• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.1-9
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• 2014

Coastal water including estuaries has distinctive environmental characteristics where sediments are transported and deposited by flowing river water, providing an environment in which fluid mud layers can be formed. Acoustic method is mostly used to detect or monitor the fluid mud layer. However, since sound propagating in this layer suffers severe attenuation, it is important to estimate the accurate attenuation coefficient for various concentrations of fluid mud layer for the successful use of the acoustic method. In this paper, measurement results of attenuation coefficient for 3.5, 5, and 7.5 MHz ultrasounds were presented. The measurements were made in a small-size water tank in which suspended sediment samples with various sediment concentrations were formed using kaolinite powder. The results were compared to the model predictions obtained by attenuation coefficient model in which the mean grain size (called as Mass-median-diameter, D50) was used as input parameter. There were reasonable agreements between measured attenuation coefficients and model outputs predicted using the particle range of D50 ${\pm}20%$. The comparison results imply that although the suspended sediments consist of various-sized particles, sound attenuation might be greatly influenced by amount of particle with a size which has a larger attenuation than that of any particle in the suspended sediments for the frequency used.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.373-380
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• 2000

It is useful to use NDE methods to assess the mechanical properties of materials since destructive methods are time-consuming and usually require cutting of sample from the material/component. In the present research, ultrasonic characteristics have been utilized to evaluate changes of mechanical properties due to heat treatment temperature and condition. The attenuation coefficient of ultrasonic wave increased as the heat treatment temperature because the grain size increased in size as the temperature. The attenuation coefficient decreased as the heat treatment has been progressed (quenched, tempered, PWHT). In the case of ultrasonic velocity measurement, velocity difference between quenched and tempered/PWHT was 40 m/s. There was a good relationship between the attenuation coefficient and the toughness. The relationship can be used for the nondestructive evaluation of the forged reactor vessels. Moreover, the method may be effectively used in the field application.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.85-86
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• 2009

A nondestructive test method based on the self-compensating frequency response function is proposed in this paper to quantitatively measure the attenuation in concrete materials. Since the proposed technique measures inherent attenuation of material itself, more stable experimental results can be expected. In advance, comparison of the experimental results to those obtained by other methods shows the repeatability and accuracy of the proposed technique.

• The Journal of the Acoustical Society of Korea
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• v.30 no.3
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• pp.158-166
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• 2011

In the present study, copper and nickel foams with an open-celled structure as trabecular-bone-mimicking phantoms were used to investigate the dependencies of group velocity and attenuation coefficient on structural properties such as trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) in trabecular bone. The group velocity and attenuation coefficient of the copper and nickel foams 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. The separation of the Biot's fast and slow waves was consistently observed in the ultrasonic signals transmitted through the copper and nickel foams. The group velocities of the copper and nickel foams showed highly positive correlations with Tb.Th and Tb.Sp. The attenuation coefficient of the copper foam showed a highly negative correlation with Tb.Th and Tb.Sp, whereas that of the nickle foam showed a highly positive correlation with Tb.Th and Tb.Sp. These results advance our understanding of those previously reported by other researchers using trabecular bone samples or phantoms.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.2
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• pp.103-111
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• 2015

The present study investigated the influence of thick cortical endplates on the ultrasonic properties of trabecular bone in a femur with a high fracture risk. Twelve trabecular bone samples were prepared from bovine femurs, and acrylic plates with thicknesses of 1.25, 1.80, and 2.75 mm were manufactured to simulate the cortical endplates using acrylic with a density and a sound speed similar to cortical bone. Although the thickness of the acrylic plates attached to the two sides of the trabecular bone increased, high correlations were observed between the speed of sound and the apparent bone density of the trabecular bone, with Pearson's correlation coefficients of 0.80-0.86. High correlations were also observed between the attenuation coefficient at 0.5 MHz and the apparent bone density of the trabecular bone, with Pearson's correlation coefficients of 0.84-0.91. These results suggest that the speed of sound and attenuation coefficient at a specific frequency measured in a femur with relatively thick cortical endplates compared to the calcaneus could be used as indices for predicting the bone mineral density of the femur.

