Hygroscopically-driven transient actuator for environmental sensor deployment

Autonomous sensor deployment in unstructured natural forests utilizing aerial vehicles is a promising alternative to manual sensor placement by humans, yet retrieval of deployed sensors still remains a challenge. A biodegradable deployment system is therefore crucial to avoid any harmful e-waste in the target environment. However, challenges arise in the choice of materials, design and manufacturing methods to develop such transient, lightweight grippers with an appropriate response time, high deformation, and versatility for diverse shapes of tree branches for sensor deployment. In this work, we propose a hygroscopically actuated, lightweight and biodegradable gripper as a practical solution for the above challenge. Our gripper utilizes dehydration of a bio-polymer to achieve sufficient deformation requiring up to 3 W to coil around a tree branch with multiple turns. The design achieves a gripping force of up to 1.3 N, which is sufficient to deploy lightweight environmental sensors on a tree. The gripper can also exhibit fast actuation capability to complete a coiling turn in less than 120 s, which enables a typical aerial vehicle to deploy tens of sensors in a single charging cycle. Furthermore, this work presents a proof-of-concept of the proposed hygroscopic gripper demonstrating the potential of aerial sensor deployment for future forest monitoring tasks. Such systems could be used to collect data with high spatial and temporal resolution while ensuring low pollution of the environment.