  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.
