Light-powered self-swing of a bistable magnetic pendulum utilizing liquid crystal elastomer fibers

Abstract

Light-powered self-oscillation allows for the direct absorption of heat from ambient illumination to maintain its movement, making it a valuable technology for sensors, energy harvesters and soft robots. However, achieving self-oscillation in pendulum systems remains experimentally challenging. To overcome this limitation, we experimentally proposes a bistable magnetic pendulum that utilizes magnetic forces to provide a lateral pulling force, where the interplay of gravity and magnetic forces allows the pendulum to transition between the light zone and the dark zone, offering a novel mechanism for self-oscillation. Base on the light-responsive characteristic curve of LCE fiber calibrated experimentally, a theoretical model for the bistable magnetic pendulum is established to investigate the dynamic behaviors of the self-swing. Numerical calculation shows that the bistable magnetic pendulum has three modes motion: static, single-periodic self-swing, and complex-periodic self-swing, which aligns with the experimental observations. The self-swing is originated from alternating gravity-to-magnetic transition in dark and magnetic-to-gravity transition in light. Furthermore, the motion state, amplitude, and period of the LCE magnetic pendulum can be controlled by adjusting the light power, magnetization coefficient and thermal time ratio. The proposed bistable magnetic pendulum, with advantages such as not requiring rapid material response, a wide range of adjustable periods, and a simple structure, can provide potential applications in environmental monitoring, robotics, and energy harvesting.