Double-stage frequency-boost mechanism for high-power wave energy harvesting from ultra-low frequency ocean excitations

Ocean wave energy is a promising renewable resource, but its ultra-low frequency makes efficient harvesting and high power conversion particularly challenging. In this paper, we present a high-performance wave energy harvester featuring a frequency double-boost mechanism (FDB-WEH). A rotatable pendulum captures wave motion and, through a sinusoidal cam, redirects horizontal oscillation into multiple vertical movements, which results in the first-stage frequency boost. These movements drive an excitation magnet (EM), inducing sudden magnetic torque shifts that trigger high-frequency oscillations of a power magnet (PM), thus enabling the second-stage frequency boost. The system converts 0.25 Hz wave excitation into PM oscillations above 30 Hz, reaching a frequency multiplication over 120. Under excitation conditions of 0.5 Hz and a tilt angle of 20°, the FDB-WEH achieves a peak power of 1.07 W (average 69 mW), with a power density of 0.5 mW/cm3, outperforming previously reported devices greatly in terms of output power. Within just 2 h, it charged a 350 mAh lithium battery with 137 mWh of energy, ensuring stable power supply for navigation lights and wireless temperature and humidity sensors. This work effectively addresses the low-power challenge caused by the ultra-low frequency of wave energy, showcasing its potential for future offshore applications.