A waterproof and ultra-elastic thermoelectric foam for underwater human signal detection

Underwater tasks such as ocean exploration and emergency rescue demand advanced wearable sensors. However, multifunctional underwater sensors capable of integrating self-powered signal transmission, effective thermal-moisture regulation, and multi-signal decoupling remain unreported. Here, we present a three-dimensional multi-functional thermoelectric device composed of highly porous polyurethane foam coated with a waterproof conductive layer made from single-walled carbon nanotubes, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate, and waterborne polyurethane. Hydrogen bonding between the sulfonate groups in poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and the -NH groups in waterborne polyurethane enhances water resistance (contact angle of 112°) and mechanical durability under repeated compression (20,000 cycles), while achieving an ultra-fast response time of 40 ms. The device exhibits high breathability (406 mm s^-1) owing to its porous three-dimensional architecture. Additionally, it enables precise temperature sensing with a resolution of 0.05 K and a response time of 400 ms. Importantly, it successfully decouples temperature and strain signals in underwater environments. Leveraging its waterproof and signal-decoupling capabilities, we further demonstrate a fully integrated underwater monitoring and interaction system encompassing sensing hardware and decision-making logic. This work represents a significant advancement in wearable underwater electronics and offers another perspective for reliable, real-time human-machine interaction in aquatic settings.