Data extension near-field acoustic holography based on improved regularization method for resolution enhancement

In recent years, patch near-field acoustic holography (NAH) has gradually emerged for the reconstruction of sound field radiated from large-scale sound source under the condition of small holographic aperture in engineering practice. However, this technique has not solved the problem that when the projection of large-scale sound source is located on the edge of the expanded hologram, high-precision reconstruction results are unavailable. In addition, the reconstruction of sound field is a typical inverse problem, so the existence of measurement errors makes the solution of the inverse problem be ill-posed and the accuracy of sound field reconstruction is greatly reduced. To overcome these difficulties, a new technique combining an improved method of orthogonal spherical wave superposition, data extension and modified regularization method is proposed to enhance the spatial resolution of reconstructed images. First, the sound pressure is reconstructed on an extended hologram using the improved method orthogonal spherical wave superposition and data extension. At the same time, the method modified Tikhonov regularization (MTR) is introduced to solve the edge error and other ill-posed reconstruction problems. Through iteration the accuracy of the regenerated data is improved. Finally, the extended data are used to reconstruct the sound field. The results of numerical simulation and experiments show that this technique can effectively improve the spatial resolution of the reconstructed image and the reconstruction is more robust. (C) 2019 Elsevier Ltd. All rights reserved.