Abstract:
The modern drive towards mobility and wireless devices is motivating intensive
research in energy harvesting technologies. To reduce the battery burden on
people, we propose the adoption of a frequency up-conversion strategy for a new
piezoelectric wearable energy harvester. Frequency up-conversion increases
efficiency because the piezoelectric devices are permitted to vibrate at
resonance even if the input excitation occurs at much lower frequency.
Mechanical plucking-based frequency up-conversion is obtained by deflecting the
piezoelectric bimorph via a plectrum, then rapidly releasing it so that it can
vibrate unhindered; during the following oscillatory cycles, part of the
mechanical energy is converted into electrical energy. In order to guide the
design of such a harvester, we have modelled with finite element methods the
response and power generation of a piezoelectric bimorph while it is plucked.
The model permits the analysis of the effects of the speed of deflection as well
as the prediction of the energy produced and its dependence on the electrical
load. An experimental rig has been set up to observe the response of the bimorph
in the harvester. A PZT-5H bimorph was used for the experiments. Measurements of
tip velocity, voltage output and energy dissipated across a resistor are
reported. Comparisons of the experimental results with the model predictions are
very successful and prove the validity of the model.