The conception of structure-borne-sound-based near-field holography

A procedure for the projection of structure-borne sound fields is introduced, following the basic idea behind Near-Field Acoustic Holography. It is shown that the bending wave field of an infinite plate subjected to point force excitation can be reconstructed by means of Fourier transform-based wave field extrapolation. All required information on the wave field is obtained by vibrational response measurement in the near-field of the excitation, using a circular geometry with a limited number of positions. The procedure is verified both numerically and experimentally, to very satisfying results. The experiments indicate that the reconstruction at the source becomes erratic when standoff distances greater than half of the minimum wavelength under consideration are used. Reconstruction of the far-field plate response is found to be less restrictive.