solids is developed, and the scattering of ultrasound by defects and its measurement using ultrasonic transducers explained. Modem experimental, storage and processing devices can record and handle large time domain ultrasonic data fields with a synthetic aperture. Synthetic aperture focussing has meant algorithmic imaging is now possible for nondestructive testing purposes. These ideas are shown to be a rigorous mat~matical consequence of inverse scattering theories.

51704 Ghorayeb, S.R. Study of beamforming techniques for ultrasound imaging in nondestruct ive testing Dissertation Abstracts International, Vol. 53, No. 3, p. 1529 (Sep, 1992)

This dissertation first describes the development and implementation of time domain synthetic aperture focusing technique (SAFT) to reconstruct flaws imbedded within Piexiglass and Graphite/Epoxy samples. A modification to the present SAFT algorithm is then proposed in order to improve the quality of the images produced by SAFT when applied to composites, in addition, since the finite element method (FEM) can be used to solve hyperbolic partial differential equations, which govern wave propagation, FEM solutions are used to mimic a SAFT measurement. Using the same FEM model as a test bed, the data independent beamformer, in its basic form, is studied to determine its performance in reducing data acquisition time. SAFT results indicate that the FEM model can be used as a Test Bed for SAFT sensitivity studies, and point out the possible use of lateral displacement data for SAFT reconstruction. Extensive beamforming test comparisons reveal that the resulting optimal filters are indeed able to predict not only A-scan signals from a set of data produced by a nonuniformly spaced transducer baseline, based on one material geometry, but also A-scan signals from a data set produced by a nonuniformly spaced transducer baseline based on a different material geometzy.

51675 Hughes, M.S.; Hsu, D.K.; Margetan, F.; Thompson, R.B.; Ghorayeb, $2~.; Holger, D.K.; Zachary, L.W.; Thompson, D.O. Application of SAFT on composites Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul.-2 Aug. 1991, Vol. 11B, pp. 1413-1419. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

SAFT reconstruction has been employed for the analysis of NDT data for over ten years. Excellent results have been obtained in both metals and biological media. In these materials the propagating medium may be modeled to first approximation as lossless and auisotropic. It is obvious however, that these assumptions are less likely to provide a good approximation to composite materials. In this report we describe tests performed on various types of composite layups in order to test the degree to which the lossless-isotropic model succeeds or falls. Our primary goal is a quantitative investigation of the image artifacts introduced into the SAFT reconstruction by material anisotropy.

51629 Ghorayeb, S.; Yamano, M.; You, Z.; Lord, W. Ultrasonic SAFT reconstruction using the finite element model ing technique Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul.-2 Aug. 1991), Vol. 11B, pp. 2185-2191. Edited by D.O. Thompson and D.E. Chimenti, Plenum Press (1992)

One particularly important factor in ultrasonic NDT studies is the detailed knowledge of the ultrasonic energy interaction with the material under test. Since the finite element method (FEM) can be used to solve the hyperbolic partial differential equations, which govern ultrasonic wave propagation, FEM solutions can be used to mimic a SAFT measurement. The goal of this project is then to use the finite element method in order to simulate the action of a transducer array, and then use the resulting signals, along with SAFT, to reconstruct the reflectors under study.

51388 Chiao, R.Y.; Kincaid, T.G.; Gilmore, R.S. Ultrasonic synthetic-aperture holographic imaging Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2. Aug. 1991. Vol. 11A, pp. 813-820. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

In this paper we discuss a method to increase the effective aperture through aperture synthesis. Waveform data, collected from a scanned transducer focused near the surface of the sample, is coberenily processed to yield a synthesized aperture which can be focused to any depth with constant resolution. The synthetic aperture method allows efficient volume inspection by trading off scan time with processing time, the latter of which is constantly decreasing with increasing computing power.

