Circular Halbach flexible electromagnetic energy harvesting from rotating machinery: design, modeling and experiments

Condition monitoring of critical rotating components, such as shafts, bearings, and gears, is essential for the reliable operation of industrial machinery and the prevention of catastrophic failures. However, existing energy harvesters often fail to meet the requirements for self-powered condition monitoring because of insufficient output power and bulky form factors, which limit their practical deployment in space-constrained industrial environments. To address these challenges, this paper proposes a circular Halbach flexible electromagnetic energy harvester (CHFEEH) with enhanced power density. The proposed device integrates a Halbach magnet array with flexible printed circuit (FPC) coils, enabling magnetic flux concentration and improved spatial adaptability. A theoretical model based on the surface magnetic charge method is developed to predict the voltage output response of the CHFEEH, and finite element simulations are performed to compare the magnetic flux distribution of three magnet array configurations and identify the optimal design. Experimental results validate the accuracy of the proposed model with a maximum error of 3.44%, and demonstrate an output power of 1783.0 mW at 296 rpm, corresponding to a volume- and linear-velocity-normalized power density of 10.58 mW/(cm³∙(m/s)²). Practical demonstrations further confirm its ability to charge a 0.22F supercapacitor and power a wireless sensor node for vibration monitoring. These results indicate that the proposed CHFEEH provides a compact and high-performance solution for self-powered sensing in low-speed rotational applications.