• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.41-41
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• 2003

Purpose: Even if the wedge filter is widely used for the radiation therapy to modify the photon beam intensity, the wedged photon beam dose calculation is not so easy. Radiation therapy planning systems (RTPS) have been used the empirical or semi-analytical methods such as attenuation method using wedge filter parameters or wedge filter factor obtained from measurement. However, these methods can cause serious error in penumbra region as well as in edge region. In this study, we propose the dose calculation algorithm for wedged field to minimize the error especially in the outer beam region. Materials and Method: Modified intensity by wedge filter was calculated using tissue-maximum ratio (TMR) and scatter-maximum ratio (SMR) of wedged field. Profiles of wedged and non-wedged direction was also used. The result of new dose calculation was compared with measurement and the result from attenuation method. Results: Proposed algorithm showed the good agreement with measurement in the high dose-gradient region as well as in the inner beam region. The error was decreased comparing to attenuation method. Conclusion: Although necessary beam data for the RTPS commissioning was increased, new algorithm would guarantee the improved dose calculation accuracy for wedged field. In future, this algorithm could be adopted in RTPS.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.41-46
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• 2002

The general purpose of this paper is Evaluation of material properties in spring steels by investigate correlation between ultrasonic attenuation and virker's hardness, charpy impact properties, microstructures. The three test speciments of the $490{\times}90 mm$ plates and 20 mm thick are used but differ in heat treatment, one is rolled plate, the second is quenched and then tempered, and the third is quenched. ultrasonic attenuation were obtained at fifteen locations on the plates. In order to investigate the correlation between hardness ( especially, HV ) and the attenuation, the virker's hardness and the microstructures were observed for three spring steels. also the charpy impact test were carried out at the room temperature in order to investigate the relationship between impact properties and the attenuation. The experimental results obtained from three different spring related to the heat treatment conditions and attenuation coefficient is increased with increasing the hardness(HV). Ultrasonic attenuation coefficients have shawn are ability to distinguish among spring steels.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.216-222
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• 2015

A previous velocity measurement system for marine sediment had several problems such as the errors occurred when picking first arrival time and the inconvenient measurement procedure. In order to resolve these problems, we developed a new acoustic properties measurement system by using PXI (PCI eXtentions for Instrumentation) module based on LabVIEW. To verify the new system, we measured the velocity and attenuation of sediment using the new system in a parallel with the previous system under the same experimental environment. The result of measurement showed 1~2% margin of error for the velocity as well as similar attenuation values. We concluded that the new system can efficiently measure the acoustic properties of marine sediment. It also has an advantage to construct the database of acoustic data and raw signal.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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• pp.18-24
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• 1989

Computer-aided high frequency ultrasonic is applied to aluminum oxide(85w%, 94w%, 96w%, and 99w%) MOR(modulus of rupture) samples to evaluate mechanical properties such as density variation, pore content, elastic modulus, shear modulus, and poisson's ratio. Ultrasonic wave velocity and attenuation measurement techniques were used as an evaluator of such properties. Pulse-echo C-Scan images with different fate setting method using 50MHz center frequency 1 inch focal length transducer allows evaluation of density variation and pore content. Elastic modulus calculated with the relation of density and ultrasonic velocity. It shows good reliability as compared with resonance method. Sintered density variation of $0.025g/cm^{3}$, that is 0.6% of theoretical density in $Al_{2}O_{3}$ samples can be observed by ultrasonic velocity measurement. Attenuation measurement method qualitatively agree with 4-point fracture testing result concerning of porosity content.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1013-1019
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• 2011

Sound attenuation of periodically arranged cylindrical rods is studied numerically and experimentally. Cross section of the cylinder is circular and arrays are in a square lattice. Cylinders are made of steel, and consist of five groups with different diameters from 27.2 mm to 48 mm. Each group has 5 rows, while number of cylinders in a row varies from 17 to 31. The area filling fraction is about 60~61 %, which leads to the stop bandgap(2.9 kHz ~ 8.4 kHz). Sound attenuation is computed using two-dimensional BEM, and measurement is done by using a speaker and microphones in a semi-anechoic room. Comparison of the results by BEM and experiment shows that attenuation spectra are qualitatively in agreement, although experiment gives higher attenuations than BEM. After results by BEM are scaled up in accordance with cylinder diameter, it is observed that attenuation curves are in good agreement, which confirms that analysis by BEM is done correctly. It is also found that the measured bandgaps are shifted toward lower frequency by 0.5 kHz ~ 1.2 kHz, when compared to the predictions obtained from infinitely repeated two-dimensional cylinder arrays.

