New developments in near-field acoustic holography

In the field of noise-control engineering, information about the individual strength, andlocation, of the most dominant sources is of vital importance. This information allows theacoustic engineer to take effective measures in his effort to reduce the emitted acoustic noiselevels. Near-field acoustic holography is a measurement-based tool which visualizes theacoustic fields radiated by the noise emitting object, giving the engineer the noise sourceinformation required. In the paper some applications of near-field acoustic holography, asapplied at Philips, will be discussed. A cylindrical version of near-field acoustic holographywas implemented and applied to a Magnetic Resonance Imaging scanner. Using an array ofmicrophones, the measurement time to obtain the holographic recordings was reducedsignificantly, whilst the cylindrical near-field acoustic holography implementation allowed anear-instant post-processing of the acquired data