• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.2
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• pp.211-217
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• 2010

This paper introduces the Hull Mounted Sonar Vertical Scanning(HMS Verscan) technique to overcome the limitation of target detection in short range shadow zone. Numerical experiments were done with the HMS Verscan taking advantage of the vertical beamforming technique for two-dimension hydrospace(range-depth). For numerical experiments, ray model and high-frequency monostatic reverberation model were used. HMS Verscan increased a sound pressure level at the short range shadow zone through reflections at the sea surface and seafloor. Inclusion of the boundary scattering improved target detection due to the sound reflected into the shadow zone.

• 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.

• Journal of KSNVE
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• v.5 no.1
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• pp.123-132
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• 1995

The microphonic phenomenon in TV(television) is a phenomenon that a stained pattern locally appears in the screen or moves like waves. This can be observed when audio signal of TV has specific frequencies under loud volume of sound. In this study, microphonic phenomenon has been investigated, and two practical ways of circumventing this has been proposed. Based on modal analysis of several TV parts(Cathod Ray Tube, shadowmask, etc.), it was proved that the microphonic phenomenon is caused by the resonance of the shadow mask. One of the proposed ways to circumvent this phenonenon is increasing the thickness of the frame, the other is removing the middle welding points between the frame and the shadow mask. The effects of these modifications are evaluated by the finite element analysis, and the results show that the magnitude of vibration of shadow mask reduced by 10 - 20dB, which is large enough to provent microphonic phenomenon even under maximum level of sound volume.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.89-95
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• 2002

A shadow mask inside the Braun tube of a TV is sustained by springs attached to the glass panel, its vibration cause the picture image to discolor, which is called the microphonic phenomenon. It is found that it results from resonance when the natural frequency of the shadow mask coincides with that of built-in speaker sound. This paper describes experimental and analytical investigations by using FEM on the vibration problem of the shadow mask assembly. The simulation scheme may be efficiently used to develop a new design for a large-screen flat TV.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.891-896
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• 2005

On the basis of theoretical studies on the effect of the cylinders attached to semi-infinite screens, the tangential sound power-transport parallel to the surface of the attached cylinder is minimized by means of a secondary sound field, which is generated from a part of the attached cylinder. The numerical study shows the possibility of deflecting the incident sound by minimizing the sound field of the upper sections. The acoustical shadow region was more pronounced in both near- and far-field compared to the passive case with rigid surface, i.e. without active control. For a relatively wide frequency range it was possible to enhance shielding effects only with few secondary sources and error microphones. In this paper effects of control parameters on the actively controlled sound field near the top edge of noise barriers are studied. Results of numerical study and model measurements are shown and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.135-138
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• 2005

On the basis of theoretical studies on the effect of the cylinders attached to semi-infinite screens, the effect of the tangential sound power-transport along the cylindrical top section of noise barriers is studied. Four types of acoustical mechanism between the surface of the cylinder and the adjacent air particles are investigated, namely Z $\rightarrow$ $\infty$, Z $\rightarrow$ pc, Z $\rightarrow$ 0 and actively controlled surface sound field. In active control case the sound power parallel to the surface of the attached cylinder is minimized by means of a secondary sound field, which is generated from a part of the attached cylinder. In each case the change in the acoustical shadow zone was shown and compared. The numerical study shows the possibility of deflecting the incident sound by minimizing the acoustical surface impedance of the upper sections.

• Journal of KSNVE
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• v.6 no.4
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• pp.493-497
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• 1996

TVs or computer monitors with speakers often have a phenomenon called microphonic which shows fringe-like dark pattern on their screens. The major source of this phenomenon is vibration of the shadow mask inside of the Cathode RAY Tube(CRT) which is caused by the sound generated from the speakers. Reducing phenomenon microphonic by modifying the structure of the shadow mask frame in CRT has been examined in this study. A 15" for computer monitor were chosen. Using finite element analysis for vibration and impact, shape of the shadow mask frame was found to reduce microphonic phenomeon. Improved 15" monitors showed good results.d results.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.3
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• pp.144-152
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• 1995

TV microphonic phenomenon (black patterns overlapped on the image when TV sound is set too high) was studied experimentally. It was found that this phenomenon was due to the vibration generated at speakers, and transmitted to the CRT through the TV cabinet structure. Based on this fact, a simulative study was carried out on the assumption that the vibratory motion of the shadow mask located in the CRT could cause the landing error of electronic beam. The result of the simulation corresponded qualitatively with experi- mentally observed facts.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.482-485
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• 2004

On the basis of theoretical studies on the effect of the cylinders attached to semi-infinite screens, the tangential sound power-transport parallel to the surface of the attached cylinder is minimized by means of a secondary sound field, which is generated from a part of the attached cylinder. The numerical study shows the possibility of deflecting the incident sound by minimizing the acoustic surface impedance of the upper sections. The acoustical shadow region was more pronounced in both near- and far-field compared to the passive case with rigid surface, i.e. without active control. For a relatively wide frequency range it was possible to enhance shielding effects only with few secondary sources and error microphones. In this paper effects of some control parameters on the actively controlled sound field near the top edge of noise barriers are studied. Results of numerical study and model measurements are shown and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1053-1056
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• 2007

The acoustical performance of noise reducing devices installed on the top of a noise barrier were tested by small-scale outdoor tests. Noise measurements before and after installation of the devices were carried out using sound intensity methods. It is well known that the sound intensity method can specify the strength and directivity of sound, and it is convenient to consider the feature of sound around a noise barrier. The noise reduction effect of each edge device was evaluated using the difference between the input and output sound power levels calculated from sound intensities. It was investigated that each device had different efficiency in the shadow zone, while there was no significant difference between edge devices in the illuminated zone.