Highly Stable and Reliable Capacitive Strain Sensor for Wearable Electronics Based on Anti-Dry Hydrogel Electrode

Abstract

Hydrogel-based capacitive strain sensors have been rapidly developed benefiting from their robust structure, excellent flexibility, and high linearity. However, the existing capacitive strain sensors usually suffer from the water evaporation of hydrogel electrodes, leading to poor long-term stability. In this work, a dry-resistant hydrogel electrode with 250 µm thickness was prepared on the dielectric elastomer by a simple and versatile template method through the synergistic water-retention effect of glycerin and lithium chloride, which can maintain high mechanical stability in a dry environment with relative humidity of 11% RH. The fabricated capacitive strain sensor can be stored in a normal environment for 45 days and can continuously operate under the environment with relative humidity of 20% RH for 40 h (over 10,000 cycles). Most importantly, the capacitive strain sensor possessed ultra-high linearity (R2 >0.998), good uniformity (>93.56%), and robustness at different humidity. With these favorable advantages, the sensor was successfully applied as a highly reliable wearable sensing system for human motion detection and human-machine interaction in real-time.

Keywords: wearable electronics, capacitive strain sensor, water-retaining ionic hydrogels, long-term stability, human-machine interaction