Composite Polyimide Foam-Based Sensors Dominated by the Piezoelectric Effect for Detecting Human Activity and Sounds

Fluorine polyimide (FPI) materials have been attracting significant attention due to their potential application as an ideal substrate for flexible piezoelectric sensors. However, the limited piezoelectric output remains a challenge to be overcome. Herein, an effective method for the synthesis of isocyanate-based fluorine polyimide foam containing BaTiO₃ nanoparticles via a one-step foaming method is proposed. Notably, the prepared FPI foams show improved piezoelectric properties with output voltage of up to 31 V at a vibration frequency of 20 Hz under the pressure of 1-5 N. In addition, the fabricated FPI foam-based sensor exhibits high sensitivity (8.232 V/N), short response time (7 ms), and outstanding durability (10,000 cycles). Moreover, the prepared FPI foams retain excellent thermal insulation and thermal stability. Specifically, when the sample was exposed to a hot stage at 220 °C for 10 min, the upper surface temperature of the samples was maintained at about 95.6 °C. In addition, the FPI foam has the ability to recognize various types of natural acoustic signals, demonstrating excellent piezoelectric sensitivity. This study provides an effective solution for enhancing the piezoelectric properties of FPI materials, showing significant potential in expanding their applications in smart, wearable microelectronic devices.