Ultra-soft, foldable, wearable piezoelectric sensor based on the aligned BaTiO3 nanoparticles

Developing the inorganic piezoelectric particles/polymer matrix composites is a simple, effective, and low-cost strategy to manufacture the flexible, wearable sensors. But their application has been hindered by an obvious trade-off between electronic performances and mechanical deformability, because of the issue of dispersion difficulty and isolated distribution of inorganic nanofillers in matrix. Here, an ultra-soft, substrate-free, wearable piezoelectric sensor with aligned barium titanate (BTO) nanoparticles was designed and fabricated. To resolve the issue of degradation of flexibility of composites, a chemical etching treatment was introduced into the process of hydrothermal, which increased the content of tetragonal BTO nanoparticles and optimized the interaction between inorganic layer and polymer matrix. Thus, a higher sensitivity of 73.5 V/MPa was obtained by the as-prepared composites with the orientation of BTO than those of the reported BTO-based composites. Notably, the sensor with the thin functional layer demonstrated excellent stability even after 200 double-folded fatigue cycles. For this reason, the designed sensor could completely wrap or attach onto the different complex surface to simultaneously detect various dynamic signals involving the fluidic flowing, pulse rate and moved direction of body. Moreover, the foldable piezoelectric sensing array was easily fabricated by the proposed method, which offers the huge opportunity for the widespread applications in health monitoring, personal safety, and activity monitoring on the complex surface.