Test of the nearfield holography technique using an unbaffled, uniformly oscillating disk

Abstract

Experimental results of nearfield holography measurements of the radiation from an unbaffled, uniformly oscillating disk have been compared with the exact theoretical solution. The experimental source is a disk 1 m in diameter constructed of an aluminum honeycomb material that is lightweight and structurally rigid. Eight drivers located beneath the disk can be individually adjusted so that the disk's surface vibrates inphase with constant amplitude. The radiation efficiency determined from the measurements at two frequencies (150 Hz, 250 Hz) agrees closely with the radiation efficiency calculated from the exact theory. The theoretical solution makes use of oblate spheroidal functions to compute the pressure on the surface of an ideal rigid disk vibrating with uniform normal velocity. [Work supported by the National Aeronautics and Space Administration.]