Nearfield Acoustic Holography in the Not-so-Nearfield

This paper investigates the ability of Nearfield Acoustic Holography to “focus” on a source from the not-so-nearfield. While the theory of Nearfield Acoustic Holography (NAH) has been around for half a century, practical commercial products using NAH are less than three decades old, with application in just about every field that measures noise from on-highway to industrial/construction to agriculture to marine to aerospace to white goods to electronics and more. With the wide variety of applications, in many cases it is not possible to measure in the nearfield over the entire measurement area. With the advent of new algorithms, one approach is to create a “conformal” array; another might be to perform patch measurements. This paper instead investigates the use of a planar array measuring at a distance from the calculation plane to identify sources. Since evanescent waves are not measured, using this technique to feed into CAE models is probably not applicable. Most NAH measurements are not done for academic reasons or to feed CAE modes, but instead carried out to solve noise source identification problems.