  We demonstrate that a rainbow-based metasurface, created by a graded array of
resonant rods attached to an elastic beam, operates as a mechanical delay-line
by slowing down surface elastic waves to take advantage of wave interaction
with resonance. Experiments demonstrate that the rainbow effect reduces the
amplitude of the propagating wave in the host structure. At the same time it
dramatically increases both the period of interaction between the waves and the
resonators, and the wavefield amplitude in the rod endowed with the harvester.
Increased energy is thus fed into the resonators over time, we show the
enhanced energy harvesting capabilities of this system.
