Triaxial Flexible Multifunctional Strain Sensors Based on Self-Assembled NdFeB@Ag Magnetic Conductive Composites

Conventional strain sensors are single function and struggle to meet the demands of applications in dynamic, complex environments. This paper presents the design, fabrication, and application of a triaxial flexible strain sensor based on magnetized neodymium iron boron microparticles with silver nanoshells (NdFeB@Ag) embedded in PDMS. Magnetized NdFeB@Ag microparticles with strong magnetism and high conductivity self-assemble to form conductive networks, facilitating efficient and scalable fabrication via stencil printing. A parylene encapsulation layer ensures long-term signal stability by mitigating moisture and oxidation effects, reducing the resistance drift in unmagnetized NdFeB@Ag/PDMS composites to just 7.7% over 12 h. The resulting strain sensor demonstrates excellent multifunctionality, with the ability to detect strain within the range of 0–1% in three orthogonal directions, monitor bending angles from 0° to 90°, and respond to temperature changes within the range of 25–45 °C due to its positive temperature coefficient. This research based on NdFeB@Ag magnetic conductive microparticles presents a convenient approach to construct multifunctional strain sensors, leading to a prevalence of low-cost devices in soft robotics, wearable electronics, and intelligent home systems.