Dual-Strain Adaptive Conductive Channels Conferred Sensing Rope with Ultrahigh Linearity, Wide Working Range, and Yoga-Asana-Monitoring Capability

Abstract

Wearable strain sensors exhibit great capability of detecting human joint activities, assisting rehabilitation training, and reflecting intelligent robots’ operation. Abundant efforts regarding improving strain-sensor performance have predominantly focused on enhancing sensitivity or expanding sensing ranges but frequently neglected the importance of response-signal linearity, a key parameter for measurement accuracy. Herein, to suppress nonlinear resistance surge, dual-strain adaptive conductive channels constructed via braiding one polypyrrole/polyurethane filament (outer filament) with the other two (core filaments) into a reef knot structure are proposed. The structure discrepancy between the outer and core filaments confers the obtained reef knot sensing rope (RKSR) dual-strain response to stretching, inducing differential crack propagation on the PPy layers. The parallel connectivity of the outer and core filaments paves the way for the formation of adaptive conductive channels, which allows RKSR’s resistance to increase linearly. The RKSR possesses excellent linearity (R2 = 0.998 for 0–100% strain and R2 = 0.999 for 0–600% strain), satisfactory detection limit (0.75–800%), great relative resolution (0.09375%), fast response time (120 ms), and favorable reciprocating stability (10,000 cycles). RKSR also adapts to various tensile rates (0.15–40 mm s–1) and can be integrated into yoga wear to monitor the postural compliance and respiratory patterns of practitioners during asana execution, signifying its potentially diverse applications (e.g., postsurgical rehabilitation and athletic assessment).