• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.1
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• pp.63-72
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• 2002

The main objective of this study is to propose a practical two-microphone impedance tube method to measure the sound transmission loss for flexible sound isolation sheets without the use of the time-consuming and expensive reverberation room. This method was based on the sound decomposition theory developed by Seybert using the spectral density functions of the incident and reflected sound waves. In order to verify the validity of the experimental results, the measured sound transmission losses from the proposed method were compared with the measured data from the reverberation room method and the calculated data from the theory satisfying the mass law of sound isolation material. The resulted trends of the sound transmission losses versus frequencies for several different sound isolation sheets were almost same for each other and agreed quite well in both methods except at some low frequency region. From the experimental results, it was found that the accuracy of sound isolation capability obtained by two-microphone impedance tube method depends upon the microphone spacing, the distance from the first microphone to the test sample surface and the test sample location.

• International Journal of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.58-63
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• 2017

The sound we hear is transmitted through the atmosphere. However, both the sound we want to hear and the surrounding sound are mixed, and noise is generated, and the sound is not clearly transmitted due to factors such as distance. In particular, in closed spaces like buildings, it is often difficult to hear sounds from outside because of the sound of reflection. People with hearing impairments, such as the elderly and the deaf, have a hard time hearing the sounds they want to hear. Thus, we are developing a hearing aid that can detect radio waves. To this end, we propose the development of a hearing aid that uses FM radio and Bluetooth. These devices are expected to be useful not only for the elderly and the deaf but also in situations where information is transmitted to a large number of people, such as students and tourists, in a large space. The main purpose of this device is to enable users to hear sound correctly without blind spots.

• Journal of Korea Multimedia Society
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• v.23 no.11
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• pp.1406-1417
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• 2020

Sounds that have been evaluated to be effective in inducing sleep are helpful to reduce sleep disorders. Generally, several sounds have been verified the effects by brainwave experiments, but it cannot be considered on all users because of individual variation for effects. Moreover, the effectiveness for inducing sleep is not known for all new sounds made by creative activities. Therefore, new classification system is required to collect new effective sounds with considering personal brainwave characteristics. In this paper, we propose a new sound classification method by applying improved MinHash cluster to brain waves. The proposed method will classify them through whether it is effective for sleep care by evaluation his brainwave during listening for each sound. In order to prove effectiveness of the proposed classification method, we conducted accuracy experiment for sleep sound classification using verified sleep induction sound. In addition, we have compared time for existing method and proposed method. The former is scored 85% accuracy in the experiment. We confirmed the latter one that the average processing time was reduced to 70%. It is expected to be one of method for pre-screening whether it is effective when a new sound is introduced as a sound for sleep induction.

• The Journal of the Korea Contents Association
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• v.18 no.8
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• pp.82-91
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• 2018

This paper examines the sound of Godard's <$Pr{\acute{e}}nom$ Carmen> from Deleuze's film aesthetics and Merleau-Ponty's phenomenological point of view. The rehearsal scene of a string quartet is a mirror-image that illuminates the music itself, and becomes a crystal-image with the indiscernibility of the present and the past in the break with the main narrative. On the other hand, urban noise and waves are the seeds composed of pure optical (sound) images and grow into pure sound crystals that collide with what is seen through the juxtaposition, substitution, and intentional connection of sound. However, these sound contradictions also lead to the integrated sound category as a 'sole movement' through Merleau-Ponty's dialectical thought, and even the dialectical sound management of pop and classical music is no longer a confrontation of the genre, but is integrated into the materialistic category of sound. This study is differentiated from the existing research by solving the sound aesthetics of the Godard's film through philosophical thought.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.115-119
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• 2009

We numerically investigated propagation of various waves in the two-phase flows such as sound wave, shock wave, rarefaction wave, and contact discontinuity in terms of pressure, void fraction, velocity and density of the two phases. The waves have been generated by a hydrodynamic shock tube, a pair of symmetric impulsive expansion, impulsive pressure and impulsive void waves. The six compressible two-fluid two-phase conservation laws with interfacial friction terms have been solved in two fractional steps. The first PDE Operator is solved by the HLL scheme and the second Source Operator by the semi-implicit stiff ODE solver. In the HLL scheme, the fastest wave speeds were estimated by the analytic eigenvalues of an approximate Jacobian matrix. We have discussed how the interfacial friction terms affect the wave structures in the numerical solution.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.193-196
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• 2002

The relativistic theory has not been properly taken up by the marine hydrodynamicists. To take on a relativistic view, we confine ourselves to a simple vector case of a wave train in spacetime, to be shown to represent a sound wave or a surface wave, and bring in an observer who is travelling on another platform. We are interested in relative position of each event on these two worldlines. It, then, will be shown that the velocity, the acceleration, the encounter frequency, the group velocity, and the time and the space distance between the wave and the observer on the worldlines should all be derivable in principle. This is interpreted to mean that we really have the relativistic events taking place with different values of time dilation in the sense of 'spacetime', and that the well-known ${\lceil}special Theory of Relativity{\rfloor}$ applies just as well in hydrodynamic waves.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.3
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• pp.190-197
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• 2006

For enhancement of flaw detactability using array transducers, focusing of ultrasonic waves on a target in an inhomogeneous medium or through a complex geometry is important. But focusing can be strongly degraded by geometrical distortion of field radiated by the array transducers or by sound speed fluctuations in the propagating medium. In recent years, the time reversal technique has been proposed. Thus, in this paper, we describe the basic principal of the time reversal technique for focusing. Then, the implementation results of the time reversal technique for ultrasonic inspections using bulk waves and guided waves generated by array transducers are presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.470-475
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• 2012

The downstream piping system of the water supply system in a supercritical power plant is affected by the fluctuation pressure waves induced by accessing to the acoustic modes of the piping systems with the rotation and impeller passing pulsations of the feed water pump. There are the phenomena amplified at the same time in the range of 415 ~ 455Hz, 830 ~ 910Hz, 1245 ~ 1365Hz and 1660 ~ 1820Hz on the spectrums of the vibration, the sound pressure, and the pressure fluctuation waves.

• Electronics and Telecommunications Trends
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• v.32 no.6
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• pp.1-7
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• 2017

A metamaterial is a material engineered to have a property that does not exist in nature. A designable material property can be achieved by tailoring its structure, and thus a metamaterial is a novel ICT material and component technology that can break through the limitations of conventional technologies. Among the metamaterials available, a perfect metamaterial absorber is a technology that can nearly absorb light, sound waves, thermal waves, and electromagnetic waves with a simple structure, and has been of significant interest in energy, display, sensor, stealth, and military applications, with wavelengths from visible light to microwaves. In this article, we introduce a brief description of metamaterial absorber technology, the critical issues for its application, as well as ETRI's developed metamaterial absorber technology and its prospects for future use.

• Journal of the Korean Society of Safety
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• v.5 no.3
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• pp.8-26
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• 1990

It is important to have exact information about the contact pressure distribution in the design of connected parts of machines and structures. In previous works, stress analyses on a two body contact problem have been carried out in large numbers. Besides, the measurement of contact stress is important to confirm the adequateness of the theoretical analysis, to verify appropriateness of Hertzian contact theory and to know the practical pressure distribution, but an excellent measuring method con't be found at present. Therefore, a quantitative measurement of contact pressure by means of ultrasonic waves using a normal probe and an angle has been proposed to measure the contact pressure distribution between two rough flat surfaces. At first, in a new proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained by using calibration blocks with various surface roughnesses made of the same material as the rectangular section beams And then, this experimental results are compared with the analytical ones, and the utility of this method is discussed.