Light-powered self-excited oscillation of a liquid crystal elastomer pendulum

Light-powered self-oscillation of liquid crystal elastomers(LCEs) has been extensively utilized in designing the promising and superb opto-mechanical systems and architectures with marvelous forms and functions, due to its diverse advantages, e.g. direct energy harvesting from the environment for motion actuation of active machines, generating periodic motion without additional human control, reducing system complexity and fulfilling portability. In this paper, the nonlinear dynamic model for light-powered motion of an LCE pendulum is originally proposed and selfexcited oscillation can be triggered under constant illumination with the longitudinal contraction and relaxation of LCE fiber periodically. The self-sustained motion can be explained by the mechanism of positive linear damping and negative nonlinear damping which corresponds to a positive net work done by the LCE fiber. Various limit cycles and critical conditions for provoking self-excited oscillation are quantitatively presented for distinct physical parameters. The results show that self-excited oscillation can be regulated and controlled through the illumination angle, the initial angular velocity, the nondimensionalized damping coefficient, the nondimensionalized acceleration, the contraction coefficient and the light intensity. Furthermore, the period and the amplitude of self-excited oscillation generally depend on the intrinsic properties of the system, which possesses the great robustness. The nonlinear opto-mechanical vibration system of LCE pendulum proposed in this study can be applied to sensing environment, energy harvesting and motion actuation of active machines, etc.