| 摘要 |
PURPOSE:To decrease the value of relative radiation strength of side lobes in the directivity and to make accurate transmission/reception operation, by slightly inclining the circumference of a sound wave radiation plane to the center toward the radiation of an acoustic wave. CONSTITUTION:A circumference of a sound wave radiation plane 7 consisting of a fixed electrode 1, oscillation film 4 and moving electrode 5 have a slope of about 12 degrees from the center to the radiation direction of sound waves. Taking the radius of an acoustic wave radiation plane 7 as 1 and the radius of the center part as 0.65, by applying an AC voltage between the fixed electrode 1 and the moving electrode 5, the sound wave radiated from the circumference leads in phase gradually to those radiated from the center part. Through the operation of the plane 7, the relative radiation strength of side lobes other than main lobe in the directivity is reduced remarkably. |
