• Journal of KSNVE
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• v.4 no.3
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• pp.295-305
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• 1994

The reflection coefficient of a material at oblique incidence is measured in a free field. The sound pressure distributions are measured at discrete points on two measurement lines and then decomposed into plane wave components by using spatial Fourier transform. The inciedent and reflected plane wave components are obtained from a set of "decomposition equations" of which uses the plane wave propagation theory. Numerical simulations and experiments have been performed to see the effect of finite size of measurement area. To reduce this effect, a window fuction has been performed to see the effects of finite size of mesurement area. To reduce this effect, a window function has been proposed and its effect on the measurement of sound absorbing material property has been studied as well. The reflection coefficient obtained by this method is compared with those obtained from other methods; 2-microphone method in a duct and an expirical equation of which determines the characteristic impedance .rho.c and propagation constant k of a material from flow resistance information.formation.

• Proceedings of the IEEK Conference
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• 2000.06e
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• pp.99-102
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• 2000

This study analyze of reflection wave to Acoustic stimulation on acupoints and contrast parts for objectification of the meridian substance. In order to verify meridian pathway and channel theory of bio-energy in body. It was analyzed response characteristic of reflection waves after acoustic stimulation by sound wave of 5 specific tones. The response characteristics of reflection are measured by the average current magnitude of meridian. The current variation ratio are Live Meridian(gung) 33.2%, Heart Meridian(sang) 30.7%, Kidney Meridian (gak) 33.1%, Spleen Meridian(chi) 33.9%, Lung Meridian (wo) 30.7% compare with contrast parts (non-acupoint and meridian). Therefore meridian is distinguished to non-meridian and 5 vital meridians have relationship with sound wave of 5 specific tones.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.67-74
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• 1989

The reflection coefficients of the sound absorbing materials are obtained from the standing wave ratio in the standin wave tube. This method is rather laborious to find the sound pressure maximum and minimum. We devised new method for determination of the complex reflection coefficients of the materials. The sound pressures and the phases are measured at least three points along the axis of the tube. The complex reflection coefficients are determined from the measured values by least square method. The measured results for the glasswool with thickness of 5cm and density of $50kg/m^3$ and the steel plate with thickness of 1.5cm are in good agreement with those of the conventional method. It is possible to measure the complex reflection coefficients at low frequencies with short standing wave tube and to interface with the personal computer which is very useful for the handling of amount of samples.

• The Journal of the Acoustical Society of Korea
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• v.26 no.1
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• pp.32-41
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• 2007

The control room has been usually designed by the consideration of only one listening position for the sound engineer. By this study. many listening positions with the very similar acoustical condition were located in the specific region, so-called 'the reflection free zone', where the several engineer could evaluate the quality of sound at the same time. For constructing the reflection free zone, the control room has been designed by the concept of the $LEDE^{TM}$, and the initial time delay gap has been controled by the structure of control room and the properties of sound-absorbing materials. diffuser, Helmholtz resonator and image source of sound. The occurrence of any harmful phenomena like the standing wave, acoustic focusing. coloring. Hass effect and flutter echo, has greatly reduced in the reflection free zone.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.297-303
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• 2021

When sound waves propagate over long distances in shallow water, measured transmission loss is greater than predicted one using underwater acoustic model with the Rayleigh reflection model due to inhomogeneity of the bottom. Accordingly, the US Navy predicts sound wave propagation by applying the empirical formula-based High Frequency Bottom Loss (HFBL) model. In this study, the measurement and analysis of transmission loss was conducted using mid-frequency (2.3 kHz, 3 kHz) in the shallow water of the East Sea in summer. BELLHOP eigenray tracing output shows that only sound waves with lower grazing angle than the critical angle propagate long distances for several kilometers or more, and the difference between the predicted transmission loss based on the Rayleigh reflection model and the measured transmission loss tend to increase along the propagation range. By comparing the Rayleigh reflection model and the HFBL model at the high grazing angle region, the bottom province, the input value of the HFBL model, is estimated and BELLHOP transmission loss with HFBL model is compared to measured transmission loss. As a result, it agrees well with the measurements of transmission loss.

