Liquid Metal Elastomer Foam-Based Soft Sensors with Decoupled Three-Axis Strain-Sensing Transmission

Soft three-axis strain sensors detect normal strains perpendicular to the interface and shear strains parallel to the interface, having potential applications in actuators and human motion monitoring. However, in the measurement process of three-axis strain sensors, issues like cross-coupling errors, nonlinear errors, and noise interference often arise. The issues originate from imperfections in the structural design of the sensor, inadequate sensor sensitivity, and the absence of a mathematical decoupling model. Consequently, the sensor faces significant challenges in accomplishing the decoupling of three-axis strain. In order to fulfill the objective of three-axis strain decoupling, this study presents a flexible capacitive three-axis strain sensor fabricated based on liquid metal elastomer foam (LMEF). Leveraging LMEF, the sensor attains enhanced sensitivity, and the nonlinear errors as well as noise interference in the measurement are diminished. By designing the cross-axis overlapping areas of the three capacitive electrodes, one capacitor is only sensitive to normal strain, while the other two capacitors are sensitive to both normal and shear strains simultaneously. By employing a capacitor that is solely sensitive to the normal strain in the Z-direction, it becomes feasible to decouple the capacitors for shear strains in the X and Y directions from the normal strain in the Z-direction. This enables a completely crosstalk-free three-axis strain measurement. Through theoretical analysis and finite element simulation, the operating principle of the sensor was thoroughly explored, and a three-axis strain decoupling model was established. As a result, the sensor has successfully achieved the decoupling of three-axis strain. Moreover, the feasibility of the sensor’s applications in object grasping and human gait monitoring has been demonstrated.