Highly Sensitive Multidirectional Strain Sensors Based on Laser-Induced Graphene for Human Activity Monitoring

The cross-shaped flexible strain sensors are crucial in motion rehabilitation, human-computer interaction, and bionic robotics. Traditional sensors often use dip coating or immersion for sensitive materials, resulting in weak bonding with stretched substrates and reduced sensitivity at low strains. In contrast, laser-induced graphene (LIG) provides a stronger bond due to chemical induction between the pattern and substrate. This study demonstrates a one-step method for creating porous graphene electrodes by laser direct writing on polyimide (PI)/polydimethylsiloxane (PDMS) composite films, forming a cross-shaped sensitive layer. The cruciform structure ensures symmetry, flexibility, and stability for multidirectional sensing, responsive to applied force direction but less perpendicularly. It exhibits excellent anisotropic sensing (0%–20% strain) with cross-axis sensitivity (GFX/GFY) ranging from 134 to 248, accurately detecting small strain changes in specific directions for micromotion monitoring. The sensor shows a good linear response (R<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}} =98.25$ </tex-math></inline-formula>%) within its directional range and maintains reproducibility over 5000 cycles at 5% strain. This method offers a convenient way to fabricate multidirectional flexible sensors. Effective micromotion monitoring is achieved by detecting neck and wrist movements under minimal strain and applying stresses from various angles, promising advancements in sports and rehabilitation.