Magnetic Field-Induced Oriented Iron Nanoparticle-Based Hydrogel Strain Sensor for Gesture Recognition

Flexible hydrogel-based strain sensors are crucial for applications in wearable devices, such as human motion detection, epidermal health monitoring, and soft robotics. However, conventional hydrogels often suffer from limited sensitivity and poor repeatability, which restrict their use. Incorporating new conductive materials can enhance hydrogel sensitivity. However, these methods may be costly or complex. In contrast, iron nanoparticles (Fe NPs), due to their low cost and significant ferromagnetism, offer a promising solution. The orientation of these nanoparticles can be easily controlled by applying a magnetic field during sensor fabrication, which enhances both the mechanical and sensing properties of the hydrogel. In this article, acrylamide (AM) and polyvinyl alcohol (PVA) were used as the hydrogel matrix, and Fe NPs were incorporated. The magnetic field-induced ordered structure significantly improved the hydrogel’s mechanical properties (stretching ability of 1391.1%) and sensing performance, with a low detection limit of 0.31%. The sensor output remained stable during human body movements (e.g., finger, wrist, and arm motion), and the sensor demonstrated good gesture recognition accuracy (94.50%). This work demonstrates a simple yet effective strategy for enhancing the performance of hydrogel-based strain sensors in wearable technologies.