Near-field acoustic levitation of 8 inches Si wafer and glass substrate using flexural vibration

In the conventional acoustic levitation, the specimen to be levitated is limited to very light ones of a few milligrams to a few tens of milligrams. The authors found out that the specimen with several kilograms can be levitated stably by direct sound radiation pressure and that the specimen irrespective of material can be levitated in order of a few kilograms. The requirement is only the surface of the specimen exposed against sound wave to be flat. In this report, the fundamental characteristics of the near filed levitation were experimentally studied with use of a flexural vibration plate. Following results were obtained: (1) The size of the 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 of unit area is in proportion to -1/2 power. (3) The levitation distance is also proportion to the displacement amplitude. This phenomenon is applicable to non-contact transportation of planar object such as 8 inch Si wafer and LCD glass substrate with superimposed ultrasonic wave on vibration plate.