Self-powered flexible piezoelectric sensor based on magnetically aligned Ni@CF composites

Advancements in electronics designed to sense physiological states have shown great promise for personal care applications. However, despite progress in flexible device development, poor adhesion and insufficient sensitivity are still main limitations. Herein, we present a high-performance and flexible piezoelectric sensor fabricated using a nickel-plated short carbon fiber (Ni@CF)/polyacrylonitrile (PAN) composite film. The Ni@CF was aligned within the PAN matrix through a magnetic field-assisted fabrication method. The effects of Ni@CF proportions and orientation degrees on the electrical properties of the Ni@CF/PAN composite film were systematically studied. The output performance of random Ni@CF/PAN flexible piezoelectric sensor first increases and then decreases as the Ni@CF proportion increases, achieving a peak output voltage of 3.99 V and a peak output current of 2.01 μA when the doping proportion of Ni@CF was 4.0 wt%. The output performance of Ni@CF/PAN flexible piezoelectric sensor is linearly correlated with Ni@CF orientation degree. The output voltage and current of the flexible piezoelectric sensor based on oriented Ni@CF/PAN film are 4.94 V and 2.31 μA, representing enhancements 27% and 11%, respectively, compared to random Ni@CF/PAN film sensor. The sensitivity of oriented Ni@CF/PAN film sensor is 0.87 V/N, making a 30% improvement than random Ni@CF/PAN film sensor. The response and recovery times of the oriented Ni@CF/PAN sensor are 29 ms and 23 ms, respectively. Furthermore, the durability of the Ni@CF/PAN flexible piezoelectric sensor was measured through a pressing-releasing test of over 10,000 cycles. The feasibility of self-powering was verified by using the Ni@CF/PAN flexible piezoelectric sensor to charge a capacitor, which was then discharged to light up a commercial red LED. Additionally, the Ni@CF/PAN composite film sensor proves effective in monitoring human activity signals from various body parts, including the neck, throat, knee, and foot. The results indicate that the Ni@CF/PAN flexible piezoelectric sensor holds great promise for widespread applications in smart healthcare, electronic skin, wearable electronic, and so on.