Patch Near-field Acoustic Holography by Extrapolation Using Orthogonal Spherical Wave Source

In order to reduce the reconstructed errors, the near-field acoustic holography requires the measurement aperture larger than the sound source area. This limitation causes heavy measurement work and makes the NAH difficult to implement on large-scale structure. To solve this problem Patch near-field acoustic holography based on hologram pressure extrapolation is developed. A new patch near-field acoustic holography (PNAH) based on exploration using orthogonal spherical wave source is proposed. According to the solution of Helmholtz equation in spherical coordinates, the sound field can be approximately expressed as a linear sum of a series of orthogonal spherical wave function, so that the sound field generated by vibrator is approximated by superposing fields generated by a series of orthogonal spherical wave sources of different orders and the pressure exploration is realized by radiating process of these spherical wave sources. After near-field exploration the fast Fourier transform (FFT) method is implemented for reconstructing the normal velocity or the field on and near the radiator. The results of numerical simulations show that the method can work well in the small measurement aperture, reduce the requirement of measurement aperture area, and is convenient for application.