Reconstructing Excitation Forces Acting on a Baffled Plate Using Nearfield Acoustical Holography

This paper deals with reconstruction of excitation forces and analyses of the root causes of vibro-acoustic responses of an elastic structure by using nearfield acoustical holography and modal expansion theory. Derivations of formulations for reconstructing excitation forces, including distributed, line, and point forces, acting on the back side of a rectangular thin plate simply supported on an infinite, rigid baffle, are presented. The reason for choosing a baffled plate is that analytic solutions to vibro-acoustic responses are readily available, so the accuracy in reconstruction can be examined rigorously. For simplicity, the effect of fluid loading is neglected, and input data are assumed error-free. Numerical examples of reconstructing excitation forces are presented, and results agree very well with benchmark values. The impacts of various parameters, such as the ratio of measurement aperture versus plate size, microphone spacing, standoff distance, the number of natural modes, etc., on reconstruction accuracy are investigated. Needless to say, in practice such idealized scenario is nonexistent and the accuracy in reconstruction of excitation forces are severely compromised by measurement errors and interfering signals. Nevertheless, the concept as presented is sound, except that more effective regularizations must be employed to enhance signal to noise ratio, and reconstruction results.