CIBNAH: a new Near-field Acoustic Holography method with no requirement for reference signals.

One of the main difficulties, in the application of Near-field acoustic holography (NAH) to noise radiating structures, is the choice of the reference signal(s). To successfully select such signals, a preliminary knowledge of the noise sources and their location is required, whereas, the purpose of the holography is precisely to locate and characterize these sources. In the absence of a well-established rule, the references are usually selected through trial and error procedures. This paper presents a newly developed holography method called CIBNAH that, through complex intensity, completely bypasses the need for reference signals, whatever the coherence among the sources and however the complexity of the acoustic field(s). This approach considerably facilitates the holography implementations to any complex system. Comparison with classical multi-reference holography through two real-life examples, i.e. machines, confirms its validity and precision. It is argued that CIBNAH, due to its simple formulation, results in smaller errors than the classical holography.