Light-powered self-oscillation in liquid crystal elastomer auxetic metamaterials with large volume change

Abstract

Self-oscillation can harvest energy directly from the environment to maintain its motion and is characterized by its autonomy, with various promising applications in the fields of actuators, soft robots and medical devices. Limited to conventional materials, challenges remain in designing novel self-oscillating systems. Auxetic metamaterials can exhibit exceptional properties of negative Poisson's ratio and volume expansion, and the integration of metamaterial structures into self-oscillation can provide additional functionality and improve existing properties and its application. This paper proposes a liquid crystal elastomer (LCE) auxetic metamaterial, and theoretically investigates the self-oscillation of the LCE auxetic metamaterial-mass system under steady illumination. The system can undergo a supercritical Hopf bifurcation between the static pattern and self-oscillation pattern, which arises from the light-driven contraction of LCE fibers and is maintained by light energy input from the environment to compensate for the damping dissipation. This paper also investigates the Hopf bifurcation conditions, as well as the vital systematic parameters affecting frequency and amplitude of the self-oscillation pattern in detail. Different from the existing self-oscillating systems, this LCE metamaterial structure can provide additional functionality and potentially improve existing properties such as large volume change. More generally, the idea of integrating LCE fibers into the re-entrant honeycomb lattices can be applied to other auxetic structures such as arrows and chirality, and it is expected to offer more diverse design ideas of metamaterial and motion control for artificial hearts, hydraulic pumps, sensors, and energy harvesters.