Harvesting environmental circadian oscillations for energy autonomy of soft robots.

Energy autonomy remains elusive in soft robotic devices, yet is essential for real-world operation beyond laboratory environments. Existing onboard energy-source strategies for air-powered soft robots require manual intervention for long-term use. We propose a thermopneumatic strategy that exploits circadian thermal oscillations and a pneumatic control circuit to enable energy autonomy in soft robotic systems. Our thermodynamic cycle harvests environmental thermal energy, stores it as pneumatic pressure, and autonomously discharges it to power soft pneumatic devices. Using a low-boiling-point fluid, our design repeatedly generates sufficient energy for pneumatic soft robots. Our model indicates this strategy is applicable worldwide under sufficient light intensity and ambient temperature. In a single real-world thermal cycle, our design triggered 142 activations of a self-oscillating actuator, while a two-limbed soft pneumatic robot harvested thermal energy to achieve locomotion. This study presents a long-term energy-harvesting strategy enabling energy autonomy in electronic-free soft robots without repeated manual intervention.