image of a subsurface defect corresponds to a two-dimensional Fourier transform. Transforms based on simulated flaws are used to infer the size and shape of the actual flaw.

36792 Thaker, D.M.; Burton, N.J. Ultrasonic exploration of adhesive bonds by acoustic microscopy Adhesion 11. 24th annual conference on adhesion and adhesives, London (United Kingdom), 1986. pp. 56-70. Edited by K.W. Allen. ELAS, 1987.

The principles and applications of acoustic microscopy will be described in detail and the application to adhesive bonding will be illustrated. The samples investigated include epoxy bonded aluminium plates with deliberate disbonds, die attach problems in the semiconductor industry and delamination studies of carbon fibre-epoxy composites.

36786 Favro, L.D.; Kuo, P.K.; Thomas, R.L Contrast mechanisms in the thermoacoustic microscope Wayne State University, Detroit, Michigan (United States), AD- A170-037, 7 pp. (1986)

In order to make full use of the thermoacoustic microscope as a quantitative NDE tool, one must be able to interpret the images in terms of the physical properties of the features being imaged. The elastic constants could lead to totally incorrect conclusions about the nature of a defect. This paper summarizes a theoretical analysis which can form a basis for assessing the relative importance of different contrast mechanisms.

36761 Soumekh, M.G.; Briggs, G.A.D.; lieu, C. Detection of surface-breaking cracks in the acoustic microscope Acoustical Imaging, Vol. 13. Proceedings of the Thirteenth Inter- national Symposium on Acoustical Imaging, Minneapolis (United States), 26-28 Oct. 1983. pp. 119-128. Edited by M. Kaveh and R.K. Mueller. Plenum Press, 605 pp. (1984)

The prime advantage of the scanning acoustic microscope lies in its ability to image the interaction of elastic waves with the specimen. Over the past two years a body of information has been accumulated which shows that the scanning acoustic microscope (SAM) is a powerful instrument for detection of cracks and elastic discontinuities. This ability is due to the dominant role played by leaky surface waves in the contrast of the SAM. When a Rayleigh wave propagates along the surface of the specimen it may be strongly scattered by defects much less than a wavelength thick. Fine cracks and grain boundaries which would not be resolvable by conventional criteria can thus be seen in acoustic micrographs. The aim of this paper is to discuss the contrast in the acoustic microscope from surface-breaking elastic discontinuities.

36760 Lin, Z.; Lee, H.; Wade, G.; Schueler, C.F. Computer-assisted tomographic acoustic microscopy for subsurface imaging Acoustical Imaging, Vol. 13. Proceedings of the Thirteenth Inter- national Symposium on Acoustical Imaging, Minneapolis (United States), 26-28 Oct. 1983. pp. 91-105. Edited by M. Kaveh and R.K. Mueller. Plenum Press, 605 pp. (1984)

Acoustic microscopy is an important branch of non-destructive evaluation which provides high-resolution imaging of the detailed structure of an object. STAM (Scanning Tomographic Acoustic Microscope) is a system capable of producing tomographic images by scanning the source or rotating the specimen to generate a sequence of tomographic projections. This system has advantages over conventional approaches, especially for complex objects with planar structure such as integrated-circuit chips. An earlier paper provided the analysis and the reconstruction algorithms for the signal processing of planar tomograpbic systems including an algorithm for "back-and-forth" propagation. This paper summarizes the modifications and revisions of this latter algorithm as applied to microscopic digital imaging.

36755 Souraekh, M.G.; Briggs, G.A.D., llett, C. The origin of grain contrast in the scanning acoustic microscope Acoustical Imaging, Vol. 13. Proceedings of the Thirteenth Inter- national symposium on Acoustical Imaging, Minneapolis (United States), 26-28 Oct. 1983. pp. 107-118. Edited by M. Kaveh and R.K. Mueller. Plenum Press, 605 pp. (1984)

The contrast in the scanning acoustic microscope may be described by the V(z) curve. The potential of the SAM lies in the fact that the V(z) curve is a strong function of the elastic properties of the material. It is thus possible to image elastic properties with spatial resolution of the order of a micron or better provided the incident radiation has a sufficiently small wavelength. The theory describing the V(z) response of the microscope on an isotopic surface has been extensively studied using both an approximate ray model and more rigorously by Fourier optics. In this paper the formulation of Fourier optics is applied to anisotropic specimens and the full V(z) curve is predicted from the independent elastic constants. Furthermore, the Fourier optics approach is employed to explain the contrasts from grains of different orientations.

