Spherical 3D fractal structured dual-mode triboelectric nanogenerator for multidirectional low-frequency wave energy harvesting

The triboelectric nanogenerator (TENG) has demonstrated an irreplaceable advantage compared with the electromagnetic generator (EMG) in featuring a greater low-frequency energy harvesting capability. However, the efficiency of energy harvesting remains challenge for wave energy under random-direction motion characteristics. In this work, a 3D fractal structure dual-mode spherical TENG (FDS-TENG) is constructed for efficient wave energy harvesting. Inspired by the structure of the burr puzzle, a three-module multiphase coupling strategy is introduced to the TENG through the ingenious 3D spatial geometric isomorphism design. The synergistic coupling motion between the modules achieves a dual-mode output in contact-separation mode and lateral sliding mode. The designed structure greatly increases the space utilization of the spherical TENG while enabling efficient capture of wave energy at low frequency, weak excitation, and in any direction of activation. The peak power density and average power density of the FDS-TENG can reach 8.3 W/m3 and 1.1 W/m3 at 2 Hz, respectively. Based on the FDS-TENG, several applications for the smart ocean, including the power supply of beacon lights and environmental sensors, have been successfully demonstrated. This novel design strategy is a significant inspiration for improving the response characteristics and output performance of TENGs in the future.