Bioinspired shape memory alloy-driven underwater soft robot enabled by pectoral–caudal-fin coordination and passive liquid thermal management

Bioinspired robotic fish can provide compliant, low-noise underwater locomotion, but compact shape memory alloy (SMA)-driven designs often suffer from slow response and poor fatigue life. We propose a grass-carp-inspired pectoral–caudal-fin (PCF) soft robot to realize body caudal-fin (BCF) and median paired-fin (MPF) multimodal swimming and specifically improve SMA performance via embedded thermal management. The robot integrates an SMA spring caudal-fin actuator and a large-strain SMA pectoral-fin actuator within a watertight compliant body and adopts a sealed-cavity liquid-cooling scheme. Experiments show markedly enhanced actuation bandwidth and durability, enabling stable multimodal locomotion with a 45.67 mm/s peak speed and 9.12 (°)/s peak turning rate, plus ultrasonic-based obstacle avoidance at 20 cm. The results suggest a compact pathway to resilient, versatile underwater soft robots for long-duration operation in cluttered environments.