36753 Kushibiki, J.; Matsumoto, Y.; Chubachi, N. Material characterization by acoustic line-focus beam Acoustical Imaging, Vol. 13. Proceedings of the Thirteenth Inter- national Symposium on Acoustical Imaging, Minneapolis (United States), 26-28 Oct. 1983. pp. 193-202. Edited by M. Kaveh and R.K. Mueller. Plenum Press, 605 pp. (1984)

In this paper, we propose a novel method of material characterization of determining both the velocity and the attenuation of leaky waves directly from

V(z) curves obtained by the acoustic line-focus beam microscope. In this method, a simple model is developed to represent transducer output V(z), which is approximately formed by a combination of ray and field theories. Experiments are demonstrated for a fused quartz sample using an acoustic line-focus-beam sapphire lens of 1.0 mm radius at 226.3 MHz. This characterization method is applied to quantitative estimation of two Mn-Zn ferrite samples with different grain size, and the results are compared with acoustic imaging information observed by the reflection type scanning acoustic microscope at a frequency of 440 MHz.

36722 Dussoulier, A. Nondestructive tests of ceramic components for aircraft turbines (In French) Turbomeca, Bizanos (France), N85-26718, 96 pp. (Oct. 1984)

Quality control techniques of ceramic pieces used in aircraft turbines are compared and a correlation between manufacturing procedures and detected defects is discussed. Silicon carbide samples presenting typical defects were prepared. The inspection techniques studied included ultrasonics, X-rays, fluorescence, and acoustic scanning microscopy. It is shown that the most traditional methods such as ultrasonic inspection do not have enough resolution while the most advanced techniques are not yet sufficiently developed for use in routine control.

36716 Klima, S.J. NDE for heat engine ceramics National Aeronautics and Space Administration, Cleveland, Ohio (United States), N85-20389, 13 pp. (1984)

Radiographic, ultrasonic, and scanning laser acoustic microscopy (SLAM) techniques were used to characterize silicon nitride and silicon carbide MOR bars in various stages of fabrication.

36667 Olympus Optical Co., Ltd. Ultrasonic microscope U.S. Patent No. 4,621,531 (11 Nov. 1986)

An ultrasonic microscope for observing an ultrasonic raster image of a specimen on a monitor by scanning the specimen by vibrating an ultrasonic head in the X direction by a vibrator and by moving a specimen stage in the Y direction on which the specimen is placed, and for observing an optical image of the sample by means of a light source, an eyepiece, and an optical head including an objective lens.

36568 Oravecz, M.G.; Kessler, L.'W. Nondestructive inspection of niobium to improve superconductivity IEEE 1985 Ultrasonics Symposium, San Francisco, California (United States), 16-18 Oct. 1985, pp. 547-552. Edited by B.R. MeAvoy, IEEE, Piscataway, New Jersey (1985)

This paper demonstrates that the information needed to select the highest quality niobium is obtainable nondestructively. Performance improvements of particle accelerators using RF superconductivity requires rapid nondestructive inspection of commercially pure niobium sheets in bulk for assurance of high purity, small grain size, freedom from critical defects and near 100% recrystallization. A total of 1.5 square meters of 3.0 and 1.5 nun thick niobium sheet was scanned with a Scanning Laser Acoustic Microscope (SLAM) using acoustic resolution of up to 25-50 microns.

36564 Vetters, H.R.; Mayr, P.; Boseck, S.; Luebben, Th.; Matthaei, R.; Schulz, A. Scanning acoustic microscopy in materials characterization Scanning Electron Microscopy, Part 3, pp. 981-989 (1985)

The scanning acoustic microscopy is a powerful tool for subsurface imaging and therefore fault detection in coated parts. In this paper several methods are established to reveal the imaging of hidden structures. First efforts were made to find out the information depth due to the various distances between lens and surface of the object. By means of a specially developed test specimen it was possible to estimate the penetration depth for monitoring structural details. The indepth analysis of layered composites is considered by the determination of the V(z)~haracteristics. Furthermore the gain of image processing by means of

' Fourier transformed patterns and simultaneous filtering is shown by a typical example.

36549 Mueller, R.K.; Soumekh, B. Theory of image reconstruction in laser scanned acoustic microscopy IEEE 1985 Ultrasonics Symposium, San Francisco, California (United States), 16-18 Oct. 1985, pp. 720-724. Edited by B.R. McAvoy. IEEE, Piscataway, New Jersey (1985)

In a laser scanned acoustic microscope (SLAM) a focused laser beam scans an acoustically excited, optically reflecting surface. The laser beam picks up the elastic surface excursion as amplitude or phase modulation which is finally recovered as amplitude modulation on one or more photodetectors. In this paper we are interested in the relationship between the surface excursion vector s(x,y) on the scanned surface, (reference surface) and the impinging elastic wave (described by its vector and scalar potentials) which causes the surface excursion. After deriving this relationship we discuss its implication on image formation and image interpretation in a SLAM.

36548 Mueller, R.K.; Robbins, W.P.; Soumekh, B.; Zhou, Z.; Skaar, T.; Rudd, E. High resolution imaging with scanning laser acoustic microscopy digital image processing

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