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Numerical investigations on negative refraction and focusing of ultrasonic Lamb waves by a thickness change in an isotropic plate

: Schubert, F.

European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS 2012. Proceedings. CD-ROM : September 10-14, 2012, Vienna, Austria; Abstractband
Vienna: Vienna University of Technology, 2012
ISBN: 978-3-9502481-8-0 (Abstract-Band)
ISBN: 978-3-9502481-9-7 (CD-ROM)
ISBN: 9783950353709
European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS) <6, 2012, Vienna>
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()

Recently a flat lens for elastic Lamb waves displaying negative refraction and focusing has been demonstrated experimentally for the first time [1]. In the present paper we investigate this phenomenon numerically by using an adapted version of the 3-D Elastodynamic Finite Integration Technique (EFIT), a highly efficient, explicit time-domain solver for elastodynamics. We study refraction of Lamb waves by a plane interface consisting of an abrupt thickness change between two different plate regions. While one region supports a backward-propagating (negative group velocity) mode the other plate region supports a forwardpropagating (positive group velocity) mode at exactly the same frequency and wave number. We demonstrate negative refraction and focusing numerically and compare it with the experimental results from [1]. The investigated plate system represents a surprisingly simple mechanical system which exhibits negative group velocity behavior in a certain frequency ba nd and thus provides a powerful test bed for negative-index physics. Moreover, by using this phenomenon a "perfect" lens approach according to Veselago should be possible. Due to the relative simplicity of the system and the well-understood behavior of ultrasonic Lamb waves the approach offers high potential for practical NDE applications, e.g. for the development of near-field lenses for ultrasonic microscopy.