Capacitive Sensor based on Self-Healing Ionic Conductive Hydrogels for Human Motion Detection

Recently, flexible electronic devices have garnered significant attention due to their potential applications in diverse fields, including wearable sensors, energy storage devices, actuators, and soft robotics engineering. However, these devices can undergo performance degradation from deformation or damage during use, leading to potential malfunctions. Consequently, the integration of self-healing capabilities, encompassing mechanical, electrical, and chemical properties, becomes vital to address scratches or mechanical damages. Ionic conductive hydrogels are regarded as ideal materials due to their distinctive 3D network structure, which arises from the physical or chemical crosslinking of polymers. This structure imparts elasticity and concurrently facilitates a favorable environment for ion movement. Furthermore, this material is recognized as a highly attractive substance due to its straightforward manufacturing process, cost-effectiveness, and high conductivity, along with its self-healing capabilities. In this study, we manufactured hydrogels using polyvinyl alcohol (PVA) known for its effective self-healing properties through hydrogen bond-forming hydroxyl groups, and we introduced LiTFSI to impart ionic conductivity. The mechanical properties, self-healing ability, and electrical characteristics of the manufactured hydrogel were analyzed. Furthermore, finite element analysis was utilized to establish the correlation between motion-induced mechanical modification and its corresponding changes in capacitance. Informed by these analysis results, we fabricated a self-healing capacitor sensor. This wearable sensor, leveraging ionic conductors, was subsequently tested in practical applications by recording capacitance variations to monitor human movement.