  In this study, we design the 3D-printed phononic crystal (PnC) beam with the
topological interface state for harvesting the mechanical energy of flexural
waves. The PnC beam is formed by arranging periodic grooves on its surface. The
PnC beam with either topologically trivial or non-trivial phase can be achieved
via changing the distance between the grooves. The topological interface state
is then generated by combining two PnCs with distinct topological phases. The
existence of the interface state of the PnC beam is verified both numerically
and experimentally. To convert the mechanical energy into the electricity, a
piezoelectric disc is attached at the interface of the proposed PnC beam.
Compared to the reference beam harvester, the measured output power is
significantly amplified by the PnC harvester at the frequency corresponding to
the interface state. Furthermore, the PnC beam energy harvester based on the
topological state exhibits robustness against geometrical disorders.
