Additive Manufacturing of Piezoelectric Force Sensors

Piezoelectric poly(vinylidene fluoride-co-trifluoroethylene), or PVDF-trFE, builds up significant electrical charges on its surface when stressed. By correlating the mechanical force with the resulting electrical charges or voltages, researchers have developed flexible, broadband, and biocompatible force sensors. PVDF-trFE force sensors are traditionally fabricated via spin coating or solvent casting, which result in large waste production and experience difficulties in forming complex geometries. To tackle these challenges, this study leveraged a commercial direct ink writing system (nScrypt microdispenser) to additively manufacture PVDF-trFE force sensors. An unprecedented piezoelectric ink was first synthesized for the nScrypt microdispenser by dissolving PVDF-trFE powders into a cosolvent system consisting of methyl ethyl ketone and dimethyl sulfoxide. The ink composition and substrate surface property were optimized simultaneously to ensure consistent and uniform printing. Postprocessing procedures, including air drying, thermal curing, and electrical poling, were then investigated to facilitate polymerization and beta phase transformation in the printed PVDF-trFE films. Eventually, this study prototyped a piezoelectric force sensor consisting of printed PVDF-trFE films and printed silver electrodes. The preliminary characterization data demonstrated that a stable force sensitivity of 7 mV/N was achieved above 1.5 kHz without any processing electrical circuits.