Soft Bidirectional Electrothermal Actuators

Electrothermal bimorph actuators are widely used in soft robotics and MEMS devices due to their simplistic design and ease of controllability. A universal design for electrothermal bimorphs exists, where two different materials are layered on top of one another with nearly the same area size. This design limits the actuator to move in a single, predetermined direction upon application of an electrical bias. The design also brings other limitations. For example, the actuator's performance strongly depends on the ambient temperature. As such passive cooling to return the system to its original shape is necessary. In this study, we propose and explore a soft bi-directional electrothermal actuator, where the direction of the actuation can be easily switched and controlled electrically. We discuss fabrication approaches and heat transfer in such thin-film soft structures. To describe actuator performance, we derive a modified Timoshenko beam theory. Emergent physical and mechanical in such thin film such soft actuators are explored. In addition to bidirectionality, we demonstrate the actuator’s insensitivity to ambient temperature changes, as well as its forced-return capability enabling faster actuation cycles. This bidirectional design expands the functionality and versatility of soft electrothermal actuators, opening new possibilities for their use in various applications.