• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.8 no.2
• /
• pp.77-84
• /
• 1994

This paper is measured partial discharge of low density polyethylene by using acoustic emission measuring method when the electrical tree grow its length in LDPE. Acoustic emission's pulses and its amplitudes of partial discharge are measured by acoustic emission measuring devices. Theorem of skewness are used for breakdown prediction of LDPE. So, it is found that the breakdown of LDPE could be predicted by its skewness's value. There are two kind of specimen of no void and specimen of artificial void, this one's electrical tree grows very faster than that one's.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.4
• /
• pp.244-252
• /
• 2012

The purpose of the present study is to investigate the correlations between acoustic properties, such as speed of sound and normalized broadband ultrasound attenuation, and bone mineral density in femur with high fracture risk. The speed of sound and the normalized broadband ultrasound attenuation in 15 bovine femoral trabecular bone samples in vitro were measured by using a through-transmission method with two matched pairs of ultrasonic transducers with center frequencies of 0.5 and 1.0 MHz. The volumetric bone mineral density of the trabecular bone samples was measured by using micro-computed tomography. The bone mineral density exhibited strong correlations with both the speed of sound and the normalized broadband ultrasound attenuation measured by using the 0.5 and the 1.0 MHz transducers. The highest correlation was found between the bone mineral density and the normalized broadband ultrasound attenuation measured by using the 0.5 MHz ultrasonic transducers. The results suggest that the acoustic properties measured in the femur in vitro can be used as indices for the prediction of femoral bone mineral density.

• Journal of the Korean Physical Society
• /
• v.73 no.12
• /
• pp.1849-1854
• /
• 2018

The present study aims to investigate the feasibility of using a simple nonlinear acoustic method for the assessment of bone status and osteoporosis in trabecular bone. Correlations of linear and nonlinear ultrasound parameters with the apparent bone density were obtained in 32 bovine femoral trabecular bone samples. Highly significant positive correlations were observed between the apparent bone density and the two linear ultrasound parameters, the speed of sound (SOS) and the normalized broadband ultrasound attenuation (nBUA), with Spearman's correlation coefficients of r = 0.85 and 0.77. In contrast, the apparent bone density was found to be negatively correlated with the nonlinear ultrasound parameter introduced in the present study, the logarithmic difference between the power spectrum levels of the fundamental frequency and the second harmonic (PSL1-PSL2), with the highest correlation coefficient of r = -0.92. These results suggest that the PSL1-PSL2, in addition to the SOS and the nBUA, may be useful for the assessment of bone status and osteoporosis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.885-891
• /
• 2003

Effects of each acoustic property on absorption characteristics of polyester fiber materials has been studied in this paper. It would be impossible for us to measure effects of each acoustic property by experimental method since we cannot make sound-absorbing materials in which only one of the properties is changed. We have adopted a numerical prediction method to carry out parameter studies for each acoustic property. And to get a general behavior of acoustic performance of the materials, the numerical simulation has been repeated to several cases of different bulk density. Finally we have obtained frequency-dependent control factors in the absorption performance which gives us design capability of acoustic absorbing materials.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.36 no.6
• /
• pp.749-756
• /
• 2003

Hydroacoustic and open-closing zooplankton net survey were conducted to understand the characteristics of the sound scattering layer (SSL) and to estimate the density of an euphausiid (Euphausia pacifica) in the SSL, in the northwestern part of the East China Sea. The survey was carried out during July 6-9 2002 at 8 sampling stations for zooplankton. The virtual echogram technique was used to identify E. pacifica from all acoustic scatters. Mean volume backscattering strength difference $(MVBS_{120kHz-38kHz})$ and target strength equation for E. pacifica were derived from the Distorted-wave Born Approximation (DWBA) model. Although vertical migration of the SSL is similar to the general pattern, dispersion at night shows some differences. Estimated mean density using acoustic data ranged from $20.4-221.4\;mg/m^3$ over the whole depth, and $87.1-553.5\;mg/m^3$ in the SSL. The density using the zooplankton net ranged from $0.2-362.4\;mg/m^3$ and was not related to net deploying method. The results from the acoustic and net survey suggest that E. pacifica might be an important zooplankton community in the northwestern part of the East China Sea.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.49 no.3
• /
• pp.270-281
• /
• 2013