ND T Abstracts

51199 Bandyopadhyay, M.; Mangsulikar, M.D.; Kulkarni, P.G. Ultrasonic imaging in flaw characterization Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, San Paulo (Brazil), 18-23 Oct. 1992. Vol. 2, pp. 799-802. Edited by C. Hallai and P. Kulcsar. Elsevier (1992)

Ultrasonic flaw sizing system converts rapidly varying voltage waveforms into a string of digits which can be stored by the computer. In this digital computer route, reconstructed images are obtained by off-line analysis. The data can be further subjected to image processing techniques. Different evaluation algorithms such as those for TOFD. SAFT etc. can be used. Some studies have been conducted using the Zipsean-3 equipment of Sonoscan make in pulse-echo as well as TOFD mode for accurate sizing and characterisation of defects.

51181 lversen, S.E. New developments of the ultrasonic P-scan technique and new perspective in the automatic ultrasonic inspection Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992. Vol. 2, pp. 896-900. Edited by C. HaUal and P. Kulcsar. Elsevier (1992)

The ultrasonic P-scan technique is a well established method for ultrasonic scanning and imaging. This paper describes recent major P- scale developments. A new scanner with an entirely new scanner control concept, defect sizing with Synthetic Aperture Focusing Technique (SuperSAFT) and with Time Of Flight Diffraction technique (TOFD), meaningful inspection of complex, "impossible" structures by a combination of P-scan and CAD/CAM.

51179 Kovalev, A.V.; Koziov, V.N.; Samodrutov, A.A.; Shevaldikin, V.G.; Yakovlev, N2¢. Ultrasonic testing of the structural ly inhomogeneous materials by one- sided access Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, San Panlo (Brazil), 18-23 Oct. 1992. Vol. 2, pp. 911-913. Edited by C. Hallai and P. Kulcsar. Elsevier (1992)

On the basis of SAFT-C technique we have developed an ultrasonic pulse thickness gauge - flaw detector for inspection of concrete, reinforced concrete or rocks. It has g-element array (2x4) with aperture dimensions 93x195 ram. This device is designed for reception of echo- signals from the depth of up to l m and makes it possible to gauge thickness of reinforced concrete items ranging from 40 to 600 mm with an error of + or -10%. It can detect cavities and delaminations with dimension of about 100 nun.

50635 Osetrov, A.V. A method of focus synthesized aper ture with nonlinear normalization in acoustic imaging Russian Journal of Nondestructive Testing, Vol. 28, No. 5, pp. 263-267 (Jan. 1993)

A method of synthesized aperture, characterized by high resistance to the error of defying the region of synthesization in advance, is proposed. The method makes it possible to identify with higher reliability defects of different form and origin. The characteristics of the method are analyzed.

50426 Capineri, L.; Tattersali, H.G.; Temple, J.A.G.; Silk, M.G. Time-of-flight diffraction tomography for NDT applications Ultrasonics, Vol. 30, No. 5; pp. 275-288 (1992)

An ultrasonic imaging system based on a direct time-space reconstruction algorithm has been developed. The radio-frequency signals are collected along a linear synthetic aperture with point sources and receivers in separate positions. This allows the investigation of defects with different incident angles and the final image is less sensitive to the defect characteristics of size, shape and orientation. Theoretical formulae for the lateral and the axial resolution are derived and the actual system performance is evaluated with a computer testing program. Theoretical models of ultrasonic scattering from simple artificial defects embedded in metals, based on the Born approximation and the geometrical theory of diffraction, are employed to simulate signals from some simplified objects covering a broad ka range, with ka up to about 5. Comparisons between theoretical, simulated and experimental lateral and axial resolution are reported, with lateral resolutions found by experiment of 1.34 lambda, by simulation lambda compared with the theoretical limit of 0.36 lamlxla.

49908 Lorenz, M.; Stelwagen, U.; Berkhout, AJ. Imaging vertically oriented defects with mul t i - s a t Physical Acoustics. Edited by O. Leroy and M.A. Breazeale. pp. 473- 478. Plenum Press (1991)

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