Experimental application of high precision k-space filters and stopping rules for fully automated near-field acoustical holography
2008 (English)In: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 13, no 4, 157-164 p.Article in journal (Refereed) Published
In general, inverse acoustics problems are ill-posed. Without proper regularization action taken noisy measurements result in an increasingly disturbed solution of the inverse acoustics wave equation as the distance from the measurement plane to the desired source grows. Two distinctive steps take place in the regularization process for planar near-field acoustical holography (PNAH): first, a low-pass filter function is defined and secondly a stopping rule is applied to determine the parameter settings of the filter. In acoustical imaging practice, it turns out to be very hard to determine the right filter for a certain case, ideally by means of an automatic search for the (near-) optimal parameters. This paper presents the practical application of a novel automated method that combines fitted filters for a broad number of possible experimental sources combined with highly efficient stopping rules by taking advantage of k-space. Also, a number of well-known and newly developed filter functions and stopping rules are discussed and compared with one another. Results based on actual measurements demonstrate the effectiveness, applicability, and precision of the fully implemented and automated regularization process for PNAH. Practical results even show acoustic source visualization below one millimeter primarily by successful application of k-space regularization. Implementations include modifications of Tikhonov, exponential and truncation low-pass filters, L-curve Generalised Cross-Validation (GCV) and the novel Cut-Off and Slope (COS) parameter selection methods for PNAH COS iteration in combination with either a modified exponential or Tikhonov low-pass filter results in an automated selection of the regularization parameters and eventually a fully automated PNAH system.
Place, publisher, year, edition, pages
2008. Vol. 13, no 4, 157-164 p.
Acoustic holography, Acoustic variables measurement, Applications, Automation, Data recording, Experiments, Holographic interferometry, Holography, Inverse problems, Laser recording, Low pass filters, Photoacoustic effect, Signal filtering and prediction, Wave equations, Acoustic sources, Acoustical holographies, Acoustics waves, Automated methods, Automated selections, Automatic searches, Experimental applications, Filter functions, High precisions, Highly efficient, K spaces, Low passes, Measurement planes, Near fields, Noisy measurements, Optimal parameters, Parameter selections, Parameter settings, Regularization parameters, Regularization processes, Stopping rules, Acoustics
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-66758OAI: oai:DiVA.org:kth-66758DiVA: diva2:498958
QC 201202152012-02-122012-01-272012-02-15Bibliographically approved