1988 Fiscal Year Final Research Report Summary
Abnormal scattering of ultrasound
| Project/Area Number |
62550041
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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 |
応用物理学一般(含航海学)
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| Research Institution | Ehime University |
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Principal Investigator |
HASEGAWA Takahi Ehime University, 理学部, 教授 (10029879)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUZAWA Kiichiro Ehime University, 理学部, 教授 (40036182)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Ultrasound / Scattering / Radiation pressure / 共振 |
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| Research Abstract |
The purpose of the present study is to investigate what we call the abnormal scattering of sound waves by scatterers of solid material which occurs over the frequency range from 1 to 20 MHz in the vicinity of the resonance frequencies of free vibration. An object placed freely in an ultrasonic field experiences a time-averaged force in the direction of wave propagation in most cases. We call such a force per unit cross section the acoustic radiation pressure which is caused by the spatial difference in energy density of sound and is closely related to the scattering itself. We have developed, in the present study, a new theory for the acoustic radiation pressure on a solid elastic sphere placed freely in the nearfield of a circular piston vibrator, while the conventional theories for the acoustic radiation pressure have considered only ideal field such as the spherical wave field of sound. The basic conclusions which were drawn from the present study are presented here. 1.The patterns of the abnormal scattering do not depend on the shape of scatterers whether it is spherical or cylindrical. 2.The effect of the mass density of scatterers on the scattering pattern is negligibly small. 3.The effects of the velocity of compressional and shear waves were most intensive. We can classify materials into four groups according to the scattering pattern; (1) materials such as bismuth and lead, for which the resonance phenomena are manifested mainly as a sequence of pronounced maxima; (2) materials such as cadmium and tin for which the resonance phenomena are manifested as both maxima and minima; (3) materials such as aluminum and nickel,for which the resonance phenomena are manifested mainly as a sequence of minima; (4) materials such as beryllium, for which the effects of resonance are minimized.
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