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 (ϕLM). 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.