Tension-Controlled Collective Dynamics in Active Solids

Navigating amongst diverse functionalities is a major goal of metamaterial design, with applications in various fields, from architecture, to soft robotics. Multifunctional materials are usually actuated from an external source of work, which allows for a good control of the targeted functions. The recent finding of selective and collective actuation in active solids, namely solids embedded with active units, opens the path towards autonomous actuation. This however immediately raises the question of its control. Here we show how mechanical tension can serve as a general mechanism for switching between different collective dynamics in active solids. We combine the experimental study of a centimetric model active solids, numerical study of an agent based model and theoretical arguments to reveal how tension allows for the reversible transition between different actuation regimes. More specifically we discuss the transition from a regime dominated by the presence of infinitesimal zero mode in the vibrational spectrum of the elastic structure, to a regime dominated by tension, with purely harmonic modes. We further demonstrate that for large enough tension and activity, any linear elastic structure favors the same type of actuation regime.