On the holographic reconstruction of vibroacoustic fields using equivalent sources and inverse boundary element method

In using the near-field acoustical holography based on the inverse boundary element method (BEM) for the reconstruction of vibroacoustic source parameters, an enormous number of measurements required in practice have limited the extended application of this method. To obtain the sufficient field data with a small number of actual measured data, the regeneration method of the radiated field using the multipoint equivalent sources is attempted in this paper. In using the equivalent source method, a vibrating source can be represented by distributed spherical sources inside the actual source surface. In this paper, the radiated field is expressed with a series of spherical Hankel functions and spherical harmonics. For suppressing the adverse effect of high-order spherical functions, spatial filtering of coefficients and wave-vector components by a regularization scheme is adopted. Restored field data appended with actual measured data can be used as input for the inverse BEM to reconstruct the source field. Numerical tests for spherical sources were performed for investigating the characteristics of the proposed technique. In order to validate the usefulness of the proposed method to actual irregular sources, a vacuum cleaner was taken as a demonstration example and good agreement between measured and reconstructed results could be observed.