Direct extrapolation in near-field acoustic holography

The size and shape of a reconstruction surface is the same as a holography surface in conventional near-field acoustic holography (NAH), which limits the size and shape of the measurement surface. To reduce the measurement points and use any shape of measurement array, the direct extrapolation in NAH based on wave superposition is proposed. According to the transitive relation of the acoustic signal in the sound field, the sound field information on a reconstruction surface could be directly extrapolated by the holography surface. A set of simulations are performed with an 18-channel wheel-type array to obtain more sound pressure data on a grid reconstruction surface. On comparing the reconstruction errors produced by different parameters, which are the source frequency, signal-to-noise ratio, reconstruction distance, point numbers, and grid spacing, the results show that the errors are all very low. Moreover, the experiment verifies the feasibility of the direct extrapolation method.