Controlled crack propagation in wireless mxene strain sensor with high sensitivity and designated working windows for soft robots

Piezoresistive strain sensor with high sensitivity, user-designated working windows, and wireless signal transmission ishighly desired for real-time monitoring of emerging multi-degree-of-freedom soft robots. Several continual challengesawait to be addressed for the required strain sensors. First, soft robots normally work under large body deformationsand require the strain sensors with high sensitivity (gauge factor > 100) to monitor the robotic actuations at largestrains (> 100%). Second, the high-sensitivity working window(s) of strain sensors is required to be tuned to meet thestrain ranges of robotic deformations. Third, for complex actuations of soft robots, multiple strain sensors are oftenneeded for picturing the entire motions, thus increasing the capacity loads of data processing and consuming moreenergy. To address these challenges, we develop various hierarchical morphologies on the piezoresistive Ti C T MXene layer to control the propagation of in-plane cracks under strains, endowing the resulting sensor with highsensitivity (gauge factor > 800) and controllable working window (from 130% to > 900%). Furthermore, by assemblingmultiple MXene sensors, we develop strain sensing modules that simultaneously achieve ultrahigh sensitivity (gaugefactor = 14,000) within user-designated linear working windows (covering 100% strain range). The sensor modules arealso capable of collectively monitoring multi-segment robotic actuations in a single database channel, largely reducingthe data processing loading for real-time sensing. We finally integrate the MXene sensor modules with the near-fieldcommunication technologies to establish the wireless, battery-free sensing systems to monitor the complex actuationsof various soft robots (origami robots, soft hand/leg exoskeletons).