Magnetically actuated L-shaped piezoelectric-electromagnetic wave energy harvester powered by wave-caused center-of-gravity displacement

Low-frequency ocean waves contain abundant renewable energy, but traditional piezoelectric energy harvesters exhibit low output performance under ultra-low frequency, multi-directional wave excitation conditions. To address this issue, this paper proposes a magnetically actuated L-shaped piezoelectric-electromagnetic wave energy harvester powered by wave-caused center-of-gravity displacement (LPEH). This device utilizes a center-of-gravity shift mechanism to convert multi-directional wave motion into rotational motion and amplifies the rotational speed under low-frequency wave conditions through a gear transmission mechanism. The use of an L-shaped piezoelectric beam lowers the structure's first-order natural frequency, thereby enabling efficient free vibration responses after each magnetic impulse release. Non-contact magnetic coupling between the rotor magnet and the beam-end magnet further enhances the structure's vibration response and output performance. Furthermore, the structure integrates an auxiliary electromagnetic coil branch, establishing a piezoelectric-electromagnetic dual-path energy harvesting architecture, in which the electromagnetic branch provides frequency-dependent auxiliary output for wave period monitoring. Results show that the first-order natural frequency of the L-shaped beam is reduced to approximately 2.214 Hz. Under optimal operating conditions with five rotor magnets and a 5 mm magnetic spacing, the device achieved a peak voltage of 141 V and a peak power of 78 mW, and was able to stably drive 92 LEDs and temperature and humidity sensors. By simultaneously reducing structural stiffness via an L-shaped beam and up-converting excitation frequency via gearing, this device outperforms existing harvesters that rely on either approach alone, while its embedded electromagnetic branch enables self-powered wave-state sensing for marine IoT applications.