Simulation study of a chaotic cavity transducer based virtual phased array used for focusing in the bulk of a solid material

Steven Delrue; Koen Van Den Abeele; Olivier Bou Matar

doi:10.1016/j.ultras.2016.01.010

Simulation study of a chaotic cavity transducer based virtual phased array used for focusing in the bulk of a solid material

Ultrasonics. 2016 Apr:67:151-159. doi: 10.1016/j.ultras.2016.01.010. Epub 2016 Jan 23.

Authors

Steven Delrue¹, Koen Van Den Abeele², Olivier Bou Matar³

Affiliations

¹ Wave Propagation and Signal Processing Research Group, KU Leuven Kulak, E. Sabbelaan 53, 8500 Kortrijk, Belgium. Electronic address: Steven.Delrue@kuleuven-kulak.be.
² Wave Propagation and Signal Processing Research Group, KU Leuven Kulak, E. Sabbelaan 53, 8500 Kortrijk, Belgium. Electronic address: Koen.VanDenAbeele@kuleuven-kulak.be.
³ Joint International Laboratory LICS/LEMAC: IEMN, UMR CNRS 8520, Univ. Nord de France, ECLille, Cité Scientifique, BP48, 59651 Villeneuve d'Ascq, France. Electronic address: olivier.boumatar@iemn.univ-lille1.fr.

PMID: 26845370
DOI: 10.1016/j.ultras.2016.01.010

Abstract

In acoustic and ultrasonic non-destructive testing techniques, it is sometimes beneficial to concentrate sound energy at a chosen location in space and at a specific instance in time, for example to improve the signal-to-noise ratio or activate the nonlinearity of damage features. Time Reversal (TR) techniques, taking advantage of the reversible character of the wave equation, are particularly suited to focus ultrasonic waves in time and space. The characteristics of the energy focusing in solid media using principles of time reversed acoustics are highly influenced by the nature and dimensions of the medium, the number of transducers and the length of the received signals. Usually, a large number of transducers enclosing the domain of interest is needed to improve the quality of the focusing. However, in the case of highly reverberant media, the number of transducers can be reduced to only one (single-channel TR). For focusing in a non-reverberant medium, which is impossible when using only one source, an adaptation of the single-channel reciprocal TR procedure has been recently suggested by means of a Chaotic Cavity Transducer (CCT), a single element transducer glued on a cavity of chaotic shape. In this paper, a CCT is used to focus elastic energy, at different times, in different points along a predefined line on the upper surface of a thick solid sample. Doing so, all focusing points can act as a virtual phased array transducer, allowing to focus in any point along the depth direction of the sample. This is impossible using conventional reciprocal TR, as you need to have access to all points in the bulk of the material for detecting signals to be used in the TR process. To asses and provide a better understanding of this concept, a numerical study has been developed, allowing to verify the basic concepts of the virtual phased array and to illustrate multi-component time reversal focusing in the bulk of a solid material.

Keywords: Chaotic cavity; Comsol; Non-destructive testing; Time reversal; Virtual phased array.