Liquid Metal-Based Capacitive Strain Sensor with Self-Shielding and Low-Hysteresis.

Soft capacitive strain sensors with soft conductive electrodes are advantageous for their ability to decouple resistance from the flexible electrodes, offering excellent repeatability, low hysteresis, low energy consumption, and good temperature stability. However, existing soft capacitive strain sensors utilize intrinsically stiff conductors as soft electrodes, limiting the sensitivity, repeatability, and hysteresis. To address these issues, this work proposes a soft capacitive strain sensor based on liquid metal. The soft electrodes are composed of a liquid metal-nickel particle conductive paste, which combines fluidity and low surface tension, thereby eliminating the elastic modulus mismatch between the soft electrodes and the elastomers. This design achieves high sensitivity, excellent repeatability, and low hysteresis. The sensor employs a three-electrode structure, which enhances resistance to parasitic and stray capacitance without applying shielding layers. The measurement and the self-shielding of the three-electrode structure are investigated through simulation analyses. Additionally, the influence of the elastic modulus compatibility between the soft electrodes and the elastomers is investigated through experiments and simulations. Furthermore, the application of this sensor in the field of wearable devices is demonstrated.