Nearfield acoustic holography: I. Theory of generalized holography and the development of NAH

Abstract

Because its underlying principles are so fundamental, holography has been studied and applied in many areas of science. Recently, a technique has been developed which takes the maximum advantage of the fundamental principles and extracts much more information from a hologram than is customarily associated with such a measurement. In this paper the fundamental principles of holography are reviewed, and a sound radiation measurement system, called nearfield acoustic holography (NAH), which fully exploits the fundamental principles, is described.

Surface Vibration Reconstruction using Inverse Numerical Acoustics

“…Therefore, NAH only works well for sources with simple geometry (planar or cylindrical) [11,12,13]. In order to take into account the evanescent field, the hologram surface on which measurements are taken must be very close to the source surface, within one-half wavelength [14].…”

“…In nearfield acoustic holography (NAH), the measurement of the sound pressure field on a two-dimensional surface is used to determine the three-dimensional sound pressure field, the particle velocity field, the sound intensity field, the surface velocity, etc. [11,12]. Measurements are usually made on a planar surface (the hologram plane), and these data are used to uniquely reconstruct the three-dimensional field.…”

“…Measurements are usually made on a planar surface (the hologram plane), and these data are used to uniquely reconstruct the three-dimensional field. Due to the exponential decay of the evanescent wave, the NAH measurement is normally done in the nearfield region [11,12].…”

Acoustic source localization exploring theory and practice

“…As stated by Williams [97], the method was originally proposed by Graham in 1969. It has been further developed by Williams, Maynard and others, starting in 1980 [97,45]. Similar methods have been developed for cylindrical and spherical coordinate systems and this large body of work was summarized by Williams in 1999 in the reference work Fourier Acoustics [94].…”

“…Near-field methods are necessary to model and solve the inverse problem in this case. In 1985, Maynard, Williams and Veronesi proposed a method known as nearfield acoustic holography (NAH) based on early research by Graham [45,85]. Contrary to earlier approaches in acoustic holography, their model accurately describes the sound field close to the source.…”