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Time-resolved acoustic microscopy simulations for micro NDE applications

: Schubert, F.; Köhler, B.; Zinin, P.

Mazal, P. ; Czech Society for Nondestructive Testing; Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin; European Federation for Non-Destructive Testing -EFNDT-:
NDT in progress : IIIrd International Workshop of NDT Experts, October 10 - 12, 2005, Prague, Czech Republic
Brno: University of Technology, 2005
ISBN: 80-2142996-8
International Meeting of NDT Experts <3, 2005, Praha>
Conference Paper
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()
acoustic microscopy; Micro NDE; EFIT

The acoustic microscope is a well-established tool for studying microstructures of solids, coatings, and biological specimens in the frequency range of 10 - 2000 MHz. In order to investigate the wave propagation and scattering process in acoustic microscopy, ray theory is often used although typical wave phenomena like interference, mode conversion, multiple scattering, leaky Rayleigh and Scholte waves etc. are not incorporated appropriately. In particular, if wavelengths become comparable or larger than typical dimensions of the sample, e.g. film thickness and defect size, ray theory is no longer applicable. In the present paper a numerical model of an acoustic microscope based on the elastodynamic finite integration technique (EFIT) is presented. It allows time-domain simulations of elastic wave propagation in both, fluids and solids, and includes focusing of the incident wave field as well as scattering at defects and the fluid-solid interface taking dissipation, mode converted echoes, and leaky Rayleigh and Scholte waves into account. The simulations can be performed for various lens geometries, different frequencies and materials and can be used for continuous and time-resolved mode as well as for transmission and reflection microscopy. The simulation results are presented by time-domain signals and wave front animations. Also formation of V(r,z) curves is possible. In the paper the simulations are applied to various problems of micro NDE applications, in particular subsurface cracks and inclusions.