Light-driven self-swing of a liquid crystal elastomer fiber-based composite pendulum in magnetic field

Since the light-driven self-oscillation facilitates the direct thermal absorption from ambient light to support operations, it proves to be particularly advantageous for sensors, energy harvesting, and soft robotics. Currently, experimental observations suggest that the liquid crystal elastomer (LCE) fibers contract much more swiftly upon heating compared to their elongation during cooling. Hence, realizing self-oscillations in monostable pendulum systems necessitates both sufficiently rapid rates of photothermal contraction and cooling elongation in LCE fibers, which complicates the experimental implementation. This paper designed a continuous steady-state composite pendulum device by establishing sustained stability through gravity-magnetic field interactions. This composite pendulum presents self-swing primarily driven by the contraction of LCE fibers that shifts the center of mass. Notably, this self-swing operates without requiring excessive photothermal contraction rates in the LCE. A theoretical model aimed at exploring the dynamic behaviors of the pendulum system is constructed by integrating the experimentally calibrated photothermally-responsive characteristic curves of the LCE. In agreement with experimental results, numerical simulations show three motion modes: complex-cycle self-swing, single-cycle self-swing, and static mode. The alternation of gravity-to-magnetic transit in the light and the magnetic-to-gravity transit in the dark is responsible for the self-swing. Furthermore, systematic parameter analysis demonstrates effective control over motion modes, amplitude, and frequency through modulation of light power, magnetization coefficient, and damping coefficient. Significant benefits of the suggested composite pendulum system include the removal of the need for quick material response, broad period tunability, and structural simplicity, indicating possible uses in energy harvesting, robotics, and environmental monitoring.