  This study presents an experimental investigation of the recently established
generalized linear sampling method (GLSM) for non-destructive evaluation of
damage in elastic materials. To this end, ultrasonic shear waves are generated
in a prismatic slab of charcoal granite featuring a discontinuity interface
induced by the three-point bending (3PB). The interaction of probing waves with
the 3PB-induced damage gives rise to transient velocity responses measured on
the sample's boundary by a 3D scanning laser Doppler vibrometer. Thus obtained
waveform data are then carefully processed to retrieve the associated spectra
of scattered displacement fields. On deploying multifrequency sensory data, the
GLSM indicators are computed and their counterparts associated with the
classical linear sampling method (LSM) for comparative analysis. Verified with
in-situ observations, the GLSM map successfully exposes the support of hidden
scatterers in the specimen with a remarkable clarity and resolution compared to
its predecessor LSM. It is further shown that the GLSM remains robust for
sparse and partial-aperture data inversion, thanks to its rigorous formulation.
For completeness, the one-sided reconstruction by both indicators is
investigated.

Applied Physics