Holographic reconstruction of active sources and surface admittance in an enclosure

Abstract

Near-field acoustic holography (NAH) is applied to reconstruct an exterior sound field, as well as an interior sound field. A numerical method is employed to reconstruct the interior sound field of an arbitrary shaped enclosure. Reconstructed sound fields are usually used in identifying noise sources. However, until now, it has not been thoroughly verified whether the reconstructed sound field of an interior also shows source distributions. Interior sound fields have been reconstructed without any thought given to this question. In contrast to an exterior sound field, reflections are added to an interior sound field and therefore, the reconstructed sound field may misrepresent the source distribution. This paper addresses a way to solve this problem. A measurement method is proposed in order to distinguish between reflections and direct radiation from noise sources.

An equivalent source technique for recovering the free sound field in a noisy environment

“…The surface admittance of the source could be measured, for example, by using the methods given in Refs. 16,39,and 40 (in Ref. 39, a method for measuring the surface admittance when the source surface is non-locally reacting is also given).…”

Sound source identification in a noisy environment based on inverse patch transfer functions with evanescent Green's functions

“…(3), the normal velocity v n can be evaluated through a finite difference approximation, as given in Eq. (16). The impedance matrix Z mk in Eq.…”

“…Kim and Ih [15] reconstructed the field of a half-scaled automotive cabin by using iBEM and regularization methods. Kim et al [16] proposed a measurement method to obtain active sources in an enclosure by measuring the admittance of the enclosed surface. The iBEM was also performed by Williams et al [17] to reconstruct the normal velocities of a fuselage in situ.…”

Single layer planar near-field acoustic holography for compact sources and a parallel reflector

“…From a data-acquisition point of view, it is a common practice to measure pressure or particle velocity in two closely spaced surfaces, or to measure Cauchy data in a single layer. Among these two categories, some studies formulate the problem with inverse boundary element and Helmholtz equation least-squares methods via the singular value decomposition [3,4,5,6,7,8], while others use the spherical wave superposition method [9,10,11], the equivalent source method [12,13,14,15,16,17] or the statistically optimized NAH method [18,19,20,21,22,23]. There is also a recent application of the equivalent source method in which the (double-layer) measurements completely cover the source region, allowing acoustic visualization of the field in small cavities [24].…”