• The Journal of the Acoustical Society of Korea
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• v.28 no.7
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• pp.661-667
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• 2009

Trabecular-bone-mimicking phantoms consisting of parallel-nylon-wire arrays were used to investigate correlations of phase velocity and attenuation coefficient with structural properties in trabecular bone. Trabecular separation (Tb.Sp) of the 7 trabecular-bone-mimicking phantoms ranged from 300 to $900\;{\mu}m$ and volume fraction (VF) from 1.6% to 8.7%. Phase velocity and attenuation coefficient of the phantoms were measured by using a through-transmission method in water, with a matched pair of broadband unfocused transducers with a diameter of 12.7 mm and a center frequency of 1 MHz. Phase velocity and attenuation coefficient at 1 MHz decreased almost linearly with increasing Tb. Sp and increased almost linearly with increasing VF. The simple and multiple linear regression models with phase velocity and attenuation coefficient as independent vanables and Tb.Sp and VF as dependent variables demonstrated that the coefficients of determination for the prediction of VF were higher than those for the prediction of Tb.Sp. The results obtained in the trabecular-bone-mimicking phantoms consisting of parallel-nylon-wire arrays were consistent with those in human trabecular bone suggesting that the structural properties can be estimated from the measurements of phase velocity and attenuation coefficient in trabecular bone.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.549-555
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• 2001

Ultrasonic is a powerful nondestructive technique for getting the information of flaws and material properties of in-services facilities. We prepared 4 different 1Cr-1Mo-0.25V specimens by Isothermal aging at $630^{\circ}C$. We evaluated material degradation using ultrasonic parameters, velocity, attenuation and harmonic generation. Attenuation and nonlinear parameter derived from harmonic generation efficiency increased as degradation. Especially the second harmonic of the fundamental wave in the 1,820h aging material was observed to exceed 20dB more than that in the un-aged material. But velocity remained virtually the same for all specimens. We concluded that nonlinear parameter and attenuation are sensitive to material degradation, but velocity was not. It'll be a good parameter for evaluating the material degradation.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.509-517
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• 2012

In the present study, temperature and frequency dependences of ultrasonic properties such as attenuation coefficient and phase velocity was investigated for six kinds of commercial MC-Nylon polymer samples. The ultrasonic properties of the samples were measured by using a pulse transmission method in water over a broadband frequency range of 2 to 8 MHz. Water temperature was varied from 10 to $60^{\circ}C$ with the $10^{\circ}C$ interval. The attenuation coefficients of the samples increased with the frequency and the exponent n of frequency dependence ranged within 1.16 to 1.44, slightly deviating from the linear dependence (n=1). The phase velocities of the samples exhibited negative dispersion, i.e., decreasing velocity with increasing frequency, except for ivory sample at $60^{\circ}C$. The frequency-dependent phase velocities of the samples showed the decreasing tendency with increasing temperature.

• The Journal of the Acoustical Society of Korea
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• v.6 no.3
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• pp.31-42
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• 1987

An ultrasonic pulse-echo diagnostic system for tissue characterization with the estimation of attenuation coefficients is developed and its performance has been examined by system implementation. The system divided into the ultrasonic generator, A/D converter, data communication, computer for signal processing. The methods for estimating the spatial distribution of acoustic attenuation coefficients using the moment analysis are proposed. The experimental results indicate the potential of the methods for tissue characterization.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.340-345
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• 2003

In this paper, the ultrasonic attenuation coefficient was measured by variation of crack length for double-cantilever beam(DCB) specimen. The energy release rate, G, was obtained by the experimental measurement of compliance. The experimental results represents that the relation between crack length for the ultrasonic attenuation coefficient and energy release rate is increased proportionally. From the results of experiments, the measurement method of crack length by the ultrasonic attenuation coefficient was proposed and discussed.