Fibrous inductance strain sensors for passive inductance textile sensing

Stretchable strain-sensitive textiles that can detect human motion and physiological information in real time have considerable potential for application in next-generation wearable electronic devices. However, the application of such textiles has been hindered largely by their vulnerability to magnetic and electrical interference, wear and tear, and baseline drift. In this article, we report a new type of highly retractable and stretchable inductive sensor with a notable reciprocal change in inductance during stretching and recovery. Our experiments indicate that yarn sensors with a small diameter (627.4 μm) have high sensitivity (0.4 μH/%), fast response (<0.1 s), and stable performance without baseline drift after 4000 cycles of testing. The mechanical performance of the strain sensors was analyzed based on a viscoelastic mechanical model. From the derived effective stress-lifespan curve, the strain sensors can undergo 2.2 × 106 cycles of stretching and recovery with only a 5% reduction in performance. Our flexible yarn sensors can be used for monitoring motion in different parts of the body using the self-inductance effect. On the other hand, by employing mutual inductance to couple the sensors and an external readout coil, strians can also be monitored passively. Thus, these capabilities facilitate new methods for all-in-one wearable motion sensing with potential applications in the field of passive sensing in electronic textiles.