Visualization of multiple incoherent sources by the backward prediction of near-field acoustic holography

When there are multiple noise sources which share the same frequency bands, a sound field measured or estimated by near-field acoustic holography (NAH) is obviously the combination of the sound fields generated by the multiple sources. The objective of this paper is to estimate the sound field generated by each source when the coherence functions between sources are zeros. This objective can be achieved by obtaining signals coherent to sources. This paper proposes a method to obtain the coherent signals by using the spatial information of NAH. The proposed method obtains the coherent signals from pressure signals at source positions estimated by the backward prediction of NAH. Thus it does not require any prior information on source positions, unlike the conventional method, which placed sensors close to sources in order to obtain the coherent signals. The proposed method was verified by a numerical simulation using two incoherent monopole sources.