Near-field acoustic levitation of planar specimens using flexural vibration

In conventional acoustic levitation, the specimens to be levitated are limited to very Light ones of a few milligrams to a few tens of milligrams. The authors have learned that specimens with a weight of several kilograms can be levitated stably by direct sound radiation pressure. The specimen material is not important. The requirement is only that the surface of the specimen exposed to the sound wave must be flat. The fundamental characteristics of near-field levitation were experimentally studied with the use of a flexural vibration plate. The following results were obtained: (1) The size of levitation specimen should be longer than 3/2 wavelength of the flexural vibration in order to levitate stably. (2) The relationship between the levitation distance and the mass per unit area is proportion to -1/2 power. (3) The levitation distance is proportional to the displacement amplitude. This phenomenon can be used in noncontact transportation of planar objects such as Si wafer and glass plates. (C) 1996 Acoustical Society of America.