Hydro-acoustic surveys with scientific echo sounder were carried out to estimate the total density and distribution of the juvenile cod in Jinhae bay, Korea. The surveys were conducted 4 times from May to June using 2 frequency method (38kHz and 120kHz) and beam trawl were used to investigate the species composition. Also the catch amounts of juvenile cod were compared with the cod density estimated by the hydro-acoustic method. It was confirmed that the juvenile cod was stayed in Jinhae bay in early June and There was the relationship between catch of juvenile cod and the estimated density by hydro-acoustic survey. The number of juvenile cod was consequently about 365,000 fish (CV 12.9%) in May and 113,000 fish (CV 9.2%) in May based on the hydro-acoustic data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.767-770
• /
• 2006

To predict vibrational energy density of simple structural-acoustic coupled systems in medium-to-high frequency ranges, Power Flow Finite Element Method(PFFEM) is used, and PFFEM sofiware, PFADS has been developed for the vibration predictions and analysis of coupled system structures in medium-to-high frequency ranges. However, it needs to consider vibro-acoustic coupled analysis to get more accurate results. Prior to implement vibro-acoustic coupled analysis functions in PFADS, research on vibro-acoustic coupled analysis using PFFEH is performed for simple models. These predictions include the indirect transmission path associated, and also the direct transmission path, and the formulation is extended to structural system model by using appropriate modifications to structural-acoustic and acoustic-acoustic joint matrices. Concerning the waves in plate and acoustic, it is possible to calculate the structural-acoustic full matrix of a model using PFFEM, and the formulations developed are implemented for two rooms surrounded by plates.

• Journal of Power System Engineering
• /
• v.3 no.2
• /
• pp.42-50
• /
• 1999

In recent years, composite materials like CFRP are increasingly used in various fields of engineering because of their unique properties which offer a high strength/density and high modulus/density. When CFRP structures are manufactured in drilling processes which are frequently practiced in an Industry, they bring on the delaminations sometimes. So, acoustic emission(AE) techniques were used for a condition monitoring of the drilling process in CFRP. In this study, the AE from CFRP estimated the delamination which reduces the strength and load carrying capacity under the drilling process and the initial delamination were well caught and measured by a video camera. From the results, it was found the relationships between failure mechanism of CFRP delamination and AE characteristics as like amplitude and count.

• Journal of the Society of Naval Architects of Korea
• /
• v.49 no.5
• /
• pp.384-390
• /
• 2012

Power Flow Analysis (PFA) is introduced for solving the noise and vibration analysis of structures in medium-to-high frequency ranges. The vibration analysis software, $PFADS_{C{+}{+}}$ R4 based on Power Flow Finite Element Method (PFFEM) and the noise prediction software, $NASPFA_{C{+}{+}}$ R1 based on Power Flow Boundary Element Method (PFBEM) are developed. In this paper, the coupling equation which represents relation between structural energy and acoustic energy is developed for vibro-acoustic coupling analysis. And vibro-acoustic coupling analysis software based on PFA and coupling equation is developed. Developed software is composed of translator, cavity-finder, solver and post-processor over all. Translator can translate FE model into PFADS FE model and cavity-finder can automatically make NASPFA BE model from PFADS FE model for noise analysis. The solver module calculates the structural energy density, intensity of structures, the fictitious source on the boundary and the acoustic energy density at the field in acoustic cavities. Some applications of vibro-acoustic coupling analysis software to various structures and cruise ship are shown with reliable results.

• IEIE Transactions on Smart Processing and Computing
• /
• v.3 no.3
• /
• pp.153-159
• /
• 2014

As the number of treatments in the therapeutic ultrasound field targeted at fat tissue increase, the performance of the equipment should be evaluated for safety using a fat phantom. In this study, a fat phantom was fabricated using olive oil and a tissue-mimicking material (TMM) phantom. To evaluate the acoustic properties of the TMM phantom according to the changes in the olive oil, the composition ratio of a liquid mixture of olive oil with a surfactant was adjusted from 5-20% in 5% steps. The acoustic properties of the phantom were evaluated using the sound velocity, attenuation coefficient, density, and acoustic impedance. The experimental results showed that the sound velocity decreased with increasing amount of olive oil but the other acoustic properties did not change. In addition, the phantom using an olive-oil mixture with a 15% composition ratio was most similar to the acoustic characteristics of fat tissue with a sound velocity of 1477.35 m/s, an attenuation coefficient of 0.514 dB/MHz-cm, a density of $1.07g/cm^3$, and an acoustic impedance of 1.575 MRayl. These experimental results are expected contribute to the accuracy of the results using a TMM phantom and will be useful for the therapeutic ultrasound field targeted at subcutaneous fat tissue.