Liquid Metal Elastomer-Based U-Shaped Electrode Flexible Strain Sensors with Enhanced Stability and Sensitivity

Soft and stretchable strain sensors are crucial for applications in human-machine interfaces, flexible robotics, and electronic skin. Among these, capacitive strain sensors are widely used and studied; however, they face challenges due to material and structural constraints, such as low baseline capacitance and susceptibility to external interference, which result in low signal-to-noise ratios and poor stability. To address these issues, we propose a U-shaped electrode flexible strain sensor based on liquid metal elastomer (LME). By incorporating liquid metal into the elastomer, we create a high-dielectric constant LME dielectric layer. Additionally, we innovatively introduce an external U-shaped flexible textile electrode in conjunction with an internal planar flexible textile electrode to form the flexible strain sensor, effectively resolving the trade-off between stability and integration in capacitive sensors. We also investigated the dielectric and mechanical properties of the LME at varying liquid metal volume fraction (ϕ_LM). A comparative simulation was conducted between parallel plate structure and U-shaped package structure designs, leading to the fabrication of the U-shaped electrode flexible strain sensor based on LME. Furthermore, we demonstrated its potential applications in monitoring human motion, soft gripper electronic skin, and robotic arm movements.