the center frequency of reflection wave depended linearly on the density of sintered materials. However, the attenuation coefficient decreased inversely as the density increased. This study shows that the shift of the center frequency in the frequency spectrum of reflection wave can be used to a nondestructive evaluation of sintered materials.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.265-268
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• 1999

감쇠가 큰 고분자 복합재료에서 초음파 다중반사파를 이용한 Pulse Echo법, 공진주파수에서 내부마찰계수 측정법과 Rheometer를 이용한 동적탄성계수 측정법을 사용하여 음향감쇠계수를 측정하고 각각의 측정자료를 비교하는 연구를 수행하였다. Pulse Echo법을 이용하여 0.5, 1.0, 2.25MHz에서 음향감쇠계수를 측정하였고, 이때 폴리에틸렌기지 복합재료의 음향감쇠계수는 강화재의 부피분율에 따라 3-15dB/cm 정도로 큰 값을 나타내었다. 폴리에틸렌기지 복합재료를 600kHz 근처에서 공진주파수를 가지도록 시편을 만든 후에 내부마찰계수를 측정한 결과로 계산된 음향감쇠계수는 Pulse Echo 실험에서 구한 값과 잘 일치하는 결과를 얻을 수 있었다. Rheometer를 이용한 동적탄성계수 측정법은 0.1-100Hz의 주파수에서 측정한 자료를 TTSP 이론을 이용하여 1MHz의 결과와 비교하였는데, 단일 고분자 재료에서는 다른 측정방법과 음향감쇠계수가 일치하였지만 복합재료에서는 음향감쇠계수값이 일치하지 않는 결과를 나타내었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• The Journal of the Acoustical Society of Korea
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• v.29 no.6
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• pp.388-394
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• 2010

In the present study, polyacetal bone mimics with circular cylindrical pores were used to investigate variations of speed of sound and attenuation coefficient with porosity and microarchitecture in bone. The speed of sound and attenuation coefficient of the 6 bone mimics with porosities from 0 % to 65.9 % were measured by a through-transmission method in water, using a pair of broadband, unfocused transducers with a diameter of 12.7 mm and a center frequency of 1.0 MHz. Independently of the structural properties of the bone mimics, the speed of sound decreased almost linearly with the increasing porosity. The attenuation coefficient measured at 1.0 MHz exhibited linear or nonlinear correlations with the porosity, depending on the structural properties of the bone mimics. These results are consistent with those previously published by other researchers using bone samples and mimics, and advances our understanding of the relationships of the ultrasonic parameters for the diagnosis of osteoporosis with the bone density and microarchitecture in human bones.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.17-24
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• 2002

The objective of the present research is to evaluate the wave propagation velocity and attenuation characteristics of kaolin clay specimens using ultrasonic testing. Test specimens with known initial micro-fabric were prepared using a two-stage slurry consolidation technique. For a known state of stress conditions, initial void ratio, and micro-fabric, a series of experiments were conducted to evaluate the longitudinal wave propagation velocity and associated damping behavior. The effects of major variables involved in ultrasonic testing of cohesive soil were considered in this study. Ultrasonic velocity was not correlated to the microfabric structure under the given consolidated pressure whereas ultrasonic attenuation was affected by the microstructural properties of the specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.501-510
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• 2000

Recently, advanced signal analysis which is called "time-frequency analysis" has been used widely in nondestructive evaluation applications. Wavelet transform(WT) and Wigner Distribution are the most advanced techniques for processing signals with time-varying spectra. Wavelet analysis method is an attractive technique for evaluation of material characterization nondestructively. Wavelet transform is applied to the time-frequency analysis of ultrasonic echo waveform obtained by an ultrasonic pulse-echo technique. In this study, the feasibility of noise suppression of ultrasonic flaw signal and frequency-dependent ultrasonic group velocity and attenuation coefficient using wavelet analysis of ultrasonic echo waveform have been verified experimentally. The Gabor function is adopted the analyzing wavelet. The wavelet analysis shows that the variations of ultrasonic group velocity and attenuation coefficient due to the change of material characterization can be evaluated at each frequency. Furthermore, to assure the enhancement of detectability and naw sizing performance, both computer simulated results and experimental measurements using wavelet signal processing are used to demonstrate the effectiveness of the noise suppression of ultrasonic flaw signal obtained from austenitic stainless steel weld including EDM notch.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.163-166
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• 2001

초음파를 이용하여 인체 조직의 특성을 알아내는 방법은 매우 광범위하게 응용되어 오고있다. 그 중에서 초음파를 발생시킨 후 반사되어 되돌아오는 신호를 측정하여 그 감쇠 정도로부터 조직의 특성을 추정하는 방법이 많이 사용되고 있다. 이러한 감쇠현상은 발생된 초음파가 조직 내에서 흡수 또는 산란현상을 거치면서 주파수가 변이를 일으키기 때문에 발생한다. 따라서, 조직의 감쇠 특성을 알아내기 위해서, 주파수의 함수로 근사할 수 있는 감쇠 계수(attenuation coefficient)를 이용하여 시간에 따라 달라지는 주파수 변화를 추정한다. 그러나, 기존의 Ah(Auto-Regressive) 모델을 통한 시간영역 및 주파수 영역에서의 추정 방법을 사용하면 잡음이 존재하는 상황에서 시변 신호를 추정하는데 성능이 많이 저하된다. 본 논문에서는 이러한 단점을 보완하기 위해서, 가변 망각 인자와 재귀적인 TLS(Total Least Squares) 방법을 사용하여 시간에 따라 변하는 신호를 정확하게 추정하고 잡음환경에도 강인한 알고리듬을 제안하였다. 또한, 제안된 알고리듬은 추정 성능을 향상시킬 뿐 아니라 감쇠정도의 강약에 관계없이 망각인자의 값을 적응적으로 변화시켜 동작하는 장점을 가진다.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.439-445
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• 2001

The destructive method is reliable and widely used lot the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials used at high temperature by nondestructive evaluation such as electric resistance method, replica method, Barkhausen noise method, electro-chemical method and ultrasonic method are strongly desired. Ultrasonic nondestructive evaluation technique has been reported good to attain efficiency of measurement, high sensitivity of measurement, and rapidity and reliability of result interpretation. In this study, it was verified experimentally the feasibility of the evaluation of degraded 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $630^{\circ}C$ by high frequency longitudinal wave method investigating the change of attenuation coefficient by FFT analysis and wavelet transform. Because of carbide precipitation increase and spheroidization near grain boundary of microstructure to aging degradation, attenuation coefficient had a tendency to increase as degradation proceeded. It was identified possibly to evaluate degradation using the characteristics of high-frequency ultrasonics. Frequency dependence of ultrasonic attenuation coefficient to aging degradation appeared large, which made sure that attenuation coefficient is an important parameter for evaluation of aging degradation.