1994 Fiscal Year Final Research Report Summary
Anomalous Scattering of Ultrasonic Pulse
| Project/Area Number |
05650053
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied physics, general
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| Research Institution | Ehime University |
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Principal Investigator |
HASEGAWA Takahi Ehime University Faculty of Science Professor, 理学部, 教授 (10029879)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Naoki Ehime University Faculty of Science Professor, 理学部, 教授 (50110771)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Creeping wave / Scattering / Diffraction / Ultrasonic pulse wave |
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| Research Abstract |
Many of the investigations on ultrasonic scattering intend to obtain information on the geometrical characters or physical properties of the obstacle by analyzing scattering waves from it. In such a case, the 'creeping waves' sometimes exert a harmful influence in the way of a mysterious goast, which behaves as if they reflected after running around the back side of the obstacle. The purpose of the study is to develop a theory which is comparable with numerical and mechanical experiments by formularzing the phenomenon of creeping waves. The development of such theory was unexpectedly difficult : it required much mathematical knowledge such as the Sommerfeld-Watson transformation and the method of steepest descent. Existing theories are restricted to fully ideal cases such as plane waves and sherical waves, while ultrasonic waves are much coherent than light waves because of their long wave-length.
In the present study we first have made a numerical experiment by use of a new method to compare them with the experimental data on the velocity and attenuation constant of the creeping waves around a rigid cylinder and a rigid sphere. We have modified and improved the exisiting theories by eliminating much vagueness from them. The resulting theory has shown a good agreement with the experiment. We next have developed the theory of the creeping waves around a sphere placed freely in the nearfield of a circular piston vibrator of finite dimension. The Following conclusion is reached. Creeping is entirely caused by diffraction of ultrasonic waves. Therefore it can be seen in the case of a radio wave as a global creeping wave around the earth.
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