• Journal of Biomedical Engineering Research
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• v.8 no.1
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• pp.41-48
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• 1987

In estimating the freguency-dependent attenuation coefficient, we analyzed the range-dependent ultrasonic beam and proposed the method of calculating the experimental equation of beam pattern in order to reduce the error on the influence of beam pattern. These experimental equations are divided into the spectral centroid and the spec ural standard deviation slope according to axial propagation length. These are repnesented by the first-order equation in the near field of the beam and the second- order eqLlatlon In the far field. In order to prove the validity of this method, the attenuation coefficients of the non-corrected ease and the corrected case are compared. Using the reflected signal from acryle plate, the attenuation coefficients were estimated by the spectral shift method ann the spectral difference method. The result shows attenuation coeffi talents after correction are better than attenuation coefficients before correction. And this method can be applied In vivo measurement.

• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1243-1246
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• 1987

To characterize the biological tissues, the new methods to measure the frequency dependent attenuation are presented in this paper. In general, ultrasonic phase information was assumed by linear function of the frequency. But, the minimum phase function which characterizes the frequency dispersion of tissue was derived in [l]. It is very significant to measure the attenuation by using the minimum phase function to characterize the frequency dispersion of tissue. Therefore, a more efficient method measuring the frequency dependent attenuation are proposed by using the estimated sound velocity and polarity of reflected signal. To verify the algorithms, pulse reflection experiments are performed.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.157-165
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• 1999

Grain size of steels is one of the most important parameters which influence yield strength and fracture toughness. Ultrasonic wave propagating in polycrystalline materials is mostly attenuated by scattering at grain boundary. Effect of ultrasonic attenuation on average ferrite grain size of carbon steels with tensile strength $40{\sim}60kgf/mm^2$ consisting of multi phases such as ferrite + pearlite and ferrite + pearlite + bainite was evaluated. The attenuation of these steels rapidly increased with average ferrite grain diameter. Average ferrite grain diameter ($D_{av}$, ${\mu}m$) could be expressed as $1.79+22.97*a^{1/2.03}$, where a is attenuation with unit of nepers/cm. From this study, it was confirmed that nondestructive ultrasonic method could be used in measuring average ferrite grain size indirectly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1696-1703
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• 2010

Increased demand for military satellite communications system and due to the depletion of resources of existing satellite communications frequencies, Ka-band and EHF-band satellite communication systems is growing demand for development. As a result, the study of rain attenuation mitigation for Ka/EHF-band frequencies has been achieved. The method to compensate rain attenuation on Ka-band(20/30) using the signal power measurement function in Digital Transponder of Next Military Satellite has been proposed in this paper. This method is more effective than generally used method by Beacon and UPC(uplink power control) in giving the precise rain attenuation measurement and correction.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.18-26
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• 2000

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operating conditions such as high temperature and high pressure for an extended period time. Conventional measurement techniques(replica method, electric resistance method, and hardness test method) for measuring creep damage have such disadvantages as complex preparation and measurement procedures, too many control parameters. And also these techniques have low practicality and applied only to component surfaces with good accessibility. In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens(Cr-Mo alloy steels) were carried out for the purpose of evaluation for creep damage. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long term creep degradation tests using life prediction formula were carried out. As a result of ultrasonic tests for crept specimens. we conformed that both the sound velocity decreased and attenuation coefficient linearly increased in proportion to the Increase of creep life fraction($\Phi$c).