Mechanical energy harvesting from electrostrictive polymeric nanocomposites.

Harvesting systems capable of transforming mechanical vibration into electrical energy have attracted considerable interest with particular focus on electroactive polymers. We are developing harvester systems compatible to a shoe sole structure and capable of recovering energy from human gait, then sustaining the energy consumption of a sensor platform to monitor biophysical parameters. In this contribution, a composite material consisting of a polyurethane matrix filled with a high-$k$ ceramic nanofiller $(CaCu_{3}Ti_{4}O_{12})$ is fabricated by doctor blade coating. Single strips, with sputtered electrodes, are electrically connected in parallel increasing electrical capacitance. The required bias voltage is provided by two alternative solutions, a rechargeable battery or a custom electret made by corona charging. When a $50 {V}$ bias was supplied by the battery, we obtained energy density output of about $5 \mu J/cm^{3}.$ Utilizing the electret, we measured an energy density output a factor 3 to 10 higher. The energy, initially stored in a supercapacitor, will then be managed in an optimized way to power sensing components integrated in the shoe sole.