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Acoustic MicroscopySecond Edition$
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Andrew Briggs and Oleg Kolosov

Print publication date: 2009

Print ISBN-13: 9780199232734

Published to Oxford Scholarship Online: February 2010

DOI: 10.1093/acprof:oso/9780199232734.001.0001

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Anisotropy

Anisotropy

Chapter:
(p.227) 11 Anisotropy
Source:
Acoustic Microscopy
Author(s):

G. A. D. Briggs

O. V. Kolosov

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199232734.003.0011

Polycrystalline materials give contrast from their grain structure in scanning acoustic micrographs. Bulk wave propagation in anisotropic materials can be calculated from the Christoffel equation. The result can be visualized as a slowness surface of k/ω, which is the reciprocal of the phase velocity (and from which the group velocity can be determined). In the surface of an anisotropic material a pure Rayleigh wave can exist only in certain symmetry directions; in general, surface and pseudo‐surface waves dominate the reflectance function and hence the contrast in acoustic microscopy. These different modes can be measured by analysing V(z) measured with a cylindrical (line‐focus‐beam) lens. The V(z) response for a spherical (imaging) lens may be calculated from a complex mean reflectance function, and this enables the contrast to be understood from polycrystalline samples of aluminium, nickel, and copper. The contrast from grain boundaries requires separate treatment.

Keywords:   slowness surface, group velocity, phase velocity, surface wave, pseudo‐surface wave, complex mean reflectance function, polycrystalline, grain, anisotropy

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