Wavenumber domain regularization for near-field acoustic holography by means of modified filter functions and cut-off and slope iteration

• Planar Near-field Acoustic Holography (PNAH) is an acoustic imaging method based on the inverse solution of the wave equation. Wavenumber domain low-pass filtering is an essential operation in the PNAH process. An increasingly higher wavenumber filter cut-off results in a "blow-up" of the inverse solution, which is a characteristic of an ill-posed problem. On the other hand, lower cut-off wavenumbers result in spatial acoustic data at very low resolution, where highly detailed information is discarded. Thus, an optimal solution for the cut-off wavenumber somewhere in between is needed. This paper introduces two modified filter functions, namely a modified exponential and a modified Tikhonov filter, that are specifically designed for application in PNAH and compares them with a number of more general applied filter functions. Regularization methods are introduced that exploit the k-space to obtain near-optimal low-pass filter parameter selection at high computational efficiency. These filter functions are discussed and their parameters are selected by k-space application of L-curve, Generalised Cross-Validation and the newly introduced and well-applicable Cut-Off and Slope iteration. Simulations of various sources show that the optimal regularization method is highly dependent on the type of source, the spatial distribution and measurement noise. Finally, a robust regularization strategy is proposed which automatically produces high quality results for a wide range of practical conditions.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Nyckelord

Acoustic holography

Acoustic imaging

Acoustics

Data recording

Dynamic loads

Holographic interferometry

Holography

Interferometry

Laser recording

Photoacoustic effect

Photonics

Signal filtering and prediction

Wave equations

Wave filters

Acoustic data

Blow-up

Cross validations

Cut-off

Filter functions

High-quality

Ill-posed problems

In-between

Inverse solutions

K-space

L curves

Low resolution

Low-pass filtering

Measurement noises

Near-field Acoustic Holography

Optimal regularization

Optimal solutions

Planar near-field

Regularization methods

Spatial distributions

Wave number domains

Wave numbers

Imaging techniques

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