FOCUS: A Four-In-One Consolidated Unison Strain Sensor with Enhanced Sensitivity.

Liquid metal strain sensors possess outstanding stretchability, low modulus, and excellent repeatability, making them ideal for large-deformation measurements. However, traditional liquid metal sensors inherently suffer from low sensitivity, which severely limits their capability in detecting subtle deformations. To achieve enhanced sensitivity, we have proposed a new paradigm: FOCUS, a Four-in-One Consolidated Unison Strain Sensor specifically created for microscale biomechanical deformation. In this work, four liquid metal strain sensors were printed on an elastic planar substrate and subsequently folded to overlap at the same location. Upon stretching, two of the sensors exhibited an increase in resistance, whereas the other two displayed a greater decrease. By leveraging this complementary response within a Wheatstone bridge configuration, FOCUS exhibits a fivefold enhancement in sensitivity compared to a single liquid metal sensor, while simultaneously maintaining signal stability against wide temperature range. FOCUS can accurately capture strains ranging from centimeters to micrometers, resolution reaches 25 micrometers. To demonstrate the powerful performance of FOCUS, we used it to perform periocular micro-motion tracking and potential deformation monitoring of other human joints.