Photomechanical self-oscillation of a bifilar pendulum with liquid crystal elastomeric fiber

Self-oscillating systems that harness ambient energy are pivotal for advancing autonomous soft robotics and micro-mechanisms. However, achieving self-oscillation with liquid crystal elastomers (LCEs) is often constrained by their intrinsic thermal relaxation hysteresis. This study introduces a novel bifilar pendulum design that employs a minimal LCE fiber as a photothermal actuator together with an elastic fiber and a mass block, thereby circumventing material response limitations via a geometric self-switching mechanism. A nonlinear dynamic model is established and experimentally validated, which suggests that the work done by light-induced tension in the LCE fiber precisely offsets damping dissipation, enabling stable in-plane self-oscillations under constant light. The results demonstrate that light intensity and structural parameters synergistically govern the static-to-oscillatory transition, and allow for controllable modulation of the amplitude and frequency. The geometry-driven self-switching strategy and the minimal-LCE-driven oscillation concept present an efficient approach for developing miniaturized energy harvesters, light-programmable soft robotics, and autonomous machines based on smart soft materials.