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Optimal Detection of Crack Echo Families in Elastic Solids
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
2003 (English)In: The Journal of the Acoustical Society of America, Vol. 113, no 5, 2732-2741 p.Article in journal (Refereed) Published
Abstract [en]

Optimal detection of a striplike crack residing in an isotropic elastic solid with coarse microstructure by means of ultrasonic nondestructive evaluation (NDE) is considered. A physics-based approach to derive an optimal detector, which achieves the theoretical limitations constrained by the underlying physics, is presented. State-of-the-art physical models of crack echoes and of stochastic backscattering from the material structure in elastic solids are introduced and unified with the theory of optimal detection to yield a practically useful nonlinear filter bank implementation of the optimal detector. Monte Carlo simulations of the detection performance for the special case of a striplike crack with uncertain angular orientation are presented in the form of receiver operating characteristics (ROCs). These new results represent the physical limitations for detecting a crack under the stated conditions and serve as performance bounds to which other detectors should be compared. A physics-based generalized likelihood ratio (GLR) detector, which relies on the same nonlinear filter bank as the optimal detector, is also presented for the special case of a striplike crack. A comparison between the optimal and the GLR detectors shows that the GLR detector only slightly reduces the performance.

Place, publisher, year, edition, pages
2003. Vol. 113, no 5, 2732-2741 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-90175PubMedID: 12765391OAI: oai:DiVA.org:uu-90175DiVA: diva2:162438
Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2013-06-14Bibliographically approved
In thesis
1. Optimal Detectors for Transient Signal Families and Nonlinear Sensors: Derivations and Applications
Open this publication in new window or tab >>Optimal Detectors for Transient Signal Families and Nonlinear Sensors: Derivations and Applications
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is concerned with detection of transient signal families and detectors in nonlinear static sensor systems. The detection problems are treated within the framework of likelihood ratio based binary hypothesis testing.

An analytical solution to the noncoherent detection problem is derived, which in contrast to the classical noncoherent detector, is optimal for wideband signals. An optimal detector for multiple transient signals with unknown arrival times is also derived and shown to yield higher detection performance compared to the classical approach based on the generalized likelihood ratio test.

An application that is treated in some detail is that of ultrasonic nondestructive testing, particularly pulse-echo detection of defects in elastic solids. The defect detection problem is cast as a composite hypothesis test and a methodology, based on physical models, for designing statistically optimal detectors for cracks in elastic solids is presented. Detectors for defects with low computational complexity are also formulated based on a simple phenomenological model of the defect echoes. The performance of these detectors are compared with the physical model-based optimal detector and is shown to yield moderate performance degradation.

Various aspects of optimal detection in static nonlinear sensor systems are also treated, in particular the stochastic resonance (SR) phenomenon which, in this context, implies noise enhanced detectability. Traditionally, SR has been quantified by means of the signal-to-noise ratio (SNR) and interpreted as an increase of a system's information processing capability. Instead of the SNR, rigorous information theoretic distance measures, which truly can support the claim of noise enhanced information processing capability, are proposed as quantifiers for SR. Optimal detectors are formulated for two static nonlinear sensor systems and shown to exhibit noise enhanced detectability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 99 p.
Keyword
Signalbehandling, optimal detection, transient signals, noncoherent detection, unknown arrival time, ultrasonic nondestructive testing, nonlinear sensor, stochastic resonance, Signalbehandling
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:uu:diva-3343 (URN)91-506-1664-1 (ISBN)
Public defence
2003-04-11, K23, Magistern, Uppsala, 13:15
Opponent
Supervisors
Available from: 2003-03-17 Created: 2003-03-17Bibliographically approved

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