A bio-inspired multi-directional pendulum energy harvester for autonomous ocean monitoring: theoretical modeling and experimental development

Wave energy harvesting is a promising approach to power marine monitoring systems in support of the Ocean Internet of Things (OIoT). However, due to the low-frequency and stochastic nature of ocean waves, conventional wave energy harvesters often rely on mechanical components such as gimbals and gears to achieve multi-directional energy harvesting. This reliance leads to complex system structures, high manufacturing costs, and reduced long-term reliability. To address these limitations, this paper presents a structurally simplified, bio-inspired multi-directional wave energy harvester based on a magnetic spherical pendulum. Inspired by the passive suspension and threat-triggered release mechanisms of bats, the device employs a magnetic coupling between a fixed iron sphere and a movable magnetic sphere, enabling passive stabilization and responsive motion under wave excitation. A comprehensive theoretical model was established to analyze the magnetic flux distribution, as well as the electromechanical dynamics of the harvester. Numerical simulations were conducted to investigate the dynamic response of the harvester under various structural parameters and excitation conditions, assessing its adaptability to complex marine wave environments. A prototype was fabricated, and its output performance was tested through various experimental setups, validating the theoretical model. The results demonstrate that the harvester exhibits good performance on a six-degree-of-freedom motion platform under composite sinusoidal excitations over 1.6–2.4 Hz, and can also operate effectively in a wave tank under simulated wave excitations over 0.9–1.1 Hz. The maximum average output power was 1.9 mW, corresponding to a power density of 7.17 W/m³. Additionally, the harvester successfully powered both custom-built and commercially available wireless sensor nodes, showcasing its potential for use in distributed marine wireless monitoring applications.