Piezoelectret sensors from direct 3D-printing onto bulk films

The development of piezoelectric sensors using ferroelectrets is a very active field that is increasingly gaining importance. Recently, 3D-printing ferroelectret sensors using fused deposition modeling technique has been extensively investigated due to its unparalleled advantages in terms of design flexibility and cost-effectiveness. Nevertheless, printed structures are more rigid than bulk materials due to the minimal printable thicknesses. In this work, we present a new method that combines the advantages of 3D-printing with the high performance of bulk materials by bonding both layers in the printing process. Hereby, a polylactic acid (PLA) filament is directly printed on a 20 mu m-thick bulk PLA film to form well-defined structures. This structure is thermally bonded with another PLA bulk film to form the ferroelectret. In order to enhance the sensitivity of the ferroelectrets, an additional elastomeric layer is utilized. By varying the material and thickness of the elastomeric cover, piezoelectric d(33)-coefficients of 713 pCN(-1) and 229 pCN(-1) are achieved using Ecoflex (TM) and foamed thermoplastic polyurethane (TPU), respectively. Increasing the thickness of the Ecoflex (TM) cover shows a significant increase of 259% of the piezoelectric d(33)-coefficient.