Tape-Casting BaTiO3/P(VDF-TrFE) Piezoelectric Composite Films with Optimized Ferroelectric–Dielectric Performances for Wearable Human Motion Monitoring

Piezoelectric sensors have been widely adopted in passive sensing applications owing to their self-powered nature, and they play a significant role in next-generation wearable electronics. Among existing piezoelectric materials, flexible P(VDF-TrFE)-based composites have emerged as promising candidates for fabricating high-performance sensors. However, pure P(VDF-TrFE) suffers from poor piezoelectric performance, which makes it difficult to achieve accurate motion detection because of its weak piezoelectric output and low signal-to-noise ratio. In this study, BaTiO3 (BT), which exhibits a significantly higher d33 than the polymer matrix, was introduced into P(VDF-TrFE) to fabricate piezoelectric films via the tape casting method. The piezoelectric, ferroelectric, and dielectric properties of the films were systematically investigated at various BT loading concentrations. At a loading concentration of 15%, the absolute d33 value reached 27.6 pC/N, representing a 50.8% increase compared with 18.3 pC/N for the unloaded film, and the β-phase content reached 86.1%. Under an external force of 50 N, the sensor delivered a piezoelectric output of 2.30 V, demonstrating excellent output and waveform characteristics for motion monitoring. Under five discrete levels of applied force, the sensor generated distinguishable piezoelectric outputs with excellent reproducibility. Based on the linear relationship between the output voltage and the external force, the sensor sensitivity was determined to be 0.0515 V/N. During the cyclic stability test, the piezoelectric output of the as-fabricated sensor exhibited a slight degradation of approximately 3% after 10,000 consecutive loading cycles, demonstrating satisfactory long-term operational stability. Furthermore, ferroelectric and dielectric analysis revealed that the maximum polarization and remanent polarization increased significantly after BT loading, while the dielectric properties exhibited a monotonic increase in permittivity while maintaining low dielectric loss. In summary, this sensor holds great potential for monitoring joint movement during physical activity.