A SOFT FREE SHAPE CASTED PIEZOELECTRIC ELASTOMER

Piezoelectric materials are largely used for sensing and energy harvesting applications as simple and reliable solutions from piezoelectric accelerometers to vibration energy harvesters. Most of the applications utilize either piezoceramic materials, exploiting their high piezoelectric coefficients, or piezoelectric polymers, thanks to their soft response, in applications where finite displacements are needed. Actual piezoceramic materials are expensive, brittle and available only in standard and flat shapes. On the other hand, piezoelectric polymers, like PVDF, are too stiff for many applications that need softer solutions. This work presents the study, development and validation of a new soft piezoelectric elastomer, which can be designed in free shape through a casting process. This study identified a novel formulation of a cold polymerizable silicone-based elastomer, enhanced with BaTiO3 (barium titanate) powder. A detailed procedure of fabrication was defined involving the mixture preparation, curing and polarization phases of the solution. To obtain disk specimen, we designed and used a dedicated 3D printed acrylonitrile butadiene styren (ABS) mold with a cylindrical cavity. The mold houses two steel electrodes for the polarization through a high voltage DC converter. This allows to perform the polarization process at the same time of the polymerization in order to easily orientate polar BaTiO3 particles in the liquid solution until the polymerization is completed. To experimentally evaluate the effect of the main variables on the fabrication procedure and the piezopolymer response, we conducted a systematic test plan. Specifically, we investigated both the effect of barium titanate powder concentration and voltage polarization level on the morphological appearance of the specimen and on its piezoelectric properties. Two quasistatic cyclic compression tests at different strain levels were performed on small cylindrical samples cut by the specimens, registering the mechanical behaviours and electric voltage output signals. The piezoelectric coefficient d33, calculated for all the configurations and for both strain levels, highlights a remarkable performance of the proposed piezoelectric polymer.