Performance of Self-Powered, Water-Resistant Bending Sensor Using Transverse Piezoelectric Effect of Polypropylene Ferroelectret Polymer

The significant growth of wearable electronics is in constant search for optimizing systems with high flexibility and self-powering capacity. In this work, we utilize flexible polypropylene ferroelectret (PPFE) thin film polymer with the large transverse piezoelectric coefficient for bending curvature self-powered sensing. The electric energy comes from the geometry distortion of the built-in macro dipoles with initial surface charge distributions. Theoretical analysis based on constitutive electromechanical equations and bi-layer bending mechanics provide a detailed understanding of the sensing mechanism and its applicability. Different evaluation methods are used to have a more comprehensive understanding of the electromechanical responses under different bending conditions. It has been found that the velocity and magnitude of the mechanical input influence the average voltage output, while instantaneous voltage is not dependent on the latter. The robustness of the material is also investigated, where the device shows no performance degradation by immersion into the water up to 12 hours and under 10k bending cycles. Thermal stability tests reveal degradation starting at ~ 75°C and an immediate failure of the device at ~ 150°C. Finally, an application is demonstrated by showing the potential use of the characterized system as a self-powered sensor for athletic assessment.