A rotational pendulum based electromagnetic/triboelectric hybrid-generator for ultra-low-frequency vibrations aiming at human motion and blue energy applications

Abstract

There is abundance of low-frequency biomechanical and blue energy that can be harvested from our ambient environment. Utilization of these energy plays a significant role for the sustainability of the wearable devices and environmental monitoring devices. Here, we presented a rotational pendulum triboelectric-electromagnetic hybrid generator (RPHG) which is able to scavenge low-frequency (<5 Hz) vibration energy from both arbitrary human motion and ocean waves. Four stacked disk-shaped rotor magnets are introduced into the generator for the rotational motion. The pendulum rotor can easily rotate around the bearing by gravity or inertia force with a broadband frequency excitation, and coupled with surrounding coils to operate electromagnetic generator (EMG). In the meantime, triboelectric nanogenerator (TENG) is realized by utilizing the rotor to trigger the contact-separation mode of the copper ring and surrounding fluorinated ethylene propylene (FEP) film. The hybridized generator is very sensitive to irregular human motion and ultra-low-frequency ocean waves. After the optimization of the configuration of the hybrid generator, the maximum power density of 3.25 W/m2 and 79.9 W/m2 are obtained at a driving frequency of 2 Hz and amplitude of 14 cm by the TENG and EMG, respectively, which can charge a capacitor of 22 μF to 7 V rapidly in 30 s. The RPHG can light up about more than hundreds of commercial lights emitting diodes (LEDs). Then, the RPHG was placed on human body and tested by running on treadmill and rope skipping. The open-circuit voltage of the EMG can be about 9 V and that of TENG can reach 150 V. Finally, the RPHG was tested on a homemade buoy in Tai Lake. When the wave frequency is about 1 Hz and the wave height is 20 cm, the open-circuit voltage of EMG can reach over 3 V and that of TENG can reach 80 V regardless of whether the RPHG is placed vertically or horizontally. Generally, the proposed device demonstrates the effectiveness towards energy harvesting from ambient environment of multidirectional and wide frequency range, i.e., human motion and blue energy, showing the great potential of being a sustainable power source for those wearable devices and monitoring devices in blue ocean.