A variable stiffness tuned nano-piezoelectric rotational energy harvester using a magnetically-modulated segmented cantilever structure

A variable-stiffness tuned nano-piezoelectric rotational energy harvester featuring a magnetically modulated segmented cantilever structure is proposed to overcome the limitations of conventional harvesters under low-frequency excitation, such as deformation drift and structural fatigue. The system integrates a central excitation magnet embedded in the cantilever beam and symmetrically arranged clamping magnets, forming a repulsive magnetic field that induces a self-correcting restoring force while enabling non-contact stiffness adjustment. This structural configuration enhances strain localization, ensures stable dynamic alignment, and improves adaptability across varying rotational speeds. A nonlinear theoretical model is developed to reveal the effects of magnetic clamping distance, excitation magnet number, and grouping configuration on voltage output and resonance behavior. Experimental results show that the VST-NPREH achieves a peak output power of 1.9 mW at 210 r/min with l_c = 15  mm, N = 4, and G = 1. Energy storage tests confirm its ability to charge multiple capacitors, and practical demonstrations verify its capability to power LEDs and low-power electronic devices. These findings demonstrate the effectiveness of the proposed design in enhancing energy conversion efficiency and mechanical resilience, providing a compact and durable solution for self-powered sensing in low-speed rotational environments.