Highly sensitive mechano-optical strain sensors based on 2D materials for human wearable monitoring and high-end robotic applications

Abstract

Recently, myriad stretchable flex sensors have been developed based on the principle of changing piezoresistance, capacitance, and impedance. However, these approaches suffer from low cycling stability, poor hysteresis, relatively lower sensitivity, and signal deterioration due to the strong interference from electromagnetic waves from the surroundings. To solve these prevalent issues, we propose a novel flexible mechano-optical sensor by modulating the transmittance of Ecoflex/molybdenum disulfide (MoS₂). Under uniaxial strain, microcracks are developed, which results in a change in the transmittance of the film. A highly sensitive mechano-optical strain sensor is fabricated through slide coating (sensing film) and 3D printing techniques (sensor casing). The results show excellent linearity, stability (up to 1000 cycles), guage factor of 8.6, and consistent response from 0 to 150% up to 5 Hz strain rate. A compact readout system is designed which sends real-time data to smartphones wirelessly with the help of an ESP32 module. The as-developed sensor was tested for a number of applications, ranging from human body motion monitoring to controlling a robot (NAO) using a hand glove with 5 sensors placed over it.