Crack-controllable waterproof strain sensor with high linearity for underwater soft robot monitoring

To address attitude inaccuracies of soft robots' flexible mechanical grippers in complex marine environments that reduce capture success rates, flexible, waterproof, and water pressure-resistant attitude monitoring sensors need to be developed. This work proposes a fully encapsulated flexible waterproof strain sensor based on a crack-controllable structure. It is fabricated by depositing a multi-walled carbon (MWCNTs)/molybdenum disulfide (MoS₂)/silver nanowire (AgNWs) conductive film onto a polydimethylsiloxane (PDMS) substrate featuring a rhombic conductive grid structure. The results show that the sensor exhibits high linearity (> 0.98) within a 55% working range, high sensitivity (GF = 432.62), and stability exceeding 4500 cycles at 12% strain. Additionally, the sensors can detect as low as 0.05% strain and respond to mechanical vibration excitation with varying waveforms. The sensor not only exhibits excellent resistance to salt and alkali corrosion but also has low sensitivity to water pressure. It can be applied to the attitude and bending angle monitoring of flexible mechanical grippers at the end of underwater soft robots and wearable devices for human motion detection, holding significant implications for the development of underwater robots and exploration in the marine field.