  In this work, a method for the simulation of guided wave propagation in
solids defined by implicit surfaces is presented. The method employs structured
grids of spectral elements in combination to a fictitious domain approach to
represent complex geometrical features through singed distance functions. A
novel approach, based on moment fitting, is introduced to restore the diagonal
mass matrix property in elements intersected by interfaces, thus enabling the
use of explicit time integrators. Since this approach can lead to significantly
decreased critical time steps for intersected elements, a "leap-frog" algorithm
is employed to locally comply with this condition, thus introducing only a
small computational overhead. The resulting method is tested through a series
of numerical examples of increasing complexity, where it is shown that it
offers increased accuracy compared to other similar approaches. Due to these
improvements, components of interest for SHM-related tasks can be effectively
discretized, while maintaining a performance comparable or only slightly worse
than the standard spectral element method.
