  The energy harvesting capability of resonant harvesting structures, such as
piezoelectric cantilever beams, can be improved by utilizing coupled
oscillations that generate favourable strain mode distributions. In this work,
we present the first demonstration of the use of a laminated carbon fibre
reinforced polymer to create cantilever beams that undergo coupled
bending-twisting oscillations for energy harvesting applications. Piezoelectric
layers that operate in bending and shear mode are attached to the bend-twist
coupled beam surface at locations of maximum bending and torsional strains in
the first mode of vibration to fully exploit the strain distribution along the
beam. Modelling of this new bend-twist harvesting system is presented, which
compares favourably with experimental results. It is demonstrated that the
variety of bend and torsional modes of the harvesters can be utilized to create
a harvester that operates over a wider range of frequencies and such
multi-modal device architectures provides a unique approach to tune the
frequency response of resonant harvesting systems.
