Source and defect localization in thin elastic plates of arbitrary geometry using eigenmodes

In this paper, we experimentally demonstrate how discrete resonances can be used to image acoustic sources and mechanical changes in thin plates with different boundary shapes. The proposed method uses coupled numerical and experimental data processing, and it only requires the knowledge of the sample geometry (and not its elastic properties). If a limited number of measurement points is available in experiments, the free modes of the plates are not orthogonal from the receivers' point of view, and this induces an artificial coupling in the post-processing of the experimental signals. However, we show that this effect can be corrected using numerical simulations and a mathematical transformation of the antenna geometry. After this correction, imaging of active sources is performed using coherent summation of the elastic field over the natural frequencies of the plates, leading to an unique localization of the sources. Imaging mechanical changes in the two plates, instead, is addressed using incoherent summation over the modes, leading to symmetry problems for the plates. This work experimentally illustrates the spatial resolution, perspectives and limitations in the use of eigenmodes to produce images in complex elastic systems of arbitrary shape and materials.

Automated summary

This paper experimentally demonstrates the use of discrete resonances to image acoustic sources and mechanical changes in thin plates with different boundary shapes. The proposed method involves coupled numerical and experimental data processing, and only requires knowledge of the sample geometry. The authors show that the artificial coupling induced by non-orthogonality of free modes can be corrected using numerical simulations and a mathematical transformation of the antenna geometry. Imaging of active sources is achieved through coherent summation of the elastic field, while imaging mechanical changes is addressed using incoherent summation over the modes, leading to symmetry problems for the plates.