Development of piezoelectric harvesters with integrated trimming devices

Piezoelectric cantilever harvesters have a large power output at their natural frequency,
but in some applications the frequency of ambient vibrations is different fromthe harvester’s frequency
and/or ambient vibrations are periodicwith some harmonic components. To copewith these operating
conditions harvesters with integrated trimming devices (ITDs) are proposed. Some prototypes are
developed with the aid of an analytical model and tested with an impulsive method. Results show
that a small trimming device can lower the main resonance frequency of a piezoelectric harvester of
the same extent as a larger tip mass and, moreover, it generates at high frequency a second resonance
peak. A multi-physics numerical finite element (FE) model is developed for predicting the generated
power and for performing a stress-strain analysis of harvesters with ITDs. The numerical model is
validated on the basis of the experimental results. Several configurations of ITDs are conceived and
studied. Numerical results show that the harvesters with ITDs are able to generate relevant power at
two frequencies, owing to the particular shape of the modes of vibration. The stress in the harvesters
with ITDs is smaller than the stress in the harvester with a tip mass trimmed to the same frequency.