In elastic wave systems, combining the powerful concepts of resonance and
spatial grading within structured surface arrays enable resonant metasurfaces to exhibit
broadband wave trapping, mode conversion from surface (Rayleigh) waves to bulk
(shear) waves, and spatial frequency selection. Devices built around these concepts
allow for precise control of surface waves, often with structures that are subwavelength,
and utilise Rainbow trapping that separates the signal spatially by frequency. Rainbow
trapping yields large amplifications of displacement at the resonator positions where
each frequency component accumulates. We investigate whether this amplification, and
the associated control, can be used to create energy harvesting devices; the potential
advantages and disadvantages of using graded resonant devices as energy harvesters is
considered.
We concentrate upon elastic plate models for which the A0 mode dominates, and take
advantage of the large displacement amplitudes in graded resonant arrays of rods,
to design innovative metasurfaces that trap waves for enhanced piezoelectric energy
harvesting. Numerical simulation allows us to identify the advantages of such graded
metasurface devices and quantify its efficiency, we also develop accurate models of
the phenomena and extend our analysis to that of an elastic half-space and Rayleigh
surface waves.