• The Journal of the Acoustical Society of Korea
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• v.25 no.5
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• pp.246-256
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• 2006

The plane wave reflection coefficient is an acoustic property containing all the information concerning the ocean bottom and can be used as an input parameter to various acoustic propagation models. In this paper, we measure the plane wave reflection coefficient, the sound speed, thd the attenuation for saturated granular medium in the water tank. Three kinds of glass beads and natural sand are used as the granular medium. The reflection experiment is performed with the sinusoidal tone bursts of 100 kHz at incident angles from 28 to 53 degrees, and the sound speed and attenuation experiment are performed also with the same signal. From the measured reflection signal, the reflection coefficient is calculated with the self calibration method and the experimental uncertainties are discussed. The sound speed and the attenuation measurements are used for the estimation of the porosity and permeability, the main Biot parameters. The estimated values are compared to the directly measured values and used as input values to the Biot theory in order to calculate the theoretical reflection coefficient. Finally, the reflection coefficient predicted by Biot theory is compared to the measured reflection coefficient and their characteristics are discussed.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2E
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• pp.69-77
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• 2003

Correlations between acoustic properties and bone density have been investigated in bovine cancellous bone. Speed of sound (SOS), broadband ultrasonic attenuation (BUA), and broadband ultrasonic reflection (BUR) were measured in 10 defatted bovine cancellous bone specimens in vitro. SOS showed a significant correlation with the apparent density of the bone. A comparable correlation was observed between BUA and the apparent density. BUR was rather highly correlated with the apparent density. It was shown that BUR had a weak correlation with BUA and a significant correlation with SOS. This indicates that the parameter BUR can provide important information that may not be contained in BUA and SOS and, therefore, can be useful as an alternative diagnostic parameter of osteoporosis. As expected, a linear combination of all three ultrasonic parameters in a multiple regression model resulted in a significant improvement in predicting the apparent bone density.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.37-47
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• 1996

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is related to determination of testing sensitivity, scanning pitch and defect location. This paper investigated the directivity of ultrasonic wave, which scattered from slit defect located in heat-affected zone (HAZ) in butt joint using visualization method. The directivity of shear waves scattered from slit defect were different according to probe direction (far defect, near defect) and probe position (forward movement, maximum echo position, backward movement). The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. In the case of 2 MHz angle probe, the directivity of reflection wave was appeared sharp form because of the relation wave length and defect size.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.183-188
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• 2003

This study is to make the fundamentals of sound quality evaluation in regard of acoustical characteristics of passenger compartment. The deviation of frequency response function level within audible frequency is evaluated at receiving point in the research of room acoustics. In this study, frequency response function is the one between speaker and driver's ear positions. The positions of driver and audio speakers are optimized by analysis of acoustic mode of acoustic cavity. The main reflection planes are determined by analysis sound ray path diffused at optimized speaker positions. Finally, designer selects acoustical material by analysis of absorption effect of acoustical materials on the main reflection planes in order to avoid to distortion and fluctuation of frequency response function..

• The Journal of the Acoustical Society of Korea
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• v.26 no.2
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• pp.55-60
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• 2007

The shadow, reflection, interference, and diffraction are proper phenomena concerning sound that is a kind of wave. By the late nineteenth century, similar optical phenomena had been detected already but these phenomena concerning sound had not been convincingly detected. It was Rayleigh who succeeded in detecting those phenomena without any reasonable doubt by the virtue of his original instruments and smart experimental settings. Rayleigh could detect the sound shadow by using the corner of a building and erase the shadow by some reflectors. And he constructed some apparatus similar to Young's interference apparatus famous in optics to detect the sonic interference. Furthermore, he first succeeded in illustrating the acoustical effectiveness of Poisson's disk by which optical diffraction had already been well known, and tested the effect of diffraction by spherical obstacles to ascertain that the result coincided with his theory.