Reconstructing acoustic field based on the normal surface velocity input data

Traditional NAH relies on the acoustic pressure collected on a hologram surface in the near field of a vibrating structure. To ensure accuracy in reconstruction, it is necessary to have a conformal array of microphones, which is not an easy task in practice. On the other hand, it is easy to use a scanning laser vibrometer to measure the normal surface velocity. This paper presents a modified Helmholtz Equation Least Squares (HELS) formulation to reconstruct the acoustic field based on the normal surface velocity input data. This approach is advantageous in that: (1) it enables one to collect input data in the far field; (2) measurement setup is very simple; and (3) the normal surface velocity contains all near-field information for reconstruction of an acoustic field. To ensure the accuracy in reconstruction, the normal surface velocity is supplemented by a few measurements of the acoustic pressure in the far field. With this combined input data, the acoustic field in three-dimensional space can be accurately reconstructed. Numerical simulations for reconstructing an acoustic field generated by arbitrarily shaped objects are demonstrated. Experimental validations on using this modified HELS formulation to reconstruct the acoustic field from a loudspeaker are also presented.