The modern drive towards mobility and wireless devices is motivating intensiveresearch in energy harvesting technologies. To reduce the battery burden onpeople, we propose the adoption of a frequency up-conversion strategy for a newpiezoelectric wearable energy harvester. Frequency up-conversion increasesefficiency because the piezoelectric devices are permitted to vibrate atresonance even if the input excitation occurs at much lower frequency.Mechanical plucking-based frequency up-conversion is obtained by deflecting thepiezoelectric bimorph via a plectrum, then rapidly releasing it so that it canvibrate unhindered; during the following oscillatory cycles, part of themechanical energy is converted into electrical energy. In order to guide thedesign of such a harvester, we have modelled with finite element methods theresponse 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 wellas the prediction of the energy produced and its dependence on the electricalload. An experimental rig has been set up to observe the response of the bimorphin the harvester. A PZT-5H bimorph was used for the experiments. Measurements oftip velocity, voltage output and energy dissipated across a resistor arereported. Comparisons of the experimental results with the model predictions arevery successful and prove the validity of the model.
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