Research project: Nearfield Acoustical Holography

Introduction

Nearfield acoustical holography (NAH) is a technique to infer the surface velocity (or vibrations) of an acoustic source from the pressure measured on a surface (i.e. the hologram) around the source. The`holy grail’ of NAH is to record a hologram of the pressure (or the velocity) in front of the acoustic source and then perfectly infer the surface velocity of the source from the hologram (see Figure 1).

At the ISVR, we are looking particularly at NAH performed in hemi-cylindrical and wedge-shaped geometries. A special sound field model was developed to describe these sound fields and the associated boundary conditions analytically.
Unlike with planar arrangements, the hologram fully surrounds the source along one out of two directions. Planar holograms, on the other hand, are always limited in both directions, as an infinite hologram cannot be measured in practice.
A striking advantage of NAH in wedge-shaped environments over NAH with full cylinders is that the aperture size for the same source can be significantly smaller, reducing the measurement effort drastically.

 

 

 

 

 

 

 

 

 

 

 

[¹] F.-M. Hoffmann, F.M. Fazi, E.G. Williams, S. Fontana, A general radiation model for sound fields and nearfield acoustical holography in wedge propagation spaces, J. of the Acoust. Soc. Am., Vol. 142, Issue 3, p. 1249-1260 (Sept. 2017)