1992 Fiscal Year Final Research Report Summary
Anomalous Negative-Pressure Effect of Ultrasound
| Project/Area Number |
03650045
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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 Faculty of Science Professor, 理学部, 教授 (10029879)
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| Co-Investigator(Kenkyū-buntansha) |
KATO Masahiko Ehime University Faculty of Science Assistant, 理学部, 助手 (70222429)
INOUE Naoki Ehime University Faculty of Science Assistant Professor, 理学部, 助教授 (50110771)
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| Project Period (FY) |
1991 – 1992
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| Keywords | ultrasound / radiation pressure / acoustic radiation pressure / anomalous negative-pressure effect / ultrasonic levitation |
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| Research Abstract |
When an obstacle is placed in an ultrasonic field, it experiences a unidirectional force even if there is no acoustic stream, which is called the acoustic radiation pressure or radiation force. The direction of the radiation force is ordinarily in the same direction as the incident wave (repulsion force). On the other hand, we sometimes observe a force of attraction as well as repulsion in a spherical wave field and a standing wave field: such an attraction force is said to be due to the anomalous negative-pressure effect. Although it has been proved that no negative forces occur in an ideal plane progressive wave field, the causes of the anomalous negative-pressure effect have never been elucidated yet. The purpose of the present research is to give a complete account of the phenomenon concerned.
We first have traced in the present work the typical theories for the acoustic radiation pressure back to their principles and have established a unified theory for it. We next have verified that the cause of the negative-pressure effect of a spherical sound wave is attributed to Bernoulli's theorem itself, and clarified the conditions in which the negative-pressure effect occurs in a standing-wave field. Furthermore, we have shown that the corresponding effects can occur even in the nearfield radiated from a finite dimension of sound source. The results shows that, in general, small and light obstacles in the nearfield of a circular piston radiator experience negative forces due to the sharp gradient of sound pressure caused by the diffraction effects of sound source itself. It has been found that the conditions for the appearance of the anomalous negative-pressure effect depend on the dimension of the sound source, the distance from the source, the density and size of the obstacle.
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