Aperture Effects in Planar Nearfield Acoustical Imaging

The influence of the size of the measurement aperture on the accuracy of reconstruction of the pressure and vector velocity fields using underwater nearfield acoustical holography technique is examined. In this measurement technique, the amplitude and phase of the pressure in the nearfield of a planar structure submerged in water is measured at a set of points on a planar surface which constitute the measurement aperture. The reconstruction of the pressure and velocity vector fields on the surface of a vibrating submerged steel plate was found to be insensitive to the aperture size down to the size of the structure. Examples of aperture sizes ranging from six (6) times down to 1/2 of the size vibrating steel plate are shown. Thus, the total length of time spent on measurements underwater can be drastically reduced.