Theoretical seminar | 22 April 2020

An active material is either a solid or a fluid in which microscopic constituents convert energy into motion. These microscopic engines can be organised to output collective macroscopic work. For active solids, we show that the theory of elasticity can be modified to describe this work-extraction process. This talk focuses on the specific example of how an antisymmetric (or odd) component of the elastic tensor leads to the extraction (or injection) of work during quasi-static cycles of elastic deformations. Such materials can be designed based on active mechanical components that include sensors and actuators. Inside the material, work-extraction cycles manifest themselves in signal propagation: in an overdamped active solid, elastic waves propagate via a balance between energy injection and dissipation. In addition, activity can be measured via static deformations, including activity-induced auxetic behaviour. This theory of odd elasticity suggests design principles for emergent autonomous materials in which work is locally injected, transported, and then extracted.