Guided wave arrays for high resolution inspection

Velichko, Alexander; Wilcox, Paul D.

doi:doi:10.1121/1.2804699

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Journal of the Acoustical Society of America / Volume 123 / Issue 1 / ACOUSTIC SIGNAL PROCESSING [60]

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Guided wave arrays for high resolution inspection

J. Acoust. Soc. Am. Volume 123, Issue 1, pp. 186-196 (2008); (11 pages)

Alexander Velichko and Paul D. Wilcox

Department of Mechanical Engineering, University of Bristol, Bristol, BS8 1TR, United Kingdom

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Abstract

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The paper describes a general approach for processing data from a guided wave transducer array on a plate-like structure. The raw data set from such an array contains time-domain signals from each transmitter–receiver combination. The technique is based on linear superposition of signals in the frequency domain with some amplitude and phase factors and can be applied to any array geometry and any types of array elements. The problem of finding optimal coefficients, which allow the best resolution to be achieved with the minimum number of array elements, is investigated. It is shown that improvements in resolution are obtained at the expense of sensitivity to noise. A method of quantifying this sensitivity is presented. Results are shown that illustrate the application of the technique to a linear array and an array of circular geometry (containing a single ring of elements). Experimental data obtained from a guided wave array containing electromagnetic acoustic transducer elements for exciting and detecting the S0 Lamb wave mode in a 5-mm-thick aluminum plate are processed with different algorithms and the results are discussed. Generalization of the technique for the case of multimode media is suggested.

ACKNOWLEDGMENTS

This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) through the UK Research Centre in NDE and by BNFL, Nexia Solutions, and DSTL.

Article Outline

INTRODUCTION
PRELIMINARIES
1. Array and data acquisition
2. Far field approximation
3. Phased methods
ANGULAR RESOLUTION
1. Basic-phased addition method
2. Maximization of contrast method
3. Direct solution to the angular resolution problem
4. Stability of angular resolution methods
5. Examples
MAXIMIZATION OF CONTRAST OVER AN INTERVAL
EXPERIMENTAL EXAMPLE
MULTIMODE RESOLUTION
1. Algorithm
2. Example
CONCLUSION

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KEYWORDS and PACS

Keywords

acoustic signal processing, acoustic transducer arrays, acoustic waveguides, array signal processing

PACS

43.60.Fg

Acoustic array systems and processing, beam-forming
43.20.Bi

Mathematical theory of wave propagation
43.35.Cg

Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Zc

Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

ARTICLE DATA

History

Received 26 Apr 2007
Accepted 05 Oct 2007
Revised 04 Oct 2007

Digital Object Identifier

http://dx.doi.org/10.1121/1.2804699

PUBLICATION DATA

ISSN

0001-4966 (print)

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$abstract.society.value is a Member of CrossRef

Acoustical Society of America

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Guided wave arrays for high resolution inspection